Nasutoceratops

The brow horns of Nasutoceratops are one of its most notable features; the supraorbital horn cores of ceratopsids were outgrowths of the postorbital bone with slight contribution from the palpebral bone above and in front of the eye sockets, but those of Nasutoceratops differ in orientation and (to a lesser degree) shape. The brow horns of Nasutoceratops are strongly curved; their bases are pointed forwards and outwards, then curve inwards, and ultimately twist their points upwards. The horns are very elongated and span approximately 40% of total skull length, almost reaching the level of the snout tip. This horn configuration has been described as superficially similar to that of a Texas Longhorn bull. With a bone core length of up to 457 mm (18.0 in) in the holotype, the brow horns of Nasutoceratops are the longest known of any centrosaurine, both in absolute and relative terms. The majority of other centrosaurines had relatively short brow horns, with elongated horns only being present in basal forms like Diabloceratops, Avaceratops, and Albertaceratops. The brow horns of Nasutoceratops also differ from those of other ceratopsids by mainly pointing up and away from the eyes, without torsion.^[4][5]

The postorbital bone forms most of the upper skull roof, and most of the upper margin of the eye socket, which was elliptical, as is typical for ceratopsids. The skull roof is very vaulted around the eye region, which gives the impression that Nasutoceratops had a forward facing "forehead" across its width, similar to Diabloceratops and Albertaceratops, as well as many chasmosaurines. The epijugal bone (or cheek horn) is roughly trihedral in shape (with three plane faces meeting at the same point) and that of the holotype is 85 mm (3.3 in) long and 78 mm (3.1 in) wide at the base, the largest known among centrosaurines. Large epijugals are more typical for chasmosaurines, but are also found in Diabloceratops.^[4][5]

The parietosquamosal neck frill at the back of the skull was formed by the fused parietal bones and paired squamosal bones, as in all other ceratopsids. The frill is almost circular with its widest point at the middle region. The total length of the frill of the holotype is around 610 mm (24 in), almost equal to the length of the basal skull (from premaxilla to the occipital condyle at the back of the skull, excluding the frill), with a width around 800 mm (31 in). While the frill is similar to those of Centrosaurus, Achelousaurus, and Einiosaurus in overall shape, it greatly differs from them in the organization of the episquamosals and epiparietals. The frill has two large, oval parietal fenestrae, one on each parietal, as is typical for centrosaurines. The longest axis of each fenestra (from front to back) is about 350 mm (14 in) long, accounting for about 57% of the frills length, and the width from side to side is 260 mm (10 in), accounting for about 33% of the frill's width. The frill is saddle-shaped, with the upper surface being convex from side to side and concave from front to back, as typical for centrosaurines. The squamosal bone is similar to those of other centrosaurines, and forms about a third of the frill. The squamosal has a high ridge on its outer surface, running from the direction of the eye socket towards the squamosal rim, which is unusual for centrosaurines, but is present in taxa like Avaceratops. The presence of four or five undulations on the margin of the squamosal suggests that episquamosals were attached to these, and their shape was probably similar to the epiparietals on the rest of the frill, which are relatively uniform.^[4][5]

The fused parietal bones form about two thirds of the frill, and unlike the squamosal which is usually conservative across centrosaurines, these bones are mostly unique to a species and used for determining interrelationships. On each side of the frill, one parietal has seven undulations on the margin, as well as an undulation on the midline at the top of the frill; these would have been capped by epiparietals. Midline epiparietals are otherwise only known in chasmosaurines, and another contrast with other centrosaurines is that the frill is rounded at the back of the midline, with no indentation there. The median bar between the fenestrae is thin near the margins but thick at the midline, and is strap-like overall. The upper side of the median bar is convex at the front, and forms a low, rounded ridge with five undulations of varying height along the midline. The median bar widens toward the top of the frill, where it widens into the also broad and strap-like transverse parietal bar. The forwards projected ramus on the side of the parietal rounds out the frill and encloses the fenestrae; the ramus is thickest near the side edges where the marginal undulations and epiparietals are located, and thinnest towards the fenestrae. The epiparietals are low, roughly crescent-shaped, and asymmetrical, and their lower surface is slightly concave. They project outward on the same plane as the underlying part of the parietal, with some downwards flexion. They are of almost the same size along the hind and side margins of the frill, but are slightly smaller towards the front. The frill lacked the well-developed hooks and spikes that are otherwise typical for centrosaurines. Since the holotype was not fully grown, it is possible such hooks would have developed as it matured, but this is considered unlikely due to the fusion of its epiparietals on the frill and fusion of other bones related to maturity.^[4]

