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The hybodont form genus Lissodus is taken under revision and found to comprise a number of lineages. Twelve species, stratigraphically extended from the Scythian, Lower Triassic to the Albian, Lower Cretaceous, are retained in Lissodus s.s. Thirteen other species can be included in Lonchidion, here considered as a justified genus, ranging from the Ladinian in the Middle Triassic to the Maastrichtian in the Upper Cretaceous. Of the species previously included in Lissodus, two new genera, Vectiselachos, gen. nov. and Parvodus, gen. nov., are described. Vectiselachos is at present a monotypic genus including a single species from the Lower Cretaceous of southern England. Parvodus comprises three species and is known from the Bathonian, Middle Jurassic to the Valanginian, Lower Cretaceous. Another species is placed in Steinbachodus, expanding the stratigraphical range of the genus from the Rhaetian in the Upper Triassic to the Cenomanian in the Upper Cretaceous. Palaeozoic small-toothed hybodonts are extremely poorly known and alleged Lissodus species fall into two genera, but these are at present kept in open nomenclature. The family Lonchidiidae is considered justified and includes the genera Lissodus, Lonchidion, Vectiselachos, Hylaeobatis and Parvodus.
Revised diagnoses of the family Tarrasiidae and of Tarrasius (Visean of Scotland) and Paratarrasius (Namurian of North America) are presented. These are used in a phylogenetic analysis also comprising one theoretical outgroup, three sarcopterygians as part of the outgroup, and eleven Palaeozoic, Triassic, and Recent actinopterygians, and based on a matrix of 75 characters of head and body. The results are that: (1) Polypterus is the sister group of the other Actinopterygii (=Actinopteri); (2) the analysed Actinopteri are a monophyletic group (Palaeoniscimorpha); and (3) Tarrasiids are monophyletic and are the sister group of the other analysed Actinopteri. This scheme supports the most recent studies in indicating that Tarrasiidae are close to stem actinopterygians.
Study of a growth series of twenty-seven specimens from the Upper Devonian of Escuminac Bay, Québec documents a complex pattern of vertebral development in the osteolepiform fish Eusthenopteron foordi. Ossification begins with elements associated with the caudal, anal, and second dorsal fins. Development of the haemal arches, caudal radials, and caudal neural arches continues anteriorly and posteriorly from near the level of the anterior margin of the caudal fin. Trunk neural arches ossify later than the caudal neural arches and as a separate sequence. Trunk intercentra most likely begin ossification posteriorly and continue forward after the ossification of haemal arches is complete. Comparisons of many different patterns of vertebral development within the modern actinopterygians demonstrates that the sequence of development in Eusthenopteron foordi is unique. The diverse patterns of vertebral development observed in fossil and modern fish presumably result from an interplay between the inherent anterior to posterior sequence of development controlled by the Hox genes, and varying selective forces imposed by the physical and biological environment in which the fish develop. Initiation of vertebral development in the caudal region of Eusthenopteron foordi can be attributed to selection for early function of the tail in propulsion. In contrast, vertebral development in Carboniferous amphibians typically proceeds from anterior to posterior. This may reflect development in the still water of ponds and lakes in contrast with the coastal environment inhabited by the hatchlings of Eusthenopteron foordi. The sequences of vertebral development seen in Carboniferous labyrinthodonts and lepospondyls are divergently derived from that observed in Eusthenopteron foordi.
The discovery of a new iguanodontian ornithopod in the lower units of the Neuquen Group (Rio Limay Formation, early Upper Cretaceous) increases the South American record of this kind of dinosaurs started few years ago with the report of Gasparinisaura cincosaltensis. Anabisetia saldiviai, gen. et sp. nov. is distinguished from all other ornithopods by several features, as a flattened fifth metacarpal, a scapula with a very strong acromial process, and an ilium with preacetabular process longer than 50% of the total ilium length. Anabisetia is more derived than Tenontosaurus and shares with Euiguanodontia (Gasparinisaura Dryomorpha) the presence of one primary lateral ridge on each maxillary tooth, a broad brevis-shelf and a reduced first metatarsal. Derived features such as the transversely flattened prepubic process and an anteroventrally oriented ischiadic foot link Anabisetia with Dryomorpha (i.e., Dryosaurus, Camptosaurus and Iguanodon). Anabisetia strengths the hypothesis that basal iguanodontian ornithopods were present in South America before its with North America in the Late Cretaceous.
