Additional Sharks with Symphyseal Teeth

Other Sharks with Symphyseal Teeth

Sorry for the long delay, folks. I have been busy wrapping up the end of the school semester, and it certainly did not help that things have gotten crazy due to people’s reaction to the coronavirus. However, I still intend on picking back up were I left off.

To briefly recap, last post, we talked about Helicoprion, a mysterious whorl of teeth that turned out to be a strange symphyseal (down the mid-line of the jaw) arrangement of teeth in a strange shark. There are sharks other than Helicoprion that have similar symphyseal teeth. In fact, there are a number of sharks, which are probably closely related to Helicoprion, that share its characteristics.

One difference is that most of these sharks do not have a complete whorl. Helicoprion and its closest relatives appear to be unique in having a tooth row that completely coils back on itself. However, many of these sharks with symphyseal teeth only have an arc of teeth, rather than a complete whorl. Thus, their teeth begin like Helicoprion, starting to coil back on itself. However, the teeth fall out of the jaw, leaving an arc rather than a complete whorl. Because these tooth sets mimic an incomplete whorl, I will still refer to them as tooth whorls, for simplicity’s sake.

Another shark with a symphyseal tooth whorl, one that was mentioned in the last post, is Ornithoprion. This shark was found with preserved skull material, giving the first big hint about the arrangement of Helicoprion‘s teeth. Ornithoprion has an elongated lower jaw. The teeth, however, were located back in the mouth itself, located on a small mound in the lower jaw (pointed out by an arrow in the illustration). Note that, like Helicoprion, the tooth whorl was found only in the lower jaw. The upper jaw probably had tooth plates that opposed the tooth whorl. The exact purpose of this elongated jaw is not known. The main suggestion is that it was used to stir up a muddy bottom, exposing creatures living there or to rake prey out of the mud.

The skull of Ornithoprion. Note the hump in the lower jaw, highlighted by the arrow. That is where the arc of teeth was located. The front part of the lower jaw was toothless, and may have been used to pry or stir up prey out of the mud. Illustration from Zangerl (1966).

Another symphyseal shark with long jaws is Caseodus. Unlike Ornithoprion, the teeth extend to the end of the jaws, but the jaws are not as nearly as long as found in Ornithoprion. Also, it appears that the upper jaw of Caseodus extends to the same length as the lower jaw. Once more, the tooth whorl is confined to the lower jaw. It has rough, ornamented tooth pavements on both sides of the tooth whorl, as well as rough tooth pavements in the upper jaw. The symphyseal teeth themselves are a bit blunter than many of these other sharks. Overall, it appears that Caseodus may have been a shell-fish crusher, using its tooth pavements and blunt teeth to crush its prey.

Aside from Helicoprion itself, the most famous of the sharks with symphyseal teeth is Edestus. Unlike many of these sharks, it has not one tooth whorl, but two. One tooth whorl is found in the lower jaw, as usual, but the other is found in the upper jaw. Having opposing rows of teeth running down the middle of the jaws is strange: how do the work against each other? Some have suggested that the tooth whorls curved around to the front of the upper and lower jaw. The whole front of the mouth would then bristle with an array of sharp, cutting teeth. Reconstructed this way, the teeth were used as blades: the head was swung up and down, slashing the teeth at fish, cutting them up and disabling them. The shark could then feed on the fish at its leisure.

Reconstruction of Edestus with the tooth whorls curving to the front of the jaws. The teeth would be used to slash at its prey, cutting them up and disabling them. Illustration from Itano (2015).

More recent materials, including new skull material, have suggested that the teeth of Edestus did not protrude from the mouth. Instead, the teeth appear to have been held entirely within the mouth and the teeth simply opposed each other. Reconstructed this way, the opposing tooth whorls would have acted like scissors. When the mouth closed, the opposing tooth rows would slice opposite each other, cutting up its prey. Like Helicoprion, Edestus may have specialized on soft bodied prey, like squids.

A more resent reconstruction of the head of Edestus. Note that in this reconstruction, the teeth are confined to the jaws and would have acted a lot more like bladed scissors. Illustration from Tapanila, et al. (2018).

Edestus and Helicoprion are neat contrasts. The former is a scissor-jawed shark, that probably swam into schools of squid, cutting up prey, and then turning back around to suck up the dismembered parts. Helicoprion is a buzz-saw shark, using its lower jaw as a saw to cut ammonites out of their shells, so as to eat the soft bodies.

There is nothing today quite like these symphyseal teeth sharks. They all belonged to the Eugeneodontiformes, a larger group that includes the modern day chimeras or ratfish, but even then, these living relatives are quite different from these strange, scissor-jawed and buzz-saw-jawed sharks. It is unfortunate that these sharks are gone: it would be wonderful to see these strange, unique sharks in life. Frankly, that is part of the consequence of the Global Flood. According to Genesis 6:5-7, God sent the Flood to destroy mankind, to wipe the slate clean, as it were. However, the Flood had greater consequences than simply punishing mankind: it left a permanent mark on the creatures on our planet. Thinks like these symphyseal teeth sharks probably went extinct shortly after, or even possibly during, the Flood. Today, we can only attempt to understand and reconstruct these sharks using sparse and fragmentary fossils. It is a sobering reminder of the consequences of mankind’s rebellion against God.

Thoughts from Steven

Sources of Information:

Itano, Wayne (2015) “An abraded tooth of Edestus (Chondrichthyes, Eugeneodontiformes): Evidence for a unique mode of predation” Transactions of the Kansas Academy of Science 118(1-2): 1-9

Mutter, Raoul and Andrew Neuman (2008) “Jaws and dentition in an Early Triassic, 3-dimensionally preserved eugeneodontid skull (Chondrichthyes)” Acta Geologica Polonica 58(2): 223-227

Tapanila, Leif; Jesse Pruitt; Cheryl Wilga; Alan Padel (2018) “Saws, Scissors, and Sharks: Late Paleozoic Experimentation with Symphyseal Dentition” The Anatomical Record Advances in Integrative Anatomy and Evolutionary Biology 303(2)

Zangerl, Rainer (1966) “A New Shark of the Family Edestidae, Ornithoprion hertwigi From the Pennsylvanian Mecca and Logan Quarry Shales of Indiana” Fieldiana: Geology 16(1): 1-44

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