Jorge Cubo

The enantiornithes, a group of Mesozoic birds, have morphological features suggesting a precocial mode of development; however, their detailed physiological characteristics, particularly hatchling metabolic rates, have yet to be explored. Here, we retrodicted metabolic rates for four Lower Cretaceous enantiornithines: one hatchling, one adult from Las Hoyas, one early post-hatching juvenile and one post-juvenile individual from the Jehol Biota, using phylogenetic comparative analyses and a comprehensive dataset of extant birds spanning the altricial–precocial spectrum. By examining vascular density (related to resting metabolic rate (RMR)) and nutrient foraminal size (proportional to blood flow rate) as proxies, we inferred the metabolic scope of the hatchling enantiornithine and determined that it fell toward the precocial end of the altricial–precocial spectrum. The RMR values of the two enantiornithine chicks were retrodicted as 0.67 mlO2 h–1 g–0.93. The peak metabolic rate (PMR) retrodicted is twice the resting metabolism for the Las Hoyas hatchling. These results are consistent with a semi-precocial/precocial development characterized by independent locomotion by climbing using the wing claws soon after hatching. However, flapping flight may have been delayed, owing to incomplete ossification of the sternum, as observed in one hatchling specimen.

Studies on paleophysiology and thermoregulation are central topics in fossil vertebrate paleobiology because they allow inferences about extinct organismal function beyond anatomical description. Pterosaur thermophysiology remains actively debated. Evidence such as relatively rapid growth and elevated metabolic rate estimates has been used to argue for endothermic-like physiologies consistent with the energetic demands of powered flight, whereas reproductive traits, including burial incubation and precocial development, have led some authors to propose ectothermic strategies more akin to those of extant non-avian diapsids. Here, we provide quantitative estimates of resting metabolic rate (RMR) for the tapejarid pterosaur Caiuajara dobruskii using phylogenetic eigenvector maps and osteocyte lacunar density as proxy. Analysis of six histological sections from three appendicular elements (femur, tibia, humerus) at different ontogenetic stages (adult and juvenile) yielded mass-independent RMR estimates of 0.24–0.76 ml O ₂ h ⁻¹ g ^−0.86 , substantially higher than those of lepidosaurs but lower than typical mammalian and avian values. The retrodicted mass-independent maximum metabolic rate (MMR) of 5.68 ml O ₂ h ⁻¹ g ^−0.87 falls between values for highly active reptiles and birds, suggesting sufficient aerobic capacity to sustain powered flight without fully matching the maximal performance of small endotherms. Together, these results suggest active-flighted pterosaurs fall among a metabolically intermediate continuum, limiting straightforward actualistic comparisons for inferring their thermoregulatory strategy.

Phylogenetic comparative methods have been used in recent literature to work with laws and test for regularities (evolutionary associations of quantitative features) and evolutionary singularities (features that evolved in a single taxon). We analyzed these uses epistemologically, taking the evolution of red‐blood‐cell mean corpuscular volume (MCV) in mammals as a case study. For this, we considered three hypotheses: (i) in the absence of natural selection, other forces or constraints acting on the variation of MCV, MCV variance increases with evolutionary time, as predicted by biology's first law. Our results show that MCV evolves following Brownian motion which, according to Donsker's theorem, is the limit of the random walks on which the law is based on; (ii) MCV decreases as mass‐independent basal‐metabolic‐rate increases, probably because smaller red‐blood‐cells are more efficient than larger ones at delivering oxygen in tissues. We show evidence for such evolutionary association so we are facing a regularity; (iii) outliers to the latter regularity (extreme MCV values) are evolutionary singularities. We show evidence for a significant difference between the value predicted by an inference model and that observed in Tragulus javanicus . Although at first sight laws and regularities have more in common with each other than with evolutionary singularities, they are fundamentally different: “biology's first law” is based on a priori , mathematical reasoning, whereas the regularity hypothesis is based on empirical data. Regularities and evolutionary singularities are two sides of the same coin, the latter appearing as the exceptions that, so to say, prove the rule.

