The Triassic is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.9 million years ago, to the beginning of the Jurassic Period 201.3 Mya. The Triassic is the shortest period of the Mesozoic Era. Both the start and end of the period are marked by major extinction events. Triassic began in the wake of the Permian–Triassic extinction event, which left the Earth's biosphere impoverished. Therapsids and archosaurs were the chief terrestrial vertebrates during this time. A specialized subgroup of archosaurs, called dinosaurs, first appeared in the Late Triassic but did not become dominant until the succeeding Jurassic Period; the first true mammals, themselves a specialized subgroup of therapsids evolved during this period, as well as the first flying vertebrates, the pterosaurs, like the dinosaurs, were a specialized subgroup of archosaurs. The vast supercontinent of Pangaea existed until the mid-Triassic, after which it began to rift into two separate landmasses, Laurasia to the north and Gondwana to the south.
The global climate during the Triassic was hot and dry, with deserts spanning much of Pangaea's interior. However, the climate became more humid as Pangaea began to drift apart; the end of the period was marked by yet another major mass extinction, the Triassic–Jurassic extinction event, that wiped out many groups and allowed dinosaurs to assume dominance in the Jurassic. The Triassic was named in 1834 by Friedrich von Alberti, after the three distinct rock layers that are found throughout Germany and northwestern Europe—red beds, capped by marine limestone, followed by a series of terrestrial mud- and sandstones—called the "Trias"; the Triassic is separated into Early and Late Triassic Epochs, the corresponding rocks are referred to as Lower, Middle, or Upper Triassic. The faunal stages from the youngest to oldest are: During the Triassic all the Earth's land mass was concentrated into a single supercontinent centered more or less on the equator and spanning from pole to pole, called Pangaea.
From the east, along the equator, the Tethys sea penetrated Pangaea, causing the Paleo-Tethys Ocean to be closed. In the mid-Triassic a similar sea penetrated along the equator from the west; the remaining shores were surrounded by the world-ocean known as Panthalassa. All the deep-ocean sediments laid down during the Triassic have disappeared through subduction of oceanic plates; the supercontinent Pangaea was rifting during the Triassic—especially late in that period—but had not yet separated. The first nonmarine sediments in the rift that marks the initial break-up of Pangaea, which separated New Jersey from Morocco, are of Late Triassic age. S. these thick sediments comprise the Newark Group. Because a super-continental mass has less shoreline compared to one broken up, Triassic marine deposits are globally rare, despite their prominence in Western Europe, where the Triassic was first studied. In North America, for example, marine deposits are limited to a few exposures in the west, thus Triassic stratigraphy is based on organisms that lived in lagoons and hypersaline environments, such as Estheria crustaceans.
At the beginning of the Mesozoic Era, Africa was joined with Earth's other continents in Pangaea. Africa shared the supercontinent's uniform fauna, dominated by theropods and primitive ornithischians by the close of the Triassic period. Late Triassic fossils are more common in the south than north; the time boundary separating the Permian and Triassic marks the advent of an extinction event with global impact, although African strata from this time period have not been studied. During the Triassic peneplains are thought to have formed in what is now southern Sweden. Remnants of this peneplain can be traced as a tilted summit accordance in the Swedish West Coast. In northern Norway Triassic peneplains may have been buried in sediments to be re-exposed as coastal plains called strandflats. Dating of illite clay from a strandflat of Bømlo, southern Norway, have shown that landscape there became weathered in Late Triassic times with the landscape also being shaped during that time. At Paleorrota geopark, located in Rio Grande do Sul, the Santa Maria Formation and Caturrita Formations are exposed.
