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Pentaceratops

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Pentaceratops
Temporal range: Late Cretaceous (Campanian), 76–73 Ma
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Holotype skull of P. sternbergii, AMNH 6325
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: †Ornithischia
Clade: †Neornithischia
Clade: †Ceratopsia
Family: †Ceratopsidae
Subfamily: †Chasmosaurinae
Genus: †Pentaceratops
Osborn, 1923
Type species
†Pentaceratops sternbergii
Osborn, 1923

Pentaceratops ("five-horned face") is a genus of herbivorous ceratopsid dinosaur from the late Cretaceous Period of what is now North America. Fossils of this animal were first discovered in 1921, but the genus was named in 1923 when its type species, Pentaceratops sternbergii, was described. Pentaceratops lived around 76–73 million years ago, its remains having been mostly found in the Kirtland Formation[1] in the San Juan Basin in New Mexico. About a dozen skulls and skeletons have been uncovered, so anatomical understanding of Pentaceratops is fairly complete. One exceptionally large specimen later became its own genus, Titanoceratops, due to its more derived morphology, similarities to Triceratops, and lack of unique characteristics shared with Pentaceratops.[2][3]

Pentaceratops was about 5.5–6 meters (18–20 ft) long, and has been estimated to have weighed around 2.5 metric tons (2.8 short tons). It had a short nose horn, two long brow horns, and long horns on the jugal bones. Its skull had a very long frill with triangular hornlets on the edge.

Discoveries and species

Map of the southeast San Juan Basin; H is the purported collection area of the P. sternbergii holotype

The first specimens were collected by Charles Hazelius Sternberg in the San Juan Basin in New Mexico. Sternberg worked in commission for the Swedish Uppsala University. In 1921 he recovered a skull and a rump, specimens PMU R.200 and PMU R.286, at the Meyers Creek near the Kimbetoh Wash in a layer of the Kirtland Formation. He sent these fossils to paleontologist Carl Wiman. In 1922 Sternberg decided to work independently and began a dig north of Tsaya Trading Post, in the Fossil Forest of San Juan County. Here he discovered a complete skeleton, which he sold to the American Museum of Natural History. The museum then sent out a team headed by Charles Mook and Peter Kaisen to assist Sternberg in securing this specimen; subsequent digging by Sternberg in 1923 brought the total of AMNH specimens to four. The rump of the main specimen was discarded by the museum because it had insufficient value as a display.

P. sternbergii holotype skull with reconstructed parts, AMNH

The species was named and described by Henry Fairfield Osborn in 1923, as Pentaceratops sternbergii. The generic name means "five-horned face", derived from the Greek penta (πέντα, meaning five), keras (κέρας, horn) and -ops (ὤψ, face),[4] in reference to its two long epijugal bones, spikes which protrude out sidewards from under its eyes, in addition to the three more obvious horns as with Triceratops. Osborn obligingly gave it the specific name sternbergii to honor its discoverer.[5] The name had been suggested to Osborn by William Diller Matthew; the specific epithet served as a consolation to the almost bankrupt Sternberg whose 1923 fossils were initially not acquired by the museum that had to use its 1923/1924 budget to process the finds of the great Asian expeditions by Roy Chapman Andrews.[6]

The holotype was the skull discovered by Sternberg in 1922, specimen AMNH 6325. It was found in a layer of the Fruitland Formation, dating from the Campanian, about seventy-five million years old. The other three AMNH specimens were AMNH 1624, a smaller skull; AMNH 1622, a pair of brow horns; and AMNH 1625, a piece of skull frill.[5]

Holotype skull diagram of P. fenestratus

In 1930, Wiman named a second species of Pentaceratops: P. fenestratus. It was based on Sternberg's 1921 specimens and the specific name referred to a hole in the left squamosal.[7] This was later considered to be the same species as Pentaceratops sternbergii and thus a junior synonym, the hole being the likely effect of an injury. Fowler and Freedman Fowler (2020) considered Pentaceratops fenestratus to be a distinct taxon from Pentaceratops sternbergi. In their opinion, it may be identical to Navajoceratops or Terminocavus, but the state of preservation of the remains makes it impossible to precisely determine the systematics of its owner.[8]

In 1929 Sternberg's son, George Fryer Sternberg, discovered specimen USNM V12002, a right squamosal. Pentaceratops proved to be a quite common fossil in the Fruitland and Kirtland formations. It has even been used as a guide fossil: the appearance of Pentaceratops sternbergii in the fossil record marks the end of the Judithian land vertebrate age and the start of the Kirtlandian.[1] Subsequent finds include specimens MNA Pl. 1668, MNA Pl. 1747, NMMNH P-27468 and USNM 2416, partial skeletons with skull; YPM 1229, a skeleton lacking the skull; UALP 13342 and UKVP 16100, skulls; UNM B-1701, USNM 12741, USNM 12743, USNM 8604, SMP VP-1596, SMP VP-1488, SMP VP-1500 and SMP VP-1712, fragmentary skulls. Apart from the San Juan Basin finds, a juvenile specimen of Pentaceratops, SDMNH 43470, was found in the Williams Fork Formation of Colorado in 2006.[9]

