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  • Extinct Reptiles » Dinosaurs
  • Biomechanics of theropod necks

    _Ceratosaurus_ skeleton from the NMNH website

    Yes, yet another entry involving dinosaurs. Given their popularity, you’d think that I’d have a better write up of them on my site. >:)

    It will happen one day. Until then, there are plenty of great places on the web to learn about dinosaurs.

    That said, let’s tackle the meat of the matter.

    Snively, E. and Russell, A.P. 2007. Functional Variation of Neck Muscles and Their Relation to Feeding Style in Tyrannosauridae and Other Large Theropod Dinosaurs. The Anatomical Record. Vol. 290: 934-957.

    This paper is just an awesome testament to just how much we can learn about animals by studying their skeletons alone.

    The authours studied the cervical (neck) vertebrae and skulls of 15 theropod dinosaurs from 3 major clades.

    The family: Tyrannosauridae

    • Daspletosaurus
    • Albertosaurus
    • Gorgosaurus
    • Tarbosaurus
    • Tyrannosaurus (Nanotyrannus as well, but it was placed as a probable junior synonym of Tyrannosaurus).

    Carnosauria

    • Allosaurus
    • Sinraptor
    • Monolophosaurus

    Neoceratosauria

    • Ceratosaurus

    Abelisauridae

    • Carnotaurus
    • Abelisaurus
    • Majungatholus

    It should be noted that, where possible, multiple species within a genus were used.

    _Allosaurus_ skull from UCMP Berkeley's site

    The authours studied the muscle scars left on the cervical vertebrae and rear skulls of every specimen. By carefully studying the location of each scar, and comparing it to the Extant Phylogenetic Bracket (EPB) – which would be birds and crocodylians – it was possible for them to determine which scar belong to which neck muscle.

    Neater still; the size of a muscle scar, at its origin, is proportional to the cross sectional area of that very muscle (at least when comparing homologous muscles).

    What does it all mean? Basically, the authours were able to deduce (with reasonable accuracy) the overall size of the muscles found in these theropod’s necks, just by measuring the size of the muscle scars left on the cervical vertebrae themselves.

    Now how cool is that?

    The end results featured 3 representative species:

    1. Tyrannosaurus rex
    2. Allosaurus fragilis
    3. Ceratosaurus nasicornis

    Each one was a “poster child” for a particular feeding method.

    _T.rex_ skull from Biocrawler dinosaur encyclopedia

    Tyrannosaurs (especially Tyrannosaurus) employed a puncture and pull method that required strong muscles for pulling the neck up and sideways (somewhat similar to the feeding method used by crocodiles when on land).

    Neoceratosaurs showed strong ventral musculature suggesting strong downward force was being used. They also show strong dorsal and lateral musculature, which suggests that they employed a “hit and run” method of attack that would be similar to white pointer sharks, or Komodo dragons.

    Last, but certainly not least, Allosaurus and its ilk were more similar to the speedy dromaeosaurs (Deinonychus, Velociraptor) in hunting style. Strong ventral musculature helps to corroborate previous studies (such as Emily Rayfield’s FEA study) that Allosaurus used its head like a hatchet, and slammed it down into prey animals. The long, strong forearms were probably used first to hold prey and brace it for the killing strike.

    All in all, this was a fascinating paper. One with the potential to change all future reconstructions of these animals.

    So keep your eyes tuned to Discovery Channel, as I’m sure they are bound to make a special that will incorporate this data (they always do).

    ~Jura


  • Of the Birds, the Bees and the Dinosaurs.

    This is actually a re-write of a previous blog post that got lost in the void of cyberspace when I clicked the “save” button.

    Needless to say, I’m not feeling as driven to write everything all over again. As such, I’m just going to touch on the highlights.

    I’ve been in internet connection hell for the past 2 weeks, so I’m a bit behind on the reptile news. This latest one comes from about a week ago.

    Study finds that dinosaurs had sex as youths.

    A study by Gregory Erickson and colleagues has found that dinosaurs did not wait until they were fully grown up, before engaging in sex.

    Though the finding is touted as a surprise, the reality is far from that. The scientists in question studied the bone microstructure of 7 theropods that were found near eggs (therefore, expected to be the parents of said eggs). These theropods were also of close relation to birds (clades: Oviraptorosauria and Deinonychosauria). What they found was that a members of each clade showed signs that they were still growing while watching their eggs.

