![]() The bones have left evidence or a “trace” of history that we can use to test our hypotheses about the lengths of the arms of T. As philosopher Carol Cleland would say, there is your “smoking gun” evidence (see Origins Science and Misconceptions of Historical Science for a further discussion and references). It is nothing more than bones turned to rock. So what is this evidence that we all find so convincing. If they lived 65 million years ago how can we be sure today that they had short arms? A Tyrannosaurus rex skeleton revealing its tiny arms. rex’s arms can how can you be sure they had short arms? Has anyone seen a T. After all, doesn’t every know that they had laughably small arms!? But ask yourself, how do you know this to be true? Have you ever seen a Tyrannosaurus rex in person? If you were not there to witness T. ![]() Rather than go on debating these speculative hypotheses, I want to look at a more fundamental question that I often ask my students: How do we know that T. These observations can be used to strongly support the hypotheses that the arms had some use even if we may not understand what that use may have been. There is also the presence of two sharp claws at the end. Analyses of these arms then suggest that they were very strong even if they were very small. The bones of the arms show evidence of large muscle/tendon attachment points. This hypothesis can be tested and shown to be unlikely to be true. In effect maybe there are just useless vestigial organs. What about the first hypothesis that the arms were useless? The assumption here is that over time the arms became useless and so atrophied to the point of being these tiny little nubs in comparison with the entire animal. For example, see my post on extinct elephant behaviors deduced from fossil footprints ( Preservation of Behavior: Fossilized Elephant Tracks from the Arabian Peninsula) or what we can learn from piles of fossil poo ( Piles of Fossil Poo: Providing a Peak into the Past). Behavior traits are notoriously difficult, by not impossible, to assess with the fossil record. Can these hypotheses be tested? Well, yes and no. rex so short? There have been many hypotheses including: 1) they had no use and were like a vestigial organ, 2) they were used to hold on to potential mates, 3) they were used to hold onto small prey while they ate, 4) they were used to help them get up when they fell down or 5) some combination of these explanations. Besides its size and menacing jaws one of the most striking features of a T.
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