Eosuchus Temporal range: Late Paleocene - Early Eocene, | |
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Holotype E. lerichei skull | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Reptilia |
Clade: | Archosauria |
Clade: | Pseudosuchia |
Clade: | Crocodylomorpha |
Clade: | Crocodyliformes |
Clade: | Metasuchia |
Clade: | Neosuchia |
Clade: | Eusuchia |
Genus: | † Eosuchus Dollo, 1907 |
Species | |
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Synonyms | |
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Eosuchus ("dawn crocodile") is an extinct genus of eusuchian crocodylomorph, traditionally regarded as a gavialoid crocodilian. It might have been among the most basal of all gavialoids, lying crownward of all other known members of the superfamily, including earlier putative members such as Thoracosaurus and Eothoracosaurus . Fossils have been found from France as well as eastern North America in Maryland, Virginia, and New Jersey. The strata from which specimens have been found date back to the late Paleocene and early Eocene epochs.
The name Eosuchus was first used in 1907 to describe a single specimen found from northern France near the Belgian border, assigned to the type species Eosuchus lerichei. [2]
A second species, Eosuchus minor, was actually discovered earlier in 1870 by Othniel Charles Marsh, but was assigned to the genus Gavialis . The Gavialis minor holotype specimen YPM 282 consisted of cranial fragments and isolated vertebrae found from the Manasquan Formation in Monmouth County, New Jersey, dating back to the Ypresian stage of the early Eocene. The species name minor refers to the relatively small estimated size of the animal, estimated at no more than 2 meters, when compared to other gavialoids such as the modern gharial, which can grow up to 5 meters in length. However, this species was later recognized as distinct from Gavialis on the basis of certain aspects of the known cranial material, in particular the large foramen aerum of the quadrate formed from the epithelial tube that connects the pneumatic chambers of the quadrate and articular. Another diagnostic feature thought to distinguish the species from Gavialis was the narrow interfenestral bar of the parietal bone that is relatively smooth and unsculptured when compared to other gavialoids such as Thoracosaurus . The new generic name Thecachampsoides was proposed for the species G. minor in 1986. [3] A close relationship between T. minor and Eosuchus lerichei was always evident, yet it was not until 2006 that the name Eosuchus was applied to the T. minor specimens, specifically on the basis of a fairly complete specimen called NJSM 15437 from the Vincetown Formation in New Jersey, of which there is a visibly exposed braincase which aids greatly in the taxonomic classification of the genus. The examination of specimens of Thecachampsoides minor with those of Eosuchus lerichei yielded many similarities between the two species, including the foramen aerum as well as other features such as a long nasal process between the premaxillae, dentary alveoli arranged in pairs, and a W-shaped basioccipital tuberosity. E. minor differs from E. lerichei on the basis of a noticeably wider nasal and prefrontals positioned anteriorly further up the skull than the lacrimals. [4]
Other material present from the Aquia Formation of Maryland and Virginia, which dates back to the early Paleocene, tends to be more complete. Some specimens found from these localities are known from nearly complete skulls that provide a more detailed view of the phylogenetic position of Eosuchus, and further aid in distinguishing E. minor from other gavialoids.
A Triassic rhynchosaur was originally named Eosuchus, although it is completely unrelated to the crocodyliform of the same name. The name of the rhynchosaur was later changed to Noteosuchus due to this preoccupation. [5]
Eosuchus is often referred to as a "thoracosaur", a group that was constructed to include many basal forms of gavialoids that cannot be placed into any specific families of their own, yet do not form a true clade. The genus is distinct from gavialoids in still having a thin descending lamina positioned next to the pterygoid.
A phylogenetic analysis conducted in 1996 suggested that Eosuchus may be closely related to tomistomines such as the extant Tomistoma . There is further evidence of this relationship shown in the humeri of these crocodilians; both Eosuchus and tomistomines have a deeply concave deltopectoral crest, unlike the more triangular crests of Gavialis. A nasal-premaxilla contact and similar dentary and maxillary tooth counts also seem to suggest that there may be a close relationship between the genus and later tomistomines, although these features represent more primitive conditions that changed later in gavialoid history. Despite this, it is currently accepted that a close relationship between Eosuchus and tomistomines is not the case, and that the similarities between the two may just be superficial and that these characteristics are plesiomorphic to all gavialoids, being lost in more derived members such as the modern Gavialis.
