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Baryonychinae gen. et sp. indet. Fig. 2 Morphological description: The three referred specimens LPUFS 5860, LPUFS 5870, and LPUFS 5871 are isolated crowns presenting the same general morphotype (Fig. 2). The teeth are well-preserved and have a similar taphonomical pattern of others at the same site (Lacerda et al. 2023). The length of the crowns varies between 17.2 mm and 32.5 mm, and the specimens share: the conidont morphology, the main crown curvature being in the mesiodistal plane, the presence of labial and lingual enamel flutes, the denticulated mesial and distal carinae being centrally positioned, the absence of interdenticular sulci, veined enamel texture (wrinkled enamel), and the carinae reaching the cervix/root. LPUFS 5860 (Fig. 2 A-H) is a completely preserved crown with a subcircular cross-sectional outline (Fig. 2E). The tooth surface has eleven well-demarcated flutes in the lingual plane and nine less-demarcated flutes on the labial surface of the crown. The flutes, in general, are equally spaced, extending from the cervix to the apex (Fig. 2F). The distal carina is better developed (more extensive) than the mesial one, being both serrated with diminutive denticles (being 7 denticles per millimetre) composed of both the dentin and enamel (Fig. 2H) and lacking interdenticular sulci. The denticles have similar sizes along the carina and also when comparing both the mesial and distal carinae. The enamel ornamentation is arranged in a veined manner. Only a small wear surface is present at the apex of the crown (Fig. 2E). LPUFS 5870 (Fig. 2 I-P) is a more robust tooth crown, preserving the mid crown and a small portion of the root. The cross-section of the specimen is subcircular in outline (Fig. 2M). The main crown curvature is noted in the mesiodistal plane; however, a subtle labiolingual curvature is also present. In the labial side the tooth has eleven flutes, and in the lingual plane are counted twelve flutes, some of which are also demarcated in the dentine below the enamel wear (Fig. 2N), which are well-developed and equally spaced. Both carinae are well-developed, the mesial one extends slightly to the cervix, with its denticles (being 6 to 7 denticles per mm) composed of both dentin and enamel (Fig. 2P). The individual minute denticles are equal in size, lacking interdenticular sulci. The main texturization of the enamel is veined arranged. In the apical-most portion, a round wear surface is noted in the tooth crown (Fig. 2M). LPUFS 5871 (Fig. 2 Q-X) is the smallest and more taphonomic damaged crown, lacking the root entirely. The cross-section is nearly circular in outline (Fig. 2U) (however, see Multivariate analyses section and Table 2). At least fourteen flutes are noted on the labial surface, some of which do not reach the apex (and therefore may overestimate the flute count); the lingual surface of the crown has at least eleven well-demarcated flutes composed by the dentin and enamel. The distal carina is poorly preserved in LPUFS 5871 specimen, however the mesial one is well-developed with equally sized diminutive denticles (being 7 denticles per mm) on the mid-to-apex portion of the carina distributed without the presence of interdenticular sulci (Fig. 2X). The enamel ornamentation is arranged in a veined manner mainly noted in the base of the lingual surface. A small and round wear surface is present at the apex of the crown (Fig. 2U). Morphological comparisons: The three specimens LPUFS 5860, LPUFS 5870, and LPUFS 5871 present a conidont morphology (composed of a conical crown and flutes distributed on the labial and lingual enamel surfaces), different from the ziphodont morphology (comprising a narrow crown labiolingually distally curved), which is observed in some archosaurs and the vast majority of theropod species (Andrade et al. 2010; Hendrickx et al. 2015a,b; 2019). In a complementary way, the materials described here present a feature considered typical in theropod dinosaurs, which is the mesiodistal plane as the main plane of curvature of the dental crown, a characteristic that allows the differentiation of these materials from conidont teeth of crocodyliforms (mainly Neosuchia), which generally have the main plain of