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

Re: Parts & Non-Recreation (was: Ceratonykus)



I'm jumping on a limb here. Both Augusto and Tom below sent emails that 
included an address with a listproc identifier, but these did not show up in 
the archives for the dates sent. I will presume they were intended for the 
list. Otherwise, I apologize. The contents are quoted in full below (as to what 
those authors wrote).

Tom Holtz wrote:

<Razor-blade teeth? Substantive array?
 
They are extremely small (although yes: more abundant than in mammalian 
mymecophages, but not so than in squamate ones) and essentially peg-like. Yes, 
they retain the ancestral xiphodont profile with lenticular cross-section. But 
they are practically peg-like (indeed, Choiniere describes them as such). Lack 
of serrations in small theropod teeth seems to be a developmental feature: 
below a certain size threshold, serrations becoming vanishingly rare.>

They are extremely small (although yes: more abundant than in mammalian 
mymecophages, but not so than in squamate ones) and essentially peg-like. Yes, 
they retain the ancestral xiphodont profile with lenticular cross-section. But 
they are practically peg-like (indeed, Choiniere describes them as such). Lack 
of serrations in small theropod teeth seems to be a developmental feature: 
below a certain size threshold, serrations becoming vanishingly rare.>

  Just because I fear constantly I make substantive mistakes, I double-checked 
with what Choiniere et al. (2010) had to say:

  "At least 30 small maxillary teeth are present in Haplocheirus, as in 
Shuvuuia (17), Pelecanimimus (26), therizinosauroids (27), and troodontids 
(28). Unlike the conical, unserrated teeth of Mononykus (28) and Shuvuuia (29), 
however, the maxillary teeth of Haplocheirus are recurved and bear small 
serrations posteriorly (fig.
S4)." [pp.571-572]

  I cannot confirm with *Shuvuuia deserti*, as the discussion of teeth in 
either ref (17) or (29) are brief and limited.

  "The dentigerous margin of the premaxilla is not preserved but the maxilla 
bears numerous tiny, unserrated teeth, identical to those of Mononykus[2]." 
[Chiappe et al., 1998:p.276]

  Suzuki et al., 2002 do not mention teeth save in their codings, which I won't 
rely on as I cannot confirm them.

  But for *Mononykus olecranus*, the situation is fairly different.

  "A single tooth was found within the braincase close to the maxilla (see 
Perle et al., 1993: fig. 3). It is extremely small, laterally compressed, 
spatulate, and leaf shaped. The tooth surface is mostly smooth, although some 
fluting is present proximal to the apex. It possesses rostral and caudal 
carinae lacking serrations. The tooth base is constricted, just proximal to the 
end of the enamel covering." [pg. 5]

  Before I continue, it should be noted that Choiniere et al. consider the 
identifications made by Perle et al. to be true, and as such that their remark 
the teeth are "conical," but which are also apparently "laterally compressed" 
is an issue of aspect, not volumetric evaluation. I make a distinction here 
between "aspect," which is the appearance likening an object to another, such 
as "triangular snouts" apart from a quantification of angularity. In this 
sense, Choiniere et al. are not contradicting my statement that the teeth are 
"razor-blade[s]." I was a little lose in my comparison, sure. I was likening 
their aspect rather to that of some troodontid and unenlagiine teeth which are, 
amazingly enough, laterally compressed, basally restricted, often devoid of 
denticulation, sometimes with fluted enamel "wrinkles," and only somewhat 
recurved to extremely so. Despite this, a meare sideways look at such teeth 
make them seem "conical," and I think this has more to do with the relative 
recurvature of the distal carina and nothing to do with the width of the crown 
compared to its mesiodistal _or_ basoapical lengths.

  In this way, I suspect my argument that the teeth were not peg-like is 
accurate, but also that the teeth may have been lined with "razor-blades" is 
far closer to the actual case, and this seems to be true in *Haplocheirus 
sollers* as well.

  As for myrmecophagous insectivorous squamates, we can focus on some of the 
more famous ones, such as "honry toads" and "horny devils," which are known for 
"sitting" in nests and just mowing through the little guys. These lizards, as 
may not be directly apparent, have fewer teeth than typical carnivorous 
lizards, among other features, which may or may not be universal for 
myrmecophagous lizards (Montanucci, 1989).

  Virtually all myrmecophagous carnivores use non-dental processing to deal 
with termites and ants, which would necessarily seem to invoke the 
"vestigialization" argument for them with regards to their teeth ... yet 
despite this, they have teeth and a lot of them. Like troodontids, this 
dentition is arrayed into a blade-like jaw margin.

