Exceptional Early Jurassic fossils with leathery eggs shed light on dinosaur reproductive biology.

Our understanding of pre-Cretaceous dinosaur reproduction is hindered by a scarcity of evidence within fossil records. Here we report three adult skeletons and five clutches of embryo-containing eggs of a new sauropodomorph from the Lower Jurassic of southwestern China, displaying several significant reproductive features that are either unknown or unlike other early-diverging sauropodomorphs, such as relatively large eggs with a relatively thick calcareous shell formed by prominent mammillary cones, synchronous hatching and a transitional prehatching posture between the crocodilians and living birds. Most significantly, these Early Jurassic fossils provide strong evidence for the earliest known leathery eggs. Our comprehensive quantitative analyses demonstrate that the first dinosaur eggs were probably leathery, elliptical and relatively small, but with relatively long eggshell units, and that along the line to living birds, the most significant change in reptilian egg morphology occurred early in theropod evolution rather than near the origin of Aves.

Bony-fish-like scales in a Silurian maxillate placoderm.

Major groups of jawed vertebrates exhibit contrasting conditions of dermal plates and scales. But the transition between these conditions remains unclear due to rare information on taxa occupying key phylogenetic positions. The 425-million-year-old fish Entelognathus combines an unusual mosaic of characters typically associated with jawed stem gnathostomes or crown gnathostomes. However, only the anterior part of the exoskeleton was previously known for this very crownward member of the gnathostome stem. Here, we report a near-complete post-thoracic exoskeleton of Entelognathus. Strikingly, its scales are large and some are rhomboid, bearing distinctive peg-and-socket articulations; this combination was previously only known in osteichthyans and considered a synapomorphy of that group. The presence in Entelognathus of an anal fin spine, previously only found in some stem chondrichthyans, further illustrates that many characters previously thought to be restricted to specific lineages within the gnathostome crown likely arose before the common ancestor of living jawed vertebrates.

Complex macroevolution of pterosaurs.

Pterosaurs, the earliest flying tetrapods, are the subject of some recent quantitative macroevolutionary analyses from different perspectives.1-2 Here, we use an integrative approach involving newly assembled phylogenetic and body size datasets, net diversification rates, morphological rates, and morphological disparity to gain a holistic understanding of the pterosaur macroevolution. The first two parameters are important in quantitative analyses of macroevolution, but they have been rarely used in previous pterosaur studies.1,3,4,2,5,6,7,8,9,10,11,12 Our study reveals an ∼115-Ma period-from Early Triassic to Early Cretaceous-of multi-wave increasing net diversification rates and disparity, as well as high morphological rates, followed by an ∼65-Ma period-from Early Cretaceous to the end of the Cretaceous-of mostly negative net diversification rates, decreasing disparity, and relatively low morphological rates in pterosaur evolution. Our study demonstrates the following: (1) body size plays an important role in pterosaur lineage diversification during nearly their whole evolutionary history, and the evolution of locomotion, trophic, and ornamental structures also plays a role in different periods; (2) birds, the other major flying tetrapod group at the time, might have affected pterosaur macroevolution for ∼100 Ma; and (3) different mass extinction events might have affected pterosaur evolution differently. Particularly, the revealed decline in pterosaur biodiversity during the Middle and Late Cretaceous periods provides further support for the possible presence of a biodiversity decline of large-sized terrestrial amniotes starting in the mid-Cretaceous,13,14 which may have been caused by multiple factors including a global land area decrease during these periods.

The oldest complete jawed vertebrates from the early Silurian of China.

