Ornithosuchidae
Encyclopedia
Ornithosuchidae is an extinct family
of reptiles from the Triassic
period that were distantly related to crocodilia
ns. They are classified as crurotarsan archosaur
s. Ornithosuchids were quadrupedal and facultatively bipedal, meaning they had the ability to walk on two legs for short periods of time. They have distinctive downturned snouts and uniquely shaped ankle bones that distinguish them from other archosaurs. Ornithosuchids were geographically widespread during the Carnian
and Norian
stages of the Late Triassic
. Three genera, Ornithosuchus
, Venaticosuchus
and Riojasuchus
are presently known. The family was first erected by German paleontologist Friedrich von Huene
in 1914.
, or gap between the teeth. When the jaw is closed, two large curved dentary teeth fit into the diastema, which is positioned between the premaxilla
and maxilla
. There are two shallow depressions on the wall of the diastema to accommodate these teeth. The large dentary teeth of Ornithosuchus and Riojasuchus are placed behind a smaller procumbent dentary tooth that sticks out from the jaw. This type of tooth position is not seen in any other basal archosaurs. Another characteristic feature of ornithosuchids is their unusual downturned, overhanging snout, seen in Riojasuchus and Venaticosuchus, but not Ornithosuchus.
Several other features distinguish ornithosuchids from all other early archosaurs. Ornithosuchus and Riojasuchus both possess a small fenestra, or hole, between the palatine
and pterygoid bones of the palate
. The contact between the nasal
and prefrontal bone
s of the skull is small or absent, excluded by a large contact between the frontals
and lacrimals
. In other archosaurs, including rauisuchians, aetosaur
s, pterosaur
s, and dinosauromorphs, the nasal-prefrontal contact separates the frontal from the lacrimal.
Unlike most other early archosaurs, the pedal ungual
s (the distalmost bones of the feet that form claws) are laterally compressed. They are sharp and recurved. The unguals are very deep, being taller than they are long, especially on the inner digits. This type of claw is not seen in any other Triassic archosaur except for pterosaurs.
Major archosaur groups have often been distinguised from each other based on the structure of their ankles. In most crurotarsans, the astragalus
has a convex projection that fits into a concave space in the calcaneum. This condition is often referred to as a "crocodile-normal" ankle, as it is the most common ankle type in crurotarsans. Ornithosuchids are unique among crurotarsans, and all other archosaurs, in their possession of a "crocodile-reversed" ankle. In a "crocodile-reversed" ankle, the placement of the concavity is reversed: instead of being on the calcaneum, it is on the astragalus. In ornithosuchids, the calcaneum bears a convex projection that is analogous to the convex projection on the "crocodile-normal" astragalus. The "crocodile-reversed" ankle is also seen in Euparkeria
, a basal Triassic archosauriform that is classified outside Archosauria.
Suchia
, which includes aetosaurs, rauisuchians, and crocodylomorphs. Below is a cladogram based on Nesbitt & Norell (2006), Nesbitt (2007), and Brusatte et al. (2010), showing the placement of Ornithosuchidae within Archosauria.
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
of reptiles from the Triassic
Triassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
period that were distantly related to crocodilia
Crocodilia
Crocodilia is an order of large reptiles that appeared about 84 million years ago in the late Cretaceous Period . They are the closest living relatives of birds, as the two groups are the only known survivors of the Archosauria...
ns. They are classified as crurotarsan archosaur
Archosaur
Archosaurs are a group of diapsid amniotes whose living representatives consist of modern birds and crocodilians. This group also includes all extinct non-avian dinosaurs, many extinct crocodilian relatives, and pterosaurs. Archosauria, the archosaur clade, is a crown group that includes the most...
s. Ornithosuchids were quadrupedal and facultatively bipedal, meaning they had the ability to walk on two legs for short periods of time. They have distinctive downturned snouts and uniquely shaped ankle bones that distinguish them from other archosaurs. Ornithosuchids were geographically widespread during the Carnian
Carnian
The Carnian is the lowermost stage of the Upper Triassic series . It lasted from about 228.7 till 216.5 million years ago . The Carnian is preceded by the Ladinian and is followed by the Norian...
