85-547: Herrerasaurus is likely a genus of saurischian dinosaur from the Late Triassic period. Measuring 6 m (20 ft) long and weighing around 350 kg (770 lb), this genus was one of the earliest dinosaurs 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 fossils of this carnivore have been discovered in
170-457: A Herrerasaurus ischigualastensis , had a pit in a skull bone attributed by Paul Sereno and Novas to a bite. Two additional pits occurred on the splenial . 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 . The holotype of Herrerasaurus (PVL 2566)
255-443: A consequent . P is the assumption in a (possibly counterfactual ) What If question. The adjective hypothetical , meaning "having the nature of a hypothesis", or "being assumed to exist as an immediate consequence of a hypothesis", can refer to any of these meanings of the term "hypothesis". In its ancient usage, hypothesis referred to a summary of the plot of a classical drama . The English word hypothesis comes from
340-1640: A clade (Herrerasauria) outside Dinosauria. Other recent studies support a view closer to the traditional Saurischia hypothesis, with theropods closer to sauropodomorphs than to ornithischians. Novas et al . (2021) support Cau's herrerasaur phylogeny but place this clade in Saurischia. † Ornithischia (incl. " Silesauridae ") [REDACTED] † Herrerasauridae [REDACTED] † Daemonosaurus [REDACTED] † Chindesaurus [REDACTED] † Tawa [REDACTED] † Saltopus [REDACTED] † Eodromaeus [REDACTED] † Sauropodomorpha [REDACTED] Theropoda [REDACTED] [REDACTED] † Silesauridae † Ornithischia [REDACTED] † Herrerasauridae [REDACTED] † Daemonosaurus [REDACTED] † Chindesaurus [REDACTED] † Tawa [REDACTED] † Sauropodomorpha [REDACTED] † Eodromaeus [REDACTED] Neotheropoda [REDACTED] [REDACTED] † Silesauridae † Herrerasauridae [REDACTED] † Sauropodomorpha [REDACTED] † Ornithischia [REDACTED] Theropoda [REDACTED] [REDACTED] † Silesauridae (incl. Pisanosaurus ) † Herrerasauridae [REDACTED] † Daemonosaurus [REDACTED] † Tawa [REDACTED] † Sauropodomorpha [REDACTED] † Eodromaeus [REDACTED] † Ornithischia [REDACTED] Theropoda [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] Hypothesis A hypothesis ( pl. : hypotheses )
425-522: A clade called Eu saurischia . 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 placed Herrerasauridae basal to Eoraptor , but closer to Dilophosaurus than Sauropodomorpha. Unlike Nesbitt, Ezcurra (2010) conducted
510-528: A clade containing only the Sauropodomorpha and Herrerasauridae . Thomas Holtz (2017) recommended using the name Sauropodomorpha to refer to a possible clade that includes traditional sauropodomorphs and herrerasaurids; alternatively, he proposed redefining the long-disused taxon Pachypodosauria to include Sauropodomorpha and Herrerasauridae as subclades. Cau (2018) also supported Ornithoscelida but placed herrerasaurids, Tawa and Daemonosaurus in
595-479: A convenient mathematical approach that simplifies cumbersome calculations . Cardinal Bellarmine gave a famous example of this usage in the warning issued to Galileo in the early 17th century: that he must not treat the motion of the Earth as a reality, but merely as a hypothesis. In common usage in the 21st century, a hypothesis refers to a provisional idea whose merit requires evaluation. For proper evaluation,
680-698: A current family. This was further supported by Benedetto in 1973, who named for the taxa the new family Herrerasauridae , which he classified as saurischians, possibly within Theropoda but not in Sauropodomorpha . However, in 1977 Galton proposed that Herrerasauridae only included Herrerasaurus , and found it to be Saurischian incertae sedis . Proposed in 1987 by Brinkman and Sues, Herrerasaurus has at times been considered basal to Ornithischia and Saurischia, although Brinkmann and Sues still considered it to be inside Dinosauria . They supported this on
765-523: A formative phase. In recent years, philosophers of science have tried to integrate the various approaches to evaluating hypotheses, and the scientific method in general, to form a more complete system that integrates the individual concerns of each approach. Notably, Imre Lakatos and Paul Feyerabend , Karl Popper's colleague and student, respectively, have produced novel attempts at such a synthesis. Concepts in Hempel's deductive-nomological model play
850-430: A hypothesis must be falsifiable , and that one cannot regard a proposition or theory as scientific if it does not admit the possibility of being shown to be false. Other philosophers of science have rejected the criterion of falsifiability or supplemented it with other criteria, such as verifiability (e.g., verificationism ) or coherence (e.g., confirmation holism ). The scientific method involves experimentation to test
