List of the prehistoric life of Colorado facts for kids

This list of amazing prehistoric life in Colorado tells us about the different ancient plants and animals whose fossils have been found in the state of Colorado. These fossils help scientists understand what life was like millions of years ago!

Ancient Life in Colorado: Precambrian Era

The Paleobiology Database doesn't show any known fossils from the Precambrian era in Colorado. This was a very, very long time ago, before complex life forms became common.

Paleozoic Era: Life in Ancient Seas and on Land

The Paleozoic Era was a time when life really started to boom! Many different kinds of creatures lived in the oceans, and eventually, plants and animals began to move onto land.

Cool Paleozoic Creatures of Colorado

Here are some of the interesting prehistoric creatures from the Paleozoic Era whose fossils have been found in Colorado:

• †Actinoceras - These were ancient squid-like animals with straight shells.
• †Aglaocrinus - A type of crinoid, also known as a "sea lily," which looked like a plant but was actually an animal.
• †Amorphognathus - Tiny, tooth-like fossils from an extinct group of eel-like creatures called conodonts.
• †Amplexus - An ancient type of coral.
• †Archaeocidaris - An early kind of sea urchin.
• 

  Life restoration of the Middle-Late Ordovician jawless fish Astraspis
  †Astraspis - This was an ancient fish without jaws, and its fossils were first found in Colorado!
  • †Astraspis desiderata - This specific type of Astraspis was also first discovered in Colorado.
• †Athyris - A type of brachiopod, which are shelled marine animals that look a bit like clams.
• †Aviculopecten - An ancient scallop-like mollusk.
• †Calamites - These were giant, tree-like plants, similar to modern horsetails.
  • †Calamites cistii
  • †Calamites cruciatus
• †Callipteris - A type of ancient fern-like plant.
  • †Callipteris lyratifolia - Or a very similar plant.
• †Camarotoechia - Another kind of brachiopod.
• †Caninia - A type of horn coral.
• 

  Fossil of the Ordovician-Silurian tabulate coral Catenipora
  †Catenipora - This was a type of coral that grew in chain-like colonies.
• †Ceraurinus - A type of trilobite, which were ancient marine arthropods with segmented bodies.
• †Charactoceras - A type of ancient squid-like animal (tentative report).
• †Chirognathus - Another type of conodont.
• †Composita - A common type of brachiopod.
  • †Composita ovata
• †Conocardium - A type of ancient mollusk with a heart-shaped shell.
• †Cordaites - Tall, tree-like plants with strap-like leaves.
• †Cornulites - Small, cone-shaped fossils, possibly from worm-like creatures.
• †Crania - A type of brachiopod that attached itself to surfaces.
• †Ctenacanthus - An ancient shark relative known from its spines.
  • †Ctenacanthus buttersi
  • †Ctenacanthus furcicarinatus
• †Cupressocrinites - A type of crinoid.
• 

  Restoration of the Permian synapsid (mammal precursor) Cutleria
  †Cutleria - This was an early reptile-like animal, a precursor to mammals, first found in Colorado!
  • †Cutleria wilmarthi - This specific species was also first found in Colorado.
• †Cyclopteris - A type of ancient fern.
• †Cyrtogomphoceras - A type of ancient squid-like animal.
• †Cyrtospirifer - A type of brachiopod with spiral-shaped internal structures.
  • †Cyrtospirifer animasensis
  • †Cyrtospirifer whitneyi
• †Echinosphaerites - An ancient marine creature (tentative report).
• †Edestus - An unusual ancient shark with a unique "scissor-like" jaw.
• †Endoceras - A very large, straight-shelled ancient squid relative.
• †Eretmocrinus - A type of crinoid.
• 

  Life restoration of the Carboniferous-Permian amphibian Eryops
  †Eryops - A large, crocodile-like amphibian that lived partly on land and partly in water.
• †Euomphalus - A type of ancient snail with a coiled shell.
• †Girvanella - Tiny, tube-like fossils made by ancient algae.
• †Halysites - A type of chain coral.
• †Isalaux - An ancient creature first discovered in Colorado.
• †Isonema - A type of ancient snail.
• †Kionoceras - A type of ancient squid relative.
• †Lambeoceras - A type of ancient squid relative.
• †Lepidodendron - Huge, tree-like plants with scale-like bark.
• †Lepidostrobus - The cones of Lepidodendron trees.
• †Limnoscelis - An early reptile.
• †Lingula - A very ancient and long-lived type of brachiopod.
• †Meristella - A type of brachiopod.
• †Neospirifer - Another type of brachiopod.
  • †Neospirifer goreii
• †Neuropteris - A type of ancient fern.
  • †Neuropteris auriculata
  • †Neuropteris gigantea - (tentative report)
  • †Neuropteris heterophylla
• 

  Restoration of the Carboniferous-Permian synapsid (mammal precursor) Ophiacodon
  †Ophiacodon - An early reptile-like animal, a precursor to mammals.
• †Oradectes - An early reptile.
• †Ormoceras - A type of ancient squid relative.
• †Orthoceras - A straight-shelled ancient squid relative.
• †Oulodus - Another type of conodont.
• †Paladin - A type of trilobite (tentative report).
• †Pecopteris - A type of ancient fern.
  • †Pecopteris arborescens
• †Plaesiomys - A type of brachiopod.
• †Platyceras - A type of ancient snail.
• 

  Life restoration of the Carboniferous-Permian sail-backed amphibian Platyhystrix
  †Platyhystrix - An amphibian with a tall, sail-like fin on its back.
  • †Platyhystrix rugosus
• †Pugnax - A type of brachiopod.
• †Receptaculites - An ancient marine organism, sometimes called a "sunflower coral."
• †Samaropsis - Ancient seeds.
• †Sandia - A type of brachiopod.
• †Seymouria - An animal that was a mix between an amphibian and a reptile.
• †Sigillaria - Tall, tree-like plants with distinctive bark patterns.
  • †Sigillaria elegans - Or a very similar plant.
• †Sphenophyllum - A type of ancient plant with wedge-shaped leaves.
• †Sphenopteris - A type of ancient fern.
• †Spirifer - A type of brachiopod.
  • †Spirifer centronatus
• Spirorbis - Small, coiled tube worms.
• †Spyroceras - A type of ancient squid relative.
• †Stigmaria - The root systems of ancient trees like Lepidodendron and Sigillaria.
• †Strepsodiscus - An ancient creature first discovered in Colorado.
• †Strophomena - A type of brachiopod.
• †Syringopora - A type of ancient coral.
• 

  Fossil of the Silurian-Carboniferous crinoid ("sea lily") Taxocrinus (right)
  †Taxocrinus - A type of crinoid.
• †Walchia - An early conifer tree.
• †Westonoceras - A type of ancient squid relative.

Mesozoic Era: The Age of Dinosaurs

The Mesozoic Era is often called the "Age of Dinosaurs" because these amazing creatures ruled the Earth during this time. But there were many other fascinating animals and plants too!

Awesome Mesozoic Animals of Colorado

Here are some of the incredible prehistoric animals from the Mesozoic Era whose fossils have been found in Colorado:

• Acmaea - A type of limpet (a marine snail).
• †Adocus - An ancient turtle.
• †Albanerpeton - A small, salamander-like amphibian.
  • †Albanerpeton nexuosus
• †Albertosaurus - A large, meat-eating dinosaur, similar to T. rex (tentative report).
• 

  Life restoration of the Late Jurassic theropod dinosaur Allosaurus
  †Allosaurus - A fierce, large meat-eating dinosaur, whose first fossils were found in Colorado!
  • †Allosaurus fragilis - This specific species was also first discovered in Colorado.
• †Amblotherium - An early mammal, first found in Colorado.
• Amia - A type of bowfin fish.
• †Amphicoelias - A very large, long-necked plant-eating dinosaur, first found in Colorado!
  • †Amphicoelias altus - This specific species was also first discovered in Colorado.
• †Amphicotylus - An ancient crocodile relative.
  • †Amphicotylus lucasii - This specific species was also first discovered in Colorado.
• †Anaklinoceras - A type of ammonite (coiled-shell squid relative).
• †Anisoceras - An unusual, partly uncoiled ammonite.
• †Anomia - A type of oyster-like mollusk.
• †Anomoepus - Dinosaur footprints (tentative report).
• †Apateodus - An ancient fish.
• †Apatopus - Dinosaur footprints.
• 

  Comparison of A. ajax (orange) and A. louisae (red) with a human (blue) and Brontosaurus parvus (green)
  †Apatosaurus - A massive, long-necked plant-eating dinosaur, first found in Colorado!
  • †Apatosaurus ajax - This specific species was also first discovered in Colorado.
  • †Apatosaurus louisae - This specific species was also first discovered in Colorado.
• †Arenicolites - Ancient worm burrows.
• Aspideretes - A type of softshell turtle.
• Astarte - A type of clam.
• †Atlantosaurus - A large plant-eating dinosaur, first found in Colorado.
  • †Atlantosaurus immanis - This specific species was also first discovered in Colorado.
• †Axonoceras - A type of ammonite.
• 

  Fossilized shell of the Late Cretaceous ammonoid cephalopod Baculites
  †Baculites - A straight-shelled ammonite.
  • †Baculites aquilaensis
  • †Baculites asper
  • †Baculites clinolobatus - This specific species was first discovered in Colorado.
  • †Baculites codyensis
  • †Baculites compressus
  • †Baculites cuneatus
  • †Baculites grandis
  • †Baculites haresi
  • †Baculites mclearni
  • †Baculites meeki - This specific species was first discovered in Colorado.
  • †Baculites reesidei
• †Barosaurus - A very long-necked plant-eating dinosaur.
• 

  Fossilized skeleton of the Cretaceous turtle Basilemys
  †Basilemys - An ancient turtle.
• †Bison - An ancient bison.
  • †Bison alticornis - This specific species was first discovered in Colorado.
• †Borealosuchus - An ancient crocodile.
  • †Borealosuchus sternbergii
• †Brachauchenius - A large marine reptile called a pliosaur (or a similar form).
• †Brachiosaurus - A towering, long-necked plant-eating dinosaur, first found in Colorado!
  • †Brachiosaurus altithorax - This specific species was also first discovered in Colorado.
• †Brachychampsa - An ancient alligator relative.
  • †Brachychampsa montana
• †Brachyphyllum - An ancient conifer plant.
• 

  Life restoration of a herd of the Late Jurassic sauropod dinosaur Brontosaurus
  †Brontosaurus - A large, long-necked plant-eating dinosaur.
  • †Brontosaurus excelsus
  • †Brontosaurus yahnahpin
• †Calycoceras - A type of ammonite.
• †Camarasaurus - A large, plant-eating dinosaur with a short, deep skull, first found in Colorado!
  • †Camarasaurus grandis
  • †Camarasaurus lewisi
  • †Camarasaurus supremus - This specific species was first discovered in Colorado.
• †Camptosaurus - A plant-eating dinosaur that could walk on two or four legs, first found in Colorado!
  • †Camptosaurus dispar - This specific species was also first discovered in Colorado.
• Carcharias - A type of sand tiger shark.
• †Caririchnium - Dinosaur footprints.
• †Cedrobaena - An ancient turtle.
• †Ceratodus - A type of lungfish, first found in Colorado.
• 

