Cricosaurus

Cricosaurus Temporal range: Late Jurassic-Early Cretaceous, 160–136 Ma PreЄ Є O S D C P T J K Pg N
C. suevicus skull
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Subclass:	Diapsida
Infraclass:	Archosauromorpha
(unranked):	Mesoeucrocodylia
Suborder:	Thalattosuchia
Family:	Metriorhynchidae
Genus:	Cricosaurus Wagner, 1858
Species
C. elegans (Wagner, 1852) (type) C. gracilis (Philips, 1871) C. macrospondylus (Koken, 1883) C. suevicus (Fraas, 1901) C. schroederi (Kuhn, 1936) C. araucanensis (Gasparini & Dellapé, 1976) C. vignaudi (Frey et al., 2002) C. saltillense (Buchy et al., 2006)
Synonyms
Enaliosuchus Koken, 1883 [1]

Cricosaurus is an extinct genus of marine crocodyliform belonging to the family Metriorhynchidae. The genus was established by Johann Andreas Wagner in 1858 for three skulls from the Tithonian (Late Jurassic) of Germany.^[2] The name Cricosaurus means "Ring lizard", and is derived from the Greek Cricos- ("ring") and σαῦρος -sauros ("lizard").

Fossil specimens referrable to Cricosaurus are known from Late Jurassic deposits in England, France, Switzerland, Germany,^[3] Argentina,^[4] Cuba,^[5] and Mexico.^[6]

History and classification

Historical reconstruction of C. suevicus by Williston, 1914

Cricosaurus was first named by Wagner in 1858,^[2] as a re-classification of a specimen he had previously described in 1852.^[7]

Several other species have since been named, including C. suevicus by Fraas in 1901 (originally as a species of Geosaurus.^[8] One former species, C. medius (named by Wagner in 1858) has since been reclassified as a junior synonym of Rhacheosaurus gracilis.^[9]

The original three skulls (all assigned to different species) were poorly known, and the genus had been considered a junior synonym of Metriorhynchus, Geosaurus or Dakosaurus by different palaeontologists in the past.^[3] Some phylogenetic analysis did not support the monophyly of Cricosaurus,^[10] However, a more comprehensive analysis in 2009 showed that the species contained in Cricosaurus were valid, and furthermore 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.^[9]

Cladogram after Cau & Fanti (2010).^[11]

Cricosaurus	C. sp. C. suevicus C. saltillense C. elegans C. vignaudi C. gracilis C. araucanensis C. schroederi C. macrospondylus

Paleobiology

Artist's impression of C. suevicus

All currently known species would have been three metres or less in length. When compared to living crocodilians, Cricosaurus can be considered moderate to small-sized. Its body was streamlined for greater hydrodynamic efficiency, which along with its finned tail made it a more efficient swimmer than modern crocodilian species.^[12]

Salt glands

Recent examination of the fossil specimens of Cricosaurus araucanensis have shown that both juveniles and adults of this species had well-developed salt glands. This means that it would have been able to "drink" salt-water from birth (necessary for a pelagic animal) and eat prey that have the same ionic concentration as the surrounding sea water (i.e. cephalopods) without dehydrating.^[13][14] Adult specimens of Metriorhynchus also have these well-developed salt glands.^[15]

Niche partitioning

Cricosaurus macrospondylus

Several species of metriorhynchids are known from the Mörnsheim Formation (Solnhofen limestone, early Tithonian) of Bavaria, Germany: Dakosaurus maximus, Geosaurus giganteus, Cricosaurus suevicus and Rhacheosaurus gracilis. It has been hypothesised that niche partitioning enabled several species of crocodyliforms to co-exist. The top predators of this Formation appear to be Dakosaurus and G. giganteus, which were large, short-snouted species with serrated teeth. The long-snouted Cricosaurus species would have feed 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.^[16]

From the slightly older Nusplingen Plattenkalk (late Kimmeridgian) of southern Germany, both C. suevicus and Dakosaurus maximus are contemporaneous. As with Solnhofen, C. suevicus feed upon fish, while D. maximus was the top predator.^[17]

