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Deinosuchas Carnegie
Deinosuchus was a Giant Crocodylian slightly related to the Alligator that lived from approximately 82 million years ago up until the end-Cretaceous extinction event began. Its main competitors as a large predator may have included sharks (such as the Ginsu Shark), marine reptiles (Mosasaurs), dinosaurs (Tyrannosaurus) and other Deinosuchus.[1] Its main prey were sea turtles and dinosaurs.[2]
File:Dino.jpg

Deinosuchus ( /ˌdnəˈsjuːkəs/ DY-nə-SEW-kəs) is an extinct genus related to the alligator. The name translates as "terrible crocodile" and is derived from the Greek deinos (δεινός), "terrible", and soukhos (σοῦχος), "crocodile". The first remains were discovered in North Carolina (United States) in the 1850s; the genus was named and described in 1909. Additional fragments were discovered in the 1940s and were later incorporated into an influential, though inaccurate, skull reconstruction at the American Museum of Natural History. Knowledge of Deinosuchus remains incomplete, but better cranial material found in recent years has expanded scientific understanding of this massive predator.

Although Deinosuchus was far larger than any modern crocodile or alligator—measuring up to 12 m (39 ft)long, 10 feet tall and weighing up to 8.5 metric tons (9.4 short tons)—in overall appearance it was fairly similar to its smaller relatives. It had large, robust teeth that were built for crushing, and its back was covered with thick hemispherical osteoderms. One study indicates that Deinosuchus may have lived for up to 50 years, growing at a rate similar to that of modern crocodilians, but maintaining this growth over a much longer period of time.

Deinosuchus fossils have been found in ten U.S. states, including Texas, Montana, and many along the East Coast. Fossils have also been found in northern Mexico. It lived on both sides of the Western Interior Seaway, and was an opportunistic apex predator in the coastal regions of eastern North America. Deinosuchus reached its largest size in its western habitat, but the eastern populations were far more abundant. Opinion remains divided as to whether these two populations represent separate species. Deinosuchus was probably capable of killing and eating large dinosaurs. It may have also fed upon sea turtles, fish, and other aquatic and terrestrial prey. They all died out in the Creataceous-Paleogene Extinction Event. While their other relatives survived and triumph what is happening today.

Contents

Description

Morphology

Despite its large size, the overall appearance of Deinosuchus was not considerably different from that of modern crocodilians.[1] Deinosuchus had an alligator-like broad snout, with a slightly bulbous tip.[1] Each premaxilla contained four teeth, with the pair nearest to the tip of the snout being significantly smaller than the other two.[2] Each maxilla (the main tooth-bearing bone in the upper jaw) contained 21 or 22 teeth.[3] The tooth count for each dentary (tooth-bearing bone in the lower jaw) was at least 22.[2] All the teeth were very thick and robust; those close to the rear of the jaws were short, rounded, and blunt.[4] They appear to have been adapted for crushing, rather than piercing.[4] When the mouth was closed, only the fourth tooth of the lower jaw would have been visible.[2]

[1][2] The osteoderms of Deinosuchus, as illustrated by W.J. Holland. They are proportionately much thicker than those of modern crocodilians.Modern American alligators, with the strongest bite of any living animal, have a maximum force of 9,452 newtons (2,125 lbf).[5] The bite force of Deinosuchus has been estimated to exceed 18,000 newtons (4,000 lbf).[1]
File:Deinoskull.jpg

Deinosuchus had a secondary bony palate, which would have permitted it to breathe through its nostrils while the rest of the head remained submerged underwater.[6] The vertebrae were articulated in a procoelous manner, meaning that they had a concave hollow on the front end and a convex bulge on the rear; these would have fit together to produce a ball and socket joint.[7][8] The secondary palate and procoelous vertebrae are advanced features also found in modern eusuchian crocodilians.[6][9]

The osteoderms (scutes) covering the back of Deinosuchus were unusually large, heavy, and deeply pitted; some were of a roughly semispherical shape.[10][11] Deep pits and grooves on these osteoderms served as attachment points for connective tissues.[11] Together, the osteoderms and connective tissues would have served as load-bearing reinforcement to support the massive body of Deinosuchus out of water.[3][11] Consequently, despite its bulk, Deinosuchus was probably almost as agile on land as its modern relatives.[3][6]

