| Nasutoceratops | |
|---|---|
 | |
| ReconstructedNasutoceratops skull at theArizona Museum of Natural History | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Clade: | †Ornithischia |
| Clade: | †Ceratopsia |
| Family: | †Ceratopsidae |
| Subfamily: | †Centrosaurinae |
| Tribe: | †Nasutoceratopsini |
| Genus: | †Nasutoceratops Sampsonet al.,2013 |
| Type species | |
| †Nasutoceratops titusi Sampsonet al., 2013 | |
Nasutoceratops is agenus ofceratopsid dinosaur that lived in North America during theLate Cretaceous period, about 76.0–75.5million years ago. The first known specimens were discovered inUtah in theKaiparowits Formation of theGrand Staircase–Escalante National Monument (GSENM) from 2006 onwards, including asubadult skull with both a partialpostcranial skeleton and rare skin impressions, and two other partial skulls. In 2013, the subadult was made theholotype of the new genus and speciesNasutoceratops titusi; thegeneric name means "large-nosed horned face", and thespecific 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 inJurassic World films.
The holotype skull ofNasutoceratops is approximately 1.5 m (4.9 ft) long; its body length has been estimated at 4.5 m (14.8 ft), and its weight at 1.5 t (1.7 short tons).Nasutoceratops is distinct in features such as the snout region being unusually deep but short from front to back, with the external nostril forming 75% of the skull length in front of the eye sockets. The nasal bones were possiblypneumatized (air-filled), which is unknown in other ceratopsids. Its nasal horn is low and blade-like while the brow horns point forward and are approximately 40% of the total skull length; they are up to 457 mm (18.0 in), the longest known of anycentrosaurine, and have been likened to those of aTexas Longhorn bull. Theneck frill is almost circular with its widest point at the middle. Theepiossifications on the margins of the frill are shaped like low crescents, and there is one at the midline at the top of the frill, unlike in other centrosaurines.Nasutoceratops was abasal (early diverging) member ofCentrosaurinae, and may have formed a distinctclade within this group, Nasutoceratopsini, with its closest relatives.
The function of the deep front of the skull ofNasutoceratops is unknown, but may have been related tomastication. The functions of ceratopsian frills and horns have been debated, and include signalling, combat, andspecies recognition. The forward oriented brow horns ofNasutoceratops may have enabled interlocking with opponents, as in modernbovids. The Kaiparowits Formation dates to the lateCampanian age and wasdeposited onLaramidia, an island continent, when North America was divided at the center by theWestern Interior Seaway. This environment was dominated bywetlands and supported a diverse fauna, including other ceratopsians. Based in part on the relationship betweenNasutoceratops and other centrosaurines from around the same time, it has been proposed that Laramidia was divided into dinosaur "provinces" with separateendemic species, but this has been contested.
Since 2000, theNatural History Museum of Utah (UMNH) and theBureau of Land Management have been conducting paleontological surveys of theKaiparowits Formation at theGrand Staircase–Escalante National Monument (GSENM) in southernUtah. Thisnational monument was established in 1996 in part for the preservation and study of itsfossils, and the surveys there have yielded a wide array of unique dinosaur fossils. Field crews from other institutions have also participated, and the collaborative effort is known as theKaiparowits Basin Project.[1][2] Among the discoveries that have been made are three newceratopsian (horned dinosaur)taxa, one of which was identified from UMNH Locality VP 940 discovered by the then graduate student and technician Eric K. Lund during the 2006 field season.[2][3] Prior to this project, the only ceratopsian remains found in the formation were uninformative, isolated teeth, and centrosaurines were known almost exclusively from the northern part of western North America.[4][5]
Excavated fossils of the new ceratopsian were transported to the UMNH, where the blocks wereprepared by volunteers with pneumaticair scribes and needles and subsequently reassembled; it took a few years for the team to assemble the skull of this dinosaur.[1][6][7] It was preliminarily referred to as "Kaiparowits newtaxon C" and identified as acentrosaurine (the first member of thisceratopsid group known from the formation) in 2010, and as "Kaiparowits centrosaurine A" in 2013. Three specimens of this dinosaur were collected; UMNH VP 16800 in 2006, and UMNH VP 19469 and UMNH VP 19466 in subsequent years.[2][3][8]
The paleontologistsScott D. Sampson, Lund, Mark A. Loewen, Andrew A. Farke, and Katherine E. Clayton briefly described andscientifically named the newgenus and speciesNasutoceratops titusi in2013, with specimen UMNH VP 16800 as theholotype (on which the scientific name is based). Thegeneric name is derived from theLatin wordnasutus meaning "large-nosed", andceratops, which means "horned face" inLatinized Greek. Thespecific nametitusi is aneponym that honors the paleontologist Alan L. Titus for his important efforts in recovering fossils from the GSENM.[5][4] Lund hadinformally used the spellingNasutuceratops for this dinosaur in his 2010thesis wherein he also described it.[9] In 2016, Lund, Sampson, and Loewen published a more detailed description of the preserved fossil material.[4]
