Avaceratops

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Avaceratops
Temporal range: Late Cretaceous, 77  Ma
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Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Ornithischia
Clade: Neornithischia
Clade: Ceratopsia
Family: Ceratopsidae
Subfamily: Centrosaurinae
Tribe: Nasutoceratopsini
Genus: Avaceratops
Dodson, 1986
Species:
A. lammersi
Binomial name
Avaceratops lammersi
Dodson, 1986

Avaceratops is a genus of small herbivorous ceratopsian dinosaurs which lived during the late Campanian in what are now the Northwest United States. Most fossils come from the Judith River Formation.

Contents

Discovery and naming

Reconstructed skeleton in the Academy of Natural Sciences, Philadelphia; it is now thought this genus did not have a nasal horn Academy of Natural Sciences, Philadelphia - IMG 7431.JPG
Reconstructed skeleton in the Academy of Natural Sciences, Philadelphia; it is now thought this genus did not have a nasal horn

The first remains of Avaceratops were found by Eddie Cole in the Judith River Formation of Montana, in 1981, on land of the Careless Creek Ranch, owned by rancher Arthur J. Lammers. [1] They were preserved scattered throughout the remains of a prehistoric stream bed. [1] This Avaceratops specimen was likely buried in the sandbar after its body was swept downstream by the current. [1] 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. [2]

The fossil was formally named and described by Dodson in 1986, as the type species Avaceratops lammersi. [3] It was the first ceratopsid named since Pachyrhinosaurus in 1950. [2] The genus was named after Ava Cole, Eddie's wife. [1] The specific epithet honors the Lammers family. [1] In 1990 George Olshevsky emended the name to A. lammersorum, with the specific name in the genitive plural because it referred to several people. [4] However, Dodson objected against this change, arguing the genitive singular might also refer to a single family name. [2] In 1990 Thomas Lehman renamed A. lammersi into Monoclonius lammersi. [5] This alternative name has found no acceptance.

The holotype, ANSP 15800, consists of a partial skeleton containing the lower skull, a left lower jaw, vertebrae, a complete shoulder girdle and most elements of forelimbs and hindlimbs. The type specimen might represent a juvenile or a subadult individual, Dodson in 1986 being inclined to consider it almost fully grown. [3] Kenneth Carpenter made a reconstruction of the skull, a cast of which was by Leroy Glenn combined with restored parts of the postcranial skeleton to create a mount that in 1986 was displayed in the Academy of Natural Sciences in Philadelphia; a copy of this skeletal mount was donated to the Upper Musselshell Valley Historical Museum in Harlowton. [2]

In 1993 Paul Penkalski referred two earlier found squamosals to Avaceratops, USNM 4802 and USNM 2415, of larger individuals. [6] In 1999, Penkalski and Dodson described a second skull, MOR 692, again of a larger individual. This specimen includes the upper skull, with the nose and brow horns. [7] However, the assignment of the latter to Avaceratops has been questioned due to differences in relative chronological position, skull morphology, and lack of intermediate forms; thus, Avaceratops is only represented by the type specimen. [8]

Description

Life restoration Avaceratops BW.jpg
Life restoration

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. [3] However, the second skull (which does not necessarily belong to Avaceratops), [8] MOR 692, indicates a body length of 4.2 metres (14 ft). [7] Paul in 2010 estimated the weight of a four-metre-long animal at one tonne. [9] 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). [7]

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, [1] although damage to the holotype allows for a small opening to be present. [3]

Classification

Size compared to a human Avaceratops Scale.svg
Size compared to a human
Squamosal bone (B) compared to those of other basal centrosaurines Basal centrosaurine squamosals.png
Squamosal bone (B) compared to those of other basal centrosaurines

Avaceratops was by Dodson in 1986 assigned to the Ceratopsidae within the Ceratopsia (both names being derived from Ancient Greek for 'horned face'), a group of herbivorous dinosaurs with parrot-like beaks which thrived in what are now North America and Asia, during the Cretaceous Period.