Eosuchus lerichei and E. minor were included in the study on the phylogenetic relationships of putative fossil gavialoids published by Lee & Yates (2018). The authors considered it most likely that Eosuchus was not a gavialoid, or even a crocodylian, but rather a member of the clade of non-crocodylian eusuchians that also included the genera Argochampsa , Eogavialis , Eothoracosaurus and Thoracosaurus . [6]
The strata from which both species of Eosuchus have been found were thought to have formed in a marginal marine depositional environment, and thus probably reflect the actual environments that these animals would have inhabited. It has been proposed that early gavialoids were originally salt-tolerant coastal forms, [7] and the evidence seen in the case of Eosuchus is consistent with this theory. The internal surface of the prefrontal and lacrimal bones of E. lerichei are characterized by concave depressions, which in several marine lizards, iguanas and birds are where salt glands are housed, suggesting this species was capable of saltwater tolerance. [8] One specimen of E. minor from the Aquia Formation, USNM 299730, has a fossil oyster attached to the dorsal surface of the rostrum.
The fact that the two species of Eosuchus lived on either side of the Atlantic Ocean implies that these populations may have been separated geographically from one another while not necessarily having to be separated stratigraphically (that is, if the temporal ranges of the two species coincide with one another). More importantly, the separate biogeographic ranges of the two species may be evidence for a transoceanic dispersal event from one continent to the other. Since the presumed ages of the localities from which specimens have been found are quite similar yet inexact, it is currently unknown just what continent this dispersal event may have originated. A recent reevaluation of the holotype material of E. lerichei, which in the past has been poorly studied, suggests that it is the more basal species and thus would have been the ancestor of E. minor in Europe. [9]
Gavialidae is a family of large semiaquatic crocodilians with elongated, narrow snouts. Gavialidae consists of two living species, the gharial and the false gharial, both occurring in Asia. Many extinct members are known from a broader range, including the recently extinct Hanyusuchus. Gavialids are generally regarded as lacking the jaw strength to capture the large mammalian prey favoured by crocodiles and alligators of similar size so their thin snout is best used to catch fish, however the false gharial has been found to have a generalist diet with mature adults preying upon larger vertebrates, such as ungulates.
Toyotamaphimeia is a genus of extinct gavialid crocodylian which lived in Japan and Taiwan during the Middle Pleistocene. A specimen recovered in 1964 at Osaka University during the construction of a new science building has been dated to around 430–380 thousand years old based on the stratum in which it was found. Toyotamaphimeia was a fairly large crocodylian measuring approximately 6.3–7.3 metres (21–24 ft) long. Two species are named, T. machikanensis from Japan and T. taiwanicus from Taiwan, both originally described as members of the genus Tomistoma.
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.
Harpacochampsa is a poorly known Early Miocene crocodilian from the Bullock Creek lagerstätte of the Northern Territory, Australia. The current specimen consists of a partial skull and fragments of a long, slender snout reminiscent of that of a false gharial, demonstrating that it was a piscivore in life.
Aktiogavialis is an extinct genus of crocodylian that lived from the Oligocene until the Miocene in what is now the Caribbean. Two species have been described: Aktiogavialis puertoricensis from the Middle Oligocene of Puerto Rico and Aktiogavialis caribesi from the Huayquerian of the Late Miocene of Venezuela.
Dollosuchus is an extinct monospecific genus of tomistomine crocodilian originally named as a species of Gavialis. It is a basal form possibly related to Kentisuchus, according to several phylogenetic analyses that have been conducted in recent years, and is the oldest known tomistomine to date. Fossils have been found from Belgium and the United Kingdom. It had large supratemporal fenestrae in relation to its orbits, similar to Kentisuchus and Thecachampsa.
Eogavialis is an extinct genus of eusuchian crocodylomorph, usually regarded as a gavialoid crocodylian. It superficially resembles Tomistoma schlegelii, the extant false gharial, and consequently material from the genus was originally referred to Tomistoma. Indeed, it was not until 1982 that the name Eogavialis was constructed after it was realised that the specimens were from a more basal form.
Eothoracosaurus is an extinct monospecific genus of eusuchian crocodylomorphs found in Eastern United States which existed during the Late Cretaceous period. Eothoracosaurus is considered to belong to an informally named clade called the "thoracosaurs", named after the closely related Thoracosaurus. Thoracosaurs in general were traditionally thought to be related to the modern false gharial, largely because the nasal bones contact the premaxillae, but phylogenetic work starting in the 1990s instead supported affinities within gavialoid exclusive of such forms. Even more recent phylogenetic studies suggest that thoracosaurs might instead be non-crocodilian eusuchians.
Euthecodon is an extinct genus of long-snouted crocodile. It was common throughout much of Africa during the Neogene, with fossils being especially common in Kenya, Ethiopia, and Libya. Although superficially resembling that of gharials, the long snout was a trait developed independently from that of other crocodilians and suggests a diet of primarily fish. Euthecodon coexisted with a wide range of other crocodiles in the areas it inhabited before eventually going extinct during the Pleistocene.
