Dakosaurus
Name:
Dakosaurus
(Tearing lizard, alt. Biter lizard).
Phonetic: Dack-oh-sore-us.
Named By: Friedrich August von Quenstedt - 1856.
Synonyms: Aggiosaurus, Dacosaurus,
Geosaurus maximus, Plesiosuchus, Steneosaurus mansellii.
Classification: Chordata, Reptilia, Diapsida,
Archosauromorpha, Thalattosuchia, Metriorhynchidae.
Species: D. maximus (type),
D.
andiniensis.
Diet: Carnivore.
Size: 4 to 5 meters long.
Known locations: Europe, North America, South
America, Russia.
Time period: Oxfordian of the Jurassic through to
the Berriasian of the Cretaceous.
Fossil representation: Numerous specimens.
The
deep skull of Dakosaurus has led to this marine
reptile being
nicknamed ‘Godzilla’ in the popular media. However unlike the
famous Japanese daikaiju, Dakosaurus was actually
a four to five
meter long crocodile
that was specially adapted for a life at sea.
It’s tall and deep skull meant that Dakosaurus was
actually quite
different from other metriorhynchid crocodiles, and had an even more
extreme body form adapted to a marine lifestyle. Whereas
Metriorhynchus
is now known to have had limbs more like legs rather
that ‘paddle-shaped’ flippers, Dakosaurus
took the transition to
aquatic life even further with developed flippers like other but
unrelated marine reptiles. Dakosaurus also had a
tail that terminated
in a fluke to provide extra propulsion through the water.
Whereas
the majority of marine crocodiles seem to have specialised in a
piscivorous fish eating lifestyle, Dakosaurus’s
skull and jaws
combined with the large serrated and laterally compressed teeth,
indicate that it was a predator of larger prey items. While this
prey may have included large fish, Dakosaurus may
have also gone
after other marine reptiles that would have required a stronger set of
jaws to deal with. While Dakosaurus was a
crocodile, it seems to
have lived a lifestyle that would become commonplace with the advent of
the mosasaurs during the Cretaceous.
Dakosaurus
appears to have been active in locations that also had other marine
crocodiles swimming in them, the most similar to Dakosaurus
being
Geosaurus.
Comparison between these two marine
crocodiles indicates
that while no salt gland has been found to be present, Dakosaurus
did
have a cavity in the location which is known to house salt glands in
other crocodiles. A salt gland in itself is an organ that extracts
excess sodium from the body which has been absorbed by exposure to
living in sea water, and can be found in a variety of animals
including other reptiles, birds and even fish. While the evidence
for a salt gland in Dakosaurus remains
circumstantial, it would be
unusual if Dakosaurus did not have one.
The
advanced marine adaptations of Dakosaurus have been
the subject of a
lot of debate about whether Dakosaurus, and also
other marine
crocodiles could give birth to live young at sea, or if they still
had to return to the land to lay eggs. Supporters of the live birth
theory point to the fact that no nest sites that can be attributed to
Dakosaurus have been found. However, just
because the nest sites
are not known does not mean that they did or do not exist. If
Dakosaurus nested, it may have used high tides to
help carry it
further up the beach so that it did not have to travel as far on its
flippers. If however the live birth theory proves to be correct,
then it would be a further testament to the remarkable adaptability
that various crocodile species have shown.
Further reading
- Die Meer-Krocodilier (Thalattosuchia) des oberen Jura unter
specieller Ber�cksichtigung von Dacosaurus und Geosaurus
-
Paleontographica 49: 1-72 - e. Fraas - 1902.
- [Marine crocodiles in the Mesozoic of Povolzh'e] - Priroda 1981: 103
- V. G. Ochev - 1981.
- An unusual marine crocodyliform from the Jurassic-Cretaceous boundary
of Patagonia - Science 311: 70-73 - Z. Gasparini, D. Pol & L.
A. Spalletti - 2006.
- First occurrence of the genus Dakosaurus
(Crocodyliformes,
Thalattosuchia) in the Late Jurassic of Mexico - Bulletin de la Societe
Geologique de France 178 (5): 391-397 - M. -C. Buchy , W. Stinnesbeck ,
E. Frey & A. H. G. Gonzalez - 2007.
- The evolution and interrelationships of Metriorhynchidae
(Crocodyliformes, Thalattosuchia). - Journal of Vertebrate Paleontology
27 (3): 170A - M. T. Young - 2007.
- New occurrence of the genus Dakosaurus (Reptilia,
Thalattosuchia) in
the Upper Jurassic of north-eastern Mexico with comments upon skull
architecture of Dakosaurus and Geosaurus.
- Neues Jahrbuch f�r Geologie
und Pal�ontologie, Abhandlungen 249 (1): 1-8. - M. -C. Buchy - 2008.
- 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 -
Mark T. Young & Marco Brandalise de Andrade - 2009.
- The oldest known metriorhynchid crocodylian from the Middle Jurassic
of North-eastern Italy - Neptunidraco ammoniticus gen. et sp. nov".
Gondwana Research 19 (2): 550–565 - Andrea Cau & Federico Fanti
- 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 - Mark T.
Young, Mark A. Bell, Marco Brandalise de Andrade & Stephen L.
Brusatte - 2011.
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