''Herrerasaurus'' is a genus of
saurischia
Saurischia ( , meaning "reptile-hipped" from the Greek ' () meaning 'lizard' and ' () meaning 'hip joint') is one of the two basic divisions of dinosaurs (the other being Ornithischia), classified by their hip structure. Saurischia and Ornithis ...
n dinosaur from the
Late Triassic
The Late Triassic is the third and final epoch (geology), epoch of the Triassic geologic time scale, Period in the geologic time scale, spanning the time between annum, Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch ...
period. This genus was one of the earliest
dinosaur
Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...
s from the fossil record. Its name means "Herrera's lizard", after the rancher who discovered the first specimen in 1958 in South America. All known
fossil
A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...
s of this carnivore have been discovered in the
Ischigualasto Formation
The Ischigualasto Formation is a Late Triassic fossiliferous formation and Lagerstätte in the Ischigualasto-Villa Unión Basin of the southwestern La Rioja Province and northeastern San Juan Province in northwestern Argentina. The formation da ...
of
Carnian
The Carnian (less commonly, Karnian) is the lowermost stage of the Upper Triassic Series (or earliest age of the Late Triassic Epoch). It lasted from 237 to 227 million years ago (Ma). The Carnian is preceded by the Ladinian and is followed by t ...
age (late
Triassic
The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest period ...
according to the
ICS, dated to 231.4 million years ago) in northwestern Argentina.
The
type species
In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specimen ...
, ''Herrerasaurus ischigualastensis'', was described by
Osvaldo Reig
Osvaldo Alfredo Reig, (14 August 1929 – 13 March 1992), was an Argentine biologist and paleontologist. He was born in Buenos Aires, Argentina.
He made numerous contributions in the fields of paleontology and biological evolution. He studied at ...
in 1963
and is the only
species
In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
assigned to the
genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
. ''Ischisaurus'' and ''Frenguellisaurus'' are
synonyms
A synonym is a word, morpheme, or phrase that means exactly or nearly the same as another word, morpheme, or phrase in a given language. For example, in the English language, the words ''begin'', ''start'', ''commence'', and ''initiate'' are all ...
.
For many years, the classification of ''Herrerasaurus'' was unclear because it was known from very fragmentary remains. It was
hypothesized
A hypothesis (plural hypotheses) is a proposed explanation for a phenomenon. For a hypothesis to be a scientific hypothesis, the scientific method requires that one can test it. Scientists generally base scientific hypotheses on previous obser ...
to be a
basal theropod
Theropoda (; ), whose members are known as theropods, is a dinosaur clade that is characterized by hollow bones and three toes and claws on each limb. Theropods are generally classed as a group of saurischian dinosaurs. They were ancestrally c ...
, a basal
sauropodomorph
Sauropodomorpha ( ; from Greek, meaning "lizard-footed forms") is an extinct clade of long-necked, herbivorous, saurischian dinosaurs that includes the sauropods and their ancestral relatives. Sauropods generally grew to very large sizes, had lon ...
, a basal
saurischia
Saurischia ( , meaning "reptile-hipped" from the Greek ' () meaning 'lizard' and ' () meaning 'hip joint') is one of the two basic divisions of dinosaurs (the other being Ornithischia), classified by their hip structure. Saurischia and Ornithis ...
n, or not a dinosaur at all but another type of
archosaur
Archosauria () is a clade of diapsids, with birds and crocodilians as the only living representatives. Archosaurs are broadly classified as reptiles, in the cladistic sense of the term which includes birds. Extinct archosaurs include non-avian d ...
. However, with the discovery of an almost complete skeleton and skull in 1988,
''Herrerasaurus'' has been classified as an early saurischian in most of the phylogenies on the origin and early evolution of dinosaurs.
It is a member of the
Herrerasauridae
Herrerasauridae is a family of carnivorous dinosaurs, possibly basal to either theropods or even all of saurischians, or even their own branching from dracohors, separate from dinosauria altogether. They are among the oldest known dinosaurs, fi ...
, a family of similar genera that were among the earliest of the
dinosaurian
Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutiona ...
evolutionary radiation
An evolutionary radiation is an increase in taxonomic diversity that is caused by elevated rates of speciation, that may or may not be associated with an increase in morphological disparity. Radiations may affect one clade or many, and be rapid ...
.
[.]
Discovery
''Herrerasaurus'' was named by
paleontologist
Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of fossi ...
Osvaldo Reig after Victorino Herrera, an Andean
goatherd
A goatherd or goatherder is a person who herds goats as a vocational activity. It is similar to a shepherd who herds sheep. Goatherds are most commonly found in regions where goat populations are significant; for instance, in Africa and South Asi ...
who first noticed its
fossil
A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...
s in outcrops near the city of
San Juan, Argentina
San Juan () is the capital and largest city of the Argentine province of San Juan in the Cuyo region, located in the Tulúm Valley, west of the San Juan River, at above mean sea level, with a population of around 112,000 as per the (over ...
in 1959.
These rocks, which later yielded ''
Eoraptor
''Eoraptor'' () is a genus of small, lightly built, basal sauropodomorph. One of the earliest-known dinosaurs, it lived approximately 231 to 228 million years ago, during the Late Triassic in Western Gondwana, in the region that is now northwest ...
'',
are part of the
Ischigualasto Formation
The Ischigualasto Formation is a Late Triassic fossiliferous formation and Lagerstätte in the Ischigualasto-Villa Unión Basin of the southwestern La Rioja Province and northeastern San Juan Province in northwestern Argentina. The formation da ...
and date from the late
Ladinian
The Ladinian is a stage and age in the Middle Triassic series or epoch. It spans the time between Ma and ~237 Ma (million years ago). The Ladinian was preceded by the Anisian and succeeded by the Carnian (part of the Upper or Late Triassic).
...
to early
Carnian
The Carnian (less commonly, Karnian) is the lowermost stage of the Upper Triassic Series (or earliest age of the Late Triassic Epoch). It lasted from 237 to 227 million years ago (Ma). The Carnian is preceded by the Ladinian and is followed by t ...
stages of the Late
Triassic
The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest period ...
period.
Reig named a second dinosaur from these rocks in the same publication as ''Herrerasaurus'';
this dinosaur, ''Ischisaurus cattoi'', is now considered a
junior synonym
The Botanical and Zoological Codes of nomenclature treat the concept of synonymy differently.
* In botanical nomenclature, a synonym is a scientific name that applies to a taxon that (now) goes by a different scientific name. For example, Linna ...
and a
juvenile of ''Herrerasaurus''.
Reig believed ''Herrerasaurus'' was an early example of a
carnosaur
Carnosauria is an extinct large group of predatory dinosaurs that lived during the Jurassic and Cretaceous periods. Starting from the 1990s, scientists have discovered some very large carnosaurs in the carcharodontosaurid family, such as ''Gig ...