We describe the osteology of the new small theropod dinosaur Masiakasaurus knopfleri, from the Late Cretaceous Maevarano Formation of northwestern Madagascar. Approximately 40% of the skeleton is known, including parts of the jaws, axial column, forelimb, pelvic girdle, and hind limb. The jaws of Masiakasaurus are remarkably derived, bearing a heterodont, procumbent dentition that is unknown elsewhere among dinosaurs. The vertebrae are similar to those of abelisauroids in the reduction of the neural spine, lack of pleurocoelous fossae on the centrum, and extensively pneumatized neural arch. The limb skeleton is relatively gracile and bears numerous abelisauroid synapomorphies, including a rounded humeral head, peg-and-socket iliac-pubic articulation, prominent femoral medial epicondyle, expanded tibial cnemial crest, and double-grooved pedal unguals. The femora and tibiae show evidence of dimorphism. More specific features shared between Masiakasaurus, the Argentine Noasaurus, and the Indian Laevisuchus suggest that these taxa form a clade (Noasauridae) within Abelisauroidea. This is supported by a cladistic phylogenetic analysis of 158 characters and 23 theropod taxa. Additionally, Ceratosauria is rendered paraphyletic in favor of a sister-taxon relationship between Neoceratosauria and Tetanurae that is exclusive of Coelophysoidea. The unique dental and jaw specializations of Masiakasaurus suggest deviation from the typical theropod diet. Finally, the distribution of noasaurids further supports a shared biogeographic history between South America, Madagascar, and India into the Late Cretaceous.
The holotype of Irritator challengeriMartill et al., 1996 from the Romualdo Member of the Santana Formation (Lower Cretaceous) in northeastern Brazil represents the most complete skull of a spinosaurid known to date. The now fully prepared specimen provides much new information on the cranial structure in these enigmatic predatory dinosaurs. The skull is remarkably narrow, especially in the region of the elongated snout. The maxillae are in broad contact along the midline, forming an extensive secondary bony palate. The maxillary teeth have straight or slightly recurved, conical crowns, with thin, fluted enamel and distinct but smooth carinae. As in Baryonyx walkeri, the anterior and ventral processes of the lacrimal meet at a more acute angle than in most non-avian theropod dinosaurs. The braincase is short anteroposteriorly but deep dorsoventrally, extending ventrally far below the occipital condyle. Irritator challengeri most closely resembles Spinosaurus aegyptiacus in the structure of its teeth, but more extensive comparisons between the two taxa are currently impossible due to the limited amount of cranial material known for the latter.
I report here on the discovery of the most complete megalosaurid skull known to date, from the Calcaire de Caen Formation of northwesten France. The specimen, which represents a new species is questionably referred to Poekilopleuron. It includes a nearly complete, unornamented skull, characterized by its low lateral profile. In addition to its historical significance, it provides additional characters that are crucial for reconstructing the phylogeny and biogeography of basal theropods. Poekilopleuron? valesdunensis new species is closely related to Eustreptospondylus and Afrovenator, and is united with Torvosaurus in the family of Megalosauridae. The Megalosauridae appear less derived than the Allosauroidea but resemble the Spinosauridae, with which they form the sister-group to the Neotetanurae. The proposed phylogenetic analysis hypothesizes two previously unrecognized major radiations of carnivorous dinosaurs.
Elongate and asymmetric eggs of the oospecies Prismatoolithus levis occur regularly in the Upper Cretaceous Two Medicine Formation of western Montana. These eggs had previously been assigned to the ornithischian Orodromeus makelai, for both juvenile and adult remains are typically associated with these eggs. Reexamination of the embryos shows them to exhibit at least 24 apomorphies of the clades Dinosauria, Theropoda and Paraves. The embryos also display a pneumatic quadrate, closely placed basal tubera, a high tooth count, a metatarsal II much narrower than IV and a strongly constricted metatarsal III, all possible synapomorphies of the Troodontidae. Presence of large basal tubera and a broadly rounded anterior border of the maxillary fenestra permit assignment to Troodon formosus. Most but not all bones appear ossified, suggesting a developmental level comparable to stages 35–38 of avian embryos and a time approaching hatching. Embryos show a consistent level of development from one egg to another indicating synchronous hatching of the clutch. Embryonic Troodon exhibit long distal segments and radically different hindlimb proportions in comparison to adults. Orodromeus and other small vertebrate remains associated with Troodon egg horizons may represent prey of the adults during egg-laying and brooding.
