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.
|Indian gharial, Gavialis gangeticus|
Gavialoidea contains the family Gavialidae and several more basal extinct forms such as Thoracosaurus and Eosuchus. Within Gavialidae are two subfamilies: Gavialinae, which includes the living gharial, and Gryposuchinae, which includes several extinct forms such as Gryposuchus and Aktiogavialis.
In addition to these groups, recent molecular studies consistently indicate that the false gharial (and by inference other related extinct forms) traditionally viewed as belonging to the crocodylian subfamily Tomistominae actually belong to Gavialoidea. As its name suggests, the false gharial was once thought to be only distantly related to the gharial despite its similar appearance. The false gharial and other tomistomines were traditionally classified within the superfamily Crocodyloidea as close relatives of crocodiles. This classification is based on morphological evidence, which, when incorporated into phylogenetic analyses, often place the group within Crocodyloidea.
Below is a cladogram from Vélez-Juarbe et al. (2007) showing the phylogenetic relationships of members of Gavialoidea, excluding tomistomines.
Aegyptosuchidae is an extinct family of eusuchian crocodyliforms from the Cretaceous period of Africa. They are characterized by their large size and flat heads. The family includes two genera, Aegyptosuchus and Aegisuchus.Allodaposuchus
Allodaposuchus is an extinct genus of crocodyliforms that includes four species that lived in what is now southern Europe during the Campanian and Maastrichtian stages of the Late Cretaceous. Although generally classified as a non-crocodylian 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 Spain, Romania, and France.Arambourgia
Arambourgia is an extinct genus of alligatorine crocodylian from Europe. It was named in 1905 and synonymized with Allognathosuchus haupti in 1990, but later reassigned as its own genus once again in 2004. It is thought to have been closely related to Hispanochampsa and Procaimanoidea. Arambourgia was likely to have been part of an early dispersal event of alligatorines from North America to Europe during the Eocene epoch. Arambourgia had non-serrated teeth and a deep altirostral snout, unlike the flatter snouts of most other alligatorids.Argochampsa
Argochampsa (meaning "Argo crocodile", in reference to the mythological Argo of Jason) 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.Argochampsa is based on OCP DEK-GE 1201, a nearly complete skull from the Oulad Abdoun Basin, in the vicinity of Khouribga, Morocco. The skull, 43.3 centimeters long (17.0 in), had a long, narrow snout, marking it as a longirostrine crocodilian; the snout made up about 70% of the skull's length. The premaxillae at the tip of the snout were downturned, and the tip somewhat squared off, with the first few tooth positions in a straight line perpendicular to the long axis of the skull. There were five teeth in each premaxilla and 26 in each maxilla (the main tooth-bearing bone of the upper jaw). The nasal bones were fused, and there were several short diastemas or gaps in the tooth row at the tip of the snout. More recently, material from the lower jaw, neck and back vertebrae, the upper arm, and armor has been recovered.Hua and Jouve performed a cladistic analysis incorporating their new taxon, and found Argochampsa to be a gavialoid, but outside of the clade Gavialidae. They noted that the snout shape of Argochampsa is unusual among crocodilians, with only pholidosaurids and Terminonaris having similarly shaped snout tips, and suggested that this layout may have facilitated precise occlusion. Argochampsa lived in an environment otherwise dominated by dyrosaurid marine crocodyliforms.Argochampsa krebsi was included in the study on the phylogenetic relationships of putative fossil gavialoids published by Lee & Yates (2018). The authors considered it most likely that Argochampsa was not a gavialoid, or even a crocodylian, but rather a member of the clade of non-crocodylian eusuchians that also included the genera Eogavialis, Eosuchus, Eothoracosaurus and Thoracosaurus.Borealosuchus
Borealosuchus (meaning "boreal crocodile") is an extinct genus of crocodylians that lived from the Late Cretaceous to the Eocene in North America. It was named by Chris Brochu in 1997 for several species that had been assigned to Leidyosuchus. The species assigned to it are:
B. sternbergii, the type species, from the Maastrichtian (Late Cretaceous) of Colorado, Montana, North Dakota, South Dakota, and Wyoming; B. acutidentatus, from the Paleocene of Saskatchewan; B. formidabilis, from the Paleocene of North Dakota; B. griffithi, from the Paleocene of Alberta; and B. wilsoni, from the Eocene of Wyoming. B. formidabilis is particularly well-known, represented by the remains of many individuals from the Wannagan Creek site in North Dakota.Borealosuchus was a mid-sized crocodylian; B. acutidentatus reached up to 2.8 metres (9.2 ft) in length with a 36 centimetres (14 in) skull.Coelosuchus
Coelosuchus is an extinct genus of goniopholidid mesoeucrocodylian. Fossils have been found from the Graneros Shale of the Benton Group in Wyoming, and are of Cenomanian age. It was slightly over 1 meter in length.Eogavialis
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
Eothoracosaurus is an extinct genus of eusuchian crocodylomorph which existed during the Late Cretaceous and early Paleocene. The animal is usually regarded as a gavialoid crocodilian, though the phylogenetic study published by Lee & Yates (2018) indicated that it was more likely to be a non-crocodilian eusuchian. If the animal was a gavialoid, it was one of the earliest and most basal gavialoids known.
