Jurassic Killing: was there active predation among different species of Jurassic pliosaurs? And did larger pliosaurs devour smaller ones – possibly even of the same genus?
The answer is a resounding yes.
Pliosaurs were a group of large-headed, short-necked plesiosaurs known as pliosauromorphs. They had powerful jaws filled with sharp teeth and four strong flippers to propel them through the water. They were also Sauropterygians. For the uninitiated, Sauropterygians were Mesozoic marine reptiles of the super order Sauropterygia, critters that are, as you know, near and dear to my heart (and its cockles). Today, I’m sharing a recent acquisition from my display case: a pliosaur centrum (vertebra) with tooth punctures from the larger predator that killed and ate it.
The centrum is Jurassic and came from the Kimmeridge clay, Oday Common, Abingdon, Oxfordshire, UK. It is missing its spinous and transverse processes. Only the body remains, with the base of the vertebral arch. The centrum itself is small – only 3 3/8 inches in width and 1.5 inches (75 mm) thick. Although the fossil dealer I acquired the piece from listed it as Pliosaurus macromerus (Phillips 1871), I have my doubts. It’s been my experience that dealers tend to arbitrarily assign almost any large pliosaur fossil to that (questionable) species.
In all honesty, it’s tough to be sure. However, based on the ventral smoothness, I suspect it is actually from a Pliosaurus brachydeiris (Owen 1841). It would’ve had to have been a young animal, as I’ve read the species reached at least 32 feet (10 meters), and I estimate the centrum’s owner was only around 16 feet (5 meters) when it was killed.
THE ATTACK
There’s no way of telling precisely what species of Jurassic pliosaur killed and fed upon the youngster, but it was almost certainly predation. This is supported by the presence of a series of tooth punctures from a much larger predator, on the body of the centrum itself. This bite mark is proceeded by smaller puncture marks (pink arrows) on the reverse side, inflicted by scavengers that fed on the dismembered carcass afterward, possibly a Hybodus (sp.) shark. The attacker (perhaps a Pliosaurus kevani – Benson et al 2013 – although other species or even a cannibalistic adult P. brachydeiris is possible) must have killed the smaller pliosaur (possibly with a skull bite – a favored mode of attack among macropredatory marine reptiles) and then savaged the carcass, biting and shaking it into bite-sized sections before swallowing them. The sacral (pelvic) region must have fallen to the sea floor, where it was scavenged.
The punctures from the attacking pliosaur (topmost image) are marked with white arrows. Interestingly, they are uniformly one inch apart (25 mm) and form an almost straight line. This strongly suggests that the punctures were caused by the smaller “ratchet teeth” toward the rear of the attacker’s jaws. These would’ve been used to manipulate the carcass as well as to help shear through it, like the carnassial teeth in cats. (see diagram of P. kevani for a visual – image credit Adam Smith).
Based on the spacing between the teeth, and using the P. kevani diagram as reference (with variances for nonspecific tooth placement), I estimate the attacking pliosaur had a skull somewhere in the range of 6.5 to 7 feet (2+ meters). That suggests a predator in the 32-35-foot range, and weighing somewhere between 10-13 tons.
Granted, there are a lot of variables in all of this, but I’m confident my size estimates are somewhere in the ball park. The rest (attacker’s species, etc) is a guessing game. Granted, a lot of deductions from such a small fossil. But when it comes to pliosaurs, oftentimes that’s all we have to work with. Ain’t paleontology fun?
-Max Hawthorne
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