An exceptionally preserved association of complete dinosaur skeletons reveals the oldest long-necked sauropodomorphs.

The rise of sauropodomorphs is still poorly understood due to the scarcity of well-preserved fossils in early Norian rocks. Here, we present an association of complete and exceptionally well-preserved dinosaur skeletons that helps fill that gap. They represent a new species, which is recovered as a member of a clade solely composed of Gondwanan Triassic taxa. The new species allows the definition of a set of anatomical changes that shaped sauropodomorph evolution along a period from 233 to 225 Ma, as recorded in the well dated Late Triassic beds of Brazil. In that time span, apart from achieving a more herbivorous diet, sauropodomorph dinosaurs increased their size in a ratio of 230% and their typical long neck was also established, becoming proportionally twice longer than those of basal taxa. Indeed, the new dinosaur is the oldest-known sauropodomorph with such an elongated neck, suggesting that the ability to feed on high vegetation was a key trait achieved along the early Norian. Finally, the clustered preservation mode of the skeletons represents the oldest evidence of gregarious behaviour among sauropodomorphs.

Osteohistological characterization of notosuchian osteoderms: Evidence for an overlying thick leathery layer of skin.

Osteoderms are mineralized structures embedded in the dermis, known for nonavian archosaurs, squamates, xenarthrans, and amphibians. Herein, we compared the osteoderm histology of Brazilian Notosuchia of Cretaceous age using three neosuchians for comparative purposes. Microanatomical analyses showed that most of them present a diploe structure similar to those of other pseudosuchians, lizards, and turtles. This structure contains two cortices (the external cortex composed of an outer and an inner layers, and the basal cortex) and a core in-between them. Notosuchian osteoderms show high bone compactness (>0.85) with varying degrees of cancellous bone in the core. The neosuchian Guarinisuchus shows the lowest bone compactness with a well-developed cancellous layer. From an ontogenetic perspective, most tissues are formed through periosteal ossification, although the mineralized tissues observed in baurusuchid LPRP/USP 0634 suggest a late metaplastic development. Histology suggests that the ossification center of notosuchian osteoderm is located at the keel. Interestingly, we identified Sharpey's fibers running perpendicularly to the outer layer of the external cortex in Armadillosuchus arrudai, Itasuchus jesuinoi, and Baurusuchidae (LPRP/USP 0642). This feature indicates a tight attachment within the dermis, and it is evidence for the presence of an overlying thick leathery layer of skin over these osteoderms. These data allow a better understanding of the osteohistological structure of crocodylomorph dermal bones, and highlight their structural diversity. We suggest that the vascular canals present in some sampled osteoderms connecting the inner layer of the external cortex and the core with the external surface may increase osteoderm surface and the capacity of heat transfer in terrestrial notosuchians.

Structure and Chemical Composition of ca. 10-Million-Year-Old (Late Miocene of Western Amazon) and Present-Day Teeth of Related Species.

Molecular information has been gathered from fossilized dental enamel, the best-preserved tissue of vertebrates. However, the association of morphological features with the possible mineral and organic information of this tissue is still poorly understood in the context of the emerging area of paleoproteomics. This study aims to compare the morphological features and chemical composition of dental enamel of extinct and extant terrestrial vertebrates of Crocodylia: Purussaurus sp. (extinct) and Melanosuchus niger (extant), and Rodentia: Neoepiblema sp. (extinct) and Hydrochoerus hydrochaeris (extant). To obtain structural and chemical data, superficial and internal enamel were analyzed by Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (SEM-EDS). Organic, mineral, and water content were obtained using polarizing microscopy and microradiography on ground sections of four teeth, resulting in a higher organic volume than previously expected (up to 49%). It is observed that both modern and fossil tooth enamel exhibit the same major constituents: 36.7% Ca, 17.2% P, and 41% O, characteristic of hydroxyapatite. Additionally, 27 other elements were measured from superficial enamel by inductively coupled mass spectrometry (ICP-MS). Zinc was the most abundant microelement detected, followed by Pb, Fe, Mg, and Al. Morphological features observed include enamel rods in the rodent teeth, while incremental lines and semiprismatic enamel were observed in the alligator species. The fossil enamel was in an excellent state for microscopic analyses. Results show that all major dental enamel's physical, chemical, and morphological features are present both in extant and extinct fossil tooth enamel (>8.5 Ma) in both taxa.

Ancient enamel peptides recovered from the South American Pleistocene species Notiomastodon platensis and Myocastor cf. coypus.

