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Holes in ceratopsian frills, etc., etc.
I have unfortunately been off line for the better part of a week. A friend
offered to install another hard drive in my computer. I got the hard drive
all right, but in doing so my original hard drive was completely erased and
computer (or what was left of it) totally confused. Don't worry, my
pathology bibliography was on back up disks. If I had lost that I'd probably
jumped off a bridge days ago. ;)
So things have been a mess here and only now I am getting settled back to
normal. I apologize for late answers to emails and if anyone sent me an
email and got no reply, plese send it again. The accident wiped out all my
past Dino Digests, so I cannot recall all that has been said about holes in
horned dinosaur frills and related topics. I do recall lots of nasties being
traded, and additional comments added to the fray. I shall add my comments
here, and in no particular order. I do specifically recall the authors of
some of the comments so I treat everyone anonymously here.
These comments mostly refer to short-frilled (centrosaurine) ceratopsians
only, and are based on my observations and years (1979-present) of field
work collecting numerous horned dinosaur specimens for Tyrrell, preparing
same, extensive reading, and a few casual and scientific observations.
1. Someone stated the weight of the ceratopsian head was supported by the
fusion of the first three neck vertebrae (the "cervical bar" of some
authors). This may be so, but we do have several examples of isolated
vertebrae from unfused "cervical bars" of adult-sized individuals. We have
examples of this rare condition in Pachyrhinosaurus, Centrosaurus and one
isolated unidentifiable specimen. The first 2 were from monospecific
bonebeds. I have no idea why these specimens had not fused, perhaps they
were "late bloomers".
2. The model shown at the end of the recent Paleoworld episode is indeed a
Pachyrhinosaurus and based on our findings at Pipestone Creek in
west-central Alberta, near the city of Grande Prairie. However, I take no
credit or responsibility for the rendition of the nasal horns represented on
this sculpture (another Brian Cooley piece). Actually there are 3
Pachyrhinosaurs, and these are outside the main entrance of the museum. They
were put up two summers ago. Two are adults and one is a very small
(small-medium-sized Dog) juvenile. In the Paleoworld shot you'd never know
it was outside what with all that dry ice fog and tacky multi-colored lights.
3. Someone said ceratopsian frills were flimsy- I disagree. A Chasmosaurus
frill might look flimsy, but what bone is there is rather thick in
cross-section. I'm no engineer, but I've been told that a piece of plate
steel with a hole in it is much stronger than a solid piece of plate steel,
because any stress or impact forces can be better redistributed and
absorbed. Now obviously ceratopsian frills are not made of steel, but
perhaps the holes (fontanelles) partly serve an analagous function. There
are a few (and I emphasize FEW) examples of fractured and healed ceratopsian
frills, which does not mean they were necessarily "flimsy". A human femur is
a very strong bone but can be broken in something as simple as a fall.
4. Function of frills. Always such a contentious issue! People on this list
and ones I've talked to over the years seem hung up on the idea that the
frill served one function and one function only. Why not have multiple
functions? Consider the following posibilities:
a. A counter-balance for the front half of the head.
b. species recognition.
c. sexual dimorphism (male/female differences).
d. neck protection. Some protection is better than none, and besides I
don't feel that tyrannosaurus bothered ceratopsians that much anyway. This
suggestion is borne out by the isolated examples of toothmarked bone we find
in Dinosaur Provincial Park. Well over 85% of it comes from hadrosaurs.
Ceratopsian toothmarked bone is found mostly in the monospecific bonebeds
which represent mass mortality events and where the tyrannosaurs are
scavenging carcasses. However, even here the toothmark evidence is not
common. Tyrannosaurs ate hadrosaurs (as we call them here "the cattle of the
Cretaceous"). Hadrosaurs did not have horns and thereby were less likely to
inflict potentially fatal injuries on the predator. I believe tyrannosaurs
were very aware of that fact and consciously pursued "easier" prey and/or
e. sexual readiness. The horns and spikes that make each genus unique,
manifest only upon attainment of full adult size. This tells me that when a
Styracosaurus "comes of age", it is recognized by other Styracosaurs as
being male/female and a potential mate/rival. It's all related to sex, which
is pretty important stuff if you plan on carrying on the species line. See
f. jaw muscle attachment. To what degree of attachment I don't really know.
