Loïc Costeur

A Revision of the Lari (Aves, Charadriiformes) from the Early Miocene of Saint-Gérand-Le-Puy (Allier, France)

ABSTRACT Three species of gull-like birds were described by Milne-Edwards in the 19th century from the early Miocene of Saint-Gérand-le-Puy, France, two of which have been since then moved to the genus Laricola. These fossils are redescribed and revised in the present study. We further describe two new species of the taxon Laricola, L. intermedia, sp. nov., and L. robusta, sp. nov., as well as two species of a new taxon Sternalara, S. minuta and S. milneedwardsi, thus substantially increasing the number of charadriiform taxa known from this locality. To find out how Laricola relates to modern taxa, we performed a phylogenetic analysis of 41 osteological characters, which resulted in Laricola being placed outside of Lariidae, as early representatives of the newly designated group Laromorphae, which encompasses terns, gulls, and skimmers. The results of our analysis have additionally enabled us to evaluate relationships between extant taxa of the Laromorphae.

Shape variation and ontogeny of the ruminant bony labyrinth, an example in Tragulidae.

Despite its growing use in anatomical and ecological studies, the morphological variability and ontogenetic development of the bony labyrinth have very rarely been investigated in ruminants. Here we study its morphology in 15 adult and 10 juvenile specimens in the three extant tragulid ruminant genera. Intraspecific and interspecific variability is quantified using morphometric and 3D geometric morphometrics analyses. The bony labyrinth of Tragulus, Hyemoschus, and Moschiola is strikingly different, clustering in clearly different morphospaces despite similar ecological adaptations. Although the bony labyrinths within two species of the same genus cannot be distinguished from each other based on the chosen semi‐landmarks, discrete interspecific differences exist. We were able to show for the first time that an artiodactyl mammal in a late fetal stage possesses an almost fully formed bony labyrinth similar to that of adults. No significant change either occurs in size or morphology after ossification of the petrosal bone. Some intraspecific variation is observed on the shape of the lateral semi‐circular canal, the size and shape of the common crus, the coil of the cochlea or the stapedial ratio. Variable structures are expected to be highly informative characters for a large cladistic analysis. They can be used for phylogenetic studies in ruminants. Incorporating juvenile specimens in studies is not problematic, as they fall within the morphological range of adults.

Prenatal growth stages show the development of the ruminant bony labyrinth and petrosal bone

Foetuses are a source of scientific information to understand the development and evolution of anatomical structures. The bony labyrinth, surrounding the organ of balance and hearing, is a phylogenetically and ecologically informative structure for which still little concerning growth and shape variability is known in many groups of vertebrates. Except in humans, it is poorly known in many other placentals and its prenatal growth has almost never been studied. Ruminants are a diversified group of placentals and represent an interesting case study to understand the prenatal growth of the ear region. We computed tomography ‐scanned five cow foetuses and an adult petrosal bone (Bos taurus, Artiodactyla, Mammalia), and describe the bony labyrinth when already ossified. The foetuses encompass the second half of the 9.3‐month‐long gestation period of the cow. They were sampled at different ontogenetic stages to understand how and when the petrosal bone and bony labyrinth ossify in ruminants. The petrosal bone and bony labyrinth ossify within about 20 days in the fourth month of gestation. The bony labyrinth is already fully ossified at least in the 6th month, while only the cochlea, most of the vestibule and the common crus are already ossified at the beginning of the 4th month. The pars canalicularis of the petrosal thus ossifies at last. The size and volume of the bony labyrinth stay similar from the 6th month (possibly even from the 5th). From the end of the 4th month of gestation, a progressive lengthening of the cochlear aqueduct and endolymphatic sac occurs, culminating in the adult form and partly explaining the larger volume of the later. The inner ear in the cow ossifies quickly during the gestation period, being fully ossified around mid‐gestation time, as in humans. The adult size and most of its volume are reached by mid‐gestation time while the petrosal bone and skull still grow. A negative ontogenetic allometry between the bony labyrinth and the petrosal bone and skull is thus observed. It matches the evolutionary negative allometry of the structure observed in earlier studies. Few changes occur after ossification is achieved; only open structures (i.e. cochlear aqueduct and endolymphatic sac) continue to grow after birth and reflect size increase of the petrosal bone.

