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Saurosuchus

Saurosuchus was a 20-foot pseudosuchian (a distant ancestor of crocodiles) which lived in Argentina during the middle Triassic Period about 230 million years ago. It was the largest carnivorous animal in its environment in terms of both length and weight, and it was likely the top predator within the Ischigualasto Formation, but that was before the dinosaurs arrived. Saurosuchus lived side-by-side with the meat-eating dinosaurs, but eventually carnivorous dinosaurs like Herrerasaurus, which were faster, more agile, and possibly more intelligent, drove these creatures to extinction.

Skull of Saurosuchus. Drawn in Crayola black marker. © Jason R. Abdale. March 11, 2021.

 

Fruitachampsa, the crocodile-bear-cat of the Morrison Formation

Meet the Jurassic Period’s analog of the common house cat. This is Fruitachampsa callisoni, a prehistoric reptile which inhabited western North America during the late Jurassic Period. However, this was not a dinosaur. In fact, Fruitachampsa was a distant relative of crocodiles.

The fossils of this animal were discovered by James M. Clark and George Callison near Fruita, Colorado during the middle and late 1970s within the rocks of the Morrison Formation dated to about 150 million years ago (MYA). By the late 1980s, this creature was unofficially known by the name “Fruitachampsa”, but since it had not been officially named or described in any scientific research article, this name could not yet be used. It wasn’t until 2011 that the animal was officially classified under the name Fruitachampsa callisoni, “George Callison’s Crocodile from Fruita”.

Clark, James M. “A new shartegosuchid crocodyliform from the Upper Jurassic Morrison Formation of western Colorado”. Zoological Journal of the Linnean Society, volume 163, issue supplement 1 (December 2011): S152–S172.

Fruitachampsa belonged to a group of reptiles which were related to crocodiles known as the “shartegosuchids”. These reptiles are known from the late Jurassic and early Cretaceous Periods, and all known specimens have been found in North America, Europe, and Asia. Shartegosuchids have distinctive skull features, including:

  1. A lack of anteorbital fenestrae (the hole between the nostril and the eye socket) in the upper jaw.
  2. Within the upper jaw’s palate, the chonae (the holes that connect the nostril to the inside of the mouth) are set within a deep depression in the center of the palate.
  3. The palatal bones, which form most of the inside of the mouth of the upper jaw, are joined together medially.
  4. The teeth in the lower jaw never extend posteriorly past the mandibular fenestrae.
  5. The edges of the teeth in both the upper and lower jaws are ridged with serrations – quite unlike the smooth cone-shaped teeth that are often associated with crocodilians.

The shartegosuchids are visibly similar to earlier primitive crocodyliforms such as Protosuchus, and have even been ascribed to the same family as that genus. However, they appear to be slightly more advanced than Protosuchus and other members of Protosuchidae, and may represent the next evolutionary development of crocodilians.

Fruitachampsa measured three feet long, and its body was more-or-less about the same size as a cat. Like a cat, it also had large eyes, and was therefore possibly nocturnal, preying upon the small rodent-like mammals which inhabited the Morrison Formation.

Fruitachampsa also possessed unusually long legs in proportion with the rest of its body. However, like a crocodile, it walked in a “plantigrade” style, walking on the flats of its feet like a human or a bear, rather than walking “digitigrade”, on its toes, like a cat. So perhaps we should think of Fruitachampsa less like a cat and more like a pygmy-sized long-legged bear.

Fruitachampsa possessed a double-row of rectangular osteoderms which ran down the middle of its back, in which the row in front slightly overlapped the row behind, like roof shingles or a ancient Roman legionnaire’s body armor.

Fruitachampsa callisoni. © Jason R. Abdale. December 19, 2020.

Keep your pencils sharp, everybody.