Aegisuchus Temporal range: Late Cretaceous: Cenomanian, | |
---|---|
Holotype braincase | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Reptilia |
Clade: | Archosauria |
Clade: | Pseudosuchia |
Clade: | Crocodylomorpha |
Clade: | Crocodyliformes |
Clade: | Neosuchia |
Clade: | Eusuchia |
Family: | † Aegyptosuchidae |
Genus: | † Aegisuchus Holliday & Gardner, 2012 |
Type species | |
†Aegisuchus witmeri Holliday & Gardner, 2012 |
Aegisuchus is an extinct monospecific genus of giant, flat-headed crocodyliform within the family Aegyptosuchidae. It was found in the Kem Kem Formation of southeast Morocco, which dates back to the Cenomanian age of the Late Cretaceous epoch. [1] The type species Aegisuchus witmeri was named in 2012 by paleontologists Casey Holliday and Nicholas Gardner, who nicknamed it "Shieldcroc" for the shield-like shape of its skull. [2] A. witmeri is known from a single partial skull including the braincase and skull roof. [1]
Aegisuchus is known only from a partial braincase and skull roof cataloged as ROM 54530. It is diagnosed by several autapomorphies, or unique features. At the center of the skull table is a raised and rough-surfaced boss on the parietal bone that is shaped like a circle. On either side of this boss are holes called dorsotemporal fenestrae, and the surrounding bone is relatively smooth. The quadrate bone in the temporal region of the skull has a rectangular projection called the adductor tubercle, which served as an attachment for muscles that closed the jaw. At the front of the skull table, projections on the laterosphenoid bones called capitate processes face out to the side. This feature is also seen in the skulls of living gharials, but evolved independently in each group. Also on the front surface are two holes of the dorsotemporal fenestrae, which pass through the skull and open at the skull table. On the front surface, a ridge of bone or torus makes up the lateral edge of each hole. The back of the skull is wide, with large projections on the exoccipital bones that would have anchored large epaxial muscles in the top part of the neck. [1]
At 40 cubic centimetres, the braincase of Aegisuchus is much larger in volume than that of any other crocodyliform. Original description in 2012, the total skull length of Aegisuchus is estimated to have been 2.08 to 2.86 metres (6.8 to 9.4 ft) in length, based on the ratio of braincase to skull length in other crocodilians. A similar ratio between braincase and body length puts Aegisuchus at 15 to 21 metres (49 to 69 ft) long when based on the proportions of long-snouted gharials, or 16 to 22 metres (52 to 72 ft) long when based on the proportions of short-snouted crocodiles. [1] However, these proportions have been met with a lot of scrutiny, and it is more likely that Aegisuchus reached less than 15 metres (49 ft) in length. [1] A reader comment posted to the original description [3] provided regression equations failed to replicate the reported skull length, suggesting actual skull length can be 62 to 90 centimetres (2.03 to 2.95 ft) long, and total length would be around 3.9 metres (13 ft). [4]
The circular boss of roughened bone on the skull table is one of the most unusual features of Aegisuchus. As in most crocodilians, the rough-surfaced region was probably covered in a thick skin that tightly adhered to the skull. Surrounding the boss, the smooth-surfaced region bears several deep parallel channels for blood vessels, suggesting that thicker, more complex skin tissue covered this region. Vascularization is not seen in any other crocodilian, and may have been unique to Aegisuchus. Given that the blood vessel channels run into the braincase, the vascularized tissue may have served a thermoregulatory role by heating blood going to the brain and eyes. The central boss may have been used in mating displays, appearing as an eyespot. Modern crocodilians raise their heads out of the water as a social signal in mating displays; as a close relative of crocodilians, Aegisuchus likely had similar mating rituals. [1]
The flattened shape of the skull of Aegisuchus suggests that it was an ambush predator resting at the surface of the water. Although only the back of the skull is known, other characteristics can be inferred from the closely related Aegyptosuchus . Aegisuchus probably had eyes that faced directly upward, with no raised ridges surrounding the sockets. A strut of bone called the postorbital bar, which in most crocodilians is vertically oriented, would have been almost flat. The flattened skull of Aegisuchus required significant alteration to jaw muscles. The adductor muscles that close the jaw shifted to a more vertical orientation in Aegisuchus. Muscles like the adductor mandibulae externus medialis, which are weak in most crocodilians, became more important as jaw closers and were greatly enlarged. The broad-surfaced occipital region at the back of the skull provides a large attachment area for the splenius capitis muscles of the neck. With a long flattened snout, Aegisuchus would have had great difficulty in raising its head and opening its mouth if it did not have large neck muscles. A depressed region in the lower part of the back of the skull suggests that the jaw adductor muscles were also large, facilitating jaw opening. A similar mechanism for lifting the head and opening the jaws is seen in the Late Triassic amphibian Gerrothorax . Aegisuchus has a very flexible articulation between the skull and vertebral column, allowing a greater degree of skull elevation than other crocodilians. [1]
Aegisuchus is a member of the family Aegyptosuchidae, along with the genus Aegyptosuchus . Aegyptosuchidae belongs to the clade Eusuchia, and is proposed to be the sister clade to the crown group Crocodylia, which contains all extant (living) crocodilians. The phylogeny can be shown in the cladogram below: [1]
During the Late Cretaceous, northern Africa was a humid region near the Tethys Ocean, a seaway between the southern continents of Gondwana and northern land masses of Laurasia. At this time, the Kem Kem Beds of Morocco were deposited in a freshwater delta system. Aegisuchus lived within this delta alongside fishes, turtles, snakes and varanid lizards, pterosaurs, and sauropod and theropod dinosaurs. Stomatosuchids are also known from the Kem Kem Beds, and probably shared a close ecological niche with Aegisuchus as river predators. [1]
With its flattened skull, Aegisuchus was probably an ambush predator. Possible prey include coelacanths, lungfish, and bichirs, all of which have been found in the Kem Kem beds. As an opportunistic predator, Aegisuchus may also have preyed on land vertebrates such as reptiles. [1] Aegisuchus could have potentially fallen prey to much larger predators such as Spinosaurus.
