''Sphenosuchus'' ("wedge crocodile") is an extinct

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial n ...

crocodylomorph Crocodylomorpha is a group of pseudosuchian archosaurs that includes the crocodilians and their extinct relatives. They were the only members of Pseudosuchia to survive the end-Triassic extinction. During Mesozoic and early Cenozoic times, cro ...

from the

Early Jurassic The Early Jurassic Epoch (in chronostratigraphy corresponding to the Lower Jurassic Series) is the earliest of three epochs of the Jurassic Period. The Early Jurassic starts immediately after the Triassic-Jurassic extinction event, 201.3 Ma ...

Elliot Formation The Elliot Formation is a geological formation and forms part of the Stormberg Group, the uppermost geological group that comprises the greater Karoo Supergroup. Outcrops of the Elliot Formation have been found in the northern Eastern Cape, south ...

South Africa South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. It is bounded to the south by of coastline that stretch along the South Atlantic and Indian Oceans; to the north by the neighbouring count ...

, discovered and described early in the 20th century. The skull is preserved very well but other than elements of the forelimb and isolated parts of the hind limb, the ''Sphenosuchus'' material is incomplete. It was probably

quadrupedal Quadrupedalism is a form of locomotion where four limbs are used to bear weight and move around. An animal or machine that usually maintains a four-legged posture and moves using all four limbs is said to be a quadruped (from Latin ''quattuo ...

, but may have been a

facultative biped A facultative biped is an animal that is capable of walking or running on two legs (bipedal), as a response to exceptional circumstances ( facultative), while normally walking or running on four limbs or more. In contrast, obligate bipedalism is ...

. ''Sphenosuchus'' was first thoroughly described in 1972 by the British palaeontologist

Alick Walker Alick Donald Walker (26 October 1925 – 4 December 1999) was a British palaeontologist, after whom the ''Alwalkeria'' genus of dinosaur is named. He was born in Skirpenbeck, near York and attended Pocklington School from 1936 to 1943. He began a ...

, in a paper in the journal ''Nature''. Walker suggested, based on detailed (but still preliminary at that time) studies of the skull of ''Sphenosuchus'' and modern

birds Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweig ...

, that crocodylomorphs and

might share an immediate

common ancestor Common descent is a concept in evolutionary biology applicable when one species is the ancestor of two or more species later in time. All living beings are in fact descendants of a unique ancestor commonly referred to as the last universal comm ...

. Walker recanted his hypothesis in 1985, but restated and elaborated on it (in essence 'de-recanting') in a monograph published in 1990, which provided the most comprehensive description and discussion of ''Sphenosuchus'' yet published. Broom believed in 1927 with the evidence present in the specimens that ''Sphenosuchus'' is a

Pseudosuchian Pseudosuchia is one of two major divisions of Archosauria, including living crocodilians and all archosaurs more closely related to crocodilians than to birds. Pseudosuchians are also informally known as "crocodilian-line archosaurs". Prior to ...

which is well along the line that leads to the true

Crocodiles Crocodiles (family Crocodylidae) or true crocodiles are large semiaquatic reptiles that live throughout the tropics in Africa, Asia, the Americas and Australia. The term crocodile is sometimes used even more loosely to include all extant m ...

. In a paper published by

Friedrich von Huene Friedrich von Huene, born Friedrich Richard von Hoinigen, (March 22, 1875 – April 4, 1969) was a German paleontologist who renamed more dinosaurs in the early 20th century than anyone else in Europe. He also made key contributions about v ...

he emphasizes ''Sphenosuchus'' as a very important stage of

crocodile Crocodiles (family Crocodylidae) or true crocodiles are large semiaquatic reptiles that live throughout the tropics in Africa, Asia, the Americas and Australia. The term crocodile is sometimes used even more loosely to include all extant ...

evolution.

Species

The

type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specimen( ...

, ''Sphenosuchus acutus'' is the only described species in this genus.

Description

Out of the early crocodylomorphs, ''Sphenosuchus'' was one of the largest. The skull was 192 mm in the length and the body an estimated total length of 1.4m. This genus is considered to have been

carnivorous A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose food and energy requirements derive from animal tissues (mainly muscle, fat and other ...

and

cursorial A cursorial organism is one that is adapted specifically to run. An animal can be considered cursorial if it has the ability to run fast (e.g. cheetah) or if it can keep a constant speed for a long distance (high endurance). "Cursorial" is often u ...

. The found specimen consists of a nearly perfect but slightly crushed skull, a shoulder girdle, and a few limb bones so most of the known features come from the skull. The primary head of the quadrate meets the prootic and

squamosal The squamosal is a skull bone found in most reptiles, amphibians, and birds. In fishes, it is also called the pterotic bone. In most tetrapods, the squamosal and quadratojugal bones form the cheek series of the skull. The bone forms an ancestral co ...

