Other Anatomy

The papers yesterday described the anatomy of Helicoprion's tooth whorl and as such, though we usually pick the most interesting anatomy and describe it on Wednesdays, we will have to discuss something slightly different this Wednesday. The topic for today still has to do with the tooth whorl; it is actually almost impossible not to discuss the only two materials that are known from Helicoprion  fossils (crushed cartilage and dental remains). Two hundred ninety million years ago Helicoprion was a successful predator in oceans globally, but what was it eating with its strange tooth whorl? The tooth whorl, according to the Smithsonian reconstruction, was not the first line of attack for this shark, and that is something important to talk about in terms of diet. When the tooth whorl is placed in the older positions (in the front of the mouth, the middle of the mouth, as an extension of the chin) the scenes we saw in the Animal Planet clip make a lot of sense; Helicoprion slicing fish and squid in half furiously as it swims about in the ocean. The interpretation of Mary Parrish (with help from Robert Purdy, Victor Springer, and Matt Carrano) places the tooth whorl in the gullet of Helicoprion. This positioning places the whorl in the same area as the gills (consisting of five gills rather than six/seven as is common in basal extant sharks for the shark enthusiasts) but without blocking their ability to extract oxygen from the water. The solution to the tooth whorl being in the throat was not having to swallow food before being able to chew it or bite at it. Instead, this reconstruction possesses a set of teeth similar to those of other sharks; a cartilaginous jaw housing rows of teeth that are used for catching, injuring, and otherwise stopping prey from getting away. The teeth in the throat, then, could have been used to snag prey as it entered the oral cavity, with the more traditional teeth pulling the prey into the mouth and the tooth whorl pulling the prey into the throat. Extant animals such as some snakes, fish, and other reptiles as well as extinct animals like mosasaurs possess teeth on the palatal bones that act in a similar way, helping to hold and move prey further into the throat and down the esophagus than mandibular and maxillary teeth are capable of doing. This version of the purpose of the tooth whorl is practical, if not as fantastic as some of the past iterations of the curious anatomical hypotheses.