Apart from being a ceratopsian, little is certain about Avaceratops's taxonomic position. Because most of the skeleton is only known from a juvenile, and juveniles tend to express ancestral traits more strongly, a cladistic analysis would likely indicate a too basal, low, position in the evolutionary tree. For this reason, Avaceratops has often been excluded from such analyses. Penkalski and Dodson in 1999 concluded that Avaceratops most likely occupied a basal position within the Centrosaurinae but that it was also possible it was a basal member of the Ceratopsinae or just outside the clade formed by both groups. A phylogenetic analysis performed by Sampson et al. (2013) found that Avaceratops was the sister taxon of the new genus Nasutoceratops , described and named in 2013. This clade containing both Avaceratops and Nasutoceratops was named the Nasutoceratopsini in 2016. [8]

The cladogram presented below follows a phylogenetic analysis by Chiba et al. (2017): [10]

Centrosaurinae

Paleobiology

Restoration of two running specimens Avaceratops dinosaur.png
Restoration of two running specimens

Avaceratops, like all ceratopsians, was a herbivore. During the Cretaceous, flowering plants were "geographically limited on the landscape", so it is likely that this dinosaur fed on the predominant plants of the era: ferns, cycads and conifers. It would have used its sharp ceratopsian beak to bite off the leaves or needles. The habitat of Avaceratops was heavily forested and wet. [9]

See also

Related Research Articles

<i>Chasmosaurus</i> Extinct genus of dinosaurs

Chasmosaurus is a genus of ceratopsid dinosaur from the Late Cretaceous Period in North America. Its given name means 'opening lizard', referring to the large openings (fenestrae) in its frill. With a length of 4.3–4.8 metres (14.1–15.7 ft) and a weight of 1.5–2 tonnes —or anywhere from 2,200 to nearly 5,000 lbs., give or take—Chasmosaurus was of a slightly smaller to ‘average’ size, especially when compared to larger ceratopsians.

<i>Styracosaurus</i> Genus of ceratopsian dinosaurs

Styracosaurus is an extinct genus of herbivorous ceratopsian dinosaur from the Late Cretaceous of North America. It had four to six long parietal spikes extending from its neck frill, a smaller jugal horn on each of its cheeks, and a single horn protruding from its nose, which may have been up to 60 centimeters long and 15 centimeters wide. The function or functions of the horns and frills have been debated for many years.

<i>Einiosaurus</i> Ceratopsian dinosaur genus from Upper Cretaceous period

Einiosaurus is a genus of herbivorous centrosaurine ceratopsian dinosaur from the Upper Cretaceous of northwestern Montana. The name means 'bison lizard', in a combination of Blackfeet Indian eini and Latinized Ancient Greek sauros; the specific name (procurvicornis) means 'with a forward-curving horn' in Latin. Einiosaurus is medium-sized with an estimated body length at 4.5 metres (15 ft).

<i>Achelousaurus</i> Genus of ceratopsid dinosaur from North America

Achelousaurus is a genus of centrosaurine ceratopsid dinosaur that lived during the Late Cretaceous Period of what is now North America, about 74.2 million years ago. The first fossils of Achelousaurus were collected in Montana in 1987, by a team led by Jack Horner, with more finds made in 1989. In 1994, Achelousaurus horneri was described and named by Scott D. Sampson; the generic name means "Achelous lizard", in reference to the Greek deity Achelous, and the specific name refers to Horner. The genus is known from a few specimens consisting mainly of skull material from individuals, ranging from juveniles to adults.

<i>Arrhinoceratops</i> Extinct species of dinosaurs

Arrhinoceratops is a genus of herbivorous ceratopsian dinosaur. The name was coined as its original describer concluded it was special because the nose-horn was not a separate bone, however further analysis revealed this was based on a misunderstanding. It lived during the latest Campanian/earliest Maastrichtian stage of the Late Cretaceous, predating its famous relative Triceratops by a few million years, although it was contemporary with Anchiceratops. Its remains have been found in Canada.

<i>Monoclonius</i> Extinct genus of dinosaurs

Monoclonius is an extinct genus of herbivorous ceratopsian dinosaur found in the Late Cretaceous layers of the Judith River Formation in Montana, United States, and the uppermost rock layers of the Dinosaur Park Formation in Alberta, Canada dated to between 75 and 74.6 million years ago.

