Francisco Serrano

Flight aerodynamics in enantiornithines: Information from a new Chinese Early Cretaceous bird

We describe an exquisitely preserved new avian fossil (BMNHC-PH-919) from the Lower Cretaceous Yixian Formation of eastern Inner Mongolia, China. Although morphologically similar to Cathayornithidae and other small-sized enantiornithines from China’s Jehol Biota, many morphological features indicate that it represents a new species, here named Junornis houi. The new fossil displays most of its plumage including a pair of elongated, rachis-dominated tail feathers similarly present in a variety of other enantiornithines. BMNHC-PH-919 represents the first record of a Jehol enantiornithine from Inner Mongolia, thus extending the known distribution of these birds into the eastern portion of this region. Furthermore, its well-preserved skeleton and wing outline provide insight into the aerodynamic performance of enantiornithines, suggesting that these birds had evolved bounding flight—a flight mode common to passeriforms and other small living birds—as early as 125 million years ago.

Aerodynamic modelling of a Cretaceous bird reveals thermal soaring capabilities during early avian evolution

Several flight modes are thought to have evolved during the early evolution of birds. Here, we use a combination of computational modelling and morphofunctional analyses to infer the flight properties of the raven-sized, Early Cretaceous bird Sapeornis chaoyangensis—a likely candidate to have evolved soaring capabilities. Specifically, drawing information from (i) mechanical inferences of the deltopectoral crest of the humerus, (ii) wing shape (i.e. aspect ratio), (iii) estimations of power margin (i.e. difference between power required for flight and available power from muscles), (iv) gliding behaviour (i.e. forward speed and sinking speed), and (v) palaeobiological evidence, we conclude that S. chaoyangensis was a thermal soarer with an ecology similar to that of living South American screamers. Our results indicate that as early as 125 Ma, some birds evolved the morphological and aerodynamic requirements for soaring on continental thermals, a conclusion that highlights the degree of ecological, functional and behavioural diversity that resulted from the first major evolutionary radiation of birds.

A diminutive perinate European Enantiornithes reveals an asynchronous ossification pattern in early birds

Fossils of juvenile Mesozoic birds provide insight into the early evolution of avian development, however such fossils are rare. The analysis of the ossification sequence in these early-branching birds has the potential to address important questions about their comparative developmental biology and to help understand their morphological evolution and ecological differentiation. Here we report on an early juvenile enantiornithine specimen from the Early Cretaceous of Europe, which sheds new light on the osteogenesis in this most species-rich clade of Mesozoic birds. Consisting of a nearly complete skeleton, it is amongst the smallest known Mesozoic avian fossils representing post-hatching stages of development. Comparisons between this new specimen and other known early juvenile enantiornithines support a clade-wide asynchronous pattern of osteogenesis in the sternum and the vertebral column, and strongly indicate that the hatchlings of these phylogenetically basal birds varied greatly in size and tempo of skeletal maturation.Fossil juvenile Mesozoic birds are exceedingly rare and can provide important insight into the early evolution of avian development. Here, Knoll et al. describe one of the smallest known Mesozoic avians, which indicates a clade-wide asynchronous pattern of osteogenesis and great variation in basal bird hatchling size and skeletal maturation tempo.

Dental caries in the fossil record: a window to the evolution of dietary plasticity in an extinct bear

During the late Pleistocene of North America (≈36,000 to 10,000 years ago), saber-toothed cats, American lions, dire wolves, and coyotes competed for prey resources at Rancho La Brea (RLB). Despite the fact that the giant short-faced bear (Arctodus simus) was the largest land carnivoran present in the fauna, there is no evidence that it competed with these other carnivores for prey at the site. Here, for the first time, we report carious lesions preserved in specimens of A. simus, recovered from RLB. Our results suggest that the population of A. simus from RLB was more omnivorous than the highly carnivorous populations from the Northwest. This dietary variation may be a consequence of different competitive pressures.

A three-dimensional analysis of tooth-root morphology in living bears and implications for feeding behaviour in the extinct cave bear

ABSTRACT The morphology of both crowns and tooth-roots reflects dietary specialisation in mammalian carnivores. In this article, we analyse the tooth-root morphology of maxillary teeth from CT scans of living bears (Ursus arctos, Ursus americanus, Ursus maritimus, Ursus thibetanus, Melursus ursinus, Helarctos malayanus, Tremarctos ornatus and Ailuropoda melanoleuca) in order to make inferences about the diet and feeding behaviour of the extinct cave bear (Ursus spelaeus sensu lato). Specifically, we investigate two major mitochondrial clades of extinct cave bears recognized by previous authors: Ursus ingressus and Ursus spelaeus (U. spelaeus spelaeus, U. spelaeus ladinicus, U. spelaeus eremus). Our results indicate a close association between tooth-root surface area and feeding behaviour in all living bear species. Tooth-root surface area values of cave bears suggest that they relied more on vegetative matter than living brown bears (Ursus arctos) but subtle differences between these species/subspecies could also indicate different feeding strategies among the members of cave bear complex.