Historical Science and the Case of T. rex’s Puny Arms and Dinosaur Diets

Everyone has encountered a T. rex in books, movies or museums.   Besides its size and menacing jaws one of the most striking features of a T. rex is its diminutive arms.   So why were the arms of T. 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.  Can these hypotheses be tested?  Well, yes and no.  Behavior traits are notoriously difficult, by not impossible, to assess with the fossil record. 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).  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.  In effect maybe there are just useless vestigial organs. This hypothesis can be tested and shown to be unlikely to be true.  The bones of the arms show evidence of large muscle/tendon attachment points.  Analyses of these arms then suggest that they were very strong even if they were very small. There is also the presence of two sharp claws at the end.  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.

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. rex had short arms?

Sounds like a simple question. 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. rex’s arms can how can you be sure they had short arms?  Has anyone seen a T. rex in person? I don’t think so.   If they lived 65 million years ago how can we be sure today that they had short arms?

A T-rex skeleton showing again showing the small arms.
A Tyrannosaurus rex skeleton revealing its tiny arms.

So what is this evidence that we all find so compelling.  It is found in nothing more than bones turned to rock.   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). 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. rex and theropod carnosaurs in general.

Ok, we know because of the bones.  So how many total bones do we have to support this conclusion?  Well we have a lot of bones from T. rex specimens from many locations so there is quite of bit of fossil data.  But you might be surprised to find out that there are very few complete sets of arm bones found.   I haven’t been able to find firm numbers but it seems that there are fewer than 15 near complete skeletons of T. rex that have ever been found.  Of those I am not sure how many of these even had the arms actually attached to the shoulder blades but I would be surprised if it were more than a couple do.  The first was not found until 1989! and yet we have drawn a T rex with short arms long before this.  Of course there have been hundreds of partial skeletons found and I am sure many arm bones have been found in the general vicinity of other T. rex bones.  The smoking gun evidence is found in those few that are actually attached.  But the observance of other small arm bones near other T. rex bones also adds to our conviction (or you could call it theory) that T. rex had short arms.

Now lets say you aren’t convinced.  You might claim that we have simply missed a few bones because T. rex had more bones than other reptiles in their arms and so we don’t have the full picture.  Finding a set of bones all connected or at least lying in a connected configuration ought to be enough evidence to dispel you of that thought, but we do have additional evidence that strongly supports these diminutive T. rex  arms. That evidence comes from bones of many other species of dinosaurs that are similar to T. rex.  It seems that there many other theropods which also had short arms.   The fact that there are more than one species with short arms provides even greater support for the short arms of T. rex because it is far less likely that we have just missed some crucial bone in all of these fossils specimens.

Reconstructions of some other theropod dinosaurs showing that many others also had puny arms.
Reconstructions of some other theropod dinosaurs showing that many others also had puny arms.

So it is just some bones found in rock that are found next to a shoulder bone of a T. rex are the foundation of every image you have ever seen of a T. rex with short arms. The lesson here is not that we should doubt that T. rex actually had short arms but rather that the historical sciences can produce results for which we have great confidence.  In this case we can have great confidence that we can “know” that these massive animals had tiny arms.   We can’t test this theory by going back in time but we can test it with evidence that we can gather in the present and this evidence can yield a high degree of confidence in our conclusions about the past.

This is just one example of something we can know about the past by examination of data from the present.  Let us look at another example of deriving conclusions about the distant past via the historical sciences and see if our study of dinosaurs will yield some more provocative conclusions than the lengths of a dinosaurs arms.

A dinosaur coprolite found in Utah that was for sale on Ebay.
A dinosaur coprolite found in Utah that was for sale on Ebay.

How do we know that some dinosaurs ate animals and some only ate plants? Can we tell what plants did they ate?

Teeth are one important clue because we can compare their teeth to teeth from various animals alive today. While this is fairly compelling evidence it is not quite smoking gun evidence in my opinion.   The smoking gun is the combination of evidence from teeth and dinosaur coprolites  (yeah, that’s dino-poop).  When coprolites are found associated with dinosaurs with teeth that imply herbivory and those dino-droppings also support a herbivorous-only diet then you have beyond reasonable doubt-type evidence of their ancient diet.

Above is shown the general appearance of fossils in the geological column.  You can see that dinosaurs are found in strata that bridge the first appearance of flowering plants. The evidence for flowering plants in coprolites of dinosaurs  also exhibit the same pattern.  Image credit:  J. Duff
Above is shown the general appearance of fossils in the geological column. You can see that dinosaurs are found in strata that bridge the first appearance of flowering plants. The evidence for flowering plants in coprolites of dinosaurs also exhibit the same pattern. Image credit: J. Duff

But we can learn so much more from these coprolites than just the general herbivorous behavior of these giants.  With these dinosaur dropping we can ask what specific kinds of plants they ate.  To find out, cross sections of plant-eating dino-poops are made.  Pieces of stems and leaves often pass right through the gut and pollen and spores of plants are especially well-preserved.  The anatomy of these plant parts and structures of these spores can be examined in detail and the types of plants determined very reliably.   In this case plant-eating dinosaurs from the Triassic and Jurassic Periods are shown to have eaten ferns, tree-ferns, lycopods, and primitive forms of conifers.  What is missing in this list?  Yes, flowering plants. Today’s the most dominant plant type on earth are flowering plants which include most trees and the grasses.  No large herbivore today could possibly eat vegetation and not get at least some flowering plant pollen in them much less any other portions of a flowering plant.   Yet, there have been many dinosaur coprolites from this time period that have been examined from all over the world and they lack pollen and flowering plant parts.  This is very striking given that there are cellular features that are unique to flowering plants which could easily be seen in these specimens if they were present.  Surely if flowering plant parts and pollen in any coprolites were present, microscope examination would reveal these features.

