Ornithosuchus longidens
length 3 meters
late Carnian of  north-central Pangea
drawing by Steve Kirk - Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals, ed.. Barry Cox

The Ornithosuchia were medium-to-large (upto 3.3 metres) carnivores, with mouths full of wicked over-sized teeth.  They were clearly active hunters, and the hindlimbs were much larger than the forelimbs.  It used to be thought that this meant the creature was a total biped (like the large carnivorous dinosaurs for example), but they were more probably only faculative bipeds; that is although they were able to run on their back legs when they wanted to, they probably preferred quadrapedal locomotion.

They have a rather short skull, with the orbits laterally directed (in other words the eyes were on the side of the head), small supratemporal and large infratemporal openings in the side of the skull (these were for the attachment of jaw muscles). The skull and hence the upper jaw is clearly longer than the lower jaw, with a conspicuous constriction in the premaxilla.  This seems to indicate a sort of mobile joint; the same adaptation is also found in primitive Proterosuchian thecodonts of the early Triassic and Dilophosaurian theropod dinosaurs of the early Jurassic.  The teeth are backwardly recurved, perhaps to prevent struggling prey getting free.

Technically, the Ornithosuchids are distinguished from most other advanced thecodonts (the Psuedosuchia) by a different sort of ankle structure: the so-called "Crocodile-Reversed" (CR) joint.  Both the Psuedosuchian "Crocodile-Normal" (CN) and the Ornithosuchia "Crocodile-Reversed" (CR) ball-and-socket ankle joints were ways of increasing the mobility of the animal; both had a definite advantage over the older Protosuchian/Erythosuchian ankle, which was only a simple hinge.

 The Ornithosuchids were also one of a number of groups of Triassic archosaurs that individually evolved a fully-erect (bird- and mammal-like) limb posture, as opposed to the crawling and semi-erect postures of more primitive thecodonts, and the semi-erect posture of crocodiles today.  Ornithosuchus itself was originally considered a psuedosuchian thecodont, then reclassified as an early theropod dinosaur, then later as a dinosaur-uncle, and is now considered to be a side-branch on the line to Crocodiles.  Well, who knows.

So far, Ornithosuchid fossil remains are known only from Scotland and Argentina, although it can be assumed their distribution was much greater.

 

Ornithosuchus longidens (Huxley 1877)

horizon: Lossiemouth Beds  (late Carnian)
locality: Elgin, Scotland (central Laurasia)
known material: skull and postcrania
size: total length to 3.3 metres
model from the Elgin Museum

comments: The first member of this family to be described, this was a large animal, without doubt the top preditor of its environment.  Originally reconstructed as a biped, and certainly capable of bipdal locomation, it probably spent most of its time on all fours. The skull is strikingly similiar to that of large theropod dinosaurs like Tyrannosaurus, leading to the suggestion (now discredited) that Ornithosuchids were actually primitive Theropod dinosaurs.

The back of the skull has well defined occipital crests, and the lower border of the orbit (eye socket) reaches a lower than in the later and more specialised genus Riojosuchus

Although at one time believed to be a primitive member of the dinosauria, Ornithosuchus, like other members of its family, have a number of primitive (plesiomorphic) features, such as a double row of bony plates down its back a short broad pelvis attached to the backbone by only 3 vertebrae, and five toes on each hind foot (as opposed to three in the case of theropod dinosaurs).  These characteristics are shared by most thecodonts (basal archosaurs), and show that Ornithosuchus is only distantly related to the dinosaurs.  The Dinosaur-like parallels recall instead Berg's and Popplebaum's concepts of "Prophetic Forms".

Life reconstruction at top of page.

Venaticosaurus rusconii Bonaparte 1971
horizon: Middle Ischigualasto Formation  (late Carnian)
locality: San Juan Province, Argentina (West Gondwana)
known material: Incomplete skull with articulated jaws, incomplete forelimb, some osteoderms
size: Lower jaw: 26 cm; Overall length: about 2 metres;

comments: A typical Ornithosuchid thecodont; very similiar to Ornithosuchus (Late Carnian) and Riojasuchus (Rhaetian), from which it differed largely in minor details of the jaw and skull.  The teeth are serrated, making them more efficient cutting tools, and each jaw carries two large canine-like teeth.

This genus differs from its probably descendent Riojasuchus in that the maxillary teeth clearly stronger; the lower jaws proportionally higher, the mandibular fenestra larger, and the lower border of the orbit reaches a lower point.  Although very similiar to Ornithosuchus, Venaticosaurus differs from the Elgin genus in the stronger constriction of the premaxilla, and in the narrower preorbital region. The only known specimen is not very well preserved.  Venaticosuchus has been found in levels with cynodont  therapsids and triaolestid crocodylomorphs.   [Ref  Bonaparte, p.670].  Scroll up for life reconstruction.

comments: Very similiar to Ornithosuchus. However, Riojasuchus has some characters that are apparently more specialized (as would be expected from its later occurance); such as the extremely dorsal position of the supraoccipital region, with the resultant disappearance of the occipital crests, well defined in Ornithosuchus.  The acetabulum is almost closed, with a very rudimentary fenestration; and no preacetabular process in the ilium blade. It has been found associated with the crocodylomorphs Hemiprotosuchius and Pseudhesperosuchus, and Tritylodont therapsids. (ref: Bonaparte).

- Ornithosuchia - Links -

Ornithosuchidae - the only other listing on the Web apart from this page devoted entirely to the Ornithosuchidae

Riojasuchus tenuiceps - short description, plus image of model of skull which you can order from here

Great Triassic Assemblages Pt 1 - The Chinle and Newark- Professor P. E. Olsen. - includes a little bit of material on Ornithosuchus

Archosauriformes - has material on archosaurian relationships, also two alternative cladograms of Ornithosuchid relationships - argues against the Ornithosuchidae being closer to the Pseudosuchia than to the Dinosaurs

- Ornithosuchia - References -

J.  F. Bonaparte", 1970 "Annoitated List of the South American Traissic Tetrapods", in Second Gondwana Symposium, Proceedings and Papers (Council of Scientific and Inustrial Research, Pretoria).  The drawings of the Venaticosaurus and Riojosuchus skulls are from this paper.

Collins/MacMillan Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals: Barry Cox, R.J.G. Savage, and Brian Gardiner, Dougal Dixon, 1988

Palaeos Page (incorporates some of this material, plus a lot of additional material)

Kingdoms of Life > Animalia > Vertebrata > Tetrapoda > Reptilia/Sauropsida > Archosauria > Thecodontia

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