. The quadrate and

pterygoid Pterygoid, from the Greek for 'winglike', may refer to: * Pterygoid bone, a bone of the palate of many vertebrates * Pterygoid processes of the sphenoid bone ** Lateral pterygoid plate ** Medial pterygoid plate * Lateral pterygoid muscle * Med ...

are not fused to the

braincase In human anatomy, the neurocranium, also known as the braincase, brainpan, or brain-pan is the upper and back part of the skull, which forms a protective case around the brain. In the human skull, the neurocranium includes the calvaria or skul ...

and the basipterygoid articulation is free. The

dentary In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...

is not gracile and has anterior swelling. The parietals are fused together. The post temporal fenestrae are known for the ''Sphenosuchus'' with the sizes being very variable among early

Archosaurs Archosauria () is a clade of diapsids, with birds and crocodilians as the only living representatives. Archosaurs are broadly classified as reptiles, in the cladistic sense of the term which includes birds. Extinct archosaurs include non-avia ...

but rather small in size for ''Sphenosuchus'' Has a

scapula The scapula (plural scapulae or scapulas), also known as the shoulder blade, is the bone that connects the humerus (upper arm bone) with the clavicle (collar bone). Like their connected bones, the scapulae are paired, with each scapula on eithe ...

blade in a triangular shape. No

clavicles The clavicle, or collarbone, is a slender, S-shaped long bone approximately 6 inches (15 cm) long that serves as a strut between the shoulder blade and the sternum (breastbone). There are two clavicles, one on the left and one on the righ ...

present.

Metatarsal The metatarsal bones, or metatarsus, are a group of five long bones in the foot, located between the tarsal bones of the hind- and mid-foot and the phalanges of the toes. Lacking individual names, the metatarsal bones are numbered from the med ...

I is reduced, II and IV are symmetrical and III is the longest. The

nasals In phonetics, a nasal, also called a nasal occlusive or nasal stop in contrast with an oral stop or nasalized consonant, is an occlusive consonant produced with a lowered velum, allowing air to escape freely through the nose. The vast majority ...

are long and narrow and pass from near the plane passing through the front of the

orbits In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as a ...

to the extreme anterior points of the

snout A snout is the protruding portion of an animal's face, consisting of its nose, mouth, and jaw. In many animals, the structure is called a muzzle, rostrum, or proboscis. The wet furless surface around the nostrils of the nose of many mammals is ...

. The frontals are large relatively and help to form a small part of the upper orbital margin and a large portion of the upper

temporal fossa The temporal fossa is a fossa (shallow depression) on the side of the skull bounded by the temporal lines and terminating below the level of the zygomatic arch. Boundaries * Medial: frontal bone, parietal bone, temporal bone, and sphenoid bon ...

. The

jugal The jugal is a skull bone found in most reptiles, amphibians and birds. In mammals, the jugal is often called the malar or zygomatic. It is connected to the quadratojugal and maxilla, as well as other bones, which may vary by species. Anat ...

is a large bone forming the whole of the lower orbital and almost all of the lower temporal bar. The parietal is a good sized element forming nearly the entire intertemporal region along with the majority of the occiput. There is no parietal foramen present. The dentary is slender and moderate in length, it appears to have roughly fourteen

teeth A tooth ( : teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, te ...

with a third of them being larger than the others. Overall the skull is similar to those of crocodiles however it is slightly deeper. From one of the forelimbs it appears that ''Sphenosuchus'' has a

carpus In human anatomy, the wrist is variously defined as (1) the carpus or carpal bones, the complex of eight bones forming the proximal skeletal segment of the hand; "The wrist contains eight bones, roughly aligned in two rows, known as the carpal ...

with the

radius In classical geometry, a radius ( : radii) of a circle or sphere is any of the line segments from its center to its perimeter, and in more modern usage, it is also their length. The name comes from the latin ''radius'', meaning ray but also the ...

and

ulna The ulna (''pl''. ulnae or ulnas) is a long bone found in the forearm that stretches from the elbow to the smallest finger, and when in anatomical position, is found on the medial side of the forearm. That is, the ulna is on the same side of t ...

elongated and

metacarpal In human anatomy, the metacarpal bones or metacarpus form the intermediate part of the skeletal hand located between the phalanges of the fingers and the carpal bones of the wrist, which forms the connection to the forearm. The metacarpal bones ...

like in structure.

Specimens

A new specimen of ''Hesperosuchus agilis'' was found from the

Upper Triassic The Late Triassic is the third and final epoch of the Triassic Period in the geologic time scale, spanning the time between Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch and followed by the Early Jurassic Epoch. T ...

New Mexico ) , population_demonym = New Mexican ( es, Neomexicano, Neomejicano, Nuevo Mexicano) , seat = Santa Fe, New Mexico, Santa Fe , LargestCity = Albuquerque, New Mexico, Albuquerque , LargestMetro = Albuquerque metropolitan area, Tiguex , Offi ...

