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We present the first detailed account of cranial ontogeny in a fossil marsupial. An exceptionally well-preserved ontogenetic sample representing 26 individuals of Nimbadon lavarackorum (Diprotodontidae, Zygomaturinae) is described from a 15 million-year-old cave deposit in the Riversleigh World Heritage Area, Queensland. Based on comparison with one of N. lavarackomrris closest living relatives, the common wombat (Vombatus ursinus), the N. lavarackorum sample represents developmental stages spanning suckling pouch young through to elderly adults. In addition to documenting ontogenetic changes, reduced major axis regression analyses of 14 cranial and seven mandibular measurements were used to analyze allometric growth. Early growth patterns in the cranium are comparable to those of other marsupials such that the bones of the facial portion of the cranium develop precociously compared with those of the neurocranium. Most differences between adult and juvenile crania result from reorganization of structures associated with the cranio-mandibular joint and the developing dentition and strengthening of areas for insertion of the muscles of mastication. These changes reflect the transition from a purely suckling function to one focused on mastication of leaves. The sample also provides a unique view into the development of the extraordinarily complex endocranial sinuses characteristic of diprotodontid marsupials.
A complete dentition of Edaphodon hesperis, sp. nov., is described from the Upper Cretaceous (lower Campanian) Haslam Formation of Vancouver Island, British Columbia, Canada. It is one of the complete specimens for Edaphodon, most species of which are known only from incomplete toothplates. This is the first Cretaceous Edaphodon from western North America, extending the geographical range of the genus from its original distribution in Australia, Europe, New Zealand, and eastern North America. The specimen also extends the stratigraphic range of the genus in North America to the lower Campanian. Edaphodon hesperis, sp. nov., is characterized by a deep symphyseal surface and a distally located posterior outer tritor with reduced size on the mandibular toothplate. The vomerine toothplate has six tritorial pads on the oral surface. A phylogenetic analysis based on discrete characters of the mandibular toothplate indicates that the new species is basal among the eight species of this genus for which a nearly complete mandibular toothplate is known. A linear discriminant analysis shows that the new species is morphologically distinct from four other Edaphodon species based on continuous characters on the mandibular toothplates.
A lag deposit that separates the underlying late Maastrichtian Arkadelphia Formation marl from the overlying Paleocene Midway Group limestone in Hot Spring County, Arkansas, U.S.A., contains osteichthyan teeth, scales, and skeletal elements belonging to: Cylindracanthus ornatusLeidy, 1856, Atractosteus sp., Lepisosteus sp., cf. Hadrodus priscusLeidy, 1857, Pseudoegertonia cf. P. granulosus (Arambourg, 1952), Paralbula caseiEstes, 1969, Enchodus feroxLeidy, 1855, Enchodus gladiolus (Cope, 1872), Enchodus petrosus (Cope, 1874), Enchodus sp., and Teleostei incertae sedis. Outcrop exposures of this lag deposit occur within the Ouachita River and are expressed as a series of partially submerged, steeply inclined fold limbs that strike obliquely to water flow. The co-occurring osteichthyans recovered in this study span a broad range of salinity tolerances, foraging behaviors, and dietary preferences. Concentration of these osteichthyans indicates transport, exhumation, and reburial associated with storm activity or sea level cyclicity across a shallow Late Cretaceous marine shelf. Arkadelphia—Midway osteichthyan taxa belong to groups that survive the Cretaceous—Paleocene extinction event.