Postcranial skeleton and skin impressions

Ceratopsids are mainly distinguished through features pertaining to their skull roofs, and the postcranial skeleton of Nasutoceratops is typical of the group. The three frontmost neck vertebrae of ceratopsids were fused into a syncervical vertebra, and that of Nasutoceratops is particularly similar to that of Styracosaurus. At the front, it has the characteristic deep socket that received the occipital condyle at the back of the skull. The dorsal vertebrae are also typical for ceratopsids, with their centra (or "bodies") being short from front to back and their neural arches (the upper part of the vertebrae) being very tall. The articular facets of the centra are almost circular to pear-shaped, similar to those of Styracosaurus. The transverse processes at the sides of these vertebrae are elevated and have prominent zygapophyses (the processes of the vertebrae that articulated with the prezygapophyses of a following vertebrae), typical for the group.^[4]

The

The three patches with skin impressions that are associated with the scapula and humerus of the left forelimb of the holotype are preserved both as casts and molds, and show three kinds of patterns formed by tubercle (round nodule) shaped scales. The patches are identified as patch A, B, and C, and cover 120 cm² (19 sq in), 84 cm² (13.0 sq in), and 25 cm² (3.9 sq in), respectively. Patch A consists of tightly packed, oval to almost circular tubercles which vary from 2–8 mm (0.079–0.315 in) in diameter, and are arranged in irregular rows. Patch B consists of larger, loosely packed almost circular tubercles, varying from 5–11 mm (0.20–0.43 in) in diameter, also arranged in irregular rows. Patch C, the most notable impression, consists of raised, hexagonal tubercles that measure 8–11 mm (0.31–0.43 in) in diameter, and are surrounded by triangular grooves. This patch is located between patch A and B.^[4][19]

Patches A and B have variably sized scales that are round to elliptical and are arranged in irregular rows, similar to what is known from other ceratopsians (including Psittacosaurus, Chasmosaurus, and Centrosaurus). Patch C differs in that it is composed of hexagonal tubercles that are relatively equal in size. These tubercles are separated from the surrounding tubercles by triangular creases and patterns that are unusual among ceratopsians. Similar hexagram-like patterns were later observed on the limbs of Psittacosaurus, and have been called "stars". There is also no evidence in Nasutoceratops of single circular scales much larger than the scales surrounding them, as seen in Chasmosaurus and Centrosaurus.^[4][19]

Classification

Nasutoceratops was assigned to Centrosaurinae by Sampson and colleagues in 2013 based on features such as the premaxilla having a pronounced downwards angle, the almost circular narial (bony nostril) region, having a spine composed of the nasal and premaxilla, and in having an abbreviated squamosal with a stepped hind margin. But despite dating to the late

In 2016, the paleontologist Héctor E. Rivera-Sylva and colleagues reported a partial centrosaurine skeleton (specimen CPC 274) from the Aguja Formation of Coahuila, Mexico, which grouped with Avaceratops and Nasutoceratops in their phylogenetic analysis.^[20] The following year, the paleontologist Michael J. Ryan and colleagues reported a centrosaurine skull (specimen CMN 8804) from the Oldman Formation of Alberta, Canada, which they also found to group with Nasutoceratops and Avaceratops. These authors named this new clade Nasutoceratopsini, with Nasutoceratops as the type genus; this group was defined as all centrosaurines more closely related to Nasutoceratops than to Centrosaurus, containing Nasutoceratops, Avaceratops, MOR 692 (previously treated as an adult Avaceratops), CMN 8804, and another undescribed ceratopsian (specimen GPDM 63) from Malta, Montana. They noted that while new family groups are traditionally named after the first named genus within it, Avaceratops being the first named member, the type specimen of that taxon is juvenile, which makes identification of distinct features problematic, whereas Nasutoceratops has several distinct adult features.^[21] In 2017, the specimen from Mexico was named Yehuecauhceratops by Rivera-Sylva and colleagues, and formally assigned to Nasutoceratopsini.^[22]