  Restoration of the Late Jurassic ceratosaur Ceratosaurus
  †Ceratosaurus - A meat-eating dinosaur with a horn on its nose, first found in Colorado!
  • †Ceratosaurus nasicornis - This specific species was also first discovered in Colorado.
• Cerithiopsis - A type of sea snail.
• †Champsosaurus - A crocodile-like reptile.
• Chara - A type of freshwater algae.
• †Chelonipus - Turtle footprints.
• †Chinlea - An ancient fish.
• †Chirotherium - Footprints of an ancient reptile.
  • †Chirotherium lulli
• †Cimolichthys - A large, predatory fish.
  • †Cimolichthys nepaholica
• †Cimolodon - An early mammal (or a similar form).
• 

  Life restoration of the face of the Late Cretaceous multituberculate mammal Cimolomys
  †Cimolomys - An early mammal.
• †Cionodon - A duck-billed dinosaur, first found in Colorado!
  • †Cionodon arctatus - This specific species was also first discovered in Colorado.
• †Cirroceras - A type of ammonite.
• †Clidastes - A type of mosasaur (large marine lizard).
• †Coelophysis - A small, agile meat-eating dinosaur (tentative report).
• †Coelurus - A small, hollow-boned meat-eating dinosaur.
  • †Coelurus fragilis
• †Compsemys - An ancient turtle.
• †Coniasaurus - A small marine lizard.
• Corbula - A type of clam.
• †Crenella - A type of small clam.
• †Cretolamna - An ancient shark.
  • †Cretolamna appendiculata
• †Cretoxyrhina - A large, powerful shark, sometimes called the "Ginsu shark."
  • †Cretoxyrhina mantelli
• Cucullaea - A type of ark clam.
• Cuspidaria - A type of deep-sea clam.
• †Didymoceras - An unusual, spirally coiled ammonite.
  • †Didymoceras cheyennense
  • †Didymoceras stevensoni
• †Dinehichnus - Dinosaur footprints.
• †Dinochelys - An ancient turtle.
• 

  Diagram illustrating the Late Jurassic sauropod dinosaurs Diplodocus carnegii (green) and D. hallorum (orange) with an anachronistic human to scale.
  †Diplodocus - A very long, slender plant-eating dinosaur, first found in Colorado!
  • †Diplodocus lacustris - This specific species was also first discovered in Colorado.
  • †Diplodocus longus - This specific species was also first discovered in Colorado.
• †Diplosaurus - An ancient crocodile relative.
• Discinisca - A type of brachiopod.
• †Discoscaphites - A type of ammonite.
  • †Discoscaphites conradi
• †Docodon - An early mammal.
• †Dorsetisaurus - An ancient lizard.
• †Dorsetochelys - An ancient turtle.
• †Dryosaurus - A small, fast plant-eating dinosaur.
  • †Dryosaurus altus
• †Edmontonia - An armored dinosaur.
• 

  Skeletal reconstruction and restored soft tissue of the Late Cretaceous duck-billed dinosaur Edmontosaurus regalis with an anachronistic human to scale
  †Edmontosaurus - A large duck-billed dinosaur.
  • †Edmontosaurus regalis - This specific species was first discovered in Colorado.
• Eilenodon - An ancient reptile, first found in Colorado.
• †Elopopsis - An ancient fish.
• †Enchodus - A type of ancient fish with long, needle-like teeth.
  • †Enchodus gladiolus - Or a very similar fish.
  • †Enchodus shumardi - Or a very similar fish.
• †Equisetum - Ancient horsetail plants.
• †Eubrontes - Large, three-toed dinosaur footprints.
  • †Eubrontes giganteus
• †Eucalycoceras - A type of ammonite.
• †Euomphaloceras - A type of ammonite.
• †Eutrephoceras - A type of nautilus (coiled-shell squid relative).
• †Eutretauranosuchus - An ancient crocodile relative, first found in Colorado!
  • †Eutretauranosuchus delfsi - This specific species was also first discovered in Colorado.
• †Exiteloceras - An unusual, spirally coiled ammonite.
• †Exogyra - A type of oyster.
• 

  Fossilized shell of the Late Cretaceous ammonoid cephalopod Fagesia
  †Fagesia - A type of ammonite.
• Ficus - Fig trees.
• †Forresteria - A type of ammonite.
• †Fruitachampsa - A small ancient crocodile relative, first found in Colorado!
  • †Fruitachampsa callisoni - This specific species was also first discovered in Colorado.
• †Fruitadens - A small, plant-eating dinosaur, first found in Colorado!
  • †Fruitadens haagarorum - This specific species was also first discovered in Colorado.
• †Fruitafossor - A small, digging mammal, first found in Colorado!
  • †Fruitafossor windscheffeli - This specific species was also first discovered in Colorado.
• †Galeamopus - A large, long-necked plant-eating dinosaur.
  • †Galeamopus pabsti
• †Glirodon - An early mammal.
  • †Glirodon grandis
• †Glyptops - An ancient turtle.
• 

  Restoration of the Late Jurassic-Early Cretaceous crocodile relative Goniopholis
  †Goniopholis - An ancient crocodile relative.
• †Grallator - Small, three-toed dinosaur footprints.
• †Hallopus - A small, agile reptile, first found in Colorado!
  • †Hallopus victor - This specific species was also first discovered in Colorado.
• †Haplocanthosaurus - A long-necked plant-eating dinosaur, first found in Colorado!
  • †Haplocanthosaurus delfsi - This specific species was also first discovered in Colorado.
  • †Haplocanthosaurus priscus - This specific species was also first discovered in Colorado.
• †Hemicalypterus - An ancient fish.
• †Herrickiceras - A type of ammonite.
• †Hoploscaphites - A type of ammonite.
  • †Hoploscaphites birkelundae
  • †Hoploscaphites nicolletii
• †Hulettia - An ancient fish (or a similar form).
• †Hypsirophus - An ancient reptile, first found in Colorado.
• †Ichthyodectes - A large, fast-swimming predatory fish.
• †Ignotornis - Ancient bird footprints, first found in Colorado.
• 

  Fossilized shell of the Early Jurassic-Late Cretaceous marine bivalve Inoceramus with a human indicating its size
  †Inoceramus - A very large, clam-like mollusk.
  • †Inoceramus altus
  • †Inoceramus altusiformis
  • †Inoceramus anomalus
  • †Inoceramus arnoldi
  • †Inoceramus balticus
  • †Inoceramus brancoiformis
  • †Inoceramus bueltenensis
  • †Inoceramus cordiformis
  • †Inoceramus crippsi - Or a very similar form.
  • †Inoceramus deformis
  • †Inoceramus erectus
  • †Inoceramus flavus
  • †Inoceramus grandis
  • †Inoceramus longealatus
  • †Inoceramus muelleri - Or a similar form.
  • †Inoceramus oblongus
  • †Inoceramus pictus
  • †Inoceramus prefragilis
  • †Inoceramus rutherfordi - Or a very similar form.
  • †Inoceramus tenuistriatus - (tentative report)
• †Ischyrhiza - An ancient ray or shark.
  • †Ischyrhiza avonicola - Or a very similar form.
• 

  Fossilized shell of the Late Cretaceous ammonoid cephalopod Jeletzkytes
  †Jeletzkytes - A type of ammonite.
  • †Jeletzkytes brevis
  • †Jeletzkytes dorfi
  • †Jeletzkytes nodosus
• †Kepodactylus - A type of flying reptile (pterosaur), first found in Colorado!
  • †Kepodactylus insperatus - This specific species was also first discovered in Colorado.
• †Laosaurus - A small plant-eating dinosaur (or a similar form).
• Lepisosteus - A type of gar fish (tentative report).
• †Leptalestes - An early mammal (tentative report).
  • †Leptalestes cooki
• †Leptolepis - A small ancient fish (or a very similar form).
• Lima - A type of scallop.
• †Lingula - A type of brachiopod.
• †Lioestheria - A type of clam shrimp.
• †Lisserpeton - A small amphibian.
  • †Lisserpeton bairdi
• †Lonchidion - An ancient shark.
• †Lucina - A type of clam.
• †Macelognathus - A crocodile relative.
• †Magnoavipes - Large bird footprints.
• †Marshosaurus - A meat-eating dinosaur (or a similar form).
• 

  Fossilized skull of the Late Cretaceous multituberculate mammal Meniscoessus
  †Meniscoessus - An early mammal.
  • †Meniscoessus collomensis - This specific species was first discovered in Colorado.
  • †Meniscoessus robustus - Or a very similar form.
• †Mesadactylus - A type of flying reptile (pterosaur), first found in Colorado!
  • †Mesadactylus ornithosphyos - This specific species was also first discovered in Colorado.
• †Mesodma - An early mammal.
  • †Mesodma formosa - Or a very similar form.
• †Mesojassoides - An ancient insect, first found in Colorado!
  • †Mesojassoides gigantea - This specific species was also first discovered in Colorado.
• †Metoicoceras - A type of ammonite.
  • †Metoicoceras geslinianum
• †Micropycnodon - An ancient fish.
• †Modiolus - A type of mussel.
• †Morosaurus - An ancient plant-eating dinosaur.
• †Morrolepis - An ancient fish.
• †Myledaphus - An ancient ray.
  • †Myledaphus bipartitus
• 

  Fossilized skeleton of the Late Jurassic armored dinosaur Mymoorapelta
  †Mymoorapelta - An armored dinosaur, first found in Colorado!
  • †Mymoorapelta maysi - This specific species was also first discovered in Colorado.
• Myrica - A type of plant (bayberry).
• †Nanosaurus - A small plant-eating dinosaur, first found in Colorado!
  • †Nanosaurus agilis - This specific species was also first discovered in Colorado.
  • †Nanosaurus rex
• Natica - A type of sea snail.
• †Neocardioceras - A type of ammonite.
  • †Neocardioceras densicostatum - This specific species was first discovered in Colorado.
  • †Neocardioceras juddii
  • †Neocardioceras laevigatum
  • †Neocardioceras minutum
  • †Neocardioceras uptonense
• †Neoptychites - A type of ammonite.
• 

