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Re: On the Issue of Beaks for Avepectorans (Long)



Kris Kripchak (MariusRomanus@aol.com) wrote:

<I could be wrong, but after reading what Jaime posted (linked above), I
might be under the impression that he seems to be leaning toward the
presence of a beak depending upon the occurrence of the crista tomialis...
the bony edge/rim of the jaw... That being the part that covers where the
teeth would "normally" go... The biting surface. It is not my premise that
a beak, or any other form of continuous keratinous covering, be it
plate-like scales or whatever, had to cover this region where the tomialis
is today, and as far as I know, no one else has implied that either.

So Jaime, I'm curious as to if you are confusing the lack of a toothless
tomialis region as evidence for or against beak-like coverings.>

  Kris will be possibly gratified that I have no issue in regards to the
tomial edge of the beak or the absence of teeth (the latter has been said
more than once before, so this should be clear by now).

<Where are there significantly more foramina in the questioned regions
compared to modern birds??? I have been looking for a long time now, and I
am not seeing this. When you talk relative totals... Reptiles, sure...
They have more foramina than birds... But as far as I can tell, reptiles
for the whole have significantly more foramina than theropod dinosaurs as
well.>

  And "reptiles" (including theropod dinosaurs) have in the definite (as
described among crocodilians and lizards (again)) a row of labial foramina
that penetrate the dentary, often in a groove or sets of grooves in
parallel to each other, as well as a set of concentrated, clustered
foramina near the symphysis. In snakes, these concentrated foramina are
typically only on the dentaries, and the premaxilla has one or two, unless
it is not retained. The remainder of non archosaurian reptiles bear a lack
of foramina that are not related to the labial and gum ennervation. In
theropods, as in sauropods, this condition is retained. There may often be
fewer or more foramina, among taxa. In BEAKED dinosaurs, one must step
away from theropods at least for a moment, instead of getting
theropod-centric. No rostral element in a marginocephalian, thyreophoran,
iguanodontian, basal ornithopod, or basal ornithischian is covered in
foramina, but rather are ridged or midlly pitted in SOME cases, but for
the most part are smooth with ridges and channels relating to
vascularization. This is nearly identical to the condition in birds and
turtles. In THEROPODS, beaked forms such as ornithomimosaurs have
extensive tomial bony beaks without foramina associated, whereas in
oviraptorosaurs, the toothless portions of the jaws (where normally there
are teeth) the premaxilla and dentary bear symphyseal pitting and grooves,
but rarely foramina. These are concentrated toward the rear jaw bones,
where oviraptorids have one large maxillary foramen and caenagnathids have
two or three large to small foramina near the external mandibular
fenestra. In beaked ornithischians, the impressions of a beaked premaxilla
in opposition to a beaked predentary (the predentary DOES have foramina,
on the posterior/dorsal [or internal] surface and the only ennervation the
bone would bear and not external) is affirmed in a lateral surface with a
rugose, ridged and pitted surface, where the rostral 1/4 tip (or more) was
toothless and, as shown in *Agilisaurus louderbacki* and *Hypsilophodon
foxi*, was not toothed and STILL lacked foramina.

<Jaime, I know from what you've said before that the foramina themselves
do not go against a beak, but are you using their placement to indicate
that one or the other is more or less probable?>

  Foramina do occur in birds' beaks. I said this before. They are
concentrated around crests and the tips of beaks. They are absent along
the beak. They occur in some turtles near the ventral edge and symphysis.
They occur in dicynodonts, albeit very minutely and rarely. The presence
of extensive foramina, as in *Velociraptor* which was initially proposed
by Paul has having a possible premaxillary/rostral dentary beak on the
basis of the rugose texture and extensive foramina, is inconsistent with
the extant data. This doesn't say it was impossible, just less likely.

<Modern birds usually have one row, extending most of its length. Bird's
also, as in theropods, usually have an increase in foramina at the
anterior most of their dentary. However, birds do show a great deal of
variation. (I have bird dentaries with almost no foramina.)>

  Which taxa have you got that show this? Because as far as my research
and jaws I have studied have uncovered, this is very, very rare. If you
could confirm this, I would love to check my own materials.

