The evolution of large-bodied theropod dinosaurs during the Mesozoic in Asia

The fossil record of large-bodied, apex carnivorous theropod dinosaurs in Eastern Asia is now among the best understood in the world, thanks to new discoveries and reinterpretations of long-neglected fossils. Asia boasts the most complete record of Middle Jurassic theropods globally, as well as one of the best-studied Late Cretaceous theropod faunas, and new research is helping to fill what was previously a 60-million-year gap in the Early-mid Cretaceous fossil record of large Asian predators. In general, the bio-geographic affinities of large-bodied Asian theropods over time were intimately related to physical geography, and progressively more derived theropod clades evolved large body size and occupied the apex predator niche throughout the Jurassic and Cretaceous. During the Middle Jurassic, largely endemic clades of basal tetanurans were prevalent in Asia, whereas during the Late Jurassic mid Cretaceous more derived “intermediate” tetanuran theropods with cosmopolitan affinities occupied the large predator role, including sinraptorids, spinosauris, and carcharodontosaurians. Finalli, during the final 20 million years of the Cretaceous, more derived, bird-like coelurosaurs attained large body size. Foremost among these were the tyrannosaurids, a radiation of northern (Asian and North American) megapredators whose ascent into the apex predator niche was a delayed event restricted to the Campanian-Masastrichian. As Asia is the focus of intense ongoing dinosaur fieldwork, our undestarnding of large-bodied theropod evolution will continue to be refined with future discoveries.El registro fósil de los dinosaurios carnívoros terópodos de gran talla en el este de Asia es uno de los mejor conocidos del mundo, gracias a nuevos descubrimientos y reinterpretaciones de fósiles que han permanecido pobremente estudiados durante mucho tiempo. Globalmente, Asia comprende el registro fósil mas completo de terópodos del Jurasico Medio, así como una de las faunas finicretácicas mejor estudiadas. Asimismo, las nuevas investigaciones están contribuyendo a completar un hiato de 60 millones de años en el registro fósil de grandes depredadores asiáticos correspondientes al Cretácico inferior-medio. En general las afinidades biogeográficas de los grandes terópodos asiáticos a través del tiempo se hallan íntimamente ligadas a la geografía física. Progresivamente, varios clados derivados de terópodos evolucionaron grandes tallas corporales, ocupando la cima del nicho de depredador durante todo el Jurasico y el Cretácico. Durante el Jurasico Medio prevalecieron clados de tetanuros basales mayormente endémicos, mientras que durante el Jurásico Superior-Cretácico Medio clados más derivados de terópodos tetanuros “intermedios” de afinidades cosmopolitas ocuparon el papel de gran depredador, incluyendo sinraptoridos, espinosauridos y carcharodontosauridos. Finalmente, durante los ultimos 20 millones de anos del Cretacico, coelurosaurios mas derivados con aspecto reminiscente a las aves alcanzaron grandes tallas corporales. Pirmordialmente entre estas formas se hallaban los tiranosauridos, una radiación septentrional (asiáticos y norteamericanos) de megadepredadores cuyo ascenso a la cumbre del nicho de gran depredador se retraso hasta el Campaniense y Maastrichtiense. Mientras Asia continua constituyendo el foco de una intensa actividad paleontológica, nuestros conocientos sobre la evolución de los grandes terópodos continuará refinándose con el estudio de futuros hallazgos

The first definitive Middle Jurassic atoposaurid (Crocodylomorpha, Neosuchia), and a discussion on the genus Theriosuchus

Atoposaurids were a clade of semiaquatic crocodyliforms known from the Late Jurassic to the latest Cretaceous. Tentative remains from Europe, Morocco, and Madagascar may extend their range into the Middle Jurassic. Here we report the first unambiguous Middle Jurassic (late Bajocian–Bathonian) atoposaurid: an anterior dentary from the Isle of Skye, Scotland, UK. A comprehensive review of atoposaurid specimens demonstrates that this dentary can be referred to Theriosuchus based on several derived characters, and differs from the five previously recognized species within this genus. Despite several diagnostic features, we conservatively refer it to Theriosuchus sp., pending the discovery of more complete material. As the oldest known definitively diagnostic atoposaurid, this discovery indicates that the oldest members of this group were small-bodied, had heterodont dentition, and were most likely widespread components of European faunas. Our review of mandibular and dental features in atoposaurids not only allows us to present a revised diagnosis of Theriosuchus, but also reveals a great amount of variability within this genus, and indicates that there are currently five valid species that can be differentiated by unique combinations of dental characteristics. This variability can be included in future broad-scale cladistics analyses of atoposaurids and closely related crocodyliforms, which promise to help untangle the complicated taxonomy and evolutionary history of Atoposauridae

