Anatomical Order

Anyone who has read a bunch of vertebrate palaeontology papers will by now (hopefully) have noticed that the description of various anatomical bits tend to be in the same order, each bone has it’s place in the queue so to speak. It’s a simple enough concept as it makes it easy to access details quickly – if you want to know what the hand looks like you need to know where in the paper you are likely to find it and not have to read the whole thing to find the information you want. This is an established protocol that is, sadly, not always followed (most especially in character lists of cladistic characters), but it worth spelling out for the interested.

Quite simply one starts with the front of the skull and describes it front to back, then the mandible, then the complete vertebral column front to back (so going through to the end of the tail, and including associated bits like ribs and gastralia), then the forelimbs from the body outwards (finishing with the last finger) and then finally the hindlimbs in the same manner (starting with the pelvis and finishing with the claw of the last toe). Of course this varies depending on exactly what bones you have both in terms of general biology (not everything has five toes, or a predentary or a palprebal, etc.) and of course preservation (you can’t describe a skull you haven’t got). The three sections being called the cranial (skull), axial (vertebral system) and appendicular (limbs and girdles).

Based on my own notes and a couple of papers I’ll try and do a full list of every archosaurian bone in order. Doubtless I’ll miss a few (even within archosaurs) and misplace a few since I don’t know every bone or where there are significant variations in where they are positioned (or specially absent or specially present), but it should be a general guide (e.g. no pteroids).

When describing the individual bones you should really start at the front and move toward the back and from the top to the bottom, beginning with an overall description and then moving to the details, then how they fit with other bones, then any accessories. When you have multiple parts, move in the same direction so in the hand start with digit 1 and go to the end, then back to digit 2 and so on.

Cranial:

Skull bones as follows – premaxilla, maxilla, nasal, lacrimal, prefrontal, frontal, postfrontal, parietal, postorbital, squamosal, jugal, quadratojugal, quadrate.

Fenesatrae (naris, anorbital fenestra, foramina etc.).

Braincase as follows – basioccipital, supraoccipital, epiotic, paroccipital, exoccipital, opisthotic, prootic, parabasisphenoid, laterosphenoid.

Palate as follows – vomer, palatine, pterygoid, ectopterygoids, hyoids

Teeth.

Mandible as follows – dentary, surangular, angular, splenial.

Mandibular teeth.

Axial:

Vertebrae – atlas, axis, cervical vertebrae, dorsal vertebrae, sacral vertebrae, caudal vertebrae.

Cervical ribs, dorsal ribs, chevrons, gastralia.

Appendicular:

Pectoral limb – scapula, coracoid, clavical, sternal plates, humerus, radius, ulna, proximal carpals, distal carpals, metacarpal I – ungual I, then II-V in the same manner.

Pelvic limb – ilium, pubis, ischium, femur, tibia, fibula, proximal tarsals, distal tarsals, metactarsal I – ungual I, then II-V in the same manner.

Additional Strucutres:

Osteoderms, scutes etc.

So there you have it. I imagine it’s of little interest to the readers who don’t already know it, but if nothing else it might yet serve as a reference for people in the future. It’s certainly useful for me to have a permanent record of it I can refer to. Feel free to suggest modifications or additions and I’ll try and keep on top of it, though do remember that while the basis of this is standardised as such, I have never seen a list like this published. Doubtless therefore, some people would do the ulna before the radius and others will include the limb girdles with the axial system on occasion too and just keep the humerus onwards and femur onwards on the appendicular side of things and that kind of difference is not likely to be important. The pelvis as a whole of course will never sit comfortably on either side of the divide given how intimately the ilium (and often the pubis and ischium) is bound to the sacrum, but this should be a decent start for any ‘describers’ out there.

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15 Responses to “Anatomical Order”


  1. 1 Mike Keesey 05/12/2009 at 10:41 am

    Interesting observation — hadn’t thought of it before.

  2. 2 Jaime A. Headden 05/12/2009 at 6:34 pm

    Dave,

    When I work on a cranial study, I segment it a little different, as my focus is on the oral complex it tends to focus therein. This follows with a functional concern towards other bones: ribs, gastralia, epipubes/propubes and the sternal complex are often interrelated (even in birds) such that disaparate disucssion may often occlude functional units of anatomy. For the limbs, it’s pretty simple, since the entire limb is a series of levers (for the most part) that all do relatively simple things each on their own and are essentially a single complex. Also true of the tail.

    In the skull at least, the palatal complex performs a wide variety of tasks that makes it difficult to categorize them into distinct functional units (except when discussing the function in relation to the bone). Epipterygoids, palatines and even vomers may often be put to the wayside to discuss the pterygoid/ectopterygoid/quadrate unit (which may even exlcude the ectopterygoid and relegate it to the palatine/vomer unit), and this is important when discussing taxa with palatine, vomerine and pterygoid teeth in relation to the oral complex as a whole.

