Pseudosuchia: Masters of survival and diversification.

In the context of an increasing interest for Pseudosuchia, we have compiled a Special Issue, comprising 14 collaborative studies that deepen our understanding of pseudosuchian evolution. These contributions range from the description of a new taxon to exhaustive reviews of thermometabolism, morphological adaptation, systematics, and detailed investigations into ontogeny, paleoneurology, paleohistology, and paleobiology. Through these papers, we explore the evolutionary history of pseudosuchian archosaurs, spotlighting their rise and diversification following the end-Permian mass extinction.

Evaluating extinct pseudosuchian body mass estimates using a femur volume-based model.

The clade Pseudosuchia appeared 250 million years ago. The exclusively semi-aquatic Crocodylia, which includes crocodiles, alligators, caimans, and gharials is the only surviving subgroup. Investigating Crocodylia biology is pivotal for inferring traits of extinct pseudosuchians.

On the origins of endothermy in amniotes.

A recent study showed evidence that endothermy was ancestral for amniotes using a variety of proxies and a large sample of taxa. However, it did not include numerous crucial taxa. We reevaluated this hypothesis using a large sample of early amniotes and tetrapodomorphs.

Inferring the lifestyles of extinct Crocodyliformes using osteoderm ornamentation.

Osteoderms are bony plates formed within the dermis of diverse vertebrate groups. They are present in all crocodylomorphs but Metriorhynchidae. Most of them show typical bone ornamentation consisting of pits and ridges on their outer surface.

A survey of osteoderm histology and ornamentation among Crocodylomorpha: A new proxy to infer lifestyle?

Osteoderms of eight extant and extinct species of crocodylomorphs are studied histologically and morphologically. Most osteoderms display the typical "crocodilian" structure with a woven-fibered matrix surrounded by an upper and a lower parallel fibered matrix. The dorsal ornamentation of those specimens consists of a pit-and-ridge structure, with corresponding remodeling mechanisms.

Osteohistological characterization of notosuchian osteoderms: Evidence for an overlying thick leathery layer of skin.

Osteoderms are mineralized structures embedded in the dermis, known for nonavian archosaurs, squamates, xenarthrans, and amphibians. Herein, we compared the osteoderm histology of Brazilian Notosuchia of Cretaceous age using three neosuchians for comparative purposes. Microanatomical analyses showed that most of them present a diploe structure similar to those of other pseudosuchians, lizards, and turtles.

Vertebrate palaeophysiology.

Physiology is a functional branch of the biological sciences, searching for general rules by which explanatory hypotheses are tested using experimental procedures, whereas palaeontology is a historical science dealing with the study of unique events where conclusions are drawn from congruence among independent lines of evidence. Vertebrate palaeophysiology bridges these disciplines by using experimental data obtained from extant organisms to infer physiological traits of extinct ones and to reconstruct how they evolved. The goal of this theme issue is to understand functional innovations imprinted on modern vertebrate clades, and how to infer (or 'retrodict') physiological capacities in their ancient relatives As such, the present collection of papers deals with different aspects of a rapidly growing field to understand innovations in: phospho-calcic metabolism, acid-base homeostasis, thermometabolism, respiratory physiology, skeletal growth, palaeopathophysiology, genome size and metabolic rate, and it concludes with a historical perspective.

Were the synapsids primitively endotherms? A palaeohistological approach using phylogenetic eigenvector maps.

The acquisition of mammalian endothermy is poorly constrained both phylogenetically and temporally. Here, we inferred the resting metabolic rates (RMRs) and the thermometabolic regimes (endothermy or ectothermy) of a sample of eight extinct synapsids using palaeohistology, phylogenetic eigenvector maps (PEMs), and a sample of 17 extant tetrapods of known RMR (quantified using respirometry). We inferred high RMR values and an endothermic metabolism for the anomodonts ( sp.

The influence of plane of section on the identification of bone tissue types in amniotes with implications for paleophysiological inferences.

The proportion of woven bone (WB) to parallel-fibered bone has been extensively used to infer bone growth rates and resting metabolic rates of extinct organisms. The aim of this study is to test in a variety of amniotes how reliably WB content can be measured using transverse sections. For this, we analyzed femoral transverse mid-diaphyseal thin sections of 14 extant and extinct taxa and the corresponding longitudinal sections for comparative purposes.

Multimethod Approach to the Early Postnatal Growth of the Mandible in Mice from a Zone of Robertsonian Polymorphism.

The western European house mouse (Mus musculus domesticus) shows high karyotypic diversity owing to Robertsonian translocations. Morphometric studies conducted with adult mice suggest that karyotype evolution due to these chromosomal reorganizations entails variation in the form and the patterns of morphological covariation of the mandible. However, information is much scarcer regarding the effect of these rearrangements on the growth pattern of the mouse mandible over early postnatal ontogeny.

Comparative postnatal histomorphogenesis of the mandible in wild and laboratory mice.

The coordinated activity of bone cells (i.e., osteoblasts and osteoclasts) during ontogeny underlies observed changes in bone growth rates (recorded in bone histology and bone microstructure) and bone remodeling patterns explaining the ontogenetic variation in bone size and shape.

Bone histological correlates of soaring and high-frequency flapping flight in the furculae of birds.