    In the grand scheme of things, this is not surprising. Sexual maturity hits reptiles, mammals, fish and amphibians before full body size is achieved. It is often represented as a time when maximal growth rate ends (as resources get diverted to egg/sperm production).

    The only exceptions to this rule are Avians. Birds reach full adult size extremely fast (1 year, or less for most species). Sexual maturity trails way behind at 2-4 years in many of the larger animals. The reasoning behind this is due to the mechanical limitations of flight in birds. The musculature required to sustain flight, is not available in birds until they reach adult size. As flight is the main means of escape from predators, it behooves birds to reach flight status as quick as possible.

    Well, needless to say, few dinosaurs flew (Microraptor gui being the only example I can think of), so the pressure to hit adult size was just not there for dinosaurs.

    In the end this report can be filed under: Assumed and Now Validated.

    This finding, along with many other findings over the past couple of years just helps to remind us that birds evolved from dinosaurs; not the other way around.

    ———————————————————–

    Reference

    Erickson, G.M., Curry Rogers, K., Varricchio, D.J., Norell, M.A., Xu, X. 2007. Growth Patterns in Brooding Dinosaurs Reveals the Timing of Sexual Maturity in Non-Avian Dinosaurs and Genesis of the Avian Condition. Biology Letters Published Online. doi: 10.1098/rsbl.2007.0254


  • The fibrolamellar smoking gun.

     

    Three different types of bone growth scene in vertebrates. A. Low vascular, lamellar bone. B, highly vascular, woven bone. C. Fibrolamellar bone. Arrows indicate Lines of Arrested Growth (LAGs). Image from http://ltc.smm.org/histology/
    Three different types of bone growth seen in vertebrates. A. Low vascular, lamellar bone. B, highly vascular, woven bone. C. Fibrolamellar bone. Arrows indicate Lines of Arrested Growth (LAGs). Image from http://ltc.smm.org/histology/

     

    For over twenty years now it has been assumed that there is a black and white divide between bone histology and thermophysiology. Automatic endothermic “warm blooded” animals tend to show a haphazard composition of bone deposition, in which bone is laid down around surrounding blood vessels very quickly, with interspersals of more organized bone deposition (for strength). The term, coined by histologist Armand de Ricqles (1980), is fibrolamellar bone.

    In contrast, bradymetabolic “cold-blooded” animals tend to show a regular deposition of layered, or lamellar zonal bone. This bone is not as well vascularized as fibrolamellar bone, and is often deposited at a much slower rate.

    Back in 1980, this evidence was used along with a chain of other circumstantial evidence to show that dinosaurs were actually “warm-blooded” animals (Bakker, 1980). This challenge did not go unanswered, and even back then there were people questioning the evidence being proposed in favour of dinosaurian automatic endothermy. As far back as 1982, there were authours claiming to have histological evidence of fibrolamellar, “warm-blooded” bone growth in crocodylians (Ferguson et al, 1982). This evidence has often been scoffed at as being questionable at best (Horner & Padian, 2004). Skeptics have pointed out that the fibrolamellar crocodylians mentioned have all been captives. Being kept in a stable environment with easy access to food has resulted in these skewed results. Wild individuals would doubtfully show these traits, as access to scenarios like those provided in captivity, are unlikely.

    For awhile this seemed to keep the argument of fibrolamellar bone, strictly in the pro-automatic endotherm camp. Well, not anymore.

    Tumarkin-Deratzian, A.R. 2007. Fibrolamellar bone in adult Alligator mississippiensis. Journal of Herpetology. Vol. 41. No.2:341-345.

    This paper reports the observation of long bone histology in alligators from Lake Griffin in Lake County, Florida. The findings are most interesting. Seven specimens were studied. Of these, three had extensive fibrolamellar growth in their long bones. In fact, one could put a fibrolamellar individual next to a lamellar zone individual and it would look like one was comparing a “classic mammal” to a “classic reptile.” The difference is incredibly dramatic; even moreso than comparing frame A with frame C in the above picture.
    That’s not the best part though. You see, these lake Griffin alligators were not only wild animals, but they were stressed animals too. Currently the Lake Griffin alligator population is suffering from an intense die off. The reasons behind the high mortality at Lake Griffin remain uncertain, but there seems to be a link to thiamine deficiency in the animals dying.

