Abstract A worldwide revision of the Cretaceous record of Neornithes (crown birds) revealed that unambiguous neornithine taxa are extremely scarce, with only a few showing diagnostic features to be confidently assigned to that group. Here we report two new neornithine specimens from Vega Island (López de Bertodano Formation). The first is a synsacrum (MN 7832-V) that shows a complex pattern of transversal diverticula intercepting the canalis synsacri, as in extant neornithines. Micro-CT scanning revealed a camerate pattern of trabeculae typical of neornithines. It further shows the oldest occurrence of lumbosacral canals in Neornithes, which are related to a balance sensing system acting in the control of walking and perching. The second specimen (MN 7833-V) is a distal portion of a tarsometatarsus sharing with Vegavis iaai a straight apical border of the crista plantaris lateralis. Osteohistologically the tarsometatarsus shows a thick and highly vascularized cortex that lacks any growth marks, resembling Polarornis gregorii. The cortex is osteosclerotic as in other extinct and extant diving neornithines. These new specimens increase the occurrences of the Cretaceous avian material recovered from the Upper Cretaceous strata of the James Ross Sub-Basin, suggesting that a Vegaviidae-dominated avian assemblage was present in the Antarctic Peninsula during the upper Maastrichtian.

Abstract Aetosauria represents a remarkable clade of armored pseudosuchians in which some of its oldest members are recovered from late Carnian units of Brazil. Three species are known: the mid-sized aetosaur Aetosauroides scagliai, which also occurs in Argentina, and two small-sized species, Aetobarbakinoides brasiliensis and Polesinesuchus aurelioi. We provide a detailed description and comparative analysis of the axial skeleton of Aetosauroides, identifying some diagnostic features as variable. These include the deep pocket pit lateral to the base of the neural spine, the presence of the infradiapophyseal laminae and the lateral fossa ventral to the neurocentral suture. These features are not found in smaller and immature Aetosauroides specimens, resembling the condition found in Polesinesuchus, which is based solely on a juvenile individual, as revealed by osteoderm microstructure analysis. As Polesinesuchus cannot be anatomically differentiated from other small individuals of Aetosauroides, we propose it as a junior synonym of Aetosauroides scagliai. Our results shrink the number of putative ‘dwarf’ aetosaurs, indicating that morphological variation related to ontogeny affects aetosaur taxonomy and phylogeny.

Abstract: The non-dinosaurian dinosauriform silesaurids are the closest relatives of crown-group dinosaurs and are thus, important for understanding the origins of that group. Here, we describe the limb bone histology of the Late Triassic silesaurid Sacisaurus agudoensis from the Candelária Sequence of the Santa Maria Supersequence, Rio Grande do Sul state, Brazil. The sampled bones comprise eight femora and one fibula from different individuals. The microscopic analysis of all elements reveals uninterrupted fibrolamellar bone tissue indicating rapid growth. A transition to slower growing peripheral parallel-fibered bone tissue in some individuals indicates a decrease in growth rate, suggesting ontogenetic variation within the sample. The osteohistology of Sacisaurus agudoensis is similar to that of other silesaurids and supports previous hypotheses that rapid growth was attained early in the dinosauromorph lineage. However, silesaurids lack the complex vascular arrangements seen in saurischian dinosaurs. Instead, they exhibit predominantly longitudinally-oriented primary osteons with few or no anastomoses, similar to those of some small early ornithischian dinosaurs. This simpler vascular pattern is common to all silesaurids studied to date and indicates relatively slower growth rates compared to most Dinosauria.

Nós reportamos aqui um novo cinodonte prozostrodonte, Botucaraitherium belarminoigen. et sp. nov., do Triássico Tardio da Zona de Assembleia (ZA) de Riograndia da Sequência Candelária (Supersequência Santa Maria), coletado no afloramento Sítio Botucaraí, no município de Candelária, Rio Grande do Sul, Brasil. O novo táxon está baseado em um único espécime (holótipo MMACR-PV003-T) o qual inclui a mandíbula esquerda, sem os ossos pós-dentários, com a raiz do último incisivo preservada, o canino e quatro dentes pós-caninos, além de uma coroa parcial, não erupcionada, do quinto pós-canino, e dois fragmentos maxilares, um com um canino quebrado, e outro portando apenas um dente pós-canino. As feições mandibulares e dentárias assemelham-se àquelas dos cinodontes prozostrodontes Prozostrodon brasiliensisda ZAde Hyperodapedon,mais antiga, e de Brasilodon quadrangularis e Brasilitherium riograndensis da mesma ZA de Riograndia. A inclusão de Botucaraitherium em uma ampla análise filogenética posicionou-o como um táxon mais derivado do que os tritilodontídeos, sendo o táxon-irmão de Brasilodon, Brasilitheriume mais Mammaliaformes. Apesar de o novo táxon ser baseado em poucos elementos cranianos, ele representa um componente faunístico adicional na ZA de Riograndiado Triássico sul-brasileiro, na qual os cinodontes não-mamaliaformes de pequeno tamanho, intimamente relacionados à origem dos mamíferos, foram ecologicamente bem sucedidos e taxonomicamente diversos.

