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 1.38 and 1.57 m (4.5 and 5.2 ft) long and weighing 10 kg (22 lb).[2][3]

Temporal range: Late Jurassic,
151 Ma
Rhacheosaurus gracilis FMNH.jpg
Fossil specimen at the Field Museum of Natural History
Scientific classification edit
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Clade: Pseudosuchia
Superorder: Crocodylomorpha
Suborder: Thalattosuchia
Family: Metriorhynchidae
Tribe: Rhacheosaurini
Genus: Rhacheosaurus
Meyer, 1831
R. gracilis
Binomial name
Rhacheosaurus gracilis
von Meyer, 1831

History and classificationEdit

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.[4] This analysis also resurrected the generic name Rhacheosaurus.

Niche partitioningEdit

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.[5]


  1. ^ Meyer, H von 1831. Neue fossile Reptilien aus der Ordung der Saurier Nova Acta Academiae Leopoldino-Carolinae Curios 15 (2): 173-184.
  2. ^ Young, M.T.; Bell, M.A.; de Andrade, M.B.; Brusatte, S.L. (2011). "Body size estimation and evolution in metriorhynchid crocodylomorphs: implications for species diversification and niche partitioning". Zoological Journal of the Linnean Society. 163 (4): 1199–1216. doi:10.1111/j.1096-3642.2011.00734.x.
  3. ^ Paul, Gregory S. (2022). The Princeton Field Guide to Mesozoic Sea Reptiles. Princeton University Press. p. 200. ISBN 9780691193809.
  4. ^ Young, M.T. and Andrade, M.B. de (2009). "What is Geosaurus? Redescription of Geosaurus giganteus (Thalattosuchia: Metriorhynchidae) from the Upper Jurassic of Bayern, Germany." Zoological Journal of the Linnean Society, 157: 551-585.
  5. ^ Andrade MB, Young MT. 2008. High diversity of thalattosuchian crocodylians and the niche partition in the Solnhofen Sea Archived 2011-06-03 at the Wayback Machine. The 56th Symposium of Vertebrate Palaeontology and Comparative Anatomy