Troodon eggs show several aspects either shared or convergent with some birds, and further demonstrate the close relationship of Troodontidae and Aves. These features include: asymmetric egg form, non-branching angusticanaliculate pores, distinct structural differentiation of the mammillary and overlying prismatic layer, barrel-shaped mammillary cones with a blocky calcite cleavage, and prismatic structure visible throughout the second structural layer.
The skull of Augustasaurus hagdorni from the Middle Triassic of northwestern Nevada is described in detail, and compared to those of Pistosaurus and Plesiosaurus. New information amends the earlier description of the postcranial skeleton of Augustasaurus. Phylogenetic analysis corroborates the sister-group relationship of Augustasaurus and Pistosaurus. These two taxa form a clade that is the sister-group of Plesiosaurus. The paleobiogeographical implication of the sister-group relationship of Augustasaurus and Pistosaurus is discussed and linked to the exotic terrane model.
We describe a new fossil crocodyliform archosaur from the Early Jurassic Kayenta Formation of the Navajo Nation that is surprisingly derived for so ancient a specimen. High-resolution X-ray CT analysis reveals that its long snout houses an extensive system of pneumatic paranasal cavities. These are among the most distinctive features of modern crocodylians, yet the evolutionary history of this unique system has been obscured by the inaccessibility of internal structures in most fossil crania. Preliminary phylogenetic analysis indicates that the new species is the oldest known member of a monophyletic Goniopholididae, and within this lineage to be the sister taxon of Eutretauranosuchus, from the Late Jurassic Morrison formation of Colorado. Goniopholididae became extinct at the end of the Cretaceous, but it is more closely related to living crocodylians than are several lineages known only from Cretaceous and younger fossils. The new taxon nearly doubles the known length of goniopholid history and implies a deep, as yet undiscovered, Mesozoic history for several crocodyliform lineages that were once thought to have relatively complete fossil records.
Isolated cranial and postcranial elements represent a new genus and species of endemic crocodilian, Volia athollandersoni, from presumed Pleistocene cave deposits of Fiji. Preliminary phylogenetic assessment indicates that it is a mekosuchine crocodylid. This material sheds further light on the Pleistocene tetrapod fauna of the southwestern Pacific islands.
A mosasaurid skull, 6 cervicals, the anterior two dorsals and a single posterior dorsal vertebra were found in Oron, Negev Desert, Israel, in latest Campanian deposits. The skull is dorsoventrally compressed and somewhat distorted, but otherwise in good condition, although sutures are often indistinct, in part due to weathering and in part due to the great size and presumable old age of the specimen. At an overall length of 1,422 mm it is one of the largest skulls ever discovered. The skull bears resemblance to those of advanced mosasaurines, in particular the type species of Prognathodon, P. solvayi, but differs from all previously known mosasaurids in having a frontal distinctly wider than long. Cladistic analysis on cranial and mandibular characters of 33 ingroup taxa were performed. A Nelsen consensus tree (1:225, ci:44 ri:76) based on 3 equally parsimonious trees placed this new specimen as the sister taxon to P. solvayi, with the American species of Prognathodon forming successive outgroups to these two. The present specimen extends the size range of known globidensine mosasaurines by around a factor two.
A diverse fauna of lizards has been recovered from the Cedar Mountain Formation (Albian–Cenomanian boundary) of central Utah. These lizards are a component of the now recognized Mussentuchit local fauna and, like many of the other vertebrate groups within this fauna, show striking similarities to their North American Late Cretaceous (Campanian–Maastrichtian) counterparts. Unlike the Late Cretaceous lizard faunas, the lizards from the Mussentuchit local fauna also include at least one “paramacellodid,” a group common to Late Jurassic and Early Cretaceous lizard faunas of North America. Comparison with other Cretaceous lizard faunas from both North America and Asia indicates that the changes in the North American lizard fauna represented by the lizards of the Mussentuchit local fauna are likely the result of the introduction of taxa from Asia during the Early Cretaceous. Supposedly herbivorous taxa are found among the Polyglyphanodontine lizards from the Late Cretaceous of North American and Asia, but the general changes in the Cretaceous lizard fauna of North America cannot be convincingly shown to be linked to the concurrent angiosperm radiation. Later influxes of Asian lizard taxa prior to the Campanian may explain the relatively sudden appearance of additional groups of lizards in the early Campanian of North America. Whereas there is good evidence to support the hypothesis of an Asian influence on the Cretaceous lizard fauna of North America, there is insufficient evidence to determine what, if any, influence may have come from Europe or South America.