    This means that, not only are we seeing different bone deposition patterns in animals from the same population, but we are also seeing them from animals that were living under stressed conditions. This throws the whole “crocodylians can only show automatic endothermic growth rates under perfect conditions” argument right out the window.

    So what does fibrolamellar deposition really show? Currently it remains unknown. It might still indicate faster growth. What it doesn’t indicate, though, is the thermophysiological preference of the animal in question.

    Id est: it doesn’t seperate the “warm-bloods” from the “cold-bloods.”

    More to come. Stay tuned.

    ~Jura

    References
    Bakker, R. 1980. “The Need for Endothermic Archosaurs.” In: Thomas, R. D. K., and Olson, F. C. (eds.). A Cold Look at the Warm-Blooded Dinosaurs. Westview Press, Boulder.
    de Ricqles, A. J. 1980. “Tissue structures of dinosaur bone: Functional significance and possible relation to dinosaur physiology.” In: Thomas, R. D. K., and Olson, F. C. (eds.). A Cold Look at the Warm-Blooded Dinosaurs. Westview Press, Boulder. Pp. 103-139.
    Ferguson, M.W.J., Honig, L.S., Bingas Jr, P., Slavkin, H.C. 1982. In vivo and in vitro development of first branchial arch derivatives in Alligator mississippiensis. Progress in Clinical nad Biological Research. Vol. 101: 275-286.
    Padian, K. and Horner, J.R. 2004. “Dinosaur Physiology.” In: Weishampel, D.B., Dodson, P. and Osmolska, H. (eds.), The Dinosauria 2nd edition. Univ. California Press., Berkeley. pp. 660-671.

  • When dinos were nixed, mammals stayed fixed.

    According to news from CNN.com, (though technically, AP), mammals weren’t itching to take over the newly vacated niches left behind by the dinosaurs 65 mya.

    A new phylogenetic study of mammals, reported that there was no burst of activity following the demise of the dinosaurs. There was some flurry of speciation in animals that left no descendants, but all extant mammals remained pretty low key until around 55-35 mya.

    As is typical for these studies, the results are somewhat controversial. Some folks are questioning the dating methods used, while others are both shocked and impressed with the results.

    Though the AP sticks in the hyperbolic: “…challenges a long-standing theory.” statement, I doubt we’ll be seeing textbooks getting rewritten anytime soon.

    ~Jura


  • Latest Paleo News

    Apparently these past couple of days have been a bit of a boon to paleontology. 3 new finds have just been announced.

    The most recent find, is that of a new species of gliding reptile from the early Cretaceous period (125 mya).

    See: New Scientist for a full description.

    The neat thing about this critter is that it is the oldest gliding lizard to date. Back in the Permian and Triassic periods, there were various gliding critters like Sharovipteryx, Coelurosauravus, and Kuehneosaurus. None of these reptiles were lizards, though.

    This new guy, Xianglong zhaoi, is the first true member of squamata that glided. The New Scientist illustration makes the critter look nearly exactly like a modern day Draco. I haven’t read the paper yet, so I’m not sure how accurate it is. Finally, another neat thing about this little guy (only 15 cm long) is that it was preserved so well that one can actually make out the wing membrane itself. Very cool stuff.

    The second bit of news is among the crocodyliformes. A new species of Metriorhynchid suchian has been unearthed in Eastern Oregon. Metriorhynchids were a completely marine group of crocodyliformes. They are easily diagnosed by their thin snouts with needle like teeth, their lack of any real scalation (in specimens that retain skin impressions) and the presence of a bifurcated, or forked tail. Imagine something like the horrible love child of a crocodile and a shark.

    Full story here

    According to the report, this new guy, who has yet to be named, lived around the middle to late Jurassic (180-150 mya). According to the report, this species retained short stubby limbs (all other Metriorhynchids evolved paddles), which suggests that it might have still made forays onto land. It was probably a coastal dweller. It must have been pretty clumsy on land, though, given its large forked tail.

    The last bit of news is in the realm of dinosaurs. Paleontologists have recently announced the discovery of an ornithischian dinosaur that was a burrower. The new dino, named: Oryctodromeus cubicularis, was found inside an ancient burrow. It also showed a couple of unique features that suggest this animal did the burrowing itself.

    One can read more on the story here.

    The paper will appear in the next issue of: Proceedings of the Royal Society B.

    Once I get ahold of these papers, I may make an update.

    Stay tuned.

    ~Jura