Saurischia is one of the two basic divisions of dinosaurs. ‘Saurischia’ translates to lizard-hipped. In 1888, Harry Seeley classified dinosaurs into two orders, based on their hip structure, though today most paleontologists classify Saurischia as an unranked clade rather than an order. All carnivorous dinosaurs are traditionally classified as saurischians, as are all of the birds and one of the two primary lineages of herbivorous dinosaurs, the sauropodomorphs. At the end of the Cretaceous Period, all saurischians except the birds became extinct in the course of the Cretaceous–Paleogene extinction event. Birds, as direct descendants of one group of 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 the pubis pointed forward; the ornithischians' pelvis is arranged with the pubis rotated backward, parallel with the ischium 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 found in modern lizards and other reptiles. He named ornithischians "bird-hipped" dinosaurs because their hip arrangement 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 in the lineage of saurischians including birds, lastly in the therizinosaurians; this would be an example of convergent evolution, therizinosaurians, ornithischian dinosaurs all developed a similar hip anatomy independently of each other 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, put forward by Othniel Charles Marsh in 1878, which divided dinosaurs into four orders: Sauropoda, Theropoda and Stegosauria.
Seeley, wanted to formulate a classification that would take into account a single primary difference between major dinosaurian groups based on a characteristic that differentiated them from other reptiles. He found this in the configuration of the hip bones, found that all four of Marsh's orders could be divided neatly into two major groups based on this feature, he placed the Stegosauria and Ornithopoda in the Ornithischia, 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" was an outdated term for two distinct orders lasted many decades in the scientific and popular literature, it was not until the 1960s that scientists began to again consider the possibility that saurischians and ornithischians were more 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 the two dinosaurian groups has stood the test of time, has been supported by modern cladistic analysis of relationships among dinosaurs. One alternative hypothesis challenging Seeley's classification 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 together in a separate group he named the Phytodinosauria; the Phytodinosauria hypothesis was based on the supposed link between ornithischians and prosauropods, the idea that the former had evolved directly from the latter by way of an enigmatic family that seemed to possess characters of both groups, the segnosaurs. However, it was found that segnosaurs were an unusual type of herbivorous theropod saurischian related to birds, the Phytodinosauria hypothesis fell out of favor. A 2017 study by Dr Matthew Grant Baron, Dr David B. Norman and Prof. Paul M. Barrett did not find support for a monophyletic Saurischia, according to its traditional definition.
Instead, the group was found to be paraphyletic, with Theropoda removed from the group and placed as the sister group to the Ornithischia in the newly defined clade Ornithoscelida. As a result, the authors redefined Saurischia as "the most inclusive clade that contains D. carnegii, but not T. horridus", resulting in a clade containing only the Sauropodomorpha and Herrerasauridae
Sauropoda, or the sauropods, are a clade of saurischian dinosaurs. They had long necks, long tails, small heads, four thick, pillar-like legs, they are notable for the enormous sizes attained by some species, the group includes the largest animals to have lived on land. Well-known genera include Brachiosaurus, Diplodocus and Brontosaurus. Sauropods first appeared in the late Triassic Period, where they somewhat resembled the related group "Prosauropoda". By the Late Jurassic, sauropods had become widespread. By the Late Cretaceous, those groups had been replaced by the titanosaurs, which had a near-global distribution. However, as with all other non-avian dinosaurs alive at the time, the titanosaurs died out in the Cretaceous–Paleogene extinction event. Fossilised remains of sauropods have been found on every continent, including Antarctica; the name Sauropoda was coined by O. C. Marsh in 1878, is derived from Greek, meaning "lizard foot". Sauropods are one of the most recognizable groups of dinosaurs, have become a fixture in popular culture due to their large sizes.
Complete sauropod fossil finds are rare. Many species the largest, are known only from isolated and disarticulated bones. Many near-complete specimens lack tail tips and limbs. Sauropods were herbivorous quite long-necked quadrupeds with spatulate teeth, they had tiny heads, massive bodies, most had long tails. Their hind legs were thick and powerful, ending in club-like feet with five toes, though only the inner three bore claws, their forelimbs were rather more slender and ended in pillar-like hands built for supporting weight. Many illustrations of sauropods in the flesh miss these facts, inaccurately depicting sauropods with hooves capping the claw-less digits of the feet, or more than three claws or hooves on the hands; the proximal caudal vertebrae are diagnostic for sauropods. The sauropods' most defining characteristic was their size; the dwarf sauropods were counted among the largest animals in their ecosystem. Their only real competitors in terms of size are the rorquals, such as the blue whale.