. According to Colbert ''Hesperosuchus'' is in a close relationship with ''Sphenosuchus'' and this assessment has been widely accepted since. There are several physical similarities between the two. The

maxilla The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The ...

of the specimen lacks a lateral

lamina Lamina may refer to: Science and technology * Planar lamina, a two-dimensional planar closed surface with mass and density, in mathematics * Laminar flow, (or streamline flow) occurs when a fluid flows in parallel layers, with no disruption betwe ...

that would conceal the medial wall of the fossa in lateral view similar to ''Sphenosuchus''. The quadrate is similar as well in that it has a distinct lateral ridge along the

anterior Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

margin. Another new specimen of an early

Crocodylomorph Crocodylomorpha is a group of pseudosuchian archosaurs that includes the crocodilians and their extinct relatives. They were the only members of Pseudosuchia to survive the end-Triassic extinction. During Mesozoic and early Cenozoic times, cro ...

was found in

Arizona Arizona ( ; nv, Hoozdo Hahoodzo ; ood, Alĭ ṣonak ) is a U.S. state, state in the Southwestern United States. It is the list of U.S. states and territories by area, 6th largest and the list of U.S. states and territories by population, 14 ...

at the

Petrified Forest National Park Petrified Forest National Park is an American national park in Navajo and Apache counties in northeastern Arizona. Named for its large deposits of petrified wood, the park covers about , encompassing semi-desert shrub steppe as well as highly ero ...

from the

. A major

synapomorphy In phylogenetics, an apomorphy (or derived trait) is a novel character or character state that has evolved from its ancestral form (or plesiomorphy). A synapomorphy is an apomorphy shared by two or more taxa and is therefore hypothesized to hav ...

shared by the specimen and ''Sphenosuchus'' is the swelling of the anterior end of the

. Parrish and his team constructed 27

parsimonious Occam's razor, Ockham's razor, or Ocham's razor ( la, novacula Occami), also known as the principle of parsimony or the law of parsimony ( la, lex parsimoniae), is the problem-solving principle that "entities should not be multiplied beyond neces ...

trees and in every one the new specimen was placed as the

sister group In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and ...

to ''Sphenosuchus''. The specimen was rather incomplete therefore if more of the fossil is to be found this could be subject to revision. Also there is a slight issue with the synapomorphy that relates the two so closely. The swelling of the denture could be in part an ontogenetic feature. However the lack of this feature in the other specimens up for debate to be related to the specimen suggests that is in fact

phylogenetically In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...

significant.

Classification

In Alick Walker's first paper looking at the origin of

and

crocodiles Crocodiles (family Crocodylidae) or true crocodiles are large semiaquatic reptiles that live throughout the tropics in Africa, Asia, the Americas and Australia. The term crocodile is sometimes used even more loosely to include all extant m ...

it is suggested that they could in fact have a close common ancestor with ''Sphenosuchus''. The evidence being similarities in several features including: quadrate articulation, inner ear regions, pneumatic spaces connected with the middle ear, the palatal structure, occiput and odd basipterygoid process, and the upper temporal bar positioning in the skull. According to these findings Walker thought that the conclusion that birds and crocodiles could be more closely related than previously thought could not be ignored. In 1990 Walker revised his previous work with a new, more comprehensive paper regarding ''Sphenosuchus'' and the relationship with modern crocodiles and birds. Several homologies were discussed. Main cavities in the crocodilian

skull The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, t ...

are also present in ''Sphenosuchus'', sometimes in a less clearly defined state. Certain pneumatic spaces in the ''Sphenosuchus'' skulls are not found in modern crocodiles but are of closer resemblance to cavities in the bird skull. The otic capsule of ''Sphenosuchus'' closely resembles those of birds and crocodiles. Modern crocodiles head is in the same morphological position as in ''Sphenosuchus'' although reduced in comparison. Due to these homologies Walker concludes that the most important steps of crocodylomorph

evolution Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...

, especially the skull, took place in Sphenosuchia and therefore they should be included in the same taxon as Protosuchia. In 1995 Johann Welman published a paper "Euparkia and the origin of birds". where he argues that while ''Sphenosuchus'' had been thought to potentially be related to birds he finds the brain case structures of ''Sphenosuchus'' to be too specialized to be the sister group of birds. Another feature he found to be different was the eustachian system. Crocodiles and ''Sphenosuchus'' have a median eustachian system while birds do not. The internal

carotid arteries In anatomy, the left and right common carotid arteries (carotids) (Entry "carotid"
in
facial nerve The facial nerve, also known as the seventh cranial nerve, cranial nerve VII, or simply CN VII, is a cranial nerve that emerges from the pons of the brainstem, controls the muscles of facial expression, and functions in the conveyance of ta ...

exits anteriorly to the otic capsule which is much more derived than birds; birds facial nerve passes between the two parts of the otic capsules. Welman finds that the evidence he presented makes it clear that crocodilomorphs are too specialized in a number of key characteristics to be closely related to birds.Welman, J. "Euparkeria and the origin of birds." South African Journal of Science 91.10 (1995): 533-537.

References

{{Taxonbar, from=Q3725154 Early Jurassic crocodylomorphs Terrestrial crocodylomorphs Jurassic reptiles of Africa Jurassic South Africa Fossils of South Africa Fossil taxa described in 1924 Prehistoric pseudosuchian genera