Avaceratops
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Avaceratops Temporal range: Late Cretaceous, 77 Ma |
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| Mounted skeleton in the ANSP | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Order: | †Ornithischia |
| Family: | †Ceratopsidae |
| Genus: |
†Avaceratops Dodson, 1986 |
| Species: | †A. lammersi |
| Binomial name | |
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Avaceratops lammersi Dodson, 1986 |
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Avaceratops is a genus of small herbivorous ceratopsian dinosaurs which lived during the late Campanian during the Late Cretaceous Period in what are now the Northwest United States. Most fossils come from the Judith River Formation.
Avaceratops was originally by Dodson considered to have been an exceptionally small species. He estimated the holotype length at 2.3 metres (7.5 ft) and assumed it had almost attained adult size. However, the second skull (which does not necessarily belong to Avaceratops), MOR 692, indicates a body length of 4.2 metres (14 ft). Paul in 2010 estimated the weight of a four-metre-long animal at one tonne. Another change in the image of Avaceratops brought about by MOR 692 concerned the brow horns. These were first thought to be rather short, although this was purely speculative, the holotype not having preserved them. The new skull showed postorbital horn cores with a length of 25 centimetres (9.8 in).
Avaceratops has a distinctive frill at the back of the skull. The squamosal, the element at the front of the frill side, is large with a continuously curving instead of a stepped edge. A raised area at the base of the squamosal divides it into two equal halves, whereas more derived species have an enlarged top part. The squamosal is separated from the parietal bone at the rear of the skull by a small indentation. The parietals however, show no indentation at the midline of the frill rear. Also the parietals are probably lacking fenestrae which are typical of many other genera except Triceratops, resulting in a solid frill, although damage to the holotype allows for a small opening to be present.
The first remains of Avaceratops were found by fossil dealer Eddie Cole in the Judith River Formation of Montana, in 1981, on land of the Careless Creek Ranch, owned by rancher Arthur J. Lammers. They were preserved scattered throughout the remains of a prehistoric stream bed. This Avaceratops specimen was likely buried in the sandbar after its body was swept downstream by the current. The finds, displayed in Cole's fossil shop, were in October 1981 inspected by Peter Dodson who in July 1982 during a visit with Cole to the site discovered additional bones, which from 1984 were excavated by Anthony Fiorillo.
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Wikipedia