But, unlike whales, sauropods were terrestrial animals. Their body structure did not vary as much as other dinosaurs due to size constraints, but they displayed ample variety. Some, like the diplodocids, possessed tremendously long tails, which they may have been able to crack like a whip as a signal or to deter or injure predators, or to make sonic booms. Supersaurus, at 33 to 34 metres long, was the longest sauropod known from reasonably complete remains, but others, like the old record holder, were extremely long; the holotype vertebra of Amphicoelias fragillimus may have come from an animal 58 metres long. However, a research published in 2015 speculated that the size estimates of A. fragillimus may have been exaggerated. The longest dinosaur known from reasonable fossils material is Argentinosaurus huinculensis with length estimates of 25 metres to 39.7 metres. The longest terrestrial animal alive today, the reticulated python, only reaches lengths of 6.95 metres. Others, like the brachiosaurids, were tall, with high shoulders and long necks.
Sauroposeidon was the tallest, reaching about 18 metres high, with the previous record for longest neck being held by Mamenchisaurus. By comparison, the giraffe, the tallest of all living land animals, is only 4.8 to 5.5 metres tall. The best evidence indicates that the most massive were Argentinosaurus, Alamosaurus, Antarctosaurus. There was poor evidence that so-called Bruhathkayosaurus, might have weighed over 175 metric tons but this has been questioned; the weight of Amphicoelias fragillimus was estimated at 122.4 metric tons but 2015 research argued that these estimates may have been exaggerated. The largest land animal alive today, the Savannah elephant, weighs no more than 10.4 metric tons. Among the smallest sauropods were the primitive Ohmdenosaurus, the dwarf titanosaur Magyarosaurus, the dwarf brachiosaurid Europasaurus, 6.2 meters long as a fully-grown adult. Its small stature was the result of insular dwarfism occurring in a population of sauropods isolated on an island of the late Jurassic in what is now the Langenberg area of northern Germany.
The diplodocoid sauropod Brachytrachelopan was the shortest member of its group because of its unusually short neck. Unlike other sauropods, whose necks could grow to up to four times the length of their backs, the neck of Brachytrachelopan was shorter than its backbone. On or shortly before 29 March 2017 a sauropod footprint about 5.6 feet long was found at Walmadany in the Kimberley Region of Western Australia. The report said; as massive quadrupeds, sauropods developed specialized graviportal limbs. The hind feet were broad, retained three claws in most species. Unusual compared with other animals were the modified front feet; the front feet of sauropods were dissimilar from those of modern
Kotasaurus is a genus of sauropod dinosaur from the Early Jurassic period. The only known species is Kotasaurus yamanpalliensis, it was discovered in the Kota Formation of Telangana and shared its habitat with the related Barapasaurus. So far the remains of at least 12 individuals are known; the greater part of the skeleton is known, but the skull is missing, with the exception of two teeth. Like all sauropods, it was a quadrupedal herbivore with long neck and tail. Kotasaurus is one of the most basal sauropods known; the general body plan was that of a typical sauropod, but in several basal features it resembles prosauropods. Like all sauropods, Kotasaurus was an obligate quadruped, while prosauropods were primitively bipedal; the body length is estimated at nine meters, with a weight of 2.5 tonnes, therefore comparable with that of sauropods. The femur was straight and oval in cross section, which means that the limbs were columnar; the teeth were spoon-shaped, like those of sauropods. Basal features, on the other hand, include the short and twisted humerus, as well as the retention of a lesser trochanter on the femur.
The neural spines of the vertebrae were built and their centra are massive, in contrast to those of the related Barapasaurus, which show more hollowing, be it without pneumatisation, of the sides as a weight-saving measure. Autapomorphies include the slender limb bones as well as the low and elongated preacetabular process, it was not clear if Kotasaurus represents a true sauropod or a basal sauropodomorph that has to be classified outside Sauropoda. Some paleontologists placed it inside a basal sauropod family called Vulcanodontidae though, together with Barapasaurus and the fragmentary Ohmdenosaurus and Zizhongosaurus; this grouping is now recognized to be paraphyletic. Today Kotasaurus is recognized as one of the most basal sauropods known; the exact relationships are not clear, however. A recent study by Bandyopadhyay and colleagues renders Kotasaurus to be more basal than Barapasaurus and Vulcanodon but more derived than Jingshanosaurus and Chinshakiangosaurus. All known fossils come from an area of 2,400 m² near the village of Yamanpalli in Telangana forty kilometres north of the Barapasaurus type locality.
