Geoscience Reference
In-Depth Information
Once in a while, two dinosaur partners of the same species contributed to making
one type of trace fossil on bones. Among my favorite examples of these are big
holes in the head shields of
Triceratops
. When paleontologists first noticed these
holes,theywereabitmystified.Forone,thesewerenotnormalpartsofhead-shield
anatomy, which admittedly can become quite holey in some ceratopsians such as
Chasmosaurus
or
Torosaurus
. Although most had roundish outlines, these holes
alsovariedinsizeandlocationontheheadshield.Mostimportant,though,theholes
showedsignsofinjuryandhealingofthebone,meaningtheywerelesions.Thisim-
plied they were wounds acquired during the lifetimes of the dinosaurs, and thus not
post-death artifacts caused by erosion, dissolution, or fracturing of the bones and
surrounding rock over tens of millions of years.
So paleontologists Andrew Farke, Ewan Wolffe, and Darren Tanke, in an at-
tempt to make sense of these holes, took a closer look at the sizes, shapes, and
placements of them on
Triceratops
and another ceratopsian,
Centrosaurus
. In
Tri-
ceratops
, most of these injuries were toward the rear and bottom part of the head
shield, having been registered on the squamosal and jugal bones; almost none were
in other bones. This clustering suggested that some type of behavior was behind
them. After all, if these lesions had been from bone infections, they more likely
would have been evenly distributed throughout the head. So were they toothmarks,
delivered by their theropod contemporaries and presumed archenemies
Tyranno-
saurus rex
? No, because
Centrosaurus
head shields showed almost no holes. Yet
because
Centrosaurus
lived at the same time as
Triceratops
and
Tyrannosaurus
, it
also should have been on a
T. rex
menu. (Paleontologists currently have no eviden-
ce of
T. rex
being a fussy eater.) Granted, we also know through trace fossils that
Triceratops
was eaten by
T. rex
, and with much gusto. But that ichnological point
will have to wait until later.
Left without disease and predation as explanations, the paleontologists who
studied these injuries identified
Triceratops
itself as the culprit. What anatomical
traits did
Triceratops
possess that could impart such grievous traumas? Were these
