Skelettreplikat of Herrerasaurus in a special exhibition at the Senckenberg Museum in Frankfurt am Main.
- Argentina ( Ischigualasto Formation )
- Herrerasaurus ischigualastensis
Herrerasaurus was one of the earliest and basalsten ( pristine ) dinosaurs. Fossils of this predator are from the early Late Triassic ( Carnian ) from northwestern Argentina. This genus was described by Osvaldo Reig in 1963 with the so far only known species Herrerasaurus ischigualastensis first time scientifically. Herrerasaurus means as much as " Herrera's lizard" and honors Victorino Herrera, a goatherd who found the first fossils of this genus.
The phylogenetic relationships of Herrerasaurus was long unclear, as were initially known only very fragmentary remains. While some researchers considered him for a basal theropods, he was considered by other researchers as basal Sauropodomorpha or as basal Saurischia; some researchers suspected even that Herrerasaurus was not a dinosaur.
1988, a nearly complete skeleton was discovered together with skulls. Today Herrerasaurus is considered either as a basal theropod or as basal Saurischia, which keep him many researchers for the most primitive known theropods. Herrerasaurus is the eponymous representative of Herrerasauridae.
Herrerasaurus was a relatively small, lightly built carnivores ( carnivores ). The body length is estimated to be 3 to 6 meters; the waist was more than 1.1 meters. The weight is estimated at 250 to 350 kilograms. The skull of a very large specimen, which was once a separate genus, Frenguellisaurus attributed, measures 56 centimeters in length. Smaller specimens had skulls of about 30 centimeters in length.
Herrerasaurus had a long, narrow skull, similar to those original archosaurs such as Euparkeria, which, however, almost all specializations, such as are typical of other dinosaurs that are missing. He pointed to each side to five skull window: between the eyes and nasal cavity was a large Antorbitalfenster and a Promaxillarfenster - a small, 1 cm long slit-like hole. Behind the eye socket was a large infra pace Ralf Rochester.
Herrerasaurus had a flexible joint in the lower jaw, which facilitated the holding of prey. This specialization is unusual for dinosaurs and has independently ( convergent ) developed in lizards. The jaws were equipped with large, jagged teeth. The neck was slender and flexible.
The forelimb of Herrerasaurus accounted for less than half the length of the hind limbs. Upper arm and forearm were quite short, while the hand was extended. The first two fingers and the thumb ended in curved, sharp claws. The fourth and fifth fingers were reduced and krallenlos.
Unlike most reptiles of its time Herrerasaurus was fully bipedal ( two-legged running). The hind legs were strongly built and were characterized by a short thighs and a relatively long walk, which has a fast runner. The foot had five toes, but only the middle three ( digits II, III, and IV) carried the weight. The outer toes (I and V) were small; the first toe had a small claw. The tail was partially stiffened by overlapping spinous processes to balance the body while running.
Derived and basal characteristics
Herrerasaurus shows a mosaic of features of different groups of dinosaurs and abgeleiteterer basalerer archosaurs. Although he shares the most characteristics with the dinosaurs, have in particular the hip and leg bones on some basal, atypical for dinosaur characteristics. The basin was similar to those of the Saurischia, but had an ossified acetabulum ( hip socket ) on that was only partially open. The ilium ( iliac ) was only supported by two sacral vertebrae - a basal property. However, the pubis ( pubic bone ) to the rear, a derived feature that Herrerasaurus shares with the Dromaeosauridae and the birds. The end of the pubic bone was boot -shaped and resembled the order of Avetheropoda. The vertebral bodies were hourglass-shaped, as in Allosaurus.
Herrerasaurus gives its name to the Herrerasauridae family that had spread throughout the Upper Triassic and includes some of the earliest and basalsten dinosaurs. Your relationships with other basal dinosaurs are unclear. Most studies of the 21st century classify them as basal theropods, although they may be out of theropods were at the base of Saurischia, or even were no dinosaurs. For example, while Sterling Nesbitt and colleagues (2009, 2011) hold the Herrerasauridae for a group of very basal theropods, suggests other researchers such as Ezcurra (2010), that they belonged neither to the theropods, nor to the Sauropodomorphen, but as a sister group of the Eusaurischia very were close to the base of Saurischia.
It is also debatable, are assigned to which other genera of Herrerasauridae. Possible Herrerasauriden were Sanjuansaurus, which also comes from the Ischigualasto Formation, Staurikosaurus from the Santa Maria Formation of southern Brazil, Chindesaurus from the Petrified Forest of the Chinle Formation of Arizona, and Caseosaurus from the Dockum Formation of Texas. Other possible basal theropods may have been related to the Herrerasauridae - including Alwalkeria are from the Maleri formation of India and Teyuwasu, which is known from very fragmentary remains from Brazil. Novas (1992 ) defined the Herrerasauridae as a node-based taxon (node based definition), including the common ancestor of Herrerasaurus and Staurikosaurus and all descendants of that ancestor with. Sereno (1998) defined by the group, meanwhile, as originating line based taxon ( system based definition); it includes all taxa that were more closely related to Herrerasaurus ischigualastensis as the house sparrow (Passer domesticus).
History of Research
Herrerasaurus was first described in 1963 by Osvaldo Reig scientifically. The name honors Victorino Herrera, a goatherd, who had found the first fossils of Herrerasaurus near the Argentine city of San Juan in 1959. These sediments in which fossils have been found of Eoraptor, belong to the Ischigualasto Formation and the late Ladinian to early Carnian dated ( Upper Triassic ). Together with Herrerasaurus Reig described a second dinosaur from the Ischigualasto Formation - Ischisaurus cattoi. Ischisaurus is today but as a juvenile of Herrerasaurus and thus as a junior synonym. Two other partial skeletons with skulls were described by Fernando Novas in 1986 as Frenguellisaurus ischigualastensis, but today also assigned to the genus Herrerasaurus.