The early Eocene great lakes of the Green River system preserved a rich fauna, allowing detailed study of the paleoecology of the area. Two genera, †Priscacara and †Mioplosus, are interesting because they are among the earliest well-known representatives of Percoidei sensu lato, and so offer a chance to explore the evolution of the North American fish fauna. A phylogenetic analysis including †Priscacara, †Mioplosus, and representatives of some ‘basal’ percoid families suggests that †Priscacara is a member of Moronidae, and that †Mioplosus has affinities with Lateolabrax, Siniperca, and Lates. †Priscacara is recovered as paraphyletic relative to the rest of Moronidae, primarily on the basis of meristic characters; in the absence of more robust evidence, both †P. serrata and †P. liops are retained within †Priscacara. The phylogenetic position of †Priscacara suggests a trans-Atlantic connection, because Moronidae contain genera from eastern North America and Europe. †Mioplosus is suggestive of an Asian link to the Eocene Green River system, due to its relationship with the Western Pacific Lateolabrax, the Asian Siniperca, and the African/Asian Lates.
We describe herein the only known fossil dipnoans from Uruguay, recovered from continental deposits of Kimmeridgian—?early Cretaceous age (Batoví Member of the Tacuarembó Formation). The material includes several tooth plates referred herein to “Ceratodus” tiguidiensisTabaste, 1963 (the current generic assignment being either Arganodus or Asiatoceratodus), and one to Ceratodus africanusHaug, 1905. “C.” tiguidiensis was so far only recorded in the Upper Jurassic—Lower Cretaceous of Saharan Africa and the ‘middle’ Cretaceous of Brazil (and perhaps the Lower Triassic of Australia), and C. africanus in the Lower to Upper Cretaceous of Saharan Africa and the ‘middle’ Cretaceous of Brazil. Hence, these are the oldest and southernmost South American records of both taxa, and the oldest and southernmost record of C. africanus in the world. These findings reveal an unrecognized dipnoan diversity in South America prior to ‘middle’ Cretaceous times. In the Late Jurassic-Early Cretaceous of western Gondwana only the ceratodontiform genera Ceratodus, Arganodus/Asiatoceratodus, and Retodus were present, Neoceratodus being absent. The Tacuarembó Formation paleoichthyofauna comprises a low-diversity freshwater assemblage including, besides dipnoans, putative semionotids (the most abundant fossils) and hybodontid sharks.
Ichthyosaurs remains from the Albian and Cenomanian of Wyoming have been assigned to Platypterygius americanus, but apart from structures of the distal humerus, few other unequivocal character states have been proposed to differentiate this species from its congeners. The purpose of this study was to reevaluate the postcranial morphology of Platypterygius americanus, in order to assess the validity of this species and distinguish postcranial traits relevant for specific diagnoses. Several applicable features were identified, including the location of extrazeugopodial facets on the distal humerus and femur, shape of the intermedium, relative degree of fusion within the atlas-axis complex, number of presacral centra, and varying lengths of the anterior caudal centra. Comparative assessment suggests that Platypterygius americanus is a valid taxon, and that it is possible to differentiate the various Platypterygius spp. independent of stratigraphical and/or geographical occurrence data. Nevertheless, a future review of cranial morphology in all Platypterygius spp. is necessary to bolster these conclusions.
A detailed re-description and revised diagnosis is given for Macroplata tenuiceps Swinton, 1930, a plesiosaurian known from a single almost complete specimen (BMNH R5488) from the Blue Lias Formation (Hettangian) of Harbury, Warwickshire, U.K. The Early Jurassic was an important time in the early evolution of the clade Plesiosauria and saw its diversification into two superfamilies, Plesiosauroidea and Pliosauroidea. As one of the earliest nearly complete, well-provenanced plesiosaurians known, M. tenuiceps is important for understanding early plesiosaurian evolution. Three new autapomorphies for Macroplata tenuiceps are presented, confirming the validity of this taxon: a triangular emargination in the posterior border of the coracoid; a triangular emargination in the posterior border of the ischium; and posterior convergence of the long axes of the posterior interpterygoid vacuities. Contrasting phylogenetic hypotheses of the position of M. tenuiceps and other Lower Jurassic plesiosaurians (some of which have not been treated scientifically since the 19th Century) highlights the need for revision of their anatomy and taxonomy for use in fine-grained species-level cladistic analysis.
