Lamanna M.C.,Section of Vertebrate Paleontology |
Sues H.-D.,Smithsonian Institution |
Schachner E.R.,University of Utah |
Lyson T.R.,Smithsonian Institution
PLoS ONE | Year: 2014
The oviraptorosaurian theropod dinosaur clade Caenagnathidae has long been enigmatic due to the incomplete nature of nearly all described fossils. Here we describe Anzu wyliei gen. et sp. nov., a new taxon of large-bodied caenagnathid based primarily on three well-preserved partial skeletons. The specimens were recovered from the uppermost Cretaceous (upper Maastrichtian) Hell Creek Formation of North and South Dakota, and are therefore among the stratigraphically youngest known oviraptorosaurian remains. Collectively, the fossils include elements from most regions of the skeleton, providing a wealth of information on the osteology and evolutionary relationships of Caenagnathidae. Phylogenetic analysis reaffirms caenagnathid monophyly, and indicates that Anzu is most closely related to Caenagnathus collinsi, a taxon that is definitively known only from a mandible from the Campanian Dinosaur Park Formation of Alberta. The problematic oviraptorosaurs Microvenator and Gigantoraptor are recovered as basal caenagnathids, as has previously been suggested. Anzu and other caenagnathids may have favored well-watered floodplain settings over channel margins, and were probably ecological generalists that fed upon vegetation, small animals, and perhaps eggs.
Grogan E.D.,Saint Josephs University |
Lund R.,Section of Vertebrate Paleontology
Zoological Journal of the Linnean Society | Year: 2011
Chondrichthyan fishes have an evolutionary history spanning over 400 million years and are characterized, in part, by internal fertilization. Traditionally, oviparity has been assumed to be the primitive birthing mode for these fishes and for vertebrates in general, with viviparity and matrotrophic nutrition being derived. The fossilized remains of two specimens of Harpagofututor volsellorhinus from the Upper Mississippian of Montana now provide the first direct evidence of matrotrophic live birth in a Palaeozoic chondrichthyan and of superfoetation in an extinct fish. Each female exhibits multiple foetuses of two size groups, indicating simultaneous gestation of multiple litters. There is no evidence of yolk sacs, only preserved organic pigments enveloping the young, suggesting matrotrophically derived material. Young were born large, as head lengths of the largest embryos measured up to 66 per cent of the mother's head length. Comparison of in utero embryos to isolated specimens suggests, unlike all extant chondrichthyans, the absence of a juvenile stage and rapid maturity. These new data suggest the advantages of superfoetative viviparity for a small bodied fish in a 318Myr old species- and predator-rich marine bay. In the greater view of gnathostome evolution, this finding combines with other recent discoveries to document that multiple, and not necessarily closely related, species of both placoderms and chondrichthyans exhibited viviparity by the Upper Devonian and the Upper Mississippian. The capacity for internal fertilization probably predisposed members of these lineages to develop viviparity so early in gnathostome history. Yet, the surprising range of viviparity exhibited at this stage of vertebrate evolution emphasizes that derived reproductive strategies had evolved in gnathostomes by 380-318 million years ago. © 2011 The Linnean Society of London.
Whitlock J.A.,University of Michigan |
Wilson J.A.,University of Michigan |
Lamanna M.C.,Section of Vertebrate Paleontology
Journal of Vertebrate Paleontology | Year: 2010
More than any other sauropod dinosaur group, the long-necked herbivores belonging to Diplodocoidea have been defined by their skulls. Their unique skull shape, which is extremely elongate antorbitally, with a transversely broad, square snout packed at its anterior extreme with narrow-crowned, pencil-like teeth, has served as a touchstone for describing the biology of these animals ever since the discovery of the first skull in the late 19th century. In particular, the unusual diplodocoid skull has been discussed frequently in the context of examining feeding behavior, spawning hypotheses ranging from branch stripping, propalinal shearing, and aquatic plant 'grazing.' Here, we describe a juvenile skull of Diplodocus (Carnegie Museum 11255) that does not share the unusually blunted snout and anteriorly sequestered teeth seen in adult specimens, suggesting that adults and juveniles may have differed greatly in their feeding behavior, an ontogenetic distinction that may be unique among sauropodomorphs. © 2010 by the Society of Vertebrate Paleontology.
Henrici A.C.,Section of Vertebrate Paleontology
Palaeobiodiversity and Palaeoenvironments | Year: 2015
The Rhinophrynidae, endemic to North America, are a highly specialised group of fossorial anurans that, despite a long geologic history, has low diversity. Today, rhinophrynids are represented by one taxon, Rhinophrynus dorsalis, which occurs in extreme southern Texas, USA, and southwards through Mexico and into Central America, in dry tropical to subtropical forests along coastal lowlands. The skeleton of R. dorsalis is highly specialised for burrowing and subterranean feeding, with individuals spending most of their time underground feeding on ants and termites and emerging only after periods of heavy rain to breed. In the fossil record, rhinophrynids with skeletons specialised for burrowing first appear in the late Paleocene (Tiffanian) of Wyoming, USA, and are subsequently known from the Western Interior of North America until the late Eocene (Chadronian), with the exception of one late Pleistocene occurrence in Mexico. From the late Paleocene (Tiffanian) until the present, rhinophrynids became more specialised for burrowing. The tibiale and fibulare became relatively shorter and stouter, the distal condyle of the femur became expanded and divided into two condyles, and the distal prehallux bone and distal phalanx of the first metatarsal were modified as spades by at least the middle Eocene (Uintan). Adaptations for feeding underground might have occurred as early as the middle Eocene (Bridgerian), as suggested by the elongate neural arch of Eorhinophrynus septentrionalis. The middle Eocene (Uintan) Chelomophrynus bayi shares several specialisations with Rhinophrynus dorsalis for feeding underground, so it is presumed that it too was a subterranean feeder. These specialisations include a somewhat protracted snout, lack of teeth on the jaws and vomers, forward shift of the jaw suspensorium and most likely the shoulder girdle, and possibly the structure of the hyoid apparatus. As the climate became more seasonal and subfreezing temperatures developed after the Eocene–Oligocene transition, rhinophrynids apparently never developed the ability to hibernate to avoid freezing and instead shifted their range south. © 2015 Senckenberg Gesellschaft für Naturforschung and Springer-Verlag Berlin Heidelberg
Luo Z.-X.,Section of Vertebrate Paleontology |
Luo Z.-X.,University of Bonn |
Ruf I.,University of Bonn |
Schultz J.A.,University of Bonn |
Martin T.,University of Bonn
Proceedings of the Royal Society B: Biological Sciences | Year: 2011
The coiled cochlea is a key evolutionary innovation of modern therian mammals. We report that the Late Jurassic mammal Dryolestes, a relative to modern therians, has derived bony characteristics of therian-like innervation, but its uncoiled cochlear canal is less derived than the coiled cochlea of modern therians. This suggests a therian-like innervation evolved before the fully coiled cochlea in phylogeny. The embryogenesis of the cochlear nerve and ganglion in the inner ear of mice is now known to be patterned by neurogenic genes, which we hypothesize to have influenced the formation of the auditory nerve and its ganglion in Jurassic therian evolution, as shown by their osteological correlates in Dryolestes, and by the similar base-to-apex progression in morphogenesis of the ganglion in mice, and in transformation of its canal in phylogeny. The cochlear innervation in Dryolestes is the precursory condition in the curve-to- coil transformation of the cochlea in mammalian phylogeny. This provides the timing of the evolution, and where along the phylogeny the morphogenetic genes were co-opted into patterning the cochlear innervation, and the full coiling of the cochlea in modern therians. © 2010 The Royal Society.