Numerous tools have been developed since the advent of phylogenetic methods to assess tree robustness. Identifying the degree of contradiction in a phylogenetic matrix, as well as the specific contribution of each taxon and character, is essential for estimating its reliability. In parsimony-based phylogenetic inferences, classically used by paleontologists, a phylogeny results from the interaction of all the characters used in the analysis. Consequently, the support initially provided by the characters in the matrix may differ from that after optimization in the final tree, severing the link between the phylogenetic content of the matrix and that of the final tree. Thus, all methods aimed at measuring support only do so indirectly and the impact of individual characters or taxa can only be assessed after the analysis. Three-taxon analysis (3ta) is a phylogenetic method that can circumvent these issues by precisely measuring the support of targeted characters and/or taxa directly from the phylogenetic matrix. In 3ta, characters are coded as trees and decomposed into three-taxon statements (3ts). The analysis searches for the largest set of non-contradicting 3ts to compute the optimal classification. Because the analysis is a compatibility procedure, not an optimization procedure, character supports on the tree are independent from one another. This enables direct assessment of support from the matrix, providing meaningful insights into the topology of the optimal trees. Moreover, the decomposition of characters into 3ts allows for precise quantification of the impact of the characters/taxa in the results. In this study, focusing on Crocodylia (a subject of ongoing debate over recent decades), we use 3ta to measure the support of specific characters and/or taxa in the recently published matrix of Rio and Mannion (Rio J.P., Mannion P.D. 2021. Phylogenetic analysis of a new morphological dataset elucidates the evolutionary history of Crocodylia and resolves the long-standing gharial problem. PeerJ 9:e12094). This conflict revolves around two competing hypotheses—Longirostres and Brevirostres—supporting a different placement of the Gavialoidea clade. We also introduce here the Relative Contradiction Index (RCI) to evaluate node support, a metric that reflects the degree of contradiction in a matrix between competing cladistic hypotheses, ranging from 0.5 (maximum contradiction) to 1 (no contradiction). We show that although the Longirostres hypothesis is best-supported, it is strongly challenged by the Brevirostres hypothesis (RCI = 0.62). Furthermore, we find that Tomistominae provides 61% of the supporting evidence for the Longirostres hypothesis, such that, when removed, the matrix supports the Brevirostres hypothesis. Individual tomistomines’ contributions vary only from 2% to 7% of the total support to the Longirostres hypothesis. Finally, we show that characters correlated to longirostry only provide a fraction (22%) of the total support to the Longirostres hypothesis. Thus, our method can quantify the impact of specific characters or taxa on a phylogenetic result. This should prove very useful to phylogeneticists, especially when dealing with incomplete material such as fossils.

We infer the neonatal metabolic rate at rest (RMR) and at maximum activity levels (MMR) of the hadrosaurid dinosaur Maiasaura peeblesorum from the Two Medicine Formation of Montana (USA) using Phylogenetic Eigenvector Maps applied to the following osteohistological features: the Relative Primary Osteon Area and the size of the femoral nutrient foramen as proxies. We investigate the locomotor/motor activity of the neonates by comparing the difference between maximum and minimum rates of oxygen consumption—referred to as aerobic scope and denoted as ΔMR, as a proxy of their activity levels. Applied to Maiasaura, this novel methodology allows for a quantitative assessment of its neonatal state and to deduce its dependence on parental care. The inferred neonatal RMR values for Maiasaura are similar to those of present-day fast-growing endotherms. As for the aerobic scope, M. peeblesorum neonates have a ΔMR value similar to those observed in present-day altricial birds that need intensive parental care. This result is consistent with the previously proposed hypothesis of nidicolous M. peeblesorum requiring parental care. Finally, based on age-estimations from M. peeblesorum neonate remains found both in and outside nest sites, we estimate that this species remained in the nest for approximately 40–75 days. Maiasaura provides a useful ecological baseline from which to infer neonatal states in an other hadrosaur of similar adult size—Hypacrosaurus stebingeri, whose differing ecological traits point to a relatively more precocial condition. The diversity of post-hatching reproductive strategy partly explains the adaptation of hadrosaurs to a wide range of paleolatitudes and environments.