These finds, altogether 840 skeletal parts, were found in the late 1970s. In 1988 they were named and described by P. M. Yadagiri as a new genus and species of sauropod, Kotasaurus yamanpalliensis; the generic name refers to the Kota Formation. The specific name reflects the provenance from Yamanpalli; the holotype is an ilium. The Geological Survey of India combined several elements into a skeletal mount and displayed it at the Birla Science Museum, Hyderabad. In 2001, Yadagiri described the osteology in more detail
Lessemsauridae is a clade of early sauropod dinosaurs that lived in the Triassic and Jurassic of Argentina and South Africa. A phylogenetic analysis performed by Apaldetti and colleagues in 2018 recovered a new clade of Sauropodiformes uniting Lessemsaurus and the described Ingentia which they named Lessemsauridae. Lessemsaurids had pneumatic cervical and dorsal vertebrae antero-posteriorly short but tall cervical vertebrae, robust cervicals, a expanded distal scapula blade, upright arms. Depending on the definition of Sauropoda, the clade is either the oldest sauropod taxon, or the sister taxon of the clade. An additional member of the clade was named in 2018, Ledumahadi. Lessemsaurids are recognised as large quadrupeds that achieved giant sizes independently of other giant sauropods; the phylogenetic analysis performed by Apaldetti and colleagues is shown below
Archaeodontosaurus is a genus of sauropod dinosaur from the Middle Jurassic. Its fossils were found in the Isalo III Formation of Madagascar; the type species, Archaeodontosaurus descouensi, was described in September 2005. The specific name honours Didier Descouens, it is a probable sauropod, with prosauropod-like teeth. Dml.cmnh.org Media related to Archaeodontosaurus at Wikimedia Commons
A chevron is one of a series of bones on the ventral side of the tail in many reptiles, including dinosaurs, some mammals such as kangaroos and manatees. Their main function is to protect critical elements in the tail such as nerves and blood vessels from being damaged when the animal either supports its weight on its tail, or pushes it against a hard surface to propel itself
A chordate is an animal constituting the phylum Chordata. During some period of their life cycle, chordates possess a notochord, a dorsal nerve cord, pharyngeal slits, an endostyle, a post-anal tail: these five anatomical features define this phylum. Chordates are bilaterally symmetric; the Chordata and Ambulacraria together form the superphylum Deuterostomia. Chordates are divided into three subphyla: Vertebrata. There are extinct taxa such as the Vetulicolia. Hemichordata has been presented as a fourth chordate subphylum, but now is treated as a separate phylum: hemichordates and Echinodermata form the Ambulacraria, the sister phylum of the Chordates. Of the more than 65,000 living species of chordates, about half are bony fish that are members of the superclass Osteichthyes. Chordate fossils have been found from as early as the Cambrian explosion, 541 million years ago. Cladistically, vertebrates - chordates with the notochord replaced by a vertebral column during development - are considered to be a subgroup of the clade Craniata, which consists of chordates with a skull.
The Craniata and Tunicata compose the clade Olfactores. Chordates form a phylum of animals that are defined by having at some stage in their lives all of the following anatomical features: A notochord, a stiff rod of cartilage that extends along the inside of the body. Among the vertebrate sub-group of chordates the notochord develops into the spine, in wholly aquatic species this helps the animal to swim by flexing its tail. A dorsal neural tube. In fish and other vertebrates, this develops into the spinal cord, the main communications trunk of the nervous system. Pharyngeal slits; the pharynx is the part of the throat behind the mouth. In fish, the slits are modified to form gills, but in some other chordates they are part of a filter-feeding system that extracts particles of food from the water in which the animals live. Post-anal tail. A muscular tail that extends backwards behind the anus. An endostyle; this is a groove in the ventral wall of the pharynx. In filter-feeding species it produces mucus to gather food particles, which helps in transporting food to the esophagus.
It stores iodine, may be a precursor of the vertebrate thyroid gland. There are soft constraints that separate chordates from certain other biological lineages, but are not part of the formal definition: All chordates are deuterostomes; this means. All chordates are based on a bilateral body plan. All chordates are coelomates, have a fluid filled body cavity called a coelom with a complete lining called peritoneum derived from mesoderm; the following schema is from the third edition of Vertebrate Palaeontology. The invertebrate chordate classes are from Fishes of the World. While it is structured so as to reflect evolutionary relationships, it retains the traditional ranks used in Linnaean taxonomy. Phylum Chordata †Vetulicolia? Subphylum Cephalochordata – Class Leptocardii Clade Olfactores Subphylum Tunicata – Class Ascidiacea Class Thaliacea Class Appendicularia Class Sorberacea Subphylum Vertebrata Infraphylum incertae sedis Cyclostomata Superclass'Agnatha' paraphyletic Class Myxini Class Petromyzontida or Hyperoartia Class †Conodonta Class †Myllokunmingiida Class †Pteraspidomorphi Class †Thelodonti Class †Anaspida Class †Cephalaspidomorphi Infraphylum Gnathostomata Class †Placodermi Class Chondrichthyes Class †Acanthodii Superclass Osteichthyes Class Actinopterygii Class Sarcopterygii Superclass Tetrapoda Class Amphibia Class Sauropsida Class Synapsida Craniates, one of the three subdivisions of chordates, all have distinct skulls.
They include the hagfish. Michael J. Benton commented that "craniates are characterized by their heads, just as chordates, or all deuterostomes, are by their tails". Most craniates are vertebrates; these consist of a series of bony or cartilaginous cylindrical vertebrae with neural arches that protect the spinal cord, with projections that link the vertebrae. However hagfish have incomplete braincases and no vertebrae, are therefore not regarded as vertebrates, but as members of the craniates, the group from which vertebrates are thought to have evolved; however the cladistic exclusion of hagfish from the vertebrates is controversial, as they ma