Testing for Depéret's Rule (Body Size Increase) in Mammals using Combined Extinct and Extant Data

Whether or not evolutionary lineages in general show a tendency to increase in body size has often been discussed. This tendency has been dubbed “Copes rule” but because Cope never hypothesized it, we suggest renaming it after Depéret, who formulated it clearly in 1907. Depérets rule has traditionally been studied using fossil data, but more recently a number of studies have used present-day species. While several paleontological studies of Cenozoic placental mammals have found support for increasing body size, most studies of extant placentals have failed to detect such a trend. Here, we present a method to combine information from present-day species with fossil data in a Bayesian phylogenetic framework. We apply the method to body mass estimates of a large number of extant and extinct mammal species, and find strong support for Depérets rule. The tendency for size increase appears to be driven not by evolution toward larger size in established species, but by processes related to the emergence of new species. Our analysis shows that complementary data from extant and extinct species can greatly improve inference of macroevolutionary processes.

Diversity trends in Neogene European ungulates and rodents: large-scale comparisons and perspectives

The ungulate and rodent fossil records are often used independently to understand mammalian evolutionary history. Few studies have directly compared both records over long time periods and large geographic areas. Here, we compiled two datasets of European fossil localities containing rodents and/or ungulates over 20 My (Early Miocene–Early Pliocene) and processed the data with the same methodology. We counted the raw diversity and calculated a measure of evenness (Pielou’s index). After controlling for potential biases on diversity estimators, we identify the evenness index as a more reliable estimator bringing interesting insights into the way both mammal groups are structured by biotic or abiotic factors. In this study, we consider that an uneven distribution of the species richness among families, when only some families successfully diversify within the “continental-scale community”, represents a lower adaptability of this community to the environmental context. Pielou’s index is used to estimate this adaptability through time. The responses of ungulates and rodents to environmental changes are very divergent, especially facing the climatic changes known since the Middle Miocene. The general patterns suggest that rodent broad-scale assemblages are affected by all kinds of perturbations, even short biotic and abiotic events, but show a better adaptability when facing long-term abiotic changes. Unlike rodents, the ungulate assemblages show more stability in periods of relative environmental stability but show less adaptability to long-term climatic changes. Life-history traits of mammals can help explain patterns of diversity and biogeography at different spatial scales and may probably partly explain the opposite patterns evidenced here.

A Dorcatherium (Mammalia, Ruminantia, Middle Miocene) petrosal bone and the tragulid ear region

ABSTRACT A petrosal bone from the French Middle Miocene locality Sansan is described. It belongs to the tragulid species Dorcatherium crassum. Using high-resolution X-ray computed tomography, we scanned this petrosal bone and segmented its embedded bony labyrinth. We compared the morphological data with those of three living Tragulidae: Tragulus javanicus, Hyemoschus aquaticus, and Moschiola meminna. We ran a phylogenetic analysis where fossil and extant pecoran ruminants were included to understand the distribution of characters of the petrosal bone and bony labyrinth within ruminants. We propose a set of new synapomorphies for the Tragulidae among the Ruminantia, including the absence of the basicapsular groove, a knob-shaped mastoid region, a knob anterior to the subarcuate fossa on the petrosal bone, a high number of cochlea turns, the dorsal insertion of the posterior limb of the lateral semicircular canal, the extension of the lateral semicircular canal beyond the plane of the posterior semicircular canal in dorsal view, and a pouch-like endolymphatic sac on the bony labyrinth. The clade constituted by Tragulus and Moschiola is confirmed by new synapomorphies such as a double convexity of the promontorium and a large pouch-like endolymphatic sac that covers the common crus. We demonstrate the potential of characters of the bony labyrinth for the phylogeny of ruminants.

Primate tarsal bones from Egerkingen, Switzerland, attributable to the middle Eocene adapiform Caenopithecus lemuroides

