Name:
Acrotholus
(High dome).
Phonetic: Ak-roe-foe-lus.
Named By: David C. Evans, Ryan K. Schott,
Derek W. Larson, Caleb M. Brown, Michael J. Ryan - 2013.
Classification: Chordata, Reptilia, Dinosauria,
Ornithischia, Pachycephalosauridae.
Species: E. audeti (type).
Diet: Herbivore.
Size: Estimated to be about 1.8 meters long.
Known locations: Canada, Alberta - Milk River
Formation, Deadhorse Coulee Member.
Time period: Santonian of the Cretaceous.
Fossil representation: Skull fragments including two
domes.
Although
so far only represented by skull fragments, Acrotholus
was still a
very exciting discovery. At the time of its description, Acrotholus
was the oldest confirmed pachycephalosaur
dinosaur from the North
American continent. Also important is that like most other known
pachycephalosaurs, Acrotholus already had a fully
developed skull
dome. However the purpose of this dome is still a controversial
matter since the old ‘head bashing’ theory is not universally
accepted by all palaeontologists. It may be that the dome was a
purely visual display device for inter species recognition. The bone
in the dome of Acrotholus seems to have been over
ten centimetres thick.
The
team that described Acrotholus also took the
opportunity to point out
that the fossil record of long extinct animals can be biased towards
the preservation of larger species. Larger animals have
proportionately larger bones which mean that it is harder for
scavengers to consume them, often because of simple things like not
having big enough mouths to fit them in. Smaller animals of course
have smaller bones which mean that a greater number of meat eating
creatures are able to process the bones for additional sustenance,
meaning that fewer bones survive to fossilise. Indeed, if you look
at the preservation of smaller animals, the best preserved
individuals are usually the result of dying in more specialised
circumstances such as being buried in landslides or buried in sediment
at the bottom of a water system. Another 2013 naming,
Albertadromeus,
was used to further support this theory.
Acrotholus
is not as old as some of the known pachcephalosaur genera from Asia,
but it does help to complete a picture of the fauna roaming around
North America earlier in the late Cretaceous. Also, now that
palaeontologists have a better idea of what is out there, Acrotholus
may be the first of many more Santonian age pachycephalosaurs.
The
genus name Acrotholus means ‘high dome' which
is a reference to the
dome shaped skull that the genus had. The species name ‘audeti'
is in honour of Roy Audet, a rancher on whose land the holotype
specimen was discovered on in 2008.
Acrotholus
may have been hunted by small predatory dinosaur genera such as
Saurornitholestes
and Richardoestesia,
fossils for which have also
been recovered from the Milk River Formation.
Further reading
- The oldest North American pachycephalosaurid and the hidden
diversity of small-bodied ornithischian dinosaurs. - David C.
Evans, Ryan K. Schott, Derek W. Larson, Caleb M. Brown,
& Michael J. Ryan - 2013.