[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
On the Issue of Beaks for Avepectorans (Long)
OK... Here it goes......
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.
This is what stumps me...
Jaime: >>There are reasons for assuming the extensive external foramina,
continuous with more further back in the dentary, conform to a more "reptilian"
design of flesh and ligamental tissue around the jaw, rather than a "beak",
including comparison to lizards.<<
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.
Jaime, are you under the impression that the foramina are usually placed
forward on the maxilla, premaxilla, and dentary in beaked modern birds, and are
usually spread out more on a reptile that has a scaled face, and that this is a
correlative feature indicating what's what??? 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
Avepectorans vary on the premaxilla. Modern birds vary as well. Avepectorans
usually have two rows of foramina across most of the dentary right? One lateral
to the teeth, the other more ventral. (I think that two rows on dromaeosaurs is
diagnostic for the group, one low and one high, but I could be wrong.) The
anterior most of their dentary also increases in foramina amount. 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.) Therefore, I see nothing on the premaxilla
and dentary of a dromaeosaur that 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
It is as B. Britt says in his paper "Theropods of dry Mesa Quarry: Torvosaurus
"The occurrence and orientation of the terminal rostral foramina on theropod
and avian muzzles is strikingly similar, and in the latter they are located
beneath the keratinous covering of the beak...."
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.)
In the paper "Cranial morphology of *Sinornithosaurus millenii*" Xu et al.
1999, from the "Canadian Journal of Earth Sciences, Volume 38, Number 12
(December 1, 2001), there is a delightful figure numbered 6 which shows the
mandible. From the text: "In lateral view, a row of elongated, oval-shaped
foramina sit in a shallow groove below the tooth row. Ventral to the row of
foramina is a second row of less developed foramina. Two rows of foramina on
the lateral surface of the dentary also occur in other dromaeosaurids and
troodontids (Currie 1995)." Now, we know this already... 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.
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.
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...
The bird's beak had to begin somewhere... somehow. It didn't just pop into
existence one day as the entity we see today.
Jaime, you said in a January 2003 post:
> ... in reptiles, the foramina are numerous, composed in regular rows, and
> result in innervating the thick but relatively immobile extra-oral tissue of
> the mouth. <
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.
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. 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.
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? What about the dentary?
The lower jaw of many reptiles show larger scales around the lip region. If one
fused these together, would that be defined as a rhamphotheca? A partial
rhamphotheca? By modern definitions, the answer would most likely be no. What
would we call it if this scale fusion was shown to have happened on some
extinct group? Would we define it as a fused-scale, or a pre-rhamphotheca? Is
it possible that such a thing occurred with dromaeosaurs? Where is the e!
dence against this possibility? Saying that lizards have similar structures is
not enough unless these structures were unique to animals without beaks. They
are not. As I've been stressing, modern birds have a singular kerationous
covering on their jaws in regions, that for the most part, look no different
than those of their so called "sister group", and this will be further
illuminated upon below.
By the way, I can't tell if *Archaeopteryx" had one or two foramina rows (not
medial). With such a very shallow dentary, it's hard for me to tell. In shallow
dentaries on modern birds, the foramina row is usually driven to the ventral
margin. An example is the swan. It seems to me that the ventral groove on the
bottom of a swan's dentary is homologous with the groove that runs down the
side with the foramina, which is what I am talking about. The problem is that
the lower jaw is just so damn shallow, making the groove end up much lower, to
the point of being ventral. Also, this groove has very few foramina in it, but
right near the rostral end, you suddenly get them with that same increase like
you see on the premaxilla. Again, this is only at the very tip. In fact, look
at a photo of mine of SUE that is on the website linked below. Not only is the
lateral foramina row set in an obvious groove like on a gull, (also pictured),
but the more ventral row is almost recessed out o!
site and it has a significantly less number of foramina... until you get to the
rostral end... and then BOOM! Foramina all over the place... just like
anseriforms. (This is as Britt talked about.)
So, since *Archaeopteryx's* dentary was so shallow, I assume that it is
possible that the lower foramina row seen in dromaeosaurs may be located
ventrally, as in modern birds. Does anyone know more about this???
And as for a completely feathered head as David and I just discussed... I see
no positive evidence whatsoever telling me that feathers covered the head
completely, all the way up to the margins of the gum line. Feather preservation
on the TOP of the premaxilla... means there were feathers on the TOP of the
premaxilla. (That is if you can rule out that the feathers preserved there
weren't simply moved from some other spot on the skull and simply settled there
during decay.) I won't repeat all that was said here. It's in the archives now
if anyone cares to read it.
Here are scans of a gull dentary, a swan premaxilla, a picture of the skull of
SUE, AMNH5027, a crocodilian skull, and the skull of *Velociraptor
As the old saying goes... Pictures really are worth a thousand words.