,
but this was the subject of much debate over the next 30 years, and the genus was variously classified during that time. In 1970, Steel classified ''Herrerasaurus'' as a
prosauropod
Sauropodomorpha ( ; from Greek, meaning "lizard-footed forms") is an extinct clade of long-necked, herbivorous, saurischian dinosaurs that includes the sauropods and their ancestral relatives. Sauropods generally grew to very large sizes, had lon ...
.
In 1972,
Peter Galton
Peter Malcolm Galton (born 14 March 1942 in London) is a British vertebrate paleontologist who has to date written or co-written about 190 papers in scientific journals or chapters in paleontology textbooks, especially on ornithischian and prosaur ...
classified the genus as not diagnosable beyond
Saurischia
Saurischia ( , meaning "reptile-hipped" from the Greek ' () meaning 'lizard' and ' () meaning 'hip joint') is one of the two basic divisions of dinosaurs (the other being Ornithischia), classified by their hip structure. Saurischia and Ornithis ...
.
Later, using
cladistic
Cladistics (; ) is an approach to biological classification in which organisms are categorized in groups (" clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is typically shared derived char ...
analysis, some researchers put ''Herrerasaurus'' and ''Staurikosaurus'' at the base of the dinosaur tree before the separation between ornithischians and saurischians.
Several researchers classified the remains as non-dinosaurian.
Two other partial skeletons, with skull material, were named ''Frenguellisaurus ischigualastensis'' by
Fernando Novas Fernando Emilio Novas (born 1960) is an Argentine paleontologist working for the Comparative Anatomy Department of the Bernardino Rivadavia Natural Sciences Museum in Buenos Aires, Argentina. in 1986, but this species too is now thought to be a synonym.
''Frenguellisaurus ischigualastensis'' was discovered in 1975, and was described by Novas (1986) who considered it a primitive saurischian, and possibly a
theropod
Theropoda (; ), whose members are known as theropods, is a dinosaur clade that is characterized by hollow bones and three toes and claws on each limb. Theropods are generally classed as a group of saurischian dinosaurs. They were ancestrally c ...
. Novas (1992) and Sereno and Novas (1992) examined the ''Frenguellisaurus'' remains and found them referable to ''Herrerasaurus''.
''Ischisaurus cattoi'' was discovered in 1960 and described by Reig in 1963. Novas (1992) and Sereno and Novas (1992) reviewed its remains and found them also to be referable to ''Herrerasaurus''.
![Herrerasaurus skeleton](https://upload.wikimedia.org/wikipedia/commons/1/13/Herrerasaurus_skeleton.jpg)
A complete ''Herrerasaurus'' skull was found in 1988, by a team of paleontologists led by
Paul Sereno
Paul Callistus Sereno (born October 11, 1957) is a professor of paleontology at the University of Chicago and a National Geographic "explorer-in-residence" who has discovered several new dinosaur species on several continents, including at sites ...
.
Based on the new fossils, authors such as
Thomas Holtz
Thomas Richard Holtz Jr. (born September 13, 1965) is an American vertebrate palaeontologist, author, and principal lecturer at the University of Maryland's Department of Geology. He has published extensively on the phylogeny, morphology, ecomorp ...
and
José Bonaparte
José Fernando Bonaparte (14 June 1928 – 18 February 2020) was an Argentine paleontologist who discovered a plethora of South American dinosaurs and mentored a new generation of Argentine paleontologists
. One of the best-known Argentine paleo ...
classified ''Herrerasaurus'' at the base of the saurischian tree before the divergence between prosauropods and theropods. However, Sereno favored classifying ''Herrerasaurus'' (and the Herrerasauridae) as primitive theropods. These two classifications have become the most persistent, with Rauhut (2003)
and Bittencourt and Kellner (2004)
favoring the early theropod
hypothesis
A hypothesis (plural hypotheses) is a proposed explanation for a phenomenon. For a hypothesis to be a scientific hypothesis, the scientific method requires that one can test it. Scientists generally base scientific hypotheses on previous obse ...
, and Max Langer (2004),
Langer and
Benton (2006),
and Randall Irmis and his coauthors (2007)
favoring the basal saurischian hypothesis. If ''Herrerasaurus'' were indeed a theropod, it would indicate that theropods,
sauropodomorph
Sauropodomorpha ( ; from Greek, meaning "lizard-footed forms") is an extinct clade of long-necked, herbivorous, saurischian dinosaurs that includes the sauropods and their ancestral relatives. Sauropods generally grew to very large sizes, had lon ...
s, and
ornithischia
Ornithischia () is an extinct order of mainly herbivorous dinosaurs characterized by a pelvic structure superficially similar to that of birds. The name ''Ornithischia'', or "bird-hipped", reflects this similarity and is derived from the Greek s ...
ns diverged even earlier than herrerasaurids, before the middle
Carnian
The Carnian (less commonly, Karnian) is the lowermost stage of the Upper Triassic Series (or earliest age of the Late Triassic Epoch). It lasted from 237 to 227 million years ago (Ma). The Carnian is preceded by the Ladinian and is followed by t ...
, and that "all three lineages independently evolved several dinosaurian features, such as a more advanced ankle joint or an open acetabulum".
This view is further supported by
ichnological records showing large tridactyl (three-toed) footprints that can be attributed only to a theropod dinosaur. These footprints date from the early Carnian
Los Rastros Formation in Argentina, which predates ''Herrerasaurus'' by several million years.
The study of early dinosaurs such as ''Herrerasaurus'' and ''Eoraptor'' therefore has important implications for the concept of dinosaurs as a
monophyletic
In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic gro ...
group (a group descended from a common ancestor). The monophyly of dinosaurs was explicitly proposed in the 1970s by Galton and
Robert T. Bakker,
who compiled a list of cranial and postcranial
synapomorphies
In phylogenetics, an apomorphy (or derived trait) is a novel character or character state that has evolved from its ancestral form (or plesiomorphy). A synapomorphy is an apomorphy shared by two or more taxa and is therefore hypothesized to have ...
(common anatomical traits derived from the common ancestor). Later authors proposed additional synapomorphies.
An extensive study of ''Herrerasaurus'' by Sereno in 1992 suggested that of these proposed synapomorphies, only one cranial and seven postcranial features were actually derived from a common ancestor, and that the others were attributable to
convergent evolution
Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last com ...
. Sereno's analysis of ''Herrerasaurus'' also led him to propose several new dinosaurian synapomorphies.
