| Sanjuansaurus | |
|---|---|
 | |
| Preserved bones of theholotype specimen | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Family: | †Herrerasauridae |
| Genus: | †Sanjuansaurus Alcober & Martinez,2010 |
| Species: | †S. gordilloi |
| Binomial name | |
| †Sanjuansaurus gordilloi Alcober & Martinez, 2010 | |
Sanjuansaurus ("San Juan Province lizard") is agenus ofherrerasauriddinosaur from theLate Triassic (Carnian)Ischigualasto Formation of theIschigualasto-Villa Unión Basin in northwestern Argentina.
Sanjuansaurus was named and described in2010 by Oscar Alcober and Ricardo Martinez. Thetype species was namedS. gordilloi after Raul Gordillo, the head fossil preparator and artist of the San Juan Museum. It is known from andbased on an associated and partially articulated partial skeleton (PVSJ 605) consisting of ajaw fragment, most of thevertebral column from theaxis to theanterior tail, theshoulder blades, anulna, part of thepelvis, most of thelong bones of the legs, and a few other bones.[1]
PVSJ 605 was discovered in 1994, in gray-green sandstone 40 meters above the base of theIschigualasto Formation, inIschigualasto Provincial Park inSan Juan, Argentina. An ash bed from the early part of the formation dates to approximately 231.4 Ma, during the lateCarnian Stage of the Late Triassic.[1] The original description indicated that the skeleton was from the earliest part of the Cancha de Bochas Member,[1] though later sources suggested that it was from the upper La Peña member.[2][3]
Sanjuansaurus was comparable in size to a medium-sizedHerrerasaurus, with athigh bone that was 395 millimetres (15.6 in) long and atibia that is 360 millimetres (14 in) in length (in the description paper the tibia is listed with 260 mm in length due to a typo).[1] Alcober and Martinez performed aphylogenetic analysis and foundSanjuansaurus to be a herrerasaurid.[1] It was determined thatSanjuansaurus andHerrerasaurus share many similarities in the morphology of the skull, neck vertebrae, back vertebrae, hip vertebrae, scapula, and the hip bones. Alcober and Martinez observed thatSanjuansaurus andStaurikosaurusshare many similarities in the morphology of the hip bones, and thetibia.[1] Thepubis ofSanjuansaurus, unlike in other herrerasaurids, points toward the cranium.
A diagnosis is a statement of the anatomical features of an organism (or group) that collectively distinguish it from all other organisms. Some, but not all, of the features in a diagnosis are also autapomorphies. An autapomorphy is a distinctive anatomical feature that is unique to a given organism or group.
According to Alcober and Martinez (2010),Sanjuansaurus can be distinguished based on the following characteristics:[1]
In the Ischigualasto Formation, dinosaurs constituted only about 6% of the total number of fossils,[4] but by the end of theTriassic Period, dinosaurs were becoming the dominant large land animals, and the other archosaurs and synapsids declined in variety and number.[5]
Studies suggest that thepaleoenvironment of the Ischigualasto Formation was a volcanically active floodplain covered by forests and subject to strong seasonal rainfalls. The climate was moist and warm,[6] though subject to seasonal variations.[7] Vegetation consisted offerns (Cladophlebis),horsetails, and giantconifers (Protojuniperoxylon). These plants formedhighland forests along the banks of rivers.[8]Sanjuansaurus lived in the jungles of Late TriassicSouth America alongside early dinosaurs,Eoraptor,Herrerasaurus,Chromogisaurus, andPanphagia, as well asSaurosuchus,[9] a giant land-livingrauisuchian (a quadrupedal meat eater with atheropod-like skull); the broadly similar but smallerVenaticosuchus, anornithosuchid; and the predatorychiniquodontids. Herbivores were much more abundant than carnivores and were represented byrhynchosaurs such asHyperodapedon (a beaked reptile);aetosaurs (spiny armored reptiles);kannemeyeriiddicynodonts (stocky, front-heavy beaked quadrupedal animals) such asIschigualastia; andtherapsidtraversodontids (somewhat similar in overall form to dicynodonts, but lacking beaks) such asExaeretodon. These non-dinosaurian herbivores were much more abundant than early ornithischian dinosaurs likePisanosaurus.[10]
