Convergent evolution of jaws between spinosaurid dinosaurs and pike conger eels

International audienceSpinosaurs represent a group of peculiar theropod dinosaurs that have often been described as “crocodile-mimic”, predominantly fish-eating predators, and recently claimed to have been semi-aquatic animals. Here we report a suite of craniodental characters unexpectedly shared by spinosaurs and pike conger eels. Pike conger eels are predatory, mainly piscivorous bottom-dwelling anguilliform fishes that inhabit marine and brackish environments. These two groups of dinosaurs and fishes show a mediolaterally compressed, elongated rostrum, a terminal “rosette” bearing enlarged teeth in both upper and lower jaws, and a notch posterior to the premaxillary “rosette” characterized by the presence of reduced teeth. The morphological convergence observed in the jaws of these two distantly related groups of vertebrates may result from similar feeding behaviours. This typical jaw morphology likely represents an effective biomechanical adaptation for biting and grabbing elusive prey items in low-light aquatic environments. Associated with this specialized snout morphology, numerous integumentary mechanoreceptors involved in prey detection are present in both spinosaurs and pike congers. Our new observations provide an additional convincing argument regarding the decades-long and widely debated lifestyle of spinosaurs

A fossil assemblage from the mid–late Maastrichtian of Gavdos Island, Greece, provides insights into the pre-extinction pelagic ichthyofaunas of the Tethys

The global body-fossil record of marine ‘fishes’ from the time interval immediately preceding the Cretaceous–Paleogene Extinction is markedly poor. This deficiency appears to be further exacerbated with regards to offshore and deep-water taxa, obscuring our understanding of the state and composition of corresponding vertebrate faunas at the onset of this major extinction event. Recent fieldwork in the mid–late Maastrichtian exposures of the Pindos Unit in Gavdos Island, Greece, yielded a small but informative sample of fossil ‘fishes’, which inhabited the Tethys approximately three to four million years before the extinction. In this work we describe this sample, which comprises between eight and nine discrete morphotypes of various size classes, belonging to †Ichthyodectoidei, Aulopiformes (†Dercetidae, †Enchodontidae, †Ichthyotringidae), cf. †Sardinioididae, as well as the hexanchid shark †Gladioserratus sp. The new material expands the faunal list for the Maastrichtian of Gavdos Island, and the Pindos Unit as a whole, and further allows for the description of a new genus and species of †Enchodontidae and a new species of †Ichthyotringidae. The two new taxa are found to be widespread in the Maastrichtian of the Pindos Unit. The overall character of the assemblage agrees with previous interpretations of an offshore and rather deep depositional environment for the fossiliferous horizons. Furthermore, it exhibits a higher diversity than, and little taxonomic overlap with penecontemporaneous teleost assemblages from the Tethys, and informs on the otherwise poorly known Maastrichtian offshore and deep-water marine ichthyofaunas of the region

A new assemblage of ray-finned fishes (Teleostei) from the Lower Oligocene "Schistes à Meletta” from the Glières plateau, Bornes Massif, eastern France

A recently discovered fish assemblage from the "Schistes à Meletta” facies (Lower Oligocene) of the Glières Plateau, Bornes Massif, Haute-Savoie, eastern France is described. The assemblage, comprising specimens ranging from fully-articulated skeletons to isolated scattered ossifications, is composed of Anenchelum cf. glarisianum, Pristigenys sp., Fistularia sp., Caranx cf. glarisianus alongside indeterminate teleosts. This new assemblage greatly increases the fish diversity previously known from the "Schistes à Meletta” of this area. The fauna shows biogeographic affinities with assemblages from the Peritethys domain, in particular from the Helvetic molassic basin and from the Paratethys. The genera identified at the Glières locality are represented today by species living in tropical nearshore environments together with species from the open sea. A possible explanation is that the environment of deposition was rather deep, and that shallow-water fishes were brought in by turbidity current

Taxonomic Composition and Trophic Structure of the Continental Bony Fish Assemblage from the Early Late Cretaceous of Southeastern Morocco

International audienceThe mid-Cretaceous vertebrate assemblage from south-eastern Morocco is one of the mostdiversified continental vertebrate assemblages of this time worldwide. The bony fish component(coelacanths, lungfishes and ray-finned fishes) is represented by relatively completespecimens and, mostly, by fragmentary elements scattered along 250 kilometres of outcrops.Here we revisit the bony fish assemblage by studying both isolated remains collectedduring several fieldtrips and more complete material kept in public collections. The assemblagecomprises several lungfish taxa, with the first mention of the occurrence of Arganodustiguidiensis, and possibly two mawsoniid coelacanths. A large bichir, cf. Bawitius, is recordedand corresponds to cranial elements initially referred to ‘Stromerichthys’ from coevaldeposits in Egypt. The ginglymodians were diversified with a large ‘Lepidotes’ plus twoobaichthyids and a gar. We confirm here that this gar belongs to a genus distinctive fromRecent gars, contrary to what was suggested recently. Teleosteans comprise a poorlyknown ichthyodectiform, a notopterid, a probable osteoglossomorph and a large tselfatiiform,whose cranial anatomy is detailed. The body size and trophic level for each taxon areestimated on the basis of comparison with extant closely related taxa. We plotted the averagebody size versus average trophic level for the Kem Kem assemblage, together with extantmarine and freshwater assemblages. The Kem Kem assemblage is characterized bytaxa of proportionally large body size, and by a higher average trophic level than the trophiclevel of the extant compared freshwater ecosystems, but lower than for the extant marineecosystems. These results should be regarded with caution because they rest on a reconstructedassemblage known mostly by fragmentary remains. They reinforce, however, theecological oddities already noticed for this mid-Cretaceous vertebrate ecosystem in NorthAfrica

