A caenagnathid oviraptorosaur metatarsal from the Mesaverde Formation (Campanian), Wyoming

A well-preserved left theropod metatarsal I from the Campanian Mesaverde Formation of Wyoming is described and identified as belonging to a caenagnathid, representing the first occurrence of this clade from the formation. The specimen is unique in being relatively small, but featuring a suite of characters (triangular shaft, less constriction between the shaft and the distal condyle, spherical distal condyle) that are seen in larger examples of Caenagnathidae such as Anzu wyliei or “Macrophalangia canadensis”. This suggests that the previously-observed differences in metatarsal I between small and large caenagnathids are not solely the result of allometry, but may represent phylogenetically informative variation. Although limited, this new specimen lends some support to the hypothesis that “Macrophalangia canadensis” does not represent a large Chirostenotes pergracilis. Furthermore, the specimen is important in establishing the presence of caenagnathids within the Mesaverde Formation fauna, in which theropod remains are poorly known.

Constraining the body mass range of Anzu wyliei using volumetric and extant-scaling methods

The ability to accurately and reliably estimate body mass of extinct taxa is a vital tool for interpreting the physiology and even behavior of long-dead animals. For this reason, paleontologists have developed many possible methods of estimating the body mass of extinct animals, with varying degrees of success. These methods can be divided into two main categories: volumetric mass estimation and extant scaling methods. Each has advantages and disadvantages, which is why, when possible, it is best to perform both, and compare the results to determine what is most plausible within reason. Here we employ volumetric mass estimation (VME) to calculate an approximate body mass for previously described specimens of Anzu wyliei from the Carnegie Museum of Natural History. We also use extant scaling methods to try to obtain a reliable mass estimate for this taxon. In addition, we present the first digital life restoration and convex hull of the dinosaur Anzu wyliei used for mass estimation purposes. We found that the volumetric mass estimation using our digital model was 216-280kg, which falls within the range predicted by extant scaling techniques, while the mass estimate using minimum convex hulls was below the predicted range, between 159-199 kg . The VME method for Anzu wyliei strongly affirms the predictive utility of extant-based scaling. However, volumetric mass estimates are likely more precise because the models are based on comprehensive specimen anatomy rather than regressions of a phylogenetically comprehensive but disparate sample.

A histological investigation of dental crown characters used in mosasaur phylogenetic analyses

Mosasaur researchers have used varieties of tooth crown ornamentation as diagnostic and phylogenetic characters for decades. Such tooth crown features include facets, flutes, striations, serrated carinae, and coarse anastomosing texture. This study investigates the relative contribution of dentine and enamel to the development of these dental characters and assesses possible homologies between these structures. Histological analysis of isolated mosasaur teeth revealed that flutes and facets develop initially from the dentine, and the external enamel morphology we observe macroscopically mirrors the shape the underlying dentine. Striations combine underlying contributions from the dentine with additional and irregular enamel deposition that results strictly from amelogenesis. In both serrated carinae and anastomosing texture the border between the dentine and the enamel is smooth, and these external ornamentations form through variations in enamel development. Based on these observations, we infer that flutes and facets are part of a morphological spectrum and should not be treated as separate phylogenetic characters. Conversely, striations develop differently than flutes and facets, and should therefore be treated as a distinct character. We recommend referring to the “serrations” on mosasaur carinae as crenulations to differentiate these enamel-only structures from true denticles possessing a dentine core. Anastomosing texture can also coincide with significant apical thickening, both of which could be adaptations for processing hard-shelled prey. Care must be taken when using tooth crown features as diagnostic or phylogenetic characters because seemingly different morphologies can have similar developmental origins, and tooth morphology can be more closely tied to diet than to common ancestry.

New species of the ground sloth Parocnus from the late Pleistocene-early Holocene of Hispaniola

Parocnus dominicanus sp. nov. represents a new species of megalonychid ground sloth from theAltagracia Province of southeastern Dominican Republic. Specimens of multiple individuals, including oneassociated partial skeleton, were recovered from two separate underwater caves in the Parque Nacional delEste through collaborations with museums and cave divers between 2009–2013. Parocnus dominicanus sp.nov. is distinguished by its small size compared to that of P. serus, with percent differences in limb elementlengths ranging from 13−24%. Numerous cranial and post-cranial elements also exhibit morphological characterstates that are not attributable to size variations. The recovery of multiple individuals within each localitydemonstrates a size dimorphism, possibly sexual, which parallels patterns exhibited by P. serus. The twospecies are also geographically distinct, with no examples of co-occurrence at any localities to date. Parocnusdominicanus sp. nov. and P. serus share character states that are distinct from those of the Cuban species, P.browni, and which suggest differential usage of the forelimb. The exact age of the specimens described here isunknown, however, Parocnus has been dated to the Holocene in Haiti.http://zoobank.org/urn:lsid:zoobank.org:pub:12E495D3-E261-4522-9854-D3B4C2D5FFB8

A comparative morphological study of the sixth and seventh spinous processes of the cervical vertebrae in extinct and extant species of Equus.

