Orthosuchus
| Orthosuchus Temporal range: Late Triassic |
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| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Crocodyliformes |
| Informal group: |
†Protosuchia Nash, 1968 |
| Species | |
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Orthosuchus is an extinct genus of protosuchian crocodyliform that lived during the Late Triassic, about 201.6 to 189.6 million years ago. It was first discovered in 1963 in the Red Beds formation in the Qacha's Nek Province of Lesotho, southern Africa. The characteristics showed on its postcranial skeleton and the skull indicated that it is a Crocodyliform. The finding is significant since some of the characteristics found on this specimen were believed to be absent until Jurassic.
Orthosuchus has a body proportion similar to lizards, with a body length about 0.6 meters, and a flattened skull, a typical skull of crocodilian.
The external skull surface is covered randomly with small pits. The orbits are huge, with a complete dorsal roof made by the paired supraorbitals. The maxilla has sharp edge, which extends forward and covers some part of the lateral notch. The ears are protected by earflaps, which prevent water inflow to the otic recess when this animal is in water. The fossil resembles some features of a primitive crocodilian, one of them is the reduced antorbital fenestra. The quadratojugal is the backbone of the skull, which connects to the jugal and quadrate. The flattened head shape of Orthosuchus is made by the posterior quadrate contact, which is below the rear end of the squamosal. This form is a typical archosaurian characteristic that had lost in modern crocodiles, and also absent in teleosaurs. It developed a short secondary bony palate, with crocodilian featuring pterygoids. The elongated choana is located behind the secondary palate, which is made by the premaxilla and maxilla. In modern crocodiles, the choana is between the vomers and the anterior processes of pterygoids. The dentary forms the largest part of the lower jaw with some shallow pits, which indicated that the animal probably has 15-18 teeth, fewer teeth in the far back. The teeth are equal in size and similar in shape.
Orthosuchus has 24 vertebrae, and 8 of them are believed to be in the cervical region. All vertebrae appear to be amphicoelous. It does not have tall neural spine but the height of them decrease from head to tail. The vertebrae in the neck region are tightly bonded together. The ribs start at the twelfth vertebra, which supports the ilium. The tail consists of 8 vertebrae of different size and shape. The first one is in contact with the sacral ribs, three vertebrae at the far end of the tail are tiny in size, and the other four vertebrae form the middle of the tail. The ribs form antero-ventral and postero-dorsal flanges, which are for the muscle attachments.
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