The protorosaur Tanystropheus longobardicus is well known from the Middle Triassic of alpine Europe. It has been described on the basis of a number of specimens that apparently range from juvenile to adult. The largest specimens have a total body length of approximately 3 m. Here we report on the first occurrence of a large tanystropheid from the Middle or early Late Triassic of southwestern China. The new specimen is indistinguishable from the largest specimens of T. longobardicus from Europe, although it lacks a skull. Both the Chinese specimen here described and the European specimens of T. longobardicus are characterized by 13 cervical vertebrae (not 12 as had previously been assumed). The new find, together with a recent specimen of Macrocnemus from Yunnan Province, highlight shared elements of the vertebrate fauna around the coastline of western and eastern Tethys during Middle to Late Triassic times.
New material of borioteiioidean lizards (Squamata: Scincomorpha) from west-central Alberta, Canada, represent the first and northernmost record of multiple articulated skull elements from the Cretaceous of North America. Specimens were recovered from the fluvial beds of the Wapiti Formation (Campanian) within a bentonitic paleosol exposed at the Kleskun Hill Park, east of the city of Grande Prairie. Such beds accumulated during the maximum transgression of the Bearpaw Seaway (73–74 Ma), thus providing crucial information on lizard faunas during a time interval represented in most of coeval North American deposits by marine strata. Cranial material ascribed to Socognathus unicuspis give the occasion for a revision of the taxon with respect to osteologically better-known Polyglyphanodon sternbergi from the Late Cretaceous of Utah as well as a comparison with several lizards reported from coeval strata of Mongolia. Furthermore, a new scincomorphan lizard, Kleskunsaurus grandeprairiensis, gen. et sp. nov., is described. Socognathus unicuspis is assigned to Chamopsiidae, taxon nov., which also includes Chamops, Leptochamops, and several other morphologically similar taxa from the Cretaceous of North America.
The Otis Chalk quarries in the Upper Triassic Dockum Group of West Texas have produced aetosaur material that most workers have suggested represents two distinct morphotypes. We use characters from aetosaur specimens with articulated or semi-articulated carapaces in which the anteroposterior placement of osteoderms can be established with certainty to compare homologous osteoderms in the Otis Chalk material. This study confirms that the genera Longosuchus and Lucasuchus are distinct morphotypes, which differ in that the former taxon has paramedian osteoderms with random pitted ornamentation and low pyramidal bosses that contact the posterior margin, and spines on the lateral osteoderms that are posteriorly emarginated, whereas the latter taxon has paramedians with a strongly radial ornamentation and large conical eminences, and spines on the lateral osteoderms that are not posteriorly emarginated. Both taxa also have paramedians that are overlapped anteriorly by the laterals, a character that may be a synapomorphy of desmatosuchine aetosaurs. The arguments that these morphotypes represent ontogenetic stages or sexual dimorphs of a single biological species cannot be corroborated using either comparisons with modern pseudosuchians, other aetosaur taxa, or stratigraphic ranges. Longosuchus is known only from the type area and has no utility as an index taxon of the Otischalkian land-vertebrate faunachron, although Lucasuchus suggests a tentative correlation between part of the Dockum Group of Texas and the Pekin Formation of North Carolina.
Tsoabichi greenriverensis, tax. nov., is based on cranial and postcranial remains from the lower Eocene (Wasatchian) Green River Formation of Wyoming. Casts of additional material in private collections include the complete skeleton of an immature specimen. It has abrupt supratemporal fenestral rims, extensive supraoccipital exposure on the skull table, and bipartite ventral osteoderms. The nasals are reduced to a thin anterior process as they approach the external naris, and the rim of the naris extends beyond the dorsal surface of the snout as a thin crest. There was no ‘spectacle’ between the orbits, but there are three distinct craniocaudally elongate ridges between the orbits. The parietal extends to the posterior margin of the skull table on either side of the large V-shaped dorsal exposure of the supraoccipital. Some of the dorsal osteoderms are mediolaterally elongate and bear two dorsal keels. A close relationship with caimans is supported by a parsimony analysis, although its precise position is unclear and some of the characters supporting a caimanine relationship also occur in poorly known Late Cretaceous and Early Tertiary alligatoroids. A possible close relationship with Paleosuchus (the living dwarf caimans) would imply a very complex biogeographic scenario with multiple dispersals between the Americas during the Tertiary.