The holotype specimen UMNH VP 16800 consists of a partial, associated, and nearly complete skull that preserves most of theskull roof. The specimen has been interpreted as being a subadult, based on the degree of fusion of skull elements and bone surface texture. It was collected with an articulated and almost complete left forelimb, an associated yet very fragmentary right forelimb (both lacking hand bones), much of thepectoral girdle, an almost completesyncervical vertebra (the three first neck vertebrae fused together), three associated but fragmentarydorsal vertebrae (of the back), as well as three patches of skin impressions associated with the left forelimb (the only ceratopsid skin impressions known from the GSENM and some of the few known worldwide). Two specimens from other quarries were assigned due to shared features with the holotype: specimen UMNH VP 19466, a disarticulated adult skull consisting of the partial right and leftpremaxillae (which form much of the upper jaw), a rightmaxilla (tooth-bearing bone of the upper jaw) and rightnasal bone (the largest bone at the top of the snout), and specimen UMNH VP 19469, an isolatedsquamosal bone (which formed part of the side of theparietosquamosal frill at the back of the skull) of a subadult. Taken together, these specimens represent about 80% of the skull and about 10% of the postcranial skeleton.[5][4]
A spate of ceratopsian discoveries were made in the early 21st century, when many new taxa were named; a 2013 study stated that half of all valid genera were named since 2003, and the decade has been called a "ceratopsid renaissance".[2][10][8] Sampson and colleagues stated that understanding of centrosaurine evolution had greatly increased in the years leading up to 2013, with 12 out of 17 known taxa having been described in the prior decade alone.[4] In the UMNH press release accompanying the description ofNasutoceratops, the large nose of the dinosaur was emphasized, with Sampson calling it a "jumbo-sized schnoz".[8] This was reflected in news outlets, with one article titled "paleontologists discover, mock, new dinosaur species", and another including humorous poems about the dinosaur by columnistAlexandra Petri, such as: "Higgledy piggledy,Nasutoceratops, Long-nosed horned just-unearthed dino du jour, Probably used its horns, For showing dominance, During its courtship (although we're not sure)".[11][12][13][14][7]Nasutoceratops was featured in the 2019Jurassic World short filmBattle at Big Rock and the 2022 feature filmJurassic World Dominion, in what a UMNH article called a "pivotal role".[15][16]Colin Trevorrow, the director of the former film, calledNasutoceratops "a beautifulherbivore that feels like aTexas Longhorn" (abreed ofcattle).[17]
The subadult holotype skull ofNasutoceratops is approximately 1.5 m (4.9 ft) long.[4]Nasutoceratops is estimated to have been 4.5 m (14.8 ft) long and to have weighed 1.5 t (1.7 short tons).[18] As a centrosaurine ceratopsid, it would have been a large bodied, quadrupedal dinosaur with a huge skull, a hooked upper beak, a heavily constructed skeleton, a shortened, down-swept tail, a large pelvis indicating powerful muscles, and short digits.[18]Nasutoceratops had three horns; the nasal horn above the nasal opening and the brow horns above theeye sockets. As is general for ceratopsians, it hadepiossifications (accessoryossifications) on the margins of the neck frill (episquamosals and epiparietals) and on the cheeks (epijugals). Their external texture was very vascularized and rugose, and they were most likely covered by akeratinous sheath when the dinosaur was alive.[4]
The front part of the skull ofNasutoceratops is unusually deep from top to bottom, especially around the nostril area, similar to that ofDiabloceratops. The external nostril forms 75% of the skull length in front of the eye sockets, more than in other ceratopsians. The snout region is almost circular overall, which is typical of centrosaurines, but it differs from more derived (or "advanced") centrosaurines and is more similar to thebasal (early diverging)Diabloceratops in that it expands upwards, giving the snout region a bulbous appearance. The shortness of the snout is a result of the abbreviated nasal and maxilla bones, and it may be the shortest of any centrosaurine. Therostral (a bone unique to ceratopsians, which forms the upper beak and contacts the front part of the premaxilla) is not preserved inNasutoceratops, but by inferring from the contact area of the premaxilla behind it, it has been interpreted as triangular in side view, similar to centrosaurines and unlikechasmosaurines (the other main group of ceratopsids). The deep, thin, and rounded septum at the front of the premaxilla appears to be more extensive than in any other ceratopsid, and extends hindwards to underlie the horn core of the nasal.[4]
