Waveform geometry dictating optimal cruising in animals.

For sustained swimming and flights, vertebrates and insects oscillate their propulsors periodically within a narrow range of Strouhal number (St), a dimensionless quantity describing the rate and density of the motion, suggesting a close relationship between the range and cruising optimality. The persistence of this range across size and fluids has puzzled biologists and engineers, resulting in multiple interpretations of its cause. Here, we propose that the optimal St range is largely constrained by power output efficiency of the trailing edge of the caudal fin.

Downsizing a heavyweight: factors and methods that revise weight estimates of the giant fossil whale .

Extremes in organismal size have broad interest in ecology and evolution because organismal size dictates many traits of an organism's biology. There is particular fascination with identifying upper size extremes in the largest vertebrates, given the challenges and difficulties of measuring extant and extinct candidates for the largest animal of all time, such as whales, terrestrial non-avian dinosaurs, and extinct marine reptiles. The discovery of , a giant basilosaurid whale from the Eocene of Peru, challenged many assumptions about organismal extremes based on reconstructions of its body weight that exceeded reported values for blue whales ().

Skeletal convergence in thunniform sharks, ichthyosaurs, whales, and tunas, and its possible ecological links through the marine ecosystem evolution.

Tunas, lamnid sharks, modern whales, and derived ichthyosaurs converged on the thunniform body plan, with a fusiform body, lunate caudal fin, compressed peduncle, and peduncle joint. This evolutionary convergence has been studied for a long time but little is known about whether all four clades share any skeletal characteristics. Comparisons of vertebral centrum dimensions along the body reveal that the four clades indeed share three skeletal characteristics (e.

Paleomass for R-bracketing body volume of marine vertebrates with 3D models.

Body mass is arguably the most important characteristic of an organism, yet it is often not available in biological samples that have been skeletonized, liquid-preserved, or fossilized. The lack of information is especially problematic for fossil species, for which individuals with body mass information are not available anywhere. Multiple methods are available for estimating the body mass of fossil terrestrial vertebrates but those for their marine counterparts are limited.

Morphological relationships between vertebrate claw unguals and sheaths and the functional morphology of these structures.

The link between claw morphology and function has been historically difficult to quantify, analyze, and interpret. A confounding factor is the ambiguous morphological relationship between the ungual and the sheath and whether one structure or the other is more useful for inferring function from morphology. In this study, the functional morphology of vertebrate claws is analyzed using sheath and ungual measurements taken from modern claw specimens spanning birds and mammals.

The oldest record of Saurosphargiformes (Diapsida) from South China could fill an ecological gap in the Early Triassic biotic recovery.

Diversification following the end-Permian mass extinction marks the initiation of Mesozoic reptile dominance and of modern marine ecosystems, yet major clades are best known from the Middle Triassic suggesting delayed recovery, while Early Triassic localities produce poorly preserved specimens or have restricted diversity. Here we describe gen. et sp.

Ecophysiological steps of marine adaptation in extant and extinct non-avian tetrapods.

Marine reptiles and mammals are phylogenetically so distant from each other that their marine adaptations are rarely compared directly. We reviewed ecophysiological features in extant non-avian marine tetrapods representing 31 marine colonizations to test whether there is a common pattern across higher taxonomic groups, such as mammals and reptiles. Marine adaptations in tetrapods can be roughly divided into aquatic and haline adaptations, each of which seems to follow a sequence of three steps.

Functional morphology of vertebrate claws investigated using functionally based categories and multiple morphological metrics.

The link between claw morphology and function has been historically difficult to quantify, analyze, and interpret. In this study, the functional morphology of vertebrate claws is analyzed using measurements taken from 80 modern claw specimens spanning birds, mammals, and one reptile. Claw measurements were chosen for their potential biomechanical significance and a revised, expanded categorization of claw function is defined and used.

Evidence Supporting Predation of 4-m Marine Reptile by Triassic Megapredator.

Air-breathing marine predators have been essential components of the marine ecosystem since the Triassic. Many of them are considered the apex predators but without direct evidence-dietary inferences are usually based on circumstantial evidence, such as tooth shape. Here we report a fossil that likely represents the oldest evidence for predation on megafauna, i.

Repeated evolution of durophagy during ichthyosaur radiation after mass extinction indicated by hidden dentition.

Marine tetrapods quickly diversified and were established as marine top predators after the end-Permian Mass extinction (EPME). Ichthyosaurs were the forerunner of this rapid radiation but the main drivers of the diversification are poorly understood. Cartorhynchus lenticarpus is a basal ichthyosauriform with the least degree of aquatic adaptation, holding a key to identifying such a driver.

The new ichthyosauriform (Reptilia, Ichthyosauromorpha) from Majiashan, Chaohu, Anhui Province, China.

A new species of ichthyosauriform is recognized based on 20 specimens, including nearly complete skeletons, and named . A part of the specimens was previously identified as and is herein reassigned to the new species. The new species differs from existing species of in a suite of features, such as the bifurcation of the caudal peak neural spine and a short femur relative to trunk length.

Flipper bone distribution reveals flexible trailing edge in underwater flying marine tetrapods.