A recent find of an articulated skeleton of Silesaurus opolensis at its early Late Triassic type locality Krasiejów (Poland), with skull, neck, pectoral girdle, and thorax, supplemented by additional preparation of previously collected articulated specimens, enables complete restoration of the vertebral column and associated skeletal parts. Cervical ribs of Silesaurus, well preserved in their original disposition, are parallel to the neck and extend backward for a few vertebral lengths. There is a sudden change in their morphology behind the seventh vertebra, although otherwise the transition from the cervical to the dorsal vertebrae is very gradual. Parapophyses slowly migrate upward along the anterior margin of the centrum and leave the centrum at the sixth or seventh dorsal vertebra. Narrowing of the dorsal extremities of the neural spines of the fourth and neighboring vertebrae suggests the ability of this region of the vertebral column to bent upward. There is thus a disparity between the structural and functional neck-thorax transition. The presence of three sacrals firmly connected by their ribs with the ilia and the long tail of Silesaurus, providing a counterbalance to the weight of the body in front of the pelvis, suggests the ability for fast bipedal running. However, unusually long but gracile forelimbs of Silesaurus suggest that it represents a transition towards secondarily quadrupedal locomotion, characterizing most of the later herbivorous dinosaurs.
In the last 30 years, the Two Medicine Formation of western Montana has provided a wealth of information about dinosaur reproductive biology. Here, we describe a fossil egg-bearing stratum that occurs approximately 105 m above the base of the formation. This site in the Sevenmile Hill outcrops south of Choteau, Montana, lies immediately above a volcanic tuff and bentonite, dated as 80.0 Ma. Spherulitic eggshells from a quarry at this locality are similar to Spheruprismatoolithus candensusBray, 1999, which were assigned to the oofamily Prismatoolithidae. However, we refer this eggshell to the Spheroolithidae Zhao, 1979, as Spheroolithus choteauensis, oosp. nov. The quarry also produced Triprismatoolithus stephensi, oogen. et oosp. nov. These symmetrical 30 mm × 75 mm prismatic eggs exhibit three structural layers of calcite and round tubercles on the shell surface. Four additional ootaxa occurred at the First Find Microsite (OTM 99-19): Prismatoolithus hirschi, oosp. nov.; Tubercuoolithus tetonensis, oogen. et oosp. nov.; Continuoolithus canadensisZelenitsky et al., 1996; and KrokolithesHirsch, 1985. Spheroolithus choteauensis, T. stephensi, P. hirschi, T. tetonensis, and Krokolithes are unique to the lowermost Two Medicine Formation, whereas C. canadensis may occur elsewhere in the middle and upper strata of the Two Medicine and Oldman formations of Montana and Alberta, respectively. Although poorly represented by dinosaur osteological remains, the lower Two Medicine Formation locality yields egg types that suggest a significant difference in faunal composition compared to the middle and upper portions of the formation.
Although they have been considered distinct genera for over a century, ontogenetic analyses reveal that Triceratops and “Torosaurus” actually represent growth stages of a single genus. Major changes in cranial morphology—including the opening of parietal fenestrae and the elongation of the squamosals—occur rapidly, very late in Triceratops ontogeny and result in the characteristic ‘Torosaurus’ morphology. This report presents the results of a 10-year field study of the dinosaurs of the Hell Creek Formation in Montana and is based on a collection of over 50 specimens of Triceratops, including over 30 skulls, which have been amassed in that time, in addition to specimens from numerous other North American museums. This large sample of individuals reveals the full ontogenetic spectrum of Triceratops. The synonymy of Triceratops and ‘Torosaurus’ contributes to an unfolding view of extremely reduced dinosaur diversity just before the end of the Mesozoic Era.
