Nicknamed the SuperCroc, the prehistoric Sarcosuchus imperator (pronounced SAR-koh-SOO-kiss IM-peh-RAH-tor, and meaning "flesh crocodile emperor") from the early Cretaceous of Africa is one of the largest giant crocodile-like reptiles that ever lived. It was almost twice as long as the largest modern crocodile, and weighed up to 10 times as much.
Until recently, all that was known of the species was a few fossilized teeth and armor plates, which were discovered in the Sahara Desert by the French paleontologist Albert-Félix de Lapparent in the 1940s or 1950s. However, in 1997 and 2000, Paul Sereno discovered a half a dozen new specimens, including one with about half the skeleton intact, and most of the spine. All of the other giant crocodiles are known only from a few partial skulls, so which is actually the biggest is an open question.
Description
When fully mature, the SuperCroc was as long as a city bus (11–12 m, or 37–40 ft), and weighed up to 8,000 kg (8.8 short tons), as much as the largest known terrestrial carnivore, the dinosaur Gigantosaurus. The saltwater crocodile is the largest modern species, and only reaches half that length (6.3 m, or 20.7 ft, is the longest confirmed individual), and a small fraction of the weight (1,000 kg, or 1.1 tons).
The largest SuperCroc was the oldest, because it kept growing through its entire 50–60 year lifespan. Modern crocodiles grow at a rapid rate, reaching their adult size in about a decade, and then grow more slowly afterwards. The SuperCroc probably grew at the same rate, but kept growing for up to 40 years before reaching its full adult size.
Its jaws alone were as big as a human adult (1.8 m, or 6 ft). The upper jaw overlaps the lower jaw, creating an overbite, and both were narrow. The snout composes about 75 percent of the skull's length.
Its contained 132 thick teeth (Larsson said they were like "railroad spikes"). The teeth are conical and designed for grabbing and holding, instead of being narrow and designed for slashing (like the teeth of most land-dwelling carnivores). It could probably exert a force of 18,000 lbf (80 kN) with its jaw, making very unlikely that prey could escape.
It had a row of overlapping bony plates, or scutes, running down its back, the largest of which were 1 m (3 ft) long. The scutes served as armor and may have helped support its great mass, but also restricted its flexibility.
Like a gharial, the SuperCroc had a air cell in a bony protrusion at the tip of its snout (a bulla), which might have augmented its sense of smell, or been used for a variety of vocalizations.
Behavior and diet
Like modern crocodiles, the SuperCroc could probably make a wide range of vocalizations, from grunts and squeaks to hisses, growls, barks, bellows, and roars. The SuperCrocs may have used these sounds to stake out territory, to attract mates, and to communicate with their progeny.
Like modern crocodiles, the SuperCroc's eye sockets rotate upwards, so it probably spent most of its time with the majority of its body submerged, watching the shore for prey.
It seems likely that it ate the large fish and turtles of the Cretaceous. But the overhanging jaw and stout teeth are designed for grabbing and crushing, so its primary prey was probably large animals and smaller dinosaurs, which it ambushed, dragged into the water, drowned, and then tore apart.
It may have even come into conflict with the Suchomimus, an 11 m (36 ft) fish-eating dinosaur with a strangely crocodilian jaw, whose fossils were found in the same rock formation as the SuperCroc. According to Sereno, "because the ancient animal was so large, it could easily handle huge dinosaurs, including the massive long-necked, small-headed sauropods that were common in that African region".
Other crocodilian biologists are skeptical of the animal's "giant killing" capabilities. The long, thin snout of the SuperCroc is very similar to the thin snouts of the gharial, false gharial , and the slender-snouted crocodile , all of which are nearly exclusive fish-eaters, and incapable of tackling large prey. This can be contrasted to both the modern Nile crocodile and the extinct Deinosuchus which have very broad, heavy skulls, suitable for dealing with large prey. This, coupled with the abundance of large, lobe-finned fish in its environment, leads many to suggest that, far from being a dinosaur killer, SuperCroc was simply a large piscivore, a scaled-up version of the modern gharial.
However, while the snout of the juvenile SuperCroc strongly resembles modern narrow-snouted crocodiles in width, it expands dramatically in mature SuperCrocs. While still considerably narrower than the snout of a Nile crocodile, in mature SuperCrocs it is also much wider than the snouts of crocodylians like the gharial. In addition, the teeth do not interlock like those of the exclusive fish-eaters, which suggests that like the Nile crocodile it may have complemented a primarily piscean diet with terrestrial animals, at least upon maturity.
