FOWLER, D.W., & SULLIVAN. R.M. (2011) The first giant titanosaurian sauropod from the Upper Cretaceous of North America, Acta Palaeontologica Polonica 56(4): 685-690 [free access PDF]

ABSTRACT

Argentinosaurus (Cenomanian, Argentina) is generally accepted as being the largest dinosaur so far discovered and is one of several giant titanosaurian sauropods known from the Upper Cretaceous of South America and Asia, but surprisingly not from North America. Here we present the first evidence of giant titanosaurian sauropods from the Upper Cretaceous of North America: two enormous vertebrae and a partial femur, from the Naashoibito Member of the Ojo Alamo Formation, New Mexico, and referred to Alamosaurus sanjuanensis. One of the new vertebrae, a posterior cervical, is comparable in size to a posterior cervical described for Puertasaurus: an Argentinosaurus-sized titanosaurian from the Maastrichtian of Argentina. This makes A. sanjuanensis the largest dinosaur from North America, and among the largest in the world. These findings indicate that A. sanjuanensis is diagnosed based on immature remains, which may have implications for cladistic analyses.

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Post-acceptance author notes

The vertebra that we identify as a caudal (SMP VP-2104) may instead be a badly crushed dorsal from a fairly average sized Alamosaurus. However, the extremely large cervical centrum SMP-VP 1850 (upon which the principal findings of the paper are based) is correctly identiified.

In Figure 1 we reconstruct SMP VP-1850 as having neural processes that are about the same height as that of the centrum. Recent preparation by Dallas Museum of the 1999 c.f. Alamosaurus cervical series from Big Bend National Park (Javelina Fm, Texas; HD videos here and here) reveals the neural processes of posterior cervicals to be much larger than in our Figure 1. As such, SMP VP-1850 was probably even larger than we illustrate in our manuscript (and the silhouette image we created for the press release).The reconstructed model that we had made for our press release was sculpted based on the Texan material, but even here I think we may have underestimated the size of the neural processes. This illustrates that we really need to go and find a complete vertebra from one of these giants; based on the video, I think SMP VP-1850 is probably a little bit bigger than the Texas cervical series, but true comparisons awaits description of their (superb) material.

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Press release notes & media information

[MSU Press release]

For the purposes of public engagement, the press release included reference to the "biggest dinosaur", and the fact that Alamosaurus lived alongside Tyrannosaurus.

We provide a series of scaled silhouettes of Alamosaurus, Argetinosaurus, and Ruyangosaurus, all of which are known from extremely large material. Body size reconstructions of dinosaurs vary considerably, depending on the reconstructon method. The silhouettes are only rough guides and not intended as precise reconstructions (this is not possible for most giant titanosaurs, although smaller individuals of Alamosaurus are known, which give good indication of body proportions at this stage of growth). The figure was supposed to visually emphasise that Alamosaurus is comparable in size to other giant titanosaurids. In reality, there is probably not much to choose in size between the largest individuals of giant titanosaur species.

We also provide a photo of a large Tyrannosaurus tooth. This tooth was recovered from alongside remains of another Alamosaurus cervical vertebra that we are yet to recover from the field (also Naashoibito Member, Ojo Alamo Formation). Whether or not the Naashoibitosaurus Tyrannosaurus species predated upon Alamosaurus directly is unknown (and extremely difficult to demonstrate, other than in cases of healed wounds with embedded tyrannosaur teeth), but association of shed teeth with Alamosaurus bones is at possibly indicative of feeding behaviour.

Somehow, an image provided for the press release did not make it online with the others. This was an image of the actual cervical fossil reconstruction compared to Puertasaurus (Fig. 1 in the paper). A version of this image can be seen here.

Various media coverage:

[KRQE Albuquerque New Mexico TV report]

[MSNBC news] - [Science Daily repeat of the press release] - [humorous take at theregister.co.uk] - [ZME Science blog] - [Fox News] - [Smithsonian blog] - [International Business Times] - [Daily Mail (UK)] -