Crassigyrinus
Name: Crassigyrinus
(Thick frog).
Phonetic: Crass-i-ji-rin-us.
Named By: Watson - 1929.
Classification: Chordata, Amphibia,
Labyrinthodontia, Ichthyostegalia, Crassigyrinidae.
Species: C. scoticus (type).
Type: Carnivore.
Size: 2 meters long.
Known locations: Scotland.
Time period: Visean of the Carboniferous.
Fossil representation: Several incomplete
specimens, three skulls.
An
interesting specimen of an early amphibian as it appears to have
completely abandoned terrestrial life in favour of an aquatic
lifestyle. Its limbs, especially those at the front, were greatly
reduced in size and would have been no use for land locomotion. They
would have still served as rudders and may have been used for
pushing through dense undergrowth of aquatic plants. It is possible
they may also have still been used for mating, allowing a male to
hold onto a female during the spawning process, the same way as many
modern amphibians do today. Further, the pelvis did not have a
solid connection to the spine as can be found in terrestrial
vertebrates.
Analysis
of the skull reveals
a predatory lifestyle. The jaws featured two rows of teeth,
including two elongated fangs, perfect for biting into fish. The
jaws could also open very wide and appear to have had the supporting
muscle structure to inflict very powerful bites, meaning that once
Crassigyrinus was clamped on, there was no
escape. Further, the
snout of the skull had several ridges to it suggesting re-enforcement
to cope with the stress of a high bite force. Its plausible that
Crassigyrinus needed these adaptations for coping
with prey that was
also powerful, hinting at a predatory specialisation. The
eyes also appear to be
enlarged, an adaptation for low ambient light, suggesting either a
nocturnal lifestyle or deep water hunting.
The
tail is not well known as
it is often not preserved very well. Given the size of the small
limbs, it may have been large to compensate for them, and from what
tail fragments that have been recovered, may have been flattened
laterally. Such an adaptation would have provided stable locomotion
in the water, as well as sudden bursts of speed.
Crassigyrinus
may have
favoured the ambush predator approach, instead of just cruising
around looking for a snack. A modern day comparison could be made
with a freshwater Pike. A Pike has a very stunted tail compared to
other fish, but it will often lurk amongst the reeds waiting for prey
items to swim close enough to be within striking distance. Once close
enough it lines itself up and uses it short but powerful tail to
produce a sudden burst of speed at its target. Its wide mouth filled
with teeth means that whatever is in front has little chance of getting
away, possibly not unlike Crassigyrinus.
Further reading
- On Crassigyrinus scoticus Watson, a primitive
amphibian from the
Lower Carboniferous of Scotland. - Palaeontology 16: 179-193. - A. L.
Panchen - 1973.
- On the amphibian Crassigyrinus scoticus Watson
from the Carboniferous
of Scotland. - Philosophical Transactions of the Royal Society of
London B 309, 505-568. - A. L. Panchen - 1985.
- The Scottish Carboniferous tetrapod Crassigyrinus scoticus
(Lydekker)
- cranial anatomy and relationships. - Transactions of the Royal
Society of Edinburgh: Earth Sciences. 88, 127-142. - J. A. Clack -
1998.
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