  Restoration of several species of the Late Cretaceous ammonoid cephalopod Nostoceras
  †Nostoceras - An unusual, spirally coiled ammonite.
  • †Nostoceras approximans - Or a very similar form.
  • †Nostoceras larimerense - This specific species was first discovered in Colorado.
  • †Nostoceras monotuberculatum
  • †Nostoceras obtusum - Or a very similar form.
  • †Nostoceras splendidum - Or a very similar form.
• Nucula - A type of nut clam.
  • †Nucula percrassa
• †Odaxosaurus - An ancient lizard.
  • †Odaxosaurus piger
• †Opisthias - An ancient lizard.
• †Opisthotriton - An ancient salamander.
• †Ornitholestes - A small, fast meat-eating dinosaur (tentative report).
• †Ornithomimipus - Bird-like dinosaur footprints.
• †Ornithomimus - A fast, ostrich-like dinosaur, first found in Colorado!
  • †Ornithomimus velox - This specific species was also first discovered in Colorado.
• Ostrea - A type of oyster.
• †Othnielia - A small plant-eating dinosaur (tentative report).
• †Othnielosaurus - A small plant-eating dinosaur.
  • †Othnielosaurus consors
• †Oxytoma - A type of clam.
• 

  Fossilized skull of the Late Cretaceous dome-headed dinosaur Pachycephalosaurus
  †Pachycephalosaurus - A dinosaur with a thick, dome-shaped skull.
• †Pachyrhizodus - A large, predatory fish.
  • †Pachyrhizodus minimus
• †Palaeobalistum - An ancient fish.
• †Palaeopteryx - An ancient bird, first found in Colorado.
• †Parabrontopodus - Large dinosaur footprints, first found in Colorado.
• †Paramacellodus - An ancient lizard.
• †Paressonodon - An early mammal, first found in Colorado.
• †Parikimys - An early mammal, first found in Colorado.
• †Parviraptor - A small meat-eating dinosaur.
• †Pentaceratops - A horned dinosaur with a very large frill.
  • †Pentaceratops sternbergii
• †Pinna - A type of pen shell mollusk.
• †Placenticeras - A type of ammonite.
  • †Placenticeras meeki
• 

  Fossilized shell of the Cretaceous marine bivalve Platyceramus
  †Platyceramus - A very large, flat clam.
  • †Platyceramus ahsenensis
  • †Platyceramus cycloides
  • †Platyceramus mantelli - Or a similar form.
  • †Platyceramus platinus
• †Platyognathus - An ancient lizard.
• †Plesiobaena - An ancient turtle.
• †Polyonax - A horned dinosaur, first found in Colorado!
  • †Polyonax mortuarius - This specific species was also first discovered in Colorado.
• †Preprismatoolithus - Dinosaur eggshell fragments.
• †Priacodon - An early mammal.
  • †Priacodon fruitaensis - This specific species was first discovered in Colorado.
• 

  Fossilized skull of the Late Cretaceous mosasaur Prognathodon
  †Prognathodon - A large, powerful marine lizard (mosasaur).
  • †Prognathodon overtoni
  • †Prognathodon stadtmani - This specific species was first discovered in Colorado.
• Propeamussium - A type of scallop.
• †Protocardia - A type of clam.
• †Protosphyraena - A large, swordfish-like fish.
• Prunus - Cherry or plum trees.
• †Pseudoperna - A type of oyster.
  • †Pseudoperna congesta
• †Pseudotetrasauropus - Dinosaur footprints (tentative report).
• †Pteraichnus - Pterosaur (flying reptile) footprints.
• †Ptychodus - An ancient shark with crushing teeth.
  • †Ptychodus anonymus
  • †Ptychodus decurrens
  • †Ptychodus occidentalis
  • †Ptychodus whipplei
• Pycnodonte - A type of oyster.
  • †Pycnodonte newberryi
• Rhinobatos - A type of guitarfish (a ray).
  • †Rhinobatos incertus
• †Rosselia - Ancient trace fossils (burrows).
• †Saurillodon - An ancient lizard.
• †Scapherpeton - An ancient salamander.
• 

  Fossilized shell of the Late Cretaceous ammonoid cephalopod Scaphites
  †Scaphites - A type of ammonite.
  • †Scaphites binneyi
  • †Scaphites depressus
  • †Scaphites hippocrepis - Or a very similar form.
  • †Scaphites nodosus
• †Scoyenia - Ancient trace fossils (burrows).
• †Selaginella - Spike moss plants.
• †Semionotus - An ancient fish.
• †Sphenodiscus - A type of ammonite.
  • †Sphenodiscus pleurisepta
• Squalicorax - A type of crow shark.
  • †Squalicorax curvatus
  • †Squalicorax falcatus
  • †Squalicorax pristodontus
• †Squatirhina - An ancient angelshark.
  • †Squatirhina americana
• 

  Restoration of the Late Jurassic stegosaur Stegosaurus
  †Stegosaurus - A famous armored dinosaur with plates on its back and a spiked tail, first found in Colorado!
  • †Stegosaurus armatus - This specific species was also first discovered in Colorado.
  • †Stegosaurus stenops - This specific species was also first discovered in Colorado.
  • †Stegosaurus ungulatus
• †Stenomyti - An ancient insect, first found in Colorado!
  • †Stenomyti huangae - This specific species was also first discovered in Colorado.
• †Stokesosaurus - A small meat-eating dinosaur (or a similar form).
• †Supersaurus - One of the longest dinosaurs ever, a long-necked plant-eater, first found in Colorado!
  • †Supersaurus vivianae - This specific species was also first discovered in Colorado.
• Tellina - A type of clam.
• †Tenea - An ancient fish.
• Teredo - Shipworms (a type of clam).
• †Thalassomedon - A large, long-necked marine reptile (plesiosaur), first found in Colorado!
  • †Thalassomedon hanningtoni - This specific species was also first discovered in Colorado.
• †Theiophytalia - A plant-eating dinosaur, first found in Colorado!
  • †Theiophytalia kerri - This specific species was also first discovered in Colorado.
• †Therangospodus - Large dinosaur footprints (or a similar form).
• †Thescelosaurus - A small, plant-eating dinosaur.
• †Titanosaurus - A large, long-necked plant-eating dinosaur.
  • †Titanosaurus montanus - This specific species was first discovered in Colorado.
• 

  Fossilized skulls of the Late Cretaceous horned dinosaurs Torosaurus (A) and Triceratops (B) to scale
  †Torosaurus - A horned dinosaur, similar to Triceratops.
  • †Torosaurus latus
• †Torvosaurus - A large, powerful meat-eating dinosaur, first found in Colorado!
  • †Torvosaurus tanneri - This specific species was also first discovered in Colorado.
• †Treptichnus - Ancient trace fossils (burrows).
• †Triceratops - A famous horned dinosaur.
  • †Triceratops galeus - This specific species was first discovered in Colorado.
  • †Triceratops horridus
• †Trinacromerum - A type of plesiosaur (or a similar form).
• Turritella - A type of sea snail with a tall, spiraled shell.
• †Tylosaurus - A very large, predatory marine lizard (mosasaur).
  • †Tylosaurus proriger
• 

  Fossilized skeleton of the Late Cretaceous tyrannosaur Tyrannosaurus
  †Tyrannosaurus - The mighty "king" of the dinosaurs, a huge meat-eater.
  • †Tyrannosaurus rex
• †Vascoceras - A type of ammonite.
• Viviparus - A type of freshwater snail.
• †Volviceramus - A type of large clam.
• †Walteria - An ancient sponge, first found in Colorado.
• †Watinoceras - A type of ammonite.
  • †Watinoceras coloradoense - This specific species was first discovered in Colorado.
• †Websteria - An ancient fish.
• †Xiphactinus - A very large, predatory bony fish.
  • †Xiphactinus audax

Cenozoic Era: The Age of Mammals

The Cenozoic Era is often called the "Age of Mammals" because, after the dinosaurs disappeared, mammals became very diverse and took over many different environments. This era also saw the rise of modern plants and animals.

Cool Cenozoic Animals and Plants of Colorado

Here are some of the interesting prehistoric animals and plants from the Cenozoic Era whose fossils have been found in Colorado:

• 

  A living Abies, or fir tree
  Abies - Fir trees.
• †Absyrtus - An ancient insect.
• †Acalles - A type of weevil (beetle).
• Acer - Maple trees.
• †Acilius - A type of diving beetle.
• Acris - Cricket frogs.
• †Acrostichum - A type of fern.
• †Adalia - Ladybugs.
• †Adelopsyche - An ancient insect, first found in Colorado.
• †Adocus - An ancient turtle.
• Aegialia - A type of scarab beetle.
• †Aelurodon - An ancient dog relative.
• 

  Life restoration of the Miocene camel Aepycamelus, or the long-necked camel. Heinrich Harder (1920).
  †Aepycamelus - A long-necked camel.
  • †Aepycamelus giraffinus
• †Aeshna - A type of dragonfly.
• Agabus - A type of diving beetle.
• †Agallia - A type of leafhopper (insect).
• †Agathemera - A type of stick insect.
• Agelaius - Blackbirds.
• †Agnotocastor - An ancient beaver.
• Agrilus - A type of jewel beetle.
• Agriotes - A type of click beetle.
• †Agromyza - A type of leaf-miner fly.
• †Agulla - A type of snakefly.
  • †Agulla protomaculata - This specific species was first discovered in Colorado.
• 

  Foliage and fruits of an Ailanthus tree
  †Ailanthus - A type of tree (tree of heaven).
• †Aletodon - An early mammal.
• Aleurites - Candlenut trees.
• †Alforjas - An ancient mammal (tentative report).
• †Allognathosuchus - An ancient alligator relative.
• †Allophylus - A type of plant.
• Altica - A type of flea beetle.
• †Alysia - A type of parasitic wasp.
• Amara - A type of ground beetle.
• †Amauropilio - An ancient spider.
• †Amblycorypha - A type of katydid (tentative report).
• †Amblyteles - A type of parasitic wasp.
• †Ambystoma - Salamanders.
  • †Ambystoma tigrinum - Tiger salamanders.
• 

  Life restoration of the Miocene elephant relative Amebelodon. Margret Flinsch (1932).
  †Amebelodon - An ancient elephant relative with shovel-like tusks.
• Amelanchier - Serviceberry plants.
• Amia - Bowfin fish.
• †Ammophila - A type of sand wasp.
• †Ampelopsis - A type of vine (like Virginia creeper).
• †Amphechinus - An ancient hedgehog.
• †Amphicerus - A type of beetle.
• †Amphicyon - A large, bear-like dog, sometimes called a "bear-dog."
  • †Amphicyon galushai
  • †Amphicyon ingens
• 

  Fossilized skull of the Miocene saber-toothed cat Amphimachairodus
  †Amphimachairodus - A type of saber-toothed cat.
• †Anabrus - A type of katydid.
• Anas - Ducks.
• †Anasa - A type of squash bug.
• †Anatis - A type of ladybug.
• †Anchitherium - An ancient horse relative.
• Andrena - Mining bees.
• †Andrias - Giant salamanders.
• †Andricus - A type of gall wasp.
• †Anelaphus - A type of longhorn beetle.
• †Anemia - A type of fern.
• †Angustidens - An ancient mammal.
• Anisotoma - A type of beetle.
• †Anobium - A type of furniture beetle.
• †Anomala - A type of scarab beetle.
• †Anomalon - A type of parasitic wasp.
• Anser - Geese.
• †Antas - An ancient insect.
• Anthaxia - A type of jewel beetle.
• †Antherophagus - A type of beetle.
• 