Description
![Herrerasaurus scale](https://upload.wikimedia.org/wikipedia/commons/c/c7/Herrerasaurus_scale.png)
''Herrerasaurus'' was a lightly built bipedal carnivore with a long tail and a relatively small head. Adults had skulls up to long and were up to in total length
and in weight.
Smaller specimens were half the size, with skulls only about long.
''Herrerasaurus'' was fully bipedal. It had strong hind limbs with short
thighs
In human anatomy, the thigh is the area between the hip ( pelvis) and the knee. Anatomically, it is part of the lower limb.
The single bone in the thigh is called the femur. This bone is very thick and strong (due to the high proportion of b ...
and rather long feet, indicating that it was 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.
The forelimbs of ''Herrerasaurus'' were less than half the length of its hind limbs. The
upper arm
In human anatomy, the arm refers to the upper limb in common usage, although academically the term specifically means the upper arm between the glenohumeral joint (shoulder joint) and the elbow joint. The distal part of the upper limb between th ...
and
forearm
The forearm is the region of the upper limb between the elbow and the wrist. The term forearm is used in anatomy to distinguish it from the arm, a word which is most often used to describe the entire appendage of the upper limb, but which in anat ...
were rather short, while the
manus (hand) was elongated. The first two fingers and the thumb ended in curved, sharp claws for grasping prey. The fourth and fifth digits were small stubs without claws.
''Herrerasaurus'' displays traits that are found in different groups of dinosaurs, and several traits found in non-dinosaurian archosaurs. Although it shares most of the characteristics of dinosaurs, there are a few differences, particularly in the shape of its hip and leg bones. Its pelvis is like that of saurischian dinosaurs, but it has a bony
acetabulum
The acetabulum (), also called the cotyloid cavity, is a concave surface of the pelvis. The head of the femur meets with the pelvis at the acetabulum, forming the hip joint.
Structure
There are three bones of the ''os coxae'' (hip bone) that c ...
(where the
femur
The femur (; ), or thigh bone, is the proximal bone of the hindlimb in tetrapod vertebrates. The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates with ...
meets the
pelvis
The pelvis (plural pelves or pelvises) is the lower part of the trunk, between the abdomen and the thighs (sometimes also called pelvic region), together with its embedded skeleton (sometimes also called bony pelvis, or pelvic skeleton).
The ...
) that was only partially open. The
ilium, the main hip bone, is supported by only two
sacrals, a
basal trait.
However, the
pubis points backwards, a
derived
Derive may refer to:
* Derive (computer algebra system), a commercial system made by Texas Instruments
* ''Dérive'' (magazine), an Austrian science magazine on urbanism
*Dérive, a psychogeographical concept
See also
*
*Derivation (disambiguatio ...
trait as seen in
dromaeosaurid
Dromaeosauridae () is a family of feathered theropod dinosaurs. They were generally small to medium-sized feathered carnivores that flourished in the Cretaceous Period. The name Dromaeosauridae means 'running lizards', from Greek ('), meaning ...
s and
bird
Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweigh ...
s. Additionally, the end of the pubis has a booted shape, like those in
avetheropods; and the
vertebra
The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic ...
l
centra
Centra is a convenience shop chain that operates throughout Ireland. The chain operates as a symbol group owned by Musgrave Group, the food wholesaler, meaning the stores are all owned by individual franchisees.
The chain has three different f ...
has an
hourglass
An hourglass (or sandglass, sand timer, sand clock or egg timer) is a device used to measure the passage of time. It comprises two glass bulbs connected vertically by a narrow neck that allows a regulated flow of a substance (historically sand) ...
shape as found in ''
Allosaurus
''Allosaurus'' () is a genus of large carnosaurian theropod dinosaur that lived 155 to 145 million years ago during the Late Jurassic epoch (Kimmeridgian to late Tithonian). The name "''Allosaurus''" means "different lizard" alluding to ...
''.
[
]
''Herrerasaurus'' had a long, narrow skull
The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, the ...
that lacked nearly all the specializations that characterized later dinosaurs, and more closely resembled those of more primitive archosaur
Archosauria () is a clade of diapsids, with birds and crocodilians as the only living representatives. Archosaurs are broadly classified as reptiles, in the cladistic sense of the term which includes birds. Extinct archosaurs include non-avian d ...
s such as ''Euparkeria
''Euparkeria'' (; meaning "Parker's good animal", named in honor of W.K. Parker) is an extinct genus of archosauriform from the Middle Triassic of South Africa. It was a small reptile that lived between 245-230 million years ago, and was close ...
''. It had five pairs of fenestra
A fenestra (fenestration; plural fenestrae or fenestrations) is any small opening or pore, commonly used as a term in the biological sciences. It is the Latin word for "window", and is used in various fields to describe a pore in an anatomical st ...
e (skull openings) in its skull, two pairs of which were for the eyes and nostrils. Between the eyes and the nostrils were two antorbital fenestra
An antorbital fenestra (plural: fenestrae) is an opening in the skull that is in front of the eye sockets. This skull character is largely associated with archosauriforms, first appearing during the Triassic Period. Among extant archosaurs, birds ...
e and a pair of tiny, slit-like holes called promaxillary fenestrae.
''Herrerasaurus'' had a flexible joint in the lower jaw that could slide back and forth to deliver a grasping bite. This cranial specialization is unusual among dinosaurs but has evolved independently in some lizard
Lizards are a widespread group of squamate reptiles, with over 7,000 species, ranging across all continents except Antarctica, as well as most oceanic island chains. The group is paraphyletic since it excludes the snakes and Amphisbaenia alt ...
s. 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.
According to Novas (1993), ''Herrerasaurus'' can be distinguished based on the following features: the presence of a premaxilla
The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammal has b ...
-maxilla
The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The t ...
fenestra, and the dorsal part of laterotemporal fenestra is less than a third as wide as the ventral part; the presence of a ridge on the lateral surface of the jugal
The jugal is a skull bone found in most reptiles, amphibians and birds. In mammals, the jugal is often called the malar or zygomatic. It is connected to the quadratojugal and maxilla, as well as other bones, which may vary by species.
Anatomy ...
bone, and a deeply incised supratemporal fossa
An infratemporal fenestra, also called the lateral temporal fenestra or simply temporal fenestra, is an opening in the skull behind the orbit (anatomy), orbit in some animals. It is ventrally bordered by a zygomatic arch. An opening in front of ...
that extends across the medial postorbital process; the subquadrate ventral squamosal process has a lateral depression, and the quadratojugal The quadratojugal is a skull bone present in many vertebrates, including some living reptiles and amphibians.
