|
|
Post by theropod on Nov 10, 2013 0:27:58 GMT 5
A place to discuss and post data on non-locomotion-related limb functions of theropods. This includes use in prey aquisition, fighting, feeding, mating etc. of both fore- and hindlimbs. Counterpart to my feeding-apparata thread→ |
|
|
|
Post by creature386 on Nov 10, 2013 1:15:46 GMT 5
|
|
|
|
Post by theropod on Nov 15, 2013 23:04:55 GMT 5
Theoretical models of theropod forelimb biomechanics are often tainted with preconceived ideas. Actualistic modeling using specimens and casts, coupled with CAT-scans and dissections of extant vertebrate forelimbs, demonstrates that forelimb motion in theropods is considerably less than hypothetical models indicate. The forelimbs ofCoelophysis, cf.Coelurus, Allosaurus, Deinonychus, andTyrannosaurus were investigated. Motion at the shoulder, elbow, wrist, and digits were analyzed and compared with those of birds and crocodiles, then motion of the entire forelimb was examined. The results have considerable implications for forelimb use in predation. Three models of predation are recognized: 1) long armed grasper —Deinonychus, cf.Coelurus; 2) clutcher -Tyrannosaurus; 3) combination grasper-clutcher -Allosaurus. Analysis of the joints ofDeinonychus show that the forelimb could not fold avian fashion. The scapula of the theropodUnenlagia was oriented incorrectly and differs little from the standard theropod scapula. Since the link doesn't seem to work anymore; link.springer.com/article/10.1007%2FBF03043773#page-1These are just the first pages (You can download them as image files by simply right-clicking on them and selecting the option). If you want the whole paper, I downloaded it while it was acessible so I can share it of course.
Casts of forelimb elements of the Cretaceous theropod dinosaur Acrocanthosaurus atokensis were manually manipulated to determine range of motion and infer function. It was found that the humerus can swing posteriorly into a horizontal position but can neither swing laterally to glenoid height nor anteriorly much beyond the glenoid. The forearm can approach but not achieve full extension and right-angle flexion. Pronation and supination are precluded by immobility of the radius relative to the ulna. Motion also seems to be restricted at the wrist. The palm faces medially, and digital movement is subtransverse. All three digits are capable of extreme hyper-extension. Digits I and II converge during flexion. Only digit III can be abducted or adducted. The limited anterior range of brachial motion infers that Acrocanthosaurus first apprehended prey orally, using the forelimb afterwards to secure its grip or deliver fatal blows. Acrocanthosaurus could only manually grasp prey that was beneath its chest, towards which it may have used its mouth to move prey. Struggling prey would have impaled itself further upon the permanently and strongly flexed first ungual. The range of motion in the forelimb of Acrocanthosaurus resembles that of Herrerasaurus and Dilophosaurus, and exceeds that of Tyrannosaurus. Acrocanthosaurus exhibits a greater manual range of motion than ornithomimid and deinonychosaurian coelurosaurs, but less at the shoulder and elbow. Coelurosaurian theropods exhibit reduced digital flexion and hyper-extension, which suggests a change in the use of the manus in coelurosaurs. I've also got a pdf of this one now. I don't know, has/does vobby already sent/send it to you creature368? |
|
|
|
Post by creature386 on Nov 15, 2013 23:17:47 GMT 5
These are just the first pages (tip: you can download them as image files by simply right-clicking on them and selecting the option). I just found out that there is another possibility, there is a PDF tool which allows you to download it (it's next to the right/down option). BTW, my PDF collection now rapidly increased. I've also got a pdf of this one now. I don't know, has/does vobby already sent/send it to you creature368? No, I haven't asked. |
|
|
|
Post by creature386 on Nov 16, 2013 0:23:53 GMT 5
Thanks for sending! Could you send me Carpenter's too?
|
|
|
|
Post by theropod on Nov 16, 2013 2:10:19 GMT 5
On its way!
|
|
|
|
Post by theropod on Nov 16, 2013 17:27:22 GMT 5
|
|
|
|
Post by theropod on Apr 6, 2014 20:35:16 GMT 5
The mouth of Acrocanthosaurus is much further forward (Currie & Carpenter, 2000: fig. 1) and therefore much more likely to have made first contact with prey. Undoubtedly, the forelimbs were used during prey capture. They are the stockiest known theropod forelimbs outside Spinosauroidea, and their huge muscle scars suggest that they were heavily muscled and therefore made to be used in activity involving forces of high magnitude, such as wrestling with large, violently struggling prey. This can likely be applied to most other Carnosaurs. We are not talking about a feline-analogy, but an animal that, like a monitor lizard, would bite first and clutch afterwards if that wasn’t enough. Which reminds me, these are some of the biggest raptorial unguals known: svpow.com/2013/04/19/friday-phalanges-megaraptor-vs-saurophaganax/The Saurophaganax claw is 26.3cm in straight-line lenght, and 36cm in total along the outer curve (measured from tip to joint) The Megaraptor claw is 28.7m in straight line, if my curve-lenght measurement of 38.6cm is accurate this isn’t even the largest claw ascribed to the genus That’s all without keratine of course. These two claw shapes probably correspond to somewhat different purposes, the allosaurid claw is obviously much more robust and blunter and made rather to pierce and grip than to stab and slash. Also, compare their respective shapes to a Velociraptor claw. |
|
|
|
Post by Infinity Blade on Apr 6, 2014 23:11:12 GMT 5
Just a question here. Do you think it's possible small enough (as in not multi ton) non-avian theropods could have used their hindlimbs for kicking foes? I remember Tyrant on Carnivora saying that they look like those of large ratites, who do kick, and thought that a non-avian theropod could easily do the same thing.