The furcula is a specialized bone in birds involved in flight function. Its morphology has been shown to reflect different flight styles from soaring/gliding birds, subaqueous flight to high-frequency flapping flyers. The strain experienced by furculae can vary depending on flight type.

Static osteogenesis does not precede dynamic osteogenesis in periosteal ossification of Pleurodeles (Caudata, Amphibia) and Pogona (Squamata, Lepidosauria).

Two successive mechanisms have been described in perichondral ossification: (1) in static osteogenesis, mesenchymal cells differentiate into stationary osteoblasts oriented randomly, which differentiate into osteocytes in the same site; (2) in dynamic osteogenesis, mesenchymal cells differentiate into osteoblasts that are all oriented in the same direction and move back as they secrete collagen fibers. This study is aimed at testing the hypothesis that the ontogenetic sequence static then dynamic osteogenesis observed in the chicken and in the rabbit is homologous and was acquired by the last common ancestor of amniotes or at a more inclusive node. For this we analyze the developmental patterns of Pleurodeles (Caudata, Amphibia) and those of the lizard Pogona (Squamata, Lepidosauria).

Palaeohistological Evidence for Ancestral High Metabolic Rate in Archosaurs.

Metabolic heat production in archosaurs has played an important role in their evolutionary radiation during the Mesozoic, and their ancestral metabolic condition has long been a matter of debate in systematics and palaeontology. The study of fossil bone histology provides crucial information on bone growth rate, which has been used to indirectly investigate the evolution of thermometabolism in archosaurs. However, no quantitative estimation of metabolic rate has ever been performed on fossils using bone histological features.

First Reported Cases of Biomechanically Adaptive Bone Modeling in Non-Avian Dinosaurs.

Predator confrontation or predator evasion frequently produces bone fractures in potential prey in the wild. Although there are reports of healed bone injuries and pathologies in non-avian dinosaurs, no previously published instances of biomechanically adaptive bone modeling exist. Two tibiae from an ontogenetic sample of fifty specimens of the herbivorous dinosaur Maiasaura peeblesorum (Ornithopoda: Hadrosaurinae) exhibit exostoses.

A quantitative assessment of bone area increase due to ornamentation in the Crocodylia.

Bone ornamentation, in the form of highly repetitive motives created by pits and ridges, is a frequent feature on vertebrate skull roofs and osteoderms. The functional significance of this character remains a matter of controversy and speculation. The many diverging hypotheses proposed to explain it all share a common logical prerequisite: bone ornamentation should increase significantly the surface area of the bones that bear it.

Morphological integration and functional modularity in the crocodilian skull.

We explored the morphological organization of the skull within Crocodylidae, analyzing functional and phylogenetic interactions between its 2 constituent functional modules: the rostrum and the postrostrum. We used geometric morphometrics to identify localized shape changes, focusing on the differences between the major clades of the crown-group Crocodylia: Alligatoridae and Crocodylidae. We used published bite performance data to correlate rostral function with postrostral morphology.

Flightlessness affects cranial morphology in birds.

Flightless birds belonging to phylogenetically distant clades share several morphological features in the pectoral and pelvic apparatus. There are indications that skull morphology is also influenced by flightlessness. In this study we used a large number of flightless species to test whether flightlessness in modern birds does indeed affect cranial morphology.

Postnatal histomorphogenesis of the mandible in the house mouse.

The mandible of the house mouse, Mus musculus, is a model structure for the study of the development and evolution of complex morphological systems. This research describes the histomorphogenesis of the house mouse mandible and analyses its biological significance from the first to the eighth postnatal weeks. Histological data allowed us to test a hypothesis concerning modularity in this structure.

The Gavialis-Tomistoma debate: the contribution of skull ontogenetic allometry and growth trajectories to the study of crocodylian relationships.

The phylogenetic placement of Tomistoma and Gavialis crocodiles depends largely upon whether molecular or morphological data are utilized. Molecular analyses consider them as sister taxa, whereas morphological/paleontological analyses set Gavialis apart from Tomistoma and other crocodylian species. Here skull allometric trajectories of Tomistoma and Gavialis were contrasted with those of two longirostral crocodylian taxa, Crocodylus acutus and Mecistops cataphractus, to examine similarities in growth trajectories in light of this phylogenetic controversy.

Bone growth marks reveal protracted growth in New Zealand kiwi (Aves, Apterygidae).

The presence of bone growth marks reflecting annual rhythms in the cortical bone of non-avian tetrapods is now established as a general phenomenon. In contrast, ornithurines (the theropod group including modern birds and their closest relatives) usually grow rapidly in less than a year, such that no annual rhythms are expressed in bone cortices, except scarce growth marks restricted to the outer cortical layer. So far, cyclical growth in modern birds has been restricted to the Eocene Diatryma, the extant parrot Amazona amazonica and the extinct New Zealand (NZ) moa (Dinornithidae).

Phylogenetic, functional, and structural components of variation in bone growth rate of amniotes.

The biological features observed in every living organism are the outcome of three sets of factors: historical (inherited by homology), functional (biological adaptation), and structural (properties inherent to the materials with which organs are constructed, and the morphogenetic rules by which they grow). Integrating them should bring satisfactory causal explanations of empirical data. However, little progress has been accomplished in practice toward this goal, because a methodologically efficient tool was lacking.