Anatomy and function
In animals with a quadratojugal bone, it is typically found connected to the jugal (cheek) bone from the front and ...
bone overlaps the posterodorsal quadrate face; the pterygoid Pterygoid, from the Greek for 'winglike', may refer to:
* Pterygoid bone, a bone of the palate of many vertebrates
* Pterygoid processes of the sphenoid bone
** Lateral pterygoid plate
** Medial pterygoid plate
* Lateral pterygoid muscle
* Medial ...
process of the quadrate has an inturned, trough-shaped ventral margin, and the presence of a slender ribbed posterodorsal dentary
In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower tooth, teeth in place. The mandible sits beneath the maxilla. It is the only movabl ...
process; the surangular
The suprangular or surangular is a jaw bone found in most land vertebrates, except mammals. Usually in the back of the jaw, on the upper edge, it is connected to all other jaw bones: dentary, angular, splenial and articular
The articular bone i ...
bone has a forked anterior process for articulation with the posterodorsal dentary process; the humerus
The humerus (; ) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius and ulna, and consists of three sections. The humeral upper extremity consists of a roun ...
' internal tuberosity
In the skeleton of humans and other animals, a tubercle, tuberosity or apophysis is a protrusion or eminence that serves as an attachment for skeletal muscles. The muscles attach by tendons, where the enthesis is the connective tissue between the ...
is proximally projected and separated from the humeral head by a deep groove (also present in coelophysoids); possesses enlarged hands, which are 60% of the size of the humerus+radius, and the humeral entepicondyle is ridge-like with anterior and posterior depressions; and the posterior border of the ilial peduncle forms a right angle with the dorsal border of the shaft on the .
According to Sereno (1993), ''Herrerasaurus'' can be distinguished based on the following features, all of which are unknown in other herrerasaurids: a circular pit is present on the humeral
The humerus (; ) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius and ulna, and consists of three sections. The humeral upper extremity consists of a round ...
ectepicondyle, a feature also present in ''Saturnalia
Saturnalia is an ancient Roman festival and holiday in honour of the god Saturn, held on 17 December of the Julian calendar and later expanded with festivities through to 23 December. The holiday was celebrated with a sacrifice at the Temple ...
''; a saddle-shaped ulnar condyle of the humerus
The humerus (; ) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius and ulna, and consists of three sections. The humeral upper extremity consists of a roun ...
, and the articular surface for the ulnare
The triquetral bone (; also called triquetrum, pyramidal, three-faced, and formerly cuneiform bone) is located in the wrist on the medial side of the proximal row of the carpus between the lunate and pisiform bones. It is on the ulnar side of the ...
on the ulna
The ulna (''pl''. ulnae or ulnas) is a long bone found in the forearm that stretches from the elbow to the smallest finger, and when in anatomical position, is found on the medial side of the forearm. That is, the ulna is on the same side of t ...
is convex; the articular surface of the ulnare is smaller than that of the ulna, a feature unknown in ''Staurikosaurus'' and ''Sanjuansaurus''; the centrale is placed distal to the radiale; a broad subnarial process of the premaxilla, and a broad supratemporal depression (noted by Sereno and Novas, 1993); the basal tuber and the occipital condyle
The occipital condyles are undersurface protuberances of the occipital bone in vertebrates, which function in articulation with the superior facets of the atlas vertebra.
The condyles are oval or reniform (kidney-shaped) in shape, and their anteri ...
are subequal in width (noted by Sereno and Novas, 1993).[
]
Classification
''Herrerasaurus'' was originally considered to be a genus within Carnosauria
Carnosauria is an extinct large group of predatory dinosaurs that lived during the Jurassic and Cretaceous periods. Starting from the 1990s, scientists have discovered some very large carnosaurs in the carcharodontosaurid family, such as ''Gig ...
, which then included forms similar to ''Megalosaurus
''Megalosaurus'' (meaning "great lizard", from Greek , ', meaning 'big', 'tall' or 'great' and , ', meaning 'lizard') is an extinct genus of large carnivorous theropod dinosaurs of the Middle Jurassic period (Bathonian stage, 166 million years a ...
'' and ''Antrodemus
''Antrodemus'' ("chamber bodied") is a dubious genus of theropod dinosaur from the Kimmeridgian-Tithonian age Upper Jurassic Morrison Formation of Middle Park, Colorado. It contains one species, ''Antrodemus valens'', first described and named a ...
'' (the latter is equivalent to ''Allosaurus
''Allosaurus'' () is a genus of large carnosaurian theropod dinosaur that lived 155 to 145 million years ago during the Late Jurassic epoch (Kimmeridgian to late Tithonian). The name "''Allosaurus''" means "different lizard" alluding to ...
''), even though ''Herrerasaurus'' lived many millions of years before them and therefore would have retained multiple primitive features. This carnosaurian classification was amended upon by Rozhdestvensky and Tatarinov in 1964, who classified ''Herrerasaurus'' within the family Gryponichidae inside Carnosauria. The same year, Walker published a differing opinion that ''Herrerasaurus'' instead was allied with Plateosauridae
Plateosauridae is a family of plateosaurian sauropodomorphs from the Late Triassic of Europe, Greenland, Africa and Asia. Although several dinosaurs have been classified as plateosaurids over the years, the family Plateosauridae is now restricte ...
, although it differed in possessing a pubic boot. Walker also proposed that ''Herrerasaurus'' may instead be close to ''Poposaurus
''Poposaurus'' (" Popo Agie reptile") is an extinct genus of pseudosuchian archosaur from the Late Triassic of the southwestern United States. It belongs to the clade Poposauroidea, an unusual group of Triassic pseudosuchians that includes sail-b ...
'' (now considered a pseudosuchia
Pseudosuchia is one of two major divisions of Archosauria, including living crocodilians and all archosaurs more closely related to crocodilians than to birds. Pseudosuchians are also informally known as "crocodilian-line archosaurs". Prior to ...
n) and the unnamed theropod from the Dockum Group
The Dockum is a Late Triassic (approximately late Carnian through Rhaetian, or 223–200 Ma) geologic group found primarily on the Llano Estacado of western Texas and eastern New Mexico with minor exposures in southwestern Kansas, eastern Color ...
of Texas
Texas (, ; Spanish language, Spanish: ''Texas'', ''Tejas'') is a state in the South Central United States, South Central region of the United States. At 268,596 square miles (695,662 km2), and with more than 29.1 million residents in 2 ...
(now assigned to the rauisuchia
"Rauisuchia" is a paraphyletic group of mostly large and carnivorous Triassic archosaurs. Rauisuchians are a category of archosaurs within a larger group called Pseudosuchia, which encompasses all archosaurs more closely related to crocodilia
...
n ''Postosuchus
''Postosuchus'', meaning "Crocodile from Post", is an extinct genus of rauisuchid reptiles comprising two species, ''P. kirkpatricki'' and ''P. alisonae'', that lived in what is now North America during the Late Triassic. ''Postosuchus'' is a me ...