Size

[3][4] The maximum size reached by Deinosuchus has been estimated at between 10 metres (33 ft) and 20 metres (60 ft). In contrast, the largest modern saltwater crocodiles reach no more than 7 metres (23 ft) in length.Because the known remains of Deinosuchus are so fragmentary, estimates of its size have varied significantly.[12] In 1954, Edwin H. Colbert and Roland T. Bird reconstructed the lower jaw of Deinosuchus with a length of 2 m (6.6 ft), and calculated "on the basis of comparative measurements" that the giant crocodilian's total body length could have been up to 15 m (50 ft).[7] A much lower estimate—8 to 10 m (26 to 33 ft)—was given by Gregory M. Erickson and Christopher A. Brochu in 1999.[13] David R. Schwimmer noted in 2002 that the smaller and more common form of Deinosuchus found in eastern North America usually had skulls about 1 m (3.3 ft) long. Using an equation based on skull size, Schwimmer estimated that they probably had a total body length of about 8 m (26 ft), and weighed about 2.3 metric tons (2.5 short tons). According to Schwimmer's research, Deinosuchus reached larger sizes in the western portion of the continent. A reasonably well-preserved skull specimen discovered in Texas indicated that the animal's head measured about 1.31 m (4.30 ft), and from this Schwimmer calculated a body length of 9.8 m (32.2 ft). Although the largest remains of Deinosuchus had skulls too poorly preserved to use this method of estimation, scaling from vertebrae indicates that some of them grew to even larger sizes. Schwimmer estimates that the biggest specimens had a total body length of up to 12 m (40 ft), and perhaps weighed 8.5 metric tons (9.4 short tons) or more.[3]

Although there is some disagreement as to its exact size, the fossil remains are nonetheless sufficient to indicate that Deinosuchus was substantially larger than any modern crocodilian. Even the relatively low estimate provided by Erickson and Brochu suggests that the maximum weight reached by Deinosuchus exceeded that of currently living species by a factor of three to five.[13] Deinosuchus has often been described as the largest crocodilian of all time, but some other crocodyliforms—including Purussaurus, Rhamphosuchus, and Sarcosuchus—may have equaled or exceeded it in size.[14]

Paleobiology

Habitat

[5][6] A Deinosuchus jaw fragment, exhibited at the North Carolina Museum of Natural Sciences. Fossils of this large alligatoroid have been discovered in ten U.S. states, plus northern Mexico.Deinosuchus was present on both sides of the Western Interior Seaway.[15] Specimens have been found in ten of the modern-day United States.[16] A Deinosuchus osteoderm from the San Carlos Formation was also reported in 2006, so the giant crocodilian's range may have included parts of northern Mexico.[17] Deinosuchus fossils are most abundant in the Gulf Coastal Plain region of Georgia, near the Alabama border.[15] All known specimens of Deinosuchus were found in rocks that date to the Campanian stage of the Late Cretaceous period. The oldest examples of this genus lived approximately 80 Ma, and the youngest lived around 73 Ma.[18]

The distribution of Deinosuchus specimens indicates that these giant crocodilians may have preferred estuarine environments.[15] In the Aguja Formation of Texas, where some of the largest specimens of Deinosuchus have been found, these massive predators probably inhabited brackish-water bays.[19] Although some specimens have also been found in marine deposits, it is not clear whether Deinosuchus ventured out into the ocean (like modern-day saltwater crocodiles); these remains might have been displaced after the animals died.[15] Deinosuchus has been described as a "conspicuous" component of a purportedly distinct biome occupying the southern half of Late Cretaceous North America.[20]

