Tuesday, December 19, 2017

Squalicorax: Beast of the Week

This week we will be checking out a another prehistoric shark.  Lets look at SqualicoraxSqualicorax was a shark that lived in the oceans that once covered North America, Europe, and Northern Africa.  There were four species of Squalicorax sharks, which between all of them, lived between roughly 84 and 68 million years ago.  Growing up to over sixteen feet long from snout to tail, Squalicorax would be considered a large shark, and a top predator in today's oceans. However, Squalicorax would have shared space with a myriad of other enormous marine animals, including giant marine lizard, Tylosaurus, which was possibly its predator.  The name, Squalicorax, translates to "Raven Shark".  I hypothesize this is due to the fact that there is strong fossil evidence of Squalicorax being a scavenger in life, and ravens are also known scavengers in their ecosystems on land.  (Although I cannot for the life of me find anything explaining the etymology on this animal.  If anyone reading this knows better and has a source, please let me know so I can fix it.)  Like all sharks, Squalicorax was a meat-eater.

Two Squalicorax falcatus feast on the remains of a dead juvenile Tylosaurus.

Squalicorax would have looked like a modern Gray Reef Shark, or possibly a Great White Shark, at a glance when alive.  It had a streamlined body, long triangular pectoral fins, and a tall dorsal fin.  However, its teeth were more similar to those of a modern Tiger Shark's, being shallow, finely serrated, and slightly curved to the side.  This means Squalicorax was adapted to cutting and gnawing at its food, an adaptation seen in sharks that frequently scavenge.  This is backed up by the fact that Squalicorax teeth marks have been found in the bones of other animals that would have been too large for it to have hunted.  Even entire Squalicorax teeth have been found embedded in some of these bones.  Fossil animals that this shark scavenged from include turtles, large fish, mosasaurs, and even a duck-billed dinosaur, which had probably died in a riverbed and washed out to sea.  Of course, there is no reason to assume Squalicorax only scavenged and never hunted live prey, too.  Most modern sharks, including all the species Squalicorax shares resemblance with, will hunt or scavenge depending on what food is available to them.

Squalicorax tooth, note how short and wide it is and the serrations.  When the shark bit into something and turned its head from side to side, these teeth would act like a saw to cut pieces of meat into bite-sized chunks.

Sharks, as you may already know, possess a skeleton that is almost entirely made of cartilage.  This soft tissue does not preserve well and hardly ever fossilizes.  Because of this, many prehistoric sharks are only known from teeth and jaws, leading experts to only hypothesize as to what they looked like by comparing their teeth to those of modern sharks.  Not the case with Squalicorax!  A wonderfully preserved fossil from this shark was unearthed in what is now Kansas that includes a fully fossilized head, spine, and pectoral fins!

Wonderfully preserved Squalicorax skeleton on display at the National Musuem in Washington D.C.

That is all for this week!  As always leave comments below!  Special thanks to paleontologist, Nathan VanVranken for his insight during the making of this article and life reconstruction above.

References

David R. Schwimmer, J. D. Stewart and G. Dent Williams. Scavenging by Sharks of the Genus Squalicorax in the Late Cretaceous of North America. PALAIOS Vol. 12, No. 1 (Feb., 1997), pp. 71-83

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