935-461: A key role in the development and testing of hypotheses. Most formal hypotheses connect concepts by specifying the expected relationships between propositions . When a set of hypotheses are grouped together, they become a type of conceptual framework . When a conceptual framework is complex and incorporates causality or explanation, it is generally referred to as a theory. According to noted philosopher of science Carl Gustav Hempel , Hempel provides
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#17327825689021020-499: A monophyletic Saurischia, according to its traditional definition. Instead, the group was found to be paraphyletic . As a solution, Theropoda was removed from the group and placed as the sister group to the Ornithischia in the newly defined clade Ornithoscelida . As another result, the authors redefined Saurischia as "the most inclusive clade that contains D[iplodocus] carnegii , but not T[riceratops] horridus ", resulting in
1105-420: A phylogenetic analysis to place his new taxon Chromogisaurus , and found that Herrerasauridae was basal to Eusaurischia. In 2010, Alcocer and Martinez described a new taxon of herrerasaurid, Sanjuansaurus . It could be distinguished from Herrerasaurus based on multiple features. In the phylogenetic analysis, Herrerasaurus , Sanjuansaurus and Staurikosaurus all were in a polytomy , and Herrerasauridae
1190-525: A polytomy with Theropoda and Sauropodomorpha, with Eoraptor also being in an unresolved position. This cladogram is shown below. Ornithischia Eoraptor Sauropodomorpha Staurikosaurus Herrerasaurus Sanjuansaurus Eodromaeus Tawa Neotheropoda Other members of the clade may include Chindesaurus from the Upper Petrified Forest ( Chinle Formation ) of Arizona, and possibly Caseosaurus from
1275-560: A proposed new law of nature. In such an investigation, if the tested remedy shows no effect in a few cases, these do not necessarily falsify the hypothesis. Instead, statistical tests are used to determine how likely it is that the overall effect would be observed if the hypothesized relation does not exist. If that likelihood is sufficiently small (e.g., less than 1%), the existence of a relation may be assumed. Otherwise, any observed effect may be due to pure chance. In statistical hypothesis testing, two hypotheses are compared. These are called
1360-444: A ridge on the lateral surface of the jugal bone, and a deeply incised supratemporal fossa that extends across the medial postorbital process; the subquadrate ventral squamosal process has a lateral depression, and the quadratojugal bone overlaps the posterodorsal quadrate face; the pterygoid process of the quadrate has an inturned, trough-shaped ventral margin, and the presence of a slender ribbed posterodorsal dentary process;
1445-511: A similar hip anatomy independently of each other, possibly as an adaptation to their herbivorous or omnivorous diets. In his paper naming the two groups, Seeley reviewed previous classification schemes put forth by other paleontologists to divide up the traditional order Dinosauria. He preferred one that had been put forward by Othniel Charles Marsh in 1878, which divided dinosaurs into four orders: Sauropoda , Theropoda , Ornithopoda , and Stegosauria (these names are still used today in much
1530-477: 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 group (a group descended from a common ancestor). The monophyly of dinosaurs was explicitly proposed in
1615-411: A useful metaphor that describes the relationship between a conceptual framework and the framework as it is observed and perhaps tested (interpreted framework). "The whole system floats, as it were, above the plane of observation and is anchored to it by rules of interpretation. These might be viewed as strings which are not part of the network but link certain points of the latter with specific places in
1700-424: A working hypothesis is constructed as a statement of expectations, which can be linked to the exploratory research purpose in empirical investigation. Working hypotheses are often used as a conceptual framework in qualitative research. The provisional nature of working hypotheses makes them useful as an organizing device in applied research. Here they act like a useful guide to address problems that are still in