  A living Anthidium, or carder bee
  †Anthidium - Carder bees.
  • †Anthidium exhumatum - This specific species was first discovered in Colorado.
  • †Anthidium scudderi - This specific species was first discovered in Colorado.
• †Anthomyia - A type of fly.
• Anthonomus - A type of weevil.
• †Anthophora - A type of digger bee.
• Antilocapra - Pronghorn.
  • †Antilocapra americana - The modern pronghorn.
• †Antocha - A type of crane fly.
• Aphaenogaster - A type of ant.
  • †Aphaenogaster donisthorpei - This specific species was first discovered in Colorado.
  • †Aphaenogaster mayri - This specific species was first discovered in Colorado.
• †Aphelops - An ancient rhinoceros.
• Aphodius - A type of scarab beetle.
• Aphrophora - A type of spittlebug.
• Apion - A type of weevil.
• †Apolysis - A type of bee fly.
• Aquila - Eagles.
  • †Aquila chysaetos - Golden eagles.
• Araneus - Orb-weaver spiders.
• †Archaeotherium - A large, pig-like mammal.
• †Archimyrmex - An ancient ant, first found in Colorado!
  • †Archimyrmex rostratus - This specific species was also first discovered in Colorado.
• †Archiponera - An ancient ant, first found in Colorado!
  • †Archiponera wheeleri - This specific species was also first discovered in Colorado.
• 

  Life restoration of the Paleocene mammal Arctocyon
  †Arctocyon - An early, bear-like mammal.
• †Argia - A type of damselfly.
• †Arhopalus - A type of longhorn beetle.
• †Aristolochia - A type of plant (birthwort).
• †Artocarpus - Breadfruit trees.
• †Asimina - Pawpaw trees.
• Asio - Owls.
• †Asplenium - Spleenwort ferns.
• †Aster - Aster flowers.
• †Astronium - A type of tree.
• Ataenius - A type of scarab beetle.
• †Athalia - A type of sawfly.
• 

  A living Athous click beetle
  †Athous - A type of click beetle.
• †Athyana - An ancient insect.
• †Attagenus - A type of carpet beetle.
• †Auraria - An ancient insect, first found in Colorado.
• Aythya - Diving ducks.
  • †Aythya affinis - Lesser scaup.
  • †Aythya americana - Redhead ducks.
• †Aztlanolagus - An ancient rabbit.
• †Baena - An ancient turtle.
• †Baris - A type of weevil.
• 

  Life restoration of the Paleocene-Eocene pantodont mammal Barylambda
  †Barylambda - A large, heavy early mammal.
• †Bassus - A type of parasitic wasp.
• †Bathornis - A large, flightless bird, first found in Colorado!
  • †Bathornis veredus - This specific species was also first discovered in Colorado.
• †Bathygenys - An ancient mammal.
• †Bathyopsis - An ancient mammal.
• †Belyta - A type of parasitic wasp.
• Bembidion - A type of ground beetle.
  • †Bembidion constricticolle
• †Bembidium - A type of ground beetle.
• †Beris - A type of soldier fly.
• Betula - Birch trees.
• Bibio - March flies.
• †Bibiodes - A type of march fly.
• †Bidessus - A type of diving beetle.
• Bison - Bison.
  • †Bison antiquus - An ancient bison (or a similar form).
  • 

    Mounted fossilized skeleton of the Pleistocene Bison latifrons, or long-horned bison
    †Bison latifrons - A giant, long-horned bison.
• †Blechnum - A type of fern.
• Bledius - A type of rove beetle.
• Boletina - A type of fungus gnat.
• †Borealosuchus - An ancient crocodile.
• †Borophagus - A bone-crushing dog.
  • †Borophagus pugnator
• †Brachinus - A type of bombardier beetle.
• †Brachycrus - An ancient mammal.
• Brachylagus - Pygmy rabbits.
• †Brachyprotoma - An ancient skunk.
  • †Brachyprotoma obtusata
• †Brachypsalis - An ancient mammal.
• 

  Skeletal reconstruction of the Eocene-Oligocene bear-dog Brachyrhynchocyon
  †Brachyrhynchocyon - A type of bear-dog.
• †Brachyspathus - An ancient insect, first found in Colorado.
• Bracon - A type of parasitic wasp.
• †Bruchus - A type of seed beetle.
• Bubo - Horned owls.
  • †Bubo virginianus - Great horned owls.
• Bufo - Toads.
  • †Bufo cognatus - Great Plains toads.
  • †Bufo woodhousei - Woodhouse's toads.
• †Buprestis - A type of jewel beetle.
• †Bursera - A type of tree (frankincense).
• 

  A living Buteo hawk
  Buteo - Hawks.
• †Caesalpinia - A type of flowering plant.
• †Calcarius - Longspurs (birds).
  • †Calcarius lapponicus - Lapland longspurs.
  • †Calcarius ornatus - Chestnut-collared longspurs.
• †Calippus - An ancient horse.
• †Caliroa - A type of sawfly.
• †Callimoxys - A type of longhorn beetle.
• †Callomyia - A type of fly (tentative report).
• Calosoma - A type of ground beetle.
• †Calyptapis - An ancient bee, first found in Colorado!
  • †Calyptapis florissantensis - This specific species was also first discovered in Colorado.
• 

  Life restoration of the Pliocene-Holocene camel Camelops
  †Camelops - An ancient camel.
  • †Camelops hesternus - The western camel.
• Camponotus - Carpenter ants.
• Canis - Dogs, wolves, and coyotes.
  • †Canis edwardii - An ancient coyote (or a similar form).
  • †Canis latrans - Coyotes.
• †Cantius - An early primate.
  • †Cantius abditus
  • †Cantius frugivorus
  • †Cantius mckennai
  • †Cantius ralstoni
• †Capnobotes - A type of katydid.
• †Capsus - A type of plant bug.
• 

  A living Carabus ground beetle
  Carabus - A type of ground beetle.
• †Cardiophorus - A type of click beetle.
• †Cardiospermum - A type of plant (balloon vine).
• †Carpocyon - An ancient dog relative.
• Carpodacus - Finches.
  • †Carpodacus cassinii - Cassin's finch.
• †Carpophilus - A type of sap beetle.
• Carya - Hickory trees.
• Castanea - Chestnut trees.
• †Catopsalis - An early mammal.
  • †Catopsalis alexanderi - This specific species was first discovered in Colorado.
• †Cecidomyia - A type of gall midge (tentative report).
• Cedrela - Cedar trees.
• †Celastrus - Bittersweet vines.
• Celtis - Hackberry trees.
• †Centron - A type of weevil, first found in Colorado.
• †Ceratina - Small carpenter bees.
• 

  Life restoration of the Paleocene-Eocene crocodilian Ceratosuchus
  †Ceratosuchus - An ancient crocodile relative, first found in Colorado!
  • †Ceratosuchus burdoshi - This specific species was also first discovered in Colorado.
• †Ceraturgus - A type of robber fly.
• Cercidiphyllum - Katsura trees.
• Cercis - Redbud trees.
• †Cercocarpus - Mountain mahogany shrubs.
• †Cercopis - A type of froghopper.
• Cervus - Deer.
  • †Cervus elaphus - Elk.
• Ceutorhynchus - A type of weevil.
• Chaetodipus - Pocket mice.
  • †Chaetodipus hispidus - Hispid pocket mice.
• †Chalcis - A type of parasitic wasp.
• †Chalybion - A type of mud dauber wasp.
• †Chamaecyparis - False cypress trees.
• 

  A stand of living Chamaedorea palms
  †Chamaedorea - Palm trees.
• Charina - Rubber boas.
• †Chauliognathus - A type of soldier beetle.
• Cheilosia - A type of hoverfly.
• †Chelonus - A type of parasitic wasp.
• †Chilocorus - A type of ladybug.
• †Chionaemopsis - An ancient insect, first found in Colorado.
• Chironomus - A type of non-biting midge.
• Chondestes - Lark sparrows.
  • †Chondestes grammacus - Lark sparrows.
• †Chriacus - An early mammal.
• †Chrysis - Cuckoo wasps.
• †Chrysobothris - A type of jewel beetle.
• †Chrysogaster - A type of hoverfly.
• Chrysomela - A type of leaf beetle.
• †Cicada - Cicadas.
• †Cicadella - A type of leafhopper.
• †Cimbex - A type of sawfly.
• †Cimexomys - An early mammal.
  • †Cimexomys arapahoensis - This specific species was first discovered in Colorado.
  • †Cimexomys minor
• 

  A living Cinnamomum, or cinnamon tree
  Cinnamomum - Cinnamon trees.
• Cissus - Grape vines.
• †Cixius - A type of planthopper (tentative report).
• †Cladius - A type of sawfly.
• †Cladura - A type of crane fly.
• †Clastoptera - A type of froghopper.
• †Cleonus - A type of weevil.
• †Closterocoris - An ancient insect, first found in Colorado!
  • †Closterocoris elegans - This specific species was also first discovered in Colorado.
• †Clubiona - A type of sac spider.
• †Clytus - A type of longhorn beetle.
• †Coccinella - Ladybugs.
• †Coeliodes - A type of weevil.
• Colaptes - Flickers (woodpeckers).
  • 

    A living Colaptes auratus, or northern flicker
    †Colaptes auratus - Northern flickers.
• †Colaspis - A type of leaf beetle.
• †Collops - A type of soft-winged flower beetle.
• †Colopterus - A type of sap beetle.
• †Colubrina - A type of plant.
• †Compsemys - An ancient turtle.
• †Coniatus - A type of weevil.
• Conotelus - A type of sap beetle.
  • †Conotelus obscurus
• †Conotrachelus - A type of weevil.
• †Conzattia - A type of flowering plant.
• †Copecion - An early mammal.
• †Copelemur - An early primate.
• †Copidita - A type of beetle.
• Corixa - Water boatmen (insects).
• †Corizus - A type of scentless plant bug.
• †Cormocyon - A type of dog relative.
• †Cormohipparion - An ancient horse.
• Cornus - Dogwood trees.
• Corticaria - A type of beetle.
• Corvus - Crows and ravens.
  • †Corvus brachyrhynchos - American crows.
  • †Corvus corax - Common ravens.
• †Corylus - Hazelnut trees.
• 