<Therefore, I see nothing on the premaxilla and dentary of a dromaeosaur
at could not be a variation found on a beaked bird. As a matter of fact,
without teeth, a *Velociraptor mongoliensis* would look pretty much
identical in the same regions of the skull on a bird where the
rhamphotheca goes.>

  I doubt this terribly. The heavily foraminated lower and upper jaws with
rounded surfaces and embayments between teeth would imply, as in extant
reptiles, the presence of "lips" (tendonous bands of tissue covered in
skin and scales, as in lizards) and not beaks. This is even more distinct
in the difference between *Velociraptor* and, say *Caudipteryx*, which has
a smoother, denticulated premaxilla where there are teeth and a sharp edge
coupled with reduced foramination, and a sparsely-foraminated dentary.
Also, *Hyspilophodon* is a nicer test. Let's stop looking at theropods as
_the_ all and end all; the diversity of extinct dinosaurs is involved in
the greater diversity seen in ornithischians than in non-avian dinosaurs.

<Britt goes on to talk about specialized scales covering these areas on
theropods that basically performed the same function as the tactile
corpuscles found in this area on birds, but under their keratinous beaks.
Other paleontologists, such as T. Ford, have basically come to the same
conslusions (using crocodilian comparisons, which will be dealt with
below). There is no scientific reason whatsoever that would bar me from
replacing Britt's "specialized scales" with a keratinous covering that
could effectively be termed a beak. (More on why below.)>

  I am glad that this was brought up, since Britt did not corroborate his
assumptions on this matter, as I have the paper on *Torvosaurus* and it
sure doesn't show how beaks or scales are indicted one versus the other.
Given this, the lateral grooves on the beaks of grebes which do have
occassional foramina can just as plausibly have scales ... and do not. The
terminal rostral foramina are, as stated above, found in a variety of
extant birds.

<But... There also seems to be a medial row of foramina on the lingual
side of the teeth... It seems to me that there is a rhamphotheca and a
gingiva like area where the teeth are. I could be wrong, but, it's hard to
show otherwise.>

  I beleive I already explained that there IS a medial, lingual set of
foramina that are primarily involved in ennervating the roots of teeth and
the gums in reptiles in general, not to mention theropods. What these have
to do with a rhamphotheca I have no idea. Foramina in birds medial in the
jaw, as in birds, are found near the symphysis and posterior dentary,
seldom if ever do they express further rostrally.

<As Jaime informed me in another post, there is one row of foramina in
theropods that exists on the medial surface of the dentary. It is between
the interdental plates. These are here for the purpose of fleshing the
gums and bringing nutrients to the tooth roots. This is comparable to
crocodilians.... But...There is a row of foramina on the medial side of at
least some anseriforms, so their presence here obviously does not negate a
beak.>

  Never said they did. These were brought up in reply to the presence of
multiple rows of foramina in non-dinosaurs, not in resemblance to the
condition in dromaeosaurids. In anseriform mandibles, there is a medial
set of foramina, perhaps best exemplified in flamingos, related to the
extensive beaks of the lower jaw and the mobile, large tongue in these
forms; large lingual and symphyseal foramina are also related to the
hyolingual musculature, as in parrots, flamingos, and mergansers.

<So, in the end, what we have are variations that could account for the
presence of a beak. How about if we can define what's considered a beak to
begin with? There may be several ways... How's abouts: (1) Partially
complete over the bone but no tomialis. (2) Complete with a tomialis but
with teeth. (3) Just a keratinous tomialis. Etc. etc. etc...>

  Oddly enough, none of this contradicts the material I have discussed.

