August 24, 2011
Sometimes fossils aren’t what they initially seem.
Back in 2008, paleontologists Jerzy Dzik, Tomasz Sulej and Grzegorz Niedźwiedzki presented what they believed was a big predatory dinosaur from an approximately 200-million-year-old Late Triassic site in Lisowice, Poland. They gave it the nickname “The Dragon of Lisowice,” and in a short summary of the find, Sulej and Niedźwiedzki speculated that the then-unnamed creature “may have initiated the evolutionary line that would eventually culminate in the famous super-predator Tyrannosaurus rex.” The Dragon was thought to signify the dawn of truly terrifying theropod dinosaurs, but it turns out this carnivore may have been a particularly imposing member of a very different lineage.
When first mentioned in the 2008 paper, the predator from prehistoric Poland was said to be known from various skeletal elements that may represent two individuals. An dinosaur-like skeleton was reconstructed on the basis of these partial remains, and now an in-press version of a paper describing the animal by the same researchers has become available through the journal Acta Palaeontologica Polonica. Now the “dragon” has a name: Smok wawelski.
The new paper records some changes from the earlier report. For one thing, the various skeletal scraps found at the excavation site are said to belong to a single individual and not two as originally hypothesized. More significantly, though, the proposed family relationships of Smok have been changed.
Despite being touted as an Allosaurus ancestor shortly after its discovery, in the new paper Smok is simply called “a new large predatory archosaur.” This is a very general statement. The Archosauria is a huge group of vertebrates whose first members evolved more than 240 million years ago; it includes crocodylians, pterosaurs, dinosaurs and various extinct lineages closely related to these major groups. Of these, Niedźwiedzki and colleagues state that Smok shows resemblances to both theropod dinosaurs and a group of extinct, land-dwelling crocodile cousins called rauisuchians, though distinguishing which lineage the animal should be assigned to is difficult. Smok is definitely some kind of archosaur, but precisely what branch of the archosaur family tree it belongs on has not yet been fully resolved.
Exactly what Smok is requires further research to sort out—the paper states that Niedźwiedzki is working on this issue as part of his PhD thesis—but the prospect that it was a dinosaur doesn’t look good. As Bill Parker and others have commented elsewhere, Smok is almost certainly more closely related to crocodile-line archosaurs than to dinosaurs. Characteristics of the skull and hips, especially, underscore this as the most likely possibility. The overall resemblance of Smok to large predatory dinosaurs is a result of evolutionary convergence, or the independent evolution of characteristics in distantly related groups, and the dinosaurian appearance of the reconstructed skeleton was primarily created through using a dinosaur-like template for the known remains.
This isn’t the first time a carnivorous croc-relative has been mistaken for an ancestor of big, bad theropod dinosaurs. In 1985, paleontologist Sankar Chatterjee described a large Triassic predator he called Postosuchus. Described as “the arch predator of its time,” Postosuchus was correctly identified as being a rauisuchian, but Chatterjee also believed that the predator also exhibited traits that foreshadowed those seen in Tyrannosaurus many millions of years later. In fact, Chatterjee proposed that many major characteristics seen in tyrannosaurs were present in Postosuchus, and therefore the Triassic creature “may [have been] close to the ancestry of tyrannosaurs.”
Chatterjee was wrong about Postosuchus being the rootstock for tyrannosaurs. Rauisuchians had nothing to do with the ancestry of Tyrannosaurus or any other dinosaurs—they were a unique group of creatures more closely related to crocodiles which overlapped in time with early dinosaurs. (The tyrannosaurs, instead, originated from small, feather-covered coelurosaurian dinosaurs which looked quite different from the latest and most famous members of the group.) The resemblances Postosuchus and Smok share with large predatory dinosaurs are the results of convergence and are not true signals of close evolutionary relationships. Dinosaur or not, though, these rauisuchians were still formidable and terrifying predators. A terrestrial, 16-foot, carnivorous crocodile-like predator is not something I would like to meet in a dark alley (or anywhere else, really).
Chatterjee, S. (1985). Postosuchus, a New Thecodontian Reptile from the Triassic of Texas and the Origin of Tyrannosaurs Philosophical Transactions of the Royal Society B: Biological Sciences, 309 (1139), 395-460 DOI: 10.1098/rstb.1985.0092
Dzik, J., Sulej, T., & Niedźwiedzki, G. (2008). A Dicynodont-Theropod Association in the Latest Triassic of Poland Acta Palaeontologica Polonica, 53 (4), 733-738 DOI: 10.4202/app.2008.0415
Niedźwiedzki, G., Sulej, T., Dzik, J. (2011). A large predatory archosaur from the Late Triassic of Poland Acta Palaeontologica Polonica DOI: 10.4202/app.2010.0045
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