  Life restoration of the Paleocene-Eocene pantodont mammal Coryphodon. Heinrich Harder (1920).
  †Coryphodon - A large, heavy early mammal.
• Cossonus - A type of weevil.
• †Cotinus - Smoke trees.
• †Crabro - A type of square-headed wasp.
• †Cratacanthus - A type of ground beetle.
• Crataegus - Hawthorn trees.
• Crotalus - Rattlesnakes.
  • †Crotalus viridis - Prairie rattlesnakes.
• †Croton - A type of plant.
• †Cryptocephalus - A type of leaf beetle.
• †Cryptocheilus - A type of spider wasp.
• Cryptophagus - A type of beetle.
• Cryptorhynchus - A type of weevil.
• †Cryptus - A type of parasitic wasp.
• 

  A living Culex mosquito
  Culex - Mosquitoes.
• †Curculio - A type of weevil.
• †Cuterebra - A type of botfly.
• †Cyclotrachelus - A type of ground beetle.
• †Cydamus - A type of insect.
• †Cylindrotoma - A type of crane fly.
• †Cynarctoides - A type of dog relative.
  • †Cynarctoides acridens
• †Cynelos - A type of bear-dog.
• Cynomys - Prairie dogs.
• †Cyphomyia - A type of soldier fly.
• †Cypris - A type of ostracod (small crustacean).
• †Daphne - A type of flowering shrub.
• Daphnia - Water fleas.
• 

  Life restoration of the Eocene-Miocene bear dog Daphoenus
  †Daphoenus - A type of bear-dog.
• †Davidia - Dove trees.
• †Denaeaspis - An ancient turtle, first found in Colorado!
  • †Denaeaspis chelonopsis - This specific species was also first discovered in Colorado.
• †Dennstaedtia - Hay-scented ferns.
• †Dermatobia - A type of botfly.
• †Dermestes - A type of carpet beetle.
• †Diabrotica - A type of cucumber beetle.
• †Diacodexis - An early hoofed mammal.
• †Dialysis - A type of fly.
• Diamesa - A type of non-biting midge.
• †Dianthidium - A type of resin bee.
• †Diceratherium - An ancient rhinoceros.
• †Dicerca - A type of jewel beetle.
• Dicranomyia - A type of crane fly.
• †Dicranota - A type of crane fly.
• †Dictyla - A type of lace bug.
• †Didymictis - An early carnivore.
• †Didymosphaeria - A type of fungus.
• †Dilophodon - An early mammal.
• 

  Life restoration of the Eocene-Miocene false saber-toothed cat Dinictis. Robert Bruce Horsfall (1913).
  †Dinictis - A type of false saber-toothed cat.
• †Dinohippus - An ancient horse.
• †Dioctria - A type of robber fly.
• Dioscorea - Yam plants.
• †Diploptera - A type of wasp.
• Diplotaxis - A type of beetle.
• Dipodomys - Kangaroo rats.
  • †Dipodomys ordii - Ord's kangaroo rat.
• Dipteronia - A type of flowering plant.
• †Dissacus - An early carnivore.
• †Docimus - An ancient insect, first found in Colorado.
• Dodonaea - Hopbush shrubs.
• 

  Preserved Dolichoderus ant
  Dolichoderus - A type of ant.
  • †Dolichoderus antiquus - This specific species was first discovered in Colorado.
  • †Dolichoderus kohlsi - This specific species was first discovered in Colorado.
  • †Dolichoderus rohweri - This specific species was first discovered in Colorado.
• †Dominickus - An ancient insect, first found in Colorado!
  • †Dominickus castnioides - This specific species was also first discovered in Colorado.
• †Domnina - An ancient shrew.
• Donacia - A type of leaf beetle.
• Dorytomus - A type of weevil.
• †Doxocopa - A type of butterfly.
• †Drassonax - An ancient mammal.
• 

  Fossilized horns, jaws, and limb bones of the Miocene deer relative Dromomeryx
  †Dromomeryx - An ancient deer relative.
  • †Dromomeryx borealis - This specific species was first discovered in Colorado.
• †Dryobius - A type of longhorn beetle.
• Dryopteris - Wood ferns.
• Dyschirius - A type of ground beetle.
• †Dysdercus - A type of cotton stainer bug.
• †Echmatemys - An ancient turtle.
• †Ectobius - A type of cockroach.
• †Ectocion - An early hoofed mammal.
• †Ectoconus - An early hoofed mammal.
• †Elaeomyrmex - An ancient ant, first found in Colorado!
  • †Elaeomyrmex coloradensis - This specific species was also first discovered in Colorado.
  • †Elaeomyrmex gracilis - This specific species was also first discovered in Colorado.
• †Elaphidion - A type of longhorn beetle.
• Elaphropus - A type of ground beetle.
• †Elater - A type of click beetle.
• Eleodes - A type of darkling beetle.
• †Emiliana - An ancient insect, first found in Colorado.
  • †Emiliana alexandri - This specific species was also first discovered in Colorado.
• †Empis - A type of dance fly.
• †Enallagma - A type of damselfly.
• Engelhardtia - A type of tree.
• Enochrus - A type of water scavenger beetle.
• †Entimus - A type of weevil.
• 

  Life restoration of a pair of the Eocene uintathere mammal Eobasileus. Charles R. Knight (1890s).
  †Eobasileus - A large, horned early mammal.
  • †Eobasileus cornutus
• †Eocuculus - An ancient bird, first found in Colorado.
• †Eogryllus - An ancient cricket.
• †Eohippus - An early horse, sometimes called the "dawn horse."
  • †Eohippus angustidens
• †Eosacantha - An ancient insect, first found in Colorado!
  • †Eosacantha delocranioides - This specific species was also first discovered in Colorado.
• †Eotitanops - An ancient rhinoceros relative.
• Ephedra - Mormon tea plants.
• †Ephemera - Mayflies.
• †Epicaerus - A type of weevil.
• Epicauta - Blister beetles.
• †Epicyon - A large, bone-crushing dog.
  • †Epicyon haydeni
• †Epihippus - An ancient horse.
• Epuraea - A type of sap beetle.
• †Epyris - A type of parasitic wasp.
• †Equisetum - Horsetail plants.
• Equus - Horses, donkeys, and zebras.
  • †Equus conversidens - An ancient horse.
  • †Equus francisci - An ancient horse.
  • 

    Restoration of the Pliocene-Holocene horse Equus scotti, or Scott's horse
    †Equus scotti - An ancient horse (or a similar form).
  • †Equus simplicidens - An ancient horse.
• Eremophila - Larks.
  • †Eremophila alpestris - Horned larks.
• Erethizon - Porcupines.
• Eriocampa - A type of sawfly.
• †Eriophyes - A type of mite (tentative report).
• †Eristalis - A type of hoverfly.
• †Ernobius - A type of beetle.
• †Ethmia - A type of moth.
• †Eubazus - A type of parasitic wasp.
• †Eucnemis - A type of beetle.
• †Eucommia - A type of tree.
• Eugenia - A type of flowering plant.
• 

  Fossil of the Eocene ant Eulithomyrmex
  †Eulithomyrmex - An ancient ant, first found in Colorado!
  • †Eulithomyrmex rugosus - This specific species was also first discovered in Colorado.
  • †Eulithomyrmex striatus - This specific species was also first discovered in Colorado.
• †Euparius - A type of fungus weevil.
• Euphorbia - Spurge plants.
• †Eurytoma - A type of parasitic wasp.
• Eutamias - Chipmunks.
  • †Eutamias minimus - Least chipmunks (or a similar form).
• †Exochus - A type of parasitic wasp.
• Fagus - Beech trees.
• Falcipennis - Spruce grouse.
• Falco - Falcons.
  • †Falco sparverius - American kestrels.
• Ficus - Fig trees.
• 

  Fossilized flower of the Eocene-Oligocene mallow relative Florissantia
  †Florissantia - An ancient flowering plant, first found in Colorado!
  • †Florissantoraphidia funerata - This specific species was first discovered in Colorado.
• Formica - A type of ant.
• †Fornax - A type of beetle.
• †Fraxinus - Ash trees.
• †Fulgora - A type of planthopper.
• †Fulica - Coots.
  • †Fulica americana - American coots.
• †Gaurotes - A type of longhorn beetle.
• †Geocoris - A type of big-eyed bug.
• Geomys - Pocket gophers.
  • †Geomys bursarius - Plains pocket gophers.
• †Geron - A type of bee fly (tentative report).
• Gerris - Water striders.
• †Gigantocamelus - A giant camel.
• †Glossina - Tsetse flies, first found in Colorado.
• Glyptostrobus - Chinese swamp cypress trees.
• Gnophomyia - A type of crane fly.
• †Gomphocerus - A type of grasshopper.
• 

  Mounted fossilized skeleton of the Miocene-Pleistocene elephant relative Gomphotherium
  †Gomphotherium - An ancient elephant relative with four tusks.
• †Gorytes - A type of sand wasp.
• †Grammoptera - A type of longhorn beetle.
• †Gyaclavator - An ancient insect, first found in Colorado!
  • †Gyaclavator kohlsi - This specific species was also first discovered in Colorado.
• †Gymnopternus - A type of long-legged fly.
• †Gymnorhinus - Pinyon jays.
• †Hadrianus - An ancient beetle.
• Halesia - Silverbell trees.
• †Hapalodectes - An early carnivore.
• †Haplolambda - An early mammal.
• Harpalus - A type of ground beetle.
• †Helaletes - An ancient tapir relative.
• †Helichus - A type of water beetle.
• †Hellwigia - A type of parasitic wasp.
• Helophorus - A type of water scavenger beetle.
• †Hemiauchenia - A type of llama.
  • †Hemiauchenia macrocephala
• 

  Life restoration of the Eocene tapir relative Heptodon
  †Heptodon - An ancient tapir relative.
• †Heriades - A type of mason bee.
• †Herpetotherium - An ancient opossum.
  • †Herpetotherium fugax
  • †Herpetotherium knighti
• Hersiliola - A type of spider.
• †Hesperocyon - An early dog.
• Heterodon - Hognose snakes.
  • †Heterodon nasicus - Western hognose snakes.
• †Hexerites - An ancient insect, first found in Colorado!
  • †Hexerites primalis - This specific species was also first discovered in Colorado.
• †Heyderia - A type of beetle.
• Holbrookia - Earless lizards.
  • †Holbrookia maculata - Lesser earless lizards.
• †Holcorpa - An ancient scorpionfly, first found in Colorado!
  • †Holcorpa maculosa - This specific species was also first discovered in Colorado.
• †Homogalax - An early tapir relative.
• †Hoplia - A type of scarab beetle.
• †Hoplocampa - A type of sawfly.
• †Hoplochelys - An ancient turtle.
• †Humulus - Hops plants.
• 