<i>Brachyceratops</i> Extinct genus of dinosaurs

Brachyceratops is a dubious genus of ceratopsian dinosaur known only from partial juvenile specimens dating to the late Cretaceous Period of Montana, United States.

<i>Ceratops</i> Extinct genus of dinosaurs

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<i>Medusaceratops</i> Extinct genus of dinosaurs

Medusaceratops is an extinct genus of centrosaurine ceratopsian dinosaur known from the Late Cretaceous Judith River Formation of Montana, northern United States. It contains a single species, Medusaceratops lokii.

<span class="mw-page-title-main">Centrosaurinae</span> Extinct subfamily of dinosaurs

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<i>Sinoceratops</i> Extinct genus of dinosaurs

Sinoceratops is an extinct genus of ceratopsian dinosaur that lived from 73.5 to 66 million years ago during the latter part of the Cretaceous Period in what is now Shandong province in China. It was named in 2010 by Xu Xing et al. for three skulls from Zhucheng, China. The name of its type species Sinoceratops zhuchengensis means "Chinese horned face from Zhucheng", after the location of its discovery.

<i>Kosmoceratops</i> Dinosaur genus from the Late Cretaceous period

Kosmoceratops is a genus of ceratopsid dinosaur that lived in North America about 76–75.9 million years ago during the Late Cretaceous period. Specimens were discovered in Utah in the Kaiparowits Formation of the Grand Staircase–Escalante National Monument in 2006 and 2007, including an adult skull and postcranial skeleton and partial subadults. In 2010, the adult was made the holotype of the new genus and species Kosmoceratops richardsoni; the generic name means "ornate horned face", and the specific name honors Scott Richardson, who found the specimens. The find was part of a spate of ceratopsian discoveries in the early 21st century, and Kosmoceratops was considered significant due to its elaborate skull ornamentation.

<i>Nasutoceratops</i> Extinct genus of dinosaurs

Nasutoceratops is genus of ceratopsid dinosaur that lived in North America during the Late Cretaceous period, about 76.0–75.5 million years ago. The first known specimens were discovered in Utah in the Kaiparowits Formation of the Grand Staircase–Escalante National Monument (GSENM) from 2006 onwards, including a subadult skull with a partial postcranial skeleton and rare skin impressions and two other partial skulls. In 2013, the subadult was made the holotype of the new genus and species Nasutoceratops titusi; the generic name means "large-nosed horned face", and the specific name honors the paleontologist Alan L. Titus for his work at the GSENM. The dinosaur was noted for its large nose in news reports, and later featured in Jurassic World films.

<i>Coronosaurus</i> Extinct genus of dinosaurs

Coronosaurus is a genus of centrosaurine ceratopsian dinosaurs which lived in the Late Cretaceous, in the middle Campanian stage. Its remains, two bone beds, were discovered by Phillip J. Currie in the Oldman Formation of Alberta, Canada, and its type and only species, Coronosaurus brinkmani, was first described in 2005, as a new species within the genus Centrosaurus. Later studies questioned the presence of a direct relationship, and in 2012 it was named as a separate genus. Coronosaurus means "crowned lizard", coming from "corona", Latin for crown, and "sauros", Greek for lizard; this name refers to the unique, crown-like shape of the horns on the top of its frill.

<i>Judiceratops</i> Extinct genus of dinosaurs

Judiceratops is an extinct horned dinosaur. It lived around 78 million years ago, during the Late Cretaceous Period in what is now Montana, United States. Like other horned dinosaurs, Judiceratops was a large, quadrupedal herbivore. It is the oldest known chasmosaurine.