Diet

[7][8]Deinosuchus may have preyed upon large ornithopods. Kritosaurus, shown above, lived alongside the giant crocodilian in the Aguja Formation ecosystem.[21]In 1954, Edwin H. Colbert and Roland T. Bird speculated that Deinosuchus "may very well have hunted and devoured some of the dinosaurs with which it was contemporaneous".[7] Colbert restated this hypothesis more confidently in 1961: "Certainly this crocodile must have been a predator of dinosaurs; otherwise why would it have been so overwhelmingly gigantic? It hunted in the water where the giant theropods could not go."[22][23] David R. Schwimmer proposed in 2002 that several hadrosaurid tail vertebrae found near Big Bend National Park show evidence of Deinosuchus tooth marks, strengthening the hypothesis that Deinosuchus fed on dinosaurs in at least some instances.[4] In 2003, Christopher A. Brochu did not find the tooth mark evidence to be compelling, but nonetheless agreed that Deinosuchus "probably dined on ornithopods from time to time."[24] Deinosuchus is generally thought to have employed hunting tactics similar to those of modern crocodilians, ambushing dinosa
File:Deinosuchus and albertosaurus.jpg
urs and other terrestrial animals at the water's edge and then submerging them until they drowned.[25]

Schwimmer and G. Dent Williams proposed in 1996 that Deinosuchus may have preyed on marine turtles.[26] Deinosuchus would probably have used the robust, flat teeth near the back of its jaws to crush the turtle shells.[4] The "side-necked" sea turtle Bothremys was especially common in the eastern habitat of Deinosuchus, and several of its shells have been found with bite marks that were most likely inflicted by the giant crocodilian.[4][26]

Schwimmer concluded in 2002 that the feeding patterns of Deinosuchus most likely varied by geographic location; the smaller Deinosuchus of eastern North America would have been opportunistic feeders in an ecological niche similar to that of the modern American alligator. They would have consumed marine turtles, large fish, and smaller dinosaurs.[3] The bigger, but less common, Deinosuchus that lived in Texas and Montana might have been more specialized hunters, capturing and eating large dinosaurs.[3] Schwimmer noted that no theropod dinosaurs in Deinosuchus's eastern range approached its size, indicating that the massive crocodilian could have been the region's apex predator.[4]

Growth rates

A 1999 study by Gregory M. Erickson and Christopher A. Brochu suggested that the growth rate of Deinosuchus was comparable to that of modern crocodilians, but was maintained over a far longer period of time.[13] Their estimates, based on growth rings in the dorsal osteoderms of various specimens, indicate that each Deinosuchus might have taken over 35 years to reach full adult size, and that the oldest individuals may have lived for more than 50 years.[13] This was a completely different growth strategy than that of large dinosaurs, which reached adult size much more quickly and had shorter lifespans.[13] According to Erickson, a full-grown Deinosuchus "must have seen several generations of dinosaurs come and go".[27]

Schwimmer noted in 2002 that Erickson and Brochu's assumptions about growth rates are only valid if the osteodermal rings reflect annual periods, as they do in modern crocodilians.[3] According to Schwimmer, the growth ring patterns observed in Deinosuchus could have been affected by a variety of factors, including "migrations of their prey, wet-dry seasonal climate variations, or oceanic circulation and nutrient cycles".[3] If the ring cycle was biannual rather than annual, this might indicate that Deinosuchus grew faster than modern crocodilians, and had a similar maximum lifespan.[3]

Discovery and naming

[9][10] Ebenezer Emmons illustrated two fossil teeth in 1858. Most likely, they belonged to the crocodilian that would later be named Deinosuchus.In 1858, geologist Ebenezer Emmons described two large fossil teeth found in Bladen County, North Carolina.[28] Emmons assigned these teeth to Polyptychodon, which he then believed to be "a genus of crocodilian reptiles".[28] Later discoveries showed that Polyptychodon was actually a pliosaur, a type of marine reptile.[11] The teeth described by Emmons were thick, slightly curved, and covered with vertically grooved enamel; he assigned them a new species name, P. rugosus.[28] Although not initially recognized as such, these teeth were probably the first Deinosuchus remains to be scientifically described.[11] Another large tooth that likely came from Deinosuchus, discovered in neighboring Sampson County, was named Polydectes biturgidus by Edward Drinker Cope in 1869.[11]