A shorthard palate is present on the premaxilla, a feature otherwise only seen inPachyrhinosaurus among centrosaurines.Nasutoceratops differs from other ceratopsids in that the dorsal ascending ramus (upwards directed portion of bone) of the maxilla has a thin-walled contact surface for the hindwards projecting process of the premaxilla. The contact surface of the maxilla for the premaxilla is very expanded (forming a contact shelf), and has a deeply excavatedsulcus (groove), unlike in other ceratopsids. Each maxilla is estimated to have contained 29 teeth, but it has not been determined whether they were double-rooted as in other ceratopsids or single-rooted as inneoceratopsians. The maxillary teeth have nearly verticalwear facets on their inwards surfaces, as is typical ofceratopsids. The tooth row is displaced downward in relation to the front part of the maxilla where it contacts the premaxilla, unlike in most ceratopsids, but similar toDiabloceratops,Avaceratops, and more basal neoceratopsians. The maxillary flange at the front of the maxilla, which contributes to the hard palate by slotting into the premaxilla, is double-socketed, a unique feature ofNasutoceratops. The back of the maxilla has a somewhat well-developed excavation on the side towards the "cheek", which seems to be less defined than in other ceratopsids.[4]
The fused nasal bones ofNasutoceratops (which form the upper hind part of the snout) are relatively short from front to back compared to more derived centrosaurines. The nasal horn core that formed the bony part of the horn above the nasal opening is low, long, and blade-like, pinched from side to side along the hind part, and with a somewhat raised, teardrop-shaped expansion at the front. The horn's texture is rugose and vascularized, as is typical for ceratopsids. The nasal bones flare out to the sides in front of the horn, forming a "roof" in front of much of the nasal cavity, similar toCentrosaurus andAchelousaurus. There is a spine formed by the nasal andpremaxilla, as is typical in centrosaurines, which extends into thenasal cavity and results in an hour glass shape when the cavity is viewed from the front. Seen from the side, the inner nasal opening is relatively small and slightly crescent-shaped, with an upwards arched front border. The longest axis of the internal nostril opening is almost horizontally oriented, whereas it is almost vertical in most other centrosaurines. The nasal bones have well-developed internal cavities behind the horn, which suggests they were hollow, and possiblypneumatized (air-filled); pneumatic nasals are unknown in other ceratopsians.[4]
The brow horns ofNasutoceratops are one of its most notable features; the supraorbital horn cores of ceratopsids were outgrowths of thepostorbital bone with slight contribution from thepalpebral bone above and in front of the eye sockets, but those ofNasutoceratops differ in orientation and (to a lesser degree) shape. The brow horns ofNasutoceratops are strongly curved; their bases are pointed forward 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 ofNasutoceratops 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 likeDiabloceratops,Avaceratops, andAlbertaceratops. The brow horns ofNasutoceratops 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 thatNasutoceratops had a forward facing "forehead" across its width, similar toDiabloceratops andAlbertaceratops, as well as many chasmosaurines. Theepijugal 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 inDiabloceratops.[4][5]
The parietosquamosal neck frill at the back of the skull was formed by the fusedparietal 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 theoccipital 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 ofCentrosaurus,Achelousaurus, andEiniosaurus in overall shape, it greatly differs from them in the organization of the episquamosals and epiparietals. The frill has two large, ovalparietal 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 likeAvaceratops. 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 forward 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 downward 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]
Ceratopsids are mainly distinguished through features pertaining to their skull roofs, and the postcranial skeleton ofNasutoceratops is typical of the group. The three frontmost neck vertebrae of ceratopsids were fused into a syncervical vertebra, and that ofNasutoceratops is particularly similar to that ofStyracosaurus. 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 theircentra (or "bodies") being short from front to back and theirneural 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 ofStyracosaurus. Thetransverse processes at the sides of these vertebrae are elevated and have prominentzygapophyses (the processes of the vertebrae that articulated with the prezygapophyses of a following vertebrae), typical for the group.[4]
