Herrerasaurus ischigualastensis

Herrerasaurus ischigualastensis was one of the largest dinosaurs in the earliest well-documented dinosaur communities. It lived on the seasonal floodplains of the Ischigualasto Formation when dinosaurs were still a minor part of the fauna. Although its overall silhouette resembles a later theropod, its skeleton combines predatory specializations with early saurischian features such as only two sacral vertebrae. Several associated skeletons make Herrerasaurus one of the anatomically best-known Late Triassic dinosaurs, but its exact position near the base of the dinosaur family tree remains sensitive to the characters and taxa used in each analysis.

Its fossils occur between approximately 231.4 and 228.9 million years ago. Values shown here are approximate and reflect the current curated seed dataset.

The skull was long, low and narrow, with large openings that reduced its weight and deep recesses for jaw-closing muscles. Recurved, finely serrated teeth and a mobile joint within the lower jaw formed an effective cutting apparatus. The forelimbs were shorter than the hind limbs but remained powerful: five manual digits were present, while the first three carried large curved claws and the outer two were reduced. Long hind limbs and three principal weight-bearing toes supported bipedal locomotion. A stiffened tail balanced the torso, and the pelvis retained only two sacral vertebrae despite a broadly dinosaurian open hip socket.

• Long, low skull with large temporal openings for jaw musculature
• Recurved teeth with finely serrated cutting edges
• Mobile intramandibular joint within the lower jaw
• Five-fingered hand with three large functional claws
• Short but muscular forelimbs suited to grasping
• Only two sacral vertebrae connecting the spine and pelvis
• Long hind limbs and three principal weight-bearing toes
• Elongated balancing tail stiffened by overlapping vertebral processes

Victorino Herrera collected the partial skeleton PVL 2566 in the Ischigualasto badlands in 1961. Osvaldo A. Reig named Herrerasaurus ischigualastensis in 1963, honouring Herrera and the fossil-bearing region. The holotype lacks a skull and much of the front half of the body, so the discovery of additional articulated skeletons transformed understanding of the animal. PVSJ 373 preserves much of the postcranial skeleton, while PVSJ 407 includes an exceptionally complete skull and skeleton described by Paul Sereno, Fernando Novas and colleagues in the early 1990s. Material originally named Ischisaurus and Frenguellisaurus was later interpreted as belonging to Herrerasaurus.

Discovery credit: Victorino Herrera.

Naming authors: Osvaldo A. Reig.

Herrerasaurus inhabited river channels and floodplains in an arid to semi-arid, strongly seasonal part of southwestern Pangaea. Droughts and episodic floods shaped the Ischigualasto ecosystem. Dinosaurs represented only a small fraction of the vertebrate assemblage; abundant neighbours included the beaked rhynchosaur Hyperodapedon, the cynodont Exaeretodon, armored aetosaurs and large crocodile-line predators such as Saurosuchus. Eoraptor and several other early dinosaurs shared the same formation.

Skull mechanics, serrated teeth and grasping hands identify Herrerasaurus as an active carnivore capable of securing and cutting relatively large prey. Its long hind limbs also indicate effective bipedal movement, although running speed cannot be calculated reliably from the skeleton alone. Bone microstructure published in 2024 records fast, sustained growth and shows that the sampled large individual was still growing when it died. No trackway, nest or mass association demonstrates coordinated pack hunting, territoriality or parental care.

• The original holotype has no skull; the familiar head is known chiefly from later San Juan specimens such as PVSJ 407.
• Three of its five fingers carried large claws, while the outer two digits were greatly reduced.
• Dinosaurs made up only about eleven percent of the sampled vertebrate fauna in its Ischigualasto ecosystem.
• Names once applied to Ischisaurus and Frenguellisaurus are generally treated as junior synonyms of Herrerasaurus.

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1. 01
   The Paleobiology Database

   Open source
2. 02
   La presencia de dinosaurios saurisquios en los ‘Estratos de Ischigualasto’ (Mesotriásico Superior) de las provincias de San Juan y La Rioja (República Argentina)

   Osvaldo A. Reig · Ameghiniana · 1963

3. 03
   The complete skull and skeleton of an early dinosaur

   Paul C. Sereno, Fernando E. Novas · Science · 1992

   Open source
4. 04
   New information on the systematics and postcranial skeleton of Herrerasaurus ischigualastensis (Theropoda: Herrerasauridae) from the Ischigualasto Formation (Upper Triassic) of Argentina

   Fernando E. Novas · Journal of Vertebrate Paleontology · 1994

   Open source
5. 05
   The skull and neck of the basal theropod Herrerasaurus ischigualastensis

   Paul C. Sereno, Fernando E. Novas · Journal of Vertebrate Paleontology · 1994

   Open source
6. 06
   A new herrerasaurid (Dinosauria, Saurischia) from the Upper Triassic Ischigualasto Formation of northwestern Argentina

   Oscar A. Alcober, Ricardo N. Martínez · ZooKeys · 2010

   Open source
7. 07
   The Early Evolution of Archosaurs: Relationships and the Origin of Major Clades

   Sterling J. Nesbitt · Bulletin of the American Museum of Natural History · 2011

   Open source
8. 08
   Dental form and function in the early feeding diversification of dinosaurs

   Antonio Ballell, Michael J. Benton, Emily J. Rayfield · Science Advances · 2022

   Open source
9. 09
   Osteohistological insight into the growth dynamics of early dinosaurs and their contemporaries

   Kristina Curry Rogers, Ricardo N. Martínez, Carina Colombi and 2 coauthors · PLOS ONE · 2024

   Open source
10. 10
    Instituto y Museo de Ciencias Naturales

    Facultad de Ciencias Exactas, Físicas y Naturales, Universidad Nacional de San Juan

    Open source
11. 11
    Colección Vertebrados Fósiles (PVL)

    Facultad de Ciencias Naturales e Instituto Miguel Lillo

    Open source
12. 12
    Ischigualasto / Talampaya Natural Parks

    UNESCO World Heritage Centre

    Open source