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The structure and relationships of the horned dinosaur Arrhinoceratops Parks(Ornithischia: Ceratopsidae)
Canadian Journal of Earth Sciences
Abstract
Only the type specimen of Arrhinoceratops brachyops Parks can be assigned without question to the ceratopsid genus Arrhinoceratops. The original description, however, requires revision. Contrary to published accounts, a nasal horn core is present, the jugal cannot be characterized by an unusually long anterior process, and there is no nasal–rostral contact in this or any other known ceratopsian. Evidence for an interparietal is ambiguous. These and other observations necessitate a redefinition of the genus.Arrhinoceratops belongs to the long-squamosaled ceratopsids but is not closely related to any other genus in this lineage. With respect to characters of the frill, Torosaurus is the closest relative of Arrhinoceratops. Since the frills of Arrhinoceratops and Torosaurus form a graded series, the practice of automatically assigning isolated, fenestrated frills from Lance equivalent sediments to Torosaurus and from Horseshoe Canyon equivalent sediments to Arrhinoceratops should be abandoned.
... A caudally oriented narial strut is seen in Chasmosaurus irvinensis (Holmes et al., 2001) and derived C. belli , but the feature is developed to a greater extreme in CMN 8801, comparable to the condition seen in K. richardsoni . The only other chasmosaurines to show this feature are Anchiceratops ornatus (Mallon et al., 2011) and Arrhinoceratops brachyops (Tyson, 1981;Mallon et al., 2014). The posterior inclination of the narial strut and the proportionately tall snout result in a distinctive internal naris that is tall, anteroposteriorly narrow, and inclined posteriorly. ...
... The quadratojugal process of the jugal descends down steeply in lateral view, such that the quadrate lies just behind the orbit. A similar condition is seen in K. richardsoni as well as derived chasmosaurs such as Arrhinoceratops (Tyson, 1981;Mallon et al., 2014) and triceratopsins (Hatcher et al., 1907). By contrast, the quadratojugal process of the jugal is more posteroventrally oriented in Chasmosaurus, and the quadrate is more posteriorly located (Godfrey and Holmes, 1995). ...
The upper Campanian of the American Southwest has produced dinosaurs that are unknown from the northern Great Plains and vice versa. This has led to the idea that North America's Campanian dinosaur fauna was characterized by high levels of endemism and distinct faunal provinces. Here, two horned dinosaurs known from the Southwest, Pentaceratops and Kosmoceratops, are described from southern Canada. Pentaceratops aquilonius sp. nov. is represented by two frill fragments from the uppermost Dinosaur Park Formation near Manyberries, southeast Alberta. Features shared with Pentaceratops include large, triangular epiparietals, an M-shaped parietal posterior bar, and an epiparietal P1 that curls up and twists laterally. The Manyberries specimens differ from Pentaceratops sternbergii and Utahceratops gettyi in that the posterior bar is broader, emargination is weakly developed, and P1 is directed dorsally, rather than anteriorly. Phylogenetic analysis places P. aquilonius as sister to a clade comprising P. sternbergii and Utahceratops. Kosmoceratops is documented by a partial skull from Dinosaur Provincial Park. Previously referred to Chasmosaurus, the skull exhibits derived features inconsistent with this referral, including a reduced septal flange, a caudally inclined narial strut, a triangular narial process, a reduced frontal fontanelle, a weakly hooked rostral, and a narrow, caudally inclined internal naris. Phylogenetic analysis recovers the animal as sister to Kosmoceratops richardsoni, but differences in the shape of the naris and nasal horn suggest that it likely represents a distinct species. The presence of Pentaceratops and Kosmoceratops in Canada argues against the idea of distinct northern and southern faunal provinces, but the fact that they differ from their southern relatives confirms that endemism was high in the Campanian. The ability of dinosaur lineages to disperse long distances across North America suggests that dinosaur distribution was not constrained by geographic barriers, climate, or flora. Instead, dinosaur endemism may result from competitive exclusion of immigrants by established populations adapted to local environmental conditions.
... Vascular sulci, another characteristic of T. latus (Lawson 1976: 163), cannot be detected on this specimen due to its fragmented state. Tyson (1981Tyson ( : 1246 has suggested that "isolated ceratopsian frill fragments from Lance equivalent or Horseshoe Canyon equivalent sediments showing thin parietals, minor undulations of the edges of the squamosals, circular or elliptical parietal fenestrae of moderate size should be classified as "Ceratopsidae, incertae sedis." Apart from Torosaurus, the only similar ceratopsian is Arrhinoceratops brachyops Parks. ...