Macroevolutionary Patterns In The Evolutionary Radiation Of Archosaurs (Tetrapoda: Diapsida)

The rise of archosaurs during the Triassic and Early Jurassic has been treated as a classic example of an evolutionary radiation in the fossil record. This paper reviews published studies and provides new data on archosaur lineage origination, diversity and lineage evolution, morphological disparity, rates of morphological character change, and faunal abundance during the Triassic–Early Jurassic. The fundamental archosaur lineages originated early in the Triassic, in concert with the highest rates of character change. Disparity and diversity peaked later, during the Norian, but the most significant increase in disparity occurred before maximum diversity. Archosaurs were rare components of Early–Middle Triassic faunas, but were more abundant in the Late Triassic and pre-eminent globally by the Early Jurassic. The archosaur radiation was a drawn-out event and major components such as diversity and abundance were discordant from each other. Crurotarsans (crocodile-line archosaurs) were more disparate, diverse, and abundant than avemetatarsalians (bird-line archosaurs, including dinosaurs) during the Late Triassic, but these roles were reversed in the Early Jurassic. There is no strong evidence that dinosaurs outcompeted or gradually eclipsed crurotarsans during the Late Triassic. Instead, crurotarsan diversity decreased precipitously by the end-Triassic extinction, which helped usher in the age of dinosaurian dominance

The osteology and systematic position of Dongusuchus efremovi Sennikov, 1988 from the Anisian (Middle Triassic) of Russia

© 2016, © 2014 Taylor & Francis. European Russia has yielded several fragmentary but potentially important archosauriform specimens from the Middle Triassic, but these have been only briefly described in the literature. One of these puzzling taxa is Dongusuchus efremovi Sennikov, 1988, described from the Donguz Svita. We present a redescription of Dongusuchus efremovi, which includes the first photographic atlas and thorough anatomical description of the holotype and referred specimens. This taxon is shown to be a gracile, probably fast-running species with elongate and slender limbs. A phylogenetic analysis recovers Dongusuchus efremovi as an early-diverging, non-archosaurian archosauriform. Previous work had suggested that this taxon was a ‘rauisuchid’. The gracile proportions of the femur and somewhat wedge-shaped head, however, are unusual for basal archosauriforms and are similar to the plesiomorphic state in crocodile and avian-line crown archosaurs. Several Early-Middle Triassic basal archosauriforms and early members of the crocodile and avian lineages were gracile with elongate, slender limbs. This suggests that the limb morphology of Dongusuchus efremovi may be plesiomorphic for Archosauria and proximal clades

A reassessment of Kelmayisaurus petrolicus, a large theropod dinosaur from the Early Cretaceous of China

The Early Cretaceous fossil record of large−bodied theropods from Asia is poor, hindering comparison of Asian predatory dinosaur faunas with those from other continents. One of the few large Asian theropod specimens from this interval is a partial skull (maxilla and dentary) from the Lianmugin Formation (?Valanginian–Albian), the holotype of Kelmayisaurus petrolicus. Most authors have either considered this specimen as an indeterminate basal tetanuran or a nomen dubium. Weredescribe K. petrolicus and note that it possesses a single autapomorphy (a deep accessory groove on the lateral surface of the anterior dentary), as well as a unique combination of characters that differentiates it from other theropods, affirming its validity. A phylogenetic analysis recovers K. petrolicus as a basal carcharodontosaurid, which is supported by various features: very deep interdental plates (a carcharodontosaurid synapomorphy), fused interdental plates (present in carchardontosaurids and a limited number of other theropods), and the absence of diagnostic features of other clades of large−bodied theropods such as abelisaurids, megalosauroids, and coelurosaurs. As such, Kelmayisaurus is the second known carcharodontosaurid from Asia, and further evidence that this clade represented a global radiation of large−bodied predators during the Early–mid Cretaceous