The first late cretaceous mawsoniid coelacanth (Sarcopterygii: Actinistia) from North America: evidence of a lineage of extinct ‘living fossils’

Today, the only living genus of coelacanth, Latimeria is represented by two species along the eastern coast of Africa and in Indonesia. This sarcopterygian fish is nicknamed a "living fossil", in particular because of its slow evolution. The large geographical distribution of Latimeria may be a reason for the great resilience to extinction of this lineage, but the lack of fossil records for this genus prevents us from testing this hypothesis. Here we describe isolated bones (right angular, incomplete basisphenoid, fragments of parasphenoid and pterygoid) found in the Cenomanian Woodbine Formation in northeast Texas that are referred to the mawsoniid coelacanth Mawsonia sp. In order to assess the impact of this discovery on the alleged characteristic of "living fossils" in general and of coelacanths in particular: 1) we compared the average time duration of genera of ray-finned fish and coelacanth in the fossil record; 2) we compared the biogeographic signal from Mawsonia with the signal from the rest of the vertebrate assemblage of the Woodbine formation; and 3) we compared these life traits with those of Latimeria. The stratigraphical range of Mawsonia is at least 50 million years. Since Mawsonia was a fresh, brackish water fish with probably a low ability to cross large sea barriers and because most of the continental components of the Woodbine Fm vertebrate assemblage exhibit Laurasian affinities, it is proposed that the Mawsonia’s occurrence in North America is more likely the result of a vicariant event linked to the break-up of Pangea rather than the result of a dispersal from Gondwana. The link between a wide geographic distribution and the resilience to extinction demonstrated here for Mawsonia is a clue that a similar situation existed for Latimeria, which allowed this genus to live for tens of millions of years

Cenomanian transgression in the Basque-Cantabrian Basin (northern Spain) and associated faunal replacement

Abstract:The available data concerning the environmental changes and faunal replacements that occurred during the Cenomanian marine transgression in the North of Iberia are integrated and discussed on the basis of new evidence from the invertebrate and vertebrate fossil record. New stratigraphical data and the reassessment of known stratigraphic sections support the correlation of the Cenomanian carbonate-ramp successions from the Iberian margin to the centre of the Basque-Cantabrian Basin during a major transgressive episode. This new stratigraphical framework is the key to understand the changing oceanographic conditions in the area that resulted from a progressive inundation of the Iberian continental platform. This transgression seems to have triggered major faunal replacements in this particular geographic area, starting out around the Albian-Cenomanian transition. Ammonite faunal replacement led to a new radiation of this group that spread out rapidly until their new decline around the Cenomanian-Turonian boundary. A new record of Calycoceras (Newboldiceras) asiaticum spinosum and the first record of a Pachyrhizodontidae indet. (Actinopterygii, Teleostei, Crossognathiformes) from the Iberian Peninsula are reported here from the Cenomanian basal units of the major Late Cretaceous transgressive episode. The two new specimens come from the same level in an outer marine ramp succession near Amurrio, Basque Country, northern Spain, and are representatives of the Cenomanian faunal turnover. The new record of a pachyrhizodontoid fish from the Cretaceous of Iberia is an indication of the ichthyofaunal replacement in this part of the world. The relict fish faunas from the Early Cretaceous of the former island of Iberia were mostly formed by basal neopterygian taxa closely related to those of the marine Jurassic of other parts of Europe. During the Early-Late Cretaceous transition they were replaced by the teleostean-based new stock that constitutes the basis of the Late Cretaceous, Cenozoic, and Recent faunas.Resumen: Se integran y discuten los datos disponibles sobre los cambios ambientales y los reemplazamientos faunísticos que sucedieron en el norte de Iberia durante la transgresión del Cenomaniense, incluyéndose nuevas evidencias de los registros fósiles de invertebrados y vertebrados. Nuevos datos estratigráficos y la revisión de secciones estratigráficas conocidas proporcionan fundamentos para la correlación de las series de rampa carbonatada cenomanienses desde el margen ibérico hasta la zona central de la Cuenca Vasco-Cantábrica, desarrolladas durante un importante episodio transgresivo. Este nuevo esquema estratigráfico configura la base para entender las cambiantes condiciones oceanográficas en la zona de estudio, las cuales resultaron de una progresiva inundación del margen continental ibérico. Esta transgresión se vislumbra como factor determinante para reemplazamientos faunísticos en esta zona, que comenzaron durante el tránsito Albiense-Cenomaniense. Los cambios en las faunas de ammonites condujeron hacia una rápida radiación del grupo hasta un nuevo declive alrededor del tránsito Cenomaniense-Turoniense. Se describen aquí un nuevo registro de Calycoceras (Newboldiceras) asiaticum spinosum y el primer registro de Pachyrhizodontidae indet. (Actinopterigii, Teleostei, Crossognathiformes) de la Península Ibérica, provenientes de la parte basaldel episodio transgresivo cenomaniense. Ambos son representativos del cambio faunístico y proceden del mismo nivel estratigráfico en una serie de rampa carbonatada externa cerca de Amurrio, País Vasco, España. Asimismo, este primer Pachyrhizodontoidei del Cretácico de Iberia indica un cambio importante en las faunas de teleósteos en esta parte del mundo. Las faunas relictas de peces del Cretácico inferior de la entonces isla de Iberia estaban básicamente compuestas por neopterigios basales directamente relacionados con los del Jurásico marino de otras partes de Europa. Durante la transición Cretácico Inferior-Cretácico Superior fueron paulatinamente reemplazados por nuevos grupos de teleósteos, los cuales constituyen la mayor parte de las formas del Cretácico Superior, del Cenozoico y actuales