... It is a thin, blade-like bone that gradually tapers posteriorly, as is typical of chasmosaurines. The distal end is expanded to a greater degree than in basal chasmosaurines such as Chasmosaurus belli, Mojoceratops perifania, and Pentaceratops sternbergi, but is similar to the condition in Anchiceratops ornatus (Mallon et al., 2011) and Arrhinoceratops brachyops (Tyson, 1981;Mallon et al., 2014). The squamosal is not expanded to the same extent as in triceratopsins such as Eotriceratops xerinsularis (Wu et al., 2007), Ojoceratops fowleri (Sullivan and Lucas, 2010), Torosaurus utahensis (Sullivan et al., 2005), and Triceratops spp. ...
The horned dinosaurs (Ceratopsidae) were a diverse family of herbivorous dinosaurs originating in the Late Cretaceous in western North America (Laramidia). As one of the most species-rich dinosaur groups, their diversity and distribution are important to understanding Cretaceous dinosaur evolution. Ceratopsids have previously been hypothesized to have high levels of endemism despite inhabiting a relatively small land mass with few barriers to dispersal. Here, we document a new chasmosaurine ceratopsid, Sierraceratops turneri gen. et sp. nov., from the Upper Cretaceous (latest Campanian–Maastrichtian) Hall Lake Formation of south-central New Mexico, consistent with the hypothesis that southern Laramidia supported an endemic dinosaur fauna. Sierraceratops is distinguished by its relatively short, robust, and mediolaterally compressed postorbital horns; a flattened medial ridge on the posterior end of the pterygoid; a jugal with pronounced anterior flanges; a long pyramid-shaped epijugal horncore; a D-shaped cross section of the median parietal bar; and a squamosal with a pointed tip and low episquamosal ossifications. Phylogenetic analysis recovers Sierraceratops as sister to Bravoceratops and Coahuilaceratops, part of a clade endemic to the southwestern United States and Mexico. Sierraceratops adds to the diversity and disparity of the Chasmosaurinae in the Late Cretaceous and provides additional evidence for Laramidian endemism. Together with Sierraceratops, the Hall Lake Formation dinosaur fauna suggests that the latest Cretaceous of southern Laramidia was characterized by endemic clades and distinct community structures.
... Only the forelimb of Torosaurus latus has been described and illustrated (MPM VP6841; Johnson and Ostrom, 1995). Arrhinoceratops is known only from a single skull (Tyson, 1981). As a result, the postcranial material of TMM 41361 can be adequately compared with Chasmosaurus mariscalensis, Pentaceratops sternbergi, Triceratops horridus, and to a limited extent Torosaurus latus. ...
... The incomplete right maxilla (Fig. 2) is 152 mm long and 93 mm tall, as preserved. The flattened anterior articular face for the premaxilla is steep (approximately 63°relative to tooth row), consistent with an abbreviated snout as in adult Arrhinoceratops (Parks, 1925;Tyson, 1981;Mallon et al., 2014). The body of the element is triangular in lateral view, but the jugal and alveolar processes are broken posteriorly. ...
Disentangling ontogenetic from interspecific variation is key to understanding biodiversity in the fossil record, yet information on growth in the ceratopsid subfamily Chasmosaurinae is sparse. Here, we describe the partial skull of a juvenile chasmosaurine, attributed to Arrhinoceratops brachyops, within the context of more mature specimens of this species, to better understand the ontogenetic transformations therein. We show that as A. brachyops matured, the postorbital horncores became longer and shifted from a posterior to an anterior inclination, the delta-shaped frill epiossifications became lower and fused to the underlying frill, and the face became more elongate. In these respects, A. brachyops closely resembled Triceratops, suggesting that these ontogenetic changes may have been common to all long-horned chasmosaurines. However, an event-paired cladistic analysis of Chasmosaurinae using a standardized matrix of 24 developmental characters reveals that the relative timing of ontogenetic events in Arrhinoceratops was more like that of Chasmosaurus, particularly in the relatively late reduction in scalloping around the frill margins. Thus, the ontogenetic similarities between Arrhinoceratops and Triceratops appear to be plesiomorphic, partly related to the retention of the elongate postorbital horncores, which are primitive for Ceratopsidae. This study elucidates the otherwise contentious evolutionary relationships of Arrhinoceratops, and highlights the importance of ontogenetic data for resolving phylogenies when morphological data from adults alone are inadequate. © 2015 The Linnean Society of London
... In lateral view, it extends rostrally beyond the nasal horncore. This is in contrast to the condition observed in the coeval Arrhinoceratops (Parks, 1925;Tyson, 1981), in which the horncores are shorter and more strongly procurved, although not as short as in CMN 8535. The narrow frontoparietal fontanelle opens to reveal a simple frontoparietal depression that excavates the supraorbital horncores proximally. ...
