Most Notosuchia were active terrestrial predators. A few were semi-aquatic, or were insectivorous, omnivorous or herbivorous. A question relative to their thermometabolism remains to be answered: were Notosuchia warm-blooded? Here we use quantitative bone palaeohistology to answer this question. Two variables were used as proxies to infer thermometabolism: resting metabolic rate and red blood cell dimensions. Resting metabolic rate was inferred using relative primary osteon area and osteocyte size, shape and density. Blood cell dimensions were inferred using harmonic mean canal diameter and minimum canal diameter. All inferences were performed using phylogenetic eigenvector maps. Both sets of analyses suggest that the seven species of Notosuchia sampled in this study were ectotherms. Given that extant Neosuchia (their sister group) are also ectotherms, and that archosaurs were primitively endotherms, parsimony suggests that endothermy may have been lost at the node Metasuchia (Notosuchia–Neosuchia) by the Early Jurassic. Semi-aquatic taxa such as Pepesuchus may have had thermoregulatory strategies similar to those of recent crocodylians, whereas the terrestrial taxa (Araripesuchus, Armadillosuchus, Iberosuchus, Mariliasuchus, Stratiotosuchus) may have been thermoregulators similar to active predatory varanids. Thermal inertia may have contributed to maintaining a stable temperature in large notosuchians such as Baurusuchus.

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In this study we provide a comprehensive investigation of the microanatomical and microstructural aspects of the carapace and limb bones of the Early Cretaceous side-necked turtle, Araripemys barretoi, from the Araripe Basin, Brazil. Inter-elemental histovariability reveals different secondary remodelling of the skeletal elements within the same individual. The vascularisation is scarce and mainly longitudinal, also it ceases towards the bone surface, forming an avascular parallel-fi bred bone with closely spaced LAGs. These traits indicate a late ontogenetic stage and a slow growth rate for one of the two A. barretoi specimens. The high cortical thickness of the costal plate suggests an increase of the shell stiffness. The elevated relative bone wall thickness of the ulna compared to other limb bones indicates a case of local pachyosteosclerosis, possibly to improve body stability in the aquatic environment.

-The fossil crocodyliforms from the Paraíba Basin in Northeastern Brazil are represented by two species, Hyposaurus derbianus, (uncertain age) and Guarinisuchus munizi, from the Paleocene Maria Farinha Formation. Herein we present new material of a dyrosaurid also collected in deposits of the Maria Farinha Formation, representing cranial, axial and appendicular remains. The specimens are housed at Centro Acadêmico de Vitória, Universidade Federal de Pernambuco (CAV-UFPE) and at Universidade Federal Rural de Pernambuco (UFRPE). The most important contribution of this find is a well-preserved mandibular specimen (CAV 0056-V) with 16 alveoli on the left side and 13 on the right side. Nine complete or partial tooth crowns are preserved, in positions 1-5. The teeth are conical and homodont with vertical striations. The largest teeth are located at positions d1 and d4. The biggest occlusion pits are located between positions d2 and d3. The seventh alveoli are reduced and close to the eighth alveoli. The mandible, CAV 0056-V, possesses three foramina in the anterior portion of the dentaries and the mandibular symphysis extends to the posterior margins of the d11-d12 dentary alveoli. Based on the features presented in the mandible and the other fossils recovered, we attribute these materials to Dyrosauridae, particularly, to Guarinisuchus cf. G. munizi. Key words:Crocodyliformes, Dyrosauridae, NE Brazil, Paleocene, Paraíba Basin. RESUMO -Os Crocodyliformes fósseis da Bacia da Paraíba, Nordeste brasileiro, são representados por duas espécies, Hyposaurus derbianus de idade incerta e Guarinisuchus munizi, dos estratos paleocênicos da Formação Maria Farinha. Aqui são apresentados novos materiais de dyrossaurídeo da Formação Maria Farinha, representados por fragmentos craniais, axiais e apendiculares. Os espécimes estão armazenados no Centro Acadêmico de Vitória da Universidade Federal de Pernambuco (CAV-UFPE) e na Universidade Federal Rural de Pernambuco (UFRPE). O novo material contém uma mandíbula bem preservada (CAV 0056-V), com 16 alvéolos do lado esquerdo e 13 do lado direito. Nove coroas dentárias estão preservadas total ou parcialmente completas, nas posições 1-5. Os dentes são homodontes com forma cônica e estrias verticais. Os dentes de maior comprimento estão localizados nas posições d1 e d4. As maiores marcas de oclusão ocorrem entre as posições d2 e d3. Os alvéolos d7 apresentam dimensões reduzidas e ocorrem próximos aos alvéolos d8. A mandíbula, CAV 0056-V apresenta três forames na porção anterior dos dentários e a sínfise mandibular estende-se até a borda posterior dos alvéolos dentários d11-d12. Portanto, fundamentado nas características apresentadas na mandíbula e pelos outros espécimes, nós associamos estes materiais à Dyrosauridae, particularmente, Guarinisuchus cf. G. munizi.

Pelomedusoides had a recognised diverse Early Cretaceous fauna of turtles in Northeast Brazil. Within them, the bothremydid Cearachelys placidoi has a relatively abundant record. This diversity contrasts with the scarcity of osteohistological studies in this group. The relatively well-preserved shell of C. placidoi (UFRPE 5600), from the Aptian age of Araripe Basin, is studied here for the purpose of filling this gap. We performed the osteohistological description of the plastron of a new specimen of C. placidoi. Also, to conduct a comparative study, we carried out histological sections in bones of the recent chelid Phrynops sp. Our histological findings indicate similarities between the histological pattern of freshwater turtles and the coastal marine C. placidoi. Moreover, osteohistological features imply metaplastic incorporation of dermal interwoven structural fiber bundles. Lastly, the xiphiplastron of C. placidoi shows an increase of bone compactness over its craniocaudal axis. This microanatomical feature is exclusive to Cearachelys so far.

The fossil crocodyliforms from the Paraíba Basin in Northeastern Brazil are represented by two species, Hyposaurus derbianus,(uncertain age) and Guarinisuchus munizi, from the Paleocene Maria Farinha Formation. Herein we present new material of a dyrosauridalso collected in deposits of the Maria Farinha Formation, representing cranial, axial and appendicular remains. The specimens are housedat Centro Acadêmico de Vitória, Universidade Federal de Pernambuco (CAV–UFPE) and at Universidade Federal Rural de Pernambuco(UFRPE). The most important contribution of this find is a well-preserved mandibular specimen (CAV 0056-V) with 16 alveoli on the leftside and 13 on the right side. Nine complete or partial tooth crowns are preserved, in positions 1–5. The teeth are conical and homodont withvertical striations. The largest teeth are located at positions d1 and d4. The biggest occlusion pits are located between positions d2 and d3. Theseventh alveoli are reduced and close to the eighth alveoli. The mandible, CAV 0056-V, possesses three foramina in the anterior portion ofthe dentaries and the mandibular symphysis extends to the posterior margins of the d11–d12 dentary alveoli. Based on the features presentedin the mandible and the other fossils recovered, we attribute these materials to Dyrosauridae, particularly, to Guarinisuchus cf. G. munizi.

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.