The phylogenetic relationships of Herrerasaurus are controversial since its first description. Reig suspected Herrerasaurus was an early proponent of Carnosauria. Steel, however, classified Herrerasaurus in 1970 as a prosauropods. Peter Galton declared the genus as not einordbaren Saurischia. Other authors saw Herrerasaurus together with Staurikosaurus very basal dinosaurs outside Saurischia. Several researchers classified Herrerasaurus outside of the dinosaurs.
Only in 1988 managed a research group led by Paul Sereno, the discovery of a complete skull. Based on this new discovery classified authors such as Thomas R. Holtz and José Bonaparte Herrerasaurus at the base of Saurischia and outside the Sauropodomorpha and the theropods. Sereno, however, it preferred, Herrerasaurus (and the Herrerasauridae ) to be regarded as basal theropods. The majority of recent studies support one of these two hypotheses: To favor Rauhut (2003) and Bittencourt and Kellner ( 2004), the hypothesis of basal theropods, while Max Langer ( 2004), Langer and Benton ( 2006), and Randall Irmis and coauthors ( 2007) support the hypothesis of basal Saurischiers. If Herrerasaurus actually have been a theropod, it would mean that the theropods, Sauropodomorpha and Ornithischia have emerged before the evolution of Herrerasauridae - perhaps even before the middle Carnian, and that these major groups of dinosaurs acquired various typical dinosaur features independently have, such as the advanced ankle or the open acetabulum. This hypothesis is supported by large, three-toed footprints that were probably left by theropod dinosaurs: These tracks are from the Ladinian ( Middle Triassic) of the Lot Rastros Formation of Argentina and are thus 3 to 5 million years older than the fossils Herrerasaurus.
Studies of early dinosaurs such as Herrerasaurus form an important basis for the definition of the dinosaurs as a monophyletic group. How can a study of Herrerasaurus by Sereno (1992 ) suggests that many common features newly acquired earlier dinosaurs were no commonly derived characteristics ( synapomorphies ) of the dinosaurs, but independently of each other ( convergent ) in different groups of dinosaurs were out. In addition, Sereno suggested, based on his study of Herrerasaurus before, various other synapomorphies of the group Dinosauria.
Herrerasaurus lived millions of years ago about 235-228 during the early Upper Triassic ( Carnian ) and thus at a time when dinosaurs were not the dominant land vertebrates. The vertebrate fauna of the Ischigualasto Formation and the somewhat younger Los Colorados Formation consisted mainly of a variety of archosaurs from the group Crurotarsi as well as synapsids. In the Ischigualasto Formation dinosaurs represented only 6 % of the fauna. By the end of the Triassic dinosaurs were the dominant land animals; the variety and number of other archosaurs and synapsids declined.
The sediments of the Ischigualasto Formation were deposited within floodplains. The area was covered with forests and volcanic activity. The climate was warm and humid, but affected by seasonal fluctuations; so there are notes on strong seasonal rainfall. Vegetation consisted of ferns such as Cladophlebis, horsetails and the giant conifer Protojuniperoxylon. These plants formed upland forests along the river valleys. Herrerasaurus seems to have been the most common predators of the Ischigualasto Formation. Other carnivores of this formation were Eoraptor, another early dinosaur; Saurosuchus, a huge Rauisuchia; the smaller Venaticosuchus, a Ornithosuchidae; and the Chiniquodontidae, a family from the group of Therapsida. Herbivores were by Rhynchosaurier as Hyperodapedon; Aetosaurier; Represented Dicynodonten from the family Kannemeyeridae such as Ischigualastia, and by therapsids from the family Traversodontidae such as Exaeretodon. Furthermore, there were herbivorous dinosaurs, such as the Ornithischia Pisanosaurus.
Paleobiology and Paleopathology
Herrerasaurus was probably an active predator, whereupon the flexible jaw indicate. He was bigger and probably more cumbersome than the smaller Related Staurikosaurus. The top predators of the Ischigualasto fauna were probably large Rauisuchier. Herrerasaurus and possibly Rauisuchier presented by the herbivorous Rhynchosauriern and synapsids.
In the Ischigualasto Formation occur coprolites ( fossil dung ) that contain small bones, but no plant residues, and may have been made Herrerasaurus. Show Mineralogical and chemical analyzes of these coprolites that Herrerasaurus was able to digest bones, the assignment of the coprolites should be correct to Herrerasaurus.
Make comparisons between the Skleralringen of Herrerasaurus and modern birds and reptiles suggest that this animal could have lived cathemeral, ie both during the day and at night in each short intervals was active.
One of the known Herrerasaurus skull has three healed puncture wounds. These sores can be found, each with a different orientation in different areas of the skull, indicating that they were added independently. Wounds laborierten an infection, followed by a porous wall surrounding the wounds indicating, which is interpreted as a swelling. Maybe stir forth these wounds of the large Rauisuchier Saurosuchus - more likely, however, is that they stem from fights with other dogs, whereupon the moderate size of the wounds and the fact point out that they did not lead to death of the animal.
Bruce Rothschild and colleagues ( 2001) examined 12 metacarpals and 20 foot bones of Herrerasaurus for evidence of fatigue fractures, but found none.