We used two fossil teeth from South American Pleistocene mammals to obtain subsuperficial acid etching samples. We employed samples from the species Notiomastodon platensis and Myocastor cf. coypus for the enamel etchings. The controls included an extant rodent (rat). After the first etching was discarded, a second 20-s etching (i.e., subsuperficial) was directly collected with a ZipTip and injected into an LTQ Orbitrap Velos for MS analysis. The peptides were identified with different software programs that used Peptide Spectrum Match (PSM) and de novo sequencing including similarity search strategies. Most of the peptides that were recovered from the enamel of the fossils belonged to enamel-specific proteins. To our knowledge, this is the first study that has described the recovery of enamel peptide molecules from extinct South American taxa, indicating that enamel peptide data from late Pleistocene fossils can be employed as an additional parameter for phylogenetic analysis, and that the sample can be obtained by a very conservative acid etching, with almost no damage to the fossils. SIGNIFICANCE: This study shows that it is possible to obtain information based on plenty of ancient peptides recovered from subsuperficial enamel of fossil teeth from South American Pleistocene. The quality of the data suggests that peptides are likely the best preserved biomolecules under certain harsh environmental conditions. The recovery procedure only lasted 20 s and was minimally destructive to the fossils. This opens a myriad of new possibilities for the study of the past.

Discovery of the oldest South American fossil lizard illustrates the cosmopolitanism of early South American squamates.

Squamates have an extremely long evolutionary history with a fossil record that extends into the Middle Triassic. However, most of our knowledge of their early evolutionary history is derived from Laurasian records. Therefore, fundamental questions regarding the early evolution of squamates in the Southern Hemisphere, such as the origins of the extremely diverse and endemic South American fauna, remain unanswered. Here, we describe a new lizard species that represents the oldest fossil squamate from South America, demonstrating that squamates were present on that continent at least 20 million years earlier than previously recorded. The new species represents the first occurrence of the extinct squamate family Paramacellodidae in South America and displays an unusual limb morphology. Finally, our findings suggest early South American squamates were part of a much broader distribution of their respective clades, in sharp contrast to the high levels of endemicity characteristic of modern faunas.

Anatomy of the dinosaur Pampadromaeus barberenai (Saurischia-Sauropodomorpha) from the Late Triassic Santa Maria Formation of southern Brazil.

Sauropodomorphs are the most abundant and diverse clade of Triassic dinosaurs, but the taxonomy of their earliest (Carnian) representatives is still poorly understood. One such taxon is Pampadromaeus barberenai, represented by a nearly complete disarticulated skeleton recovered from the upper part of the Santa Maria Formation of Rio Grande do Sul, Brazil. Here, the osteology of Pam. barberenai is fully described for the first time. Detailed comparisons with other Carnian sauropodomorphs reveal a unique anatomy, corroborating its status as a valid species. Potential autapomorphies of Pam. barberenai can be seen in the articulation of the sacral zygapophyses, the length of the pectoral epipodium, the shape of the distal articulation of the femur and the proximal articulation of metatarsal 1. A novel phylogenetic study shows that relationships among the Carnian sauropodomorphs are poorly constrained, possibly because they belong to a "zone of variability", where homoplasy abounds. Yet, there is some evidence that Pam. barberenai may nest within Saturnaliidae, along with Saturnalia tupiniquim and Chromogisaurus novasi, which represents the sister group to the larger sauropodomorphs, i.e. Bagualosauria.

A new desert-dwelling dinosaur (Theropoda, Noasaurinae) from the Cretaceous of south Brazil.

Noasaurines form an enigmatic group of small-bodied predatory theropod dinosaurs known from the Late Cretaceous of Gondwana. They are relatively rare, with notable records in Argentina and Madagascar, and possible remains reported for Brazil, India, and continental Africa. In south-central Brazil, the deposits of the Bauru Basin have yielded a rich tetrapod fauna, which is concentrated in the Bauru Group. The mainly aeolian deposits of the Caiuá Group, on the contrary, bear a scarce fossil record composed only of lizards, turtles, and pterosaurs. Here, we describe the first dinosaur of the Caiuá Group, which also represents the best-preserved theropod of the entire Bauru Basin known to date. The recovered skeletal parts (vertebrae, girdles, limbs, and scarce cranial elements) show that the new taxon was just over 1 m long, with a unique anatomy among theropods. The shafts of its metatarsals II and IV are very lateromedially compressed, as are the blade-like ungual phalanges of the respective digits. This implies that the new taxon could have been functionally monodactyl, with a main central weight-bearing digit, flanked by neighbouring elements positioned very close to digit III or even held free of the ground. Such anatomical adaptation is formerly unrecorded among archosaurs, but has been previously inferred from footprints of the same stratigraphic unit that yielded the new dinosaur. A phylogenetic analysis nests the new taxon within the Noasaurinae clade, which is unresolved because of the multiple alternative positions that Noasaurus leali can acquire in the optimal trees. The exclusion of the latter form results in positioning the new dinosaur as the sister-taxon of the Argentinean Velocisaurus unicus.