Specimen being airlifted with help from the New Mexico National Guard, 2015

Sometimes the identification of a specimen as Pentaceratops has proven to be highly contentious. In 1998 Thomas Lehman described OMNH 10165, a very large skull and its associated skeleton found in New Mexico in 1941. The skull is presently on display at the Sam Noble Oklahoma Museum of Natural History, and is the largest Pentaceratops exemplar known, with the distinction of having produced the largest known skull of any land vertebrate.[10][11] However, in 2011, the skeleton was renamed as a separate genus, Titanoceratops, due to its more derived morphology, similarities to Triceratops, and lack of unique characteristics shared with Pentaceratops.[2]

In 2014 Nicholas Longrich named a new species: Pentaceratops aquilonius, "the northern one", based on fragmentary fossils discovered during the 1930s near Manyberries in Alberta, Canada. The species has been described as having a first epiparietal pointing upwards instead of forwards.[12] In 2016, Mallon et al. found P. aquilonius to be morphologically similar to Spiclypeus shipporum, with it possibly being the same species, and considered P. aquilonius a nomen dubium.[13]

Description

Restoration of P. sternbergii

Pentaceratops was a large ceratopsid; Dodson estimated the body length at 6 meters (20 ft). The skull length of AMNH 1624 is 2.3 meters (7.5 ft) while PMU R.200 has a length of 2.16 meters (7.1 ft).[7] In 2016 Paul estimated its length at 5.5 meters (18 ft) and its weight at 2.5 metric tons (2.75 short tons).[14] The nose horn of Pentaceratops is small and pointing upward and backward. The brow horns are very long and curving strongly forward. The somewhat upward tilted frill of Pentaceratops is considerably longer than that of Triceratops, with two large holes (parietal fenestrae) in it. It is rectangular, adorned by large triangular osteoderms: up to twelve episquamosals at the squamosal and three epiparietals at the parietal bone. These are largest at the rear corners of the frill, and are separated by a large U-shaped notch at the midline, a feature not recognized until 1981 when specimen UKVP 16100 was described.[15] Within the notch the first epiparietals point forwards. The very thick jugal and the squamosal do not touch each other, a possible autapomorphy.[2]

The torso of Pentaceratops is tall and wide. The rear dorsal vertebrae bear long spines from which ligaments possibly ran to the front, to balance the high frill. The prepubis is long. The ischium is long and strongly curves forward. In smaller specimens the thigh bone bows outwards.[16]

Classification

Osborn originally assigned Pentaceratops to Ceratopsia. Within this group Pentaceratops belonged to the Ceratopsinae or Chasmosaurinae. It appears to be most closely related to Utahceratops. Their clade was perhaps more derived than the earlier genus Chasmosaurus but more basal than Anchiceratops, the latter representing a line of which Triceratops was a member, which lived a few million years later, right at the end of the Cretaceous period, when all ceratopsians died out.

The cladogram of the phylogeny of Pentaceratops according to a study by Scott Sampson et al. in 2010 found that the genus was most closely related to Utahceratops, from a similar age and region.[17] The below cladogram follows Longrich (2014), who named a new species of Pentaceratops, and included nearly all chasmosaurine species.[18]

Paratype of P. aquilonius (CMN 9813), interpreted as an epiparietal of P. aquilonius (left) or Spiclypeus
Size of P. sternbergi compared to a human
Chasmosaurinae

Mercuriceratops

Judiceratops

Chasmosaurus

Chasmosaurus sp. CMN 2280

Chasmosaurus belli

Chasmosaurus irvinensis

Mojoceratops

Agujaceratops

Pentaceratops aquilonius

Williams Fork chasmosaur

Pentaceratops sternbergii

Utahceratops

Kosmoceratops

Kosmoceratops richardsoni

Kosmoceratops sp. CMN 8301

Anchiceratops

Almond Formation chasmosaur

Longrich stated that the holotype and referred specimen of P. aquilonius fall within the diagnosis of Pentaceratops, and were recovered very close to the type species in the phylogeny. He noted that the placement of Utahceratops does not make the genus paraphyletic, as there is no requirement that genera are monophyletic. The Williams Fork chasmosaur differs from the Pentaceratops and Utahceratops species, and might require a new specific or generic name.[18]

Paleobiology

Restoration of Bistahieversor hunting Pentaceratops

Pentaceratops, like all ceratopsians, was an herbivore. During the Cretaceous, flowering plants were "geographically limited on the landscape"[according to whom?][clarification needed] and 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 branches which were then shredded - leaves, needles and all - by the tooth batteries, providing a self-sharpening continuous cutting edge in both upper and lower jaws. Ultimately the plant material was digested by the large gut.

