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

Re: Paronychodon teeth are NOT homalocephalid fangs - killing an internet rumor

Jaime A. Headden wrote-

I doubt this shows as much clear data as described, though somewhat
misleading in the extent that it would skew results toward a particular taxon,
when the tooth crowns recovered demonstrate a type recovery versus sampling. 

Er.... what?

Tooth type, rather than taxon type, tends to differ in that some taxa has
similar types of teeth despite being wildly different. Historic confusion among
predatory archosaur teeth throughout, say, the Jurassic and Triassic has led to
some amusing confusing uses of "teratosaurid" ("rauisuchian") teeth for
dinosaurs, among others. Finding what are conventionally a predatory morphology
in some non-predaceous-seeming taxa, such as recurved, ziphodont teeth in basal
"prosauropods" and basal ornithischians, skews the assumption bias based on
isolated teeth. Applying these assumptions to mass collections without
extensive comparisons to morphological variation in even a single jaw (e.g.,
assuming as has been historically popular that "reptiles" are homodont [bearing
a single dental morphology]) causes such a biased skew towards types.

My anatomical and stratigraphic points stand regardless of how many taxa have Paronychodon teeth. The frequency analysis might be compromised, as some small percentage of Paronychodon teeth could hypothetically be pachycephalosaur fangs, leading to a properly large ratio between cheek teeth and fangs.
The assumption of homodonty was not made in my post.

*Goyocephale*'s dentary teeth are worn, from the apex basally down the
margins and onto the lingual as well as the labial surfaces, causing a pair of
longitudinal wear surfaces and the formation of not one, but three lingual
"ridges", one of which lies between the two wear facets and is produced more
distinctly as a result, and one "ridge" at each external boundary to these
facets. This is not a "normal" morphology of the tooth which would never be
found unworn or intact, due to diet. This is also not normal for a vegatarian.
One has but to look at tusked vegatarians to examine the functionality of
elongated "canine" teeth, though this begins to cause issues that arise when
one makes comparisons between reptiles and mammals.

That only strengthens my argument, as the ridges of Paronychodon teeth are not caused by wear. Rather, the apex and the base get worn first, then the entire lingual surface is worn, sometimes eroding away the ridges. The completely different wear facets are a powerful argument the teeth are not homologous, as they were obviously interacting with other teeth differently.

*Stegoceras* is not a representative pachycephalosaur, but is abundant in the
DPP to some degree, this is largely due to its dome. Collections in the DPP
have produced numerous other taxa, some with intact jaws (e.g.,
*Sphaerotholus*), but with a strong bias towards domes. Some flat-headed taxa
are known from overlying levels, such as *Dracorex* which presumably has
premaxillary teeth, and the undescribed "Sandy" specimen which may or may not
be related or like *Pachycephalosaurus* (which also has premaxillary teeth).
However, these teeth differ in morphology from those of *Goyocephale*, and
*Homalocephale* is incomparable as it lacks this region of the jaws.
Additionally, no pachycephalosaur jaw has been recovered to date that compares
to *Goyocephale*, upper or lower, in development of the mesial dentary
dentition or the distal premaxillary dentition. It then seems curious why it is
possible to use this data of known pachycephalosaur material to rate
comparisons to one, argually "basal" taxon? The sampling bias also seems
curious if given in relation to the dietary functionality of pachycephalosaur
teeth, but also in the referal of both the collection to particular taxa or no
particular taxa (junkbin taxa), and the arguably testy concept of making
general morphology referals to particular taxa, even particular species. A
valid criterion or two would be helpful when evaluating tooth-based taxa before
one starts dismissing a referal, or supporting it, for that matter.

Stegoceras may not be representative (or it may be, how are we to know?), but it is one of the few pachycephalosaurs known from anterior dentition besides Goyocephale. It is also known from the same strata as Paronychodon, so is good for comparison for that reason. Sphaerotholus has very poorly preserved anterior dentary teeth, which nonetheless are different from Paronychodon in having labial and lingual cingula, and a labial wear facet. There is no mention of grooves, and though broken, the crowns appear to be very short.
Dracorex actually lacks premaxillary teeth (Bakker et al., 2006), while no Pachycephalosaurus premaxillae are known (though Brown and Schlaikjer sggested it lacked premaxillary teeth due to anterior maxillary morphology).
As for why I would compare the frequency of pachycephalosaurid teeth with Paronychodon teeth, when Goyocephale-like taxa are the concern, I was giving Olshevsky the benefit of the doubt. The best case scenario if you will- that some Late Cretaceous North American pachycephalosaur teeth may be from Goyocephale-like taxa. As I previously mentioned, the fact Goyocephale-like taxa are restricted stratigraphically is another argument against them having Paronychodon teeth.
Obviously Baszio had criteria for assigning teeth to each taxon. The fact he did that work means I don't have to, though obvously further confirmation and examination is always valuable in science.

So far, body fossils of a number of curious dental taxa are unknown, despite
extensive sampling, which suggests that we do, in fact, have body fossils for
these taxa, or that these are more on the line of predators in which dentition
is left more frequently than body parts, or that the animals in question are
not lowlands/watershed dwellers and don't normally arrive at the regions in
which their teeth arrive sedimentologically or geologically.

I agree that we have body fossils for these taxa, though they are currently unrecognized. If Richardoestesia, Paronychodon and Zapsalis are dromaeosaurids, as I believe, then some of the non-dental remains currently assigned to Saurornitholestes, Dromaeosaurus or even Troodon may belong to them instead. In addition, there are numerous unidentified small theropod elements from the Dinosaur Park Formation which may belong to them.
Your second point is also true. Just look at how many coelurosaur bones are known versus teeth from the Dinosaur Park Formation. Or how few published North American avimimid or mononykine elements there are.

We don't know sh*t about tooth-based taxa.

We can be fairly certain that Paronychodon teeth are not cf. Goyocephale fangs though. None of your points have made that possibility more likely, and your wear discussion made it considerably less likely.

Mickey Mortimer