Scientists who famously discovered the lobe-finned fish fossil Tiktaalik roseae, a species with some of the clearest evidence of the evolutionary transition from fish to limbed animals, have described another new species of predatory fossil lobe-finned fish fish from the same time and place. By describing more Devonian species, they’re gaining a greater understanding of the “fish-eat-fish world” that drove the evolution of limbed vertebrates.
“We call it a ‘fish-eat-fish world,’ an ecosystem where you really needed to escape predation,” said Dr. Ted Daeschler, describing life in the Devonian period in what is now far-northern Canada.
This was the environment where the famous fossil fish species Tiktaalik roseaelived 375 million years ago. This lobe-finned fish, co-discovered by Daeschler, an associate professor at Drexel University in the Department of Biodiversity, Earth and Environmental Science, and associate curator and vice president of the Academy of Natural Sciences of Drexel University, and his colleagues Dr. Neil Shubin and Dr. Farish A. Jenkins, Jr., was first described in Nature in 2006.This species received scientific and popular acclaim for providing some of the clearest evidence of the evolutionary transition from lobe-finned fish to limbed animals, or tetrapods.
Daeschler and his colleagues from the Tiktaalik research, including Academy research associate Dr. Jason Downs, have now described another new lobe-finned fish species from the same time and place in the Canadian Arctic. They describe the new species, Holoptychius bergmanni, in the latest issue of the Proceedings of the Academy of Natural Sciences of Philadelphia.
“We’re fleshing out our knowledge of the community of vertebrates that lived at this important location,” said Downs, who was lead author of the paper. He said describing species from this important time and place will help the scientific community understand the transition from finned vertebrates to limbed vertebrates that occurred in this ecosystem.
“It was a tough world back there in the Devonian. There were a lot of big predatory fish with big teeth and heavy armor of interlocking scales on their bodies,” said Daeschler.
Daeschler said Holoptychius and Tiktaalik were both large predatory fishes adapted to life in stream environments. The two species may have competed with one another for similar prey, although it is possible they specialized in slightly different niches; Tiktaalik’s tetrapod-like skeletal features made it especially well suited to living in the shallowest waters.
The fossil specimens of Holoptychis bergmanni that researchers used to characterize this new species come from multiple individuals and include lower jaws with teeth, skull pieces including the skull roof and braincase, and parts of the shoulder girdles. The complete fish would have been 2 to 3 feet long when it was alive.
“The three-dimensional preservation of this material is spectacular,” Daeschler said. “For something as old as this, we’ll really be able to collect some good information about the anatomy of these animals.”
The research on Holoptychius bergmanni was led by Downs, a former post-doctoral fellow working with Daeschler who also teaches at Swarthmore College. Other co-authors of the paper with Downs and Daeschler are Dr. Neil Shubin of the University of Chicago, and the late Dr. Farish Jenkins, Jr. of Harvard University, who passed away in 2012.
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