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Re: HUMPING ARCHAEOCETES (SNIGGER)



>Archaeocetes, as you probably know, are a paraphyletic assemblage of basal
>cetaceans, some were and some probably were not ancestral to later groups. As
>such, they (archaeocetes) present several grades in whale evolution, ranging
>form the sea-lion like, amphibious _Ambulocetus_ and its relatives on one hand,
>to the huge, oceanic basilosaurids on the other.
>
>Unlike derived extant whales, basal cetaceans do not seem to have been fully
>adapted for an oceanic lifestyle. Some of the protocetids, for example, appear
>less inclined for a marine existence than modern pinnipeds. It is thus
>reasonable to conclude that they still gave birth on land, rested on beaches,
>that kind of thing. A number of cetologists, E. Fordyce, Michael Bonner (I
>think) and Lyall Watson among them, have advocated 'humping' in these animals.
>Fordyce (for those of you who don't know, one of THE 'top minds' in cetacean
>evolution) has even suggested that the giant basilosaurids could wriggle across
>sandbars like giant seals. I doubt this, they seem as well adapted for a
>pelagic
>lifestyle as more 'advanced' basal odontocetes and mysticetes.
>
>So, does that answer your question Jason?
>
>>

        Hmmm...   Looking at the anatomy of archaeocetes, and comparative
anatomy between pinnipeds and archaeocetes doesn't really support a humping
archaeocete.  For example, Ambulocetus, Rohdocetus, Indocetus, and several
new remingtonocetids (not yet described) all possess Hindlimbs that, while
reduced in length,  are well formed for active participation in some form
of terrestrial locomotion (extremely robust femora, enlarged patellae,
large degree of movement of the femur when articulated w/ the pelvis).  The
femur of Rohdocetus articulates w/ the acetabulum in such a way the the
limb is angled outward ("sprawling", for lack of a better word).  In all
but Rohdocetus and Protocetus, the sacrum is fused, indicating that the
pelvic girdle could support the weight of the hind region of the body
during terrestrial locomotion.  Also, all of the early archaeocetes (for
whom post crania is known) possess elongate tails, which could suggest the
development of an early fluke.  A large tail could make humping locomotion
a bit difficult.  The bodies of pinnipeds are rather short and stout, where
the bodies of archaeocetes are elongate. I'm not advocating the notion of
these early archaeocetes running around like mesonychids,  but there's not
much to archaeoectes that suggests humping.
        The main morphological similarities between archaeocetes and
pinnipeds is in the overall structure of the pectoral girdle (Fan shaped
scapula w/ enlarged spinatus muscular attachment sites, humerus w/
hyperextended deltapectoral crest, downturned ulna w/ greatly enlarged
olecranon process).   These similarities may indicate similar forelimb
function, during aquatic locomotion (EG "sculling").  Sirenians possess a
very similar lower forelimb structure (the scapula is different), and do
the same things as pinnipeds w/ them (on a basic level).
         As for basilosaurids, Philip Gingerich, THE "top mind" in cetacean
evolution has suggested that the unusual morphology of the hindlimbs may
indicate a use as a copulatory guide (really humping archaeocetes).  Theres
no way a basilosaurid could do anything terrestrial, except die.  Take a
look at their axial skeletons, those critters most probably couldn't even
swim fast (by todays standards).

        For anyone who is interested, Gingerich has published on most of
these critters in the Contributions from the Museum of Paleontology, The
University of Michigan.  For pinniped functional morphology/ anatomy, check
out just about anything by Arthur W. English.


Jason J. Head
V.P. graduate student
Dept. of Geological Sciences
Southern Methodist University
Dallas, Tx. 75275