and Norian
Norian
The Norian is a division of the Triassic geological period. It has the rank of an age or stage . The Norian lasted from 216.5 ± 2.0 to 203.6 ± 1.5 million years ago. It was preceded by the Carnian and succeeded by the Rhaetian.-Stratigraphic definitions:The Norian was named after the Noric Alps in...
stages of the Late Triassic
Late Triassic
The Late Triassic is in the geologic timescale the third and final of three epochs of the Triassic period. The corresponding series is known as the Upper Triassic. In the past it was sometimes called the Keuper, after a German lithostratigraphic group that has a roughly corresponding age...
. Three genera, Ornithosuchus
Ornithosuchus
Ornithosuchus is an extinct genus of crurotarsan from the Late Triassic Lossiemouth Sandstone of Scotland...
, Venaticosuchus
Venaticosuchus
Venaticosuchus is a genus of Late Triassic quadrupedal crurotarsan archosaur. Originally it was thought to be the ancestor to the carnosaur dinosaurs ; however, now it is known to be more closely related to crocodilians than dinosaurs...
and Riojasuchus
Riojasuchus
Riojasuchus is an extinct genus of quadrupedal crurotarsan archosaur. Riojasuchus is a member of Ornithosuchidae, a family of facultatively bipedal carnivores that were geographically widespread during the Late Triassic. Two other genera, Ornithosuchus and Venaticosuchus, are currently known....
are presently known. The family was first erected by German paleontologist Friedrich von Huene
Friedrich von Huene
Friedrich von Huene was a German paleontologist who named more dinosaurs in the early 20th century than anyone else in Europe.-Biography:...
in 1914.
Description
Ornithosuchids can be identified by the presence of an arched diastemaDiastema (dentistry)
Diastema is a space or gap between two teeth. Many species of mammals have diastemata as a normal feature, most commonly between the incisors and molars.-In humans:...
, or gap between the teeth. When the jaw is closed, two large curved dentary teeth fit into the diastema, which is positioned between the premaxilla
Premaxilla
The incisive bone is the portion of the maxilla adjacent to the incisors. It is a pair of small cranial bones at the very tip of the jaws of many animals, usually bearing teeth, but not always. They are connected to the maxilla and the nasals....
and maxilla
Maxilla
The maxilla is a fusion of two bones along the palatal fissure that form the upper jaw. This is similar to the mandible , which is also a fusion of two halves at the mental symphysis. Sometimes The maxilla (plural: maxillae) is a fusion of two bones along the palatal fissure that form the upper...
. There are two shallow depressions on the wall of the diastema to accommodate these teeth. The large dentary teeth of Ornithosuchus and Riojasuchus are placed behind a smaller procumbent dentary tooth that sticks out from the jaw. This type of tooth position is not seen in any other basal archosaurs. Another characteristic feature of ornithosuchids is their unusual downturned, overhanging snout, seen in Riojasuchus and Venaticosuchus, but not Ornithosuchus.
Several other features distinguish ornithosuchids from all other early archosaurs. Ornithosuchus and Riojasuchus both possess a small fenestra, or hole, between the palatine
Palatine bone
The palatine bone is a bone in many species of the animal kingdom, commonly termed the palatum .-Human anatomy:...
and pterygoid bones of the palate
Palate
The palate is the roof of the mouth in humans and other mammals. It separates the oral cavity from the nasal cavity. A similar structure is found in crocodilians, but, in most other tetrapods, the oral and nasal cavities are not truly separate. The palate is divided into two parts, the anterior...
