• Tag Archives dinosaur
  • 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


  • The “Dawn Shark” and “Hidden Face”

    As I strolled along internet looking for something to blog about, the only thing that I could find was a report that was mentioned a few days ago.

    As is typical, it features the world’s most popular reptiles: Dinosaurs.

    Eocarcharia and Kryptops
    From left to right: “Fierce eyed Dawn Shark” Eocarcharia dinops and “Old hidden face Kryptops palaios

    In this case, it is two theropods that were described by paleontological superstar Paul Sereno, and somewhat paleo-newbie Steve Brusatte. For members of the Dinosaur Mailing List, Brusatte is well known for his previous work on the internet, as a paleo-journalist. This description is credit well deserved for Steve. So good on him for that.As for the report, what is there to really say. It’s the discovery of two new theropods. In the world of dinosaur diversity, dinosaurs are usually broken up into 3 categories:

    1. Theropoda
    2. Sauropoda
    3. Ornithischia

    In terms of diversity, the previous categories are essentially in reverse order. Easily the most diverse dinosaur group was the Ornithischia. They included “duck billed” hadrosaurs, crested lambeosaur…hadrosaurs, horned ceratopians like Triceratops horridus, armoured stegosaurs and super-armoured ankylosaurs. Two legged hypsilophodonts, and helmeted pachycephalosaurs. Ornithischians were all over the map in terms of diversity.

    Next up we have the sauropoda (or to be more inclusive: the sauropodomorpha). On the outset one might think that these guys weren’t really that diverse. I mean if you’ve seen one long necked, long tailed behemoth, then you’ve seen them all right?

    Er, no.

    Sauropods ranged in size from the super tiny Mussaurus patagonicus*, which topped out at 37cm (15 inches), to titans like Argentinosaurus huinculensis, Sauroposeidon proteles, and Amphicoelias fragillimus; all of which grew to excesses of 39.6m (130ft), and had masses 1,000 times greater, with some estimates as high as 122 metric tonnes!

    Besides this humongous size range, we also had sauropods that had sail-backs (Amargasaurus cazaui), sauropods that had tail clubs and armour like ankylosaurs (Shunosaurus lii, Saltasaurus loricatus). We even had sauropods with strange beaks and short necks (Bonitasaura salgadoi, Brachytrachelopan mesai).

    Finally we come to the theropoda. All are bipedal carnivores (one possible exception in segnosaurs). They came in two size classes: Frickin huge, and medium sized. Some had long necks (Coelophysis bauri), some had display crests (Dilophosaurus wetherilli, Cryolophosaurus ellioti). Many show reduction in arm size, with Tyrannosaurus rex and Carnotaurus sastrei taking the cake for tiniest arms. There was also one weird group that had sail-backs and crocodile like heads (the spinosaurs). Still, in terms of overall diversity, a theropod was a theropod.

    Oh, and one group spawned birds, if you’re into that angle.

    It never ceases to amaze me at how often the Dinosaur Mailing list, or dinosaur related websites, devote so much time to theropods. Even news stories seem to put more focus on the big meat eaters rather than the numerous plant eaters. Heck just look at how often we watched theropods fight in the Jurassic Park movies (do you know there was never a scene in the JP movies where a theropod attacked a plant eater?).

    One is forced to ask why that is. I believe the answer lies in the ecology alluded to above. Though sauropods and ornithischians were a highly diverse bunch, they were all herbivores. The only carnivorous dinosaurs were theropods.

    To elucidate this hypothesis even further, check out this story on Digg.com:

    Evolution Explains Why Lolcats Control Your Mind

    Psychologists at Yale University found that the human brain is biased towards images of animals. We are more likely to notice a change in an image, if that change involves animals. I’m going to take this one step further and say that not only are we biased towards pictures of animals, but that bias is even stronger for predatory animals. Especially predators that are large enough to pose a threat to ourselves (e.g. lions, tigers, crocodiles, large sharks, and of course: big theropods).

    So there you have it. Theropods might be the plane Jane group of the Dinosauria, but they will always hog the spotlight. Evolution would have it no other way.

    ~Jura

    *Technically M.patagonicus wasn’t actually that small. The type specimen was a hatchling. Adults were closer to 5m (16ft) in total length. Still small for a sauropod though.