How do scientists interpret this coprolite evidence?

Another fossil dinosaur coprolite from Utah. Many are prized by gemstone carvers because of the minerals that form in them during the fossilization process.
Another fossil dinosaur coprolite from Utah. Many are prized by gemstone carvers because of the minerals that form in them during the fossilization process.

These fossilized coprolites tell us that some dinosaurs only ate plants and that globally what the vast majority of all plant-eating dinosaurs had to eat during the Triassic and Jurassic Periods were non-flowering plants most of which are extinct today.   How confident are scientists that most dinosaurs had nothing to eat by a fern and conifer diet?  I would say that their confidence level approaches that of their confidence level that T. rex had short arms and that some dinosaurs ate plants and some ate meat.

The bottom line is that the preponderance of evidence regarding the arms of T. rex and the diet of dinosaurs produces a compelling pictures of the life of past organisms.   These images of life are also supported by many other independent lines of evidence that I don’t have time to explore here today.

Young Earth Creationists, Dinosaurs and Historical Data

If you were to visit Ken Ham’s Creation Museum in Kentucky you would find dinosaurs of various kinds on display there including plant and meat eaters and a model of T. rex with his short arms.  Ken Ham is fond of asking people who think the world is old: “Were you there?”  He frequently suggests that we can’t be confident about things from the distant past because we were not witnesses and only the Bible is a witness to these events.  So I ask you, why does he have such confidence that T. rex had short arms? Was he or anyone else alive and reported that they saw a T. rex with short arms?  Does the Bible provide us with a physical description of T. rex? No! So the evidence that T. rex has short arms comes from observations of fossils and the assumptions about those fossils (eg. they actually represent parts of formerly living things and that bones next to other bones represent their order of attachment in the real organism).    Ken Ham and AIG have published numerous books with recreations of dinosaurs and even discuss their behaviors all based solely on bones of stone found in the ground.   He clearly accepts the evidence and interpretations of this evidence derived via the historical sciences without qualification.   But what happened to that origins science vs operational science distinction that Ham and others of so fond of espousing? (see HERE for more about this distinction).  Origins science is the label YECs like to slap on any conclusion of historical science that they deem contradictory to their interpretation of scripture.  But how do they know when something is or isn’t under the purview of what they call origins science?  To me re-creating the shape and size of an animal now extinct and never spoken of in the Bible sounds a whole like what they want to call origins science but since the don’t have a problem with these particular interpretations of historical science they don’t call them into question.

I’m really can’t blame Ham and company for accepting that T. rex had short arm as the evidence, though not abundant, is very strong.  It is not unreasonable at all that they accept this but then what are we to make of the diets of the plant eaters?  I am sure young earth creationists would readily accept the observation of coprolites full of bones as evidence that T. rex was a carnivore but then what do they do with the coprolites of dinosaurs from the Triassic and Jurassic ages that contain 100% ferns, lycopods and conifers and 0% flowering plants.   Maybe they could dismiss a single coprolite as a dinosaur browsing in a bog full of ferns and confers.   But when all coprolites from a single geological period all lack flowering plant pollen and plant parts and those coprolites are found associated with multiple species of dinosaurs in multiple locations on earth, it become very difficult to deny that the food that dinosaurs had available to eat did not include flowering plants.   Someone might claim that dinosaurs found in these geological periods just didn’t like flowering plants and avoided them.  This is very unlikely and would clearly be an ad-hoc hypothesis.  Today all large herbivores very much prefer flowering plant leaves like grass over pine needles and ferns, but even if they tried to avoid all leaves and stems of flowering plants they should have still eaten pollen grains inadvertently since they are everywhere in the environment.   When you combine the lack of flowering plants in dino poop along with the lack of flowering plant pollen and plant parts in the rocks that the same dinosaurs skeletons are found preserved in this becomes the smoking gun evidence for the theory that flowering plants did not even exist at the time that the dinosaurs lived in the Triassic and most of the Jurassic Periods.

****A side note here:  For YECs, the dinosaurs preserved in the fossil record were preserved during a Global flood and they generally view those dinosaurs as running to escape the flood which is their explanation for why dinosaur fossils are not found in the lower portions of the geological column.  There are millions and probably many billions of preserved dino-poops in the same rock layers that the dinosaur bones are found.  Since these dinosaurs were presumably running around trying to avoid this chaotic flood the food they ate would have been whatever they could find which should have been a random mixture of the plants alive at the time of the flood.  This makes it even more unlikely that they could have avoided eating flowering plants and that we would observe such a distinct pattern in their coprolites.****

An scan of a page from Ken Ham's "Dinosaurs in Eden" book. Here we can see Tyranosaurus-like dinosaurs with small arms enjoying a diet of flower plants.
An scan of a page from Ken Ham’s “Dinosaurs in Eden” book. Here we can see short-armed theropod dinosaurs with small arms enjoying a diet of flowering plants.