1785-581: Is a member of the Herrerasauridae , a family of similar genera that were among the earliest of the dinosaurian evolutionary radiation . Herrerasaurus was named by paleontologist Osvaldo Reig after Victorino Herrera, an Andean goatherd who first noticed its fossils in outcrops near the city of San Juan, Argentina in 1959. These rocks, which later yielded Eoraptor , are part of the Ischigualasto Formation and date from
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#17327825689021870-417: 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 observations that cannot satisfactorily be explained with the available scientific theories. Even though the words "hypothesis" and " theory " are often used interchangeably, a scientific hypothesis
1955-423: Is not the same as a scientific theory . A working hypothesis is a provisionally accepted hypothesis proposed for further research in a process beginning with an educated guess or thought. A different meaning of the term hypothesis is used in formal logic , to denote the antecedent of a proposition ; thus in the proposition "If P , then Q ", P denotes the hypothesis (or antecedent); Q can be called
2040-547: 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 . A complete Herrerasaurus skull was found in 1988, by a team of paleontologists led by Paul Sereno . Based on the new fossils, authors such as Thomas Holtz and José Bonaparte classified Herrerasaurus at
2125-585: The Greek sauros ( σαῦρος ) meaning 'lizard' and ischion ( ἴσχιον ) meaning 'hip joint') is one of the two basic divisions of dinosaurs (the other being Ornithischia ), classified by their hip structure. Saurischia and Ornithischia were originally called orders by Harry Seeley in 1888 though today most paleontologists classify Saurischia as an unranked clade rather than an order. All carnivorous dinosaurs (certain types of theropods ) are traditionally classified as saurischians, as are all of
2210-452: The Ischigualasto Formation of Carnian age (late Triassic according to the ICS , dated to 231.4 million years ago) in northwestern Argentina. The type species , Herrerasaurus ischigualastensis , was described by Osvaldo Reig in 1963 and is the only species assigned to the genus . Ischisaurus and Frenguellisaurus are synonyms . For many years, the classification of Herrerasaurus
2295-584: The Norian 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,
2380-793: The Tecovas Formation of the Dockum Group in Texas, although the relationships of these animals are not fully understood, and not all paleontologists agree. Other possible basal theropods, Alwalkeria from the Late Triassic Lower Maleri Formation of India , 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
2465-401: The ancient Greek word ὑπόθεσις hypothesis whose literal or etymological sense is "putting or placing under" and hence in extended use has many other meanings including "supposition". In Plato 's Meno (86e–87b), Socrates dissects virtue with a method used by mathematicians, that of "investigating from a hypothesis". In this sense, 'hypothesis' refers to a clever idea or to
2550-646: The birds and one of the two primary lineages of herbivorous dinosaurs, the sauropodomorphs . At the end of the Cretaceous Period , all saurischians except birds became extinct in the course of the Cretaceous–Paleogene extinction event . Birds, as a group of maniraptoran theropod dinosaurs, are a sub- clade of saurischian dinosaurs in phylogenetic classification . Saurischian dinosaurs are traditionally distinguished from ornithischian dinosaurs by their three-pronged pelvic structure, with
2635-555: The humerus , and the articular surface for the ulnare on the ulna 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 are subequal in width (noted by Sereno and Novas, 1993). Herrerasaurus
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2720-463: The null hypothesis and the alternative hypothesis . The null hypothesis is the hypothesis that states that there is no relation between the phenomena whose relation is under investigation, or at least not of the form given by the alternative hypothesis. The alternative hypothesis, as the name suggests, is the alternative to the null hypothesis: it states that there is some kind of relation. The alternative hypothesis may take several forms, depending on
2805-470: The pubis pointed forward. The ornithischians' pelvis is arranged with the pubis rotated backward, parallel with the ischium , often also with a forward-pointing process, giving a four-pronged structure. The saurischian hip structure led Seeley to name them " lizard -hipped" dinosaurs, because they retained the ancestral hip anatomy also found in modern lizards and other reptiles. He named ornithischians "bird-hipped" dinosaurs because their hip arrangement