We report the discovery of a specimen of Tenontosaurus tilletti from the Cloverly Formation that bears lesions we interpret as bite marks of Deinonychus antirrhopus. Some of the bite marks are in the form of exceptionally deep punctures through the long bone cortices. These provide a rare opportunity to estimate the bite-force capacities of this taxon through tooth indentation simulations. These experiments showed that approximately 4100 N of bite force were required to generate one of the bite marks, and 8200 N would have been generated simultaneously at a distal-most tooth position. These values are higher than those reported for large carnivoran mammals but similar to values recorded for comparably sized crocodilians. Although current evidence does not indicate how D. antirrhopus actually used its claws and teeth to acquire prey resources, it is clear that large individuals were capable of generating forces great enough to bite through bone.
Recent field efforts in the Mahajanga Basin of northwestern Madagascar have recovered a diverse Late Cretaceous terrestrial and freshwater vertebrate fauna, including a growing diversity of avialans. Previous work on associated bird skeletons resulted in the description of two named avialans (Rahonavis, Vorona). Other materials, including two synsacra and numerous appendicular elements, represent at least five additional taxa of basal (non-neornithine) birds. Among the materials described herein are two humeri tentatively referred to Rahonavis and numerous elements (e.g., humeri, ulnae, tibiotarsi, tarsometatarsi) assigned to Vorona. A near-complete carpometacarpus exhibits a minor metacarpal that exceeds the major metacarpal in length, documenting an enantiornithine in the fauna. Moreover, two additional, small humeri, an ulna, a femur, and a tarsometatarsus also compare favorably with enantiornithines. Finally, two other isolated humeri and a synsacrum are referable to Ornithurae. The latter specimen is notable in the presence of distinct, transversely oriented lumbosacral canals along the inner surface of the bony neural canal. This reveals for the first time a hard-tissue correlate of an anatomical specialization related to increased sensorimotor integration, one likely related to the unique form of avialan bipedal locomotion. Bird fossils recovered from the Maevarano Formation document one of the most size- and phylogenetically diverse Cretaceous-age Gondwanan avifaunas, including representative (1) basal pygostylian, (2) enantiornithine, (3) nonenantiornithine, ornithothoracine, and (4) ornithurine taxa. This Maastrichtian avifauna is notable in that it demonstrates the co-existence of multiple clades of basal (non-neornithine) birds until at least the end of the Mesozoic.
We present a detailed account on the skeletal structure of the traversodont cynodont Boreogomphodon jeffersoni on the basis of a considerable quantity of excellently preserved craniodental remains and several referred postcranial bones from the Tomahawk Creek Member of the Vinita Formation (Upper Triassic: Carnian) of the Richmond basin (Newark Supergroup) in eastern Virginia. The small size, proportionately short snout and mandible, low number of molariform postcanine teeth, and presence of up to three sectorial postcanines all indicate that most of the specimens recovered to date represent immature individuals. The superbly preserved dental material permits detailed inferences regarding tooth replacement and dental function during ontogeny. Boreogomphodon differs from other known traversodont cynodonts primarily in the possession of lower molariform postcanine teeth with three rather than two anterior cusps in all but the smallest specimens, zygomatic arches that are bowed laterally at about mid-length, and pronounced, irregular sculpturing on the dorsal surface of the snout. Plesiomorphic features of traversodont cynodonts retained by Boreogomphodon include the position of the paracanine fossa anterolingual to the upper canine as well as the presence of a distinct central cusp and a posterior cingulum on the upper molariform postcanines. Phylogenetic analysis suggests the existence of a clade comprising Boreogomphodon plus two other taxa (Arctotraversodon and Nanogomphodon) in the Northern Hemisphere that is the sister group to most other known Middle and Late Triassic traversodonts from Gondwana.