The paleontologist Sebastian G. Dalman and colleagues named

The cladogram below follows the 2023 phylogenetic analysis by Ishikawa and colleagues, and shows the position of Nasutoceratops within Ceratopsidae:^[25]

Ceratopsidae

Chasmosaurinae Chasmosaurus belli Pentaceratops sternbergii Centrosaurinae Diabloceratops eatoni Machairoceratops cronusi Nasutoceratopsini Avaceratops lammersi CMN 8804 MOR 692 (cf. Avaceratops) Nasutoceratops titusi Furcatoceratops elucidans Xenoceratops foremostensis Albertaceratops nesmoi Medusaceratops lokii Wendiceratops pinhornensis Sinoceratops zhuchengensis Eucentrosaura Coronosaurus brinkmani Centrosaurus apertus Spinops sternbergorum Styracosaurus albertensis Styracosaurus ovatus Stellasaurus ancellae Pachyrhinosaurini Einiosaurus procurvicornis Achelousaurus horneri Pachyrhinosaurus lakustai Pachyrhinosaurus canadensis Pachyrhinosaurus perotorum

Paleobiogeography

centrosaurines known by 2016 (right); Nasutoceratops lived in southern Laramidia

Sampson and colleagues stated in 2013 that the discovery of Nasutoceratops provided support for the "dinosaur provincialism hypothesis", which postulates that there was separation between the fauna of northern and southern Laramidia for more than a million years during the late Campanian, with at least two coeval dinosaur communities. They pointed out that though the northern Avaceratops was the sister taxon of Nasutoceratops, it was several million years older, and by the time of Nasutoceratops, this genus was distinct from the northern centrosaurines, which belonged to another clade. Samspon and colleagues concluded that ceratopsids went through a rapid evolutionary turnover during the Campanian, and became the most diverse dinosaur clade in Laramidia. No centrosaurines known from northern Laramidia have been found in the south, and centrosaurines underwent substantial diversification in southern Laramidia early in the Campanian.[5]

In 2016, Lund and colleagues also found that the presence of a northern centrosaurine clade with short brow horns and a southern clade with long brow horns that were separated geographically for a million years supported the idea of dinosaur provinciality. They pointed out that particularly the time overlap between Styracosaurus in the north and Nasutoceratops in the south shows that these provinces were evolutionary centers for endemism. They also noted that, apart from Nasutoceratops, all centrosaurines with elongated brow horns were of much older age, and since the derived northern forms with short brow horns probably descended from long-horned forms, both the northern and southern branches may have originated independently from basal, long-horned centrosaurines. Following this scenario, centrosaurines would have originated in the south 80 million years ago (as indicated by basal forms like Diabloceratops from Utah) and dispersed to the north 79 million years ago (as indicated by Xenoceratops from Alberta), and the Avaceratops-Nasutoceratops clade was present in both north and south by 78.5–78 million years ago. Then speciation occurred after the northern and southern centrosaurines became isolated from each other, while Avaceratops went extinct in the north, but Nasutoceratops persisted in the south.^[4]

Ryan and colleagues stated in 2017 that the nasutoceratopsin specimen CMN 8804 from Alberta showed that the group persisted in both northern and southern Laramidia, and that their geographically and temporally large distribution weakened the idea that there would have been distinct provinciality between northern and southern Laramidia. These researchers found that nasutoceratopsins overlapped briefly in time with the other two main clades of Centrosaurinae (Centrosaurini and

bonebeds in northern Laramidia, or that their fragmentary remains may have been mistaken for members of Centrosaurini.^[21]

