Travel Reference
In-Depth Information
lection of dinosaur specimens in the world. But it holds other fossils as well,
including a huge collection of ammonites. By far the most abundant of these
belong to the genus
Placenticeras
, a large, discoid ammonite from the Upper
Cretaceous and, coincidentally, the same genus first examined by Erie Kauff-
man in his pioneering mosasaur bite study.
Placenticeras
is an extraordinary fossil from an extraordinary creature.
The fossil shells of this species are large for an ammonite; specimens a meter
in diameter are quite common. (The largest ammonite ever collected is
about 3 meters in diameter). In certain Canadian deposits they are very
common, surely mirroring their abundance in the shallow Upper Cretaceous
oceans that covered this part of Canada from 80 to 70 million years ago. The
shells are compressed, like giant discs, and often are found with the mother-
of-pearl shell material still beautifully iridescent. It is within the shells of this
taxon that the great preponderance of circular holes have been found—the
same holes originally described by Kauffman and Kesling as mosasaur bite
marks. But in the Tyrell there are so many of these shells, collected over the
years, that an efficient numbers game can be played: How many of the shells
have holes, and do all or any of the hole marks suggest the spacing that a
mosasaur jaw would produce?
My guide to the "mosasaur bites ammonite" story, as least as it was
being played out in 1996, was Dr. Paul Johnson of the Tyrell Museum, a spe-
cialist in Upper Cretaceous bivalves. Some months earlier, Johnson had
been contacted by Dr. Tatsuro Kase, a researcher in Japan, asking whether
the Tyrell had ammonites with circular holes in them. Kase had been study-
ing Upper Cretaceous ammonites from Japan and had begun to suspect that
many of the circular holes found in these ammonites were the innocuous
product of boring (literally and figuratively) limpets of the time, rather than
the exciting evidence of ancient predatory behavior.
Kase visited the Tyrell's collections, and in every case the circular holes
seemed to conform to the sizes and shapes produced by limpets. When I
heard this story, I had to laugh—I certainly preferred that the many holes
give us a glimpse into predatory sea monsters instead of snails. The clincher,
at least to me, was that the patterns of these holes seemed random; only once