In 1903, at Willow Creek, Montana, several fossil osteoderms were discovered "lying upon the surface of the soil" by John Bell Hatcher and T.W. Stanton.[10] These osteoderms were initially attributed to the ankylosaurid dinosaur Euoplocephalus.[10] Excavation at the site, carried out by W.H. Utterback, yielded further fossils, including additional osteoderms as well as vertebrae, ribs, and a pubis.[10] When these specimens were examined, it became clear that they belonged to a large crocodilian and not a dinosaur; upon learning this, Hatcher "immediately lost interest" in the material.[10] After Hatcher died in 1904, his colleague W.J. Holland studied and described the fossils.[10] Holland assigned these specimens to a new genus and species, Deinosuchus hatcheri, in 1909.[10] Deinosuchus comes from the Greek δεινός/deinos, meaning "terrible", and σοῦχος/suchos, meaning "crocodile".[10] [11][12] This skull reconstruction, exhibited at the American Museum of Natural History for nearly a half-century, is probably the best known of all Deinosuchus fossils. The darker shaded portions are actual fossil bone, while the light portions are plaster.A 1940 expedition by the American Museum of Natural History yielded more fossils of giant crocodilians, this time from Big Bend National Park in Texas.[7] These specimens were described by Edwin H. Colbert and Roland T. Bird in 1954, under the name Phobosuchus riograndensis.[7] Donald Baird and Jack Horner later assigned the Big Bend remains to Deinosuchus, which has been accepted by most modern authorities.[11][29] The genus name Phobosuchus, which was initially created by Baron Franz Nopcsa in 1924, has since been discarded because it contained a variety of different crocodilian species that turned out to not be closely related to each other.[11]

The American Museum of Natural History incorporated the skull and jaw fragments into a plaster restoration, modeled after the present-day Cuban crocodile.[7] Colbert and Bird stated that this was a "conservative" reconstruction, since an even greater length could have been obtained if a long-skulled modern species such as the saltwater crocodile had been used as the template.[7] Because it was not then known that Deinosuchus had a broad snout, Colbert and Bird miscalculated the proportions of the skull, and the reconstruction greatly exaggerated its overall width and length.[11] Despite its inaccuracies, the reconstructed skull became the best-known specimen of Deinosuchus, and brought public attention to this giant crocodilian for the first time.[11] [13][14] Skull cast of Deinosuchus at the American Museum of Natural History Numerous additional specimens of Deinosuchus were discovered over the next several decades. Most were quite fragmentary, but they expanded knowledge of the giant predator's geographic range. As noted by Christopher A. Brochu, the osteoderms are distinctive enough that even "bone granola" can adequately confirm the presence of Deinosuchus.[11][30] Better cranial material was also found; by 2002, David R. Schwimmer was able to create a composite computer reconstruction of 90% of the skull.[1][15]

Classification

[15][16]Deinosuchus scutes and vertebra, Carnegie Museum of Natural HistoryDeinosuchus was classified in the family Crocodylidae by Colbert and Bird, primarily on the basis of dental features resembling those of modern crocodiles.[7] However, a phylogenetic re-evaluation conducted in 1999 by Brochu determined that Deinosuchus was actually a primitive member of Alligatoroidea. Thus, Deinosuchus "is not the world's largest crocodile—it is one of the largest alligators."[14] This classification was bolstered in 2005 by the discovery of a well-preserved Deinosuchus braincase from the Blufftown Formation of Alabama, which shows some features reminiscent of those in the modern American alligator.[31] Although it was a prehistoric member of the same clade, Deinosuchus was not a direct ancestor of modern alligators.[32] Its closest relatives may have been Leidyosuchus and Diplocynodon.[32]

Schwimmer (2002) considered all Deinosuchus specimens to belong to one species.[2] He noted that there were more similarities than differences between the eastern and western populations, and that most of these differences related only to the larger size of the western specimens.[2] Under the International Code of Zoological Nomenclature's rules of priority, this species would be named D. rugosus.[2] Lucas et al. (2006) also considered Deinosuchus a monospecific genus.[18] However, Brochu (2003) questioned Schwimmer's analysis, suggesting that size might be a significant diagnostic feature and that several of the features used by Schwimmer to establish synonymy between the two populations are actually primitive traits shared by other genera as well.[24] Schwimmer (2002) informally referred to the western populations as D. riograndensis, and several other researchers, including Anglen and Lehman (2000) and Westgate et al. (2006) have also recently assigned western Deinosuchus remains to this species.[2][17][19]

References

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