Holonema facts for kids
Quick facts for kids HolonemaTemporal range: Givetian to Frasnian
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| H. westolli | |
Scientific classification  |
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| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | †Placodermi |
| Order: | †Arthrodira |
| Family: | †Holonematidae |
| Genus: | †Holonema Newberry, 1889 |
| Type species | |
| Pterichthys rugosum Claypole, 1883
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Holonema was a type of ancient fish that lived in the oceans a very long time ago, during the Devonian Period. These fish are now extinct, meaning they no longer exist. They were quite large and had a unique barrel-shaped body. Holonema belonged to a group of armored fish called placoderms. Their fossils have been found all over the world.
Most of what we know about Holonema comes from pieces of their bony armor. However, one special species, H. westolli, was found almost completely preserved at the Gogo Reef in Australia. These amazing fossils show that Holonema likely ate by grazing on hard, horn-shaped algae called oncholite. They probably used a special snout to snip off pieces of this algae. The last of these fish disappeared during a big event called the Frasnian-Fammian extinction event.
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Meet the Holonema Species
Scientists have discovered several different species of Holonema. Each one has unique features and was found in different parts of the world.
H. rugosum
H. rugosum is the first species of Holonema ever described. It was initially thought to be a different type of armored fish. Fossils of this species have been found in New York and Pennsylvania in the USA, and also in Wisconsin and Michigan. It was a fairly large fish. Even a small piece of its armor, called a median dorsal plate, could be about 18 centimeters long. Some other fossil finds might also belong to this species, including those from Iran.
H. arcticum
This was a large species found in Novaya Zemlya, Russia. We only know about H. arcticum from two pieces of its body armor. These pieces came from a single fish.
H. bruehni
H. bruehni is a newer discovery from Germany. Interestingly, young H. bruehni fish had bumpy skin armor. But as they grew into adults, their armor became smooth.
H. farrowi
This species is known from fragments found in Michigan, USA. The median dorsal plates of H. farrowi could be up to 20 centimeters long. These plates were wide at the back but got narrower towards the front.
H. haiti
Fossils of H. haiti were found in Idaho, USA. Its median dorsal plate is estimated to have been about 28 centimeters long. This plate was very narrow compared to other Holonema species.
H. harmae
H. harmae was discovered in Estonia. What makes this species special is how the edges of its lower armor plates met. They formed almost a perfect right angle.
H. obrutshevi
This species was also found in Eifelian-aged rocks in Estonia. Its median dorsal plate had a small, horn-like bump. When viewed from above or below, its body armor looked somewhat round.
H. ornatum
H. ornatum comes from the Shetland Islands. We don't know much about this species. Some scientists even think it might not be a true Holonema at all.
H. radiatum
This species is mainly known from fossils found in Russia and the Baltic region. It was a large fish with a moderately narrow median dorsal plate. This plate averaged about 30 centimeters in length. Fossils have also been found in Poland and Spitzbergen.
H. westolli
H. westolli is the most well-known species of Holonema. Many complete fossils, some with full skeletons, have been found at the Gogo Reef in Australia. This species looks a lot like H. rugosum, but its body armor was a bit narrower. The median dorsal plate was about 23 centimeters long. Scientists estimate that a living H. westolli fish could have been around 150 centimeters (about 5 feet) long!
- Case, Gerald Ramon. A Pictorial Guide to Fossils
- Long, John. Swimming In Stone