Hydrofoil-shaped limbs (flipper-hydrofoils) have evolved independently several times in secondarily marine tetrapods and generally fall into two functional categories: (1) those that produce the majority of thrust during locomotion (propulsive flipper-hydrofoils); (2) those used primarily to steer and resist destabilizing movements such as yaw, pitch, and roll (controller flipper-hydrofoils). The morphological differences between these two types have been poorly understood. Theoretical and experimental studies on engineered hydrofoils suggest that flapping hydrofoils with a flexible trailing edge are more efficient at producing thrust whereas hydrofoils used in steering and stabilization benefit from a more rigid one.

Early Triassic marine reptile representing the oldest record of unusually small eyes in reptiles indicating non-visual prey detection.

The end-Permian mass extinction (EPME) led to reorganization of marine predatory communities, through introduction of air-breathing top predators, such as marine reptiles. We report two new specimens of one such marine reptile, Eretmorhipis carrolldongi, from the Lower Triassic of Hubei, China, revealing superficial convergence with the modern duckbilled platypus (Ornithorhynchus anatinus), a monotreme mammal. Apparent similarities include exceptionally small eyes relative to the body, snout ending with crura with a large internasal space, housing a bone reminiscent of os paradoxum, a mysterious bone of platypus, and external grooves along the crura.

Separating sexual dimorphism from other morphological variation in a specimen complex of fossil marine reptiles (Reptilia, Ichthyosauriformes, Chaohusaurus).

The Early Triassic Chaohu Fauna from Anhui Province, China, contains the oldest record of Mesozoic marine reptiles, such as Cartorhynchus and Sclerocormus. Most specimens from the fauna belong to the ichthyosauriform Chaohusaurus, more specifically resembling C. chaoxianensis.

The sea as deathtrap: comment on a paper by miller and wiens.

Miller & Wiens (2017) claim that low marine as compared with terrestrial diversity results from more frequent extinctions and insufficient time for diversification in marine clades. Their data on marine amniotes are unrepresentative of marine diversity, their analysis of clade dynamics is flawed, and they ignore previously proposed explanations for the diversity difference.

Pre- versus post-mass extinction divergence of Mesozoic marine reptiles dictated by time-scale dependence of evolutionary rates.

The fossil record of a major clade often starts after a mass extinction even though evolutionary rates, molecular or morphological, suggest its pre-extinction emergence (e.g. squamates, placentals and teleosts).

Eccentricity and obliquity paced carbon cycling in the Early Triassic and implications for post-extinction ecosystem recovery.

The timing of marine ecosystem recovery following the End Permian Mass Extinction (EPME) remains poorly constrained given the lack of radiometric ages. Here we develop a high-resolution carbonate carbon isotope (δ(13)Ccarb) record for 3.20 million years of the Olenekian in South China that defines the astronomical time-scale for the critical interval of major evolutionary and oceanic events in the Spathian.

Palaeobiology: Born and Gone in Global Warming.

Why ichthyosaurs - marine Mesozoic reptiles - disappeared before the dinosaur extinction has remained a mystery. New research suggests they may have gone extinct stepwise, during one of the most extreme greenhouse periods in the history of complex life-forms.

A large aberrant stem ichthyosauriform indicating early rise and demise of ichthyosauromorphs in the wake of the end-Permian extinction.

Contrary to the fast radiation of most metazoans after the end-Permian mass extinction, it is believed that early marine reptiles evolved slowly during the same time interval. However, emerging discoveries of Early Triassic marine reptiles are questioning this traditional view. Here we present an aberrant basal ichthyosauriform with a hitherto unknown body design that suggests a fast radiation of early marine reptiles.

A new Lower Triassic ichthyopterygian assemblage from Fossil Hill, Nevada.

We report a new ichthyopterygian assemblage from Lower Triassic horizons of the Prida Formation at Fossil Hill in central Nevada. Although fragmentary, the specimens collected so far document a diverse fauna. One partial jaw exhibits isodont dentition with blunt tipped, mesiodistally compressed crowns and striated enamel.

Adult sex ratio, sexual dimorphism and sexual selection in a Mesozoic reptile.

The evolutionary history of sexual selection in the geologic past is poorly documented based on quantification, largely because of difficulty in sexing fossil specimens. Even such essential ecological parameters as adult sex ratio (ASR) and sexual size dimorphism (SSD) are rarely quantified, despite their implications for sexual selection. To enable their estimation, we propose a method for unbiased sex identification based on sexual shape dimorphism, using size-independent principal components of phenotypic data.

How warm is too warm for the life cycle of actinopterygian fishes?

We investigated the highest constant temperature at which actinopterygian fishes can complete their lifecycles, based on an oxygen supply model for cleavage-stage eggs. This stage is one of the most heat-sensitive periods during the lifecycle, likely reflecting the exhaustion of maternally supplied heat shock proteins without new production. The model suggests that average eggs would not develop normally under a constant temperature of about 36 °C or higher.

A New Specimen of Carroll's Mystery Hupehsuchian from the Lower Triassic of China.

A new specimen of an enigmatic hupehsuchian genus is reported. The genus was first recognized by Robert L. Carroll and Zhi-ming Dong in 1991, who refrained from naming it because of the poor quality of the only specimen known at the time.