The Late Cretaceous was an important time in crocodilian evolution because many land masses were breaking up. What is now Europe and Asia was drifting away from Africa to form the Tethys Ocean, while North America continued to separate from the rest of Laurasia as the Atlantic Ocean widened. With the presence of several early crocodilians like Borealosuchus , North America is often hypothesized as the continent of origin for Crocodylia. However, the presence of aegyptosuchids such as Aegisuchus in northern Africa suggests that early crocodilian evolution was focused instead around the Tethys Ocean. The aegyptosuchids represent a highly specialized and highly endemic branch of crocodyliforms at a time when crocodilian diversity and geographic range were expanding. [1]
Carcharodontosaurus from the “Carcharodon lizard ”This lizard was named for the Greek Carcharodon, the great white shark. Named by German paleontologist Ernst Stromer von Reichenbach in 1931. is a genus of carnivorous theropod dinosaur that lived in North Africa from about 100 to 94 million years ago during the Cenomanian age of the Late Cretaceous. Two teeth of the genus, now lost, were first described from Algeria by French paleontologists Charles Depéret and Justin Savornin as Megalosaurus saharicus. A partial skeleton was collected by crews of German paleontologist Ernst Stromer during a 1914 expedition to Egypt. Stromer did not report the Egyptian find until 1931, in which he dubbed the novel genus Carcharodontosaurus, making the type species C. saharicus. Unfortunately, this skeleton was destroyed during the Second World War. In 1995 a nearly complete skull of C. saharicus, the first well-preserved specimen to be found in almost a century, was discovered in the Kem Kem Beds of Morocco; it was designated the neotype in 1996. Fossils unearthed from the Echkar Formation of northern Niger were described and named as another species, C. iguidensis, in 2007.
Sarcosuchus is an extinct genus of crocodyliform and distant relative of living crocodilians that lived during the Early Cretaceous, from the late Hauterivian to the early Albian, 133 to 112 million years ago of what is now Africa and South America. The genus name comes from the Greek σάρξ (sarx) meaning flesh and σοῦχος (souchus) meaning crocodile. It was one of the largest pseudosuchians, with the largest specimen of S. imperator reaching approximately 9–9.5 metres (29.5–31.2 ft) long and weighing up to 3.45–4.3 metric tons. It is known from two species; S. imperator from the early Albian Elrhaz Formation of Niger, and S. hartti from the Late Hauterivian of northeastern Brazil. Other material is known from Morocco and Tunisia and possibly Libya and Mali.
Dakosaurus is an extinct genus of crocodylomorph within the family Metriorhynchidae that lived during the Late Jurassic and Early Cretaceous. It was large, with teeth that were serrated and compressed lateromedially. The genus was established by Friedrich August von Quenstedt in 1856 for an isolated tooth named Geosaurus maximus by Theodor Plieninger in 1846. Dakosaurus was a carnivore that spent much, if not all, its life out at sea. The extent of its adaptation to a marine lifestyle means that it is most likely that it mated at sea, but since no eggs or nests have been discovered that have been referred to Dakosaurus, whether it gave birth to live young at sea like dolphins and ichthyosaurs or came ashore like turtles is not known yet. The name Dakosaurus means "biter lizard", and is derived from the Greek dakos ("biter") and σαῦρος -sauros ("lizard").
Allodaposuchus is an extinct genus of crocodyliforms that lived in what is now southern Europe during the Campanian and Maastrichtian stages, and possibly the Santonian stage, of the Late Cretaceous. Although generally classified as a non-crocodylian eusuchian crocodylomorph, it is sometimes placed as one of the earliest true crocodylians. Allodaposuchus is one of the most common Late Cretaceous crocodylomorphs from Europe, with fossils known from Romania, Spain, and France.
Orthosuchus is an extinct genus of crocodyliform that lived during the Early Jurassic, about 196 million years ago. It was first discovered in 1963 in the Red Beds Formation in the Qacha's Nek Province of Lesotho, southern Africa. The characteristics showed on its postcranial skeleton and the skull indicated that it is a crocodyliform. The finding is significant since some of the characteristics found on this specimen were believed to be absent until Jurassic.