And just to sweeten this up a bit... I'm staring at my large lithograph print
of *Tyrannosaurus rex* from the AMNH (Bought it at allposters.com and I
recommend it to all of ya). The detail it shows of the skull is grand to say
the least. What is funny, is that the mandible's foramina arrangement (and I've
compared this to MY photographs of other rexes), is nearly identical to that on
the gull's mandible. A single row in a shallow recess set across nearly the
entire length for both. The rex does have another row with less foramina,
placed more ventrally, which is just the continuation of the top row that
looped around the front of the dentary. But, unlike Sue and the swan, this rex
only has a single line at the anterior most part of the dentary. The foramina
are not scattered here. A nice bit of variation for your enjoyment.
Tyrannosaurs also exhibits the same type of foramina pattern as is found on the
premaxilla of dromaeosaurs.
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. The croc's appear to be set more medial to the
teeth, and for over most of the length AND breadth of the dentary, they are
very numerous and scattered (They could be set in multiples rows, but it's hard
for me to tell if this is the case since I have skulls that are not
Think of it this way... In Avepectorans, the rex, etc, and most modern birds,
there is a neatly organized lateral foramina row roughly about a third of the
way down from the top of the dentary. This could be homologous.
As I sit here and fondle my various alligator skulls, I can see that crocs for
the most part don't have that much in the way of a pattern to begin with...
Sure, it's a nice single line at the posterior end of the dentary... but as you
move forward... (only after 3 or so foramina) it begins to look like buckshot.
(Their drastic dramatic increase in number, as I understand it, is due to
having a hodgepodge of hundreds of tactile sensors and nutrient foramina all
mixed together.) Repeating myself....This is unlike theropods and birds who's
increase in foramina finally takes place at the very tip of the dentary.
My cast of the skull of AMNH's *Velociraptor mongoliensis* also fits the
anseriform/gull pattern, more so even in that the smooth grooves on its maxilla
and premaxilla come close to matching those on a swan. The croc's maxilla, on
the other hand, looks like a cross between the surface of the moon and the skin
of a grapefruit... Nothing like most theropods at all, who have a single row.
I say "most theropods" here, only because I am not sure if there are any
exceptions. *Majungatholus* may be croc-like in the maxilla. Right now I am in
the process of looking into *Gastornis*, which I know does not have a smooth
surface under where the rhamphotheca went, in order to see if there is any
resemblance here with *Majungatholus*. I know the rough surface areas seem to
be similar between the two, but I do not think *Gastornis* has an area with
large amounts of foramina like *Majungatholus* does on its maxilla. And another
thing... the entire skull of *Majungatholus* is very, for the lack of a better
word, "rugose". This could mean it was comparably croc-like in form, but from
what I've seen of *Gastornis* so far, *Majungatholus* is built more like a bird
that had huge keratinous crests and massive head ornaments. But, I have no real
conclusions just yet.
To finally wrap this Beast up.........
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.)
As for *Tyrannosaurus rex*... my only comment is... "Spooky man...... Really,
Now, getting back to my second and third questions: "...... 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???" In the aforementioned post from January 2003, you also
>>The presences of regularization of blood vessels and nervous foramina in
>>ceratopsids is, infact, a logically concluding description of the keratinous
>>face in these animals; note that these foramina on the lower jaw are limited
>>to the predentary, and the maxilla and dentary have large, regular foramina
>>in rows which innervate and feed the lateral oral muscules and skin...<<
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 onl!
to Avepectorans at this time.)
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* ???
What is a bit obvious in all this, is that the premaxilla of *Archaeopteryx*
(and other theropods) was no bigger in relative surface area than the very tip
of modern bird premaxillas, which have actually increased significantly in size
over the course of avian evolution. So in getting back to the tomialis issue...
In small animals like *Archaeopteryx* and *Microraptor*, if they were beaked
without a keratinous covering extending over the tomialis, then the
rhamphotheca that was there would not have been held in place very well at all.
I can remove beaks from some of my bird skulls and slip them right back on
again because of the keratinous covering over the tomial crest makes the beak
fit groove-like. (Ceratopsians, for which I know of no keratinous beaks being
preserved, also would have had keratinous sleeves that fitted groove-like over
their premaxilla and predentary tomialis.) Without this effect, the
rhamphotheca on the premaxilla would simply sluff-off like a thin toe !
il. This toe-nail-like rhamphotheca would not have been very large because the
premaxilla itself in these animals was not large. Hence, it would be lost very,
very easily by either decay or by other means.
That there is what I have been saying from the very start.
And one more thing...
Jaime: > I explained this data both before (my very FIRST reply to David, to
which YOU initially responded) and above. <
Start here and follow the "Next by thread" links... I think you will find what
you said above to be false.
I have to admit that through the course of this discussion, my assessment in
favor of beaks, on at least Avepectorans, has been strengthened.