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Re: *Fruitafossor*



----- Original Message -----
From: "Jaime A. Headden" <qilongia@yahoo.com>
Sent: Saturday, April 02, 2005 3:34 AM

<To answer my own questions, yes, it's the metacoracoid, and yes, epipubes are
at least reconstructed...>


As noted above, the epipubes may not be statistically very important, present
as they are throughout crown mammals up into rootward crown eutherians.

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 Placentalia.


So I am using two test terms to replace "basal" and "derived" when
using a phyllogram, and instead am using "root" and "stem" in that this is both
more aesthetic with the idea of a phyllogram (of leaves and bushes) or a
cladogram (of branching), and it carries no "worse than/better than" baggage
(his big complaint). Root and rootward = at or towards the root of a phyllogram
or a given node or stem; stem and stemward = at or towards an operational
taxonomic unit or group of such units; i.e., any clade, taxon, or rank you may
chose to determine.

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".


BTW...
phylon = stem
phyllon = leaf
...therefore phylogram.

<Which one? The procoracoid or the metacoracoid? Monotremes retain both. In
Trechnotheria (spalacotheriids + us), at least, the procoracoids form the caps
on the medial ends of the clavicles, while the metacoracoids form the processus
coracoidei on the scapulae.>


These may not be the same osseous centers as in the basal amniote coracoid.

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*.


<Does it have epipubes? I bet it does... and I bet palaeanodonts don't...>

I can only hazard a guess that any rootward member of the crown Eutheria is
more likely to retain epipubes than stemward, given their retention in "basal"
eutherians like *Eomaia*

...and *Zalambdalestes* and *Ukhaatherium*...

"*Fruitafossor windscheffeli* differs from all Cenozoic fossil therians
(including palaeanodonts) and extant placentals (including tubulidentates
and xenarthrans) in retaining a long list of plesiomorphies including:
presence of a broad Meckel's sulcus on the mandible [no comment, but
appears to be related to a basal middle-ear complex,

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.


in the presence of widely separated and spherical radial and ulnar condyles of
the humerus [this is locomotory in nature],

Yes -- but AFAIK it's not related to digging; it's related to pronation vs supination of the forearm. *Fruitafossor* sprawled like a monitor lizard or triconodont or multituberculate. Somewhere around the base of Cladotheria or so the limbs became vertical...


    in the presence of a cynodont-like, broad peroneal shelf of the
   calcaneus [lacking in more rootward crown mammals],

Lacking in less rootward ones. :-)

and in the vertical
orientation and medial placement of the astraglar and sustentacular facets
on the calcaneus [restricted range of ankle movement could very well be
related to a hindlimb component to digging].

Then why does it mimic the plesiomorphy present in all manner of terrestrial mammali...morphs?


*F. windscheffeli* and Early Tertiary placental palaeanodonts both have single,
and openrooted cheek teeth with elliptical cross-sections; but palaeanodonts
retains only one or two cheek teeth (Simpson, 1931; Emry, 1970), far fewer
than the six cheek teeth of *F. windscheffeli* [plesiomorphy; the authors
should know better, but this IS a full differential diagnosis]."

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.


Though this says something, Ross et al. refer *Articanodon* to the
Palaeanodonta based on the relative shape of the mandibular ramus and the shape
of the canine. We all know how rare convergent jaw shape and tooth shape is in
Mammalia. Enough said. Based on the double rooted postcanines, I would likely
have been a LOT more cautious about systematic assignment of this taxon.

Then forget *A.* and read the rest of its description! Several other basal palaeanodonts are mentioned there: *Tubulodon*... *Mylanodon*...


Evidence of the Meckelian groove is lacking.

Of course. It's a placental (...or perhaps a cimolestan...).

<I can't hazard a guess about whether the middle ear was still connected to the
lower jaw (as the authors infer) or if the Meckelian groove just housed a big
splenial. However, the vestigial angular process is interesting -- that's
exactly how the missing link between the australosphenidan grade (bigger
angular process) and the triconodont-multituberculate grade (no trace of an
angular process) is supposed to look like! :-)>


[...] If nothing else, this resembles the triconodont jaw structure more than
it does any therian condition.

No wonder, because that is also the multituberculate jaw structure...

I do not see more substantial evidence to
support a complex of middle ear bones medial to the mandible.

Just the surangular and angular and/or prearticular would extend that far rostrally. Compare *Teinolophos*.


Poor character selection or lack of discussion of the derived or
"obliterated" condition in slender-jawed mammals like *Ornithorhynchus* and
xenarthrans appears to also affect the scoring of jaw features.

*Kollikodon* could have been interesting... but I'm already glad that, for the first time, an echidna is included!


While I am at it... all characters are unordered! That's not a good idea.