Ichthyosaur Odds and Ends

I have been a little bit obsessed with the alien creatures of the deep sea for the last week or so. I blame last week's research on the shastasaurids, a cool group of ichthyosaurs whose short snout, long bodies, and enlarged hyoids make them out to be precursors to the bodyplan of today's beaked whales.

In my post about the Shastasaurus paper, I shared my infatuation with the vision of shastasaurs diving deep to hunt bioluminescent cephalopods, and ended my post with a friendly challenge to paleoartists to make this happen. I'm happy to report that at least one has responded! Here's a take on that theme by Maija Karala, who posted it at DeviantArt.


Illustration © Maija Karala, via DeviantArt.

This little obsession has also added a stop on my future road trip that keeps getting bigger and bigger. In northeastern Nye County, Nevada is Berlin-Ichthyosaur State Park, where over three dozen ichthyosaurs have found their final watery resting places transformed into arid desert by the Earth's intractable geological processes. In addition to multiple skeletal remains in situ, the site boasts this enormous mural of Shonisaurus, the specific ichthyosaur discovered on the site. It's a bit outdated, as Shonisaurus is now believed not to have sported a dorsal fin, given its close affinity to Shastasaurus.


Photo by AlishaV, via Flickr.

I'd feel like a failure of a blogger if I mentioned Shonisaurus without sharing illustrator Shyama Golden's recent surreal take on it, housing what appears to be the call center of Sterling Cooper.


Illustration © Shyama Golden, via Flickr.

Finally, I'll share one more place that my deep sea imaginings have taken me: the Youtube channel of the Monterey Bay Aquarium Research Institute. Here's a new one posted this week, exploring the diverse forms of gelatinous dwellers of the deep. As you watch it, take a moment to think about how lucky we are to be a part of this endlessly wonderful natural world. Maybe you're having a crummy day. Maybe it will help. It helps me.

Shastasaurus sucks, in a good way.

It's too easy to think "ichthyosaur" and automatically conjure an image of a vaguely dolphin-shaped Mesozoic reptile, represented by a famous member of the group like Ichthyosaurus or Opthalmosaurus. It becomes just another role-player in the Mesozoic seas that now exist solely in our imaginations. But these were living animals, important members of lost ecosystems. Like a host of other extinct organisms, the deeper scientists look, the more nuanced and fascinating they become.

New research published in PLoS ONE demonstrates just how much you miss if you arrive at a superficial description of these animals and stop there. The study, by the University of Bonn's P. Martin Sander and Xiaohong Chen, Long Cheng, and Xiaofeng Wang of the Wuhan Institute of Geology and Mineral Resources in Hubei, China, takes a look at new fossil material representing the genus Shastasaurus, as well as a reevaluation of S. pacificus.

The shastasaurs are an odd offshoot of the ichthyosaur family, with short, slender snouts that appear to be truly toothless. While not entirely unknown in the ichthyosaur fossil record, toothlessness this plainly obvious is a unique characteristic of Shastosaurus: the upper surface of the Shastosaurus dentary, one of the lower jawbones, is smooth with no trace of grooves or pits for teeth. In others, toothlessness may be a mere artifact of poor preservation.

In seeking an explanation for these strange features, the authors draw a comparison to a living family of the ocean dwellers, the beaked whales of the family Ziphiidae, which have reduced dentition and similarly proportioned snouts as well as enlarged hyoid bones. In the PLoS ONE paper, the team writes, "the ziphiid whales are suction feeders in which the tongue is pulled back rapidly by strong retractor muscles that are attached to hypertrophied hyoid bones. In this way, prey items are taken up by the negative pressure generated in the oral cavity, obviating the need for teeth to hold them before swallowing."


Cuvier's Beaked Whale, shared by Navy Currents Magazine on Flickr.

The Ziphiids are a poorly understood family overall, with only a few species having been the subject of study. One thing we do know is that they are some of the whale family's gold medal divers, able to hunt deep water cephalopods and fish and crustaceans from near the sea floor, sometimes as deep as 500 meters. The authors paint a picture of Triassic oceans populated by a diverse range of ichthyosaurs including swift-swimming Shastasaurus in the open ocean, diving deep to prey on bioluminescent cephalopods, among other benthic delicacies. They suggest that as oxygen levels rose at the end of the Triassic, gill-breathing fish were able to supplant many of the creatures the ichthyosaurs relied on, instigating the dramatic decrease in ichthyosaur diversity in the Jurassic, presaging the family's eventual extinction. Except, naturally, in the imagination of a bizarre primate millions of years later.

What I'm getting at here is... let's see some Shastasaurus hunting glowing cephalopods, paleoartists!