''). In 1985, Charig noted that ''Herrerasaurus'' was of uncertain classification, showing similarities to both "prosauropod
Sauropodomorpha ( ; from Greek, meaning "lizard-footed forms") is an extinct clade of long-necked, herbivorous, saurischian dinosaurs that includes the sauropods and their ancestral relatives. Sauropods generally grew to very large sizes, had lon ...
s" and "carnosaurians". Romer (1966), simply noted that ''Herrerasaurus'' was a prosauropod possibly within Plateosauridae. In the description of ''Staurikosaurus'', Colbert noted that there were many similarities between his taxon and ''Herrerasaurus'', but classified them in separate families, with ''Herrerasaurus'' in Teratosauridae. In 1970, Bonaparte also proposed similarities between ''Herrerasaurus'' and ''Staurikosaurus'', and while classifying them both clearly as in Saurischia
Saurischia ( , meaning "reptile-hipped" from the Greek ' () meaning 'lizard' and ' () meaning 'hip joint') is one of the two basic divisions of dinosaurs (the other being Ornithischia), classified by their hip structure. Saurischia and Ornithis ...
, he stated that they appeared as though they could not be placed in a current family. This was further supported by Benedetto in 1973, who named for the taxa the new family Herrerasauridae
Herrerasauridae is a family of carnivorous dinosaurs, possibly basal to either theropods or even all of saurischians, or even their own branching from dracohors, separate from dinosauria altogether. They are among the oldest known dinosaurs, fi ...
, which he classified as saurischians, possibly within Theropoda
Theropoda (; ), whose members are known as theropods, is a dinosaur clade that is characterized by hollow bones and three toes and claws on each limb. Theropods are generally classed as a group of saurischian dinosaurs. They were ancestrally ca ...
but not in Sauropodomorpha
Sauropodomorpha ( ; from Greek, meaning "lizard-footed forms") is an extinct clade of long-necked, herbivorous, saurischian dinosaurs that includes the sauropods and their ancestral relatives. Sauropods generally grew to very large sizes, had lon ...
. However, in 1977 Galton proposed that Herrerasauridae only included ''Herrerasaurus'', and found it to be Saurischian ''incertae sedis
' () or ''problematica'' is a term used for a taxonomic group where its broader relationships are unknown or undefined. Alternatively, such groups are frequently referred to as "enigmatic taxa". In the system of open nomenclature, uncertainty ...
''.
Proposed in 1987 by Brinkman and Sues, ''Herrerasaurus'' has at times been considered basal to Ornithischia
Ornithischia () is an extinct order of mainly herbivorous dinosaurs characterized by a pelvic structure superficially similar to that of birds. The name ''Ornithischia'', or "bird-hipped", reflects this similarity and is derived from the Greek s ...
and Saurischia, although Brinkmann and Sues still considered it to be inside Dinosaur
Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...
ia. They supported this on the basis that ''Herrerasaurus'' has a large pedal digit V, and has a well developed medial wall on the acetabulum. Brinkmann and Sues considered ''Staurikosaurus'' and ''Herrerasaurus'' to not form a true group called Herrerasauridae, and that instead they were successively more primitive forms. Also, they considered the characters used by Benedetto to be invalid, instead representing only the plesiomorphies
In phylogenetics, a plesiomorphy ("near form") and symplesiomorphy are synonyms for an ancestral character shared by all members of a clade, which does not distinguish the clade from other clades.
Plesiomorphy, symplesiomorphy, apomorphy, and ...
state that was found in both taxa. This was disagreed with in 1992 by Novas, who stated many derived synapomorphies
In phylogenetics, an apomorphy (or derived trait) is a novel character or character state that has evolved from its ancestral form (or plesiomorphy). A synapomorphy is an apomorphy shared by two or more taxa and is therefore hypothesized to have ...
of Herrerasauridae, such as a distinct pubic boot, but still classified them as basal to Ornithischia and Saurischia. Novas defined the family as the least common ancestor of ''Herrerasaurus'' and ''Staurikosaurus'' and all its descendants. A differing definition of Herrerasauridae as the most inclusive clade including ''Herrerasaurus'' but not ''Passer domesticus
The house sparrow (''Passer domesticus'') is a bird of the sparrow family Passeridae, found in most parts of the world. It is a small bird that has a typical length of and a mass of . Females and young birds are coloured pale brown and grey, an ...
'' was first suggested by Sereno (1998), and more closely follows the original inclusion proposed by Benedetto. Another group, Herrerasauria
Saurischia ( , meaning "reptile-hipped" from the Greek ' () meaning 'lizard' and ' () meaning 'hip joint') is one of the two basic divisions of dinosaurs (the other being Ornithischia), classified by their hip structure. Saurischia and Ornithis ...
was named by Galton in 1985, and defined as ''Herrerasaurus'' but not ''Liliensternus
''Liliensternus'' is an extinct genus of basal neotheropod dinosaur that lived approximately 210 million years ago during the latter part of the Triassic Period in what is now Germany. ''Liliensternus'' was a moderate-sized, bipedal, ground-dwel ...
'' or ''Plateosaurus
''Plateosaurus'' (probably meaning "broad lizard", often mistranslated as "flat lizard") is a genus of plateosaurid dinosaur that lived during the Late Triassic period, around 214 to 204 million years ago, in what is now Central and Northern Eur ...
'' by Langer (2004), who used the node-based definition for Herrerasauridae.
In a revision of basal Dinosauria, Padian and May (1993) discussed the definition of the clade, and redefined it as the latest common ancestor of ''Triceratops
''Triceratops'' ( ; ) is a genus of herbivore, herbivorous Chasmosaurinae, chasmosaurine Ceratopsidae, ceratopsid dinosaur that first appeared during the late Maastrichtian stage of the Late Cretaceous Period (geology), period, about 68 m ...
'' and bird
Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweigh ...
s. They also discussed what this definition would do to the most basal taxa, such as Herrerasauridae, and ''Eoraptor
''Eoraptor'' () is a genus of small, lightly built, basal sauropodomorph. One of the earliest-known dinosaurs, it lived approximately 231 to 228 million years ago, during the Late Triassic in Western Gondwana, in the region that is now northwest ...
''. Padian and May considered that since both Herrerasauridae and ''Eoraptor'' lack many diagnostic features of Saurischia or Ornithischia, that they could not be considered inside Dinosauria.
