The osteology of Triisodon crassicuspis (Cope, 1882): New insights into the enigmatic "archaic" placental mammal group "Triisodontidae".

Following the end-Cretaceous mass extinction, mammals underwent an increase in body size, taxonomic diversity and ecological specialization throughout the Paleocene, exemplifying their adaptability. One especially enigmatic group is the "Triisodontidae", medium- to large-sized ungulate-like placentals from the Paleocene which are best known from their teeth that exhibit adaptations towards carnivory. The "triisodontids" were the first large carnivorous mammals and pre-date, and may have given rise to, Mesonychia, a group of more specialized placental carnivores.

Skull sinuses precluded extinct crocodile relatives from cetacean-style deep diving as they transitioned from land to sea.

During major evolutionary transitions, groups develop radically new body plans and radiate into new habitats. A classic example is cetaceans which evolved from terrestrial ancestors to become pelagic swimmers. In doing so, they altered their air-filled sinuses, transitioning some of these spaces to allow for fluctuations in air capacity and storage via soft tissue borders.

The post-cranial anatomy and functional morphology of Conoryctes comma (Mammalia: Taeniodonta) from the Paleocene of North America.

Conoryctes comma is a member of the enigmatic group Taeniodonta, Paleogene mammals that have been found only in North America. Taeniodonts were part of the first wave of placental mammal diversification after the end-Cretaceous extinction. The lack of postcranial elements has limited the understanding of the anatomy and locomotion of Conoryctes, and how it compared to other taeniodonts.

Thought for food: the endothermic brain hypothesis.

The evolution of whole-body endothermy occurred independently in dinosaurs and mammals and was associated with some of the most significant neurocognitive shifts in life's history. These included a 20-fold increase in neurons and the evolution of new brain structures, supporting similar functions in both lineages. We propose the endothermic brain hypothesis, which holds that elaborations in endotherm brains were geared towards increasing caloric intake through efficient foraging.

The osteology of the Late Triassic reptile Scleromochlus taylori from μCT data.

Scleromochlus taylori is one of the most enigmatic members of the herpetofauna from the Lossiemouth Sandstone Formation (Upper Triassic) of Elgin (Moray, Scotland). For many years it was thought to be closely related to pterosaurs and dinosaurs, but the anatomy of this animal is difficult to interpret because of the notoriously poor preservation of the six available specimens, which comprise void space in the sandstone after the bones were destroyed by diagenesis. Historically, these fossils have been studied using physical molds, which provide only incomplete, and potentially distorted, information.

The virtual brain endocast of Trogosus (Mammalia, Tillodontia) and its relevance in understanding the extinction of archaic placental mammals.

After successfully diversifying during the Paleocene, the descendants of the first wave of mammals that survived the end-Cretaceous mass extinction waned throughout the Eocene. Competition with modern crown clades and intense climate fluctuations may have been part of the factors leading to the extinction of these archaic groups. Why these taxa went extinct has rarely been studied from the perspective of the nervous system.

Paleontology: All dinosaurs big and small.

Two new studies illuminate how some dinosaurs were able to grow to enormous sizes, while others shrank to become today's birds.

Evidence for a novel cranial thermoregulatory pathway in thalattosuchian crocodylomorphs.

Thalattosuchian crocodylomorphs were a diverse clade that lived from the Early Jurassic to the Early Cretaceous. The subclade Metriorhynchoidea underwent a remarkable transition, evolving from semi-aquatic ambush predators into fully aquatic forms living in the open oceans. Thalattosuchians share a peculiar palatal morphology with semi-aquatic and aquatic fossil cetaceans: paired anteroposteriorly aligned grooves along the palatal surface of the bony secondary palate.

Shifts in food webs and niche stability shaped survivorship and extinction at the end-Cretaceous.

It has long been debated why groups such as non-avian dinosaurs became extinct whereas mammals and other lineages survived the Cretaceous/Paleogene mass extinction 66 million years ago. We used Markov networks, ecological niche partitioning, and Earth System models to reconstruct North American food webs and simulate ecospace occupancy before and after the extinction event. We find a shift in latest Cretaceous dinosaur faunas, as medium-sized species counterbalanced a loss of megaherbivores, but dinosaur niches were otherwise stable and static, potentially contributing to their demise.

The ecological diversification and evolution of Teleosauroidea (Crocodylomorpha, Thalattosuchia), with insights into their mandibular biomechanics.

Throughout the Jurassic, a plethora of marine reptiles dominated ocean waters, including ichthyosaurs, plesiosaurs and thalattosuchian crocodylomorphs. These Jurassic ecosystems were characterized by high niche partitioning and spatial variation in dietary ecology. However, while the ecological diversity of many marine reptile lineages is well known, the overall ecological diversification of Teleosauroidea (one of the two major groups within thalattosuchian crocodylomorphs) has never been explored.