References

1. ^ Koken E. 1883. Die Reptilien der norddeutschen unteren Kreide. Zeitschrift der deutschen Geologischen Gesellschaft 35: 735-827.
2. ^ ^{a b} Wagner A. 1858. Zur Kenntniss der Saurier aus den lithographischen Schiefern. Abhandlungen der Mathemat.-Physikalischen Classe der Königlich Bayerischen Akademie der Wissenschaften 8: 415-528.
3. ^ ^{a b} Steel R. 1973. Crocodylia. Handbuch der Paläoherpetologie, Teil 16. Stuttgart: Gustav Fischer Verlag,116 pp.
4. ^ Gasparini ZB, Dellapé D. 1976. Un nuevo cocodrilo marino (Thalattosuchia, Metriorhynchidae) de la Formación Vaca Muerta (Jurasico, Tithoniano) de la Provincia de Neuquén (República Argentina). Congreso Geológico Chileno 1: c1-c21.
5. ^ Gasparini ZB, Iturralde-Vinet M. 2001. Metriorhynchid crocodiles (Crocodyliformes) from the Oxfordian of Western cuba. Neues Jahrbuch für Geologie und Paläontologie, Monatshefte 9: 534–542.
6. ^ Frey, E., Buchy, M.-C., Stinnesbeck, W. & López-Oliva, J.G. 2002. Geosaurus vignaudi n. sp. (Crocodylia, Thalattosuchia), first evidence of metriorhynchid crocodilians in the Late Jurassic (Tithonian) of central-east Mexico (State of Puebla). Canadian Journal of Earth Sciences 39: 1467–1483.
7. ^ Wagner A. 1852. Neu-aufgefundene Saurier-Überreste aus dem lithographischen Schiefern und dem oberen Jurakalk. Abhandlungen der Mathemat.-Physikalischen Classe der Königlich Bayerischen Akademie der Wissenschaften 6: 661-710.
8. ^ Fraas E. 1901. Die Meerkrokodile (Thalattosuchia n. g.) eine neue Sauriergruppe der Juraformation. Jahreshefte des Vereins für vaterländische Naturkunde, Württemberg 57: 409-418.
9. ^ ^{a b} Young, M.T. and de Andrade, M.B. (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.
10. ^ Young MT. 2007. The evolution and interrelationships of Metriorhynchidae (Crocodyliformes, Thalattosuchia). Journal of Vertebrate Paleontology 27 (3): 170A.
11. ^ Andrea Cau; Federico Fanti (2010). "The oldest known metriorhynchid crocodylian from the Middle Jurassic of North-eastern Italy: Neptunidraco ammoniticus gen. et sp. nov.". Gondwana Research in press. doi:10.1016/j.gr.2010.07.007. 
12. ^ Massare JA. 1988. Swimming capabilities of Mesozoic marine reptiles; implications for method of predation. Paleobiology 14 (2):187-205.
13. ^ Fernández M, Gasparini Z. 2000. Salt glands in a Tithonian metriorhynchid crocodyliform and their physiological significance. Lethaia 33: 269-276.
14. ^ Fernández M, Gasparini Z. 2008. Salt glands in the Jurassic metriorhynchid Geosaurus: implications for the evolution of osmoregulation in Mesozoic crocodyliforms. Naturwissenschaften 95: 79-84.
15. ^ Gandola R, Buffetaut E, Monaghan N, Dyke G. 2006. Salt glands in the fossil crocodile Metriorhynchus. Journal of Vertebrate Paleontology 26 (4): 1009-1010.
16. ^ Andrade MB, Young MT. 2008. High diversity of thalattosuchian crocodylians and the niche partition in the Solnhofen Sea. The 56th Symposium of Vertebrate Palaeontology and Comparative Anatomy
17. ^ Dietl G, Dietl O, Schweigert G, Hugger R. 2000. Der Nusplinger Plattenkalk (Weißer Jura zeta) - Grabungskampagne 1999.