curvature of the crown in the labiolingual direction (Sánchez-Hernández et al. 2007; Buffetaut et al. 2008; 2019; Hone et al. 2010; Sales et al. 2017). Even ziphodont crocodyliforms (e.g., Riff & Kellner 2001) can be distinguished from the materials described here by the curvature of the crown and the size/ morphology of the denticles. Furthermore, the teeth described here can be distinguished from marine reptiles (e.g., plesiosaurs) on the basis of compression and enamel morphology, in addition to the presence of minute denticles on the carinae (Hone et al. 2010; Buffetaut et al. 2019). Unlike other theropods, the teeth of spinosaurids have a subcircular-elliptical cross-section, straighter crowns, and a deeply veined or anastomosed enamel (Alonso & Canudo 2016; Hendrickx et al. 2015a; 2019). Based on the mentioned features, it is possible to differ the LPUFS specimens from non-archosaur reptiles; moreover, the conidont morphology, the mesiodistal plane of curvature as the main plane, the wrinkled enamel at the base of the tooth crown, the presence of mesiodistal carinae reaching the crown cervix, and the distribution of flutes on the labial and lingual sides (although variable in spinosaurids - Alonso & Canudo 2016), allow us to safely assign the specimens as belonging to spinosaurids. As noted by Hendrickx et al. (2019), tooth enamel in spinosaurids may be veined in texture, as observed in Baryonyx, Suchomimus, Spinosaurus, and Iberospinus (Mateus & Estraviz-López 2022), or it may have an anastomosing texture, particularly noted in some Spinosaurus individuals. The materials described here present enamel with a veined texture, most similar to the morphology noted in baryonychines, as well as the presence of labial and lingual enamel flutes common in spinosaurids, albeit some unfluted teeth are also known (Fowler 2007; Hone et al. 2010). Even with some degree of variation in Baryonyx, flutes are present on both sides of the crowns in Suchomimus and Suchosaurus (Hendrickx et al. 2019) as well as in the materials described here. As described by Charig & Milner (1997), Baryonyx presents teeth with six to eight flutes; meanwhile Suchosaurus presents between ten and 12 flutes; and Suchomimus between two and ten (Hendrickx et al. 2019). The largest number of flutes is noted in spinosaurines, approximately 24 in “ Sinopliosaurus ” (Buffetaut et al. 2008), and 20 in materials referring to Spinosaurus (Hendrickx et al. 2019). The teeth described here show a number of flutes greater than that generally observed in baryonychines, but smaller than that observed in non-serrated crowns of spinosaurine (e.g., Buffetaut et al. 2019). Compared with other baryonychine teeth (e.g., Fowler 2007; Canudo et al. 2008), the flutes approach the carinae more closely, and are “thinner” (less deep, and closer spaced) in the specimens described here. The morphofunction of the fluted crowns is probably broad, however, this structure may be related to some perforation/gripping function, in this way the sharp ridges allow the perforation of the skin and enlargement the flesh as the tooth penetrates, as well as keeping slippery prey trapped in the mouth (Charig & Milner 1997; Sues et al. 2002; Hendrickx et al. 2019). Although baryonychine teeth have a more pronounced distal curvature than in spinosaurine species (Alonso & Canudo 2016), the LPUFS specimens have a less pronounced distal curvature of the crown (Fig. 2). Denticles are present in both carinae of LPUFS 5860, LPUFS 5870, and LPUFS 5871, and in general, the denticles are the same size. This feature differs from Iberospinus, which has smaller mesial denticles (Mateus & Estraviz-López 2022). In Baryonyx, on the other hand, variation in the size of the denticles is more developed than in Suchomimus (Hendrickx et al. 2019). Furthermore, the presence of 6-7 minute denticles per millimetre and equal in size, distributed along both carinae lacking the interdenticular sulci (Fig. 3), represents the morphological condition observed only in baryonychine species (Charig & Milner 1997; Sereno et al. 1998; Fowler 2007; Hone et al. 2010; Alonso & Canudo 2016; Hendrickx et al. 2019; Fig. 3), which allows the taxonomic attribution of the specimens described here to baryonychines (see discussion).