  Life restoration of the Eocene-Miocene creodont mammal Hyaenodon
  †Hyaenodon - A large, hyena-like carnivore.
  • †Hyaenodon crucians
  • †Hyaenodon horridus
  • †Hyaenodon mustelinus
• †Hydnobius - A type of beetle.
• Hydrangea - Hydrangea plants.
• Hydriomena - A type of moth.
• †Hydriomena? protrita - A type of moth (tentative report).
• Hydrobius - A type of water scavenger beetle.
  • †Hydrobius fuscipes
• †Hydromystria - A type of plant.
• Hydrophilus - A type of water scavenger beetle.
• Hydroporus - A type of diving beetle.
• Hydropsyche - A type of caddisfly.
• †Hydroptila - A type of microcaddisfly.
• 

  A living Hygrotus predaceous diving beetle
  Hygrotus - A type of diving beetle.
• †Hylobius - A type of weevil.
• †Hymenophyllum - Filmy ferns.
• †Hyopsodus - An early hoofed mammal.
• †Hypertragulus - A small, deer-like mammal.
• †Hypisodus - A small, deer-like mammal.
• †Hypohippus - An ancient horse.
• †Hypolagus - An ancient rabbit.
• †Hyporhina - An ancient insect.
  • †Hyporhina galbreathi - This specific species was first discovered in Colorado.
• †Hyrachyus - An ancient tapir relative.
• 

  Life restoration of the Eocene-Oligocene odd-toed ungulate Hyracodon. Charles R. Knight (1896).
  †Hyracodon - An ancient rhinoceros relative.
• †Hyracotherium - An early horse.
  • †Hyracotherium vasacciense
• †Ichneumon - A type of parasitic wasp.
• Ilex - Holly trees.
• †Indusia - Ancient insect cases.
• †Iridomyrmex - A type of ant.
  • †Iridomyrmex florissantius - This specific species was first discovered in Colorado.
  • †Iridomyrmex obscurans - This specific species was first discovered in Colorado.
• †Ischyromys - An early rodent.
• †Isomira - A type of beetle.
• †Isothea - An ancient insect, first found in Colorado.
• †Isotrilophus - An ancient mammal.
• †Iulus - Millipedes.
• †Jadera - A type of soapberry bug.
• †Janus - A type of sawfly.
• Jassus - A type of leafhopper (tentative report).
• †Judolia - A type of longhorn beetle.
  • †Judolia antecurrens - This specific species was first discovered in Colorado.
• 

  A living Juglans, or walnut tree
  Juglans - Walnut trees.
• Junco - Juncos (birds).
  • †Junco hyemalis - Dark-eyed juncos.
• †Juncus - Rush plants.
• †Kalmia - Mountain laurel shrubs.
• †Kimbetohia - An early mammal.
• Koelreuteria - Golden rain trees.
• †Lacon - A type of click beetle.
• †Lagopus - Ptarmigans (birds).
  • †Lagopus leucurus - White-tailed ptarmigans.
• †Lambdotherium - An early mammal.
• †Lapton - A type of beetle.
• 

  A living Larus gull
  Larus - Gulls.
• Lasiopodomys - A type of vole.
• Lasius - A type of ant.
• Lathrobium - A type of rove beetle.
• Laurus - Laurel trees.
• †Lebia - A type of ground beetle.
• †Leia - A type of fungus gnat.
• †Lema - A type of leaf beetle.
• Lemmiscus - Sagebrush voles.
  • †Lemmiscus curtatus - Sagebrush voles.
• Lepisosteus - Gar fish.
• †Leptauchenia - An ancient mammal.
• †Leptis - A type of fly.
• †Leptocyon - An early dog.
• 

  Life restoration of the Eocene-Oligocene even-toed ungulate Leptomeryx
  †Leptomeryx - A small, deer-like mammal.
• †Leptomorphus - A type of fungus gnat.
• Leptophloeus - A type of beetle.
• †Leptostylus - A type of longhorn beetle.
• †Leptura - A type of longhorn beetle.
• Lepus - Hares.
  • †Lepus townsendii - White-tailed jackrabbits.
• †Leucosticte - Rosy finches.
  • †Leucosticte atrata - Black rosy finches.
  • †Leucosticte tephrocotis - Gray-crowned rosy finches.
• †Leucozona - A type of hoverfly.
• †Ligyrocoris - A type of seed bug.
• †Ligyrus - A type of scarab beetle.
• 

  A living Limnephilus caddisfly
  †Limnephilus - A type of caddisfly.
• †Limnobium - Frogbit plants.
• †Limnophila - A type of crane fly.
• †Limonius - A type of click beetle.
• Lindera - Spicebush shrubs.
• †Linnaea - Twinflower plants, first found in Colorado.
• †Linyphia - A type of sheet weaver spider.
• †Liometopum - A type of ant.
  • †Liometopum miocenicum - This specific species was first discovered in Colorado.
  • †Liometopum scudderi - This specific species was first discovered in Colorado.
• †Lithocharis - A type of rove beetle.
• 

  Life restoration of the Eocene butterfly Lithodryas
  †Lithodryas - An ancient butterfly, first found in Colorado!
  • †Lithodryas styx - This specific species was also first discovered in Colorado.
• †Locusta - Locusts (grasshoppers).
• Lomatia - A type of flowering plant.
• Longitarsus - A type of flea beetle.
• Lontra - Otters.
  • †Lontra canadensis - North American river otters (or a similar form).
• †Lucanus - Stag beetles.
• †Lycosa - Wolf spiders.
• †Lygaeus - A type of seed bug.
• Lygodium - Climbing ferns.
• Lynx - Lynx.
  • †Lynx rufus - Bobcat.
• Lytta - Blister beetles.
• 

  Life restoration of the Eocene mammal Macrocranion
  Macrocranion - A small, agile early mammal.
• †Macrodactylus - A type of scarab beetle.
• †Macrophya - A type of sawfly.
• †Macrorhoptus - A type of weevil.
• Magdalis - A type of weevil.
• Magnolia - Magnolia trees.
• Mahonia - Barberry shrubs.
• †Maiorana - An ancient insect.
• †Malachius - A type of soft-winged flower beetle.
• †Malus - Apple trees.
• †Mammuthus - Mammoths.
  • 

    Life restoration of a herd of Mammuthus columbi, or Columbian mammoths. The extent of the fur depicted is hypothetical. Charles R. Knight (1909).
    †Mammuthus columbi - Columbian mammoths.
• Marmota - Marmots.
  • †Marmota flaviventris - Yellow-bellied marmots.
• Martes - Martens.
• †Megacerops - A large, rhinoceros-like mammal.
• Megachile - Leafcutter bees.
• †Megacyllene - A type of longhorn beetle.
• †Megahippus - An ancient horse.
• †Megalictis - A large, badger-like carnivore.
• †Megapenthes - A type of click beetle.
• †Megatylopus - A giant camel.
• †Melanactes - A type of click beetle.
• †Melanophila - A type of jewel beetle.
• †Melieria - A type of picture-winged fly.
• †Melittomma - A type of beetle.
• †Mellinus - A type of sand wasp.
• Melospiza - Sparrows.
  • †Melospiza lincolnii - Lincoln's sparrows.
• †Meniscotherium - An early hoofed mammal.
• 

  Life restoration of the Miocene rhinoceros Menoceras
  †Menoceras - A type of rhinoceros.
• Mephitis - Skunks.
  • †Mephitis mephitis - Striped skunks.
• †Merychippus - An ancient horse.
  • †Merychippus sejunctus
• †Merychyus - An ancient mammal.
• †Merycochoerus - An ancient mammal.
• †Merycodus - An ancient pronghorn relative.
• †Merycoidodon - An ancient mammal, first found in Colorado.
• †Mesatirhinus - An ancient rhinoceros relative.
• †Mesochorus - A type of parasitic wasp.
• †Mesocyon - An early dog.
• †Mesodma - An early mammal.
  • †Mesodma hensleighi
• †Mesohippus - An ancient horse.
• †Mesoleptus - A type of parasitic wasp.
• †Mesonyx - An early carnivore.
  • †Mesonyx obtusidens
• †Mesostenus - A type of parasitic wasp.
• Messor - Harvester ants.
• 

  Life restoration of the Eocene pangolin relative Metacheiromys
  †Metacheiromys - An ancient pangolin relative.
• Metachroma - A type of leaf beetle.
• †Metarhinus - An ancient rhinoceros relative.
• Metasequoia - Dawn redwood trees.
  • †Metasequoia occidentalis
• †Miacis - An early carnivore.
• Miagrammopes - A type of spider.
• †Michenia - An ancient insect.
• †Microplitis - A type of parasitic wasp.
• †Microsyops - An early primate.
• †Microtomarctus - An ancient dog relative.
• Microtus - Voles.
  • 

    A living Microtus californicus, or California vole
    †Microtus californicus - California voles (or a similar form).
  • †Microtus longicaudus - Long-tailed voles.
  • †Microtus ochrogaster - Prairie voles.
• †Mimoperadectes - An ancient opossum.
• †Mindarus - A type of aphid, first found in Colorado.
• †Miniochoerus - An ancient mammal.
• †Miodytiscus - An ancient diving beetle, first found in Colorado.
• †Miohippus - An ancient horse.
• †Miomyrmex - An ancient ant, first found in Colorado!
  • †Miomyrmex impactus - This specific species was also first discovered in Colorado.
  • †Miomyrmex striatus - This specific species was also first discovered in Colorado.
• 

  Restoration of the Pliocene-Pleistocene Miracinonyx, or American cheetah
  †Miracinonyx - The American cheetah.
  • †Miracinonyx inexpectatus - Or a very similar form.
  • †Miracinonyx studeri
• †Monosaulax - An ancient rodent.
• Mordella - A type of tumbling flower beetle.
  • †Mordella atrata - Or a very similar form.
  • †Mordella lapidicola - This specific species was first discovered in Colorado.
  • †Mordella priscula - This specific species was first discovered in Colorado.
  • †Mordella stygia - This specific species was first discovered in Colorado.
• Mordellistena - A type of tumbling flower beetle.
  • †Mordellistena florissantensis - This specific species was first discovered in Colorado.
  • †Mordellistena nearctica - This specific species was first discovered in Colorado.
  • †Mordellistena scudderiana - This specific species was first discovered in Colorado.
  • †Mordellistena smithiana - This specific species was first discovered in Colorado.
• †Moropus - A strange hoofed mammal with claws.
• Morus - Mulberry trees.
• Musca - House flies.
• Mustela - Weasels.
  • †Mustela richardsonii - Short-tailed weasels.
  • †Mustela nigripes - Black-footed ferrets.
• †Myas - A type of ground beetle.
• †Mycetophagus - A type of fungus beetle.
• Mycetoporus - A type of rove beetle.
• Myrica - Bayberry plants.
• Myrmica - A type of ant.
• Nebria - A type of ground beetle.
• †Nemognatha - A type of blister beetle.
• †Neoliotomus - An early mammal.
  • †Neoliotomus conventus
  • †Neoliotomus ultimus
• Neogale - Weasels and minks.
  • Neogale frenata - Long-tailed weasels.
  • Neogale vison - American minks.
• Neotoma - Woodrats.
  • †Neotoma cinerea - Bushy-tailed woodrats.
• †Nepa - Water scorpions.
• †Nephila - Golden orb-weaver spiders.
• †Netelia - A type of parasitic wasp.
• †Nicocles - A type of robber fly.
• 

