Lanthosuchus
Lanthosuchus was the first member of a group of ancient reptiles that was named the Lanthosuchidae after that first specimen. There are very few remains of these animals. These creatures were around well before the time of the dinosaurs. They first cropped up in the Early Permian period, about 260 million years ago. The relationships of this group to the other anapsid reptiles is not entirely clear, as there is some evidence that this group is a sub-group to the Hallucicrania, and thus distantly related to turtles. They may also be an entirely separate branch on the anapsid family tree. The most notable feature of this group is the extremely flattened head. The eyes holes in the skull suggest that the eyes were either only looking upward (version A) or were protruding above the head (version B). The skull shown above is roughly 20 centimeters across the base. From this it is reasonable to estimate that the whole animal would have been about 1 meter from end to end. That's assuming that the body was in reasonable proportion to the head as shown in the drawings.
Obviously of the two options the second one with the protruding eyes is the most sensible. To me this suggests an ambush lifestyle, possibly hiding in the mud or sand in a river bed and snapping up passing fish or other creatures. Unfortunately the fossil remains recovered so far do not give any clues as to their way of life.
The flounder shown to the right seems to me to be similar in appearance though in its case the entire body is flattened. Flounders also lie of the bottom of the water covered with sand or silt. Other animals that use the bottom of the ocean or river to conceal themselves are rays. By flapping their wings they are able to create a cloud of sediment that covers them when they settle. It's not too hard to imagine Lanthosuchus scratching up clouds of mud or sand and then settling down to wait for a meal to come swimming by.
Lifestyle Drives Body ShapeThere is little doubt that this animal was a highly specialized one, adapting to a specific environment. Since Lanthosuchus has no surviving descendants, this was clearly not the way forward. What this creature does show us is the consistent pressure that the environment has on the body of a species. Several ancient amphibians had very similar body shapes and these are known to have been aquatic. The example below is called Pelorocephalus. Note the similarity in head shape. Combine this with the behavior of rays and flat fish and we can see that being an aquatic ambush predator is most successful with a flattened body and / or head. Yet another classic example of convergent evolution.
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