O estudo das estruturas osteológicas e da musculatura a estas relacionadas permite compreender, em animais extintos, a evolução dos traços associados aos seus hábitos locomotores, especialmente se este estudo considerar os seus representantes atuais, a fim de se estabelecer as relações de homologia e analogia entre as estruturas comparadas e suas respectivas funções inferidas. Além disso, em uma análise biomecânica de espécies fósseis, deve-se considerar, mesmo que de forma aproximada, a massa corporal como atributo fundamental. Prestosuchus chiniquensis é uma espécie extinta de arcossauro terrestre relacionada à linhagem dos crocodilos atuais. Para testar as hipóteses de hábitos locomotores deste táxon, foi feita a reconstrução muscular da coxa do espécime UFRGS-PV-0629-T, com base nas descrições musculares de aves e crocodilos. Observou-se que o conjunto muscular considerado em P. chiniquensis, de uma forma geral, é bastante semelhante ao dos representantes atuais. Dos dezesseis grupos musculares da coxa avaliados, treze foram reconhecidos como presentes e homólogos entre os dois grupos de arcossauros viventes comparados, de modo que a reconstrução destes músculos, no exemplar fóssil analisado, se mostrou a opção mais parcimoniosa, envolvendo o menor número de passos evolutivos. Por outro lado, a morfologia da cintura pélvica e dos membros posteriores confere uma disposição distinta dos locais de origem e inserção desta musculatura, com possível alteração das linhas de ação dos mesmos. Por fim, a comparação com formas arcossaurianas extintas e atuais mostrou uma condição basal mantida para a morfologia do fêmur e a flexão do joelho, enquanto a morfologia do púbis e do ísquio – e a origem da musculatura a eles associada – revelou um padrão derivado. Paralelamente, diversas metodologias para a estimativa da massa de formas extintas foram aplicadas e comparadas, com o intuito de realizar inferências biomecânicas para o hábito locomotor de P. chiniquensis. O espécime considerado, com 4,5 m de comprimento total, apresentou uma massa média estimada de 400 kg, a qual, em conjunto com a morfologia geral dos ossos dos membros posteriores, se mostrou compatível com um hábito locomotor subcursorial, além de uma postura preferencialmente mesógrada e quadrúpede. Contudo, devido ao caráter generalista inferido – permitindo uma ampla gama de posturas admissíveis – foi sugerida uma estratégia de caça por emboscada, na qual P. chiniquensis adotaria uma postura bípede e ortógrada, que poderia conferir à espécie vantagens, tal como uma maior velocidade em relação à postura usual. Studying osteological structures and its associated musculature may help to understand the evolution of locomotor traits in extinct animals, especially if this study considers their extant relatives, in order to set up homologies and analogies between the compared structures and their inferred functions. Furthermore, in a biomechanical analysis of the fossil record one should consider the estimated body mass as a fundamental attribute. Prestosuchus chiniquensis is an extinct species of terrestrial archosaur related to extant crocodiles. To test different hypotheses related to the locomotion of this taxon, the muscular reconstruction of the thigh of the specimen UFRGS-PV-0629-T was realized, based on the muscular descriptions of extant birds and crocodiles. It was observed that the main muscular groups considered for the reconstruction of P. chiniquensis were similar in birds and crocodiles in a general manner. Among sixteen muscular groups of the thigh that were analyzed, thirteen were recognized as present and homolog to both extant groups of archosaurs, so that the reconstruction of those muscles in the analyzed fossil specimen showed to be the most parsimonious option, involving the least number of evolutionary steps. On the other hand, the morphological particularities of the pelvic girdle and the hindlimbs gave a distinct arrangement for the origin and insertion sites of this musculature, possibly changing their line of actions. Finally, the comparison between extinct and extant archosaurs showed a basal condition sustained in some aspects, such as the morphology of the femur and the flexion of the knee, though, other aspects were considered as derived, such as the morphology of the pubis and ischium, and their associated muscle origins. At the same time, different methodologies for estimating body mass of fossil specimens were applied, and compared in order to make biomechanical inferences of the locomotors habits of P. chiniquensis. The specimen considered, approximately 4.5 m long (15 ft), presented an estimated mass of 400 kg (around 880 lbs), which, with the general morphology of the hindlimbs, were consistent with a subcursorial locomotor habit, with a preferential “semi-improved” and quadruped posture. However, due to the generalist character inferred for P. chiniquensis – which permitted a wide range of feasible postures – an ambush hunting strategy, with a biped and totally improved posture, may be admitted, possibly conferring some advantages, such as higher speeds, if compared to usual postures.