Septentrogon madseni, gen. et sp. nov. is assigned to the family Trogonidae (Aves: Trogoniformes), based on a well-preserved neurocranium from the latest Paleocene–earliest Eocene Fur Formation in north-western Denmark. The taxonomic assignment to Trogonidae is based on an overall similarity and the diagnostic character state of the zygomatic processes, being mediolaterally flattened and rounded in circumference. The specimen is identified as a separate genus and species based on slight proportional differences of the frontals, braincase and zygomatic processes. This new fossil trogon exceeds the hitherto oldest known trogon (and only other known fossil trogon with cranial elements preserved), Primotrogon wintersteiniMayr (1999) by more than 20 Ma. The significant similarity between S. madseni and extant trogons implies that trogons as a taxonomic group morphologically has stayed nearly stationary through time. The palaeoenvironment and palaeoclimate of northern Europe in late Paleocene and early Eocene corresponds well with that in which extant trogons live, and trogons may have followed the movement of the (sub-)tropical climatic belt toward the equator through the Cenozoic rather than adapt to new climatic and environmental conditions.
New specimens of procellariiform birds are described from the Oligocene of Germany and Belgium, including a virtually complete and extraordinarily well preserved articulated skeleton. These birds show a peculiar foot morphology which to a striking degree resembles that of the recent Polynesian Storm-petrel Nesofregetta fuliginosa (Oceanitinae, Hydrobatidae). The pedal phalanges are dorso-ventrally compressed and especially the proximal phalanx of the fourth toe is grotesquely widened. The Oligocene Procellariiformes trenchantly differ, however, from Nesofregetta, the closely related genus Fregetta, and all other taxa of recent Hydrobatidae in the remainder of the skeleton. Possibly the feet served as a brake for rapid stops in order to catch prey, and we consider the similarities to Nesofregetta to be a striking example of convergence among birds. The specimens described in this study are referred to Diomedeoides brodkorbi, D. lipsiensis, and to Diomedeoides sp. The genus Frigidafons is a junior synonym of Diomedeoides, and Diomedeoides minimus is a junior synonym of Diomedeoides (= “Gaviota”) lipsiensis. An incomplete articulated specimen of Diomedeoides brodkorbi is of special taphonomic interest, since in the close vicinity of its left wing two fairly large shark teeth can be discerned which probably stuck in the soft tissues of the bird when it was embedded in the sediment.
The recovery of an almost complete skull and partial associated mandible of Catonyx tarijensis from Puerto Arazatí, Department of San José, is the first record of this species from Uruguay. Catonyx tarijensis is only known from the Ensenadan land mammal age. Mammals from multiple land mammal ages have been recovered from the San José formation and suggest that it is time transgressive and may range in age from the Montehermosan to the Ensenadan.
Two well-preserved specimens of a “cetothere” from the Lower Miocene Awa and Mizunami Groups, Japan, are described as Isanacetus laticephalus, gen. et sp. nov. It is distinguished by the following combination of characters: fossa for the stapedial muscle elongated anteroposteriorly, with a fully ossified floor; anteroposteriorly broad supraorbital process of frontal, with the orbital margin concave in dorsal view; posterior thrust of the medial rostral elements reaches the level of the center of the orbit; apex of the occipital shield reaches beyond the level of the anterior end of the zygomatic process of the squamosal; nasal slender, elongate, and partly located anterior to level of the preorbital angle of the supraorbital process of the frontal; and zygomatic process of the squamosal slender, elongate, and directed forward and slightly outward.
A parsimony analysis of 16 cetaceans and 77 characters failed to identify any synapomorphies for the “Cetotheriidae.” The analysis supports the following hypotheses: “Cetotheriidae” as commonly used is a paraphyletic grade; “cetotheres” are more closely related to Balaenopteridae Eschrichtiidae than they are to Balaenidae; and “cetotheres” form two subgroups, one which includes Cetotherium and another which includes Isanacetus, Parietobalaena, and Aglaocetus. The latter subgroup is more closely related to Balaenopteridae Eschrichtiidae, but is also paraphyletic.