Molecular studies suggest that the origin of jawed vertebrates was no later than the Late Ordovician period (around 450 million years ago (Ma))1,2. Together with disarticulated micro-remains of putative chondrichthyans from the Ordovician and early Silurian period3-8, these analyses suggest an evolutionary proliferation of jawed vertebrates before, and immediately after, the end-Ordovician mass extinction. However, until now, the earliest complete fossils of jawed fishes for which a detailed reconstruction of their morphology was possible came from late Silurian assemblages (about 425 Ma)9-13. The dearth of articulated, whole-body fossils from before the late Silurian has long rendered the earliest history of jawed vertebrates obscure. Here we report a newly discovered Konservat-Lagerstätte, which is marked by the presence of diverse, well-preserved jawed fishes with complete bodies, from the early Silurian (Telychian age, around 436 Ma) of Chongqing, South China. The dominant species, a 'placoderm' or jawed stem gnathostome, which we name Xiushanosteus mirabilis gen. et sp. nov., combines characters from major placoderm subgroups14-17 and foreshadows the transformation of the skull roof pattern from the placoderm to the osteichthyan condition10. The chondrichthyan Shenacanthus vermiformis gen. et sp. nov. exhibits extensive thoracic armour plates that were previously unknown in this lineage, and include a large median dorsal plate as in placoderms14-16, combined with a conventional chondrichthyan bauplan18,19. Together, these species reveal a previously unseen diversification of jawed vertebrates in the early Silurian, and provide detailed insights into the whole-body morphology of the jawed vertebrates of this period.

The rapid evolution of lungfish durophagy.

Innovations relating to the consumption of hard prey are implicated in ecological shifts in marine ecosystems as early as the mid-Paleozoic. Lungfishes represent the first and longest-ranging lineage of durophagous vertebrates, but how and when the various feeding specializations of this group arose remain unclear. Two exceptionally preserved fossils of the Early Devonian lobe-finned fish Youngolepis reveal the origin of the specialized lungfish feeding mechanism. Youngolepis has a radically restructured palate, reorienting jaw muscles for optimal force transition, coupled with radiating entopterygoid tooth rows like those of lungfish toothplates. This triturating surface occurs in conjunction with marginal dentition and blunt coronoid fangs, suggesting a role in crushing rather than piercing prey. Bayesian tip-dating analyses incorporating these morphological data indicate that the complete suite of lungfish feeding specializations may have arisen in as little as 7 million years, representing one of the most striking episodes of innovation during the initial evolutionary radiations of bony fishes.

Early evolution of beetles regulated by the end-Permian deforestation.

The end-Permian mass extinction (EPME) led to a severe terrestrial ecosystem collapse. However, the ecological response of insects-the most diverse group of organisms on Earth-to the EPME remains poorly understood. Here, we analyse beetle evolutionary history based on taxonomic diversity, morphological disparity, phylogeny, and ecological shifts from the Early Permian to Middle Triassic, using a comprehensive new dataset. Permian beetles were dominated by xylophagous stem groups with high diversity and disparity, which probably played an underappreciated role in the Permian carbon cycle. Our suite of analyses shows that Permian xylophagous beetles suffered a severe extinction during the EPME largely due to the collapse of forest ecosystems, resulting in an Early Triassic gap of xylophagous beetles. New xylophagous beetles appeared widely in the early Middle Triassic, which is consistent with the restoration of forest ecosystems. Our results highlight the ecological significance of insects in deep-time terrestrial ecosystems.

Deep time diversity and the early radiations of birds.

Reconstructing the history of biodiversity has been hindered by often-separate analyses of stem and crown groups of the clades in question that are not easily understood within the same unified evolutionary framework. Here, we investigate the evolutionary history of birds by analyzing three supertrees that combine published phylogenies of both stem and crown birds. Our analyses reveal three distinct large-scale increases in the diversification rate across bird evolutionary history. The first increase, which began between 160 and 170 Ma and reached its peak between 130 and 135 Ma, corresponds to an accelerated morphological evolutionary rate associated with the locomotory systems among early stem birds. This radiation resulted in morphospace occupation that is larger and different from their close dinosaurian relatives, demonstrating the occurrence of a radiation among early stem birds. The second increase, which started ∼90 Ma and reached its peak between 65 and 55 Ma, is associated with rapid evolution of the cranial skeleton among early crown birds, driven differently from the first radiation. The third increase, which occurred after ∼40 to 45 Ma, has yet to be supported by quantitative morphological data but gains some support from the fossil record. Our analyses indicate that the bird biodiversity evolution was influenced mainly by long-term climatic changes and also by major paleobiological events such as the Cretaceous-Paleogene (K-Pg) extinction.

An oviraptorid preserved atop an embryo-bearing egg clutch sheds light on the reproductive biology of non-avialan theropod dinosaurs.

