Microleter facts for kids
Quick facts for kids Microleter |
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| Skull diagram | |
Scientific classification  |
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| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | †Parareptilia |
| Order: | †Procolophonomorpha |
| Node: | †Ankyramorpha |
| Genus: | †Microleter Tsuji et al., 2010 |
| Type species | |
| †Microleter mckinzieorum Tsuji et al., 2010
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Microleter was an extinct (meaning it no longer exists) type of reptile. It lived a very long time ago, during the Early Permian period, in what is now Oklahoma.
This ancient creature belongs to a group called parareptiles. The only known species of Microleter is Microleter mckinzieorum. Scientists learned about Microleter from fossils found in a special place called Richards Spur.
Discovering Microleter
The only known fossil of Microleter is a very well-preserved skull and lower jaw. Scientists call this special fossil the holotype specimen, and its official name is OMNH 71306.
This amazing fossil was found at the Dolese Brothers limestone quarry. This quarry is near Richards Spur in Comanche County, Oklahoma.
The quarry is famous for its "fissure fills." These are cracks in an Ordovician cave system that got filled with sediment. This sediment then preserved many fossils.
These fissure fills are from the Early Permian period, about 289 to 286 million years ago. They have given us many well-preserved tetrapod fossils. In fact, it's one of the best places in North America to find parareptile fossils from the Permian period.
Scientists Linda A. Tsuji, Johannes Muller, and Robert R. Reisz officially named Microleter mckinzieorum in 2010. The name Microleter means "small" (from "micro") and "-leter," which is a common ending for parareptile names. The second part of the name, mckinzieorum, honors the McKinzie family. Mark McKinzie was the one who discovered this important fossil.
What Microleter Looked Like
Scientists believe the Microleter fossil was from a young animal. They think this because its eye holes (called orbits) were quite large. Also, the skull bones were not very tightly joined together.
Most of the skull bones had a rough surface with pits and grooves. However, some parts, like the upper jaw and cheekbones, were smooth.
The upper jaw (called the maxilla) was long and narrow. It had many cone-shaped teeth, about 32 or 33 of them! This is a lot more teeth than most other parareptiles.
Microleter had a special type of tooth structure called plicidentine. This means the inside part of its teeth (the dentine) was folded. This kind of tooth is often seen in ancient amphibians.
The bone near its eye (the lacrimal) likely reached its nostril holes (called nares). This is a feature also seen in other parareptiles like millerettids and pareiasaurs.
The front edge of its eye socket was thick. This was due to a special part of the prefrontal bone. The frontal bone, which is on top of the head, also contributed a little to the eye socket.
The jugal and postfrontal bones, located near the cheek and eye, were small and shaped like a crescent moon. However, the postorbital bone was larger.
Microleter had a tall, narrow opening at the back of its skull. This opening is called a temporal emargination. It was bordered by several bones, including the postorbital, jugal, squamosal, and quadratojugal. This opening is similar to the temporal opening found in other parareptiles.
The back of the skull was not very long. It had a wide parietal bone on top. The squamosal and quadratojugal bones were tall and boxy.
Most of the roof of its mouth (the palate) is hidden in the fossil. However, scientists could see that the palatine bone was very wide.
The lower jaw (called the dentary) had small pits on its surface. Unfortunately, the teeth on the lower jaw are not clear enough to count.
Microleter is one of the few parareptiles where parts of its sclerotic ring were preserved. This ring was made of tall, curved plates and helped support the eye. Only a few poorly preserved neck bones (called cervical vertebrae) were found from the rest of its body.
Where Microleter Fits In
Microleter is considered one of the most basal (meaning early or primitive) parareptiles. When it was first discovered, scientists thought it was the earliest parareptile found in Laurasia. Laurasia was a supercontinent that included what is now North America and Asia.
Before Microleter was found, some scientists believed parareptiles first appeared in Gondwana. Gondwana was another supercontinent, including what is now South America, Africa, and Australia.
However, Microleter appeared in Laurasia very early in the Permian period. This discovery helped scientists consider that parareptiles might have actually started in Laurasia. Other reasons supporting a Laurasian origin include the early appearance of bolosaurians (another group of parareptiles) in Laurasia. Also, the other main groups of amniotes (reptiles, birds, mammals) are thought to have started in Laurasia.
Scientists use special computer programs to figure out how different animals are related. This is called phylogenetic analysis. In their first study, scientists placed Microleter as more advanced than millerettids but less advanced than lanthanosuchoids.
Here's a simplified family tree showing where Microleter fits in with other parareptiles:
| Parareptilia |
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Since its first description, other studies have had slightly different ideas about Microleter's exact place in the family tree. Some studies suggest it's a sister taxon (very closely related) to Australothyris. Others place it as more basal than Australothyris or as a basal ankyramorph that is more advanced than lanthanosuchoids.