|
|
|
|
Post by theropod on Apr 7, 2014 1:48:53 GMT 5
Almost certainly, the question is, how small is small enough? A typical ornithomimosaur for example, something a little larger than an ostrich, would definitely have had the capability to kick in a similar manner, although I don’t know whether it’s body shape would be more or less well-suited for that. I think this is the case in theropods up to the size of very large phorusrhacids (i.e. about the size of the largest extant terrestrial predators), small carnosaurs ( Monolophosaurus, Fukuiraptor, Shaochilong etc.) and Tyrannosaurs ( Eotyrannus etc.) for example. Not sure about larger ones tough. There are two points that are important: - How well can the animal recover its body equilibrium?
- How dangerous is it if it cannot?
I think the latter point is fairly well known, a T. rex-sized theropod for example could quite easily experience lethal forces, crushing its ribcage or spine if it fell (because its mass grows more quickly than its resistance to force, and the mass will factor in in the force experienced, force = mass × acelleration). The smaller the animal, the smaller the problem here. This likely also applies to the first point to some degree, the bigger the more difficult it is to keep the weight under control, the less acrobatic it will be. But its more difficult to assess. A full-on fall is a pretty straightforward thing, but the mechanisms an animal uses to balance and shift its weight are not. Now, I think ratites are our best analogy, and of course there are many similarities, between ratites and non-avian theropods, but also differences: - Ratites have only a vestigial musculoskeletal tail (phygostylum), while it is massive and very important for balance and locomotion in most non-avian reptiles.
- Most theropods have anteroposteriorly longer bodies, shifting their hips back relative to the anterior end of the animal.
- Ratites have their femora in near-horizontal position to counteract their lack of a large tail and the resulting more anterior center of mass.
- Terrestrial avians typically have very long necks in an S-curved, overall near-vertical position.
- Terrestrial avians typically lack functional forelimbs
So these are some important things to investigate further in these regards. However I would be very surprised if other theropods did not use their hind-limbs in a some similar manner on occasion. If nothing else, at least the metatarsal pathologies of Allosaurus seem to be solid evidence that it used its legs for predatory purposes. Here again, I see these different types of theropods using their hindlimbs in different ways. Broad-footed ones will rather use a lot of force to grapple with their feet, using their body weight to push prey to the ground. Narrow-footed forms will rather specialize in velocity to deliver kicks. |
|
|
|
Post by Infinity Blade on Apr 7, 2014 2:12:56 GMT 5
I can agree with what you've stated. So narrow-footed ones could probably kick and broad-footed ones grappled and subdued. Huh, interesting.
Edit: I've always wondered why IIRC Allosaurus specimens had the most stress fractures on its feet of any theropod.
|
|
Fragillimus335
Member
Sauropod fanatic, and dinosaur specialist
Posts: 573
|
Post by Fragillimus335 on Apr 7, 2014 7:07:25 GMT 5
Imagine those suckers with keratin intact! I looked up eagle x-rays, and this was the result.  Looks to be an increase in length of between 25-40% over bone length. Applying these ratios to the above theropods yields ~35cm straight line claws in life. Baryonyx goes from 28.5cm to ~38cm. Applying a scaling ratio to Spinosaurus assuming an adult's length at ~16 meters, and Baryonyx at 9.5 meters, that gives you a 64cm thumb claw for Spinosaurus! The only claw that might make Therizinosaurus sweat. |
|
|
|
Post by theropod on Apr 7, 2014 17:18:39 GMT 5
Therizinosaurus' claws would get longer as well tough, however those of Spinosaurus were likely far more massive, since they are much stouter and more robust.
However I'm not convinced the difference would be as extreme as in eagle claws. The keratine sheathing adds a tremendous amount of curvature in them. For example, if you look at the top hallux claw in the x-ray above, the claw is only 18% longer in straight line, while it is 63% longer along the outer curve.
|
|
Fragillimus335
Member
Sauropod fanatic, and dinosaur specialist
Posts: 573
|
Post by Fragillimus335 on Apr 8, 2014 1:06:24 GMT 5
Therizinosaurus' claws would get longer as well tough, however those of Spinosaurus were likely far more massive, since they are much stouter and more robust. However I'm not convinced the difference would be as extreme as in eagle claws. The keratine sheathing adds a tremendous amount of curvature in them. For example, if you look at the top hallux claw in the x-ray above, the claw is only 18% longer in straight line, while it is 63% longer along the outer curve. I thought the same, so I used lower estimates. ~30% increase. |
|
|
|
Post by theropod on Apr 8, 2014 2:28:14 GMT 5
In straight line the increase is not that big, in curvature it is much bigger. It just depends on what you use, both are similarly important if you want to know the overall size of a claw.
I guess I should measure the other unguals in that X-ray. In any case, manual claws of some theropods were definitely humungous elements, even the bone cores alone are!
btw you don’t happen to have comparable information on some varanid, do you?
|
|