A later 1994 study by Novas instead classified ''Herrerasaurus'' within Dinosauria, and strongly supported its position within Saurischia, as well as provided synapomorphies that it shared with Theropoda. Novas found that the primitive features of lacking a brevis fossa and having only two sacral vertebrae were simply reversals found in the genus. In 1996, Novas went further by supporting a theropod position for ''Herrerasaurus'' with a phylogenetic
In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...
analysis, which placed it closer to Neotheropoda
Neotheropoda (meaning "new theropods") is a clade that includes coelophysoids and more advanced theropod dinosaurs, and is the only group of theropods that survived the Triassic–Jurassic extinction event. All neotheropods became extinct by the e ...
than ''Eoraptor'' or Sauropodomorpha. Langer (2004) mentioned that this hypothesis was widely accepted, but that more later authors instead preferred to place ''Herrerasaurus'' as well as ''Eoraptor'' basal to Theropoda and Sauropodomorpha, a clade called Eusaurischia
Saurischia ( , meaning "reptile-hipped" from the Greek ' () meaning 'lizard' and ' () meaning 'hip joint') is one of the two basic divisions of dinosaurs (the other being Ornithischia), classified by their hip structure. Saurischia and Ornithis ...
. Langer (2004) conducted a phylogenetic analysis, and found that it was much more likely that ''Herrerasaurus'' was a basal saurischian, than either a theropod or a non-dinosaurian. Langer's proposal was supported by multiple studies until the discovery of '' Tawa'', when Nesbitt ''et al.'' conducted a more inclusive analysis, and the resulting cladogram
A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to d ...
placed Herrerasauridae basal to ''Eoraptor'', but closer to ''Dilophosaurus
''Dilophosaurus'' ( ) is a genus of theropod dinosaurs that lived in what is now North America during the Early Jurassic, about 193 million years ago. Three skeletons were discovered in northern Arizona in 1940, and the two best preserved ...
'' than Sauropodomorpha. Unlike Nesbitt, Ezcurra (2010) conducted a phylogenetic analysis to place his new taxon ''Chromogisaurus
''Chromogisaurus'' is an extinct genus of saturnaliid sauropodomorph which existed in Argentina during the Late Triassic (Carnian) period. It is from the Cancha de Bochas, Valle Pintado member of the Ischigualasto Formation. It was a herbivore ...
'', and found that Herrerasauridae was basal to Eusaurischia.
In 2010, Alcocer and Martinez described a new taxon of herrerasaurid, ''Sanjuansaurus
''Sanjuansaurus'' (" San Juan Province lizard") is a genus of herrerasaurid dinosaur from the Late Triassic (Carnian) Cancha de Bochas and La Peña Members of the Ischigualasto Formation of the Ischigualasto-Villa Unión Basin in northwestern Ar ...
''. It could be distinguished from ''Herrerasaurus'' based on multiple features. In the phylogenetic analysis, ''Herrerasaurus'', ''Sanjuansaurus'' and ''Staurikosaurus'' all were in a polytomy
An internal node of a phylogenetic tree is described as a polytomy or multifurcation if (i) it is in a rooted tree and is linked to three or more child subtrees or (ii) it is in an unrooted tree and is attached to four or more branches. A tr ...
, and Herrerasauridae was the most primitive group of saurischian, outside Eusaurischia, ''Eoraptor'' and ''Guaibasaurus
''Guaibasaurus'' is an extinct genus of basal saurischian dinosaur known from the Late Triassic Caturrita Formation of Rio Grande do Sul, southern Brazil. Most analyses recover it as a sauropodomorph, although there are some suggestions that it ...
''.[ In 2011, Martinez ''et al.'' described '']Eodromaeus
''Eodromaeus'' (meaning "dawn runner") is an extinct genus of probable basal theropod dinosaurs from the Late Triassic of Argentina. Like many other of the earliest-known dinosaurs, it hails from the Carnian-age (~230 Ma) Ischigualasto Formation ...
'', a basal theropod from the same formation as ''Herrerasaurus''. In a phylogenetic analysis, ''Eoraptor'' was placed within Sauropodomorpha, Herrerasauridae was placed as the most basal theropods, and ''Eodromaeus'' was placed as the next most basal. A more recent analysis, by Bittencourt ''et al.'' (2014), placed Herrerasauridae in a polytomy with Theropoda and Sauropodomorpha, with ''Eoraptor'' also being in an unresolved position. This cladogram is shown below.
Other members of the clade
A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...
may include ''Chindesaurus
''Chindesaurus'' ( ) is an extinct genus of basal saurischian dinosaur from the Late Triassic (213-210 million years ago) of the southwestern United States. It is known from a single species, ''C. bryansmalli'', based on a partial skeleton recovere ...
'' from the Upper Petrified Forest
Petrified wood, also known as petrified tree (from Ancient Greek meaning 'rock' or 'stone'; literally 'wood turned into stone'), is the name given to a special type of ''fossilized wood'', the fossilized remains of terrestrial vegetation. ''P ...
(Chinle Formation
The Chinle Formation is an Upper Triassic continental geological formation of fluvial, lacustrine, and palustrine to eolian deposits spread across the U.S. states of Nevada, Utah, northern Arizona, western New Mexico, and western Colorado. In Ne ...
) of Arizona, and possibly '' Caseosaurus'' from the Tecovas Formation
The Tecovas Formation is a geological formation in Texas.Weishampel, David B; et al. (2004). "Dinosaur distribution (Late Triassic, North America)." In: Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berk ...
of the Dockum Group
The Dockum is a Late Triassic (approximately late Carnian through Rhaetian, or 223–200 Ma) geologic group found primarily on the Llano Estacado of western Texas and eastern New Mexico with minor exposures in southwestern Kansas, eastern Color ...
in Texas, although the relationships of these animals are not fully understood, and not all paleontologists agree. Other possible basal theropods, ''Alwalkeria
''Alwalkeria'' (; "for Alick Walker") is a genus partly based on basal saurischian dinosaur remains from the Late Triassic, living in India. A thighbone found indicates a small bipedal form. It has been seen as a chimera.
Etymology
This taxon w ...
'' from the Late Triassic Lower Maleri Formation
The Lower Maleri Formation is a sedimentary geological formation, rock formation found in Andhra Pradesh and Telangana, India. It is the lowermost member of the Pranhita–Godavari Basin. It is of late Carnian to early Norian age (Upper Triassi ...
of India
India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...
, and '' Teyuwasu'', known from very fragmentary remains from the Late Triassic of Brazil, might be related. Paul (1988) noted that it had been incorrectly suggested that ''Staurikosaurus pricei'' was a juvenile ''Herrerasaurus''. This claim was refuted when pelvic bones from a juvenile ''Herrerasaurus'' were discovered, which upon examination did not resemble the pelvic bones of ''Staurikosaurus''.[
]
Paleobiology
The teeth of ''Herrerasaurus'' indicate that it was a carnivore
A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose food and energy requirements derive from animal tissues (mainly muscle, fat and other sof ...