<i>Wendiceratops</i> Extinct genus of dinosaurs

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<i>Machairoceratops</i> Extinct genus of dinosaurs

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<i>Yehuecauhceratops</i> Extinct genus of dinosaurs

Yehuecauhceratops is a genus of horned centrosaurine ceratopsid dinosaur from the Late Cretaceous of Coahuila, Mexico. It contains a single species, Y. mudei, described from two partial specimens by Rivera-Sylva et al. in 2016 and formally named by Rivera-Sylva et al. in 2017. It was a small centrosaurine with a body length of 3 metres (9.8 ft), making it smaller than Agujaceratops and Coahuilaceratops, the other two ceratopsids in its environment; the three may have been ecologically segregated. A ridge bearing a single roughened projection near the bottom of the squamosal bone, which probably supported a small horn, allows Yehuecauhceratops to be distinguished from other centrosaurines. Its affinities to nasutoceratopsin centrosaurines, such as Avaceratops and Nasutoceratops, are supported by various morphological similarities to the former.

<i>Crittendenceratops</i> Extinct genus of dinosaurs

Crittendenceratops is a genus of horned centrosaurine ceratopsid dinosaur from the late Campanian Fort Crittenden Formation of Arizona. It contains a single species, C. krzyzanowskii, and represents the first species of dinosaur from the Fort Crittenden Formation to receive a formal scientific name.

<i>Furcatoceratops</i> Extinct genus of dinosaurs

Furcatoceratops is a genus of centrosaurine ceratopsid dinosaur from the Late Cretaceous Judith River Formation of Montana. The type species is Furcatoceratops elucidans.

References

Notes

  1. 1 2 3 4 5 6 "Avaceratops." In: Dodson, Peter & Britt, Brooks & Carpenter, Kenneth & Forster, Catherine A. & Gillette, David D. & Norell, Mark A. & Olshevsky, George & Parrish, J. Michael & Weishampel, David B. The Age of Dinosaurs. Publications International, LTD. p. 129. ISBN   0-7853-0443-6.
  2. 1 2 3 4 Dodson, P. (1996). The Horned Dinosaurs . Princeton University Press, Princeton, New Jersey. ISBN   0-691-05900-4.
  3. 1 2 3 4 Dodson, P. (1986). "Avaceratops lammersi: a new ceratopsid from the Judith River Formation of Montana". Proceedings of the Academy of Natural Sciences of Philadelphia. 138 (2): 305–317.
  4. Olshevsky, G., 1991, A revision of the parainfraclass Archosauria Cope, 1869, excluding the advanced Crocodylia. Mesozoic Meanderings 2 196 pp
  5. Lehman, T.M., 1990, "The ceratopsian subfamily Chasmosaurinae: sexual dimorphism and systematics". In: K. Carpenter and P. J. Currie (eds.), Dinosaur Systematics: Perspectives and Approaches, Cambridge University Press, Cambridge pp 211-229
  6. Penkalski, P.G., 1993, "The morphology of Avaceratops lammersi, a primitive ceratopsid from the Campanian of Montana". Journal of Vertebrate Paleontology13(3, suppl.): 52A
  7. 1 2 3 Penkalski, P. & Dodson, P. (1999). "The morphology and systematics of Avaceratops, a primitive horned dinosaur from the Judith River Formation (Late Campanian) of Montana, with the description of a second skull". Journal of Vertebrate Paleontology. 19 (4): 692–711. Bibcode:1999JVPal..19..692P. doi:10.1080/02724634.1999.10011182.
  8. 1 2 3 Ryan, M.J.; Holmes, R.; Mallon, J.; Loewen, M.; Evans, D.C. (2017). "A basal ceratopsid (Centrosaurinae: Nasutoceratopsini) from the Oldman Formation (Campanian) of Alberta, Canada". Canadian Journal of Earth Sciences. 54 (1): 1–14. Bibcode:2017CaJES..54....1R. doi: 10.1139/cjes-2016-0110 .
  9. 1 2 Paul, G.S., 2010, The Princeton Field Guide to Dinosaurs, Princeton University Press p. 264
  10. Kentaro Chiba; Michael J. Ryan; Federico Fanti; Mark A. Loewen; David C. Evans (2018). "New material and systematic re-evaluation of Medusaceratops lokii (Dinosauria, Ceratopsidae) from the Judith River Formation (Campanian, Montana)". Journal of Paleontology. 92 (2): 272–288. Bibcode:2018JPal...92..272C. doi:10.1017/jpa.2017.62.