In 2018, Dalman and colleagues found the specimen that was later named Menefeeceratops to be the oldest centrosaurine from North America, and to have been basal to both nasutoceratopsins and centrosaurins. While not a nasutoceratopsin itself, it shared features with them that suggests this group originated in southern Laramidia. They also pointed out that Crittendenceratops from Arizona, the so far youngest nasutoceratopsin, bridged the

evolutionary gap between the slightly older Yehuecauhceratops and the nasutoceratopsins from the late Campanian of northwestern North America. They stated that the distribution of Nasutoceratopsini in time and space further weakened the hypothesis that there would have been distinct northern and southern Laramidian provinces.^[23][24] In 2021, when naming Menefeeceratops, Dalman and colleagues found this genus and other basal centrosaurines (including members of Nasutoceratopsini, which they did not recognize as a distinct group by then) to have lived at the same time as the rather quickly evolving, derived centrosaurines. They concluded that the fossil evidence indicates that Centrosaurinae originated in southern Laramidia and dispersed north during the late Campanian.^[24]

Paleobiology

In 2016, Lund and colleagues stated that the functional adaptations associated with the very short and deep front part of the skull of Nasutoceratops were unknown; they suggested these may have been related to a change toward more derived

olfactory sensors are located further back in the head, closer to the brain.^[8]

Ryan and colleagues proposed in 2017 that differences in jaw mechanics between nasutoceratopsins and centrosaurins may have prevented resource competition, which allowed them to coexist, or the rarity of nasutoceratopsins may have made them ineffective competitors.

gregarious lifestyle. The tall snouts and robust jaws of nasutoceratopsins also suggest distinct feeding habits.^[25]

In a 2017 Master's thesis, the paleontologist Nicole Marie Ridgwell described two

niche partitioning among the herbivores of the Kaiparowits Formation ecosystem, or that there was seasonal variation in diet.^[26]

Function of skull ornamentation

Sampson and colleagues stated in 2013 that while various hypotheses about the function of ceratopsid skull ornamentation have been proposed, the consensus at the time was use in

mate competition (driven by sexual selection). Other ideas have ranged from protection against predators and thermoregulation. They pointed out that either way, the evolutionary changes in the two centrosaurine clades were concentrated in different parts of the skull, with the clade that included Avaceratops and Nasutoceratops reducing frill ornamentation but elaborating the brow horns, and the clade that indluded Spinops and Pachyrhinosaurus reducing the brow horns but enlarging their nasal horns and frill ornamentation, which distributed their distinct signalling structures all across the skull roof.^[9][8] Loewen stated in the 2013 press release that the horns were probably used as visual signs of dominance, and as weapons against rivals when that was not enough.^[8]

In 2016, Lund and colleagues suggested that if the mate competition hypothesis applied to the very long and robust brow horns of Nasutoceratops, their orientation towards the front and sides and torsional twist may have enabled interlocking of horns with opponents of the same species, as seen in many modern

bovids. They noted that the paleontologist Andrew A. Farke had earlier studied the function of ceratopsid brow horns by using scale models, and found three plausible horn locking positions for Triceratops that could also apply to Nasutoceratops; "single horn contact", "full horn locking", and "oblique horn locking". Farke and colleagues examined pathologies (signs of disease, such as injuries and malformations) in the skulls of Triceratops and Centrosaurus in 2009, and concluded that those in the former were consistent with trauma resulting from antagonistic behaviour, but found those of the latter less conclusive, and Lund and colleagues found that such a hypothesis could not be ruled out for Nasutoceratops.^[4] The paleontologist Gregory S. Paul suggested in 2016 that the forwards directed horns of Nasutoceratops indicated a frontal thrusting action.^[18]

Paleoenvironment

swamplands of Louisiana

, with which the Kaiparowits Formation environment has been compared.

