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Although several well-preserved crania are known for the Mesozoic Eutriconodonta, three-dimensional reconstructions of the character-rich inner ear and basicranial region based on high-resolution computed tomography scans have previously only been published for the Late Jurassic Priacodon. Here we present a description of the petrosal and inner ear morphology of a triconodontid eutriconodontan from the Lower Cretaceous Cloverly Formation, which we provisionally assign to Astroconodon. The bony labyrinth of Astroconodon is plesiomorphic for mammaliaforms in lacking a primary osseous lamina, cribriform plate, and osseous cochlear ganglion canal. However, as in Priacodon and the zhangheotheriid Origolestes, Astroconodon has a secondary osseous lamina base that extends nearly the complete length of the cochlear canal. The cochlear canal is straighter in Astroconodon and other eutriconodontans compared to several basal mammaliaform clades (e.g., morganucodontans, docodontans), that exhibit varying degrees of cochlear canal curvature. The pars cochlearis of the petrosal was well vascularized in Astroconodon, exhibiting a network of venous canals that crossed the cochlea transversely on its ventral and dorsal aspects. Of particular note are several canals that passed along the base of the secondary osseous lamina. As in Priacodon and Origolestes, those canals do not show the extensive connections to the cochlear labyrinth as seen in the basal mammaliaforms Morganucodon and Borealestes. The inner ear of Astroconodon thus highlights the complex history of the mammaliaform cochlear canal, in which different clades appear to follow independent evolutionary trajectories and various key morphological features (e.g., cochlear canal length, curvature, vascularization and osseous supports for the basilar membrane) exhibit considerable homoplasy. 

Lakotemys australodakotensis is an Early Cretaceous paracryptodire known from two shells and a skull from the Lakota Formation of South Dakota, USA. Along with the Early Cretaceous Arundelemys dardeni and the poorly known Trinitichelys hiatti , Lakotemys australodakotensis is generally retrieved as an early branching baenid, but more insights into the cranial anatomy of these taxa is needed to obtain a better understanding of paracryptodiran diversity and evolution. Here, we describe the skull of Lakotemys australodakotensis using micro-computed tomography to provide the anatomical basis for future phylogenetic analyses that will be needed to investigate more precisely the intrarelationships of Paracryptodira . Preliminary comparisons reveal that the cranial anatomy of Lakotemys australodakotensis is very similar to that of the Aptian-Albian basal baenid Arundelemys dardeni , that both taxa exhibit a remarkable combination of derived characters found in baenodds and characters found in non-baenid paracryptodires, particularly Pleurosternidae , and that Lakotemys australodakotensis is the only known baenid to date to possess a canal for the palatine artery. 

We present a previously discovered but undescribed late Early Cretaceous vertebrate fauna from the Holly Creek Formation of the Trinity Group in Arkansas. The site from the ancient Gulf Coast is dominated by semi-aquatic forms and preserves a diverse aquatic, semi-aquatic, and terrestrial fauna. Fishes include fresh- to brackish-water chondrichthyans and a variety of actinopterygians, including semionotids, an amiid, and a new pycnodontiform, Anomoeodus caddoi sp. nov. Semi-aquatic taxa include lissamphibians, the solemydid turtle Naomichelys , a trionychid turtle, and coelognathosuchian crocodyliforms. Among terrestrial forms are several members of Dinosauria and one or more squamates, one of which, Sciroseps pawhuskai gen. et sp. nov., is described herein. Among Dinosauria, both large and small theropods ( Acrocanthosaurus , Deinonychus , and Richardoestesia ) and titanosauriform sauropods are represented; herein we also report the first occurrence of a nodosaurid ankylosaur from the Trinity Group. The fauna of the Holly Creek Formation is similar to other, widely scattered late Early Cretaceous assemblages across North America and suggests the presence of a low-diversity, broadly distributed continental ecosystem of the Early Cretaceous following the Late Jurassic faunal turnover. This low-diversity ecosystem contrasts sharply with the highly diverse ecosystem which emerged by the Cenomanian. The contrast underpins the importance of vicariance as an evolutionary driver brought on by Sevier tectonics and climatic changes, such as rising sea level and formation of the Western Interior Seaway, impacting the early Late Cretaceous ecosystem. 

Abstract Triconodon mordax, from the lowest Cretaceous (Berriasian) part of the Purbeck Group, Dorset, is known by an ontogenetic series of specimens that document aspects of tooth eruption and replacement. Based on micro‐computed tomography of four specimens we refer one mandible to a new species,Triconodon averianovi, which differs fromT. mordaxin having a more slender, curved c; p4 notably low crowned with slender main cusp and smaller accessory cusps; and molars with weak cingula, m4 being notably smaller with weak cusps a and c.T. mordaxis variable in the number of mental foramina and posterior jaw morphology. Scans reveal an earlier developmental stage (p3 in early eruption) than previously recognized forTriconodon, and demonstrate sequential, anteroposterior replacement of premolars; it remains unclear whether p1–2 were replaced. Scans also support an earlier hypothesis that m4 erupted late in life. Onset of m4 mineralization is likely to have coincided with eruption of p3, followed by replacement of dp4 by p4 and eruption of c. The m4 developed within the lingual side of the coronoid process, well above the tooth row. It remained in position and was subsequently accommodated in the active tooth row through unusually prolonged and localized growth of the posterior part of the mandible. This pattern is seen in some later triconodontids and appears to be unique to the family.