2890-891: The rauisuchian Postosuchus ). In 1985, Charig noted that Herrerasaurus was of uncertain classification, showing similarities to both " prosauropods " 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 , he stated that they appeared as though they could not be placed in
2975-419: The surangular bone has a forked anterior process for articulation with the posterodorsal dentary process; the humerus ' internal tuberosity 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
3060-426: The 1970s by Galton and Robert T. Bakker , who compiled a list of cranial and postcranial synapomorphies (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
3145-479: 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
3230-536: The Stegosauria and Ornithopoda in the Ornithischia, and the Theropoda and Sauropoda in the Saurischia. Furthermore, Seeley used this major difference in the hip bones, along with many other noted differences between the two groups, to argue that "dinosaurs" were not a natural grouping at all, but rather two distinct orders that had arisen independently from more primitive archosaurs . This concept that "dinosaur"
3315-690: The Triassic Period, dinosaurs were becoming the dominant large land animals, and the other archosaurs and synapsids declined in variety and number. Studies suggest that the paleoenvironment of the Ischigualasto Formation was a volcanically active floodplain covered by forests and subject to strong seasonal rainfalls. The climate was moist and warm, though subject to seasonal variations. Vegetation consisted of ferns ( Cladophlebis ), horsetails , and giant conifers ( Protojuniperoxylon ). These plants formed lowland forests along
3400-405: The ability of some hypothesis to adequately answer the question under investigation. In contrast, unfettered observation is not as likely to raise unexplained issues or open questions in science, as would the formulation of a crucial experiment to test the hypothesis. A thought experiment might also be used to test the hypothesis. In framing a hypothesis, the investigator must not currently know
3485-1105: The banks of rivers. Herrerasaurus remains appear to have been the most common among the carnivores of the Ischigualasto Formation. It lived in the jungles of Late Triassic South America alongside other early dinosaurs, such as Sanjuansaurus , Eoraptor , Panphagia , and Chromogisaurus , as well as rhynchosaurs ( Scaphonyx ), cynodonts (e.g., Exaeretodon , Ecteninion and Chiniquodon ), dicynodonts ( Ischigualastia ), pseudosuchians (e.g., Saurosuchus , Sillosuchus and Aetosauroides ), proterochampsids (e.g., Proterochampsa ) and temnospondyls ( Pelorocephalus ). [REDACTED] [REDACTED] [REDACTED] Saurischia 1st row (early saurischians): Herrerasaurus ischigualastensis ( herrerasaur ), Eodromaeus murphi ( basal theropod ); 2nd row ( theropods ): Pelecanus occidentalis , Tyrannosaurus rex ; 3rd row ( sauropodomorphs ): Apatosaurus louisae , Plateosaurus trossingensis . Saurischia ( / s ɔː ˈ r ɪ s k i ə / saw- RIS -kee-ə , meaning "reptile-hipped" from
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3570-499: The basal saurischian hypothesis. If Herrerasaurus were indeed a theropod, it would indicate that theropods, sauropodomorphs , and ornithischians diverged even earlier than herrerasaurids, before the middle Carnian , 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
3655-515: 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 , and Max Langer (2004), Langer and Benton (2006), and Randall Irmis and his coauthors (2007) favoring
3740-418: 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 plesiomorphic state that
3825-461: 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 (where the femur meets the pelvis ) 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 trait as seen in dromaeosaurids and birds . Additionally,
3910-674: The clade, and redefined it as the latest common ancestor of Triceratops and birds . They also discussed what this definition would do to the most basal taxa, such as Herrerasauridae, and Eoraptor . 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
3995-514: The end of the pubis has a booted shape, like those in avetheropods ; and the vertebral centra have an hourglass shape as found in Allosaurus . Herrerasaurus had 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 . It had five pairs of fenestrae (skull openings) in its skull, two pairs of which were for