. The contact between the nasal
Nasal bone
The nasal bones are two small oblong bones, varying in size and form in different individuals; they are placed side by side at the middle and upper part of the face, and form, by their junction, "the bridge" of the nose.Each has two surfaces and four borders....
and prefrontal bone
Prefrontal bone
The prefrontal bone is a bone separating the lacrimal and frontal bones in many tetrapod skulls. It first evolved in the sarcopterygian clade Rhipidistia, which includes lungfish and the Tetrapodomorpha. The prefrontal is found in most modern and extinct lungfish, amphibians and reptiles...
s of the skull is small or absent, excluded by a large contact between the frontals
Frontal bone
The frontal bone is a bone in the human skull that resembles a cockleshell in form, and consists of two portions:* a vertical portion, the squama frontalis, corresponding with the region of the forehead....
and lacrimals
Lacrimal bone
The lacrimal bone, the smallest and most fragile bone of the face, is situated at the front part of the medial wall of the orbit. It has two surfaces and four borders.-Lateral or orbital surface:...
. In other archosaurs, including rauisuchians, aetosaur
Aetosaur
Aetosaurs are an extinct order of heavily armoured, medium- to large-sized Late Triassic herbivorous archosaurs. They have small heads, upturned snouts, erect limbs, and a body covered by plate-like scutes. All aetosaurs belong to the family Stagonolepididae...
s, pterosaur
Pterosaur
Pterosaurs were flying reptiles of the clade or order Pterosauria. They existed from the late Triassic to the end of the Cretaceous Period . Pterosaurs are the earliest vertebrates known to have evolved powered flight...
s, and dinosauromorphs, the nasal-prefrontal contact separates the frontal from the lacrimal.
Unlike most other early archosaurs, the pedal ungual
Ungual
An ungual is a highly modified distal toe bone which ends in a hoof, claw, or nail. Elephants and other ungulates have ungual phalanges, as did the sauropods and horned dinosaurs. A claw is a highly modified ungual phalange.As an adjective, ungual means related to nail, as in periungual .-External...
s (the distalmost bones of the feet that form claws) are laterally compressed. They are sharp and recurved. The unguals are very deep, being taller than they are long, especially on the inner digits. This type of claw is not seen in any other Triassic archosaur except for pterosaurs.
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Major archosaur groups have often been distinguised from each other based on the structure of their ankles. In most crurotarsans, the astragalus
Astragalus
Astragalus is a large genus of about 3,000 species of herbs and small shrubs, belonging to the legume family Fabaceae, subfamily Faboideae. The genus is native to temperate regions of the Northern Hemisphere...
has a convex projection that fits into a concave space in the calcaneum. This condition is often referred to as a "crocodile-normal" ankle, as it is the most common ankle type in crurotarsans. Ornithosuchids are unique among crurotarsans, and all other archosaurs, in their possession of a "crocodile-reversed" ankle. In a "crocodile-reversed" ankle, the placement of the concavity is reversed: instead of being on the calcaneum, it is on the astragalus. In ornithosuchids, the calcaneum bears a convex projection that is analogous to the convex projection on the "crocodile-normal" astragalus. The "crocodile-reversed" ankle is also seen in Euparkeria
Euparkeria
Euparkeria was a small African reptile of the early Triassic period between 248-245 million years ago, close to the ancestry of the archosaurs.- Palaeobiology :...
, a basal Triassic archosauriform that is classified outside Archosauria.
Phylogeny
Ornithosuchidae is generally considered to be within the larger cladeClade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
Suchia
Suchia
Suchia is a clade of archosaurs that includes all pseudosuchians except ornithosuchids. It includes crocodilians and their extinct relatives. Paul Sereno defined Suchia as the least inclusive clade containing Aetosaurus ferratus, Rauisuchus tiradentes, Prestosuchus chiniquensis, Gracilisuchus...
, which includes aetosaurs, rauisuchians, and crocodylomorphs. Below is a cladogram based on Nesbitt & Norell (2006), Nesbitt (2007), and Brusatte et al. (2010), showing the placement of Ornithosuchidae within Archosauria.