Researchers use new calculations to reveal downsizing and thick details about
The species Dunkleosteus terrelli was Earth’s first vertebrate “superpredator” and lived during the Age of Fish (Devonian Period) – when North America was close to the latitude of what is now Rio de Janeiro.
But in nearly 150 years of research since fossil remains of the prehistoric big fish were discovered on the shores of Lake Erie in 1867, scientists may have made some erroneous assumptions about Dunkleosteus’ size and shark-like shape.
In research published this month, a researcher from Case Western Reserve University suggests that the length of this prehistoric predator may have been greatly exaggerated – that it was much shorter and thicker.
Cleveland mascot and Ohio’s best fossil fish
“Dunkleosteus is already a strange fish, but it turns out that the old size estimates resulted in us overlooking many features that made this fish even more strange, like a very tuna-like torso,” said Russell Engelman, a PhD student in biology from Case Western Reserve. and lead author on a study published in the journal Diversity in February. “Some colleagues have called it ‘Chunky Dunk’ or ‘Chunkleosteus’ after seeing my research.”
Engelman said he recognizes downsizing of the iconic Dunkleosteus may not be welcome news because the big fish is “essentially Cleveland’s mascot when it comes to paleontology” (The the species even had a Twitter account for a few years). As a native Clevelander, he said he initially had similar feelings.
Most research on Dunkleosteus is based on specimens in the Cleveland Museum of Natural History, which has the largest and highest quality collection of Dunkleosteus remains in the world. And the name honors both a former museum curator (David Dunkle) and a local business owner (Jay Terrell) who discovered the fossilized species.
Dunkleosteus is as homegrown an icon as in 2020, the Ohio General Assembly declared Dunkleosteus terrelli the state’s fossil fish.
Yet little research has been done on the fish since the 1930s, Engelman said.
“Without reliable size estimates, not much can be said about Dunkleosteus scientifically beyond ‘look at that big, scary fish!'” Engelman said. “These length estimates were an example of something that just slipped by everyone because it was assumed that this fish has been well studied.”
Short head, short body
Most estimates of the species’ length were not based on hard evidence, Engelman said.
It is because Dunkleosteus was a type of extinct fish called an arthrodire. Unlike modern fish, arthrodires like Dunkleosteus had bony, armored heads but internal skeletons made of cartilage. This means that only the heads of these animals were preserved as fossils, leaving their size and shape a mystery.
The new study suggests estimating length based on the 24-inch-long head, minus the snout — considered a way of measurement that is consistent among groups of living fish and smaller relatives of Dunkleosteus known from complete skeletons.
“The rationale behind this study can be summed up in a simple observation,” Engelman said. “Short fish generally have short heads and long fish generally have long heads.”
Based on that method, Engelman concluded Dunkleosteus was only 11 to 13 feet long—much shorter than any researcher had previously suggested.
‘Wrecking balls’ of the deep
“Dunkleosteus has often been reconstructed assuming it had a body shape like a shark,” Engelman said.
But a shorter body and shape of the body armor also mattered Dunkleosteus was probably much thicker.
“An 11-footer Dunkleosteus is essentially the same weight as a 15-foot great white shark,” Engelman said. “These things were built like wrecking balls. The new proportions for Dunkleosteus may look clumsy until you realize it has the body shape of a tuna … and a mouth twice the size of a great white shark.”
These new size estimates also help set Dunkleosteus in a wider scientific context. Dunkleosteus is part of a larger evolutionary story, there
Reference: “A Devonian Fish Tale: A new method of body length estimation suggests much smaller sizes for Dunkleosteus terrelli (Placodermi: Arthrodira)
by Russell K. Engelm, February 21, 2023, Diversity.
Engelman conducted her research under advisor Darin Croft, professor of anatomy at Case Western Reserve School of Medicine, who also advises undergraduate biology students in the College of Arts and Sciences.