Abrictosaurus
Name:
Abrictosaurus
(Wakeful lizard).
Phonetic: Ah-brik-toe-sore-us.
Named By: James A. Hopson - 1975.
Synonyms: Lycorhinus consors.
Classification: Chordata, Reptilia, Dinosauria,
Ornithischia, Heterodontosauridae, Heterodontosaurinae.
Species: A. consors (type).
Diet: Herbivore/Omnivore?
Size: 1.2 meters long.
Known locations: South Africa, Cape Province -
Upper Elliot Formation.
Time period: Hettangian to Sinemurian of the
Jurassic.
Fossil representation: Two individuals.
The
description of Abrictosaurus was born out of the
naming of a species of
Lycorhinus
earlier in 1974. The palaeontologist Richard Thulborn
had named Lycorhinus consors, based upon a
partial skull and
skeleton, UCL B54, of what seemed to be a Lycorhinus
angustidens,
but lacked the tusk like teeth at the front of the mouth. Then in
1975, another palaeontologist named James Hopson was studying UCL
A100, another partial skull of a heterodontosaurid that had been
assigned to Lycorhinus angustidens by Thulborn.
Hopson found the
skull to be both different to Lycorhinus angustidens,
but also
similar to UCL B54, and thus split them from Lycorhinus
and placed
them within the newly created Abrictosaurus.
Abrictosaurus
is still defined by the remains of two individuals, one with the tusk
like front teeth (a.k.a. caniniforms) the other without. This
raises the serious possibility that the front tusks seen in
Abrictosaurus, and by extension other
heterodontosaurids were simply
signs of sexual dimorphism, with the teeth being present in males,
but absent in females, just like in many kinds of tusked animals
known today. An alternative theory however is that the lack of teeth
in one specimen could be because the genus Abrictosaurus
is considered
to be basal (primitive) to other heterodontosaur genera, with the
teeth in this specimen simply not evolving yet. Alternatively again,
the proportions of the skull of UCL B54 are similar to those of
known juveniles of other genera, and this raises the notion that the
tusks had yet to grow in this individual.
Aside
from show, the next popular theory about the tusks is that they were
feeding adaptations. This could be either for the digging up of
plants such as roots, or even the killing of other small animals.
These tusks were the only teeth in the anterior (front) portion of
the mouth which was shaped into a cutting beak. Again this beak could
have been used to crop vegetation, or slice flesh from a carcass. A
further support for the meat eating theory is that the tusks of
Abrictosaurus were serrated on the front half, and
in other genera
like Lycorhinus, the tusks were serrated upon
both sides. The cheek
teeth towards the rear of the mouth however overlap one another to
provide a grinding surface, something of use for a herbivorous diet.
It may simply be that dinosaurs like Abrictosaurus
and other
heterodontosaurids were omnivores, eating both animals and plants.
Further reading
- On the generic separation of the ornithischian dinosaurs Lycorhinus
and Heterodontosaurus from the Stormberg Series
(Upper Triassic) of
South Africa, James A. Hopson - 1975.
- A new heterodontosaurid dinosaur (Reptilia: Ornithischia)
from the Upper Triassic Red Beds of Lesotho, Richard A. Thulborn
- 1974.
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