We report here on a new prozostrodontian cynodont, Botucaraitherium belarminoigen. et sp. nov., from the Late Triassic RiograndiaAssemblage Zone (AZ) of the Candelária Sequence (Santa Maria Supersequence), collected in the Botucaraí Hill Site, Candelária Municipality, state of Rio Grande do Sul, Brazil. The new taxon is based on a single specimen (holotype MMACR-PV-003-T) which includes the left lower jaw, without postdentary bones, bearing the root of the last incisor, canine and four postcanines plus one partial crown inside the dentary, not erupted, and two maxillary fragments, one with a broken canine and another with one postcanine. The features of the lower jaw and lower/upper postcanines resemble those of the prozostrodontians Prozostrodon brasiliensis from the older HyperodapedonAZ and Brasilodon quadrangularis and Brasilitherium riograndensisfrom the same RiograndiaAZ. The inclusion of Botucaraitheriumwithin a broad phylogenetic analysis, positioned it as a more derived taxon than tritylodontids, being the sister-taxon of Brasilodon, Brasilitheriumplus Mammaliaformes. Although the new taxon is based on few cranial elements, it represents a additional faunal component of the Triassic RiograndiaAZ of southern Brazil, in which small-sized derived non-mammaliaform cynodonts, closely related to the origin of mammaliaforms, were ecologically well succeed and taxonomically diverse.

O triteledontídeo Riograndia guiabensis foi o primeiro cinodonte descrito para a fauna da "Formação Caturrita" do Triássico Superior do sul do Brasil (Sequência Santa Maria 2). Os materiais da série-tipo não forneceram informações anatômicas relativas à caixa craniana, ociput, basicrânio, arco zigomático, ossos pós-dentários e articulação crânio-mandibular. Neste artigo são descritos novos materiais que suprem as informações anatômicas não contempladas anteriormente. Riograndia apresenta um conjunto de importantes aspectos anatômicos derivados dentre os eucinodontes não-mammaliaformes, tais como fechamento parcial da parede orbital medial e da caixa craniana, extenso palato ósseo secundário, palato primário alargado, basicrânio com separação do forame jugular e da fenestra rotunda, arco zigomático estreito e ossos pós-dentários extremamente reduzidos. Muitas destas feições constituem sinapomorfias compartilhadas somente com os demais membros do clado Mammaliamorpha. Assim, as praticamente completas informações crânio-mandibulares e dentárias de Riograndia trazem uma significante contribuição ao conhecimento da anatomia dos triteledontídeos e suas relações filogenéticas e auxiliam na elucidação sobre os passos transformacionais envolvidos na transição cinodonte-mamífero. Adicionalmente, Riograndia figura como um táxon-chave no refinamento bioestratigráfico da "Formação Caturrita", através da integração de vários afloramentos fossilíferos os quais apresentam uma rica fauna de tetrápodes que pode ser correlacionada com outras faunas triássicas do Gondwana e da Laurásia.

The tritheledontid Riograndia guaibensis was the first cynodont described for the "Caturrita Formation" fauna from the Late Triassic of southern Brazil (Santa Maria 2 Sequence). The type materials did not preserve anatomical information regarding braincase, occiput, basicranium, zygomatic arch, postdentary bones and craniomandibular joint. Here new materials are described and supply the missing information. Riograndia shows a suite of important anatomical features quite derived among the non-mammaliaform eucynodonts, such as the partial closure of the medial orbital wall and braincase, extensive secondary osseous palate, wide primary palate, basicranium with jugular foramen separated from the periphery of fenestra rotunda, narrow zygomatic arch and much reduced postdentary bones. Many of these features constitute synapomorphies shared only with the other members of mammaliamorpha. Thus, the almost complete cranial, mandibular and dental information from the new fossils of Riograndia can bring a significant improve in the understanding of the anatomy and phylogenetic relationships of the tritheledontids and help to elucidate the transformational steps involved in the cynodont-mammal transition. Additionally, Riograndia is a key taxon in refining the "Caturrita Formation" biostratigraphy, enabling the connection of several fossiliferous outcrops that have a rich tetrapod fauna that can be correlated with other Triassic faunas from Gondwana and Laurasia.