The development of distinct regions in the amniote vertebral column results from somite formation and Hox gene expression, with adult morphology displaying remarkable variation among lineages. Mammalian regionalization is reportedly very conservative or even constrained, but there has been no study investigating count across Amniota as a whole, undermining attempts to understand phylogenetic, ecological, developmental factors affecting variation. Here, we show that mammalian (synapsid)...

Examining the geological past of our planet allows us to study periods severe climatic and biological crises recoveries, biotic abiotic ecosystem fluctuations, faunal floral turnovers through time. Furthermore, recovery dynamics large predators provide a key for evaluation pattern tempo because are interpreted react most sensitively environmental turbulences. The end-Permian mass extinction was crisis experienced by life on Earth, common paradigm persists that from event unusually slow...

Sauria is the crown-group of Diapsida and subdivided into Lepidosauromorpha Archosauromorpha, comprising a high percentage diversity living fossil tetrapods. The split between lepidosauromorphs archosauromorphs (the crocodile-lizard, or bird-lizard, divergence) considered one key calibration points for molecular analyses tetrapod phylogeny. Saurians have very rich Mesozoic Cenozoic record, but their late Paleozoic (Permian) record problematic. Several Permian specimens been referred to...

ABSTRACT Here, we provide a comparative survey of the histology postcranial dermal-armor osteoderms ankylosaurs, including material polacanthids (Polacanthus foxii, Gastonia sp.), ankylosaurids (e.g., Saichania chulsanensis, Pinacosaurus grangeri, Ankylosauridae indet.), and nodosaurids Struthiosaurus austriacus, Nodosauridae indet.). Samples osteoderm-bearing outgroups (Scelidosaurus harrisonii, phytosaurs, crocodiles) as well literature data on Stegosaurus stenops plates spikes helped to...

The palaeoecology of basal turtles from the Late Triassic was classically viewed as being semi-aquatic, similar to lifestyle modern snapping turtles. Lately, this view questioned based on limb bone proportions, and a terrestrial suggested for turtle stem. Here, we present independent shell microstructural evidence habitat oldest most well-known turtles, i.e. Upper Proterochersis robusta Proganochelys quenstedti . Comparison their histology with that extant preferring either aquatic habitats...

The interest in mammalian palaeohistology has increased dramatically the last two decades. Starting 1849 via descriptive approaches, it been demonstrated that bone tissue and vascularisation types correlate with several biological variables such as ontogenetic stage, growth rate, ecology. Mammalian displays a large variety of tissues patterns reaching from lamellar or parallel-fibred to fibrolamellar woven-fibred bone, depending on taxon individual age. Here we systematically review...

Bone microstructure reflects physiological characteristics and has been shown to contain phylogenetic ecological signals. Although mammalian long bone histology is receiving increasing attention, systematic examination of the main clades not yet performed. Here we describe Xenarthra based on thin sections representing twenty-two species. Additionally, patterns in compactness humeri femora are investigated. The primary tissue xenarthran bones composed a mixture woven, parallel-fibered...

As in other archosauriforms, phytosaurs and aetosaurs are characterized by the presence of well-developed osteoderms. Here we provide a comparative study on microstructure phytosaur (five taxa) aetosaur (thirteen For outgroup comparison, sampled osteoderms sister taxon to Aetosauria, Revueltosaurus callenderi, doswelliid Jaxtasuchus salomoni. Phytosaur, aetosaur, composed diploe structure, whereas osteoderm microanatomy is more compact. The external cortex phytosaurs, mainly parallel-fibered...

Abstract We investigated the development of whole skeleton soft‐shelled turtle Pelodiscus sinensis, with particular emphasis on pattern and sequence ossification. Ossification starts at late Tokita‐Kuratani stage (TK) 18 maxilla, followed by dentary prefrontal. The quadrate is first endoskeletal ossification appears TK 22. All adult skull elements have started 25. Plastral bones are postcranial to ossify, whereas nuchal carapacial bone appearing as two unstained anlagen. Extensive...

A new, thin-shelled fossil from the Upper Triassic (Revueltian: Norian) Chinle Group of New Mexico, Chinlechelys tenertesta , is one most primitive known unambiguous members turtle stem lineage. The nature new combined with its likely terrestrial habitat preference hint at taphonomic filters that basal turtles had to overcome before entering record. possesses neck spines formed by multiple osteoderms, indicating earliest were covered rows dermal armour. More importantly, primitive,...

Body size variation within clades of mammals is widespread, but the developmental and life-history mechanisms by which this achieved are poorly understood, especially in extinct forms. An illustrative case study that dwarfed morphotypes Candiacervus from Pleistocene Crete versus giant deer Megaloceros giganteus, both a clade together with Dama dama among extant species. Histological analyses long bones teeth phylogenetic context have been shown to provide reliable estimates growth life...

Background Ichthyosaurs are Mesozoic reptiles considered as active swimmers highly adapted to a fully open-marine life. They display wide range of morphologies illustrating diverse ecological grades. Data concerning their bone microanatomical and histological features rather limited suggest that ichthyosaurs spongious, "osteoporotic-like" inner structure, like extant cetaceans. However, some taxa exhibit peculiar features, suggesting the analysis characteristics various ichthyosaur long...

Current characterizations of early dinosaur evolution are incomplete: existing palaeobiological and phylogenetic scenarios based on a fossil record dominated by saurischians the implications ornithischian often overlooked. Moreover, timings deep divergences within Dinosauria poorly constrained owing to absence rigorous chronostratigraphical framework for key Late Triassic-Early Jurassic localities. A new from earliest Venezuelan Andes is first basal recovered terrestrial deposits directly...

Abstract Recently it was suggested that the phylogenetic clustering of Mesozoic marine reptile lineages, such as thalattosaurs, very successful fish-shaped ichthyosaurs and sauropterygians (including plesiosaurs), among others, in a so-called ‘superclade’ is an artefact linked to convergent evolution morphological characters associated with shared lifestyle. Accordingly, partial ‘un-scoring’ problematic proposed. Here we report new, exceptionally preserved mostly articulated juvenile...

The largest extinct turtle from South America had males with horned shells.

The genus Macrocnemus is a member of the Tanystropheidae, clade non-archosauriform archosauromorphs well known for their very characteristic, elongated cervical vertebrae. Articulated specimens are from Middle Triassic Alpine Europe and China. Although multiple articulated known, description cranial morphology has proven challenging due to crushed preservation specimens. Here we use synchrotron micro computed tomography analyse specimen type species bassanii Besano Formation Monte San...