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head or neck injury, and hence would not have lasted very long in a pachycephalo-
saurlineage.Theythenrepeatedtheiranalysisonthreespeciesofmodernmammals
that habitually head-smash one another: white-bellied duikers (
Cephalophus leu-
cogaster
), which look much like deer; giraffes (
Giraffa camelopardalis
) of Africa;
and musk oxen (
Ovibos moschatus
) of North America. Other mammals they stud-
iedascontrolgroupswere:bighornsheep(
Ovis canadensis
),whichhead-buttwhen
youngerbutstopsuchshenanigansonceolder;pronghorns(
Antilocapra americana
)
of North America, which hit each other with their antlers, but not their skulls; and
three mammals that eschew head-knocking altogether, llamas (
Lama glama
), elk
(
Cervus canadensis
), and peccaries (
Tayassu tajacu
).
Their conclusions were that a few modern head-butting mammals and
Stego-
ceras
shared the same types of skull tissue and other cranial traits for absorbing
head-to-head blows. Having a more rounded, dome-like head was an advantage, as
well as having more compacted (
cortical
) bone supported by more porous (
cancel-
lous
) bone, like a motorcycle helmet with cushioning just below its hard exterior.
Somewhat surprisingly, duiker skulls were the most similar to those of the pachy-
cephalosaurs, despite these animals being much smaller than pachycephalosaurs.
This led these paleontologists to suggest that we should look at these hoofed mam-
mals in particular as models for pachycephalosaur behavior.
But wait! Don't give up on trace fossils just yet. If pachycephalosaurs were
knockingnogginswithoneanother,surelythisleftmarksontheirskullswherethey
impacted. Alternatively, if pachycephalosaurs went for flank butting, this behavior
would have broken ribs in the one receiving the blow, and in a definite, localized
pattern.Justtoputtheirbone-breakingpotentialinperspective,thelargestofpachy-
cephalosaurs,
Pachycephalosaurus
,mayhaveweighedasmuchas400kg(880lbs),
or about three times that of the largest linebackers in the NFL. Imagine, then, this
bipedaldinosaurrunningatfullspeed,headdownandpointedforward,andthecon-
sequencesofitsheadmeetinganyothersolidobject,suchasanotherhead,andwith
the rest of another
Pachycephalosaurus
behind it. Adaptations or no adaptations,