What do YECs do with this data.  They generally ignore it but when forced to confront it they deny that flowering plants were not present and prefer to say “How do you know, where you there?” In addition it is likely they would suggest that historical scientists don’t have the right worldview and so can’t interpret the data properly.  They put models of dinosaurs in their museum surrounded by fruit trees and print books with dinosaurs helping people pluck fruit from trees.   At the end of the day, they are sure that T. rex has short arms based on a couple of bones but they are more than willing to ignore hundreds of pieces of data that all point to the lack of flowering plants in most dinosaur diets.  There seems to a picking and choosing what historical science data they want to accept.

Another image from a page of Ken Ham's "DInosaurs in Eden."  In this case we are being shown a scene not only after Eden but after Noah's flood at the time of the tower of Babel.  Here he is depicting friendly Tyranasaurus-like dinosaurs as tamed beasts living in harmony with people. The implication here is that 400 years after the flood dinosaurs where still living with people.
Another image from a page of Ken Ham’s “Dinosaurs in Eden.” In this case we are being shown a scene not only after Eden but after Noah’s flood at the time of the tower of Babel. Here he is depicting friendly Tyrannosaurus-like dinosaurs as tamed beasts living in harmony with people. The implication here is that 400 years after the flood dinosaurs where still living with people.

11 thoughts on “Historical Science and the Case of T. rex’s Puny Arms and Dinosaur Diets

  1. I just recently started following your blog, and I really like this article. It sets up a situation that demonstrates the inconsistency of YEC use of fossil evidence very well.

    Also thanks for introducing me to the book Dinosaurs in Eden. It is now on my to-buy list.


    1. Thanks for the encouragement. I was quite dismayed when I started to rewrite this article at how poorly written the original version was. Its good to hear this one makes some sense. Only spend as much as you would for the entertainment that that book will be. The content is certainly not worth much:-)


      1. It will be entertaining I’m sure, but it is also very sad. My reason for buying it is to document Ham’s argument and possibly use it as an example of bad creatiponist ‘science’.


  2. teeth can tell you more about diet than you think. Microwear on the enamel surface is distinctly different for different diets. The isotopic composition of the enamel also reflects the type of diet. This is done routinely for fossil mammals — I don’t know if anyone has extended this to dinosaurs.

    Also note that T rex trying to eat vegetation would be as clumsy as a cat eating grass. Those teeth can’t grip or grind up leaves, and would be unable to pulp melons (if melons were indeed available), only to spear them. The YEC like to refer to the “sharp teeth” of pandas and fruit bats, but neglect to mention that those are the teeth at the front of the mouth, not the ones at the back that actually process the food.


    1. Thanks for the comment. Yes, I shortchanged the importance of teeth. I was trying to emphasize the greater strength we have with the consilience of multiple sources of data. Yes, that picture of a T-rex like thing eating a banana leaf pretty much makes your point perfectly. Great point about the selective reporting of data about the positions of teeth.


      1. Consilience —- that’s a word avoided by creationists (even by my spell checker). I just wanted to point out that there are multiple approaches (and resultant concilience) *within* studies of teeth and diet. But I really enjoyed the post. Excellent point about the near absence of evidence for eating angiosperms.


        1. I just realized that consilience wasn’t the most apt term since it seems that it implies the use of many week pieces of data to converge on a high confidence result. But teeth are a very strong form of data and as you say contain multiple convergent lines of evidence themselves. Seems I should stick to simpler terms. I have enough trouble with them without compounding my problems.


  3. I think that “consilience” is an excellent term. That’s why creationists avoid it!


  4. I really enjoyed this post! I think it’s really interesting to look at the way evidence interlinks to show the reliability of historical sciences.

    I am shocked sometimes by the breadth of data of which I’m even unaware. I fully realize I’m at best an interested layperson when it comes to science, but I continually find that there are whole avenues of evidence and research that I didn’t even know existed. It’s a humbling and awesome experience.


  5. Thanks for the clear & patient explanations of different kinds of evidence and how we evaluate them. I’m downloading the Cleland pdf to think about it some more.

    I’m a high-school biology teacher working my way through our origins unit right now, and your posts are very helpful in considering ways to approach student concerns. My current method is “Here are several sets of observations; the theory of evolution is how we explain them in a way that makes sense.” Any suggestions you can offer, especially regarding instances where YECs not only reject the explanation, but even deny the observations, would be very helpful!

    Would you mind if I used your T. rex example with my kids? Some of them are coming from Ken Ham-type backgrounds, and it’s tricky to address misconceptions & bad science without trampling on their faith.


    1. Hi, thanks for much for the comment. I’m glad that was helpful. You are most welcome to use any more material from this blog in any form that you wish. I will send you some other material to your email address. Joel


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