The lateral profile of the 6th and 7th cervical spinous processes (CSPs) were examined in four extantspecies of Equus (n=33); E. caballus (n=26), E. przewalskii (n=3), E. quagga boehmi (n=1), E. asinus (n=3)and compared to pre-domesticated Equus specimens (n=66) representing three known species: E. occidentalis(n=56), E. mosbachensis (n=2), E. curvedins/insulatis (n=1) and unknown Equus species (n=7) from five museums.Six common morphological profiles were revealed: cuneate, curvate, falcate, rudimentary, scalenate,and truncate. For the 6th CSP, the distribution of these morphologies amongst extant Equus is: cuneate, onlyE. asinus; curvate, E. caballus and E. przewalskii always in combination with ligamentum lamina nuchae (lig.lamina nuchae) attachments from the 2nd through to 7th CSP inclusive; falcate, E. caballus and E. przewalskiialways in combination with lig. lamina nuchae attachments from the 2nd through to 7th CSP inclusive;rudimentary, E. caballus always associated with lig. lamina nuchae attachments from the 2nd through to 5thCSP inclusive; scalenate, E. caballus in association with lig. lamina nuchae attachments from the 2nd throughto 5th (n=11) or 7th (n=4) CSP inclusive; truncate, not present. The 6th CSP in museum specimens of Equusexhibits one of four profiles: cuneate (n=10), curvate (n=14), scalenate (n=11) and truncate (n=4). For the 7thCSP, the distribution of these morphologies amongst extant Equus is: curvate, E. caballus mostly associatedwith lig. lamina nuchae attachments from the 2nd through to 5th CSP inclusive, falcate, E. caballus mostly associatedwith lig. lamina nuchae attachments from the 2nd through to 7th CSP inclusive, scalenate, E. caballusassociated with lig. lamina nuchae attachments from the 2nd through to 5th CSP inclusive. Only Rancho LaBrea and Tar Pits Museum provided samples suitable for examination of the 7th CSP. These exhibited fourprofiles: curvate (n=7), falcate (n=11), scalenate (n=2), and truncate (n=7). These findings suggest that thelateral profile of the 6th CSP is of potential use in identification of species; attachments of the lig. lamina nuchaealter the morphology of the 6th and 7th CSP; and that attachments of the lig. lamina nuchae on the 2ndto 7th CSP were likely present in species of Equus prior to domestication.

CSVP 2021 abstracts

volume for 2021 virtual online meeting of the Canadian Society of Vertebrate Palaeontology

New mid-cervical vertebral morphotype of Spinosauridae from the Kem Kem Group of Morocco

An unusual mid-cervical vertebra belonging to a large spinosaurid from the Cenomanian Kem Kem Group of Morocco is described. It is compared to the characteristic morphology of each reconstructed cervical position in Spinosaurus aegyptiacus, based on a recent composite reconstruction that incorporates most previously referred material from this unit. Rather than conforming to any of the previously identified cervical positions in its morphology, the specimen displays a unique combination of mid-cervical characters, with the relatively compact centrum suggesting a position as C4, and the form of the neural arch laminae suggesting a position as C5 or C6. Furthermore, it displays two characters that are previously unknown in spinosaurid mid-cervicals from the Kem Kem Group: a rounded hypapophyseal tuberosity that is not continuous with a ventral keel, and a moderately developed, dorsally oriented epipophysis that does not overhang the postzygapophysis posteriorly. The diagnostic value of positionally variable cervical vertebral characters in spinosaurid systematics is discussed. Although limited, the new data could lend support to the controversial hypothesis that two spinosaurid taxa are represented in the Kem Kem Group.