Thescapula (shoulder blade) is long and relatively slender, its hind part is flattened and flared, and is similar to those of other centrosaurines overall. Thecoracoid (part of theshoulder-girdle) is fused to the front end of the scapula, as is often the case in ceratopsids, and has a largeforamen (opening) at the front. Thehumerus (upper arm bone) is 475 mm (18.7 in) long, and has a hemispheric humeral head (upper part) and prominentdeltopectoral crest, which accounts for of almost half the whole length of the humerus, as common for the group. The humerus is long and slender, but otherwise typical. Theulna (one of two lower arm bones) is 400 mm (16 in) long and has a largeolecranon process where thetriceps muscle inserted. Theradius (the other lower arm bone) is thin with expanded ends, a general feature of ceratopsids.[4]
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 bytubercle (round nodule) shapedscales. 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 (includingPsittacosaurus,Chasmosaurus, andCentrosaurus). 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. Similarhexagram-like patterns were later observed on the limbs ofPsittacosaurus, 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 inChasmosaurus andCentrosaurus.[4][19]
Nasutoceratops was assigned to Centrosaurinae by Sampson and colleagues in 2013 based on features such as the premaxilla having a pronounced downward 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 lateCampanian age of theLate Cretaceous, and being contemporary with the derived northern centrosaurinesStyracosaurus andCentrosaurus,Nasutoceratops retained more "primitive" features, such as the maxillary tooth row being displaced downward, elongated brow horns, and pronounced epijugals, which were absent in other centrosaurines of the time. Thephylogenetic analysis of the study foundNasutoceratops to be thesister taxon ofAvaceratops from theJudith River Formation ofMontana, the two forming a previously unknown clade near the base of Centrosaurinae. They shared features such as simplified frills without prominent epiparietal ornamentation, and an undulation of the frill's midline instead of an indentation.[5]
Sampson and colleagues stated that the current knowledge indicated that centrosaurines originated onLaramidia (an island continent consisting of what is now western North America) 90–80million years ago, and that this group split near the base, with most known centrosaurines in one clade from north Laramidia that evolved towards having abbreviated or absent brow horns and more elaborate frills, andNasutoceratops andAvaceratops in the other, which de-emphasized their frill ornamentation in favor of enlarged brow horns. The late CampanianNasutoceratops lived about 2 million years later than the early CampanianAvaceratops, and their clade existed in both northern and southern Laramidia.[5] In their 2016 follow-up article, Lund and colleagues stated that the discovery ofNasutoceratops clarified overall patterns in centrosaurine evolution, and conducted aBayesian analysis of ceratopsians, the first for the group, which agreed with the results of the 2013 analysis.[4]
In 2016, the paleontologist Héctor E. Rivera-Sylva and colleagues reported a partial centrosaurine skeleton (specimen CPC 274) from theAguja Formation of Coahuila, Mexico, which grouped withAvaceratops andNasutoceratops in their phylogenetic analysis.[20] The following year, the paleontologist Michael J. Ryan and colleagues reported a centrosaurine skull (specimen CMN 8804) from theOldman Formation of Alberta, Canada, which they also found to group withNasutoceratops andAvaceratops. These authors named this new clade Nasutoceratopsini, withNasutoceratops as the type genus; this group was defined as all centrosaurines more closely related toNasutoceratops than toCentrosaurus, containingNasutoceratops,Avaceratops, MOR 692 (previously treated as an adultAvaceratops), CMN 8804, and another undescribed ceratopsian (specimen GPDM 63) fromMalta, 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, whereasNasutoceratops has several distinct adult features.[21] In 2017, the specimen from Mexico was namedYehuecauhceratops by Rivera-Sylva and colleagues, and formally assigned to Nasutoceratopsini.[22]
The paleontologist Sebastian G. Dalman and colleagues namedCrittendenceratops in 2018 based on two partial specimens from theFort Crittenden Formation of Arizona, and assigned the genus to Nasutoceratopsini. These authors foundYehuecauhceratops to be the sister taxon ofNasutoceratops within the group.[23] The 2021 phylogenetic analysis by Dalman and colleagues accompanying the description of the basal centrosaurineMenefeeceratops from theMenefee Formation ofNew Mexico did not result in Nasutoceratopsini forming amonophyletic (natural) group; all members were found to be basal centrosaurines, forming apolytomy, or unresolved group. They cautioned that more material, especially parietal bones, was needed to determine the position of potential nasutoceratopsins near the base of Centrosaurinae, as well as the potential membership ofMenefeeceratops to the group.[24] The paleontologist Hiroki Ishikawa and colleagues did recover Nasutoceratopsini as a natural, basal group in their 2023 analysis, and found the new genusFurcatoceratops from the Judith River Formation to be close toNasutoceratops. They did not includeYehuecauhceratops,Crittendenceratops, andMenefeeceratops in their analysis due to their fragmentary nature, and considered the presence of a well-developed squamosal ridge asynapomorphy (shared derived feature) of Nasutoceratopsini.[25]