The middle Eocene species Caenopithecus lemuroides, known solely from the Egerkingen fissure fillings in Switzerland, was the first Paleogene fossil primate to be correctly identified as such (by Ludwig Rütimeyer in 1862), but has long been represented only by fragmentary mandibular and maxillary remains. More recent discoveries of adapiform fossils in other parts of the world have revealed Caenopithecus to be a biogeographic enigma, as it is potentially more closely related to Eocene adapiforms from Africa, Asia, and North America than it is to any known European forms. More anatomical evidence is needed, however, to provide robust tests of such phylogenetic hypotheses. Here we describe and analyze the first postcranial remains that can be attributed to C. lemuroides-an astragalus and three calcanei held in the collections of the Naturhistorisches Museum Basel that were likely recovered from Egerkingen over a century ago. Qualitative and multivariate morphometric analyses of these elements suggest that C. lemuroides was even more loris-like than European adapines such as Adapis and Leptadapis, and was not simply an adapine with an aberrant dentition. The astragalus of Caenopithecus is similar to that of younger Afradapis from the late Eocene of Egypt, and parsimony and Bayesian phylogenetic analyses that include the new tarsal data strongly support the placement of Afradapis and Caenopithecus as sister taxa to the exclusion of all other known adapiforms, thus implying that dispersal between Europe and Africa occurred during the middle Eocene. The new tarsal evidence, combined with previously known craniodental fossils, allows us to reconstruct C. lemuroides as having been an arboreal and highly folivorous 1.5-2.5 kg primate that likely moved slowly and deliberately with little or no capacity for acrobatic leaping, presumably maintaining consistent powerful grasps on branches in both above-branch and inverted postures.

Diversity and body size in giant caviomorphs (Rodentia) from the northern Neotropics—a study of femoral variation

ABSTRACT New discoveries of numerous fossil femora from giant caviomorph rodents from the Miocene of Venezuela and a specimen of aMiocene giant rodent from Trinidad in the collections of the Naturhistorisches Museum in Basel made possible the first examination of taxonomic, ontogenetic, and functional variation in these animals. We provide comparisons of femoral shape, metrics, and growth (epiphyseal closure), finding that four morphotypes are distinguishable based largely on degrees of robustness or gracility. This indicates that the diversity of giant caviomorphs was larger than previously known; Phoberomys pattersoni was not the only giant caviomorph that inhabited the Miocene of the northern Neotropics. The study of cortical cross-sectional area of fossils serves to estimate the body mass for two giant caviomorphs at 420–580 kg. The first description of patterns of bone microstructure in three fossil giant caviomorph femora reveals similarities to extant rodents: absence of Haversian tissue and presence of layers of lamellar followed by reticular-like bone.

Evidence of northern Turolian savanna-woodland from the Dorn-Dürkheim 1 fauna (Germany)

Western European Turolian mammalian faunas and palaeoenvironments are less well known than middle and early late Miocene ones for which more data exist at a time when major climate events occurred (Middle Miocene Climatic Optimum followed by Late Middle Miocene Climatic Cooling). In this respect, rich faunas represent exceptional windows into mammalian diversity and biogeography. They constitute key points to understand local palaeoenvironments and refine larger-scale patterns. Dorn-Dürkheim 1 is one of the richest mammalian faunas of Western Europe with at least 79 species of mammals. We investigate this fauna and compare its composition to the faunal and biogeographic context of the European late Miocene. A community-based analysis of body masses of the constituent species together with an original approach on predator–prey biomasses are also attempted to reconstruct its palaeoenvironment. While its composition reflects the known late Miocene context and fits in the biogeographic North–South pattern evidenced by earlier studies, the reconstructed landscape is different from previous hypotheses of densely forested habitats. Our results suggest the presence of a savanna-woodland biome more open than previously thought, in a subtropical-like and seasonal climate. Other palaeoecological studies on elements of the large mammal fauna confirm this interpretation.

The Moschidae of Dorn-Dürkheim 1 (Germany)

The locality of Dorn-Dürkheim houses the youngest record for the family Moschidae in Europe besides Micromeryx mirus from Kohfidisch (Austria; Vislobokova Paleontol J 41(4):451–460, 2007) and Hispanomeryx sp. from Puente Minero (Spain; Sánchez et al. Palaeontology 53(5):1023–1047, 2010). In describing the moschid material from Dorn-Dürkheim, we intend to update the data on the European late Miocene representatives of the family. With a nearly closed anterior valley in p4 and brachy- to mesodont (sensu Damuth and Janis Biol Rev 86(3):733–758, 2011) lower molars, the material of small ruminants from Dorn-Dürkheim shows typical features of the Miocene Moschidae that clearly distinguish them from dental remains of similar sized but more brachydont taxa, such as Lagomeryx (Rössner Palaeontogr A 277:103–112, 2006). Dimensionally, both the teeth and the postcranial material fit well within the variability of the genus Micromeryx. Morphologically, the postcranial material clearly differs from that of Hispanomeryx. Therefore, we assign the material from Dorn-Dürkheim 1 to Micromeryx sp. A brief review of the biochronologic and palaeogeographic range of the European Miocene Moschidae is given.