Um esqueleto parcialmente completo e semi-articulado de um rauissuquídeo, proveniente de níveis pertencentes à Cenozona de Therapsida (Mesotriássico) da Formação Santa Maria, foi coletado em 2003, no município de Dona Francisca, RS, Brasil. Neste espécime, os ossos do crânio e mandíbula estavam quase todos desarticulados e puderam ser retirados isoladamente da rocha. Tal forma de preservação possivelmente seria uma evidência de que os ossos do crânio deste animal poderiam apresentar mobilidades entre si. Para verificar tal hipótese, foram utilizadas como metodologias tomografias computadorizadas e programas específicos de manipulação digital em três dimensões com o objetivo de criar modelos animados que permitissem o estudo das possibilidades de movimento entre os ossos do crânio deste exemplar de maneira isolada e integrada em todo o crânio. Como resultado, vídeos animados, simulando as possibilidades de movimento entre os ossos do crânio foram gerados e, para cada elemento craniano tomografado, um arquivo em 3D contendo o modelo de sua superfície foi elaborado. Este material foi preparado para publicação em uma revista eletrônica (i.e. Palaeontologia electronica) que permite a exposição e divulgação de conteúdos digitais animados. Os resultados apresentados neste estudo indicaram um número maior de evidências que favorecem um tipo passivo de cinetismo craniano, sendo elas: - movimentos restritos, porém possíveis, entre vários ossos intracranianos; e, - a presença de contatos frouxamente ligados, incapazes de realizar movimentos amplos ou incapazes de realizar qualquer tipo de movimento quando o crânio como um todo é considerado. Apesar disso, mais estudos referentes à reconstrução de tecidos moles e ao desenvolvimento ontogenético de rauissuquídeos são necessários para se testar ou falsear a hipótese de um possível modelo de cinetismo craniano ativo. Partially disarticulated skull bones of an unidentified rauisuchid were found in Dona Francisca, south Brazil (Therapsid Cenozone, Mesotriassic). The skull bones and mandible of this specimen were almost all disarticulated and could be isolated from the rock separately. This peculiar type of preservation may probably be an evidence of possible intracranial mobility. To verify this hypothesis, computer tomography (CT) scan and specific 3D software methodologies were used to analyse suture morphology and articulation areas of each individual pair of adjacent bones and for an integrated mechanical model, which considered all bones that comprises the skull of the studied specimen. As results, illustrative 3D animations for each discussed videos that simulated possible mobility between skull bones were generated and, a 3D surface model of each CT scanned skull element. Illustrative 3D animations for each discussed movements were created and 3D surface model files for each CT scanned skull element are presented. This material was prepared to be submitted in an electronic journal (i.e. Palaeontologia Electronica), where animated digital documents could be published. As results, this study presented more evidences in favour of passive cranial kinesis, which includes: -restricted, but possible mobility between a considerable number of bones; and, -presence of loosely contacts that would not be able to do extensive movements or would present no mobility at all when the integrated model is considered. Though, more studies on soft tissue reconstructions and ontogenetic development of rauisuchids are needed to testify or falsify the hypothesis of an active cranial kinesis.