Gryposuchus is an extinct genus of gavialid crocodilian. Fossils have been found from Argentina, Colombia, Venezuela, Brazil and the Peruvian Amazon. The genus existed during the Miocene epoch. One recently described species, G. croizati, grew to an estimated length of 10 metres (33 ft). Gryposuchus is the type genus of the subfamily Gryposuchinae, although a 2018 study indicates that Gryposuchinae and Gryposuchus might be paraphyletic and rather an evolutionary grade towards the gharial.
Ikanogavialis is an extinct genus of gavialid crocodilian. Fossils have been found in the Urumaco Formation in Urumaco, Venezuela and the Solimões Formation of Brazil. The strata from which remains are found are late Miocene in age, rather than Pliocene as was once thought. A possible member of this genus survived into the Late Holocene on Muyua or Woodlark Island in Papua New Guinea.
Kentisuchus is an extinct genus of gavialoid crocodylian, traditionally regarded as a member of the subfamily Tomistominae. Fossils have been found from England and France that date back to the early Eocene. The genus has also been recorded from Ukraine, but it unclear whether specimens from Ukraine are referable to Kentisuchus.
Thoracosaurus is an extinct genus of long-snouted eusuchian which existed during the Late Cretaceous and Early Paleocene in North America and Europe.
Paratomistoma is an extinct monospecific genus of gavialoid crocodylian. It is based on the holotype specimen CGM 42188, a partial posterior skull and lower jaw discovered at Wadi Hitan, Egypt, in Middle Eocene-age rocks of the Gehannam Formation. The skull is unfused but considered morphologically mature. Paratomistoma was named in 2000 by Christopher Brochu and Philip Gingerich; the type species is P. courti in honor of Nicholas Court, who found CGM 42188. They performed a phylogenetic analysis and found Paratomistoma to be a derived member of Tomistominae, related to the false gharial. It may have been a marine or coastal crocodilian.
Prodiplocynodon is an extinct genus of basal crocodyloid crocodylian. It is one of the only crocodyloids known from the Cretaceous and existed during the Maastrichtian stage. The only species of Prodiplocynodon is the type species P. langi from the Lance Formation of Wyoming, known only from a single holotype skull lacking the lower jaw.
Thecachampsa is an extinct genus of gavialoid crocodylian, traditionally regarded as a member of the subfamily Tomistominae. Fossils have been found from the eastern United States in deposits of Miocene age. Those named in the 19th century were distinguished primarily by the shape of their teeth, and have since been combined with T. antiquus. More recently erected species were reassigned from other genera, although their assignment to Thecachampsa has since been questioned.
Gryposuchinae is an extinct subfamily of gavialid crocodylians. Gryposuchines lived mainly in the Miocene of South America. However, "Ikanogavialis" papuensis may have survived more recently, into the Late Pleistocene/Holocene. Most were long-snouted coastal forms. The group was named in 2007 and includes genera such as Gryposuchus and Aktiogavialis, although a 2018 study indicates that the group might be paraphyletic and rather an evolutionary grade towards the gharial.
Gavialoidea is one of three superfamilies of crocodylians, the other two being Alligatoroidea and Crocodyloidea. Although many extinct species are known, only the gharial Gavialis gangeticus and the false gharial Tomistoma schlegelii are alive today, with Hanyusuchus having become extinct in the last few centuries.
Noteosuchus is an extinct genus of basal rhynchosaur known from the earliest Triassic deposits of Eastern Cape Province, South Africa. It was first named by David Meredith Seares Watson in 1912 and the type species is Eosuchus colletti. The generic name Eosuchus is preoccupied by the generic name of Eosuchus lerichei Dollo, 1907, a gavialoid crocodilian known from northern France. Thus, an alternative generic name, Noteosuchus, was proposed by Robert Broom in 1925. The generic name erected by Broom (1925) is a compound, meaning "Not Eosuchus", while "Eosuchus" is derived from the name of Eos, the goddess of the dawn in Greek mythology, and suchus, Latinized from the Greek souchos, an Egyptian crocodile god, thus meaning "dawn crocodile". The specific name, colletti, honors Mr. Collett for the discovery of the holotype and only known specimen.
Tomistoma cairense is an extinct species of gavialoid crocodilian from the Lutetian stage of the Eocene era. It lived in North East Africa, especially Egypt. Remains of T. cairense have been found in the Mokattam Formation, in Mokattam, Egypt. Tomistoma cairense did not have a Maxilla process within their lacrimal gland, whereas all extant (living) crocodilians do.