In these formations, one of the earliest dinosaurs, Staurikosaurus, as well as the mammal ancestors Brasilitherium and Brasilodon have been discovered. The Triassic continental interior climate was hot and dry, so that typical deposits are red bed sandstones and evaporites. There is no evidence of glaciation near either pole. Pangaea's large size limited the moderating effect of the global ocean; the strong contrast between the Pangea supercontinent and the global ocean triggered intense cross-equatorial monsoons. The Triassic may have been a dry period, but evidence exists that it was punctuated by several episodes of increased rainfall in tropical and subtropical latitudes of the Tethys Sea and its surrounding land. Sediments and fossils suggestive of a more humid climate are known from the Anisian to Ladinian of the Tethysian domain, from the Carnian and Rhaetian of a larger area that includes the Boreal domain, the North
An infratemporal fenestra called the lateral temporal fenestra is an opening in the skull behind the orbit in some animals. An opening in front of the eye sockets, conversely, is called an antorbital fenestra. Both of these openings reduced the weight of the skull. Infratemporal fenestrae are seen in the fossilized skulls of dinosaurs. Temporal fenestra
Lepidosauromorpha is a group of reptiles comprising all diapsids closer to lizards than to archosaurs. The only living sub-group is the Lepidosauria: extant lizards, snakes and tuataras. Lepidosauromorpha are distinguishable from Archosauromorphs by their primitive sprawling gait, which allows for the same sinusoidal trunk and tail movement seen in fish, the sliding "joint" between the coracoids and the sternum, their pleurodont dentition. In contrast, Archosauromorphs possess a parasagittal gait, a reduction in their dermal girdle, a reduction and/or loss of the sternum, a more thecodont dentition. Lepidosauromorpha have retained cold blood because of their low-energy sprawling stance
In taxonomy, a group is paraphyletic if it consists of the group's last common ancestor and all descendants of that ancestor excluding a few—typically only one or two—monophyletic subgroups. The group is said to be paraphyletic with respect to the excluded subgroups; the arrangement of the members of a paraphyletic group is called a paraphyly. The term is used in phylogenetics and in linguistics; the term was coined to apply to well-known taxa like Reptilia which, as named and traditionally defined, is paraphyletic with respect to mammals and birds. Reptilia contains the last common ancestor of reptiles and all descendants of that ancestor—including all extant reptiles as well as the extinct synapsids—except for mammals and birds. Other recognized paraphyletic groups include fish and lizards. If many subgroups are missing from the named group, it is said to be polyparaphyletic. A paraphyletic group cannot be a clade, or monophyletic group, any group of species that includes only a common ancestor and all of its descendants.
Formally, a paraphyletic group is the relative complement of one or more subclades within a clade: removing one or more subclades leaves a paraphyletic group. The term paraphyly, or paraphyletic, derives from the two Ancient Greek words παρά, meaning "beside, near", φῦλον, meaning "genus, species", refers to the situation in which one or several monophyletic subgroups of organisms are left apart from all other descendants of a unique common ancestor. Conversely, the term monophyly, or monophyletic, builds on the Ancient Greek prefix μόνος, meaning "alone, unique", refers to the fact that a monophyletic group includes organisms consisting of all the descendants of a unique common ancestor. By comparison, the term polyphyly, or polyphyletic, uses the Ancient Greek prefix πολύς, meaning "many, a lot of", refers to the fact that a polyphyletic group includes organisms arising from multiple ancestral sources. Groups that include all the descendants of a common ancestor are said to be monophyletic.
A paraphyletic group is a monophyletic group from which one or more subsidiary clades are excluded to form a separate group. Ereshefsky has argued that paraphyletic taxa are the result of anagenesis in the excluded group or groups. A group whose identifying features evolved convergently in two or more lineages is polyphyletic. More broadly, any taxon, not paraphyletic or monophyletic can be called polyphyletic; these terms were developed during the debates of the 1960s and 1970s accompanying the rise of cladistics. Paraphyletic groupings are considered problematic by many taxonomists, as it is not possible to talk about their phylogenetic relationships, their characteristic traits and literal extinction. Related terminology that may be encountered are stem group, budding cladogenesis, anagenesis, or'grade' groupings. Paraphyletic groups are a relic from previous erroneous assessments about phylogenic relationships, or from before the rise of cladistics; the prokaryotes, because they exclude the eukaryotes, a descendant group.
Bacteria and Archaea are prokaryotes, but archaea and eukaryotes share a common ancestor, not ancestral to the bacteria. The prokaryote/eukaryote distinction was proposed by Edouard Chatton in 1937 and was accepted after being adopted by Roger Stanier and C. B. van Niel in 1962. The botanical code abandoned consideration of bacterial nomenclature in 1975. Among plants, dicotyledons are paraphyletic. "Dicotyledon" has not been used as an ICBN classification for decades, but is allowed as a synonym of Magnoliopsida. Phylogenetic analysis indicates. Excluding monocots from the dicots makes the latter a paraphyletic group. Among animals, several familiar groups are not, in fact, clades; the order Artiodactyla is paraphyletic. In the ICZN Code, the two taxa are orders of equal rank. Molecular studies, have shown that the Cetacea descend from artiodactyl ancestors, although the precise phylogeny within the order remains uncertain. Without the Cetacean descendants the Artiodactyls must be paraphyletic; the class Reptilia as traditionally defined is paraphyletic because it excludes mammals.
