Describer

Reig, 1963

Time

Triassic Late Carnian

Classification

Saurischia Theropoda Herrerasauria Herrerasauridae

Diet

Carnivore

Fossilsite

Ischigualasto Formation, San Juan, Argentina

Length

3 meter

Info

Genus - Typespecies - Skull

Herrerasaurus is named after Victorino Herrera, the Andean farmer who first stumbled on its skeleton. It is one of the earliest known dinosaurs. a medium-sized, bipedal carnivore, it had sharp teeth, short arms, and three-fingered hands with curved claws.

Seemingly \\\\\\\"old- fashioned\\\\\\\" features of the leg and foot bones made scientist think Herrerasaurus more primitive than any in the two main groups, the Saurischia and the Ornithischia but in 1992 Paul Sereno and Fernando Novas proved Herrerasaurus was an early theropod, not a pre-saurichian, pre- ornithischian dinosaur.

The discovery of a complete skull revealed that it had a sliding lower jaw joint in common with some other theropods. Like most theropods Herrerasaurus had a small first toe that faced backwards instead of pointing forwards. Several skeletons, one complete skull, have give scientist a full picture of this creature. The skull of Herrerasaurus was long and narrow, with small nostril holes.

A flexible ( lower jaw) let the front half move against the rear half, to give a grasping bite. Herrerasaurus differs from Staurikosaurus in its considerably larger size (length of the femur 47.3 cm vs 22.9 cm in the respective holotypes.) and in a number of features of the postcranial skeleton (Reig, 1963; Benedetto, 1973).

3 partical skeletons, isolated postcrania, skull.

From: Reig, O.A. (1963). La presencia de dinosaurios saurisquios en los \\\\\\\"Estrados de Ischigualasto\\\\\\\" (Mesotriasico superior) de las provincias de San Juan y La Rioja (Republica Argentina). Ameghiniana 3, 3-20 [The presence of Saurischian Dinosaurs in the \\\\\\\"Ischigualasto beds\\\\\\\" (upper Middle Triassic) of the provinces of San Juan and La Rioja, Argentina.

_{Translated by Matthew T. Carrano University of Chicago, 2/98}

Herrerasaurus, n. gen.

Etymology

In honor of Don Victorino Herrera, settler of the Ischigualasto zone, guide and experienced collector, who was converted into an irreplaceable collaborator of the scientific undertakings developed in these pages.

Diagnosis

A carnosaur of slightly smaller size than Gryponyx africanus; robust, high premaxilla with three teeth; tall maxilla with eight teeth; robust, wide teeth surrounded by rounded alveoli. Antorbital fossa apparently very withdrawn from the nares. Dentary with twelve teeth; mandibular symphysis strong and taller than the rest of the alveolar ramus. Sacrum with three vertebrae. Short, tall ilium with very robust anterior spine, similar to Plateosaurus. Pubis almost as long as the tibia, nearly perpendicular to the vertebral axis, expanded at its distal end forming an extensive \\\\\\\"foot\\\\\\\" similar to that of Antrodemus. Ischium shorter than the pubis, similar to that of Plateosaurus. Gracile femur, slightly curved in the form of an S, with very clear greater trochanter and very distinct, aliform fourth trochanter more proximally located, in the upper 2/5 of the bone. Humerus longer than half the femur. Robust tibia, shorter than the femur (tibia/femur index: 87). Wide astragalus without ascending process; very small calcaneum. Foot similar to that of the plateosaurids; however, as in Ammosaurus, the central metatarsals are more elongate (3rd Mt./femur index: 45), and lateral metatarsals are slender and elongate; the first is more than 2/3 the length of the second, and the fifth is 2/3 the length of the fourth.

Type species

Herrerasaurus ischigualastensis , n. sp.

Holotype

Complete series of vertebrae from the third anterior to the sacrum up to the last caudals; both ilia and ischia, nearly complete right pubis and portions of the left; nearly complete right hindlimb; left astragalus. Fossils very well preserved, without deformation, discovered by Victorino Herrera in May 1961 in the Ischigualasto Valley, a few Km. ESE of the Aguada de La Peña, in the lower beds of the Ischigualasto Beds. The specimen was prepared by Galileo J. Scaglia in the laboratories of the Instituto Miguel Lillo and the Museo Argentino de Ciencias Naturales. It was deposited in the collections of the first institution, and labeled with No. PVL 2566.