  Mounted fossilized skeleton of the Eocene primate Notharctus
  †Notharctus - An early primate.
  • †Notharctus robustior
• Notonecta - Backswimmers (insects).
• Numenius - Curlews (birds).
  • †Numenius madagascariensis - Far Eastern curlews.
• †Numitor - An ancient insect, first found in Colorado.
• †Nyctea - Snowy owls.
  • †Nyctea scandiaca - Snowy owls.
• Nymphaea - Water lilies.
• Nysius - A type of seed bug.
• †Nyssa - Tupelo trees.
• Ochotona - Pikas.
  • †Ochotona princeps - American pikas.
• †Odaxosaurus - An ancient lizard (or a similar form).
  • †Odaxosaurus piger
• Odocoileus - Deer.
  • 

    Living male (right) and female (left) Odocoileus hemionus, or mule deer.
    †Odocoileus hemionus - Mule deer.
• †Odynerus - A type of potter wasp.
• †Oedipoda - A type of grasshopper.
• †Ogygoptynx - An ancient owl, first found in Colorado.
• †Oligoaeschna - An ancient dragonfly, first found in Colorado.
• †Oligomerus - A type of beetle.
• †Oligotricha - A type of caddisfly.
• Omalium - A type of rove beetle.
• Omus - Tiger beetles.
• Ondatra - Muskrats.
• †Oodectes - An early carnivore.
• Ophisaurus - Glass lizards.
• Ophryastes - A type of weevil.
• †Ophyra - A type of fly.
• †Opisthotriton - An ancient salamander.
• †Orchelimum - A type of katydid.
• Orchestes - A type of weevil.
• Oreamnos - Mountain goats (or a similar form).
  • 

    A living Oreamnos harringtoni, or Harrington's mountain goat
    †Oreamnos harringtoni - Harrington's mountain goat.
• †Oreopanax - A type of flowering plant.
• †Orohippus - An ancient horse.
• †Orontium - Golden club plants.
• †Orphilus - A type of beetle.
• †Orthocentrus - A type of parasitic wasp.
• †Osmanthus - A type of flowering plant.
• †Osmunda - Royal ferns.
  • †Osmunda greenlandica
• †Otiorhynchus - A type of weevil.
• Ovis - Sheep.
  • †Ovis canadensis - Bighorn sheep.
• †Oxyacodon - An early mammal.
• 

  Restoration of the Paleocene-Eocene creodont mammal Oxyaena
  †Oxyaena - An early carnivore.
• †Oxycera - A type of soldier fly.
• †Oxyomus - A type of scarab beetle.
• †Pachyaena - A large, early carnivore.
• †Paederus - A type of rove beetle.
• †Palaeogale - An ancient carnivore.
• †Palaeolagus - An ancient rabbit.
• †Palaeonictis - An early carnivore.
• †Palaeosinopa - An early mammal.
  • †Palaeospiza bella - An ancient bird.
• 

  Restorative model and fossilized skull of the Eocene brontothere mammal Palaeosyops
  †Palaeosyops - A large, rhinoceros-like mammal, first found in Colorado.
• †Palaeovespa - An ancient wasp, first found in Colorado!
  • †Palaeovespa florissantia - This specific species was also first discovered in Colorado.
  • †Palaeovespa gillettei - This specific species was also first discovered in Colorado.
  • †Palaeovespa relecta - This specific species was also first discovered in Colorado.
  • †Palaeovespa scudderi - This specific species was also first discovered in Colorado.
  • †Palaeovespa wilsoni - This specific species was also first discovered in Colorado.
• †Palatobaena - An ancient turtle.
• †Panax - Ginseng plants.
• †Panorpa - Scorpionflies.
• †Paracynarctus - An ancient dog relative.
• †Parahippus - An ancient horse.
  • †Parahippus leonensis - Or a very similar form.
• 

  Fossilized skeleton of the Pliocene-Pleistocene ground sloth Paramylodon
  †Paramylodon - A giant ground sloth.
  • †Paramylodon harlani
• †Paramys - An early rodent.
• †Parandra - A type of longhorn beetle.
• †Paratylopus - An ancient camel.
• †Parectypodus - An early mammal.
  • †Parectypodus lunatus
• †Parictis - An early bear relative.
• †Parthenocissus - Virginia creeper vines.
• †Passaloecus - A type of wasp.
• †Patriofelis - A large, cat-like carnivore.
• Pediacus - A type of beetle.
• Pekania - Fishers (mammals).
• †Pellea - Cliff brake ferns.
• 

  Fossilized skull of the Eocene-Oligocene lizard Peltosaurus
  †Peltosaurus - An ancient lizard.
  • †Peltosaurus granulosus - This specific species was first discovered in Colorado.
• †Pelycodus - An early primate.
  • †Pelycodus danielsae
  • †Pelycodus jarrovii
• Penthetria - A type of march fly, first found in Colorado.
• †Pepsis - Tarantula hawk wasps.
• †Peraceras - An ancient rhinoceros.
• †Peratherium - An ancient opossum.
• Peromyscus - Deer mice.
  • †Peromyscus maniculatus - Deer mice.
• Persea - Avocado trees.
• 

  Fossil of the Oligocene ant Petraeomyrmex
  †Petraeomyrmex - An ancient ant, first found in Colorado!
  • †Petraeomyrmex minimus - This specific species was also first discovered in Colorado.
• †Phaca - A type of plant.
• Phalacrocorax - Cormorants.
• Phalaropus - Phalaropes (birds).
  • †Phalaropus lobatus - Red-necked phalaropes.
• †Phasmagyps - An ancient vulture, first found in Colorado.
• Pheidole - A type of ant.
• †Phenacodus - An early hoofed mammal.
• Phenacomys - Heather voles.
  • †Phenacomys intermedius - Heather voles.
• Philadelphus - Mock-orange shrubs.
• †Philanthus - Beewolves (wasps).
• 

  Illustration of a fossilized skull in multiple views of the Oligocene-Miocene bone-crushing dog Phlaocyon
  †Phlaocyon - A type of bone-crushing dog.
• Phloeosinus - A type of bark beetle.
• †Phora - A type of scuttle fly.
• Phryganea - A type of caddisfly.
• Phrynosoma - Horned lizards.
  • †Phrynosoma douglassi - Short-horned lizards.
• †Phylledestes - An ancient insect, first found in Colorado!
  • †Phylledestes vorax - This specific species was also first discovered in Colorado.
• †Phyllobaenus - A type of beetle.
• Phyllobius - A type of weevil.
• †Phyllophaga - May beetles.
• †Phymatodes - A type of longhorn beetle.
• Pica - Magpies.
  • †Pica hudsonia - Black-billed magpies.
• Picea - Spruce trees.
• Picoides - Woodpeckers.
  • †Picoides villosus - Hairy woodpeckers.
• †Pidonia - A type of longhorn beetle.
• †Pimpla - A type of parasitic wasp.
• Pinus - Pine trees.
• †Pipiza - A type of hoverfly.
• †Pison - A type of wasp.
• Pituophis - Gopher snakes.
  • †Pituophis melanoleucus - Gopher snakes.
• Platanus - Sycamore trees.
• Plateumaris - A type of leaf beetle.
• †Platycheirus - A type of hoverfly.
• Platydema - A type of darkling beetle.
• 

  Life restoration of a herd of alarmed Miocene-Pleistocene peccaries of the genus Platygonus. Charles R. Knight (1922).
  †Platygonus - An ancient peccary (pig-like mammal).
• Platynus - A type of ground beetle.
• Platystethus - A type of rove beetle.
• Plecia - March flies.
• †Plesiadapis - An early primate.
• †Plesiobaena - An ancient turtle.
• †Pliohippus - An ancient horse.
• †Plochionus - A type of ground beetle.
• †Poabromylus - An ancient mammal.
• Podabrus - A type of soldier beetle.
• Podiceps - Grebes (birds).
• Podilymbus - Grebes.
  • †Podilymbus podiceps - Pied-billed grebes.
• 

  Life restoration of the Eocene-Oligocene camel Poebrotherium
  †Poebrotherium - An ancient camel.
• †Poecilocapsus - A type of plant bug.
• †Poecilognathus - A type of bee fly, first found in Colorado.
• †Pogonomyrmex - Harvester ants.
  • †Pogonomyrmex fossilis - This specific species was first discovered in Colorado.
• †Polysphincta - A type of parasitic wasp.
• Populus - Poplar trees.
• Porzana - Rails (birds).
  • †Porzana carolina - Sora rails.
• †Potamogeton - Pondweed plants.
• †Praepapilio - An ancient butterfly, first found in Colorado!
  • †Praepapilio colorado - This specific species was also first discovered in Colorado.
  • †Praepapilio gracilis - This specific species was also first discovered in Colorado.
• †Priabona - An ancient insect.
• †Pristichampsus - A crocodile relative.
• †Probathyopsis - An early mammal.
• †Procas - A type of weevil.
• 

  Illustration of a fossil of the Eocene butterfly Prodryas
  †Prodryas - An ancient butterfly, first found in Colorado!
  • †Prodryas persephone - This specific species was also first discovered in Colorado.
• †Proiridomyrmex - An ancient ant, first found in Colorado!
  • †Proiridomyrmex vetulus - This specific species was also first discovered in Colorado.
• †Prolimnocyon - An early carnivore.
• †Proscalops - An ancient mole.
• Prosopis - Mesquite trees.
• †Protazteca - An ancient ant, first found in Colorado!
  • †Protazteca capitata - This specific species was also first discovered in Colorado.
  • †Protazteca elongata - This specific species was first discovered in Colorado.
  • †Protazteca hendersoni - This specific species was also first discovered in Colorado.
  • †Protazteca quadrata - This specific species was also first discovered in Colorado.
• †Protohippus - An ancient horse.
• †Protolabis - An ancient camel.
• †Protomarctus - An ancient dog relative.
• 

  Protorohippus
  †Protorohippus - An ancient horse.
• †Protostephanus - An ancient wasp, first found in Colorado!
  • †Protostephanus ashmeadi - This specific species was also first discovered in Colorado.
• †Protungulatum - An early hoofed mammal.
  • †Protungulatum donnae
• Prunus - Cherry or plum trees.
  • †Prunus gracilis
• †Psephenus - Water penny beetles.
• Pseudacris - Chorus frogs.
  • †Pseudacris triseriata - Western chorus frogs.
• 