In the ICZN Code, the three taxa are classes of equal rank. However, mammals hail from the synapsids and birds are descended from the dinosaurs, both of which are reptiles. Alternatively, reptiles are paraphyletic. Birds and reptiles together make Sauropsids. Osteichthyes, bony fish, are paraphyletic when they include only Actinopterygii and Sarcopterygii, excluding tetrapods; the wasps are paraphyletic, consisting of the narrow-waisted Apocrita without the bees. The sawflies are paraphyletic, forming all of the Hymenoptera except for the Apocrita, a clade deep within the sawfly tree. Crustaceans are not a clade; the modern clade that spans all of them is the Tetraconata. Species have a special status in systematics as being an observable feature of nature itself and a
Amniotes are a clade of tetrapod vertebrates comprising the reptiles and mammals. Amniotes lay their eggs on land or retain the fertilized egg within the mother, are distinguished from the anamniotes, which lay their eggs in water. Older sources prior to the 20th century, may refer to amniotes as "higher vertebrates" and anamniotes as "lower vertebrates", based on the discredited idea of the evolutionary great chain of being. Amniotes are tetrapods that are characterised by having an egg equipped with an amnion, an adaptation to lay eggs on land rather than in water as the anamniotes do. Amniotes include sauropsids, as well as their ancestors, back to amphibians. Amniote embryos, whether laid as eggs or carried by the female, are protected and aided by several extensive membranes. In eutherian mammals, these membranes include the amniotic sac; these embryonic membranes and the lack of a larval stage distinguish amniotes from tetrapod amphibians. The first amniotes, referred to as "basal amniotes", resembled small lizards and evolved from the amphibian reptiliomorphs about 312 million years ago, in the Carboniferous geologic period.
Their eggs could survive out of the water, allowing amniotes to branch out into drier environments. The eggs could "breathe" and cope with wastes, allowing the eggs and the amniotes themselves to evolve into larger forms; the amniotic egg represents a critical divergence within the vertebrates, one enabling amniotes to reproduce on dry land—free of the need to return to water for reproduction as required of the amphibians. From this point the amniotes spread around the globe to become the dominant land vertebrates. Early in their evolutionary history, basal amniotes diverged into two main lines, the synapsids and the sauropsids, both of which persist into the modern era; the oldest known fossil synapsid is Protoclepsydrops from about 312 million years ago, while the oldest known sauropsid is Paleothyris, in the order Captorhinida, from the Middle Pennsylvanian epoch. Zoologists characterize amniotes in part by embryonic development that includes the formation of several extensive membranes, the amnion and allantois.
Amniotes develop directly into a terrestrial form with a thick stratified epithelium. In amniotes, the transition from a two-layered periderm to a cornified epithelium is triggered by thyroid hormone during embryonic development, rather than by metamorphosis; the unique embryonic features of amniotes may reflect specializations for eggs to survive drier environments. Features of amniotes evolved for survival on land include a sturdy but porous leathery or hard eggshell and an allantois evolved to facilitate respiration while providing a reservoir for disposal of wastes, their kidneys and large intestines are well-suited to water retention. Most mammals do not lay eggs; the ancestors of true amniotes, such as Casineria kiddi, which lived about 340 million years ago, evolved from amphibian reptiliomorphs and resembled small lizards. At the late Devonian mass extinction, all known tetrapods were aquatic and fish-like; because the reptiliomorphs were established 20 million years when all their fishlike relatives were extinct, it appears they separated from the other tetrapods somewhere during Romer's gap, when the adult tetrapods became terrestrial.
The modest-sized ancestors of the amniotes laid their eggs in moist places, such as depressions under fallen logs or other suitable places in the Carboniferous swamps and forests. Indeed, many modern-day amniotes require moisture to keep their eggs from desiccating. Although some modern amphibians lay eggs on land, all amphibians lack advanced traits like an amnion; the amniotic egg formed through a series of evolutionary steps. After internal fertilization and the habit of laying eggs in terrestrial environments became a reproduction strategy amongst the amniote ancestors, the next major breakthrough appears to have involved a gradual replacement of the gelatinous coating covering the amphibian egg with a fibrous shell membrane; this allowed the egg to increase both its size and in the rate of gas exchange, permitting a larger, metabolically more active embryo to reach full development before hatching. Further developments, like extraembryonic membranes and a calcified shell, were not essential and evolved later.
