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!

Dinosaurs in a Trash Heap

Earlier this year, The National Archives UK released a collection of photographs as part of a project called Africa Through a Lens. Originally held by the Colonial Office, a government agency that handled the affairs of British colonial territories, they document a hundred years of British involvement on the continent. The photos have also been shared at Flickr. The sets are organized by country, and in the Lesotho set, I found this 1955 photo depicting an excavation in Triassic rocks in a village called Mahputseng.



In his essential 1968 book Men and Dinosaurs (republished by Dover in 1984 as The Great Dinosaur Hunters and Their Discoveries, Edwin Colbert touches on this dig briefly. He writes,

One of the most interesting of recent excavations in this part of the world was carried on at a locality known as Maphutseng, in Lesotho. Here, in the very backyard of an African house - a typical Basuto house with walls of mud and a thatched roof - a shallow quarry was developed by two French residents among the Basutos, the brothers Ellenberger, with [AW] Crompton and his associates participating in the dig. Many bones of large Triassic dinosaurs not unlike the bones excavated by von Huene at Trossingen in southern Germany were dug up...

The brothers he refers to are François and Paul Ellenberger, who would later erect the name Thotobolosaurus for the Maphutseng bones. It's likely that it's one of the brothers in the photo. The name Thotobolosaurus is derived from the Sesotho word for "trash heap," referring to the village refuse pile near the spot where the fossils were found.

In the early sixties, the Ellenbergers wrote that the bones "represent nearly all parts of the skeleton except the skull, and come from 7 to 8 individuals of variable size but, it seems, a single species... The preparation of all this material and the reconstruction of the skeleton evidently will be long-term." (PDF). Long-term is right; unfortunately, they still have never been formally described. They describe the dinosaur as being something close to Plateosaurus or Melanorosaurus, another basal sauropodomorph from South Africa. Considering all of the work recently done at the bottom of the sauropod family tree, it would be interesting to see some serious attention given to the Ellenberger's refuse pile find, especially since there's some doubt about whether any of the bones are sufficient to support a unique genus.

As an additional bit of colonial African history, notice the name in the lower right corner, Alwyn Bisschoff, presumably the photographer. Formerly an aircraft technician for the South African air force, at the time this photo was taken he was an agricultural officer for the British government in Basutoland, Lesotho's colonial name until independence in 1966. As it turns out, he's also a bit of a hero among the Land Rover off-roading crowd.

Cheerio, Chromogisaurus

Paleontologist Martin Ezcurra, who has been pretty prolific lately, has just published a description of a new Argentinian dinosaur, Chromogisaurus novasi, in the Journal of Systematic Paleontology. Additionally, Ezcurra takes on the issue of diversity among the earliest dinosaurs.


A canyon in the Ischigualasto region of Argentina. By Richard E. Ducker, via Flickr.

Chromogisaurus comes from the Ischigualasto geological formation of Argentina, one of the world's most important windows into the Triassic period. The Triassic is the first of the three periods that make up the Mesozoic era, a time when life on the supercontinent Pangaea was evolving in new directions in the wake of the devastating extinction event that closed the Permian period. One of those new directions was the dinosaurs, and Ischigualasto is one of the best areas to look into those early days of a biological dynasty that would last the better part of 200 million years.

We're talking about the lowest branches of the dinosaur family tree here. Chromogisaurus and its closest kin, including Saturnalia, Guaibasaurus, and Panphagia, were the very beginnings of the line that would lead to Diplodocus, Brachiosaurus, and the other titanic sauropods. Called sauropodomorphs, they display a mix of features between true sauropods and the theropods with whom they shared a common ancestor. As is suggested by the generic name Panphagia ("eater of everything"), these critters were so closely related to the earliest theropods that they likely were omnivorous. The skull of Chromogisaurus has not been found, but it's not too great a stretch to guess that it probably was, too. Omnivory wasn't a path the basal sauropods walked for long, and it would be their adaptation to a fully herbivorous diet that would lead to their exponential increase in size.

What's frustrating about the Triassic fossil record concerning dinosaurs is that when they first pop up - during a subdivision called the Carnian stage, about 230 million years ago - the three main branches of dinosaurs are present. We simply do not have many good places where the earlier stages of the Triassic are available for study, and none of them reveal earlier dinosaurs. There are plenty of near-dinosaur archosaurs, and it's a fool's errand to try to find "the first dinosaur," as it is to find the mythical "missing link" between man and ape. Life is a fuzzy thing. So we keep looking for new fossils that give a higher resolution picture of how life changed over time, when certain adaptations arose.

Ezcurra's analysis of the diversity of these earliest dinosaurs indicates that it was quite high, though these dinosaurs made up a small fraction of land vertebrates. This may mean that once the essential elements came together to form the most basic dinosaur body plan, they diversified rather quickly. Carnivorous theropods (Eoraptor and Herrerasaurus) and omnivorous ancestors of sauropods (Chromogisaurus and kin) and ornithischians (Pisanosaurus) took little time to evolve vital adaptations allowing them to live alongside lesser-known but still fascinating beasts like the crurotarsans and near-dinosaur archosaurs, and greatly diversify when another great extinction event cleared the stage for them at the beginning of the Jurassic.

The Triassic is one area I feel like I've neglected in the first year of this blog, owing in part to my loose grasp of it. I intend to write more on it. One of the best places for Triassic news is Bill Parker's Chinleana blog. I get such a large number of hits from Bill that I'd feel silly not mentioning it here. Triassic Life on Land, a book throughly documenting the era, was recently released; check out Brian Switek's review here.