Baby Food for Ichthyosaurs

Last week, an [article] was published describing an old specimen that was hidden away in a museum collection at the University of Birmingham, United Kingdom. This specimen was of a baby ichthyosaur, only 70 cm long.

Some different ichthyosaurs. From here.

Ichthyosaurs were marine reptiles that lived during the Mesozoic Era. They had torpedo-shaped bodies, similar to modern dolphins and great white sharks. They came in all sorts of sizes and shapes!

Figure 1 from the paper showing the ichthyosaur fossil.

The authors know the specimen is a baby because some of its bones are still being developed and because of the proportions of the eyes and different bones in the skull. It was not found near an adult, so it wasn’t an embryo. This is the smallest specimen of Ichthyosaurus communis ever found!

Figure 9b from the article showing the hooklets in the stomach (by the black arrows). The long grey bones are ribs.

The interesting thing, though, is what they found in the stomach. Inside the ribs, the authors found several cephalopod hooklets. Remember, cephalopods are animals like octopus, squid, and nautilis. These hooklets are found on the underside of their tentacles, exactly where you’d find the suckers on an octopus arm.

A comparison of suckers and hooks on two different cephalopods. From here and here.

This indicates that the baby ichthyosaur was eating squid as its preferred food! Other species of ichthyosaur ate mostly fish as babies and transitioned to eating cephalopods as adults. This baby specimen shows that Ichthyosaurus communis ate cephalopods as babies, giving us a more thorough view of the diets of ichthyosaurs through their lifetimes.

The Mysterious Sea Bear

Sometimes we find fossils that we can’t quite compare to living animals. We can get a rough idea of what kind of animal they are and maybe what they might have eaten, but the details are unknown. Sometimes it’s because we don’t have enough of the animal’s body parts, but sometimes it’s because they are different from anything alive today.

The animal Kolponomos is like that. From the shape of its head, we knew it was related to the group Carnivora. Carnivorans include dogs, foxes, cats, bears, seals, sea lions, walruses, weasels, skunks, otters, hyenas, mongooses, and a few other animals, that eat other animals.

kolpy skull

Drawing of a Kolponomos skull done by C. Tarka and L. Meeker at the AMNH.

The odd thing about Kolponomos is that it might be a close relative of bears, but it had molars (those are the teeth in the back that grind up our food) like an otter. Otters eat hard-shelled animals using their molars, but they use tools to crush the shells open if they are too big:

Walruses also eat hard-shelled ocean creatures like clams by sucking the shell until it opens and eating the delicious insides.

walrusxi         walrus skull
“The walrus has the longest canines of all Carnivorans.” (says Jack Tseng, lead author on the paper)

Scientists couldn’t figure out how Kolponomos was eating these things, until this article came out in Proceedings of the Royal Society B. The authors tested how strong the skull was and how it moved while it bit down.

They found that Kolponomos would dive into the ocean, support its head using its lower front teeth, clamp down on the clam, and twist it off the rock using its strong neck muscles. Then it would move the clam to its molars where it would be crushed open.

fig1

Figure 1 from the article.

An interesting point about this is that sabre-tooth cats, like Smilodon would use the same method of supporting its head using its lower front teeth to drive its sabres into its prey.

Smilodon-jaw-opening

Diego

© Disney

So Kolponomos is a bear-relative, with a diet like an otter or walrus, with a bite like a sabre-tooth, that lived by the ocean. Probably not in a pineapple though.