WEIRD SHARKS
Weird Sharks Wright State Students
& Ryan Shell, SA-7165, Paige Wilms, SA-9748, Connor Motzko
Throughout history, as the world became more thoroughly explored, our understanding of “monsters” caused the total number of animals considered “monstrous” to drop. Sharks, however, always seem to remain on these subconscious lists. Their primitive two body plans, large sizes, and razor-sharp teeth all come together to create this image of a terrifying predator. As a student of paleontology, I have noticed that many of the features that make sharks interesting to the casual observer seem to magnify with geologic time. The strange, primitive body plans seen in modern sharks and rays (the elasmobranchs) appear stretched to their limit as we peer into the past. The large sizes seen today (in the White shark, for example) are dwarfed by the likes of the mega-toothed sharks of the earlier Cenozoic. Finally, their razor-sharp teeth, though ubiquitous, leave much less information for paleontologists to work from than the fossils of other vertebrate groups. In many ways, sharks are as mysterious to paleontologists as they are to beachgoers, albeit for different reasons.
My name is Ryan Shell. I am a PhD candidate at Wright State University. As you could guess, the bulk of my research deals with sharks in deep time (specifically the Permian Period of Texas and Kansas). I would like to introduce three ancient sharks: species that are not as well-known in popular culture as the Megalodon yet deserve more than a passing glance by museum visitors.
At Wright State University, it has been my privilege to join several paleontology field courses (and to plan a few as well) with a focus on sharks and other ancient marine predators. I wrote an article last year (Student Edition volume 50, issue 1) with David Peterman detailing some of these experiences and what they taught us. For this article, I would like to change course somewhat and discuss the ancient marine predators themselves. Two former students , Paige Wilms and Connor Motzko, are each weighing in on their favorite species.
Paige is doing her undergraduate research on a Pennsylvanian shark community in central Ohio. Following in the footsteps of a field course I helped to teach, Connor has been searching for the remains of Miocene and Cretaceous sharks in North Carolina.
34 TPG •
Oct.Nov.Dec 2020 Ryan’s entry:
The trilobite that was a fish and the fish that was
a trilobite. The shark genus Janassa is an atypical shark in the modern
sense (or rather, a chondrichthyan since it pre-dates the evo- lution of true sharks). In fact, I think it is atypical in almost every respect. Its flattened teeth, arranged into “tooth families” are unlike any modern shark teeth, and it is one of the rare few Paleozoic chondrichthyans to be preserved as a body fos- sil. I first encountered this genus when I recovered its fossil teeth from Permian sediments in southern Texas and eastern Kansas during my dissertation field work. The bizarre shape of the teeth, however, isn’t what keeps me talking about it. The history of how this animal was classified, as science the concept was invented, is almost poetic. A poetic comedy to be specific.
First, a lesson in tooth anatomy. There are two ‘faces’ of a shark tooth, these faces are where most of the anatomical information that we use to identify teeth and describe new species can be found. The labial, or lip-side, of the tooth is the surface that faces outward while the lingual, or tongue side, faces inward.
The lingual side of a Janassa tooth has most of the features
useful to taxonomists. The crown of the tooth itself is usually shaped like a half-circle, and there is a washboard-like row of ridges (cristae) beneath the main cusp that is often as thick or thicker than the crown itself. Finally, there is the root which is fairly small and featureless (see the figure below). The three anatomical zones of this tooth, coupled with the fact that many Janassa fossils are only single teeth, combined to create a perfect storm in 1820 when Ernst Friedrich, Baron von Schlotheim discovered and described the type species (the species to which all other members of the genus are compared), Janassa bituminosa, as a trilobite.
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