Cheirolepis canadensis
Name: Cheirolepis canadensis [Canadian Scale-hand]
When: Middle to Late Devonian Period, about 385 - 370 million years ago
Where: Numerous localities in Quebec, Belarus, and Estonia
Claim to fame: The Devonian Period is called not called "the age of fishes" because the first fish lived then. Fish have been around much longer, but the diversification of fish accelerated in the Devonian. A huge part of this the explosion of the bony fish - Osteichthyes. Living bony fish fall into two great groups:
- Ray-finned fish - including most living bony fish from guppies to blue marlins.
- Lobe-finned fish - common in early oceans, but rare today as fish - limited to coelacanths and lungfish. (Psst! Land vertebrates are lobe-finned fish whose ancestors left the water!)
So, what about Cheirolepiss. It is more than a predator that inhabited fresh water and estuaries? This fish provides a snapshot of what ray-finned fish looked like just barely after their split with lobe-finned fish. Like other bony fish of the time, it shows the basic adaptations of its group - in this case having only one dorsal fin and a shark-like heterocercal tail fin, but it retains ancestral features of primitive jawed vertebrates, including pelvic fins that take the form of elongate "fin-folds," and jaws that open and close like scissors rather than expanding into a tube. In its preferred environments, Cheirolepis was a dominant predator with a very wide gape, enabling it to swallow prey over half its own length, that topped out at ~ 22 cm. Its large eyes suggest that it inhabited clear water, where it hunted using its vision.