<Two foramina rows on the lateral dentary may... I repeat... MAY imply
that Avepectorans had a gum region where the tomialis is now, with
thickened scales lining the rim. But... this foramina configuration does
not conclusively imply that because they most likely had a gingiva, they
did not possess beaks or a continuous keratinous covering instead of
scales. Let's say that a covering just followed along the margin. I do not
know... They could have even of had regions that possessed a tomialis
along with teeth. I do not have anything for or against that either.>

  A tomial crest refers to the shape of the bone, nothing to do with
foramina. Some birds, turtles, and likely dicynodonts, bear keratin over
smooth, flattened or rounded portions of the beak or palate, or floor of
the mandible. A tomial crest simply related to a slicing or wedging
function, to replace teeth. Under this condition, the large flat region of
the premaxilla lateral to the tooth row in basal ornithopods such as
*Hypsilophodon* is dorsal and in parallel to the surface of the predentary
lateral basin. The posterior rostral edges in ceratopsids are flat. None
of my work contends that a tomial crest is the condition to a beak. It
only implies a condition of the beak, when or IF present.

<This brings me to lizards and their lips... I have always known what the
skull of a varanid looks like. The point is, we are talking about theropod
dinosaurs... a group of animals that are so close to birds, that trying to
draw a line between what a bird is and what a theropod is, has become
terribly difficult, if not almost entirely impossible.>

  I thought we were debating the presence or lack of a keratinous beak,
and evidences relating to these. My statements have brought up
ornithischians again and again, in fact, to the exclusion of theropods,
until now. In these, the taxa I have stated lack the conditions applied
and show that both teeth and beaks can coexist, and the relationship
between the beak and surface anatomy of the tooth-bearing bones remain
constant. In extant reptiles, grooves lead from the foramina to the dorsal
margin of the dentary, in shallow channels between teeth, rather that as
fits between crowns (only in crocodiles); this condition exists in the
offered non-avian theropod, *Velociraptor*. I enjoin anyone to bring up
more basal forms or more derived (relative to birds) examples that
indicate the presence or lack thereof of a beak, to support or refute the
current data that would seem to offer that *Velociraptor* can actually
have a lateral rhamphotheca. The most effective test, of course, if extant
animals.

<Yes... the foramina patterns are somewhat similar in the jaws on a lizard
and on a bird... But more similar than theropods are to birds? No way.>

  Yes, WAY. Non-avian theropods and lizards, for example *Iguana* or
*Anolis*, have distinct grooved foramina whereas extant birds and most
basal extinct birds LACK rows of external foramina as concentrated or
numerous as those in theropods. Place these in discreet characters, and a
logic machine can form conclusions that the pattern is more similar
between lizards and dromaeosaurids than is found between
crows/ducks/pelicans and dromaeosaurids. Try it.

<Many lizards have on the tips of their upper and lower jaws, singular
scales that go across both sides. That is to say, it's not 2 scales
meeting in the middle on the front of the snout. It is a single scale. Did
dromaeosaurs have something similar? We are talking about the region of
the premaxilla, so one should wonder, owing to the fact that their
descendants (birds) have this region covered by a single covering, did
dromaeosaurs also have have their premaxilla covered completely with a
single covering?>

  The origin of the beak tells us nothing about how likely one taxa is to
have one versus another when it is a test-by-test and example-by example
case being made, taxon by taxon. The above is a futile thought excercise
given the purpose of this debate is evidence pro and con on only bony
material.

<In shallow dentaries on modern birds, the foramina row is usually driven
to the ventral margin. An example is the swan.>

  If you could provide me with a photograph of this, I would love to see
your eviendence of a comparable foramina row to other reptiles.

<Not that I am even coming close to insinuating anything with this, and
Jaime, I know you said "reptilian" instead of crocodilian... but since a
comparison is usually made bewteen crocs and theropods when it comes to
this topic... I have to say that I do not see a hint of a crocodile-like
pattern to the foramina in theropods for the dentary.>

  This is good that crocs are being brought up. The living crocs are
distinct in having extensive facial pitting and new foramina formed in
response to the electro-receptive organs in the face of alligators and
crocodiles (living). These are not universal to crocodylians in the
broadest sense, however, and earlier posts of mine brought up the absence
of the extant condition in the earlier crocodylomorphans and other
archosaurs. I voiced the term reptile, as explicitly stated by myself
using examples, on turtles and lizards, and crocs with reference to the
entire group of crocodylomorphans.