On the other hand, the lobe-finned fish that shared the waters with Sarcosuchus were often in excess of 6 feet (1.8 m) long and 200 lb (90 kg) in weight, raising the possibility those adaptions which seem to indicate large or moderate-sized terrestrial prey may instead be adaptations to dealing with exceptionally large fish (many species of which possessed a layer of bony scales, called osteoderms, for protection).
Environment
A 100 million years ago, in the late Cretaceous, the Sahara was still a great tropical plain, dotted with lakes and crossed by rivers and streams that were lined with vegetation. Based on the number of fossils discovered, the aquatic Sarcosuchus was probably plentiful in these warm, shallow, freshwater habitats.
Unlike modern crocodiles, which are very similar in size and shape to one another, and tend to live in different areas; the SuperCroc was just one of many crocodiles, of different sizes and shapes, all living in the same area. Four other species of prehistoric crocodile were also discovered in the same rock formation along with the SuperCroc, including a dwarf crocodile with a tiny, 8 cm (3 in) long skull. They filled a diverse variety of ecological niches, instead of competing with each other for resources.
Scientific study
The SuperCroc remains are from several individuals, and include a spine (vertebrae), limb bones, hip bones (a pelvic girdle), the bony armored plates that ran down its back (scutes), and more than a half-dozen skulls. Crocodile skulls are thick and heavy, and are found more frequently than the rest of the body. This is quite a contrast with dinosaurs, whose relatively fragile skulls rarely become part of the fossil record.
The scutes can also be used to determine age, since they have growth rings like those found in trees. One 80 percent-grown specimen was discovered with 40 rings, indicating that it had lived for 40 years, which also suggests a reasonable maximum.
No skeleton was complete enough to measure directly, so the maximum length estimate was calculated by measuring the largest skull and comparing it to modern crocodiles. In modern crocodiles, the skull and body are the same relative size in both juvenile and adults, and in both sexes. The primary difference is that species with a long snout have larger heads in proportion to their bodies than species with relatively broad snouts. The length of the SuperCroc is the average of the expected length of a the narrow-snouted gharial and the intermediate-snouted saltwater crocodile, while the mass is the expected mass of a saltie. Sereno also measured living crocodilians in India and Costa Rica, and used that in his analysis.
As part of a National Geographic Special, Greg Erickson of Florida State University, Kent Vliet of the University of Florida, and Kristopher Lapping of Northern Arizona University, provoked American alligators at the St. Augustine Alligator Farm and Zoological Park in Florida into biting a bar studded with piezoeletric sensors. The largest alligator they tested was able to exert a force of 2,125 lbf (9.45 kN). By comparing the force exerted by more than 60 animals, they were able to determine that the force exerted was proportional to the size of the animal, which allowed an estimate of the biting power of the SuperCroc.
The giant croc phenomenon
- "With today's crocs, you basically have a period of fast growth, then a little bit of growth — this guy wasn't slowing down."
- —Paul C. Sereno
Giant crocodiles seem to be a good example of convergence, because according to Schwimmer, "the idea of really big crocs is a repeat theme in evolution." This may be in part due to body design (the armored plates the back can provide structural support to a massive body), and in part due to environment (water can buoy up their massive bodies). (See also: Cope's law.)
A study of another giant croc, the Deinosuchus, indicated that it grew at about the same rate as modern crocodiles, up to 0.5 m (1.5 ft) per year. It was larger because it kept growing, reaching full adulthood in 35 years, instead of 10. While there is a genetic component, growing that large also requires a rich diet. All the different giant crocodiles must have lived in near-perfect environments, with vast areas of warm, shallow water, and abundant prey.
The Deinosuchus, from the late Cretaceous in North America, is also a good example of an giant crocodile that is only distantly related to the SuperCroc. The Deinosuchus is only known from skulls, which are smaller than that of the SuperCroc. But the Deinosuchus has a broad snout, like an alligator, while the Sarcosuchus has a narrow snout, like a gharial. This means that the skull of the Deinosuchus is probably a smaller portion of its total body length than the skull of the long-nosed SuperCroc, so its total size may be as large, or even larger. Other rivals in size of the SuperCroc are Purrusaurus from the Miocene of Brazil, and Rhamphosuchus from the Miocene and Pliocene of India, but their fossils are less complete.
