Ctenosauriscus

Abstract: Background Archosaurs (birds, crocodilians and their extinct relatives including dinosaurs) dominated Mesozoic continental ecosystems from the Late Triassic onwards, and still form a major component of modern ecosystems (>10,000 species). The earliest diverse archosaur faunal assemblages are known from the Middle Triassic (c. 244 Ma), implying that the archosaur radiation began in the Early Triassic (252.3–247.2 Ma). Understanding of this radiation is currently limited by the poor early fossil record of the group in terms of skeletal remains. Methodology/Principal Findings We redescribe the anatomy and stratigraphic position of the type specimen of Ctenosauriscus koeneni (Huene), a sail-backed reptile from the Early Triassic (late Olenekian) Solling Formation of northern Germany that potentially represents the oldest known archosaur. We critically discuss previous biomechanical work on the ‘sail’ of Ctenosauriscus, which is formed by a series of elongated neural spines. In addition, we describe Ctenosauriscus-like postcranial material from the earliest Middle Triassic (early Anisian) Rot Formation of Waldhaus, southwestern Germany. Finally, we review the spatial and temporal distribution of the earliest archosaur fossils and their implications for understanding the dynamics of the archosaur radiation. Conclusions/Significance Comprehensive numerical phylogenetic analyses demonstrate that both Ctenosauriscus and the Waldhaus taxon are members of a monophyletic grouping of poposauroid archosaurs, Ctenosauriscidae, characterised by greatly elongated neural spines in the posterior cervical to anterior caudal vertebrae. The earliest archosaurs, including Ctenosauriscus, appear in the body fossil record just prior to the Olenekian/Anisian boundary (c. 248 Ma), less than 5 million years after the Permian–Triassic mass extinction. These earliest archosaur assemblages are dominated by ctenosauriscids, which were broadly distributed across northern Pangea and which appear to have been the first global radiation of archosaurs.

Abstract: The Lifua Member of the Manda Beds of Tanzania (Middle Triassic: ?latest Anisian) has yielded an exceptionally important assemblage of early archosaurs, including numerous well-preserved specimens. However, the majority of this material has not been described formally, frustrating attempts to incorporate it into studies on early archosaur diversity and evolution. We describe an anterior dorsal vertebra from the Lifua Member as the holotype of a new taxon, Hypselorhachis mirabilis. Hypselorhachis is characterised by the possession of an elongate neural spine that is at least 5.5 times the height of the centrum, and can be diagnosed on the basis of a single autapomorphy relating to the morphology of the prezygapophysis. Hypselorhachis is similar to other early Middle Triassic archosaurs with elongate neural spines, including Arizonasaurus, Ctenosauriscus, and Lotosaurus. It is possible that these taxa form a clade, Ctenosauriscidae, but further anatomical and phylogenetic work is required before th...

Abstract: In 1970, A new Thecodont, Lotosaurus (new genus and new species) was dis-covered in Middle Triassic Batung formation from sangzhi counfy, westcrn Hunan.It has extremely high dorsal neural spines. The shape of each spine is something likea narrow plate. There is no teeth on both upper and lower jaws. The snout isbeak-like. The ungual phalanges are flattened dorso-ventrally. Specimens with Lo-tosaurus-like neural spines have been found in various parts of northern and southerncontinents. Because the material is too scanty, their systematic position is difficultto determine. They had been assigned to Pelycosauria, Coelurosauria, Carnosauria,Prosauropoda or even to Amphibia. Among them Ctenosauriscus rugosus and Ctenos-pondylus casei were supposed to be the earliest archosaurs, and Ctenosauriscus koemoni, Hypselorachis mirabilis and Spondglosoma absconditum are closely related toLotosaurus. Their geographical and stratigraphcal distribution would probably pro-vide fossil evidence for the correlation of the continental and marine Middle Triassicdeposits of northern and southern hemispheres.