Pachyrhinosaurus paleopathologies

["D. Tanke" <dtanke@dns.magtech.ab.ca>]

 I have seen some comments and discussion on Pachyrhinosaurus over the past
day or two and regarding the use of the nasal boss and possible resultant
injuries, so I thought it helpful to add my comments. I was a field
assistant in the Pachyrhinosaurus bonebed S.W. of Grande Prairie, Alberta in
1986, ran the dig from 1987-1989, and have prepared most of the material
collected there. I am also engaged in work on the pathologies found at this
site. 1. First, the function of the boss. This really is anyone's guess.
Surprisingly, juvenile pachyrhinosaurs had a long and low nasal HORNCORE
which quickly transforms in the subadult animals to the BOSS so
characteristic of the genus. The full development of the boss and other
cranial developments upon reaching full adult size suggests to me an
indicator of sexual maturity/dimorphism. The internal structure of the boss
is not solid bone as every popular publication, etc would have you believe,
but actually quite cancellous, surprisingly, even more so than tyrannosaur
bone. The trabecular bone inside an adult nasal boss is best described as
"frothy" in appearance. The boss was not very heavy and seems to me ill
suited for a "battering ram". About half of the 20 skulls/isolated bosses
from the site are of a "gracile" morphology with a concave boss, while the
other half are "robust" morphology with a thickened convex boss [are the
males/females interlocking bosses? :-) ]. Sexual dimoprphism is suspected.
There is no other sexually dimorphic cranial features that I can see. As to
what covering was attached to the boss is a real contentious issue. While I
have seen many reconstructions showing short, medium and long "horn(s)"
attached to this boss, I have seen no evidence in the field or while
preparing the many specimens here at Tyrrell to confirm this. Langston's
reconstruction of the frill for P. canadensis is essentially correct. The
presence of an upward pointing "parietal bar spike" at the base of the
Grande Prairie skulls is very real too- although I have only seen a couple
life restorations which show the spike (or spikes- we have one specimen with
three spikes) in the correct position.
2. Pathologies. According to my recollections, since starting with the
embryonic Tyrrell in 1979 I have spent 1 year, 9 months total fieldwork
working in Centrosaurus, Styracosaurus and Pachyrhinosaurus bonebeds, or
years subsequently preparing fossil material of same. When I grew up, I read
many dinosaur books which stated horned dinosaurs were aggressive animals
that often fought with predators and each other. I grew up believing this.
Such statements still appear in books today. One thing that really stands
out when working on the sites/fossils is how rare paleopathology really is.
I can't vouch for chasmosaurines, but in centrosaurines, paleopathology is
rare, especially when taken into context with all the other uninjured bones
found in the same site. Only in "monospecific" or low diversity bonebeds can
one get a real idea as to the frequency or occurrences of pathology within a
dinosaur "herd". With the Grande Prairie pachyrhinosaurs, out of many (well
over ten thousand) bones observed first hand, mapped, or collected and
catalogued, (and keeping a careful eye open for anything pathological) I
still only saw about 25 examples of pathology. Juveniles and disease-related
pathology were ruled out as being caused by violent intra- and interspecific
interactions.
I was left with about 12 adult bones exhibiting trauma lesions, and well
over half of these were from the posterior ribcage, where the ribs are
greatly rounded thus forming a hippo-like abdominal region. These ribs would
be more prone to fracture by virtue of their rounded shape, plus the
straighter anterior ribs would be afforded some lateral protection by the
shoulder girdle and accompanying musculature. Similar rarity or distribution
of injuries are documented 3 Centrosaurus bonebeds, and in 1 Styracosaurus
bonebed (although this site has yet to be worked intensively). Due to the
rarity of pathologies, I believe centrosaurines were no way near as
aggressive as previously believed. Acts of bluff and possible flank-butting
behavior (with the animals standing end to end) with occasional resultant
rib fractures is postulated. 

  

   
 Darren Tanke, Technician I, Dinosaur Research Program, Royal Tyrrell Museum
of Palaeontology, Box 7500, Drumheller, AB, Canada T0J 0Y0. (403) 823-7707;
(403) 823-7131 (fax); e-mail= dtanke@dns.magtech.ab.ca
 Paleo Interests: fossil identification and preparation, ceratopsians, Upper
Cretaceous vertebrate faunas of North America and East Asia, paleopathology;
senior editor on annotated bibliography of extinct/extant vertebrate dental
pathology, osteopathy and related topics (9,200 entries as of Jan. 10, 1996).