Old Earth Ministries Online Dinosaur Curriculum
Free online curriculum for homeschools and private schools
From Old Earth Ministries (We Believe in an Old Earth...and God!)
NOTE: If you found this page through a search engine, please visit the intro page first.
Lesson 7 - Herrerasaurus
Herrerasaurus (meaning "Herrera's lizard", after the name of the rancher who discovered the first fossil of the animal) was one of the earliest dinosaurs. All known specimens of this carnivore have been discovered in rocks of early Carnian age (late Triassic, around 228 million years ago) in northwestern Argentina. The type species, Herrerasaurus ischigualastensis, was described by Osvaldo Reig in 1963 and is the only species assigned to the genus. The names Ischisaurus and Frenguellisaurus are synonymous with Herrerasaurus.
Length: 10-20 feet
Weight: 463 - 772 lbs
Date Range: 228 - 225 Ma
Carnian Age, Triassic Period
|Mounted Herrerasaurus skeleton cast, at the Field Museum in Chicago (Picture Source)|
Herrerasaurus was a lightly-built bipedal carnivore with a long tail and a relatively small head. Its length is estimated at 3 to 6 meters (10 to 20 ft), and its hip height at more than 1.1 meters (3.3 ft). It may have weighed around 210–350 kilograms (463–772 lb). In a large specimen at first thought to belong to a separate genus, Frenguellisaurus, the skull measured 56 centimeters (1.8 ft) in length. Smaller specimens had skulls which measured around 30 centimeters (1 ft) in length.
Herrerasaurus had a long, narrow skull that lacked nearly all the specializations that
Herrerasaurus had a flexible joint in the lower jaw, allowing it to slide back and forth to deliver a grasping bite. This cranial specialization is unusual among the dinosaurs but has evolved independently in some lizards. The rear of the lower jaw also had fenestrae. The jaws were equipped with large serrated teeth for biting and eating flesh, and the neck was slender and flexible.
The forelimbs of Herrerasaurus were less than half the length of its hind limbs. The upper arm and forearm were rather short, while the manus (hand) was elongated. The first two fingers and the thumb ended in curved, sharp claws for grasping prey. Its fourth and fifth digits were small stubs without claws.
Unlike most reptiles of its era, Herrerasaurus was fully bipedal. It had strong hind limbs with short thighs and rather long feet, indicating that it was most likely a swift runner. The foot had five toes, but only the middle three (digits II, III, and IV) bore weight. The outer toes (I and V) were small; the first toe had a small claw. The tail, partially stiffened by overlapping vertebral projections, balanced the body and was also an adaptation for speed.
Derived and basal characteristics
Herrerasaurus is something of an enigma in that it displays traits that are found in different groups of dinosaurs, and several traits found in non-dinosaurian archosaurs. Although it shared most of the characteristics of dinosaurs, there were a few differences, particularly in regard to the shape of its hip and leg bones. Its pelvis was similar to that of saurischian dinosaurs, but it had a bony acetabulum (where the femur meets the pelvis) that was only partially open. The ilium, the main hip bone, was supported only by two sacrals, a basal trait, but the pubis pointed backwards, a derived trait that parallels what is seen in dromaeosaurids and birds. Additionally, the end of the pubis had a booted shape, similar to what is present in avetheropods, and the vertebral centra had an Allosaurus-like hourglass shape.
Herrerasaurus gives its name to its family, Herrerasauridae, a group of similar animals from the Late Triassic. The most recent analysis (Nesbitt et al. 2009) found Herrerasaurus and its relatives in Herrerasauridae to be very basal theropods. The situation is further complicated by uncertainties in correlating the ages of late Triassic beds bearing land animals. Other members of the clade may include Eoraptor from the same Ischigualasto Formation of Argentina as Herrerasaurus, Staurikosaurus from the Santa Maria Formation of southern Brazil, Chindesaurus from the Upper Petrified Forest (Chinle Formation) of Arizona, and possibly Caseosaurus from the Dockum Formation of Texas, although the relationships of these animals are not fully understood, and not all paleontologists agree. Other possible basal theropods, Alwalkeria from the Late Triassic Maleri Formation of India, and Teyuwasu, known from very fragmentary remains from the Late Triassic of Brazil, might be related.
Herrerasaurus was named by paleontologist Osvaldo Reig after Victorino Herrera, an
A complete Herrerasaurus skull was not found until 1988, by a team of paleontologists led by Paul Sereno.
Although Herrerasaurus shared the body shape of the large carnivorous dinosaurs, it lived about 230 million years ago, a time when dinosaurs were small and insignificant. It was the time of non-dinosaurian reptiles, not dinosaurs, and a major turning point in the Earth's ecology. The vertebrate fauna of the Ischigualasto Formation and the slightly later Los Colorados Formation consisted mainly of a variety of crurotarsal archosaurs and synapsids. For instance, in the Ischigualasto Formation, dinosaurs constituted only about 6% of the total number of fossils. By the end of the Triassic Period, dinosaurs were becoming the dominant large land animals, and the other archosaurs and synapsids declined in variety and number.
Studies suggest that the paleoenvironment of the Ischigualasto Formation was a volcanically active floodplain covered by forests and subject to strong seasonal rainfalls. The climate was moist and warm, though subject to seasonal variations. Vegetation consisted of ferns (Cladophlebis), horsetails, and giant conifers (Protojuniperoxylon). These plants formed highland forests along the banks of rivers. Herrerasaurus remains appear to have been the most common among the carnivores of the Ischigualasto Formation. It lived in the jungles of Late Triassic South America alongside another early dinosaur, the one metre long Eoraptor, as well as Saurosuchus, a giant land-living rauisuchian (a quadrupedal meat eater with a theropod-like skull); the broadly similar but smaller Venaticosuchus, an ornithosuchid; and the predatory chiniquodontids. Herbivores were much more abundant than carnivores and were represented by rhynchosaurs such as Hyperodapedon (a beaked reptile); aetosaurs (spiny armored reptiles); kannemeyeriid dicynodonts (stocky, front-heavy beaked quadrupedal animals) such as Ischigualastia; and traversodontids (somewhat similar in overall form to dicynodonts, but lacking beaks) such as Exaeretodon. These non-dinosaurian herbivores were much more abundant than early ornithischian dinosaurs like Pisanosaurus.
The teeth of Herrerasaurus indicate that it was a carnivore; its size indicates it would have
Coprolites (fossilized dung) containing small bones but no trace of plant fragments, discovered in the Ischigualasto Formation, have been assigned to Herrerasaurus based on fossil abundance. Mineralogical and chemical analysis of these coprolites indicates that this carnivore could digest bone.
End of Reading
Return to the Old Earth Ministries Online Dinosaur Curriculum homepage.
Bay State Replicas - Herrerasaurus Skull