Arrhinoceratops brachyops is a poorly understood chasmosaurine ceratopsid from the Upper Cretaceous Horseshoe Canyon Formation of Alberta, previously described on the basis of only a single skull. Here, we report on a second specimen attributable to this species, including a relatively complete skull, syncervical, and partial left forelimb. This second specimen clarifies aspects of morphology not visible in the holotype, and also elucidates variation in A. brachyops. The species is distinguished by a square-shaped triangular process of the premaxilla, a steeply inclined triturating surface of the predentary, and a triangular nasal horncore in horizontal section. The dentary is also distinctive in bearing a bony lateral ridge similar to that of Anchiceratops ornatus, but more strongly developed. Phylogenetic analysis cannot resolve the relationships of Arrhinoceratops beyond the level of Chasmosaurinae, owing to both missing data and conflicting characters. However, we do find some support for a deep split within Chasmosaurinae, contrary to conventional topologies. We also report on other fragmentary specimens plausibly attributable to A. brachyops that suggest a minimum age range of approximately 750 ka for this species.
... In lateral view, it extends rostrally beyond the nasal horncore. This is in contrast to the condition observed in the coeval Arrhinoceratops (Parks, 1925;Tyson, 1981), in which the horncores are shorter and more strongly procurved, although not as short as in CMN 8535. The narrow frontoparietal fontanelle opens to reveal a simple frontoparietal depression that excavates the supraorbital horncores proximally. ...
Anchiceratops is a chasmosaurine ceratopsid from the Upper Cretaceous Horseshoe Canyon Formation (HCF) of Alberta. It is distinguished primarily by its unique parietosquamosal frill ornamentation and possibly by the presence of a ventrally flexed olfactory bulb of the brain. Although Anchiceratops is known from at least ten partial skulls, only two of these have been formally described. These skulls are not stratigraphically segregated, but they differ markedly in their proportions (e.g., supraorbital horncore and frill dimensions), causing previous authors to account for this disparity with reference to either interspecific or sexual differences. Both of these hypotheses assume that variation in Anchiceratops is dimorphic; however, this assumption has never been tested with reference to all available material. The present study describes all material from the HCF that can be positively attributed to Anchiceratops, and tests the assumption of dimorphism by subjecting this material to a series of morphometric analyses. We find no compelling evidence for dimorphism in Anchiceratops, although sample size is still too small for convincing statistical support. We conclude that there is a single, variable species of Anchiceratops, A. ornatus. Average sedimentation rates for the HCF suggest that A. ornatus is a particularly long-lived species compared with other ceratopsids (∼1.5–2.0 Ma), and the paleoecological implications of this are discussed. A cladistic analysis that includes the new data presented here indicates that Anchiceratops is more closely related to Chasmosaurus than to Triceratops, in contrast with previous studies.
In connection with the excavation of the Danek Bonebed in 2011, a half-metre long, well preserved right ceratopsian orbital horncore was recovered. The horncore belongs to the taphonomic group of larger, heavier elements from the bonebed. So far, no other ceratopsian elements have been identified from the bonebed. Ceratopsids from the Horseshoe Canyon Formation of southern Alberta include Anchiceratops, Arrhinoceratops, Eotriceratops, and Pachyrhinosaurus. The size, proportions, and gently anterolaterally procurving morphology of the horncore indicates that it is from a chasmosaurine ceratopsid. There is weak morphological information to suggest that it may represent Anchiceratops ornatus, which is the most common chasmosaurine at this stratigraphic level. The base of the specimen has been hollowed out by a sinus system, which in conjunction with its large size indicates it is probably from a mature animal. The rarity of ceratopsian remains in this and other hadrosaur bonebeds suggests horned dinosaurs were excluded from anywhere that was occupied by herds of large numbers of Edmontosaurus.
