[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Making Mincemeat of Condylarthra and the "Ungulate" Radiation

 ... oh, and Dinosaurs are in here, too. :)
Eric Lurio (elurio@aol.com) writes:

<This critter's descendants included the protoungulatae, which
were once a single species.>

  We assume that all condylarthran mammals were descendant from
the same stock, as we assume the same for ungulates, etc.

<In other words, during the Cretaceous, the Ungulata went from a
single species to small number of closely related species. They
evolved into many directions, and those survivors are the crown
groups we know and love today.>

  Those survivors enjoin status in being unresolved to each
other, or even within a clade that could be even closely marked
as "Condylarthra." Litopterns (camels and allies), afrotheres,
perissodactyls, and artiodactyls (the last two are traditional
Ungulata, and I think this is the restricted clade, but could be
wrong), whales and allies (including mesonychians, sirenians,
and desmostylians -- possibly polyphyletic association), etc.
are all from the same general stock as suggested in their fossil
members. There has been a great deal of morphological and
molecular difficulty in resolving them to each other, as whales
will fall in as artiodactyls, sister to them, or to
perissodactyls, or etc., while camels and their allies
(protoceratids etc.) will shift about, and this affects the
positions of others. Extinct members that did not leave extant
branches (as the ones named above did) are even more difficult
to resolve, and these are those taxa that have been lumped into
traditional Condylarthra. Unfortunately, some studies have
suggested that some of these may not be subungulate or ungulate
at all, or are basal members of known ungulate groups, and this
has lessened the credibility of the term "Condylarthra" and
paradigms associated with it. Eric is right in disparaging the
term as others have for the last two decades with the advance of
molecular analysis in mammal phylogeny.

<Well, since both had a common ancestor in the middle

  In this, Eric is also right. I have a common ancestor with
*Dimetrodon*, for instance way back the Permian, but it might be
more explicit to state that I have a more recent common ancestor
with *Didelphis* than I do with *Dimetrodon,* which I do. Thus,
*Tyrannosaurus* and *Emberiza* do have a common ancestor in the
mid Trias, but so do *Allosaurus* and *Emberiza*, *Stegosaurus*
and *Emberiza*, *Herrerasaurus* and *Emberiza*, etc. By recent
phylogenentic studies, the closest this pairing becomes is
possibly in the mid Jura (Dogger), though it could have happened
earlier. By Eric's statement, I get the feeling that the split
between birds and dinosaurs was explicit, and that birds do not
stem from dinosaurs, as no dinosaurs are known from the mid
Trias (speculative fossils and trace fossils may indicate
this...). Maybe I'm just blathering...

<Okay, a tuatara "looks like" an iguana. Simple, no?>

  A caecilian looks like a snake, as does a glass snake. They're
not snakes, however. One's an amphibian (Lissamphibia) and the
others a lizard (Lacertilian). Tuatara's (*Sphenodon*) are part
of a group (Sphenodontia) that diversified in a variety of
niches (especially aquatic ones) and have physiological and
osteological considerations that demonstrate that they are not
lizards (= Lacertilia) at all, but outside the snake + lizard
group, though they are reptiles in any sense of the word. [HP
Pharris] Nick's -ops was not meant to be a generic "looks like"
term, or a statement of actual similarity, but apparently a
sense of effect, as in the titanothere *Brontops,* whose name
means "Like the Thunder." Herpetopsida, as was pointed out by HP
Marjanovic, was to suggest the use of the term "[h]erpeto-" in a
sense of reptiles in general, as herpetologists do not study
things that crawl, but are general.

<...and a hyrax looks like a guinea pig. [I know this for a fact
as I've seen both close up.]>

  I can tell the difference between the Guinea pig and a Tree
hyrax from a hundred paces, if not more. They are substantially
different from one another, even in general appearance. No way
that hyraces are rodent-analogs, either, as they are prone to a
varied diet, will eat flesh and bugs, and are nasty little
buggers you may not care to put in a cage and feed from a water
bottle. They can also shred your little fingers to bits, while
rodents have to _work_ at it.

<Therefore, looking at the modern hyrax and the reconstructions
of early ungulates, we can conclude that the modern hyrax looks
like an early ungulate, a condylarth. GET IT NOW?>

  An early ungulate probably looked like a cross between the
Dawn Horse and a chevrotain or water deer. It may have resembled
pigs to some degree, and basal suines have a lot of similarity
with early equimorphs and *Hyracotherium*, *Tragulus* and
duikers, basal litopterns and even *Camelus* itself, suggesting
that this was probably the basal morphology to some degree.
Hyraxes do not look like the basal ungulate morphology,
especially in the jaws and legs, which are advanced and derived
for their form. Aardvarks (other afrotheres) resemble the basal
ungulate condition more than hyracoids do, but are not ungulates either.

Jaime A. Headden

  Where the Wind Comes Sweeping Down the Pampas!!!!

Do You Yahoo!?
Yahoo! Auctions - buy the things you want at great prices