Ingroup relationships of Lagerpetidae (Avemetatarsalia: Dinosauromorpha): a further phylogenetic investigation on the understanding of dinosaur relatives.

Despite representing a key-taxon in dinosauromorph phylogeny, Lagerpertidae is one of the most obscure and enigmatic branches from the stem that leads to the dinosaurs. Recent new findings have greatly increased our knowledge about lagerpetids, but no phylogenetic analysis has so far included all known members of this group. Here, we present the most inclusive phylogenetic study so far conducted for Lagerpetidae. Phylogenetic analyses were performed based on three independent data matrixes. In two of them, Lagerpeton chanarensis Romer, 1971 is the sister taxon to all other known Lagerpetidae, whereas Ixalerpeton polesinensis Cabreira et al., 2016 is in a sister group relationship with a clade that includes PVSJ 883 and Dromomeron. Conversely, the other analysis supports an alternative topology, where I. polesinensis is the sister taxon to either L. chanarensis or all other Lagerpetidae. Although coeval and geographically close, I. polesinensis and PVSJ 883 do not form a clade exclusive of other lagerpetids. As previously suggested D. gigas Martínez, Apaldetti, Correa Abelín, 2016 is the sister taxon of D. romeri Irmis et al., 2007. The phylogenetic analyses also indicate that the earliest lagerpetids are restricted to southwestern Pangea, whereas later forms spread across the entire western portion of the supercontinent. Finally, quantification of the codified characters of our analysis reveals that Lagerpetidae is one of the poorest known among the Triassic dinosauromorph groups in terms of their anatomy, so that new discoveries of more complete specimens are awaited to establish a more robust phylogeny.

Inferring ancestral range reconstruction based on trilobite records: a study-case on Metacryphaeus (Phacopida, Calmoniidae).

Metacryphaeus is a calmoniid trilobite genus from the Devonian Malvinokaffric Realm, exclusive to the Gondwanan regions. It includes eleven species, which are for the first time included here in a single phylogenetic analysis. The resulting hypotheses establish relations among the Metacryphaeus species with few ambiguities, also suggesting the inclusion of both Plesiomalvinella pujravii and P. boulei within the genus, as originally considered. The results of palaeobiogeographic analyses employing the Dispersal-Extinction-Cladogenesis (DEC) model reinforce the hypothesis that Bolivia and Peru form the ancestral home of Metacryphaeus. The radiation of the genus to other Gondwanan areas took place during transgressive eustatic episodes during the Lochkovian-Pragian. The Lochkovian dispersal occurred from Bolivia and Peru to Brazil (Paraná and Parnaíba basins) and the Falklands, and Pragian dispersal occurred towards South Africa. Dispersal events from Bolivia and Peru to the Parnaíba Basin (Brazil) were identified during the Lochkovian-Pragian, suggesting the presence of marine connections between those areas earlier than previously thought.

A Unique Late Triassic Dinosauromorph Assemblage Reveals Dinosaur Ancestral Anatomy and Diet.

Dinosauromorpha includes dinosaurs and other much less diverse dinosaur precursors of Triassic age, such as lagerpetids [1]. Joint occurrences of these taxa with dinosaurs are rare but more common during the latest part of that period (Norian-Rhaetian, 228-201 million years ago [mya]) [2, 3]. In contrast, the new lagerpetid and saurischian dinosaur described here were unearthed from one of the oldest rock units with dinosaur fossils worldwide, the Carnian (237-228 mya) Santa Maria Formation of south Brazil [4], a record only matched in age by much more fragmentary remains from Argentina [5]. This is the first time nearly complete dinosaur and non-dinosaur dinosauromorph remains are found together in the same excavation, clearly showing that these animals were contemporaries since the first stages of dinosaur evolution. The new lagerpetid preserves the first skull, scapular and forelimb elements, plus associated vertebrae, known for the group, revealing how dinosaurs acquired several of their typical anatomical traits. Furthermore, a novel phylogenetic analysis shows the new dinosaur as the most basal Sauropodomorpha. Its plesiomorphic teeth, strictly adapted to faunivory, provide crucial data to infer the feeding behavior of the first dinosaurs.