  Restoration of the Miocene cat Pseudaelurus
  †Pseudaelurus - An ancient cat.
• †Pseudhipparion - An ancient horse.
• Pseudomyrmex - A type of ant.
• †Pseudoprotoceras - An ancient mammal.
• †Psittacotherium - An early mammal.
• Ptelea - Hoptree shrubs.
• Pterocarya - Wingnut trees.
• †Pteromalus - A type of parasitic wasp.
• Pterostichus - A type of ground beetle.
• †Ptilodus - An early mammal.
  • †Ptilodus kummae
• †Ptosima - A type of jewel beetle.
• Quedius - A type of rove beetle.
• Quercus - Oak trees.
• Rallus - Rails (birds).
  • †Rallus limicola - Virginia rails.
• †Ramoceros - An ancient pronghorn relative.
• 

  Life restoration of the Miocene-Pliocene pronghorn Ramoceros and Cosoryx. Robert Bruce Horsfall (1913).
  †Ramoceros - An ancient pronghorn relative.
• †Rana - Frogs.
  • †Rana catesbeiana - Bullfrogs.
• †Raphidia - Snakeflies.
• Reithrodontomys - Harvest mice.
• Reticulitermes - Termites.
• Rhabdomastix - A type of crane fly.
• †Rhagio - A type of snipe fly.
• Rhagonycha - A type of soldier beetle.
• †Rhamnus - Buckthorn shrubs.
• †Rhamphomyia - A type of dance fly.
• 

  A living Rhineura floridana, or North American worm lizard
  Rhineura - Worm lizards.
• †Rhingia - A type of hoverfly.
• Rhizophagus - A type of beetle.
• Rhus - Sumac shrubs.
• †Rhyssa - A type of parasitic wasp.
• †Ribes - Currant and gooseberry shrubs.
• †Robinia - Locust trees.
• †Rogas - A type of parasitic wasp.
• Rosa - Roses.
• †Rothschildia - A type of moth.
• Rubus - Blackberry and raspberry plants.
• Sabal - Palmetto palms.
• †Saccoloma - A type of fern.
• Salix - Willow trees.
• †Sambucus - Elderberry shrubs.
• 

  Fossilized skeleton of the Eocene monitor lizard Saniwa
  †Saniwa - An ancient monitor lizard.
• †Saperda - A type of longhorn beetle.
  • †Saperda florissantensis - This specific species was first discovered in Colorado.
• †Sapindus - Soapberry trees.
• †Sapromyza - A type of fly.
• Sassafras - Sassafras trees.
  • †Sassafras hesperia
• Scaphinotus - A type of ground beetle.
• Sceloporus - Spiny lizards.
  • †Sceloporus undulatus - Eastern fence lizards.
• Sciara - A type of fungus gnat.
• †Sciophila - A type of fungus gnat.
• Sciurus - Squirrels.
• Scolytus - Bark beetles.
• †Segestria - A type of spider.
• †Selaginella - Spike moss plants.
• †Semanotus - A type of longhorn beetle.
• Sequoia - Redwood trees.
  • 

    Fossilized branch fragment from a Sequoia affinis
    †Sequoia affinis - An ancient redwood.
• Serica - A type of scarab beetle.
• †Sespia - An ancient mammal.
• †Sialia - Bluebirds.
• †Sibinia - A type of weevil.
• †Sifrhippus - An early horse.
• Sigmodon - Cotton rats.
• †Silpha - A type of carrion beetle.
• †Silvius - A type of horse fly.
• †Sinonyx - An early carnivore (or a similar form).
• Sitona - A type of weevil.
• †Sitones - A type of weevil.
• Sitta - Nuthatches.
  • †Sitta carolinensis - White-breasted nuthatches.
• †Smilax - Greenbrier vines.
• 

  Mounted fossilized skeleton of the Eocene primate Smilodectes
  †Smilodectes - An early primate.
  • †Smilodectes gracilis
  • †Smilodectes mcgrewi
• Sonoma - A type of spider.
• Sorex - Shrews.
  • †Sorex arcticus - Arctic shrews.
  • †Sorex hoyi - American pygmy shrews.
• †Sparganium - Bur-reed plants.
• Spea - Spadefoot toads.
  • †Spea bombifrons - Plains spadefoot toads.
• †Spermophagus - A type of seed beetle.
• Spermophilus - Ground squirrels.
  • †Spermophilus elegans - Wyoming ground squirrels (or a similar form).
  • †Spermophilus lateralis - Golden-mantled ground squirrels.
  • †Spermophilus richardsonii - Richardson's ground squirrels.
  • †Spermophilus tridecemlineatus - Thirteen-lined ground squirrels.
• †Sphegina - A type of hoverfly.
• 

  Life restoration of the Eocene brontothere mammal Sphenocoelus
  †Sphenocoelus - An ancient rhinoceros relative.
• Spilogale - Spotted skunks.
  • †Spilogale putorius - Eastern spotted skunks.
• Spizella - Sparrows.
  • †Spizella breweri - Brewer's sparrows.
• †Staphylea - Bladdernut shrubs.
• Staphylinus - A type of rove beetle.
• †Stenolophus - A type of ground beetle.
• †Stenosphenus - A type of longhorn beetle.
• Stenus - A type of rove beetle.
• Sterculia - A type of tree.
• Stilbus - A type of beetle.
• †Stipa - A type of grass.
• †Strategus - A type of rhinoceros beetle.
• †Stylinodon - An early mammal.
• 

  Life restoration of the Eocene-Oligocene cow-sized rhinoceros Subhyracodon. Charles R. Knight (1890s).
  †Subhyracodon - An ancient rhinoceros.
• Sylvilagus - Cottontail rabbits.
  • †Sylvilagus audubonii - Desert cottontail rabbits.
• †Symphoromyia - A type of snipe fly.
• Syrphus - A type of hoverfly.
• †Systena - A type of flea beetle.
• †Tabanus - Horse flies.
• Tachycineta - Swallows.
  • †Tachycineta bicolor - Tree swallows.
• Tachyporus - A type of rove beetle.
• †Tachys - A type of ground beetle.
• Tamiasciurus - Tree squirrels.
  • †Tamiasciurus hudsonicus - Red squirrels.
  • †Tanysphyrus lemnae - A type of weevil.
• Tapirus - Tapirs.
• Taxidea - Badgers.
  • †Taxidea taxus - American badgers.
• †Teilhardina - An early primate.
• 

  Restoration of the Miocene-Pliocene rhinoceros Teleoceras
  †Teleoceras - An ancient rhinoceros.
• †Tenor - An ancient insect, first found in Colorado.
• †Tenthredo - A type of sawfly.
• †Tetragnatha - A type of long-jawed orb weaver spider.
• †Tetraonyx - A type of blister beetle.
• †Tetraopes - A type of longhorn beetle.
  • †Tetraopes submersus - This specific species was first discovered in Colorado.
• †Tetrapus - A type of beetle.
• Thamnophis - Garter snakes.
  • 

    A living Thamnophis elegans, or western terrestrial garter snake
    †Thamnophis elegans - Western terrestrial garter snakes.
  • †Thamnophis sirtalis - Common garter snakes.
• †Thanasimus - A type of checkered beetle.
• †Themira - A type of fly.
• †Thomisus - A type of crab spider.
• Thomomys - Pocket gophers.
  • †Thomomys talpoides - Northern pocket gophers.
• †Thouinia - A type of flowering plant.
• †Thuja - Arborvitae trees.
• †Ticholeptus - An ancient mammal.
• Tilia - Linden trees.
• †Tingis - A type of lace bug.
• Tipula - Crane flies, first found in Colorado.
• †Titanoeca - A type of spider.
• 

  Life restoration of the Paleocene pantodont mammal Titanoides
  †Titanoides - A large, early mammal.
  • †Titanoides looki
  • †Titanoides primaevus
• †Tomarctus - An ancient dog.
  • †Tomarctus brevirostris - This specific species was first discovered in Colorado.
• †Tomoxia - A type of tumbling flower beetle.
  • †Tomoxia inundata - This specific species was first discovered in Colorado.
• †Torreya - A type of conifer tree.
• †Tortricites - A type of moth.
• †Tortrix - A type of moth.
  • †Tortrix florissantana - This specific species was first discovered in Colorado.
• †Torymus - A type of parasitic wasp.
• Trechus - A type of ground beetle.
• †Trichilia - A type of tree.
• †Triga - A type of beetle.
• †Trigonias - An ancient rhinoceros.
• †Trigonoscuta - A type of weevil.
• †Triplax - A type of pleasing fungus beetle.
• †Tritemnodon - An early carnivore.
• †Triumfetta - A type of flowering plant.
• †Trixoscelis - A type of fly.
• †Trogosus - An early mammal.
• Trogoxylon - A type of beetle.
• †Trogus - A type of parasitic wasp.
• †Tropisternus - A type of water scavenger beetle.
• Trox - A type of skin beetle.
• †Trypherus - A type of beetle.
• †Tryphon - A type of parasitic wasp.
• †Tychius - A type of weevil.
• Typha - Cattail plants.
• †Uintacyon - An early carnivore.
• †Uintascorpio - An ancient scorpion, first found in Colorado.
• Ulmus - Elm trees.
• †Ulus - A type of darkling beetle.
• Urocyon - Gray foxes.
  • 

    A living Urocyon cinereoargenteus, or gray fox
    †Urocyon cinereoargenteus - Gray foxes.
• †Ursavus - An early bear.
• Ursus - Bears.
  • †Ursus americanus - American black bears.
• †Ustatochoerus - An ancient mammal.
• †Vanessa - A type of butterfly.
• †Vauquelinia - A type of flowering plant.
• †Viburnum - Viburnum shrubs.
• †Vicia - Vetch plants.
• †Villa - A type of bee fly, first found in Colorado.
• Vitis - Grape vines.
• †Viverravus - An early carnivore.
• †Vrilletta - A type of beetle.
• 

  Mounted fossilized skeleton of the Eocene mammal Vulpavus
  †Vulpavus - An early carnivore.
• Vulpes - Foxes.
  • †Vulpes velox - Swift foxes.
  • †Vulpes vulpes - Red foxes.
• †Weinmannia - A type of tree.
• †Woodwardia - Chain ferns.
• †Xantholinus - A type of rove beetle.
• †Xestobium - A type of beetle.
• †Xylocopa - Carpenter bees.
• †Xylomya - A type of fly.
• †Xyronomys - An ancient rodent.
• †Yumaceras - An ancient insect.
• †Zamia - Cycad plants.
• Zelkova - Zelkova trees.
• Zizyphus - Jujube trees.
• Zonotrichia - Sparrows.
  • †Zonotrichia leucophrys - White-crowned sparrows.
• †Zootermopsis - Termites.
• 

  Known material diagram depicting the Miocene-Pleistocene mastodon relative Zygolophodon with a human to scale
  †Zygolophodon - An ancient mastodon relative.