Thecladogram below follows the 2023phylogenetic analysis by Ishikawa and colleagues, and shows the position ofNasutoceratops within Ceratopsidae:[25]
| Ceratopsidae |
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Sampson and colleagues stated in 2013 that the discovery ofNasutoceratops 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 northernAvaceratops was the sister taxon ofNasutoceratops, it was several million years older, and by the time ofNasutoceratops, 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 betweenStyracosaurus in the north andNasutoceratops in the south shows that these provinces were evolutionary centers forendemism. They also noted that, apart fromNasutoceratops, 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 likeDiabloceratops from Utah) and dispersed to the north 79 million years ago (as indicated byXenoceratops from Alberta), and theAvaceratops-Nasutoceratops clade was present in both north and south by 78.5–78 million years ago. Thenspeciation occurred after the northern and southern centrosaurines became isolated from each other, whileAvaceratops went extinct in the north, butNasutoceratops persisted in the south.[4]
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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 andPachyrhinosaurini), and thatcentrosaurines were loosely latitudinally distributed during the Late Cretaceous. While nasutoceratopsins occurred in both southern and northern Laramidia, centrosaurins dominated the lower northern Laramidian regions, and pachyrhinosaurins occurred only in the north. They suggested that nasutoceratopsin fossils are rare in the well-sampled Laramidian sediments because they may have had otherecological preferences or social behavior than the contemporary ceratosaurines of the clade Centrosaurini, which are often found in extensivebonebeds 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 namedMenefeeceratops 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 thatCrittendenceratops from Arizona, the so far youngest nasutoceratopsin, bridged theevolutionary gap between the slightly olderYehuecauhceratops 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 namingMenefeeceratops, 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]
In 2024, Loewen and colleagues discussed the high endemism and seemingly restricted distribution of centrosaurid species and why this was the case. They usedNasutoceratops as an example of a centrosaurine not documented from other stratigraphic units outside where it was originally found, and pointed out that while it may have been wide-ranging across southern Laramidia, no non-marine of the same age have been found elsewhere, and the preserved ranges therefore underestimate the true ranges. They also found that the Nasutoceratopsini (includingNasutoceratops andAvaceratops) have a known geographic range distance of 2,000 km (1,200 mi) and a range area of ca 200,000 km2 (77,000 sq mi), and along with similar patterns seen in other centrosaurines, they suggested these animals had a high level of endemism, where lineages evolved in isolation and then regional diversification that produced multiple species in the same areas.[26]
In 2016, Lund and colleagues stated that the functional adaptations associated with the very short and deep front part of the skull ofNasutoceratops were unknown; they suggested these may have been related to a change toward more derivedmasticatory functions in basal ceratopsians. Thismorphology increased the mechanical advantage during mastication by moving the beak closer to the joint of the lower jaw. The narial region ofNasutoceratops was deep mainly due to the premaxilla and maxilla having steeply rising, enlarged contact surfaces, but the function of this is unknown. This feature may have been connected to absorbing larger bite forces. Pneumaticity in the snout region has been associated with a variety of functions in vertebrates such as moisture exchange,shock absorption,vocal resonance, and weight reduction, but the function inNasutoceratops is unclear.[4] Sampson stated in a 2013 press release that the large snout probably did not have anything to do with a heightened sense of smell, sinceolfactory 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.[21] Ishikawa and colleagues noted in 2023 that only a single nasutoceratopsin specimen was recovered from each quarry in the Judith River Formation, which suggests they were solitary animals or rare in floodplain habitats, whereas other centrosaurines have been found in quarries with multiple individuals, indicating agregarious 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 twocoprolites (fossilized dung) from the Kaiparowits Formation which, due to their size, may have been produced by a member of one of three herbivorous dinosaur groups known from the formation: ceratopsians (includingNasutoceratops),hadrosaurs, orankylosaurs (the rarest of the three groups). The coprolites contained fragments ofangiosperm wood (which indicates a diet ofwoody browse); though there was previously little evidence of dinosaurs consuming angiosperms, these coprolites showed that dinosaurs adapted to feeding on them (angiosperms only became common in theEarly Cretaceous, diversifying in the Late Cretaceous). The coprolites also contained traces ofmollusc shell,arthropod cuticle, and lizard bone that may have been ingested along with the plant material. They were found near other herbivore coprolites that containedconifer wood. Ridgwell pointed out that the dental anatomies of ceratopsians and hadrosaurs (with dental batteries comprising continuouslyreplaced teeth) were adapted to process large quantities of fibrous plants. The different diets represented by the coprolites may indicateniche partitioning among the herbivores of the Kaiparowits Formationecosystem, or that there was seasonal variation in diet.[27]
