Rhacheosaurus

Rhacheosaurus is an extinct genus of marine crocodyliform belonging to the family Metriorhynchidae. The genus was established by Christian Erich Hermann von Meyer in 1831 for skeletal remains from the Tithonian (Late Jurassic) of Germany.^[1] It was a relatively small reptile, measuring between 1.39 and 1.57 m (4.6 and 5.2 ft) long.^[2]

Rhacheosaurus Temporal range: Late Jurassic, 151 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Fossil specimen at the Field Museum of Natural History
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Clade:	Archosauria
Clade:	Pseudosuchia
Clade:	Crocodylomorpha
Suborder:	†Thalattosuchia
Family:	†Metriorhynchidae
Tribe:	†Rhacheosaurini
Genus:	†Rhacheosaurus Meyer, 1831
Species:	†R. gracilis
Binomial name
†Rhacheosaurus gracilis von Meyer, 1831

History and classification

Historical reconstruction by Williston, 1914

Referred specimen

A phylogenetic analysis in 2009 showed that several long-snouted species formerly classified in the related genera Geosaurus, Enaliosuchus, and Metriorhynchus were in fact more closely related to the original specimens of Cricosaurus, and thus were re-classified into this genus.^[3] This analysis also resurrected the generic name Rhacheosaurus.^[3]

Niche partitioning

Several species of metriorhynchids are known from the Mörnsheim Formation (Solnhofen limestone, early Tithonian) of Bavaria, Germany: Rhacheosaurus gracilis, Dakosaurus maximus, Geosaurus giganteus and Cricosaurus suevicus. It has been hypothesised that niche partitioning enabled several species of crocodyliforms to co-exist. The top predators of this Formation appear to be D. maximus and G. giganteus, which were large, short-snouted species with serrated teeth. The long-snouted C. suevicus and R. gracilis would have fed mostly on fish, although the more lightly built Rhacheosaurus may have specialised towards feeding on small prey. In addition to these four species of metriorhynchids, a moderate-sized species of Steneosaurus was also contemporaneous.^[4]