Dakosaurus

Dakosaurus is an extinct genus of crocodylomorph within the family Metriorhynchidae that lived during the Late Jurassic and Early Cretaceous. It was large, with teeth that were serrated and compressed lateromedially (flattened from side to side). The genus was established by Friedrich August von Quenstedt in 1856 for an isolated tooth named "Geosaurus maximus" by Theodor Plieninger in 1846. "Dakosaurus" was a carnivore that spent much, if not all, its life out at sea. The extent of its adaptation to a marine lifestyle means that it is most likely that it mated at sea, but since no eggs or nests have been discovered that have been referred to "Dakosaurus", whether it gave birth to live young at sea like dolphins and ichthyosaurs or came ashore like turtles is not known. The name "Dakosaurus" means "biter lizard", and is derived from the Greek ' ("biter") and -' ("lizard").
Discovery and species.
 
When isolated "Dakosaurus" teeth were first discovered in Germany, they were mistaken for belonging to the theropod dinosaur "Megalosaurus". In 1856 von Quenstedt made Plieninger's "Geosaurus maximus" teeth a new genus with the name "Dakosaurus". He explained the etymology as Greek "dakos" "Biss" [bite] in 1858 in German, adding "denn wenige kommen seinem furchtbaren Gebiss gleich" [for few can match its terrible set of teeth]. He gave the meaning of Greek "dakos" more correctly as "Beisser" [biter] in another description in 1859 in which he classified "Dakosaurus" as a dinosaur.
Fossil specimens referrable to "Dakosaurus" are known from Late Jurassic deposits from England, France, Switzerland, Germany, Poland, Russia, Argentina, and Mexico. Teeth referrable to "Dakosaurus" are known from Europe from the Oxfordian.
Valid species.
The type species "Dakosaurus maximus", meaning "greatest biter lizard", is known from fossil discoveries in Western Europe (England, France, Switzerland and Germany) of the Late Jurassic (Late Kimmeridgian-Early Tithonian).
"Dakosaurus andiniensis", meaning "biter lizard from the Andes", was first discovered in 1987 in the Neuquén Basin, a very rich fossil bed in the Vaca Muerta, Argentina. However, it was not until 1996 that the binomen "Dakosaurus andiniensis" was erected. Two recently discovered skulls have indicated that "D. andiniensis" is unique among the metriorhynchids (the family of stem-crocodilians most specialised for marine life) with its short, tall snout, which lent it the popular nickname "Godzilla" in press reports about its description. This species has a fossil range from the late Jurassic to early Cretaceous (Late Tithonian-Early Berriasian).
"Dakosaurus nicaeensis", named in 1913 by Ambayrac, was mistakenly classified as a megalosaurid dinosaur; now it is assigned as the sole species in the genus "Aggiosaurus". Buffetaut in 1982 demonstrated that it was in fact a metriorhynchid, closely related to, if not a member of "Dakosaurus". As the type specimen is poorly preserved it is considered "nomen dubium".
Unnamed species.
Incomplete skull specimens of "Dakosaurus" have been discovered in Kimmeridgian age rocks from Mexico.
Synonyms.
The type species "D. maximus" was originally named as a species of "Geosaurus" in 1846 by Theodor Plieninger, creating the species "G. maximus".
Named in 1871 by Emanuel Bunzel, the remains attributed to "Megalosaurus schnaitheimi" (found in Schnaitheim, Germany) are now believed to have belonged to "Dakosaurus maximus".
Taxonomy and phylogeny.
 
Dacosaurus is a misspelling of "Dakosaurus", and thus a synonym.
"Dakosaurus"–when it contained the species "D. andiniensis", "D. maximus", and "D. manselii"–had long been considered paraphyletic, that is, not consisting of a common ancestor and its descendants, until a 2012 study moved "D. manselii" to the formerly invalid genus "Plesiosuchus".
Palaeobiology.
Morphology.
All currently known species would have been approximately 4 to 5 metres in length, which when compared to living crocodilians, "Dakosaurus" can be considered large-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.
Salt glands.
The incomplete skull specimens from the Mexican species of "Dakosaurus" preserves the chamber in which the well-developed salt glands (known from "Geosaurus" and "Metriorhynchus") would have been housed. Unfortunately, there was no preservational evidence of the glands themselves.
Niche partitioning.
"Dakosaurus maximus" is one of several species of metriorhynchids known from the Mörnsheim Formation (Solnhofen limestone, early Tithonian) of Bavaria, Germany. Alongside three other metriorhynchid species, it has been hypothesised that niche partitioning enabled several species of crocodyliforms to co-exist. "Dakosaurus" and "Geosaurus giganteus" would have been top predators of this Formation, both of which were large, short-snouted species with serrated teeth. The remaining two species ("Cricosaurus suevicus" and "Rhacheosaurus gracilis") and the teleosaurid "Steneosaurus" would have fed mostly on fish.
From the slightly older Nusplingen Plattenkalk (late Kimmeridgian) of southern Germany, both "D. maximus" and "C. suevicus" are contemporaneous. As with Solnhofen, "Dakosaurus" was the top predator, while "C. suevicus" was a fish-eater.
Diet.
"Dakosaurus" was the only marine crocodyliform to have evolved teeth both lateromedially compressed and serrated; not only that, but they were much larger than those of metriorhynchid genera. These characteristics, along with their morphology falling into the 'Cut' guild of Massare (1987) - which are analogous to modern killer whale teeth - are indicative of "Dakosaurus" being an apex predator.
The enlarged supratemporal fenestrae of "Dakosaurus" skulls would have anchored large adductor muscles (jaw closing), ensuring a powerful bite. As their skulls are triangular in shape, with deeply rooted large, serrated teeth and a bulbous, deep mandibular symphysis (like pliosaurs), dakosaurs would also have been able to twist feed (tear chunks of flesh off potential prey).