Anatosaurus and the Name Game

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One of the most frequently asked questions during Saurian's development and Kickstarter campaign relates to Hell Creek's resident "duck-billed" dinosaur (hadrosaurid), namely 'where is it?'. This is a fair question; as the ever quotable RJ Palmer has noted, it's absence is "like having the farm without the cow". It might seem strange that we kept this animal a secret for so long, but here's why: The Dinosaur Mummy

Unlike the vast majority of fossil species, we actually know a lot about the Hell Creek hadrosaur. It is known from a treasure trove of fossils, second only to Triceratops in the number of specimens known from the formation. The animal is well represented, from young juveniles to enormous, long-snouted adults. Bonebeds containing remains of up to 20,000 individuals are known from Wyoming and South Dakota. Detailed study of the dinosaur's jaws and teeth reveal it was supremely adapted for chewing, having some of the most complex teeth and jaw mechanics of any known animal. We know more about the locomotion, diet, habitat preference, pathologies and predatory interactions of this dinosaur than perhaps any other. Much of our detailed understanding of its appearance, however, comes from an incredibly complete specimen nicknamed "Dakota". The animal was preserved with the skeleton wrapped in mineralized soft tissue, including muscle and skin, giving us a good idea on the external appearance of this dinosaur. This type of fossil is often called a "mummy", in reference to its overall similarity to the ancient Egyptian mummies. Even more incredible is that this is not the only mummy known from this taxa; there are at least two more, one housed in the Senckenberg Museum in Frankfurt, Germany and another at the American Museum of Natural History. We were extremely lucky to have one of our former developers examine the latter specimen in person, and from his observations we were able to match the skin of our model almost exactly to what is actually preserved. Taken together, there is so much data available for Anatosaurus that there is very little 'wiggle room' in depicting its appearance.

A detailed guide to the scale pattern of the AMNH specimen.

Lets Play the Name Game

Even after revealing that this animal will indeed be featured in Saurian, it remains one of the most frequently mentioned animals within our community, but for a different reason: its name. We refer to this animal as Anatosaurus. This has of course, brought out near constant cries of "why not Edmontosaurus", "isn't that Edmontosaurus?", "You know that Anatosaurus is a synonym of Edmontosaurus, right?"

While its cute when people think they know something we don't, it is much more complicated that this. The first thing that needs to be addressed is that a genus name is almost completely arbitrary. A genus (the first part of an animal's name, the Tyrannosaurus in Tyrannosaurus rex or the Canis in Canis lupus) is just a name for a group of animals (clade) that share a close common ancestor. Most clades are given a definition (for example the clade Dinosauria is anything descended from the common ancestor of Passer and Triceratops) but the "genus" level usually is not which means how large a group of animals the group covers is almost entirely up for debate. The only true rule that exists is that the oldest name for that animal takes priority. As Saurian deals with genera, we obviously have to make a call the names that appear in our game. What mattered most to us was that whatever we did, we were internally consistent, so we decided to lay down our own set of rules. The most prominent of these rules was that if an animal was separated from its closest relative by over a million years then this is grounds for being given its own genus. The Hell Creek hadrosaurid fits this rule as it appears on the scene 2 million years after the last occurrence of its next closest relative, Edmontosaurus regalis. For this same reason, you will see the names Pectinodon, Denversaurus and Acheroraptor in our game as opposed to Troodon, Panoplosaurus/Edmontonia and Velociraptor, respectively. On the reverse front, if we had included the controversial taxon Torosaurus latus in the game as its own species, it would have been as Triceratops latus.

One true rule for genus names that must be followed (with some exceptions) is that the oldest known possible name for the animal takes all priority. This stops new names being given to the same taxa continuously. With this in mind, some would argue that Thespesius occidentalis is the proper name for the Hell Creek hadrosaurid, but we agree with Lull & Wright (and Lambe before them) regarding the material this name is based on as inadequate for proper classification and therefore a dubious name (scientifically: a nomen dubium based on non-diagnostic material, even if 'western wondrous one' is a pretty cool moniker). This leaves Anatosaurus as the oldest available name that can be confidently assigned to this animal, and therefore the correct one in our scheme.

Not the Edmonton Saurian

Aside from naming convention, Anatosaurus actually differs morphologically from Edmontosaurus in a number of ways. The most notable skeletal difference comes in the skull. Anatosaurus has a much longer and more delicate skull throughout it's life series, as can be seen in the image below:

Skull growth comparison between Edmontosaurus (A) and Anatosaurus (B).

 

Until recently, skulls with the very long, low and especially duck-like beaks were classified under a third name, Anatotitan copei, but a 2011 study found that they are almost certainly just large adult Anatosaurus. Other differences are more recently discovered and relate to the soft tissue details discussed above. Recently, a mummified partial skeleton of Edmontosaurus was discovered revealing some interesting soft tissue details. These included a cock's-comb-like crest on the back of the skull, and a series of large, raised, scaly bumps covering the neck of the animal. Neither of these features are present in the 3 mummified specimens of Anatosaurus. Additionally, the segmented dorsal ridge we know ran down the back of Anatosaurus is not present in this specimen of Edmontosaurus.

Internal draft of Saurian's Anatosaurus concept by Alex Lewko, Chris Masna, RJ Palmer and Jake Baardse.

 

We Don't Need no Stinkin' Sauropods

By now many of you have also probably heard rumors that Anatosaurus was HUGE. We are here to report that those rumors are true, based off of two specimens housed at the Museum of the Rockies (MOR 1609 and MOR 1142) that indicate animals around 15m from nose to tail, and likely massing over 10 tons.

MOR 1142 ("X-rex" as it was originally thought to be from a tyrannosaur) on display. Fossil measures 7.6m total length. Photo courtesy Museum of the Rockies Twitter page.

Maximum adult size of Anatosaurus based on Super Adult specimens from the Museum of the Rockies.

Its important to note, however, that very few individuals reached these immense dimensions. The vast majority of Anatosaurus fossils found in the Hell Creek formation come from animals measuring around 8.5m in length. When the bones of these individuals were analyzed, they were found to have a texture consistent with rapid, active growth, and despite their relatively large size, were only about half grown. A recent study on the related hadrosaur Maiasaura found that 90% of hatchlings died before reaching one year of age, sexual maturity was reached at 3 years of age and about 1/3rd average adult size, and skeletal growth essentially ceased by age 8. Anatosaurus likely shared a similar 'live fast, grow fast, breed fast, die young' lifestyle, and the few giants we have are lucky survivors.

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