A comparative morphological study of the ligamentum lamina nuchae and ligamenta interspinalia reveals enthesis patterns at the sites of attachment from the second to seventh cervical vertebrae in four extant species of Equus

Morphological variation in the attachment sites of the ligamentum lamina nuchae and ligamentainterspinalia to the 2nd to 7th cervical vertebrae is described in four species of Equus, and enthesis patterns inrelation to these attachment sites are explored. This comparative study provides new insights with respect tothis variation in the zebrine and asinine clades within Equus. In zebrines (Equus caballus, E. quagga boehmiand E. przewalskii), the ligamentum lamina nuchae attaches to the eminence of the cervical dorsal spinesfrom either the 2nd to 5th, and or 2nd to 7th. These attachments resemble digits and between each digit anaperture is apparent. The ligamenta interspinalia attach to the base of each cervical dorsal spine from the 2ndto 7th before progressing caudally onto the thoracic dorsal spines. Three enthesis patterns per cervical dorsalspine correspond to the size and shape of these ligaments. In contrast, in asinines (as represented by Equusasinus), the ligamentum lamina nuchae attaches without digitation to the complete sagittal ridge of the cervicalvertebra including the dorsal spine and exhibits no ligamenta interspinalia. Consequently, the enthesispattern is represented by a raised sagittal ridge only, excluding the 7th cervical dorsal spine. These differencesbetween the ligamentum lamina nuchae and ligamenta interspinalia attachment sites create distinct enthesispatterns that differentiate zebrines from asinines. Findings include: differing ligamentous morphology; associatedenthesis patterns corresponding to attachment sites of the ligaments to the cervical vertebrae; influencesin dorsal spine morphology subject to the presence or absence of the ligaments; and the postulation ofevolutionary functional adaptions in response to environmental influences between the two Equus clades.These results may be useful for palaeontologists in the identification of isolated cervical vertebrae.

A chasmosaurine ceratopsid premaxilla from the basal sandstone of the Hell Creek Formation, Montana

A well-preserved large chasmosaurine ceratopsid premaxilla (MOR 1122 7-22-00-1) collected from the basal sandstone of the Cretaceous Hell Creek Formation (HCF) represents one of the stratigraphically lowest ceratopsid occurrences in the formation. The specimen was discovered in 2000, during the excavation of a large Torosaurus latus skull (MOR 1122) which was later hypothesized to represent an advanced growth stage of the more commonly recovered HCF ceratopsid Triceratops. MOR 1122 7-22-00-1 compares favorably with the incomplete premaxillae of the MOR 1122 skull and reveals details of premaxilla morphology from this stratigraphic zone. It preserves large, closely spaced ventromedial foramina, a narrow triangular process, and a thin septal flange at the base of the narial strut. The nasal process is narrow, caudally inclined and has a forked dorsal surface which appears to represent an intermediate between the morphology expressed in the slightly stratigraphically lower ceratopsid Eotriceratops xerinsularis from the Horseshoe Canyon Formation of Alberta and specimens recovered higher in the HCF. MOR 1122 7-22-00-1 expresses a deep recess extending medial to the strut of the triangular process, a feature shared with other HCF ceratopsid specimens but not Eotriceratops or other earlier occurring triceratopsin taxa. The morphology of MOR 1122 7-22-00-1 is consistent with noted stratigraphic trends in HCF ceratopsids and highlights the increased complexity of the narial region in uppermost Cretaceous triceratopsins.

Caenagnathids of the Dinosaur Park Formation (Campanian) of Alberta, Canada: anatomy, osteohistology, taxonomy, and evolution

Our understanding of caenagnathid anatomy, diversity, and ecology has improved considerably in the past twenty years, but numerous issues still remain. Among these, the diversity and taxonomy of caenagnathids from the Dinosaur Park Formation of Alberta, Canada, have remained problematic. Whereas some authors recognize three genera, others suggest only two were present, and there is considerable disagreement about which specimens are referable to which genus. This study aims to resolve this issue by reviewing the known specimens and using osteohistology, to establish a testable taxonomic framework of Dinosaur Park Formation caenagnathids. Numerous new specimens from all regions of the skeleton provide insight into morphological variation in caenagnathids, and three morphotypes are recognized based on a combination of morphological features and body size. Osteohistology shows that representatives in each body size class are at skeletal maturity, and therefore supports the delineation of three taxa: the smaller Citipes elegans gen. nov., the intermediate Chirostenotes pergracilis, and the larger Caenagnathus collinsi, new material of which shows it rivalled Anzu wyliei in size. However, these analyses also raise concerns about the referral of isolated material to each taxon in the absence of skeletal overlap between specimens or osteohistological analysis. Caenagnathids are consistently recovered throughout the Dinosaur Park Formation interval, and two geographic clusters of increased abundance probably reflect collection and taphonomic biases. The coexistence of three taxa was apparently facilitated by differences in both adult body size and functional morphology of the dentary and pes, which suggests that caenagnathids minimized niche overlap rather than subdividing niche space. Regardless, little is known of the exact roles caenagnathids played in Late Cretaceous ecosystems. Incorporation of the new material and taxonomic framework into a phylogenetic analysis drastically improves our understanding of the relationships between caenagnathines, and sheds light on the evolution of body size in caenagnathids and its role in their diversification.