Choiniere, J. N., Xu X., Clark, J. M., Forster, C. A., Guo Y. & Han F.-l. 2010. 
A basal alvarezsauroid theropod from the early Late Jurassic of Xinjiang, 
China. _Science_ 327:571-574.
Chiappe, L. M., Norell, M. A. & Clark, J. M. 1998. Skull of a relative of the 
stem-group bird *Mononykus*. _Nature_ 392:275-277.
Montanucci, R. R. 1989. The relationship of morphology to diet in the horned 
lizard genus Phrynosoma. _Herpetologica_ 45:208-216.
Perle D., Chiappe, L. M., Barsbold R., Clark, J. M. & Norell, M. A. 1994. 
Skeletal morphology of *Mononykus olecranus* (Theropoda: Avialae) from the Late 
Cretaceous of Mongolia. _American Museum Novitates_ 3105:1-29.

Augusto Haro wrote:

<May that be due to their their phylogenetic inheritance? I mean, if you have a 
bear with bunodont ancestors that starts eating more insects, you will find an 
ant-eating bear with smaller bunodont teeth. If you have some coelurosaur with 
blade-like teeth, and then dental reduction operates because of social insect 
feeding habits, then I would expect seeing animals with reduced blades instead 
of reduced bunodont teeth.>

   While I would agree in general principle that the relevance of phylogeny 
matters here, such that *Ceratonykus oculatus* itself inherited an opisthopubic 
pelvis, this sin't true for alvarezsaurids as a whole: *Haplocheirus sollers* 
has a propubic pelvis, and *Patagonykus puertai* either propubic, mesopubic, or 
just slightly opisthopubic. None of them are remotely as odd as the 
ornithischian-level of "parvicursorines" where the pubis and ischium are in 
contact for nearly their entire lengths, thin, slender, and fairly short. In 
*Patagonykus puertai,* for example, the arm is highly modified from the 
condition in *Haplocheirus sollers,* as is the pelvis, based on the preserved 
fragements; yet the pubis is not attenuated or modified into the splint-like 
rods of "parvicursorines." Based on its curvature, and I think that alone, I 
suspect the pubis is procurved and mesopubic, which is the inverse of what is 
usually depicted. Here, is the Chinese wiki:

  
http://upload.wikimedia.org/wikipedia/commons/thumb/5/55/Patagonykus.jpg/591px-Patagonykus.jpg

  The pubis is shown angled backward, and this places the bulk of the boot 
posterior to the shaft, while I might subject it the revere, as it is in many 
other theropods with similar pubic shafts. But even if it were opisthopubic, it 
is drastically different from that in *Haplocheirus sollers* or any 
"parvicursorine." The pelvis is "more primitive," then, than the arm, in 
comparison to the mechanical inference of use for forelimb scratch-digging, if 
indeed it was doing so.

  Augusto also wrote, addressing Tim:

<2011/4/28 Tim Williams <tijawi@gmail.com>:

<<Extant myrmecophages are not cursorial, because the energy derived from a 
myrmecophagous diet does not permit high metabolic rates in mammals higher than 
1 kg mass (McNab, 1984; J. Zool. Lond. 203: 485-510).  Termites have higher 
calorific value than ants, but still not great.>>
 
But the aardwolf is cursorial and weights around 10 kg., being mostly 
myrmecophagous (including termes).>

  I have no response to this particular point. I am not versed on energetics 
enough to evaluate preference to smaller or larger size for myrmecophagous 
animals. Most myrmecophages are, in fact, fairly small (snakes, lizards, 
birds), while we are discussing several mammalian myrmecophages that are are 
the "small mammal" (in cat and dog-sized ranges) rather than "micromammal" 
range as in mice and such. It may indeed be more efficient to be smaller as a 
consumer, but I think only were it a generalist, as with most snakes and 
lizards that have a highly selective diet (they are seasonal generalists, 
exploitative of their adapted or preferred food when it becomes available; this 
is true for egg-eating animals as well). Even highly modified diets still 
permit generalistic feeding, as in the kiwi and giant anteaters, where 
modifications of the feeding apparatus do not limit other types of foods.

Cheers,

  Jaime A. Headden
  The Bite Stuff (site v2)
  http://qilong.wordpress.com/

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)


"Ever since man first left his cave and met a stranger with a
different language and a new way of looking at things, the human race
has had a dream: to kill him, so we don't have to learn his language or
his new way of looking at things." --- Zapp Brannigan (Beast With a Billion 
Backs)