Thursday, 19 December 2019

SARCOSUCHUS IMPERATOR

Sarcosuchus is an extinct genus of crocodyliform and distant relative of living crocodylians that lived ~129-112 million years ago. Fossil remains date from the Lower Cretaceous of what is now Africa and South America.

Strictly speaking, Sarcosuchus was not a crocodile as we know them today, but a kind of pre-crocodile. These early croc-types were Crocodylomorphs.

This crocodylian lineage (clade Pseudosuchia, formerly Crurotarsi) was a very diverse and adaptive group of reptiles. We used to lump all known living and extinct crocodiles indiscriminately into the order Crocodilia. Sometime in the late 1980s, we finally moved all living species into the order Crocodilia, segregating closely related extinct relatives such as Mekosuchus. Our true "modern" crocodiles, now all safely ensconced in the order Crocodilia without their ancient ancestors, arrived millions of years after the first crocodylomorphs, with the first members of the modern species arriving on the scene in the Upper Cretaceous.

The Crocodylomorpha were a very ancient group of animals, at least as old as the dinosaurs, who evolved into a very diverse spectrum of weird and wonderful forms you might not recognize as croc-like. During the Jurassic and the Cretaceous, marine Crocodylomorphs in the family Metriorhynchidae, such as Metriorhynchus, evolved forelimbs that were paddle-like and had a tail similar to modern fish. Dakosaurus andiniensis, a species closely related to Metriorhynchus, had a skull that was adapted to feast upon large marine reptiles. We see several (unexpected) herbivorous terrestrial species during the Cretaceous, such as the tiny and adorable Simosuchus clarki and Chimaerasuchus paradoxus, both roughly the size of a dog. During the Cenozoic, a number of lineages left their ancient river homes and became wholly terrestrial predators.

Sarcosuchus was one of the largest early crocodile-like reptiles, reaching up to 9.5 m in body length and weighing up to 8 to 10 tons. He was almost twice as long as our modern saltwater crocodiles, so one big croc! These big beasts lived and hunted in ancient rivers, grabbing and crushing prey that came too close to the water.

The first remains were discovered during field expeditions in the Sahara led by French paleontologist, Albert-Félix de Lapparent, from 1946 to 1959. Remains were found of skull fragments, vertebrae, teeth, and scutes.

In 1964, an almost complete skull was found in Niger by the French CEA, but it was not until 1997 and 2000 that most of its anatomy became known to science when an expedition led by the American paleontologist Paul Sereno discovered six new specimens, including one with about half the skeleton intact and most of the spine.

A common method to estimate the size of crocodiles and crocodile-like reptiles is the use of the length of the skull measured in the midline from the tip of the snout to the back of the skull table since in living crocodilians there is a strong correlation between skull length and total body length in subadult and adult individuals irrespective of their sex, this method was used by Sereno et al. (2001) for Sarcosuchus due to the absence of a complete enough skeleton. Two regression equations were used to estimate the size of S. imperator, they were created based on measurements gathered from 17 captive gharial individuals from northern India and from 28 wild saltwater crocodile individuals from northern Australia, both datasets supplemented by available measurements of individuals over 1.5 m (4.92 ft) in length found in the literature.

The largest known skull of Sarcosuchus imperator (the type specimen) is 1.6 m (5.25 ft) long (1.5 m (4.92 ft) in the midline), and it was estimated that the individual it belonged to had a total body length of 11.65 m (38.2 ft), its snout-vent length of 5.7 m (18.7 ft) was estimated using linear equations for the saltwater crocodile and in turn, this measurement was used to estimate its body weight at 8 tonnes (8.8 short tons). These new measurements meant Sarcosuchus was able to reach a maximum body size not only greater than previously estimated but also greater than that of the Miocene "Beak crocodile" Rhamphosuchus, the Late Cretaceous Deinosuchus crocodilian related to our modern alligators, and the Miocene Purussaurus.

However, extrapolation from the femur of a subadult individual as well as measurements of the skull width further showed that the largest S. imperator was significantly smaller than was estimated by Sereno et al. (2001) based on modern crocodilians. O’Brien et al. (2019) estimated the length of the largest S. imperator specimen at 9.5 meters and body weight at 4.7 tons based on longirostrine crocodylians skull width to total length ratio. This estimate is very close to the femur based estimate is 9.1 m (29.9 ft).

Sereno, Paul C.; Larson, Hans C. E.; Sidor, Christian A.; Gado, Boubé (2001). "The Giant Crocodyliform Sarcosuchus from the Cretaceous of Africa". Science. 294 (5546): 1516–9. Bibcode:2001Sci...294.1516S. doi:10.1126/science.1066521. PMID 11679634.