Measuring Those Arms

The holotype and paratype of Tyrannotitan were found 1 km apart. The paratype indicated an individual 7% (a somewhat random seeming number) larger than the indicated size of the holotype specimen. The question from yesterday remains; how long were the arms (or forelimbs to be scientifically accurate) of Tyrannotitan? The length of the humerus and ulna recovered for the holotype are not noted in the describing paper (which I have a  copy of now thanks to a friendly reader); however, they are described as composing an arm that is "short and robust" and compared as equivalent to the forelimb of Acrocanthosaurus in size. Strangely the paper notes that the humerus and ulna are shown with size bars in the second figure published. The second figure, though, is a series of views of the dentary from the paratype. Thus, we do not have a size mentioned or shown in scale in figures for the humerus or ulna. Perhaps I will be able to dig that up. The forelimbs, judged to be like those of Acrocanthosaurus, can therefore be asserted to be larger and, as it says they are robust, stronger than those of Tyrannosaurus, but without measurement I cannot possibly say they are either larger or smaller, weaker or stronger, than the arms of its carcharodontosaur family members which appear in the fossil record after it. One positive thing we can assert thanks to the paper is that Acrocanthosaurus, according to the results interpreted by this team, is undeniably removed from the carcharodontosaur family and is, by these authors, allied with Allosaurus. We know now, with this information, that Acrocanthosaurus was not a far northern carcharodontosaur though it did appear to have some similar traits to some of the carcharodontosaurs. We have also learned that the forelimbs of Tyrannotitan were short but strong, though we still cannot compare their size directly to that of related animals without the measurements of the discovered remains.

Additionally, the hindlimbs of Tyrannotitan were described by the authors as having uniquely carcharodontosaurid characteristics; the femoral head projection and the length of the fibula in relation to the femur were the noted characteristics. The hindlimb, the femur in particular, was also noted to be shorter that Giganotosaurus, making the basal Tyrannotitan just a bit shorter than its later relative. The authors phylogenetically placed Tyrannotitan between the family that branched off toward Allosaurus and Acrocanthosaurus at the base of the branch that contains Giganotosaurus and Carcharodontosaurus, as shown below:

From Novas et al., using rooting of Currie and Carpenter 2000