• Tag Archives archosaur
  • The 3D alligator

    Model organisms are a staple of biology. They are taxa that are used to answer larger questions about that group as a whole, or some general biological problem. Model organisms are chosen for their ease of handling, cheap acquisition, generally “generic” structures, or all of the above. Every major class has a model organism to represent it. Just among vertebrates we have:

     

    A stillborn hatchling rests inside the left nostril of a large 3.7m (12ft) adult which is some 5000 times larger!
    A stillborn hatchling rests inside the left nostril of a large 3.7m (12ft) adult which is some 5000 times larger!

    Mammals with mice (Mus musculus), dogs (Canis familiaris [or Canis lupus familiaris if you lean that way]), cats (Felis catus [or Felis sylvestris catus for the same reason as dogs]), guinea pigs (Cavia porcellus) and rhesus monkeys (Macaca mulatta).

    Birds with chickens (Gallus gallus), pigeons (Columba livia), and zebrafinch (Taeniopygia guttata).

    Ray finned fish with zebrafish (Danio rerio), swordtails (Xiphophorous) and cichlids (Cichlidae).

    Amphibians with the African clawed frog (Xenopus laevis), and axolotol (Ambystoma mexicanum).

    Reptiles with anoles (Anolis), fence lizards (Sceloporous), painted turtles (Chrysemys picta) and finally, the American Alligator (Alligator mississippiensis).

    Alligators are relatively new to the model organism realm, but they have proven to be extremely informative. They seem to the be most even tempered of extant crocodylians, making them “more safe” for researchers to work with. Hatchlings start off as miniscule 68 gram (0.15 lbs) animals that later can grow to 363 kg (800 lbs) adults, passing through an enormous size range throughout ontogeny. This growth rate is very food dependent, making it possible to raise alligators almost as bonsai trees. Also, with their unique position on the organismal family tree, alligators are one of the closest living relatives to dinosaurs. Along with birds, they have the potential to help constrain our assumptions about dinosaurs; thus making them very popular subjects for paleontological research as well.

    Today, alligators get to make one more stamp on human knowledge with the release of the 3D alligator project from the Holliday and Witmer labs.

    Researchers from both labs went through the painstaking process of digitizing the skulls of an adult and a hatchling American alligator, and then digitally separated each bone. The result is a 3D model that can have each bone turned on and off at will. The neat thing is that both labs have made these data freely available for anyone to look at, and download as 3D pdfs, wirefusion models, and multiple movies.

    So if one every wanted to know just how many bones make up a crocodylian skull, or how each bone aligns to each other, I highly recommend downloading the 3D pdfs of the adult and hatchling. Not only will one learn all the different bones that compose the skull, but by comparing hatchling to adult, one can see just how radically these bones change throughout ontogeny.

    It’s neat, free, informative and reptilian. What more can one ask for. 🙂

    ~Jura


  • T-U-R-T-L-E Power! Part 2: The weird and wacky origin of turtles.

    A Galapagos tortoise struts about, secure in the knowledge that no one will ever know where the hell it came from. Photo from petcaregt.com

    This is a long overdue follow up to my original Turtle Power article back in…yeah never mind the date.

    As established previously, turtles are a strange, and highly diverse group of animals, but how did they come to be this way?

    The turtle bauplan has been a phylogenetic double edged sword. On the one hand, the unique shell design, and the necessary body contortions associated with it, make chelonians a very easy group to classify. However, it is these same peculiarities that keep us from finding the ancestor to turtles. To date, there are no half-turtles. No good transitionals between one reptile group to that of turtles. As such, the list of turtle ancestors runs all over Reptilia. Some paleontologists believe the origin lies at the base with reptiles like procolophonoids, and pareiasaurs. Others believe turtles are a bit more closely related to extant reptiles, and belong in, or alongside the sauropterygians (plesiosaurs, nothosaurs, and placodonts). There is even some evidence to suggest turtles are actually in the same reptile group as dinosaurs and crocodylians (Archosauria).

    Curse that shell! - Photo by tompain

    How can the list be this extensive? Read on to find out.

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