<There is nothing in the arrangement of the foramina on dromaeosaurs that
denies the presence of a beak of some. The lateral dentary looks much like
the gull. The premaxilla and anterior-most dentary close to some
anseriforms. (I'm sure this is a pattern seen in other birds as well, but
as it is, most of my skulls come from water birds.)>

  I am sadly in much disagreement here. The implications being that a row
of foramina can be used for both rhamphothecal and more soft-tissue
ennervation has already been made by myself; this bears on the
concentration of foramina, not their presence. The majority of birds have
a ridge and groove leading along the dentary, but foramina are hardly
universal. These do not, as I have said, contradict the presence of an
extensive facial beak in *Velociraptor*. The presence in modern beaked
animals does not bear up in non-avian theropods where evidences imply the
opposite other than the plesiomorphic condition. The majority of birds
lack such estensive foramina. The presence of foramina and their
arrangement are entirely more similar in structure and arrangement on both
sides of the  upper AND lower jaws to more basal reptiles. The surface
texture (which was ignored earlier in this post as a smooth versus rugose
pattern when discussing *Gastornis*/*Diatryma*, where I argued in my very
first reply that this bird had a rugose and non-foraminated beak, as in
many other large-beaked birds).

<So Jaime... I take it that since theropod premaxillas, maxillas, and
dentaries generally show this same type of pattern as in the one you gave
for ceratopsians... which as you plainly stated is indicative for your
acceptance of them having keratinous coverings in the way of beaks on the
muzzle (a lizardly-lipped combination of some sort thereafter)... and your
answer to my second question should be a YES (You do seem to be using
placement of foramina to indicate who had a beak and where it was on the
jaw.)... and if your answer is NO for confusing the lack of a toothless
tomialis region as the evidence for or against beak-like coverings (my
first question to you)... and taking into account everything else that I
talked about and presented in this post/website... I can safely say that
theropod premaxillas, and maybe even the anterior most part of their
dentaries, do indeed show that they quite possibly possessed a beaked
covering of some sort. (I'm limiting this diagnosis only to Avepectorans
at this time.)>

  Why limit it? It should be expanded and show as many test examples as
possible. I suggest you look at a LOT of other beaked animals aside from
birds, a few of which show odd variations on what is essentially a norm.
Piciforms, coraciiforms, gruiforms, passeriforms, etc., all lack these
conditions, as applied using a gull jaw. There are exceptiosn to the rule.
I have merely pointed out what appear to be rules. Kris seems to contend
the rules by the few exceptions.

<One more question Jaime... By way of everything in this post/website,
what correlation might one be able to derive as to what variations may
have been more or less possible in an *Archaeopteryx*?>

  Thankfully with one question mark, Kris. I see a smooth dentary with
sparse foramina, a shallow groove, and a rounded dorsal margin; the
maxilla has a rounded margin and raised areas around the crowns with
evidence of channels between maxillary foramina and the margin between
teeth, as in the premaxilla. This implies to me two things: 1) possible
beak on the lower jaw, and 2) no beak on the upper, even rostrally. What I
KNOW is very little beyond the inferrences made from the extant record and
their evidenciary proofs in the extinct record where a beak is assumed to
be present or not. There is not much that can be drawn further. It leads
to artistic license. Using only mammals, Witmer has proposed that
*Leptoceratops* lacks muscular cheeks, but failed to see the evidence for
non-muscular cheek tissue, including the recessed dentary and maxillary
tooth rows. And it's "maxillae" and "premaxillae", not "maxillas" etc..

<Start here [http://www.cmnh.org/dinoarch/2003Mar/msg00274.html] and
follow the "Next by thread" links... I think you will find what you said
above to be false.>

  Actually, it is not false. I wish you would stop calling me a liar:

  http://www.cmnh.org/dinoarch/2003Mar/msg00277 ... second paragraph. The
essential structure of the beak above which lies the keratin, in various
birds, is indicated. This was my reply to Kris.

  http://www.cmnh.org/dinoarch/2003Mar/msg00289.html ... is another reply
that offers similar data.

  http://www.cmnh.org/dinoarch/2003Mar/msg00288.html ... is an early reply
to another poster on the nature of the keratin in another non-theropod
(ignored subsequently).

  Cheers,

=====
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)

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