Paleoecology

Pentaceratops lived around 76–73 million years ago, its remains having been mostly found in the Kirtland Formation[1] in the San Juan Basin in New Mexico. Other dinosaurs that shared its habitat include Parasaurolophus cyrtocristatus, the pachycephalosaur Sphaerotholus, the armored dinosaur Nodocephalosaurus and the tyrannosauroid Bistahieversor.

See also

References

  1. ^ a b c d Sullivan and Lucas (2006).[permanent dead link]
  2. ^ a b c d Longrich, Nicholas R. (1 June 2011). "Titanoceratops ouranos, a giant horned dinosaur from the late Campanian of New Mexico". Cretaceous Research. 32 (3): 264–276. Bibcode:2011CrRes..32..264L. doi:10.1016/j.cretres.2010.12.007. ISSN 0195-6671.
  3. ^ Wick, S. L.; Lehman, T. M. (2013). "A new ceratopsian dinosaur from the Javelina Formation (Maastrichtian) of West Texas and implications for chasmosaurine phylogeny". Naturwissenschaften. 100 (7): 667–82. Bibcode:2013NW....100..667W. doi:10.1007/s00114-013-1063-0. PMID 23728202. S2CID 16048008.
  4. ^ a b Liddell, et al. (1980). pp. 373, 542-43, 804.
  5. ^ a b H.F. Osborn, 1923, "A new genus and species of Ceratopsia from New Mexico, Pentaceratops sternbergii, American Museum Novitates 93: 1-3
  6. ^ Sullivan, R.M. and S.G. Lucas, 2011, "Charles Hazelius Sternberg and his San Juan Basin Cretaceous dinosaur collections: Correspondence and photographs (1920–1925)", New Mexico Museum of Natural History and Science Bulletin 53: 429-471
  7. ^ a b C. Wiman, 1930, "Über Ceratopsia aus der Oberen Kreide in New Mexico", Nova Acta Regiae Societatis Scientiarum Upsaliensis, Series 4 7(2): 1-19
  8. ^ Fowler, D.W.; Freedman Fowler, E.A. (2020). "Transitional evolutionary forms in chasmosaurine ceratopsid dinosaurs: evidence from the Campanian of New Mexico". PeerJ. 8: e9251. doi:10.7717/peerj.9251. PMC 7278894. PMID 32547873.
  9. ^ a b Lucas, et al. (2006).
  10. ^ Lehman, T.M., 1998, "A gigantic skull and skeleton of the horned dinosaur Pentaceratops sternbergi from New Mexico: Journal of Paleontology, 72(5): 894-906
  11. ^ a b Delayed Debut for Jumbo Dino Skull
  12. ^ Longrich, N., 2014, "The horned dinosaurs Pentaceratops and Kosmoceratops from the upper Campanian of Alberta and implications for dinosaur biogeography", Cretaceous Research, 51: 292-308
  13. ^ Jordan C. Mallon; Christopher J. Ott; Peter L. Larson; Edward M. Iuliano; David C. Evans (2016). "Spiclypeus shipporum gen. et sp. nov., a Boldly Audacious New Chasmosaurine Ceratopsid (Dinosauria: Ornithischia) from the Judith River Formation (Upper Cretaceous: Campanian) of Montana, USA". PLOS ONE. 11 (5): e0154218. Bibcode:2016PLoSO..1154218M. doi:10.1371/journal.pone.0154218. PMC 4871577. PMID 27191389.
  14. ^ Paul, Gregory S. (2016). The Princeton Field Guide to Dinosaurs (2nd ed.). New Jersey: Princeton University Press. p. 298.
  15. ^ Rowe, T.; Colbert, E. H.; Nations, J. D. (1981). "The occurrence of Pentaceratops with a description of its frill". In Lucas, S. G.; Rigby, J. K.; Kues, B. S. (eds.). Advances in San Juan Basin Paleontology. Albuquerque: University of New Mexico Press. p. 29-48. ISBN 0-8263-0554-7.
  16. ^ Paul, G. S. (2010). The Princeton Field Guide to Dinosaurs. Princeton University Press. p. 272.
  17. ^ Scott D. Sampson, Mark A. Loewen, Andrew A. Farke, Eric M. Roberts, Catherine A. Forster, Joshua A. Smith, and Alan L. Titus (2010). Stepanova, Anna (ed.). "New Horned Dinosaurs from Utah Provide Evidence for Intracontinental Dinosaur Endemism". PLOS ONE. 5 (9): e12292. Bibcode:2010PLoSO...512292S. doi:10.1371/journal.pone.0012292. PMC 2929175. PMID 20877459.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  18. ^ a b Longrich, N. R. (2014). "The horned dinosaurs Pentaceratops and Kosmoceratops from the upper Campanian of Alberta and implications for dinosaur biogeography". Cretaceous Research. 51: 292–308. Bibcode:2014CrRes..51..292L. doi:10.1016/j.cretres.2014.06.011.

Sources

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