| Dakosaurus | |
|---|---|
 | |
| D. maximus neotype SMNS 8203, Staatliches Museum für Naturkunde Stuttgart | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Archosauria |
| Clade: | Pseudosuchia |
| Clade: | Crocodylomorpha |
| Suborder: | †Thalattosuchia |
| Family: | †Metriorhynchidae |
| Tribe: | †Geosaurini |
| Clade: | †Dakosaurina |
| Genus: | †Dakosaurus von Quenstedt, 1856[1] |
| Type species | |
| †Geosaurus maximus Plieninger, 1846 | |
| Species | |
| Synonyms | |
Dakosaurus is anextinctgenus ofcrocodylomorph within thefamilyMetriorhynchidae that lived during theLate Jurassic andEarly Cretaceous. It was large, with teeth that wereserrated and compressed lateromedially (flattened from side to side). The genus was established byFriedrich August von Quenstedt in 1856 for an isolated tooth namedGeosaurus maximus byTheodor Plieninger in 1846.[2]Dakosaurus was acarnivore that spent much, if not all, of 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 toDakosaurus, whether it gave birth to live young at sea likedolphins andichthyosaurs or came ashore liketurtles is not known yet. The nameDakosaurus means "biter lizard", and is derived from theGreekdakos ("biter") andσαῦρος -sauros ("lizard").
Thetype speciesDakosaurus maximus, meaning "greatest biter lizard", is known fromfossil discoveries in Western Europe (England, France, Switzerland and Germany) of the Late Jurassic (LateKimmeridgian-EarlyTithonian).[7][8]
When isolatedDakosaurus teeth were first discovered inGermany, they were mistaken for belonging to thetheropoddinosaurMegalosaurus.[9] The type speciesD. maximus was originally named as a species ofGeosaurus in 1846 byTheodor Plieninger, creating the speciesG. maximus.[2]
In 1856 von Quenstedt made Plieninger'sGeosaurus maximus teeth a new genus with the nameDakosaurus. He explained the etymology as Greekdakos "Biss" [bite] in 1858 in German, adding "denn wenige kommen seinem furchtbaren Gebiss gleich" [for few can match its terrible set of teeth].[10] He gave the meaning of Greekdakos more correctly as "Beisser" [biter] in another description in 1859 in which he classifiedDakosaurus as a dinosaur.[11]
Named in 1871 byEmanuel Bunzel,[6] the remains attributed toMegalosaurus schnaitheimi (found inSchnaitheim,Germany) are now believed to have belonged toDakosaurus maximus as per Carranoet al. (2012).[12]
Fossil specimens referrable toDakosaurus are known from Late Jurassic deposits fromEngland,France,Switzerland,Germany,[7]Poland,[13]Russia,[14]Argentina,[3] andMexico.[15] Teeth referrable toDakosaurus are known from Europe from theOxfordian.[16][17]
Dacosaurus (Sauvage, 1873) is a misspelling ofDakosaurus, and thus a synonym.[4]
Dakosaurus andiniensis, meaning "biter lizard from the Andes", was first reported in 1985 from theNeuquén Basin, a very rich fossil bed in theVaca Muerta, Argentina. However, it was not until 1996 that the binomenDakosaurus andiniensis was erected.[3] Two later discovered skulls, the specimina MOZ 6146P and MOZ 6140P, have indicated thatD. 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 (LateTithonian-EarlyBerriasian).[18]
Dakosaurus nicaeensis, named in 1913 by Ambayrac, was mistakenly classified as amegalosaurid dinosaur; now it is assigned as the sole species in the genusAggiosaurus. Buffetaut[19] in 1982 demonstrated that it was in fact a metriorhynchid, closely related to, if not a member ofDakosaurus. As the type specimen is poorly preserved it is considerednomen dubium.
Incomplete skull specimens ofDakosaurus have been discovered in Kimmeridgian age rocks from Mexico; they have not yet been referred to a specific species ofDakosaurus.[15][20]
All currently known species would have been large, measuring approximately 4–5 m (13–16 ft) long.[21][22] Its body was streamlined for greater hydrodynamic efficiency, which along with its finned tail made it a more efficient swimmer than modern crocodilian species.[23]
Dakosaurus–when it contained the speciesD. andiniensis,D. maximus, andD. manselii–had long been consideredparaphyletic, that is, not consisting of a common ancestor and its descendants,[24][25][26][27] until a 2012 study movedD. manselii to the formerly invalid genusPlesiosuchus.[28]
| |||||||||||||||||||||||||||||||
The incomplete skull specimens from the Mexican species ofDakosaurus preserves the chamber in which the well-developedsalt glands (known fromGeosaurus[29] andMetriorhynchus[30]) would have been housed. Unfortunately, there was no preservational evidence of the glands themselves.[15]
Dakosaurus was the only marine crocodyliform to have evolved teeth that are both lateromedially compressed and serrated; not only that, but they were much larger than those of metriorhynchid genera.[18] These characteristics, along with their morphology, which fall within the 'Cut' guild of Massare (1987) - and are analogous to modernkiller whale teeth - indicate thatDakosaurus was anapex predator.[31]
The enlargedsupratemporal fenestrae ofDakosaurus skulls[8] would have anchored largeadductor muscles (jaw closing),[32] ensuring a powerful bite. As their skulls are triangular in shape, with deeply rooted, large, serrated teeth and a bulbous, deep, mandibular symphysis (likepliosaurs), dakosaurs would also have been able to twist feed (tear chunks of flesh off potential prey).[33] Thewear andspall patterns ofDakosaurus teeth suggest it cut large prey items apart into chunks it could swallow, further pointing to the genus being macroraptorial.[34]
Dakosaurus maximus is one of several species of metriorhynchids known from the Altmühltal Formation (Solnhofen limestone, early Tithonian) ofBavaria, Germany. Alongside three other metriorhynchid species, it has been hypothesised thatniche partitioning enabled several species of crocodyliforms to co-exist.Dakosaurus andGeosaurus 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 elegans andRhacheosaurus gracilis) and theteleosauridAeolodon would have fed mostly on fish.[35]
From the slightly olderNusplingen Limestone (late Kimmeridgian) of southern Germany, bothD. maximus andC. suevicus are contemporaneous. As with Solnhofen,Dakosaurus was the top predator, whileC. suevicus was a fish-eater.[36]
| ||||||||||||||||||||||
| ||||||||||||||||||||||
.jpg)
