Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Order: Saurischia
Family: †Herrerasauridae
Genus: †Herrerasaurus
Reig, 1963
Species: †H. ischigualastensis
Paleobiology
The holotype of Herrerasaurus (PVL 2566) was discovered in the Cancha de Bochas Member of the Ischigualasto Formation in San Juan, Argentina. It was collected in 1961 by Victorino Herrera, in sediments that were deposited in the Carnian stage of the Triassic period, approximately 235 to 221 million years ago. Herrerasaurus was a lightly built bipedal carnivore with a long tail and a relatively small head. Adults had skulls up to 56 cm (22 in) long and were up to 6 metres (20 ft) in total length and roughly 350 kg (770 lb) in weight. Smaller specimens were half the size, with skulls only about 30 cm (12 in) long.
Herrerasaurus possesses a long, narrow skull that lacked nearly all the specializations that characterized later dinosaurs, and more closely resembled those of more primitive archosaurs such as Euparkeria (a primitive dinosaurian predecessor from the earlier Triassic) . It had five pairs of fenestrae (skull openings) in its skull, two pairs of which were for the eyes and nostrils. Between the eyes and the nostrils were two antorbital fenestrae and a pair of tiny, 1-centimeter-long (0.4 in) slit-like holes called promaxillary fenestrae. Marked supratemporal depressions for jaw adductor musculature on the skull roof and a well-developed, sliding intra-mandibular joint suggest that Herrerasaurus ischigualastensis was an a active predator within its habitat.
Different features of the skull, such as the loss of the postfrontal and small post-temporal opening, constitute dinosaurian synapomorphies. These synapomorphies, however, remain equivocal at the level of Dinosauria because they cannot be evaluated in immediate dinosaurian outgroups for which cranial information is lacking. Comparisons of the skull and neck of Herrerasaurus ischigualastensis to other basal dinosaurs reveals several derived similarities with saurischians and, in particular, theropods. These synapomorphies include a subnarial foramen (between premaxilla and maxilla) shared with saurischians and an intra-mandibular joint shared with theropods
Behavior and Ecology
Herreasaurus are by far the most primitive of all theropods observed in the wild being one of the most ancient of the clade dinosauria and most notably one of the ancestors of numerous groups within it. Despite being top
Predators in their normal arid habitat in the Triassic period of southern Argentina they stand at a rather low position in the islands food web. Weighing at more than 4x as much as the average human they are still considered "small" by dinosaur standards and are constantly under threat from the landscapes larger more powerful animals. Throughout most of the year Herreasaurus are solitary and live in the dense forests and jungles alone but have been known to congregate at large carcasses. Both sexes are the same size but distinguished by their stripe coloration. Although possessing the same pattern the striping down the length of the tail, chin and upper body is a bright orange pigmentation in males with the females being dark grey and more subdued patterning. One trait that the species is most particularly known for is their unique calls. Using vocalizations with their bulging neck apparatus air is forced up through the larynx to produce an almost crocodilian like growl. These calls can be heard from more than a quarter mile away , allowing different individuals to communicate with one another and portray a vast assortment of signals to conspecifics. Unlike more gregarious theropods Herreasaurus are not all that tolerant of others of their own kind and one of the very few times they are ever seen together is when collectively feeding at carcasses.
Unexpectedly upon closer observations on their daily habits Herreasaurus are proportionately more active at night rather than day and boast excellent night vision. It as at these times that they are seen most actively searching for food such as small mammals , frogs , lizards and large insects. This is also one of the prime periods for communication amongst the species , with different calls echoing through the dense forest and alerting others to their status.
Hunting and Diet
Herreasaurus are particularly specialized to hunt small or similarly sized prey items within their range. Being highly adaptable to various ecological niches Their diet has been known to include Avaceratops , Gallimimus, Psittacosaurus,Dryosaurus and Orodromeus on a regular basis. As opportunists they are known to eat whatever meal they can manage and aren't opposed to consuming fish , the eggs of turtles, crocodilians as well as other dinosaurs and hatchlings as well. Carrion accounts for approximately 40% of their usual diet and are one of the few occasions where large numbers of individuals are known to aggregate and collectively feed on the remains. Their long arms and equally impressive claws are vital for capturing and subduing quarry , allowing them to grab onto and slash prey whilst they deliver repeated bites into their target. Being primarily nocturnal they are also known to attempt to attack the juveniles of much larger species than usual in low light hours such as Maiasaura, Corythosaurus and Diabloceratops. By using the darkness to their advantage they have been observed constantly harassing and nipping at youngsters relentlessly throughout the night, it's not unusual for multiple unrelated individuals to join in this assault collaborating just long enough to secure their prize in a sort of "temporary" alliance, as many as 5-10 different animals have been reported in numerous instances to cooperate in this way when engaged with larger prey in the dark . These occasional aggregation of hunters is sometimes called a "Posse" by wildlife biologists. Given the phylogenetic significance of Herreasaurus within the fossil record it is speculated that perhaps this could be where the slightly gregarious behavior of other later theropods evolved from.
Interspecific competition
The most common occurrences of competition for Herreasaurus are among others within the scavenger guild. As well as clashes for territory with their own kind they face challenges from other similarly sized theropods such as Austroraptor,Dilophosaurus and Monolophosaurus. At kill sites Herreas can often be seen squabbling amongst themselves for prime pieces of liver, flesh and viscera as well as scavenging pterosaurs such as the immense Quetzecoatlus. To even larger predators they themselves are considered prey and are hunted by Canotaurus , Ceratosaurus and utahraptor. It is speculated by wildlife biologists that this is the primary reason they do inhabit densely forested localities for most of their lives.
Breeding and Reproduction
Female Herreasaurus may come into season twice within a year but are very selective of the males they choose. Makes during this time will call out loudly in their distinctive voices . The female homes in on the all she finds the most inviting and follows it intently. Upon reaching her potential partner he seeks immediately to seduce her first by lifting his head and using a slightly different pitch in his vocal repertoire exposing his throat , once she becomes less tense he gently nibbles at the sides of her head (a sort of grooming gesture) and if she accepts she reciprocates the act. After the two have copulated the male will depart and the female will be left to her own devices to raise the young. Mothers typically lay between 10-12 eggs in a clutch , nests like most theropods are a shallow depression within the soil in which the eggs will be deposited. Once laid female herreasaurus will often place ferns over their nests in order to mildly shield them from the sun and maintain a moderate temperature. After about 8 weeks the young will hatch and form a vital one with their mothers , essential for their survival. After finding their feet they will instinctively follow her as she leads them off. Throughout the day she will feed them whatever food she can manage to find as well as allow them to occasionally forage for themselves under her protection. A brooding mother will not tolerate males or other conspecifics near her children and will angrily warn them off with an aggressive threat display (this is primarily due to Herreasaurus being avid cannibals). After around 3 years (0.6) of their mothers caring protection the youngsters will leave her to fend for themselves and make their own way in the wild
Fast Facts
Packing: 10 per pack
Nesting: Unlimited
Aggression: Medium towards other Herreas and Austros, Low towards everything else.
Mating: Asexual
Other: Children become independent from their mothers at about 3 years old (0.6) . Most creatures should disregard Herrerasaurus unless they lack food. Herrerasaurus are extremely vocal, unless they feel they are in immediate danger, in which they will flee. This dinosaur is classified as a scavenger.