I doubt the "strong jaw muscles" (one point which all combatants on this
list seem to agree on) strech way back and attach directly to the
fontanelles. The fontanelle edges are smooth and importantly, very thin on
their margins (only one-two playing cards thick). This seems too fragile a
point of attachment. I am in total agreement with a previous contributor who
thought the epoccipitals did not serve as anchors for muscles but had a horn
covering only. Their surface texture is like that of the orbital and nasal
g. heat dissipator. Why not? This idea did not get the consideration it
h. disuade a potential rival of predator by dropping the nose and suddenly
appearing much bigger. The frill could have been brightly colored. I have no
problem with the idea of eye spots that some talented paleo-artists like to
put on their ceratopsian renderings.
i. anyone have other ideas?
5. Aggressiveness in ceratopsians. The isolated and important bonebed
evidence for intraspecific fighting in short-frilled horned dinosaurs is
just not there in numbers large enough to support this suggestion. I have
had a paper "in press" on this for 5 years but due to publisher problems it
still is just "in press". Extra holes in the frills of chasmosaurines had
been linked to intraspecific horn thrust injuries, but they don't look
traumatic in origin when closely examined. I have seen traumatic punctures
in ceratopsians and they look different and typically show secondary bone
infection. Chasmosaurine frill "horn thrust injuries" do not. I'd love
nothing more than to have my ceratopsians as mean and aggressive animals,
regularly beating up on each other and those pesky tyrannosaurs, but the
evidence just isn't convincing.
6. Loss of epoccipitals (limpet-shaped bones on edge of frill). Someone
said they are often lost in horned dionsaur skulls. In centrosaurines, it is
evident that at some point in life (probably upon reaching adult-size) they
completely fused to the edge of the frill and this suture is subsequently so
obliterated that it appears the epoccipital has been lost. When we do find
isolated epocipitals, they are small (from immature animals), or, curiously,
in adult animals, represent the epocipital that bridges the gap between the
squamosal/parietal suture along the external edge of the frill. This does
not appear to fuse at all or perhaps is the last epoccipital to fuse.
7. Hooks in Centrosaurus acting as muscle attachment points. The author of
this point thought the large, forward-hooking horns served as muscle
attachment points. This has been suggested previously, especially in older
popular literature. Typically the idea is (1) that the hypothetical jaw
muscles in and around the fontanelle grow up and back and are attached to
these horns which existed throughout the animals life. Another contributor
to this list thought that (2) the jaw muscles attached to the underside of
the frill and the eppocipitals. There are problems with both ideas. Sampson,
Ryan and Tanke "in press", Biological Journal of the Linnean Society, looked
closely at centrosaurine skull growth during ontogeny. (This long overdue
paper should be out in 1997). We know that in juveniles centrosaurines (such
as Centrosaurus), the edge of the frill in all species of this group had a
simple undulating edge ("bumps") to the frill, much like the edge of a pie
crust. At or near attainment of adult-size, some of these "bumps" stay the
same while other then grow and develop into the characteristic hooks and
horns that make each genus unique from the other. In the case of the
forward-directed spikes which covered the fontanelles (hereinafter called
"***") in Centrosaurus, a pair the now subadult (late subadult/early adult)
ceratopsian "bumps" must grow back, rapidly curving up and over, then flip
forward and grow anteriorly, going through about a 180 degree turn in doing
so, while simultanously growing and developing in to a ***. I can't see a
jaw muscle mass attachment as suggested in (2) following along. This would
result in a muscle mass suspended above and beginning at the mid-section of
the frill and then being tightly wrapped underneath. In (1), the problem is
the fontanelle muscles in young animals could not attach to the *** because
they simply had not developed yet. Upon full adult size, did the fontanelle
musculature reach out and anchor itself to the newly arrived ***'s? I think
not. The idea of jaw muscles attaching to these ***'s is further refutted by
their widely varying size; bilateral vs. unilateral occurrences (though most
are bilateral); and their surface texture which is identical to nasal horns
and main frill spike ornamentation; absence in some forms and very small in
others (such as in Styracosaurus).
Just some thoughts and personal observations.......
Technician I, Dinosaur Research Program
Royal Tyrrell Museum of Palaeontology.
Visit the pathology bibliography homepage at: http://dns.magtech.ab.ca/dtanke