The Upper Cretaceous deltaic and fluvial strata lying between the marine Bearpaw and nonmarine Paskapoo Formations along the eastern side of the Alberta Syncline have been known, for many years, as the Edmonton Formation. Several subdivisions of these strata have been made based on lithologic differences in the exposure along Red Deer River valley. Owing, however, to the interlensed nature of the beds and lack of widespread marker zones, these divisions are useful for local correlation only.
The Whitemud and Battle units within the Edmonton succession have been correlated with the Whitemud and Battle Formations of southeastern Alberta. Together the two units are easily recognized in outcrop and form a marker zone for field mapping; the Battle Formation is readily distinguished also on electric logs of drilled wells and is, therefore, an excellent datum for subsurface correlation. Furthermore, the Kneehills tuff bed within the Battle unit is a time marker. Field work has shown that the lithology of these units is similar throughout the southern Plains of Alberta and, together, they are the only reliable lithologic marker above the marine Bearpaw Formation.
Paleontology, particularly the vertebrate dinosaurian fauna, lends support to a division of the strata above and below the Whitemud and Battle units.
For these reasons the Whitemud and Battle units have been given formational status and the name Horseshoe Canyon Formation is proposed for the nonmarine strata between the Bearpaw and Whitemud Formations. The three formations; Horseshoe Canyon, Whitemud, and Battle are considered to comprise the Edmonton Group.
Owing to the difficulty in defining the rather obscure boundary between Upper Cretaceous strata above the Battle and the overlying Paskapoo Formation it is considered preferable to include those beds, of Lance age, in the Paskapoo Formation. Such a revision results in an upper and a lower boundary for the Edmonton Group that are easily recognized both in outcrop and on mechanical logs of drilled wells.
9001, I have 3-5, 20-29, 50-57, 68-69, 140-143, 156-157
Ceratopsian dinosaurs were characterized by a number of peculiar features that set them apart from all other tetrapods. The development of these features, reflected to varying degrees in the array of North American genera, constituted the major evolutionary trends within the group. Some of these have been noted before, others have not. The most conspicuous evolutionary developments were 1) extreme enlargement of the head, 2) two divergent trends of frill enlargement, 3) the development of large turtle-like beaks, 4) the perfection of unique shearing dentitions, 5) a general tendency for increased size, 6) increased quadrupedalism, and 7) development of either brow or nasal horns. The first four of these are related directly to problems of food-gathering or preparation, and are considered in detail here. The origin and enlargement of both long (Torosaurus type) and short (Triceratops type) parieto-squamosal frills is correlated with extreme enlargement of the jaw muscles (M. adductor mandibulae externus) that attached to the coronoid process. The resultant magnification of jaw power is believed to have been related to the unusual shearing dentition of advanced ceratopsians. Perfection of the shearing dentition involved 1) development of a long edentulous anterior jaw segment behind the beak, 2) a progressive increase in the number of tooth positions in the tooth row, 3) longitudinal compaction of tooth rows to unite individual teeth into long, continuous dental batteries, 4) increase in tooth replacement rate, 5) enlargement of tooth size, 6) increased transverse curvature of tooth root and crown, 7) lateral displacement of upper teeth relative to lower teeth, 8) increase in size of the central carina of tooth crowns, and 9) a progressive backward displacement of the entire tooth row. Except for Leptoceratops, all post-Protoceratops taxa reflect each of these modifications to varying degrees. Associated with these changes were structural alterations in the design of the mandibular lever. The short-frilled line is shown to have been characterized by progressive improvement in the jaw mechanics, resulting in progressively greater leverage for the jaw muscles in successive forms. This was effected by an increased height of the coronoid process, increased depression of the jaw articulation, and lowering of the angle of muscle application. The long-frilled line cannot now be analyzed completely, because of a lack of critical material of the latest members of the lineage, but limited analyses indicate that this line may not have been characterized by comparable mechanical improvements in the mandibular lever. This may be the reason for the development of much longer parieto-squamosal frills in the Torosaurus line, reflecting the greater size of the external adductor muscles. Exclusive shearing dentitions, efficient and powerful jaw mechanics, and extremely large jaw muscles equipped these reptiles to feed on a peculiar unknown diet. Whatever this diet was, it clearly was very resistant and probably very fibrous-perhaps like the fronds of cycads, or palms.
Thesis (M. Sc.)--University of Alberta, 1977. Includes bibliographical references (leaves 321-339). Microfiche of typescript.
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