Hypodigm

Apart from the holotype, we refer the following specimens to this species which, together with those mentioned, constitute the hypodigm:

PVL 2558. Proximal and distal portions of two femora, of two tibiae and fibulae; terminal portions of both humeri; portions of the ilium, the proximal portion of both pubes; various presacral vertebrae, some caudals; portions of the ulna and radius, portions of the metatarsals, proximal phalanges of the pes, ungual phalanx of the first manual digit; right premaxilla, both incomplete maxillae, the better part of both dentaries, articular portion of the right mandible. It is basically the remains of a skeleton disintegrated by weathering, and of which remains this collection of very significant fragments, in a very good state of preservation and without deformation. Apart from the mentioned materials, other small pieces of the tibiae and other long bones show that originally there existed the skeletons of two associated individuals. The remains were discovered by Galileo J. Scaglia in May 1961, about 3000 meters ESE of the Aguada de La Peña, Ischigualasto Valley, in the lower beds of the Ischigualasto Beds.

PVL 2045. The greater part of both femora, both tibiae and fibulae, and both hind feet, fragments of gastralia and both pubes. These remains were discovered by O. A. Reig in April 1959, about 6000 meters WNW of the Aguada de La Peña, about 200 meters to the right of the dry river bed of the Arroyo de la Pintada. They were found in the middle beds of the Ischigualasto Beds, and associated with both mandibular rami and loose cranial teeth from a cynodont of the genus Exaeretodon. About fifty meters from this specimen, and in the same beds, were exhumed the skull of a rhynchosaur and two skulls of Exaeretodon. Both incomplete pelves, articulated, in a poor state of preservation. Ischigualasto Valley, intermediate beds of the \\\\\\\"Ischigualasto Beds\\\\\\\". Discovered during the 1960 expedition.

PVL 2264. Incomplete left femur. Discovered by Galileo J. Scaglia in June 1960 in the Los Colorados Beds, about 3000 meters N of the Aguada de La Peña. Bone strong, flattened anteroposteriorly, recovered from hard matrix. Figured by Bonaparte (1960) as a femur from an ornithosuchid thecodont.

Provenance and age

Ischigualasto Valley, department of Valle Fertíl, province of San Juan, Argentina. \\\\\\\"Ischigualasto Beds\\\\\\\" [Ischigualasto Formation] and \\\\\\\"Los Colorados Beds\\\\\\\" [Los Colorados Formation]of the \\\\\\\"Ischigualasto-Ischichuca\\\\\\\" Series. Upper Middle Triassic.

Diagnosis

As for the genus.

Discussion

Herrerasaurus can be attributed to the infraorder Carnosauria without much doubt; however it offers a fairly confusing view with regard to its closest relations. The form of the pelvis, with the pubis expanded distally to form a \\\\\\\"foot\\\\\\\" as in Allosauridae and Tyrannosauridae from the Jurassic and Cretaceous, is different from that of all known Triassic carnosaurs. The reduced number of the teeth in the maxilla and lower jaw is another character of advanced evolution that is difficult to resolve in so ancient a carnosaur. The foot is also unusual, having metatarsal proportions recalling more those of Ammosaurus than those of teratosaurids and gryponychids. At the same time, in vertebral morphology, the sacrum, the form of the ilium and ischium, and the morphology of the astragalus, it has features typical of Triassic pachypodosaurs.

It is without doubt curious to have a megalosaur of fairly specialized characters, like this taxon, associated with cynodonts. It is a discovery that does not agree with the data collected up to now on carnosaur evolution. The phylogenetic appraisal of Herrerasaurus could require modifying the accepted alignment of evolutionary sequence in the megalosaurs, which would indicate, as Welles suspected (1954), a certain regularity in the progressive changes of the skeletal structure from the oldest forms at the base of the Upper Triassic to Tyrannosaurus of the Upper Cretaceous. Herrerasaurus, which in certain characters indicates having reached the evolutionary level of Megalosaurus and in others that of Antrodemus, in spite of its great antiquity and retention of primitive traits in other characters presents the possibility that from its origins the carnosaur stock had a plural differentiation, having definite lineages with distinct evolutionary rates. For now, and until we have not given up on the possibility of a direct comparison with known Triassic and Jurassic carnosaurs - which would also permit deciding on the familial assignment of Herrerasaurus - there is no other alternative left to us than to leave the problem as it is.

PVL, abbreviation characterizes the collections of the Laboratorio de Vertebrados Fósiles of the Instituto Miguel Lillo, of the Universidad de Tucumán.

MLP, abbreviation indicates the collections of the División de Paleontología de Vertebrados of the Museo de La Plata.

_{Source: Polyglot Paleontologist}

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