4080-420: The eyes and nostrils. Between the eyes and the nostrils were two antorbital fenestrae and a pair of tiny, 1-centimeter-long (0.39 in) 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 lizards . The rear of
4165-403: The family Gryponichidae inside Carnosauria. The same year, Walker published a differing opinion that Herrerasaurus instead was allied with Plateosauridae , although it differed in possessing a pubic boot. Walker also proposed that Herrerasaurus may instead be close to Poposaurus (now considered a pseudosuchian ) and the unnamed theropod from the Dockum Group of Texas (now assigned to
4250-484: The framer of a hypothesis needs to define specifics in operational terms. A hypothesis requires more work by the researcher in order to either confirm or disprove it. In due course, a confirmed hypothesis may become part of a theory or occasionally may grow to become a theory itself. Normally, scientific hypotheses have the form of a mathematical model . Sometimes, but not always, one can also formulate them as existential statements , stating that some particular instance of
4335-475: The hypothesis is proven to be either "true" or "false" through a verifiability - or falsifiability -oriented experiment . Any useful hypothesis will enable predictions by reasoning (including deductive reasoning ). It might predict the outcome of an experiment in a laboratory setting or the observation of a phenomenon in nature . The prediction may also invoke statistics and only talk about probabilities. Karl Popper , following others, has argued that
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#17327825689024420-520: The idea that the former had evolved directly from the latter, possibly by way of an enigmatic family that seemed to possess characters of both groups, the segnosaurs . However, it was later found that segnosaurs were an unusual type of herbivorous theropod saurischian closely related to birds , and the Phytodinosauria hypothesis fell out of favor. A 2017 study by Matthew Grant Baron, David B. Norman and Paul M. Barrett did not find support for
4505-468: The late Carnian stage of the Late Triassic 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 and a juvenile of Herrerasaurus . Reig believed Herrerasaurus was an early example of a carnosaur , but this was the subject of much debate over the next 30 years, and the genus
4590-428: The length of its hind limbs. The upper arm and forearm were rather short, while the manus (hand) was elongated. The first two fingers and the thumb ended in curved, sharp claws for grasping prey. 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
4675-413: 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 - maxilla fenestra, and the dorsal part of laterotemporal fenestra is less than a third as wide as the ventral part; the presence of
4760-474: The more plentiful rhynchosaurs and synapsids . Herrerasaurus itself may have been preyed upon by giant " rauisuchians " ( loricatans ) like Saurosuchus ; puncture wounds were found in one skull. Coprolites (fossilized dung) containing small bones but no trace of plant fragments, discovered in the Ischigualasto Formation, have been assigned to Herrerasaurus based on fossil abundance. Mineralogical and chemical analysis of these coprolites indicates that if
4845-440: The nature of the hypothesized relation; in particular, it can be two-sided (for example: there is some effect, in a yet unknown direction) or one-sided (the direction of the hypothesized relation, positive or negative, is fixed in advance). Conventional significance levels for testing hypotheses (acceptable probabilities of wrongly rejecting a true null hypothesis) are .10, .05, and .01. The significance level for deciding whether
4930-430: The null hypothesis is rejected and the alternative hypothesis is accepted must be determined in advance, before the observations are collected or inspected. If these criteria are determined later, when the data to be tested are already known, the test is invalid. The above procedure is actually dependent on the number of the participants (units or sample size ) that are included in the study. For instance, to avoid having
5015-525: The others were attributable to convergent evolution . Sereno's analysis of Herrerasaurus also led him to propose several new dinosaurian synapomorphies. 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 m (20 ft) in total length and 350 kg (770 lb) in weight. Smaller specimens were about 4.5 m (15 ft) long and weighed about 200 kg (440 lb). Herrerasaurus
