AboutArctica Expertise I can answer a broad range of questions about the history of life on Earth, from the origins of single-celled organisms to the evolutionary history of plants, invertebrates and, particularly, vertebrates. I am also experienced in debating creationists and can provide rebuttals of many common creationist arguments. I cannot, however, answer questions about archaeology, and I generally cannot answer technical questions about rocks, bone structures or fossils - I am a reader, not a digger.
Experience Many years of research into the history of life on Earth. I have no formal qualifications, but what I lack in technical expertise I make up for in range. I have spent many months debating creationists on the BBC''s science forum, and have consequently thoroughly researched a great deal of creationist and anti-creationist material.
Question What features are diagnostic of theropods and what types of behavior can we infer from these features?
Answer Hi Vince - thanks for your question. Unfortunately after a couple of days of mulling it over, I really don't have a good answer for you. It's a surprisingly tough nut to crack! The reason for this is that your question could be taken in a couple of different ways, neither of which is very helpful. The words I'm struggling over are "diagnostic" and "theropods". Firstly, hardly anyone agrees on what a theropod is, exactly. Once you get into the origins of theropods, there are so many partial remains of poorly-known species that honestly we're not sure what features are diagnostic of theropods and what are simply characteristics of early saurischians in general. In short, I cannot find a single feature that everyone agrees belongs to basal theropods but not to their immediate ancestors. Example: most sources mention the well-developed intramandibular joint as being diagnostic (this was an adaptation improving bite efficiency), but this joint was well-developed in Herrerasaurus, which most people these days agree was not a true theropod. Other basal theropod features, such as the reduced 5th digit on the manus (actually absent in more advanced theropods), are similarly ambiguous.
So this is where I'm getting bogged down. The answer to your question could fill a book, and I have neither the time nor the expertise for that.
So that was "firstly". The second way your question could be approached is by putting it like this: "What features did most theropods possess, which most non-theropods did not, and what types of behaviour etc. etc." The problem with this approach is that there are way too many such features to discuss, and once again I'm writing a book.
So here's my rather poor attempt at striking a balance between the two extremes. Note that generally these features belong to basal theropods and not necessarily to more advanced theropods (for instance, birds, which are theropods, have longer forelimbs than hind-limbs, and no bony jaws!)
1) Forelimbs considerably shorter than hind limbs - obligate bipedalism, freeing up forelimbs for other uses
2) Jointed lower jaw - for biting efficiency
3) Hollow, thin-walled bones - for lightness/speed
4) 5th and (in most theropods) 4th digit on manus (hand) reduced or absent - possibly a consequence of bipedalism
5) 1st and 5th digits on pes (foot) reduced - nothing behaviour related as far as I know, just that a theropod's weight was borne on its central three toes.
6) Sharp, recurved teeth - for predation
7) Sharp claws on the ends of fingers and toes - also for predation
Again, a lot of these features were lost in later theropod groups, and some were present in non-theropod ancestors, so this is a list of "typical" traits rather than "diagnostic" traits. Perhaps this is what you were after. I hope so! Anyway I hope I have helped.
