[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
David Marjanovic (email@example.com) wrote:
<IMHO the absence of the epipubes is very important. Epipubes are absent only
in placentals (and apparently in cimolestans, which are either placentals or
their sistergroup), but in all of those. Epipubes make it impossible for the
abdomen to expand much. Thus they make a placental pregnancy impossible. The
loss of the epipubes seems to correspond to a dramatic shift in the mode of
reproduction -- something which doesn't happen often, I think. Indeed, recent
unweighted cladograms put both Zalambdalestidae and Zhelestidae out of
I cannot respond on the topic of the biomechanical effect epipubes have on
abdominal expansion, since tests of musculature are lacking in the effect of
their precence in true placentals. The above it less certain than it sounds,
and should be couched in terms of a hypothesis; not offense, David. No living
placental has epipubes, and epipubes are known in living non-placental, so
obviously there is a lack of muscle studies to show what effect there is when a
placental, even perhaps a basal one, has epipubes and is gestating. The fact
is, until recently, it was determined that eutherians were defined anatomically
[in part] by their lack of epipubes, and now we don't know precisely when these
bones were lost in the therian lineages.
So what we CAN say is that no known placental has them, and that it is
present in "brief-gestating" and egg-laying mammals, but NOT that it restricts
"long-gestating" mammals from bearing young for longer periods of time with
greatly expanded bellies. Such an issue requires better data than saying "no
placental has them, so it must be related to being a placental."
<So you've merely coined a synonym of "basal", which after all means "far away
from the clade I am at this very moment interested in". -- The opposite of
"derived", though, isn't "basal". It's "plesiomorphic".>
No, I am coining a tree-specific set of terms for use of phylogenetics. One
can still refer to a basal mammal, but I seriously would have no idea what
you're talking about. I think it is too vague. When one has a tree, how much of
that tree is "basal" and the other "derived"? Or "plesiomorphic"? Indeed,
plesiomorphic refers to features shared in common with ancestors, and has
nothing to do with trees or the terms basal and derived, except that the term
can be related to them. There are such derived plesiomorphic animals, but one
needs start picking out anatomical features. Among Placentalia, for example,
presumably afrotheres are fairly "basal" (say, they correspond to the most
rootward branch of Placentalia using Asher's tree; or you can say they are at
the "bottom of the tree" -- which is more precise?), yet *Paleoparadoxia* is a
very derived "basal" taxon. The terms are not exclusively bipolar, and for
this, a set of polar terms was considered neccessary. Plus, I join Jon in
disliking "basal," but he's sorta given up on the run, since people will tend
to use imprecision where it is comfortable. Man fears change.
<phylon = stem
phyllon = leaf
Or I can use phyllogram, and demonstrate the OTU's not as stems (acts of
divergence or the lineage stemming [ha! see?!] from such an event) but at
terminal events in a lineage known, thus leaves. Does a phylogram demonstrate a
branching, and a phyllogram an arrangement of species? Semantics. The two words
in Greek are virtually uselessly separated, and most sources I've seen list
them as synonyms of *phylon*.
<Isn't it textbook wisdom that amniotes plesiomorphically have a pro- and a
metacoracoid, and that sauropsids have lost the metacoracoid? -- As for where
our coracoids have ended up, that's from the description of *Zhangheotherium*.>
In the authors' opinions. Different animals have been doing similar things in
concert, and this is true with regards to the inner ear incorporation,
reduction of the postdentary, complexity of the postcanines, cerebellar
expansion, manual and pedal development, hip modifications, for the last 200
million years or mammal evolution. I don't take things for granted and looking
for one simple explanation is often, in my study of teeth at least, an example
of not looking hard enough. This is why I tend to split characters up, because
I can look at complexes of character traits and test for character congruence
or "suites" in the big picture. But then, this is why I can claim 24 different
characters that link Therizinosauroidea and Oviraptorosauria....
On this same note, reading the description of *Pehuenchesuchus,* the new
sebecosuchid from the new _JVP_ I noted a semantic issue that may involve a few
misconceptions and involve a character complex: sigmoid curvature of the tooth
row and medial inflection of the symphysis are apparently gradations of the
same feature, if not BEING the same feature, also known as "festooning." One
could actually make a complex of some 3-4 states off of croc tooth-row shape,
and I'd be tempted to try for the fun of it.
