Thursday, November 7, 2013

A new and old tyrannosaur

A reconstructed skeleton of Lythronax at the Utah Museum of Natural
History.  Credit: Mark Loewen, BBC.  Image source.
A reader requested my thoughts on a new story about a new type of tyrannosaur found in Utah, so I will review the article here, and not just because today happens to be this particular reader's birthday.

The remains of the creature, named Lythronax agrestes, were found in 2009 at Grand Staircase-Escalante National Monument in Utah.  After extensive preparation and study, a reconstructed skeleton was mounted in the Utah Museum of Natural History, and a report of the findings and interpretations was published online yesterday.  According to the report, Lythronax is closely related to the well-known Tyrannosaurus, but it is the earliest of any in the tyrannosaurid family, which includes Gorgosaurus, Albertasaurus, Daspletosaurus, Teratophoneus, Bistahieversor, Tarbosaurus, Zhuchengtyrannus, and, of course, Tyrannosaurus.  The geographic origins of tyrannosaurs were a matter of debate among paleontologists, because while most tyrannosaurs are found in western North America, their closest relatives are found in Asia.  The fact that the oldest tyrannosaur was found in Utah now seems to support the idea that they originated in western North America and dispersed from there.  The authors then propose that rising sea levels isolated populations of tyrannosaurs on numerous occasions, leading to a wide variety of genera (types) in a relatively short period of time.

I am always a bit wary of claims of new species.  As mentioned in previous posts, designating the boundaries of species and other taxonomic levels is a bit tricky, particularly with extinct creatures.  Bones give no real idea of who was breeding with whom unless they are preserved in a particularly revealing position.  Instead, any skeletal differences are generally considered grounds for claiming a new species.  For example, Lythronax was considered distinct from Tyrannosaurus due to the number of alveoli (tiny holes) in its maxilla (upper jaw bone) and the relative height of a part of its astragalus (ankle bone).  We cannot really know what skeletal differences exist between genders and individuals of extinct creatures, so paleontologists seem to err on the side of division, relying on later studies to confirm or deny their assertions.  In the tyrannosaur family, the best example of the fluidity of classification can be seen in the case of Nanotyrannus.  Shortly after the first specimen discovered in 1942, it was considered to be a new species of Gorgosaurus.  In 1988, the specimen was reexamined and given its own genus, Nanotyrannus.  Then, in 1999, a study concluded that it was just a juvenile Tyrannosaurus, but the validity of this conclusion is still debated among paleontologists.

In the creationist view, all members of the tyrannosaur family were likely part of the same original created kind, able to interbreed and diversify.  It is entirely possible that several species arose from this kind in the 1656 years between Creation and the Flood, but they should have retained the ability to interbreed, even if they didn't do so due to geographic barriers.  Individual variation itself may be enough to account for the differences between tyrannosaur genera.

I should also note that creationists believe that all creatures, even tyrannosaurs, were herbivores at the time of their creation.  This is based on Genesis 1:30, "'And to all the beasts of the earth and all the birds of the air and all the creatures that move on the ground—everything that has the breath of life in it—I give every green plant for food.'"  And it was so."  That is not to say that the tyrannosaurs we find buried were herbivores, however.  Carnivory came into effect soon, if not immediately, after the Fall of mankind, so the tyrannosaurs like Lythronax that we dig up were still probably carnivorous.  Whether their sharp teeth and claws were part of their creation or developed after the Fall is yet unknown.

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