; its size indicates it would have preyed upon small and medium-sized plant eaters. These might have included other dinosaurs, such as ''Pisanosaurus
''Pisanosaurus'' () is an extinct genus of early dinosauriform, likely an ornithischian or silesaurid, from the Late Triassic of Argentina. It was a small, lightly built, ground-dwelling herbivore, that could grow up to an estimated long. Onl ...
'', as well as the more plentiful rhynchosaur
Rhynchosaurs are a group of extinct herbivorous Triassic archosauromorph reptiles, belonging to the order Rhynchosauria. Members of the group are distinguished by their triangular skulls and elongated, beak like premaxillary bones. Rhynchosaurs ...
s and synapsid
Synapsids + (, 'arch') > () "having a fused arch"; synonymous with ''theropsids'' (Greek, "beast-face") are one of the two major groups of animals that evolved from basal amniotes, the other being the sauropsids, the group that includes reptil ...
s. ''Herrerasaurus'' itself may have been preyed upon by giant rauisuchid
Rauisuchidae is a group of large (up to or more) predatory Triassic archosaurs. There is some disagreement over which genera should be included in Rauisuchidae and which should be in the related Prestosuchidae and Poposauridae, and indeed whethe ...
s like ''Saurosuchus
''Saurosuchus'' (meaning "lizard crocodile") is an extinct genus of large loricatan pseudosuchian archosaur that lived in South America during the Late Triassic period. It was a heavy, ground-dwelling, quadrupedal carnivore, likely being the apex ...
''; puncture wounds were found in one skull.
Coprolite
A coprolite (also known as a coprolith) is fossilized feces. Coprolites are classified as trace fossils as opposed to body fossils, as they give evidence for the animal's behaviour (in this case, diet) rather than morphology. The name is de ...
s (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 if the referral to ''Herrerasaurus'' was correct, this carnivore could digest bone.
Comparisons between the scleral ring
Sclerotic rings are rings of bone found in the eyes of many animals in several groups of vertebrates, except for mammals and crocodilians. They can be made up of single bones or multiple segments and take their name from the sclera. They are bel ...
s of ''Herrerasaurus'' and modern birds and reptiles suggest that it may have been cathemeral
Cathemerality, sometimes called metaturnality, is an organismal activity pattern of irregular intervals during the day or night in which food is acquired, socializing with other organisms occurs, and any other activities necessary for livelihood ar ...
, active throughout the day at short intervals.
In a 2001 study conducted by Bruce Rothschild and other paleontologists, 12 hand bones and 20 foot bones referred to ''Herrerasaurus'' were examined for signs of stress fracture
A stress fracture is a fatigue-induced bone fracture caused by repeated stress over time. Instead of resulting from a single severe impact, stress fractures are the result of accumulated injury from repeated submaximal loading, such as running or ...
, but none were found.[Rothschild, B., Tanke, D. H., and Ford, T. L., 2001, Theropod stress fractures and tendon avulsions as a clue to activity: In: ''Mesozoic Vertebrate Life'', edited by Tanke, D. H., and Carpenter, K., Indiana University Press, pp. 331–336.]
PVSJ 407, a ''Herrerasaurus ischigualastensis'', had a pit in a skull bone attributed by Paul Sereno
Paul Callistus Sereno (born October 11, 1957) is a professor of paleontology at the University of Chicago and a National Geographic "explorer-in-residence" who has discovered several new dinosaur species on several continents, including at sites ...
and Novas to a bite. Two additional pits occurred on the splenial
The splenial is a small bone in the lower jaw of reptiles, amphibians and birds, usually located on the lingual side (closest to the tongue) between the angular and surangular
The suprangular or surangular is a jaw bone found in most land verteb ...
. The areas around these pits are swollen and porous, suggesting the wounds were afflicted by a short-lived non-lethal infection. Because of the size and angles of the wound, it is likely that they were obtained in a fight with another ''Herrerasaurus''.[Molnar, R. E., 2001, Theropod paleopathology: a literature survey: In: ''Mesozoic Vertebrate Life'', edited by Tanke, D. H., and Carpenter, K., Indiana University Press, pp. 337–363.]
Paleoecology
The holotype
A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...
of ''Herrerasaurus'' (PVL 2566) was discovered in the Cancha de Bochas Member of the Ischigualasto Formation
The Ischigualasto Formation is a Late Triassic fossiliferous formation and Lagerstätte in the Ischigualasto-Villa Unión Basin of the southwestern La Rioja Province and northeastern San Juan Province in northwestern Argentina. The formation da ...
in San Juan, Argentina. It was collected in 1961 by Victorino Herrera, in sediments that were deposited in the Carnian
The Carnian (less commonly, Karnian) is the lowermost stage of the Upper Triassic Series (or earliest age of the Late Triassic Epoch). It lasted from 237 to 227 million years ago (Ma). The Carnian is preceded by the Ladinian and is followed by t ...
stage of the Triassic
The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest period ...
period, approximately 231 to 229 million years ago. Over the years, the Ischigualasto Formation produced other fossils ultimately referred to ''Herrerasaurus''. In 1958, A.S. Romer discovered specimen MCZ 7063, originally referred to ''Staurikosaurus
''Staurikosaurus'' (Pronounced "STORE-ee-koh-SAWR-us", "Southern Cross lizard") is a genus of herrerasaurid dinosaur from the Late Triassic of Brazil, found in the Santa Maria Formation.
Description
Colbert (1970) described ''Staurikosaurus' ...
'' in Carnian sediments. ''Herrerasaurus'' specimens PVL 2045 and MLP(4)61, were collected in 1959 and 1960, respectively, in sediments that were deposited in the Norian
The Norian is a division of the Triassic Period. It has the rank of an age (geochronology) or stage (chronostratigraphy). It lasted from ~227 to million years ago. It was preceded by the Carnian and succeeded by the Rhaetian.
Stratigraphic defi ...
stage of the Triassic period, approximately 228 to 208 million years ago. However, these specimens are no longer regarded as pertaining to ''Herrerasaurus''. In 1960, Scaglia collected specimen MACN 18.060, originally the holotype of ''Ischisaurus cattoi'', in sediments deposited in the Carnian stage. In 1961, Scaglia collected ''Herrerasaurus'' specimen PVL 2558, in the Carnian beds of this formation. In 1990, the Cancha de Bochas Member produced more ''Herrerasaurus'' specimens, also from its Carnian beds. Specimen PVSJ 53, originally the holotype of ''Frenguellisaurus ischigualastensis'', was collected by Gargiulo & Oñate in 1975 in sediments that were deposited in the Carnian stage.[
Although ''Herrerasaurus'' shared the body shape of the large carnivorous dinosaurs, it lived during a time when dinosaurs were small and few. 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
The Los Colorados Formation is a sedimentary rock formation of the Ischigualasto-Villa Unión Basin, found in the provinces of San Juan and La Rioja in Argentina. The formation dates back to the Norian age of the Late Triassic.