<Actually not. It's related to the rostral and middle parts of Meckel's
cartilage, not to the caudal part that ossifies as the articular.>
I was wondering if anyone would catch it, but when I wrote "basal part" I was
not using a morphological sense but a phylogenetic one. This is why confusion
on the terminology "toward the base" needs to be looked at a little more
critically by people who use it. I would also like to note that when I use jaw
terminology, the "origin" point is mesial, and distal to which lies the jaw
joint. This is due to teeth orientation terminology, and it's easier to use one
for one bone in all animals than the three to four possible sets of terms I CAN
<Yes -- but AFAIK it's not related to digging; it's related to pronation vs
supination of the forearm.>
I didn't say it was FOR digging. I noted this as an aspect relating to
fossorial habits, so is a possible covergent structure.
<*Fruitafossor* sprawled like a monitor lizard or triconodont or
Because of the reconstruction? The humerus is at odds with a primary
weight-bearing bone for walking around on. Oh, not saying it didn't walk around
on it, but that the orientation is in keeping with other such humeri you see in
platypi and moles and chrysochlorids: not sprawled, but spread out limbs. The
forearms are oddly inconsistent with this, implying possible transistory
behavior OR I'm getting it all wrong ... or they are.
<Then why does it mimic the plesiomorphy present in all manner of terrestrial
Restricted hindlimb behavior can be plesiomorphic as well as functional, and
thus retained in a fossorial lifestyle or developed because of it.
<Basal palaeanodonts, like *Arcticanodon*, retain 6 cheek teeth as well -- 3
premolars and 3 molars as interpreted in *Fruitafossor*. The difference is that
in *F.* all teeth are single-rooted, while in *A.* the last premolar and the
molars are double-rooted.>
Very odd that. And this relates to *Articanodon* being a palaeanodont how?
Because I did bring up a lack of strong corroboration to palaeanodont
affinities based on superficial similarities and the issue of multirooted,
numerous teeth without _TEETH_ to show for the allusion. Superficiality has
been the cause of vague referals in the history of paleontology from
"kink-snout" spinosaurs as coelophysoids or *Elaphrosaurus'* body proportions
as one.... It's not that I disagree with the authors on these matters, but that
I think their details are lacking to support the conclusion they favor. Maybe
it's sexier for their hypothesis without all the trappings of details that some
learned fellow is going to crack like a walnut, or in the case of mammal
relationships, find one thing wrong and suddenly "everything is out the
window." Hence mammalian "Orders" and their lovely names. I think I'd rather
rename everything from the get-go and abandon the last two decades of
gene-based names. Bye bye baggage-ridden Euarchonta (it's carrying Archonta's
baggage, a far superior name, and it's nothing of a "true Archonta" since it
REJECTS Archonta), we'll call it "Monkeybats." Afrotheria is
"Elephanthyraxshrewmanateeaardvarkia," and be done with it.
<<Evidence of the Meckelian groove is lacking.>>
<Of course. It's a placental (...or perhaps a cimolestan...).>
Not what I meant. And I was referring to *Articanodon* here. There is NO
preserved portion of the jaw exhibiting the groove. Thus inferences about it's
presence or lack thereof cannot be made, including the phylogenetic utility of
xenarthan jaws or anteater-like mandibles, which lack Meckel's fossa and the
associated groove (more semantics in Meckelian terminology!).
<No wonder, because that is also the multituberculate jaw structure...>
Big wonder, if it looks nothing so much as an odd, if therian-like monotreme.
<While I am at it... all characters are unordered! That's not a good idea.>
Are we to make _a priori_ assumptions about order of character state changes
and how reversals are to be treated by the machine and thus influence
bootstraps and tree numbers? Perhaps. I like to run characters all ordered,
unordered, then variable ordering in my analyses; I will aslo run ACCTRAN and
DELTRAN in PAUP* to test their supporting points, bootstrap and jackknife,
Adams and strict concensuesesesesuses. I keep track of the data. It helps me
test for character change and "hard character states" without using MacClade.
Getting that program on a Windows shell may be harder than not....
Jaime A. Headden
Little steps are often the hardest to take. We are too used to making leaps
in the face of adversity, that a simple skip is so hard to do. We should all
learn to walk soft, walk small, see the world around us rather than zoom by it.
"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)
Do you Yahoo!?
Make Yahoo! your home page