Thalattosuchia are a particularly diverse group of mostly marine crocodylomorphs that lived during most of the Jurassic and Lower Cretaceous. Previous studies have sought to uncover the factors influencing Crocodylomorpha evolution, yielding mixed results, possibly due to Thalattosuchia's unique ecological niche and controversial phylogenetic placement among crocodylomorphs. Here, we propose a Thalattosuchia‐focused study using phylogenetically‐informed statistical analyses. First, we tested the phylogenetic structure of thalattosuchian extinction at various geological transitions. We then tested the influence of biotic and abiotic factors explaining thalattosuchian diversity at the aforementioned crises. Finally, we tested whether diet was an additional explanatory factor. We found that: (1) thalattosuchian extinction at the Lower–Middle Jurassic transition was phylogenetically structured and associated with signs of snout reduction possibly explained by the colonization of emptied ecological niches, allowing the emergence of Machimosaurinae and Geosaurinae; (2) we observed higher local temperatures for Thalattosuchia after the Middle–Upper Jurassic and Jurassic–Cretaceous transitions, the former being in accordance with most climatic literature and the latter being subject to more caution; finally, (3) we corroborated previous studies about skull shape and found that durophagous teleosauroids tended to have larger body sizes than any other diet, possibly as a result of ecological specialization. We also found evidence for niche partitioning among piscivorous and macrophagous metriorhynchoids that is observable by a size range extension.

Powered flight has evolved separately in three tetrapod clades: pterosaurs, birds (avian dinosaurs), and bats. To meet the challenges of powered flight, tetrapods acquired structural, mechanical, and physiological adaptations. Circumferential vascular canals, forming laminar bone, have been proposed to be an adaptation linked to withstanding torsional loading during flight in birds. However, whether laminarity serves as an indicator of biomechanical torsion in pterosaurs, remains to be elucidated. Through a comparative statistical approach, we investigate the association between cortical bone laminarity and skeletal stress in pterosaur flight. For the first time, the presence of laminarity in pterosaur bones was analyzed to observe torsion in bones associated with flight, using thirty-five thin sections of the tapejarid Caiuajara dobruskii, Anhangueridae, and Dsungaripteroidea pterosaurs. We conclude that adaptive relationships arise between bone microstructure and biomechanical function, with forelimb elements (humerus, ulna, and wing phalanges) exhibiting higher laminarity rates compared to hindlimb bones. Additionally, the results provide insights into the possible flight style of these pterosaurs through comparison with bird groups. The presence of laminarity in pterosaurs and birds, but not in bats, highlights that this feature, once considered exclusive to birds, may have convergently evolved in pterosaurs and birds.

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.

Paleophysiology is an emergent discipline. Organismic (integrative) approaches seem more appropriate than studies focusing on the variation of specific features because traits are tightly related in actual organisms. Here, we used such an organismic approach (including lifestyle, thermometabolism, and hunting behavior) to understand the paleobiology of the lower Jurassic (Toarcian) thalattosuchian metriorhynchoid Pelagosaurus typus. First, we show that the lifestyle (aquatic, amphibious, terrestrial) has an effect on the femoral compactness profiles in amniotes. The profile of Pelagosaurus indicates that it was amphibious, with a foraging activity in shallow marine environments (as suggested by the presence of salt glands) and thermoregulatory basking behavior in land (as suggested by the presence of osteoderms with highly developed ornamentation). As for the thermometabolism, we show that the mass‐independent resting metabolic rate of Pelagosaurus is relatively high compared to the sample of extant ectothermic amniotes, but analysis of vascular canal diameter and inferences of red blood cell size refute the hypothesis suggesting incipient endothermy. Finally, the foraging behavior was inferred using two proxies. Pelagosaurus had a mass‐independent maximum metabolic rate and an aerobic scope higher than those measured in the almost motionless Iguana iguana, similar to those measured in the sit‐and‐wait predator Crocodylus porosus but lower than those quantified in the active hunter Varanus gouldii. These results suggest that Pelagosaurus may have had a hunting behavior involving a slow sustained swimming or a patient waiting in shallow waters, and may have caught preys like gharials, using fast sideways sweeping motions of the head.