The up to thick f ...
consisted mainly of a variety of crurotarsal A crurotarsal joint is one that’s situated between the bones of ''crus'', i.e. shin (tibia and fibula) and the proximal tarsal bones, i.e. astragalus and calcaneum.
The ankle joint of therian mammals (marsupials and placentals) is a crurotarsal ...
archosaur
Archosauria () is a clade of diapsids, with birds and crocodilians as the only living representatives. Archosaurs are broadly classified as reptiles, in the cladistic sense of the term which includes birds. Extinct archosaurs include non-avian d ...
s and synapsid
Synapsids + (, 'arch') > () "having a fused arch"; synonymous with ''theropsids'' (Greek, "beast-face") are one of the two major groups of animals that evolved from basal amniotes, the other being the sauropsids, the group that includes reptil ...
s. In the Ischigualasto Formation, dinosaurs constituted only about 10% of the total number of fossils, but 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
Paleoecology (also spelled palaeoecology) is the study of interactions between organisms and/or interactions between organisms and their environments across geologic timescales. As a discipline, paleoecology interacts with, depends on and informs ...
of the Ischigualasto Formation was a volcanically active floodplain
A floodplain or flood plain or bottomlands is an area of land adjacent to a river which stretches from the banks of its channel to the base of the enclosing valley walls, and which experiences flooding during periods of high discharge.Goudi ...
covered by forests and subject to strong seasonal rainfalls. The climate was moist and warm, though subject to seasonal variations. Vegetation consisted of fern
A fern (Polypodiopsida or Polypodiophyta ) is a member of a group of vascular plants (plants with xylem and phloem) that reproduce via spores and have neither seeds nor flowers. The polypodiophytes include all living pteridophytes except t ...
s (''Cladophlebis
''Cladophlebis'' is an extinct form genus of fern, used to refer to Paleozoic and Mesozoic fern leaves that have "fern fronds with pinnules that are attached to the rachis, and have a median vein that runs to the apex of the pinnule, and veins ...
''), horsetail
''Equisetum'' (; horsetail, snake grass, puzzlegrass) is the only living genus in Equisetaceae, a family of ferns, which reproduce by spores rather than seeds.
''Equisetum'' is a "living fossil", the only living genus of the entire subclass Eq ...
s, and giant conifer
Conifers are a group of conifer cone, cone-bearing Spermatophyte, seed plants, a subset of gymnosperms. Scientifically, they make up the phylum, division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a single ...
s (''Protojuniperoxylon''). These plants formed lowland 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
South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the southe ...
alongside other early dinosaurs, such as ''Sanjuansaurus
''Sanjuansaurus'' (" San Juan Province lizard") is a genus of herrerasaurid dinosaur from the Late Triassic (Carnian) Cancha de Bochas and La Peña Members of the Ischigualasto Formation of the Ischigualasto-Villa Unión Basin in northwestern Ar ...
'', ''Eoraptor
''Eoraptor'' () is a genus of small, lightly built, basal sauropodomorph. One of the earliest-known dinosaurs, it lived approximately 231 to 228 million years ago, during the Late Triassic in Western Gondwana, in the region that is now northwest ...
'', ''Panphagia
''Panphagia'' is a genus of sauropodomorph dinosaur described in 2009. It lived around 231 million years ago, during the Carnian age of the Late Triassic period in what is now northwestern Argentina. Fossils of the genus were found in the La ...
'', and ''Chromogisaurus
''Chromogisaurus'' is an extinct genus of saturnaliid sauropodomorph which existed in Argentina during the Late Triassic (Carnian) period. It is from the Cancha de Bochas, Valle Pintado member of the Ischigualasto Formation. It was a herbivore ...
'', as well as rhynchosaurs (''Scaphonyx
''Hyperodapedon'' is a genus of rhynchosaurs (beaked, archosaur-like reptiles) from the Late Triassic period (Carnian stage). Fossils of the genus have been found in Africa, Asia, Europe and North and South America. Its first discovery and naming ...
''), cynodonts (e.g., ''Exaeretodon
''Exaeretodon'' is an extinct genus of fairly large, low-slung traversodontid cynodonts from the southern parts of Pangea. Four species are known, from various formations. ''E. argentinus'' is from the Carnian-age (Late Triassic) Cancha de Boch ...
'', ''Ecteninion
''Ecteninion'' is an extinct genus of meat-eating cynodonts that lived during the Late Triassic (Carnian) in South America. The type species ''Ecteninion lunensis'' was named by R.N. Martinez, C.L. May, and C.A. Forster in 1996. ''E. lunensis'' ...
'' and ''Chiniquodon
''Chiniquodon'' is an extinct genus of carnivorous cynodonts, which lived during the Late Triassic (Carnian) in South America (Argentina and Brazil) and Africa (Namibia and Madagascar). ''Chiniquodon'' was closely related to the genus '' Aleodo ...
''), dicynodonts (''Ischigualastia
''Ischigualastia'' is an extinct genus of large dicynodont therapsids that lived during the Late Carnian age and the Early Norian age of the Late Triassic Period. The genus was found in and named after the Ischigualasto Formation (Cancha de Boc ...
''), pseudosuchians (e.g., ''Saurosuchus
''Saurosuchus'' (meaning "lizard crocodile") is an extinct genus of large loricatan pseudosuchian archosaur that lived in South America during the Late Triassic period. It was a heavy, ground-dwelling, quadrupedal carnivore, likely being the apex ...
'', ''Sillosuchus
''Sillosuchus'' is a genus of shuvosaurid poposauroid archosaur that lived in South America during the Late Triassic period. Shuvosaurids were an unusual family of reptiles belonging to the group Poposauroidea; although their closest modern relati ...
'' and ''Aetosauroides
''Aetosauroides'' (meaning "''Aetosaurus''-like") is an extinct genus of aetosaur from the Late Triassic of South America. It is one of four aetosaurs known from South America, the others being ''Neoaetosauroides'', '' Chilenosuchus'' and ''Aetob ...
''), proterochampsids (e.g., '' Proterochampsa'') and temnospondyls ('' Pelorocephalus'').
References
External links
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Introduction to ''Herrerasaurus''
from the University of California Museum of Paleontology
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Prehistoric saurischians
Dinosaur genera
Carnian genera
Late Triassic dinosaurs of South America
Triassic Argentina
Fossils of Argentina
Fossil taxa described in 1963