    Mandibularly, there are also the articular, coronoid, extra-coronoid bones, supradentary, and even the surpaarticular (Bagaraatan and Allosaurus), likely the latter being an ossified tendon.

    I split the hyoids after the skull. I see no reason to place them as part of the palatal function as they are nested among the functional respiratory and feeding complexes too closely.

    Dentition should always — and I stress always — be placed after the mandibular structure (if present) and after any and all cranial bones bearing them are described, if not compeltely after the whole skull. It should be fairly safe to describe the maxillary dentition after the maxilla, or after the entire skull is described, because in most taxa, the teeth are general “enough” to be covered in a distinct section. This is especially important when shed teeth are described as their actual origin bone is uncertain (as well as issues in distinguishing lateral marginal reptilian teeth into upper and lower suites).

  3. 3 Mickey Mortimer 06/12/2009 at 3:57 pm

    Obscure bones ancestral to Archosauria besides those mentioned by Jaime- prearticular, stapes, proatlas, sacral ribs, interclavicle.

  4. 4 Marcia Neil 07/12/2009 at 12:05 am

    It’s no doubt a scientific rule that a paleontologist can’t “describe a skull you haven’t got” but working from occult memory-images you can describe a skull anyway, even if the piece of bone no longer exists. Memory-images are stored in and transmitted from people’s living brain-mass, but also can be viewed within a mucousal oracle-bead artifact — both as occult phenomena.

    • 5 David Hone 07/12/2009 at 8:52 am

      Marcia, please don’t post things like this. If you have a scientific case then go and publish it in a scientific journal, do not put things like this here. Repeatedly reposting what is effectively the same comment on multiple threads referring to your own ideas as a proven fact in not what this blog is for. I’m bored of it and will start deleting them if you carry on ion thie vein.

  5. 6 Mike Taylor 07/12/2009 at 7:34 pm

    David, at first I thought you’d omitted the sternal plates; then I found myself wondering whether they could possibly be homologous with the clavicle. Is it so?

    • 7 David Hone 08/12/2009 at 9:10 am

      It’s certainly been suggested, and off the top of my head I can’t think of anything that has both. But I’m not sure now you put me on the spot – I’ll have to go rooting in my notes (or ask someone who knows more than me!).

      • 8 Mike Taylor 08/12/2009 at 7:14 pm

        Better shove sternal plates into your list for now, then!

      • 9 David Hone 09/12/2009 at 8:47 am

        Yep, I was thinking about this last night and there are indeed several things with a furcula (fused clavicles) and sternal plates, so they are indeed missing. Missed it! Thanks for the heads-up Mike – though I’m a little worried it took me several days to remember….

  6. 10 David Marjanović 09/12/2009 at 10:33 pm

    Erm… what happened to the long-ass comment I just wrote?!?

  7. 12 David Marjanović 09/12/2009 at 10:39 pm

    It’s still not there. Anyway, paired clavicles and paired sterna occur together all the time, even in embryonic mammals, and sterna are endochondral, while clavicles are dermal. I’m not aware of any journal that prescribes any anatomical order; most people do generally describe their animals from rostral to caudal, but that’s pretty much where the commonalities end, and I posted a long example (full of bones that don’t occur in archosaurs) which was also highly unusual in putting most of the appendicular skeleton before the axial skeleton and the ribs before the vertebrae. I also pointed out that some people describe the dermal shoulder girdle before the endochondral one, and while most put the pectoral girdle and forelimb before the pelvic girdle and hindlimb, some describe first both girdles and then both limb pairs.

    Also, what is the epiotic supposed to be? And there is no paroccipital bone, just the paroccipital process of the opisthotic. And the parasphenoid (a dermal bone, BTW) is not always fused to the basisphenoid (an endochondral bone).

    • 13 David Hone 10/12/2009 at 9:06 am

      I did say that this is not a hard and fast set of rules and that there is lots of variation. This is simply a reproduction of the guide I was given as a student and enlarged and expanded at various times and from various sources. It is supposed to be a guide, not a rulebook.

    • 14 Nick Gardner 11/12/2009 at 2:01 am

      Also, what is the epiotic supposed to be? And there is no paroccipital bone, just the paroccipital process of the opisthotic. And the parasphenoid (a dermal bone, BTW) is not always fused to the basisphenoid (an endochondral bone).

      David M., this a great point to bring up (that the parasphenoid and basisphenoid are not the same elements and have different developmental origins), and its relevant to a manuscript I currently have in review. So thanks for bringing that up before I got the chance to do so. =D

      Cheers,
      Nick

  8. 15 David Marjanović 09/12/2009 at 10:41 pm

    And why would anyone describe the hyoid with the palate? It’s in the ventral neck wall, and it belongs to the “visceral” (branchial) skeleton just like the stapes… which is sometimes described together with the braincase, sometimes after the skull and the mandible.


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