Mastodonsaurus
Name:
Mastodonsaurus
(Breast tooth lizard).
Phonetic: Mas-toe-don-sore-us.
Named By: G. F. Jaegar - 1828.
Synonyms: Batrachosaurus, Labyrinthodon,
Mastodonsaurus acuminatus, Mastodonsaurus conicus, Mastodonsaurus
maximus , Mastodonsaurus tantus, Salamandroides.
Additionally, Mastodonsaurus ventricosus is
conisderd to be a nomen nudum.
Classification: Chordata, Amphibia,
Temnospondyli, Stereospondyli, Capitosauria, Mastodonsauridae.
Species: M. giganteus, M. jaegeri,
M. torvus.
Diet: Carnivore/Piscivore.
Size: Total length between 4 to 6 meters
long, skull up to 1.25 meters long, some variation between
species.
Known locations: England - Bromsgrove Sandstone
Formation, Wales - Sully Beds Formation, Germany - Erfurt
Formation, and Russia - Bukobay Formation.
Time period: Anisian through to the Rhaetian of the
Triassic.
Fossil representation: Remains of multiple
individuals.
The
name Mastodonsaurus means ‘breast tooth
lizard’, and this came
about from the observation of G. F. Jaegar who was describing a
broken tooth. Later, when other teeth of Mastodonsaurus
were found
they were found to be no different from the teeth of most other
temnospondyls.
The
signature features of Mastodonsaurus are the two
teeth in the front of
the lower jaw that have enlarged to the point of becoming tusks.
These are so large that there are two openings in the upper jaw which
these tusks fit through when the mouth is closed. Without these
openings the mouth simply would not be able to close fully due to the
size of the tusks. These tusks may have been for prey capture,
allowing a Mastodonsaurus to get a grip upon
prey. However, other
temnospondyls seem to have managed just fine without these
specialisations, so they may have also served a display purpose that
allowed Mastodonsaurus to differentiate between
themselves and similar
temnospondyls.
Mastodonsaurus
seems to have been a genus that spent most if not indeed all of its
time in the water. The evidence for this is quite compelling, but
we’ll begin with noted observations of the body. The head of
Mastodonsaurus was so large that it took up almost a
quarter of the
total body length, something that would have been very cumbersome if
on land. The eyes are situated midway on top of the skull, which
meant that they were best placed for looking up at whatever may have
been swimming above them. Sensory sulci that formed a lateral line of
sensory organs were also present, and this would have allowed a
Mastodonsaurus to pick up upon changes in water
pressure caused by the
movement of other aquatic animals. Finally for the body, the limbs
were greatly reduced in size, and would have been incapable of
lifting the body clear off the ground if out of the water. The joints
of these limbs are also particularly weak, in turn suggesting limited
muscles.
Further
support for an entirely aquatic lifestyle comes from the discoveries of
several Mastodonsaurus that seem to have died
together after the body
of water that they were living in dried out. Had they been able to
walk about well on land, they should have at least wandered around
for a bit searching for another water source. Coprolites associated
with Mastodonsaurus are also mostly composed of
fish remains, a prey
source that would only be abundant within water.
With
all of these factors combined, it seems very likely that
Mastodonsaurus were restricted to a lifetime in the
water. The wide
distribution of the genus across Europe might be explained by
individuals using ancient river systems to get around, and perhaps
spreading into new areas when these rivers flooded, granting
temporary access to new locations, as well as possibly creating traps
as new bodies of water were isolated when the flood waters receded,
but were not replenished by subsequent floods before they dried
out. While the limbs were weak, they were likely plenty strong
enough for aquatic life where the weight of the body would have been
supported by the water. So it is more likely that the limbs were used
for locomotion along the bottom, pushing through dense aquatic
plants, to even steering by gentle paddling. Also, while fish
seem to have been the main prey source for Mastodonsaurus,
there are
bones from other temnospondyl amphibians that bear tooth marks
seemingly created by the teeth of creatures that had teeth similar to
Mastodonsaurus. With this in mind it is possible
that Mastodonsaurus
may have occasionally hunted other temnospondyl amphibians, or they
were quite aggressive in defending their territories against
competition from other species.
There
have been a great many species assigned to the Mastodonsaurus
genus
over the years, though at the time of writing only three are
considered to be valid. Some of the other former species are now
considered to be synonymous to these, while other species have been
assigned to different genera. As such, some fossils formerly
assigned to Mastodonsaurus have now been moved to Capitosaurus,
Cyclotosaurus, Eupelor, Heptasaurus,
Parotosuchus,
Plagiosternum and Stenotosaurus.
Further species such as M.
andriani, M. indicus, M.
laniarius, M. lavisi, M.
meyeri, M. pachygnathus and M.
silesiacus are considered to be
based upon remains that are so indeterminate that their placement
within the genus is highly questionable.
Further reading
- �ber die fossile Reptilien, welche in W�rtemberg aufgefunden
worden sind - G. F. Jaeger - 1828.
- Comparative osteology of Mastodonsaurus giganteus
(Jaeger,
1828) from the Middle Triassic (Lettenkeuper: Longobardian) of
Germany (Baden-W�rttemberg, Bayern, Th�ringen) - R. R.
Schoch - 1999.
- Revision of the type material and nomenclature of Mastodonsaurus
giganteus (Jaeger) (Temnospondyli) from the middle
Triassic of
Germany - Markus Moser & Rainer Schoch - 2007.
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