New papers:
The origins of one of the most successful groups to roam the Earth, the dinosaurs, have been the subject of intense investigation. Dozens of new early members of the group have been discovered in recent years and novel, sometimes challenging, hypotheses attempt to explain the relationships among the major dinosaur lineages and their early offshoots of Triassic age. The oldest unequivocal dinosaur fossils were collected in beds of Carnian (ca. 237-227 million years ago; Late Triassic) age in Brazil and Argentina, suggesting that the group emerged in southwestern Pangea, before gradually expanding its distribution around the globe. Although controversial in cases, the three main dinosaur lineages: ornithischians, theropods, and sauropodomorphs have Carnian representatives, but only the latter group, along with the enigmatic herrerasaurs, was relatively diverse at that time. After the Carnian, Triassic dinosaurs achieved a much greater abundance, before becoming the most diverse group of terrestrial tetrapods from the Jurassic onwards. Some anatomical traits, such as a longer deltopectoral crest in the humerus, an increasing number of sacral vertebrae, an open acetabulum, a well-developed femoral head, and a larger ascending process of the astragalus, are typical of dinosaurs and are also related to the upright bipedal locomotion that characterizes most early members of the group. Together with some physiological adaptations, such as fast growth, more efficient thermoregulation and breathing, these features probably provided the means for dinosaurs to thrive across the Triassic-Jurassic extinction, allowing the group to become a unique example of evolutionary success.
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Free pdf:
The early radiation of Neoaves has been hypothesized to be an intractable âhard polytomyâ. We explore the fundamental properties of insertion/deletion alleles (indels), an under-utilized form of genomic data with the potential to help solve this. We scored >5 million indels from >7000 pan-genomic intronic and ultraconserved element (UCE) loci in 48 representatives of all neoavian orders. We found that intronic and UCE indels exhibited less homoplasy than nucleotide (nt) data. Gene trees estimated using indel data were less resolved than those estimated using nt data. Nevertheless, Accurate Species TRee Algorithm (ASTRAL) species trees estimated using indels were generally similar to nt-based ASTRAL trees, albeit with lower support. However, the power of indel gene trees became clear when we combined them with nt gene trees, including a striking result for UCEs. The individual UCE indel and nt ASTRAL trees were incongruent with each other and with the intron ASTRAL trees; however, the combined indel+nt ASTRAL tree was much more congruent with the intronic trees. Finally, combining indel and nt data for both introns and UCEs provided sufficient power to reduce the scope of the polytomy that was previously proposed for several supraordinal lineages of Neoaves.
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