No abstract

Tanystropheus represents one of the most characteristic genera of Triassic reptiles and is typified by easily recognizable, hyperelongate cervical vertebrae. First described in 1852, isolated cervical vertebrae and other remains have been referred to the genus and various species have been erected and rejected based on this material. This has resulted in a complicated and convoluted taxonomic history of the genus and confusion as to the validity of species and the referral of specimens. With the exception of the well-represented T. longobardicus, the five other species of Tanystropheus are known from isolated elements or a single, partial specimen. Here, we provide a complete overview of the taxonomic history and a revision of the genus based on first hand observations of the type material of most of the species. From this, we conclude that T. conspicuus and T. haasi should be considered nomina dubia and that T. meridensis constitutes a junior synonym to T. longobardicus. Furthermore, T. longobardicus can be subdivided into two discrete morphotypes that might represent separate species. However, a more detailed study is required to test this hypothesis. Finally, T. fossai is considered distinctly different from the other Tanystropheus taxa and is therefore referred to a separate genus, Sclerostropheus.

the genus Macrocnemus is a member of the Tanystropheidae, a clade of non-archosauriform archosauromorphs well known for their very characteristic, elongated cervical vertebrae. Articulated specimens are known from the Middle Triassic of Alpine Europe and China. Although multiple articulated specimens are known, description of the cranial morphology has proven challenging due to the crushed preservation of the specimens. Here we use synchrotron micro computed tomography to analyse the cranial morphology of a specimen of the type species Macrocnemus bassanii from the Besano Formation of Monte San Giorgio, Ticino, Switzerland. The skull is virtually complete and we identify and describe the braincase and palatal elements as well the atlas-axis complex for the first time. Moreover, we add to the knowledge of the morphology of the skull roof, rostrum and hemimandible, and reconstruct the cranium of M. bassanii in 3D using the rendered models of the elements. The circumorbital bones were found to be similar in morphology to those of the archosauromorphs Prolacerta broomi and Protorosaurus speneri. In addition, we confirm the palatine, vomer and pterygoid to be tooth-bearing palatal bones, but also observed heterodonty on the pterygoid and the palatine. The genus Macrocnemus was described in the early twentieth century by Baron von Nopcsa based on a fragmentary specimen from Monte San Giorgio 1,2. After subsequent expeditions to the Besano Formation, which crops out in the Monte San Giorgio area, resulted in the discovery of additional specimens, the taxon was more properly described 3. Unfortunately, the holotype, stored in Milan, has since been lost as it was destroyed during the Second World War 4. The phylogenetic affinities of Macrocnemus were initially unclear. Early researchers observed similarities in the shape of the cervical vertebrae with contemporaneous taxa and erected the taxon Protorosauria 5,6. Notable members of this formerly recognised 'superorder' were Tanystropheus, Protorosaurus, Macrocnemus and Prolacerta, and all these taxa have elongated cervical vertebrae. The elongation of the cervical vertebrae is expressed most extremely in the genus Tanystropheus, of which the neck is three times the length of its trunk 7. Researchers were unsure whether to place the clade closer to the Lepidosauria or to the Archosauromorpha (e.g. 7,8). Currently, the members of the Protorosauria are all considered non-archosauriform archosauromorphs (e.g. 9-11). However, the clade itself has been observed to be paraphyletic or even polyphyletic in recent phylogenetic analyses 9 and references therein. Nonetheless, the recent analyses noted above have all recovered a monophyletic Tanystropheidae at the base of Archosauromorpha that includes Macrocnemus as well as Tanystropheus, Amotosaurus, Langobardisaurus, and Tanytrachelos, with Jesairosaurus often recovered as sister taxon to the clade.

Crocodylomorpha is the stem-lineage of modern crocodylians and the only pseudosuchian (i.e. crocodylian-line archosaurs) clade that survived the Triassic–Jurassic mass extinction event. Its earliest members, the non-crocodyliform crocodylomorphs, also known as ‘sphenosuchians’, were terrestrial and mostly small-bodied (<2 m long), although some large-bodied forms are known. Saltoposuchus connectens is one of the first described crocodylomorph species but it remains poorly studied, in part due to its contentious taxonomy. Here, all referred Saltoposuchus specimens are described in detail for the first time and its taxonomy is revised, with additional taxonomic implications for the British crocodylomorph Terrestrisuchus gracilis and the coelophysoid theropod Procompsognathus triassicus. Saltoposuchus connectens is clearly distinguished from Terrestrisuchus gracilis based on both cranial and postcranial features. The phylogenetic analysis finds that Saltoposuchus connectens, Terrestrisuchus gracilis, and Litargosuchus leptorhynchus form a clade of gracile, long-legged crocodylomorphs, identified as Saltoposuchidae Crush 1984. A histological section of a femur reveals highly vascularized fibrolamellar tissue in the second-largest specimen of Saltoposuchus connectens (SMNS 12596), indicating sustained high growth rates. A similar pattern was previously observed in Terrestrisuchus sp., contrasting with slower growth rates in the crocodylomorph Hesperosuchus agilis. These findings suggest that saltoposuchids had a high resting metabolic rate and active lifestyle.