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 inintraspecific signalling andintraspecific combat, with the debate focusing on eitherspecies recognition (driven bynatural selection) ormate competition (driven bysexual selection). Other ideas have ranged from protection against predators andthermoregulation. 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 includedAvaceratops andNasutoceratops reducing frill ornamentation but elaborating the brow horns, and the clade that indludedSpinops andPachyrhinosaurus 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 ofNasutoceratops, 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 modernbovids. 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 forTriceratops that could also apply toNasutoceratops; "single horn contact", "full horn locking", and "oblique horn locking". Farke and colleagues examinedpathologies (signs of disease, such as injuries and malformations) in the skulls ofTriceratops andCentrosaurus 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 forNasutoceratops.[4] The paleontologistGregory S. Paul suggested in 2016 that the forward directed horns ofNasutoceratops indicated a frontal thrusting action.[18]
Nasutoceratops is known from the Kaiparowits Formation of Utah, which dates to the late Campanian age of the Late Cretaceous epoch, andstratigraphically occurs in the formation's middle unit, which ranges 200–350 m (656.2–1,148.3 ft) inthickness, insediments dating to 75.51–75.97 million years ago. Specimen UMNH VP 19469 was found lower in the middle unit than the holotype. The formation wasdeposited in the southern part of abasin (the Western Interior Basin) on the eastern margin of Laramidia within 100 km (62 mi) of theWestern Interior Seaway, ashallow sea in the center of North America that divided the continent (the eastern landmass is known asAppalachia).[4][28][29] The basin was broad, flat, crescent-shaped, and bounded by mountains on all sides except the Western Interior Seaway at the east.[30] The formation represents analluvial to coastal plain setting that was wet, humid, and dominated by large, deep channels with stable banks and perennialwetland swamps, ponds, and lakes. Rivers flowed across the plains and drained into the Western Interior Seaway; theGulf Coast region of the United States has been proposed as a good modern analogue (such as the current dayswamplands of Louisiana). The formation preserves a diverse and abundant range of fossils, including continental and aquatic animals, plants, andpalynomorphs (organicmicrofossils).[31][6]
Otherornithischian dinosaurs from the Kaiparowits Formation include ceratopsians such as the chasmosaurinesUtahceratops andKosmoceratops (and possibly a second yet unnamed centrosaurine), indeterminatepachycephalosaurs, theankylosauridAkainacephalus, an indeterminatenodosaurid, the hadrosaursGryposaurus andParasaurolophus, and an indeterminate, basalneornithischian.Theropods include thetyrannosauridTeratophoneus, theoviraptorosaurHagryphus, an unnamedornithomimid, thetroodontidTalos, indeterminatedromaeosaurids, and the birdAvisaurus. Othervertebrates include crocodiles (such asDeinosuchus andBrachychampsa), turtles (such asAdocus andBasilemys),pterosaurs, lizards, snakes, amphibians, mammals, and fishes.[30][32][33] The two most common groups of large vertebrates in the formation are hadrosaurs and ceratopsians (the latter representing about 14 percent of associated vertebrate fossils), which may either indicate their abundance in the Kaiparowits fauna or reflectpreservation bias (a type of sampling bias) due to these groups also having the most robust skeletal elements.[3] Eggs from dinosaurs, crocodiles, and turtles have also been found.[34] The swamps and wetlands were dominated bycypress trees up to 30 m (98 ft) tall,ferns, and aquatic plants including giantduckweed,water lettuce, and other floating angiosperms. Better-drained areas were dominated by forests ofdicot trees up to 10–20 m (33–66 ft) tall and occasionalpalms, with anunderstory including ferns. Well-drained areas further away from wet areas were dominated byconifers up to 30 m (98 ft) tall, with an understory consisting ofcycads, small dicot trees or bushes, and possibly ferns.[30]
In 2010, the paleontologist Michael A. Getty and colleagues examined thetaphonomy (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 asandstone channellithofacies (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 turtleDenazinemys.[2]
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