5100-400: The outcome of a test or that it remains reasonably under continuing investigation. Only in such cases does the experiment, test or study potentially increase the probability of showing the truth of a hypothesis. If the researcher already knows the outcome, it counts as a "consequence" — and the researcher should have already considered this while formulating the hypothesis. If one cannot assess
5185-402: The phenomenon under examination has some characteristic and causal explanations, which have the general form of universal statements , stating that every instance of the phenomenon has a particular characteristic. In entrepreneurial setting, a hypothesis is used to formulate provisional ideas about the attributes of products or business models. The formulated hypothesis is then evaluated, where
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#17327825689025270-414: The plane of observation. By virtue of those interpretative connections, the network can function as a scientific theory." Hypotheses with concepts anchored in the plane of observation are ready to be tested. In "actual scientific practice the process of framing a theoretical structure and of interpreting it are not always sharply separated, since the intended interpretation usually guides the construction of
5355-460: The posterior border of the ilial peduncle forms a right angle with the dorsal border of the shaft on the ischium . 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 ectepicondyle, a feature also present in Saturnalia ; a saddle-shaped ulnar condyle of
5440-410: The predictions by observation or by experience , the hypothesis needs to be tested by others providing observations. For example, a new technology or theory might make the necessary experiments feasible. A trial solution to a problem is commonly referred to as a hypothesis—or, often, as an " educated guess " —because it provides a suggested outcome based on the evidence. However, some scientists reject
5525-517: 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 analysis, which placed it closer to Neotheropoda 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,
5610-473: The referral to Herrerasaurus was correct, this carnivore could digest bone. Comparisons between the scleral rings of Herrerasaurus and modern birds and reptiles suggest that it may have been cathemeral , 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 , but none were found. PVSJ 407,
5695-428: The remains as non-dinosaurian. Two other partial skeletons, with skull material, were named Frenguellisaurus ischigualastensis by Fernando Novas 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 . Novas (1992) and Sereno and Novas (1992) examined
5780-481: The same way to refer to suborders or clades within Saurischia and Ornithischia). Seeley, however, wanted to formulate a classification that would take into account a single primary difference between major dinosaurian groups based on a characteristic that also differentiated them from other reptiles. He found this in the configuration of the hip bones, and found that all four of Marsh's orders could be divided neatly into two major groups based on this feature. He placed
5865-576: The sample size be too small to reject a null hypothesis, it is recommended that one specify a sufficient sample size from the beginning. It is advisable to define a small, medium and large effect size for each of a number of important statistical tests which are used to test the hypotheses. Mount Hypothesis in Antarctica is named in appreciation of the role of hypothesis in scientific research. Several hypotheses have been put forth, in different subject areas: hypothesis [...]— Working hypothesis ,
5950-451: The term "educated guess" as incorrect. Experimenters may test and reject several hypotheses before solving the problem. According to Schick and Vaughn, researchers weighing up alternative hypotheses may take into consideration: A working hypothesis is a hypothesis that is provisionally accepted as a basis for further research in the hope that a tenable theory will be produced, even if the hypothesis ultimately fails. Like all hypotheses,
6035-399: The theoretician". It is, however, "possible and indeed desirable, for the purposes of logical clarification, to separate the two steps conceptually". When a possible correlation or similar relation between phenomena is investigated, such as whether a proposed remedy is effective in treating a disease, the hypothesis that a relation exists cannot be examined the same way one might examine
