Name:
Temnodontosaurus
(Cutting-toothed lizard).
Phonetic: Tem-noe-don-toe-sore-us.
Named By: Richard Lydekker - 1889.
Classification: Chordata, Reptilia, Diapsida,
Ichthyopterygia, Ichthyosauria, Temnodontosauridae.
Species: T. platyodon (type),
T. acutirostris, T. azerguensis, T. crassimanus, T.
eurycephalus, T. nuertingensis, T. trigonodon.
Diet: Cephalopods like ammonites.
Size: Up to 12 meters long.
Known locations: Europe including British Isles and
Germany.
Time period: Hettangian through to Toarcian of the
Jurassic.
Fossil representation: Several specimens.
Temnodontosaurus
is one of the oldest and largest ichthyosaurs
known to science, and
while there are a few species associated with the genus, the most
obvious differences between these are the size and proportions of the
jaws. Temnodontosaurus fossils have been so well
preserved that they
reveal stomach contents of ammonites and cephalopods like squid.
Juvenile specimens have also been reported inside Temnodontosaurus
remains, but in a position that suggests they were waiting to be born
rather than being digested. Live birth in ichthyosaurs like
Temnodontosaurus has long been suspected as their
fusiform bodies that
are so much like fish would make it impossible for them to climb onto
land.Study of other genera such as Ophthalmosaurus
amongst others have
helped to confirm the theory of live birth in ichthyosaurs. Like most
large ichthyosaurs, Temnodontosaurus
is thought to
have been a marine reptile of deep water, mostly rising to the
surface just to breathe in fresh air.
Temnodontosaurus
had large eyes that were roughly twenty centimetres across. These
large eyes would have enabled Temnodontosaurus to
see better when in
deep water where most of the above sunlight could not penetrate. The
large eyes providing a greater catch area for the little available
light would allow Temnodontosaurus to distinguish
ammonite forms
against the dim oceanic backdrop. Aside from ammonites found inside
Temnodontosaurus fossils, further support for this
hunting behaviour
comes from study of the teeth which reveals that they had robust roots
so that they could withstand the stresses of cracking shells without
breaking off.
Ammonites
would have been a plentiful food supply back in the Jurassic oceans,
and one that could not have required a great amount of energy
expenditure to catch. This suited the large body of Temnodontosaurus
as it would require large amounts of a stable food supply to keep
going. It is hard to say how the large size came about however but a
larger body can carry more oxygen for Temnodontosaurus
to stay hunting
down in the depths for longer. It’s possible that the earlier
ancestors of Temnodontosaurus came across the
plentiful supply of deep
water cephalopods and grew larger to take better advantage of it.
However this greater size also brought a greater reliance upon them,
a specialisation that could bring the end of the genus with the
disappearance of the prey.
Further reading
- A revision of the longipinnate ichthyosaurs of the Lower Jurassic of
England, with descriptions of two new species (Reptilia: Ichthyosauria)
- C. McGowan - 1974.
- Temnodontosaurus risor is a Juvenile of T.
platyodon (Reptilia:
Ichthyosauria) - C McGowan - 1995.
- A longirostrine Temnodontosaurus (Ichthyosauria)
with comments on
Early Jurassic ichthyosaur niche partitioning and disparity - Jeremy E.
Martin, Valentin Fischer, Peggy Vincent & Guillaume Suan - 2010.
- First temnodontosaurid (Ichthyosauria, Parvipelvia) from the Lower
Jurassic of the Atacama Desert, northern Chile. - Journal of South
American Earth Sciences. - R. A. Otero & P. 2020 - 2020.
- A revision of Temnodontosaurus crassimanus (Reptilia: Ichthyosauria)
from the Lower Jurassic (Toarcian) of Whitby, Yorkshire, UK. -
Historical Biology. - E. J. Swaby & D. R. Lomax - 2020.