It has been suggested that shelled terrestrial eggs without extraembryonic membranes could still not have been more than about 1 cm in diameter because of diffusion problems, like the inability to get rid of carbon dioxide if the egg was larger. The only way for the eggs to increase in size would be to develop new internal structures specialized for respiration and for waste products; as this happened, it would affect how much the juveniles could grow before they reached adulthood. Fish and amphibian eggs have the embryonic membrane; the amniote egg ev
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
Tortoises are reptile species of the family Testudinidae of the order Testudines. They are distinguished from other turtles by being land-dwelling, while many other turtle species are at least aquatic. However, like other turtles, tortoises have a shell to protect from other threats; the shell in tortoises is hard, like other members of the suborder Cryptodira, they retract their necks and heads directly backwards into the shell to protect them. Tortoises are unique among vertebrates in that the pectoral and pelvic girdles are inside the ribcage rather than outside. Tortoises can vary in dimension from a few centimeters to two meters, they are diurnal animals with tendencies to be crepuscular depending on the ambient temperatures. They are reclusive animals. Tortoises are the longest living land animal in the world, although the longest living species of tortoise is a matter of debate. Galápagos tortoises are noted to live over 150 years, but an Aldabra giant tortoise named Adwaita may have been the longest living at an estimated 255 years.
In general, most tortoise species can live 80–150 years. Differences exist in usage of the common terms turtle and terrapin, depending on the variety of English being used; these terms do not reflect precise biological or taxonomic distinctions. The American Society of Ichthyologists and Herpetologists uses "turtle" to describe all species of the order Testudines, regardless of whether they are land-dwelling or sea-dwelling, uses "tortoise" as a more specific term for slow-moving terrestrial species. General American usage agrees. In America, for example, the members of the genus Terrapene dwell on land, yet are referred to as box turtles rather than tortoises. British usage, by contrast, tends not to use "turtle" as a generic term for all members of the order, applies the term "tortoises" broadly to all land-dwelling members of the order Testudines, regardless of whether they are members of the family Testudinidae. In Britain, terrapin is used to refer to a larger group of semiaquatic turtles than the restricted meaning in America.
Australian usage is different from both British usage. Land tortoises are not native to Australia, yet traditionally freshwater turtles have been called "tortoises" in Australia; some Australian experts disapprove of this usage—believing that the term tortoises is "better confined to purely terrestrial animals with different habits and needs, none of which are found in this country"—and promote the use of the term "freshwater turtle" to describe Australia's aquatic members of the order Testudines because it avoids misleading use of the word "tortoise" and is a useful distinction from marine turtles. Most species of tortoises lay small clutch sizes exceeding 20 eggs, many species have clutch sizes of only 1–2 eggs. Incubation is characteristically long in most species, the average incubation period are between 100 and 160 days. Egg-laying occurs at night, after which the mother tortoise covers her clutch with sand and organic material; the eggs are left unattended, depending on the species, take from 60 to 120 days to incubate.
The size of the egg depends on the size of the mother and can be estimated by examining the width of the cloacal opening between the carapace and plastron. The plastron of a female tortoise has a noticeable V-shaped notch below the tail which facilitates passing the eggs. Upon completion of the incubation period, a formed hatchling uses an egg tooth to break out of its shell, it begins a life of survival on its own. They are hatched with an embryonic egg sac which serves as a source of nutrition for the first three to seven days until they have the strength and mobility to find food. Juvenile tortoises require a different balance of nutrients than adults, so may eat foods which a more mature tortoise would not. For example, the young of a herbivorous species will consume worms or insect larvae for additional protein; the number of concentric rings on the carapace, much like the cross-section of a tree, can sometimes give a clue to how old the animal is, since the growth depends on the accessibility of food and water, a tortoise that has access to plenty of forage with no seasonal variation will have no noticeable rings.
Moreover, some tortoises grow more than one ring per season, in some others, due to wear, some rings are no longer visible. Tortoises have one of the longest lifespans of any animal, some individuals are known to have lived longer than 150 years; because of this, they symbolize longevity in some cultures, such as China. The oldest tortoise recorded, one of the oldest individual animals recorded, was Tu'i Malila, presented to the Tongan royal family by the British explorer Captain Cook shortly after its birth in 1777. Tu'i Malila remained in the care of the Tongan royal family until its death by natural causes on May 19, 1965, at the age of 188; the record for the longest-lived vertebrate is exceeded only by one other, a koi named Hanako whose death on July 17, 1977, ended a 226-year lifespan. The Alipore Zoo in India was the home to Adwaita, which zoo officials claimed was the oldest living animal until