Two late middle Miocene to early late Miocene (12–11 Ma) soricid populations from Spain and Germany are re-described and assigned to Crusafontina and Darocasorex, gen. et sp. nov., primitive genera within the Anourosoricini. The relatively advanced morphology of these oldest Anourosoricini genera known suggest a much earlier date for the origin of the tribe. Molecular phylogenetics support an early origin (∼15 Ma), but ages up to ∼18 Ma are possible after re-evaluating the calibration points that use early-middle Miocene occurrences of Soricinae and their potential ancestors. Both molecular phylogenetics and paleontology consistently point to Anourosoricini being the sister clade of the combined Nectogalini and Notiosoricini. Synapomorphies in morphology relate to the condylar structure, the morphology of the lower premolar (p4) and reduction of the upper antemolars. The phylogenetic roots of the Anourosoricini within the Soricinae will remain elusive until more early-middle Miocene rests are found. The paucity of fossils is probably related to the lack of terrestrial sedimentary rocks at northern latitudes, where primitive Anourosoricini and their soricine ancestors might have been residing during the early-middle Miocene thermal optimum.
In addition to its abundance in the middle Eocene of the Western Interior of North America, fossils of the brontothere Metarhinus are known from similar aged deposits in Southern California. Because of additional material from the Friars and Santiago Formations, San Diego County, California, M. pater Stock (1937), a dubious species formerly known from a single specimen, can now be differentiated from other nominal species of Metarhinus, M. fluviatilis Osborn (1908), and M. abbotti (Riggs, 1912). Inclusion of M. pater into an analysis of brontotheriid phytogeny establishes Metarhinus as a monophyletic genus of uncertain origin. The three species of Metarhinus differ in the shapes of their nasals and the lengths of their nasal incisions, whereas other aspects of their skulls are undifferentiated. The majority of Metarhinus specimens lack species-diagnostic features and thus have unknown specific identities. At least two species co-occur wherever Metarhinus is abundant. We question whether these morphospecies represent population-lineage units (i.e., species), or if they are intraspecific variants possibly explained by ontogeny or sexual dimorphism. Dental wear stages, used as an age proxy, are uncorrelated with Metarhinus morphospecies. Likewise, variation observed within Metarhinus samples is inconsistent with sexual dimorphism. Coefficients of variation (CVs) suggest that the cheektooth dimensions of Metarhinus assemblages are more variable than monospecific referent samples, and that most assemblages are mixtures of two size-differentiated species. The persistent sympatry of Metarhinus species is a biogeographic pattern that appears to be atypical in comparison to other brontotheriids and could indicate an unusual case of sympatric speciation.
The Cambay Formation at Vastan Mine in Gujarat, western India, has yielded the oldest artiodactyls and other land mammals from India, which are dated as middle Ypresian (∼53 Ma) based on foraminiferids. Here we describe new dentitions, including dentaries and upper teeth of Diacodexis indicus ( = Gujaratia indica) from Vastan. These provide better characterization of this Asian diacodexeid (Artiodactyla: Mammalia) than was available earlier. A new combination, Diacodexis indicus, is proposed in place of Gujaratia indica, and G. pakistanensis is referred back to Diacodexis. A new, very small species of Diacodexis, D. parvus, is reported based on isolated teeth. Whereas D. indicus is approximately the size of the largest known species of Diacodexis, D. parvus represents the smallest recorded species of the genus and is one of the smallest known artiodactyls. Diacodexeidae indet. from Vastan is exemplified by a fragment of a dentary and an upper molar, which are of intermediate size. Several isolated teeth represent a new genus and species, unrelated to Diacodexeidae, and are assigned to Artiodactyla indet. pending discovery of more adequate specimens. Early Eocene diacodexeid postcrania are described for the first time from India. Early Eocene artiodactyls from India are phenetically close to Euroamerican species of Diacodexis, providing further evidence of phylogenetic connections particularly with European faunas. A few postcranial features of the Vastan artiodactyls are also seen in primitive archaeocetes (Cetacea) indicating a possible relationship between Vastan artiodactyls and basal Cetacea.