Anatomy For All

©Brian Greenstone

Heliobatis fossils from the Green River Formation are very nearly the epitome of lagerstätten fossils. Because the preservation is so exceptional, there is a lot known about Heliobatis and its anatomy. The life history of these freshwater rays is well known because of this as well. We know that Heliobatis most likely ate small crustaceans, fish, and mollusks because we have found teeth in the fossils. Those teeth are small triangular biting teeth that are oriented very closely together.  These teeth could have been used defensively, however; like extant rays Heliobatis had a barbed stinger on their tails. Their stingers consisted of approximately three modified placoid scales (also called dermal denticles). The placoid scales were also found on the skin of these prehistoric rays and are very similar to the dermal denticles that are found attached to the skin of extant rays, skates, and sharks. One of the other very important characteristics of that we know of from the exquisite preservation of these animals is that they were sexually dimorphic. Male chondrichthyians, including Heliobatis, possessed clasping organs that are used to fertilize the female's eggs. More can be read about this topic in various places; the shortest version can be found here.