Nasutoceratops is known from the Kaiparowits Formation of Utah, which dates to the late Campanian age of the Late Cretaceous epoch, and

microfossils).^[30][6]

Other

cycads, small dicot trees or bushes, and possibly ferns.^[29]

In 2010, the paleontologist Michael A. Getty and colleagues examined the taphonomy (changes occurring during decay and fossilization) of the holotype specimen and the sedimentological circumstances under which it was preserved. The more or less articulated specimen was found in a sandstone channel lithofacies (the rock record of a sedimentary environment), and may have been much more complete when it was deposited. While the skull and forelimb were in close association, most of the postcranial skeleton was disarticulated and displaced before being deposited, which is indicated by the random distribution of those bones around the skull. The sandstone that entombed the forelimb preserved patches of skin, which is very rare for ceratopsians, and it seems plausible that the carcass was partially articulated with flesh and skin when it was washed into a stream bed. The winnowing and displacement of most of the skeleton, which left just the skull and forelimb in articulation at the time of burial, would have resulted from some rotting and disarticulation in the river channel. The missing parts of the skull were eroded and lost.^[3] Specimen UMNH VP 19466 was found in a bonebed with a partial ankylosaur skeleton and a shell of the turtle Denazinemys.^[2]

See also

• Timeline of ceratopsian research

References

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7. ^ ^{a b} Salt Lake City Tribune (17 July 2013) [Updated: 29 April 2016]. "Dinosaur gets named for his really big nose". Retrieved 9 January 2024 – via The Denver Post.
8. ^ ^{a b c d e f} Carpenter, Patti (17 July 2013). "Big-nosed, long-horned dinosaur discovered in Utah". Natural History Museum of Utah. Archived from the original on 8 October 2013. Retrieved 9 January 2024.
9. ^ ^{a b} Lund, Erik K. (2010). Nasutuceratops titusi, a new basal centrosaurine dinosaur (Ornithischia: Ceratopsidae) from the upper cretaceous Kaiparowits Formation, Southern Utah (Thesis). Department of Geology and Geophysics University of Utah.
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11. ^ Ohlheiser, Abby (17 July 2013). "Paleontologists discover, mock, new dinosaur species". The Atlantic. Retrieved 9 January 2024.
12. ^ Petri, Alexandra (17 July 2013). "Three-horned poems for the new dinosaur, Nasutoceratops, relative of the Triceratops". Washington Post. Retrieved 9 January 2024.
13. ^ Memmott, Mark (17 July 2013). "Newly discovered dinosaur sure had one 'supersize schnoz'". NPR. Retrieved 9 January 2024.
14. ^ Dell'Amore, Christine (16 July 2013). "New big-nosed horned dinosaur found in Utah". National Geographic News. Archived from the original on 4 November 2013. Retrieved 9 January 2024.
15. ^ Whalen, Andrew (16 September 2019). "All 7 dinosaurs in Battle at Big Rock, including Nasutoceratops, new to Jurassic Park series". Newsweek. Retrieved 9 January 2024.
16. ^ Irmis, Randall B. (21 June 2022). "NHMU dinosaur stars in Jurassic World Dominion". Natural History Museum of Utah. Retrieved 9 January 2024.
17. ^ Russell, Steve (12 September 2019). "Jurassic World's short film will introduce two new dinosaurs". CBR. Retrieved 31 January 2024.
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23. ^ ^{a b} Dalman, Sebastian G.; Hodnett, John-Paul M.; Lichtig, Asher J.; Lucas, Spencer G. (2018). "A new ceratopsid dinosaur (Centrosaurinae: Nasutoceratopsini) from the Fort Crittenden Formation, Upper Cretaceous (Campanian) Of Arizona". New Mexico Museum of Natural History and Science Bulletin. 70: 141–164.
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26. ^ Ridgwell, Nicole M. (2017). Description of Kaiparowits coprolites that provide rare direct evidence of angiosperm consumption by dinosaurs. Museum and Field Studies Graduate Theses & Dissertations (Thesis). 6. Archived from the original on 30 June 2019. Retrieved 30 June 2019.
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External links

Wikimedia Commons has media related to Nasutoceratops.

Wikispecies has information related to Nasutoceratops.

• Meet Nasutoceratops: Big-Nose Horned Face - 11 minute NPR audio interview with describer Scott D. Sampson
• NHMU's Nasutoceratops features in Jurassic World Dominion - 4 minute video interview with curator Randall B. Irmis
• Battle at Big Rock - 10 minute Jurassic World short film featuring Nasutoceratops

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