Cephalic salt gland evolution in Mesozoic pelagic crocodylomorphs

Secondarily marine tetrapod lineages have independently evolved osmoregulatory adaptations for life in salt water but inferring physiological changes in extinct marine tetrapods is difficult. The Mesozoic crocodylomorph clade Thalattosuchia is unique in having both direct evidence from natural endocasts and several proposed osteological correlates for salt exocrine glands. Here, we investigate salt gland evolution in thalattosuchians by creating endocranial reconstructions from CT scans of eight taxa (one basal thalattosuchian, one teleosauroid, two basal metriorhynchoids and four metriorhynchids) and four outgroups (three extant crocodylians and the basal crocodyliform Protosuchus) to identify salt gland osteological correlates. All metriorhynchoids show dorsolateral nasal cavity expansions corresponding to the location of nasal salt glands in natural casts, but smaller expansions in teleosauroids correspond more with the cartilaginous nasal capsule. The different sizes of these expansions suggest the following evolutionary sequence: (1) plesiomorphically small glands present in semi-aquatic teleosauroids draining through the nasal vestibule; (2) moderately sized glands in the basalmost metriorhynchoid Pelagosaurus; and (3) hypertrophied glands in the clade comprising Eoneustes and metriorhynchids, with a pre-orbital fenestra providing a novel exit for salt drainage. The large gland size inferred from basal metriorhynchoids indicates advanced osmoregulation occurred while metriorhynchoids were semi-aquatic. This pattern does not precisely fit into current models of physiological evolution in marine tetrapods and suggests a unique sequence of changes as thalattosuchians transitioned from land to sea.Fil: Cowgill, T.. University of Edinburgh; Reino UnidoFil: Young, M.. University of Edinburgh; Reino UnidoFil: Schwab, J.. University of Edinburgh; Reino UnidoFil: Walsh, S.. National Museum Of Scotland; Reino UnidoFil: Witmer, Lawrence. Ohio University; Estados UnidosFil: Herrera, Laura Yanina. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Paleontología Vertebrados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; ArgentinaFil: Dollman, K.. University of the Witwatersrand; SudáfricaFil: Turner, A. H.. State University of New York. Stony Brook University; Estados UnidosFil: Brusatte, S.. University of Edinburgh; Reino Unid

The taxonomy and anatomy of rauisuchian archosaurs from the Late Triassic of Germany and Poland

The German Late Triassic archosaur Teratosaurus suevicus is a historically important taxon, being the first described rauisuchian. Unfortunately the holotype is a single element, a maxilla, which is poorly preserved and incomplete. We redescribe this maxilla and identify a single potential autapomorphy. The fragmentary type specimen complicates attempts to refer additional material to this taxon, and other unassociated archosaur and rauisuchian specimens from the Mittlerer Stubensandstein of Germany cannot be referred to T. suevicus with any degree of confidence. The stratigraphically older T. silesiacus, from the upper Carnian of Poland, is represented by a much more complete and better preserved specimen. Comparison of the maxillae of T. suevicus and T. silesiacus reveals that the two are distinct taxa, contra recent suggestions, but also that they do not share any synapomorphies or a unique combination of characters relative to Postosuchus kirkpatricki and other rauisuchians. Thus, the Polish material must be transferred to a new genus, Polonosuchus gen. nov. Both Polonosuchus and Teratosaurus are very similar to Postosuchus kirkpatricki, and the three taxa are likely closely related

Revision of the Late Jurassic teleosaurid genus Machimosaurus (Crocodylomorpha, Thalattosuchia)

© 2014 The Authors. Published by the Royal Society under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/4.0/, which permits unrestricted use, provided the original author and source are credited. The attached file is the published version of the article

Temporal and phylogenetic evolution of the sauropod dinosaur body plan

The colossal size and body plan of sauropod dinosaurs are unparalleled in terrestrial vertebrates. However, to-date there have been only limited attempts to examine temporal and phylogenetic patterns in the sauropod bauplan. Here we combine three-dimensional computational models with phylogenetic reconstructions to quantify the evolution of whole-body shape and body segment properties across the sauropod radiation. Limitations associated with the absence of soft tissue preservation in fossils result in large error bars about mean absolute body shape predictions. However, applying any consistent skeleton:body volume ratio to all taxa does yield changes in body shape that appear concurrent with major macroevolutionary events in sauropod history. A caudad shift in centre-of-mass in Middle Triassic Saurischia, associated with the evolution of bipedalism in various dinosaur lineages, was reversed in Late Triassic sauropodomorphs. A craniad centre-of-mass shift coincided with the evolution of quadrupedalism in the Late Triassic, followed by a more striking craniad shift in Late Jurassic–Cretaceous titanosauriforms, which included the largest sauropods. These craniad CoM shifts are strongly correlated with neck enlargement, a key innovation in sauropod evolution and pivotal to their gigantism. By creating a much larger feeding envelope, neck elongation is thought to have increased feeding efficiency and opened up trophic niches that were inaccessible to other herbivores. However, we find that relative neck size and center-of-mass position are not strongly correlated with inferred feeding habits. Instead the craniad center-of-mass positions of titanosauriforms appear closely linked with locomotion and environmental distributions, potentially contributing to the continued success of this group until the end-Cretaceous, with all other sauropods having gone extinct by the early Late Cretaceous