Mahajangasuchus is an extinct genus of crocodyliform which had blunt, conical teeth. The type species, M. insignis, lived during the Late Cretaceous; its fossils have been found in the Maevarano Formation in northern Madagascar. It was a fairly large predator, measuring up to 4 metres (13 ft) long.
Pachycheilosuchus is an extinct genus of neosuchian from the Early Cretaceous of Texas, United States. Previously known, in part, as the "Glen Rose form", this crocodylomorph is notable for its procoelous vertebrae, otherwise found only in derived eusuchian crocodilians, a thick margin on the maxillae, and a shield of armor on the neck formed by the fusion of six individual scutes.
Junggarsuchus is an extinct genus of sphenosuchian crocodylomorph from the Middle or Late Jurassic period of China. The type and only species is J. sloani. The generic name of Junggarsuchus comes from the Junggar Basin, where the fossil was found, and the Greek word "souchos" meaning crocodile. The specific name, "sloani" is in honor of C. Sloan, who is credited with finding the holotype.
Argochampsa is an extinct genus of eusuchian crocodylomorph, usually regarded as a gavialoid crocodilian, related to modern gharials. It lived in the Paleocene of Morocco. Described by Hua and Jouve in 2004, the type species is A. krebsi, with the species named for Bernard Krebs. Argochampsa had a long narrow snout, and appears to have been marine in habits.
Aegyptosuchus is an extinct monospecific genus of aegyptosuchid eusuchian crocodyliform. It was found in the Bahariya Formation of Egypt, which dates back to the Cenomanian age of the Late Cretaceous. The type and only species is Aegyptosuchus peyeri.
Eusuchia is a clade of neosuchian crocodylomorphs that first appeared in the Early Cretaceous, which includes modern crocodilians. Along with Dyrosauridae and Sebecosuchia, they were the only crocodyliformes who survived the K-Pg extinction.
Iharkutosuchus is an extinct genus of basal eusuchian crocodyliform. Its fossils have been found in the Santonian-age Upper Cretaceous Csehbánya Formation in the Bakony Mountains of western Hungary.
Isisfordia is an extinct genus of crocodyliform closely related to crocodilians that lived in Australia during the Middle Cretaceous (Albian–Cenomanian).
Kaprosuchus is an extinct genus of mahajangasuchid crocodyliform. It is known from a single nearly complete skull collected from the Upper Cretaceous Echkar Formation of Niger. The name means "boar crocodile" from the Greek κάπρος, kapros ("boar") and σοῦχος, soukhos ("crocodile") in reference to its unusually large caniniform teeth which resemble those of a boar. It has been nicknamed "BoarCroc" by Paul Sereno and Hans Larsson, who first described the genus in a monograph published in ZooKeys in 2009 along with other Saharan crocodyliformes such as Anatosuchus and Laganosuchus. The type species is K. saharicus.
Sebecus is an extinct genus of sebecid crocodylomorph from Eocene of South America. Like other sebecosuchians, it was entirely terrestrial and carnivorous. The genus is currently represented by two species, the type S. icaeorhinus and S. ayrampu. Several other species have been referred to Sebecus, but were later reclassified as their own genera.
Stratiotosuchus is an extinct genus of baurusuchid mesoeucrocodylian from the Adamantina Formation in Brazil. It lived during the Late Cretaceous. The first fossils were found in the 1980s, and the type species Stratiotosuchus maxhechti was named in 2001. A hyperpredator, it and other baurusuchids may have filled niches occupied elsewhere by theropod dinosaurs.
Duerosuchus is an extinct genus of crocodilian. Remains have been found from Corrales del Vino in Zamora, Spain, and are middle Eocene in age. Duerosuchus is known from a single skull that is incomplete but otherwise well preserved, as well as a lower jaw, some osteoderms, and possibly some vertebrae.
Planocraniidae is an extinct family of eusuchian crocodyliforms known from the Paleogene of Asia, Europe and North America. The family was coined by Li in 1976, and contains three genera, Boverisuchus, Duerosuchus and Planocrania. Planocraniids were highly specialized crocodyliforms that were adapted to living on land. They had extensive body armor, long legs, and blunt claws resembling hooves, and are sometimes informally called "hoofed crocodiles".
Longirostres is a clade of crocodilians that includes the crocodiles and the gavialids, to the exclusion of the alligatoroids. Defined in 2003 by Harshman et al., Longirostres is a crown group defined phylogenetically as including the last common ancestor of Crocodylus niloticus and Gavialis gangeticus and all of its descendants.
Titanochampsa is a genus of large mesoeucrocodylian from the Maastrichtian Marilia Formation of Brazil. Although only known from a single skull roof, the material shows that Titanochampsa was not a member of Notosuchia, which were previously believed to have been the only crocodyliforms present in the strata of the Bauru Group. Body size estimates vary greatly and range between 2.98–5.88 m due to the incomplete nature of the holotype fossil. The overall anatomy of the skull roof, alongside its size and possible affinities with Neosuchians, may suggest that it was a semi-aquatic ambush hunter similar to modern crocodilians.