Herrerasaurus

The Herrerasaurus is Not the Most Commonly Recognized Dinosaur Species

Herrerasaurus may not be one of the most commonly recognized dinosaur species, but this Theropod carnivore still plays a significant role in our Earth’s history. In this article we will cover everything you ever wanted to know about this carnivore including: when it lived, what it fed on, what it looked like and the history of its discovery.

What Was Herrerasaurus?

Herrerasaurus was one of the earliest known dinosaur species and lived during the middle Triassic period some 231.4 million years ago. All species of this carnivorous dinosaur have been found in northwestern Argentina which suggests that this dinosaur was limited to a single location; however, not enough specimens of this species have been discovered to confirm this assumption. The type species of Herrerasaurus ischigualastensis was discovered in 1963 by Osvaldo Reig – it is the only species within the Herrerasaurus genus. There are currently two recognized synonyms for the Herrerasaurus ischigualastensis species: Ischisaurus Cattoi and Frenguellisaurus ischigualastensis. There seems to be some disagreement of just where Herrerasaurus belongs in terms of being a Saurischian, a theropod or a sauropodomorph but most tend to believe that it was a primitive theropod. There are also some who believe that this relatively small carnivore should not be classified as a dinosaur at all. The reason behind those who believe that this carnivore is not actually a dinosaur is due to the similarities that Herrerasaurus has with non-dinosaur archosaurs. While classification of this theropod remains somewhat cloudy, for the time being however, researchers are going under the assumption that Herrerasaurus is a theropod dinosaur.

What Did Herrerasaurus Look Like?

Herrerasaurus was a bipedal carnivore but as an early theropod like dinosaur it was particularly lightly built and does not begin to compare to some of the later theropod species. Like many theropods, Herrerasaurus had a long tail that would have been utilized as a counterbalance, small forelimbs which likely played a role in holding prey and longer stronger legs than forelimbs. The head of Herrerasaurus is rather small when comparing this species to other later theropod species. It is believed that this species grew to around ten to twenty feet long and was just over three feet tall at its hip. Weight estimates put Herrerasaurus in the 450 to 780 lb weight range. The skull size of Herrerasaurus varies depending upon the specific specimen as some have been found with skulls that measure approximately one foot in length while another large specimen has been discovered with a skull that measured in at around two feet long.

The skull of Herrerasaurus is particularly significant because it distinguishes large differences that can be identified between primitive theropods like Herrerasaurus and later more specialized theropods. The slender skull of Herrerasaurus was long and had five different pairs of fenestrae. The purpose of fenestrae for the dinosaur’s skull is not only to serve as areas for the eyes and nostrils, but additional fenestrae serve to lighten the skull. In addition to featuring different types of fenestrae, the skull of Herrerasaurus featured a somewhat unique lower jaw structure, an adaptation that can be found in some lizards but one that was not common in other dinosaurs. The lower jaw of Herrerasaurus features a flexible joint which allows for the jaw to move back and forth in a sliding motion.

The Limbs of Herrerasaurus

The limbs of Herrerasaurus are very much like the limbs of other later theropods with forelimbs that measure around half the length of the hind limbs. The hands on the forelimbs of Herrerasaurus were long and featured a thumb and two fingers that each had long claws in addition to two more shortened fingers that lacked claws completely. While bipedal modality was certainly not something that was new to theropods, in the middle Triassic period when Herrerasaurus lived it was somewhat unique for a dinosaur species to be completely bipedal. Where some of the later much larger theropods were incapable of fast movement because of their sheer size, the Herrerasaurus was most likely a fast runner. The feet of this small theropod feature five toes with just the middle three digits being weight bearing and the first toe featuring a claw. The claw of the first toe is particularly small however, and should not be confused with the much larger claws that were found on the later raptor species. It is believed that the long stiff tail of Herrerasaurus also played a role in enabling this small carnivore to move quickly and change direction rapidly without losing its balance.

Characteristics of Herrerasaurus

Herrerasaurus is somewhat unique in terms of other dinosaur species that have been noted because as an early species it combines a number of different dinosaur characteristics. Some of the things seen in Herrerasaurus are unique in that they are actually traits of non-dinosaurian archosaurs, rather than in dinosaurs. The features of Herrerasaurus that are less dinosaurian in appearance include the pelvis shape. Most notably the Herrerasaurus had a pelvis that looked like that of Saurischian dinosaurs but with a bony acetabulum. The hip bone of Herrerasaurus was supported only by two sacrals and the pubis pointed backwards. In addition the end of the pubis was boot shaped and the vertebral centra had an hourglass shape much like that of the Allosaurus.

The Diet of Herrerasaurus

Herrerasaurus had rather large teeth for the size of its jaw and each of these teeth was serrated making them perfect for tearing and biting flesh. In addition to the length and serration of the teeth, the long, slender neck was particularly flexible which would have allowed fast tearing and snapping motions. There is no doubt from the tooth structure of Herrerasaurus that it was a carnivorous species. From the smaller size of this theropod however, it is believed that it fed on smaller plant eaters as there is no evidence that these dinosaurs hunted in packs large enough to take on big prey items. Paleontologists are able to tell the basic diet of Herrerasaurus from looking at fossilized droppings that show evidence of digested dinosaur bones. There have been no findings that suggest that Herrerasaurus ever ate or digested plant material ruling out the possibility that this was an omnivorous dinosaur. Among the dinosaurs that Herrerasaurus likely fed on are: rhynchosaurs, Pisanosaurus and synapsids. Fossilized remains of Herrerasaurus have also been found that suggest that this small theropod was also a prey item for other larger carnivores.

Where Did Herrerasaurus Live?

Herrerasaurus specimens have been found among the Ischigualasto Formation and Los Colorados Formation. It is believed that the Ischigualasto Formation was a floodplain that was not only volcanically active but also covered by forests. The small size of Herrerasaurus meant that this fast moving carnivore would have been able to quickly dash between the forest trees as it chased prey items. Due to the forest environment the climate preferred by Herrerasaurus was damp and similar to that of rainforests with thick vegetation. Of all of the dinosaur species in the area of the Ischigualasto Formation, Herrerasaurus is the most abundant carnivores. Fortunately for Herrerasaurus and other carnivores of the era, herbivorous dinosaurs were far more abundant which provided a regular supply of food.

What Can Herrerasaurus Tell Us About Early Dinosaur Life?

Herrerasaurus plays an important role in what we know about dinosaur evolution because it is one of the first known early dinosaur species. The characteristics of Herrerasaurus that are uncommon to later dinosaur species provide us with an inside view as to how dinosaurs evolved in to much more specialized creatures. Taking a look at how the Herrerasaurus of the middle Triassic period evolved and how the large theropods of the late Cretaceous period were structured helps to draw connections between the various specialized developments of later dinosaur species. Why is this connection so important? The connection between early and later dinosaurs not only helps paleontologists to track the evolution of theropods and carnivores but it also allows researchers to see just how specialized characteristics evolve over time.