The relationship between the giant crocs can be seen in the following simplified evolutionary tree:
- Neosuchia
- Sarcosuchus
- Order Crocodylia
- Superfamily Alligatoroidea
- Superfamily Crocodyloidea
- Family Crocodylidae
- Deinosuchus
- Rhamphosuchus
Classification
The SuperCroc is not an ancestor of modern crocodiles. It is not even a crocodile, at least in the technical sense. A "crocodile" is a member of a species belonging to the taxon Crocodylia. And Crocodylia includes all modern species, and all extinct species descended from the nearest common ancestor of all the living crocodiles. The SuperCroc is a pholidosaur, a branch that split off before the first ancestral crocodile.
But "crocodile" is commonly used in a much broader sense. After all, even the first "crocodile-like reptiles" (the Crocodylomorpha ), who split off from the archosaurs (Archosauria is the group of reptiles that include the dinosaurs, though crocodiles are even more ancient) about 230 million years ago (in the late Triassic) looked like crocodiles. They were bizarre crocodiles with long legs, but they still had big mouths full of teeth, long bodies covered with armor, and powerful tails. The SuperCroc is more recent, but it is still technically a crocodyliform.
Based on the structure of the snout, the closest relative of Sarcosuchus is the pholidosaur Terminonaris, with Dryosaurus and Pholidosaurus as slightly more distant relatives. As a group, they are narrow-snouted fish-eaters from saltwater environments, except for the broader snouted, river-dwelling Sarcosuchus.
Until the 1980s, the pholidosaurids were classifed as part of the suborder Mesosuchia , within the order Crocodylia. However Benson and Clark determined in 1988 that Mesosuchia was a precursor group from which the ancestor of all modern crocodiles is descended, so at least according to phylogenic classification the pholiosaurids fall outside of Crocodylia. A simplified evolutionary tree, or cladogram (Sereno, 1998):
- Crocodyliformes
- Mesoeucrocodylia
- Metasuchia
- Neosuchia
- Pholidosauridae
- Crocodylia (modern crocodiles)
Teeth and scutes have also been found in Brazil, belonging to a close relative of the SuperCroc. This is additional evidence that land bridges between Africa and South America existed much later than was previously believed.
Desert discoveries
The fossils were discovered in Gadoufaoua, Niger in the Ténéré Desert, which is part of the Sahara. The first SuperCroc teeth and scutes were recovered by the French paleontologist Albert-Félix de Lapparent, in the 1940s or 1950s. But it was 1964 before a skull was discovered by geologists, and brought to the attention of Philippe Taquet . He shipped it to Paris, where it was examined by France de Broin . Together, they formally named and described the species in 1966, before returning the specimen to Niger.
The crocodile was given the name Sarcosuchus imperator, which is dervived from sarco (meaning "flesh"), suchus (meaning "crocodile"), and imperator (Latin, meaning "emperor"). The holotype specimen is MNN 604, which indicates that it is 604th exhibit at the Musee National du Niger .
The next major expedition was Paul C. Sereno's trip in 1997, and the follow-up trip in 2000. He recovered partial skeletons, numerous skulls, and 20 tons of assorted other fossils from the deposits of the El Rhaz Formation, which has been dated to the Aptian to Albian stages of the late Cretaceous. It took about a year to prepare the SuperCroc remains. The discovery was then published on October 25, 2001, in the scientific journal Science by Paul C. Sereno, of the University of Chicago and National Geographic's Explorer-in-Residence; Hans C. E. Larsson, from Yale University and the University of Toronto (formerly a student at the University of Chicago); Christian Sidor, of the New York College of Osteopathic Medicine in Old Westbury, New York; and Boubé Gado, of the Institut de Recherches en Sciences Humaines in Niamey, Niger.
References
Further reading
Further viewing
- National Geographic Special on SuperCroc. National Geographic Channel, December, 2001. (See also: IMDb)
External links
- "Sarcosuchus imperator". Prehistorics Illustrated. (illustrations)
- "African fossil find: 40-foot crocodile". Guy Gugliotta. Washington Post, October 26, 2001. Retrieved November 17, 2004.
- SuperCroc: Sarcosuchus imperator. Gabrielle Lyon. Retrieved November 17, 2004.
- "'SuperCroc' fossil found in Sahara". D. L. Parsell. National Geographic News, October 25, 2001. Retrieved November 17, 2004.
- Dinosaur Expedition 2000. Paul C. Sereno. Retrieved November 17, 2004.
- "SuperCroc's jaws were superstrong, study shows". John Roach. National Geographic News, April 4, 2003. Retrieved November 17, 2004.
- "Sereno, team discover prehistoric giant Sarcosuchus imperator in African desert." Steve Koppes. The University of Chicago Chronicle, volume 21, number 4, November 1, 2001. Retrieved November 17, 2004.