Fossils are present from the Ripley Formation in Mississippi and date back to the early Maastrichtian stage of the Late Cretaceous. Some fragmentary material from the Coon Creek Formation of western Tennessee dating back to the late Campanian (slightly older than the specimens from Mississippi) has been referred to Eothoracosaurus as well. The Coon Creek Formation seems to have been deposited in a marine setting, with oceanic fauna such as the sharks Otodus and Squalicorax, the sea turtle Toxochelys, and mosasaurs including Plioplatecarpus and Globidens present from these strata. This suggests that Eothoracosaurus may also have led a marine lifestyle. Certain aspects of the cranial morphology of known specimens, such as a long anterior frontal process and widely spaced supratemporal fenestrae, distinguish it from the closely related Thoracosaurus neocesariensis from the late Maastrichtian and early Paleocene of New Jersey.Eusuchia
The Eusuchia ("true crocodiles") are a clade of crocodylomorphs that first appears in the Early Cretaceous with Hylaeochampsa. Along with Dyrosauridae and Sebecosuchia, they were the only crocodyliformes who survived the K-T extinction. Since the other two clades died out 35 and 11 million years ago, all living crocodilian species are eusuchians, as are many extinct forms.Gavialidae
Gavialidae is a family of reptiles within the order Crocodilia. Gavialidae have conventionally consisted of only one surviving species, the gharial (Gavialis gangeticus), which is native to India and Nepal. Many extinct species are also known. The false gharial (Tomistoma schlegelii) has usually been thought to be a member of the family Crocodylidae based on several characters including skull morphology, but has sometimes been viewed as a member of this family due to general similarities in morphology and habit. However, numerous molecular studies have consistently shown the two species to be very closely related, supporting the view that they are in the same family.Gavialids are large semiaquatic reptiles, resembling crocodiles, but with much thinner snouts. The thin snout is used to catch fish. Gavialids lack the jaw strength to capture the large mammalian prey favoured by crocodiles and alligators of similar size.Gryposuchinae
Gryposuchinae is an extinct subfamily of gavialid crocodylians. Gryposuchines lived mainly in South America during the Oligocene and Miocene epochs, though "Gavialis" papuensis 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.Harpacochampsa
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 slender snout reminiscent of that of a false gharial. It is tentatively placed within Mekosuchinae, though some experts disagree with this, as H. camfieldensis would be the only known mekosuchine with a long, thin snout. Its long snout demonstrates that it was a piscivore in life.Maroccosuchus
Maroccosuchus zennaroi is an extinct tomistomine crocodylian from the early Eocene of Morocco. A recent phylogenetic assessment of Tomistoninae determined that M. zennaroi is the basalmost tomistomine.Nannosuchus
Nannosuchus (meaning "dwarf crocodile") is an extinct genus of goniopholidid mesoeucrocodylian from the Berriasian of England.Neosuchia
Neosuchia is a clade within Mesoeucrocodylia that includes all modern extant crocodilians and their closest fossil relatives. It is defined as the most inclusive clade containing all crocodylomorphs more closely related to Crocodylus niloticus (the Nile Crocodile) than to Notosuchus terrestris. Neosuchia is very diverse and may be polyphyletic, as the clade has undergone many revisions since it was first named in 1988. Neosuchians first appear in the Early Jurassic with the earliest known goniopholid Calsoyasuchus, which lived during the Sinemurian and Pliensbachian stages.Symptosuchus
Symptosuchus is an extinct genus of goniopholidid mesoeucrocodylian. It is known from the Late Cretaceous of Argentina. Argentine paleontologist Florentino Ameghino named the genus in 1899, along with the type species S. contortidens. It was formally described by Carlos Rusconi in 1934.Thoracosaurus
Thoracosaurus is an extinct genus of eusuchian crocodylomorph which existed during the Late Cretaceous and early Paleocene. The animal is usually regarded as a gavialoid crocodilian, though the phylogenetic study published by Lee & Yates (2018) suggests that it might have been a non-crocodylian eusuchian. The genus contains the species Thoracosaurus neocesariensis in North America and Thoracosaurus isorhynchus (T. macrorhynchus being a junior synonym of T. isorhynchus) in Europe. A number of species have been referred to this genus, but most are dubious.Thoracosaurus scanicus was a fairly large gavialoid, with a length of more than 4.4 m (14.4 ft) and a 55 cm skull.Tomistominae
Tomistominae is a subfamily of crocodylians that includes one living species, the false gharial. Many more extinct species are known, extending the range of the subfamily back to the Eocene epoch. In contrast to the false gharial, which is a freshwater species that lives only in southeast Asia, extinct tomistomines had a global distribution and lived in estuaries and along coastlines.
The classification of tomistomines among Crocodylia has been in flux; while traditionally thought to be within Crocodyloidea, molecular evidence indicates that they are more closely related to true gharials as members of Gavialoidea.