Monday, March 10, 2014

Torvosaurus, the Terror of Europe

Figure 4 from Hendrickx and Mateus, 2014, showing full skeleton and skull reconstructions of Torvosaurus gurneyi.  The bones highlighted in red were used to define the new species.  The bones in blue were found separately but are thought to belong to the same species.
As was announced quite widely on the news last week, a new species of dinosaur has been identified.  New species are actually named quite frequently, but this particular species, called Torvosaurus gurneyi, grabbed the attention of the media because it is thought to have been the largest land predator in Europe.  Some headlines sensationally and mistakenly claimed it was the largest predator ever overall, but that title currently still belongs to Spinosaurus aegyptiacus, the sail-backed star of Jurassic Park III.

Although this specimen was found in Portugal, it strongly resembles another species found in western North America, Torvosaurus tanneri.  In fact, other Torvosaurus bones previously found in Portugal were assigned to the North American species.  However, America and Portugal are thought to have been separated by ocean even 150 million years ago, leading the scientists to search for differences that could distinguish it as a separate species.  As the authors stated, "If the assignation of [the specimen] to Torvosaurus is hardly doubtable, it is legitimate to assess its affiliation to the species T. tanneri given the paleogeographical context."  I suspect, then, that if the bones were found in North America rather than in Portugal, no new species would have been declared.

To clarify, a full skeleton was not found of this creature.  The new study is based almost entirely on a maxilla (upper-jaw bone) with a tooth stuck in it.  The rest of the reconstruction seen above is based on the remains of other closely-related dinosaurs, including the North American Torvosaurus.  Nevertheless, some minor differences were found:
  1. Fewer teeth.  The Portuguese specimen appears to only have room for ten teeth in its maxilla, while the North American species has eleven or twelve.  The authors note, however, that tooth count can vary between individuals and even within the same individual.  Therefore, this difference by itself does not justify a new species.
  2. Longer interdental plates.  The thin plates of bone that separate the tooth sockets (alveoli) extend a bit further in the European specimen, and they aren't v-shaped at the bottom as in the North American variety.  The authors expressed some doubt about the significance of these plates, noting that "it is difficult to know whether this feature... can genuinely distinguish two taxa."  Nevertheless, they use it as a defining feature anyway, citing previous cases in which it has been used to distinguish other species.
  3. Anteromedial process morphology.  I won't attempt to detail this difference, but suffice to say that the anteromedial process, which is a projection of bone on the inside of the maxilla toward the nostrils, has a slightly different shape between the American and European specimens.  Again, the authors noted that such differences don't necessarily denote a distinct species.
Though these differences do not individually justify assigning the specimen to a new species, the authors decided that they collectively provide enough reason to do so, along with the geographic separation.

While it is possible that this creature is part of a distinct species, the creationist model tends to group together more than it distinguishes.  T. gurneyi is doubtless in the same baramin (created kind) as T. tanneri, implying that they could produce viable offspring.  In theory, this would place them in the same species, but species designations often depend on whether two groups do interbreed rather than whether they can.  However, the creationist baramin may be even more general than that, including other megalosaurids such as Megalosaurus and Eustreptospondylus.  Unfortunately, the fossilized bones do not tell us who they mated with or who their parents were, so some guesswork and interpretation is required for classification in both creationist and evolutionist systems.

The age of about 153 million years (or "Late Kimmeridgian" in the paper, which is a named age near the end of the Jurassic period) assigned to the specimen is apparently derived from a combination of radioactive strontium dating and biostratigraphy.  The article the authors cited for this age is inaccessible without a subscription to the Journal of Vertebrate Paleontology, and mine expired several years ago, so I can't do much to investigate the details of the dating.  However, I have discussed both radiometric dating and biostratigraphy previously.

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