Scleromochlus and the early evolution of Pterosauromorpha.

Pterosaurs, the first vertebrates to evolve powered flight, were key components of Mesozoic terrestrial ecosystems from their sudden appearance in the Late Triassic until their demise at the end of the Cretaceous. However, the origin and early evolution of pterosaurs are poorly understood owing to a substantial stratigraphic and morphological gap between these reptiles and their closest relatives, Lagerpetidae. Scleromochlus taylori, a tiny reptile from the early Late Triassic of Scotland discovered over a century ago, was hypothesized to be a key taxon closely related to pterosaurs, but its poor preservation has limited previous studies and resulted in controversy over its phylogenetic position, with some even doubting its identification as an archosaur.

The origin of placental mammal life histories.

After the end-Cretaceous extinction, placental mammals quickly diversified, occupied key ecological niches and increased in size, but this last was not true of other therians. The uniquely extended gestation of placental young may have factored into their success and size increase, but reproduction style in early placentals remains unknown. Here we present the earliest record of a placental life history using palaeohistology and geochemistry, in a 62 million-year-old pantodont, the clade including the first mammals to achieve truly large body sizes.

Brawn before brains in placental mammals after the end-Cretaceous extinction.

Mammals are the most encephalized vertebrates, with the largest brains relative to body size. Placental mammals have particularly enlarged brains, with expanded neocortices for sensory integration, the origins of which are unclear. We used computed tomography scans of newly discovered Paleocene fossils to show that contrary to the convention that mammal brains have steadily enlarged over time, early placentals initially decreased their relative brain sizes because body mass increased at a faster rate.

'Ear stones' in crocodylians: a cross-species comparative and ontogenetic survey of otolith structures.

The vestibular system of the inner ear is a crucial sensory organ, involved in the sensation of balance and equilibrium. It consists of three semicircular canals that sense angular rotations of the head and the vestibule that detects linear acceleration and gravity. The vestibule often contains structures, known as the otoliths or 'ear stones'.

A skeleton from the Middle Jurassic of Scotland illuminates an earlier origin of large pterosaurs.

Pterosaurs were the first vertebrates to evolve flight and include the largest flying animals in Earth history. While some of the last-surviving species were the size of airplanes, pterosaurs were long thought to be restricted to small body sizes (wingspans ca. <1.

An exquisitely preserved theropod dinosaur embryo sheds light on avian-like prehatching postures.

Despite the discovery of many dinosaur eggs and nests over the past 100 years, articulated embryos are remarkably rare. Here we report an exceptionally preserved, articulated oviraptorid embryo inside an elongatoolithid egg, from the Late Cretaceous Hekou Formation of southern China. The head lies ventral to the body, with the feet on either side, and the back curled along the blunt pole of the egg, in a posture previously unrecognized in a non-avian dinosaur, but reminiscent of a late-stage modern bird embryo.

Ontogenetic variation in the crocodylian vestibular system.

Crocodylians today live in tropical to subtropical environments, occupying mostly shallow waters. Their body size changes drastically during ontogeny, as do their skull dimensions and bite forces, which are associated with changes in prey preferences. Endocranial neurosensory structures have also shown to change ontogenetically, but less is known about the vestibular system of the inner ear.

Spinosaurus.

Steve Brusatte introduces Spinosaurus, the largest known predatory dinosaur.

Petrosal Anatomy of the Paleocene Eutherian Mammal (Cope, 1881).

Unlabelled: We describe the tympanic anatomy of the petrosal of an enigmatic Paleocene mammal based on cranial specimens recovered from New Mexico, U.S.A.

Pterosaurs.

150 million years ago, an animal no bigger than a herring gull soared above shallow lagoons in what is now Bavaria. It had obscenely long fingers on each hand, which anchored thin wings of skin, and long toothy jaws, perfectly suited to snatching squids and fishes from the warm waters. Our animal was probably doing just that before its untimely death.

Rostral neurovasculature indicates sensory trade-offs in Mesozoic pelagic crocodylomorphs.

Metriorhynchoid thalattosuchians were a marine clade of Mesozoic crocodylomorphs that evolved from semi-aquatic, "gharial"-like species into the obligately pelagic subclade Metriorhynchidae. To explore whether the sensory and physiological demands of underwater life necessitates a shift in rostral anatomy, both in neurology and vasculature, we investigate the trigeminal innervation and potential somatosensory abilities of metriorhynchoids by digitally segmenting the rostral neurovascular canals in CT scans of 10 extant and extinct crocodyliforms. The dataset includes the terrestrial, basal crocodyliform Protosuchus haughtoni, two semi-aquatic basal metriorhynchoids, four pelagic metriorhynchids and three extant, semi-aquatic crocodylians.