Recent studies demonstrate that many avialan features evolved incrementally prior to the origin of the group, but the presence of some of these features, such as bird-like brooding behaviours, remains contentious in non-avialan dinosaurs. Here we report the first non-avialan dinosaur fossil known to preserve an adult skeleton atop an egg clutch that contains embryonic remains. The preserved positional relationship of the adult to the clutch, coupled with the advanced growth stages of the embryos and their high estimated incubation temperatures, provides strong support for the brooding hypothesis. Furthermore, embryos in the clutch are at different developmental stages, suggesting the presence of asynchronous hatching-a derived feature even among crown-group birds-in non-avialan theropods. These findings demonstrate that the evolution of reproductive biology along bird-line archosaurs was a complex rather than a linear and incremental process, and suggest that some aspects of non-avialan theropod reproduction were unique to these dinosaurs.

A new possible megalosauroid theropod from the Middle Jurassic Xintiangou Formation of Chongqing, People's Republic of China and its implication for early tetanuran evolution.

Tetanurae is a special group of theropod dinosaurs that originated by the late Early Jurassic. It includes several early-diverging groups of generally large-bodied predators (megalosauroids, allosauroids, tyrannosauroid coelurosaurs) as well as morphologically disparate small-bodied coelurosaurs, including birds. Aspects of the evolutionary history of tetanurans remain contested, including the topology of their deep phylogenetic divergences (among Megalosauroidea, Allosauroidea and Coelurosauria). We report a new theropod, Yunyangosaurus puanensis gen. et sp. nov., based on a fragmentary specimen recovered from the Middle Jurassic Xintiangou Formation of Chongqing, southwestern China. It shares several features uniquely with some megalosauroids (the clade of megalosaurids + spinosaurids + piatnitzkysaurids), such as prominent rims around the anterior articular surfaces of cervical centra and bifurcated anterior dorsal neural spines (present in piatnitzkysaurids). Nevertheless, it also shows several features that are rare or absent among megalosauroids and more crownward tetanurans, including prominent spinopostyzgopophyseal laminae (also present in non-tetanurans and metriacanthosaurid allosauroids), flat anterior articular surfaces of the cervical centra (also present in piatnitzkysaurids and some earlier-diverging tetanurans), and the presence of a posterior pneumatic foramen or fossa (absent in most tetanurans, but sporadically present in some cervical vertebrae of piatnitzkysaurids). Yunyangosaurus therefore presents a combination of derived and apparently primitive character states that are not seen in other theropods. This suggests that patterns of morphological evolution associated with deep tetanuran divergences were more complex than currently recognized, with implications for understanding the character evolution in theropods.

A new caenagnathid dinosaur from the Upper Cretaceous Wangshi Group of Shandong, China, with comments on size variation among oviraptorosaurs.

The bone-beds of the Upper Cretaceous Wangshi Group in Zhucheng, Shandong, China are rich in fossil remains of the gigantic hadrosaurid Shantungosaurus. Here we report a new oviraptorosaur, Anomalipes zhaoi gen. et sp. nov., based on a recently collected specimen comprising a partial left hindlimb from the Kugou Locality in Zhucheng. This specimen's systematic position was assessed by three numerical cladistic analyses based on recently published theropod phylogenetic datasets, with the inclusion of several new characters. Anomalipes zhaoi differs from other known caenagnathids in having a unique combination of features: femoral head anteroposteriorly narrow and with significant posterior orientation; accessory trochanter low and confluent with lesser trochanter; lateral ridge present on femoral lateral surface; weak fourth trochanter present; metatarsal III with triangular proximal articular surface, prominent anterior flange near proximal end, highly asymmetrical hemicondyles, and longitudinal groove on distal articular surface; and ungual of pedal digit II with lateral collateral groove deeper and more dorsally located than medial groove. The holotype of Anomalipes zhaoi is smaller than is typical for Caenagnathidae but larger than is typical for the other major oviraptorosaurian subclade, Oviraptoridae. Size comparisons among oviraptorisaurians show that the Caenagnathidae vary much more widely in size than the Oviraptoridae.