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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