6120-501: The two dinosaurian groups has stood the test of time, and has been supported by modern cladistic analysis of relationships among dinosaurs. A node-base clade, Eusaurischia , was named for the least inclusive group containing sauropodomorphs (represented by Cetiosaurus ) and theropods (represented by Neornithes ). Any saurischian that diverged before the theropod-sauropodomorph split is therefore outside clade Eusaurischia. One alternative hypothesis challenging Seeley's classification
6205-428: 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 . The teeth of Herrerasaurus indicate that it was a carnivore ; its size indicates it would have preyed upon small and medium-sized plant eaters. These might have included other dinosaurs, such as Pisanosaurus , as well as
6290-434: Was an outdated term for two distinct orders lasted many decades in the scientific and popular literature, and it was not until the 1960s that scientists began to again consider the possibility that saurischians and ornithischians were more closely related to each other than they were to other archosaurs. Although his concept of a polyphyletic Dinosauria is no longer accepted by most paleontologists, Seeley's basic division of
6375-793: 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 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 in Carnian sediments. Herrerasaurus specimens PVL 2045 and MLP(4)61, were collected in 1959 and 1960, respectively, in sediments that were deposited in
6460-406: Was first suggested by Sereno (1998), and more closely follows the original inclusion proposed by Benedetto. Another group, Herrerasauria was named by Galton in 1985, and defined as Herrerasaurus but not Liliensternus or Plateosaurus 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
6545-467: Was found in both taxa. This was disagreed with in 1992 by Novas, who stated many derived synapomorphies 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
6630-465: Was fully bipedal. It had strong hind limbs with short thighs 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
6715-511: Was originally considered to be a genus within Carnosauria , which then included forms similar to Megalosaurus and Antrodemus (the latter is probably equivalent to Allosaurus ), 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
6800-501: Was proposed by Robert T. Bakker in his 1986 book The Dinosaur Heresies . Bakker's classification separated the theropods into their own group and placed the two groups of herbivorous dinosaurs (the sauropodomorphs and ornithischians) together in a separate group he named the Phytodinosauria ("plant dinosaurs"). The Phytodinosauria hypothesis was based partly on the supposed link between ornithischians and prosauropods , and
6885-518: Was superficially similar to that of birds, though he did not propose any specific relationship between ornithischians and birds. However, in the view which has long been held, this "bird-hipped" arrangement evolved several times independently in dinosaurs, first in the ornithischians, then in the lineage of saurischians including birds ( Avialae ), and lastly in the therizinosaurians . This would then be an example of convergent evolution : avialans, therizinosaurians, and ornithischian dinosaurs all developed
6970-477: Was the most primitive group of saurischian, outside Eusaurischia, Eoraptor and Guaibasaurus . In 2011, Martinez et al. described Eodromaeus , 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
7055-403: Was the time of non-dinosaurian reptiles, not dinosaurs, and a major turning point in the Earth's ecology. The vertebrate fauna of the Ischigualasto Formation and the slightly later Los Colorados Formation consisted mainly of a variety of crurotarsal archosaurs and synapsids . In the Ischigualasto Formation, dinosaurs constituted only about 10% of the total number of fossils, but by the end of
7140-438: Was unclear because it was known from very fragmentary remains. It was hypothesized to be a basal theropod , a basal sauropodomorph , a basal saurischian , or not a dinosaur at all but another type of archosaur . 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
7225-409: Was variously classified during that time. In 1970, Steel classified Herrerasaurus as a prosauropod . In 1972, Peter Galton classified the genus as not diagnosable beyond Saurischia . Later, using cladistic analysis, some researchers put Herrerasaurus and Staurikosaurus at the base of the dinosaur tree before the separation between ornithischians and saurischians. Several researchers classified
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