Courtship display
A courtship display is a set of display behaviors in which an animal attempts to attract a mate and exhibit their desire to copulate. These behaviors include ritualized movement, mechanical sound production, or displays of beauty, strength, or agonistic ability. In some species, males will perform ritualized movements to attract females; the male Six-Plumed bird-of-paradise, Parotia lawesii, exemplifies male courtship display with its ritualized "ballerina dance" and unique occipital and breast feathers that serve to stimulate the female visual system. This stimulation, along with many other factors, results in subsequent rejection. In other species, males may exhibit courtship displays that serve as both visual and auditory stimulation. For example, the male Anna's hummingbird and Calliope hummingbird perform two types of courtship displays involving a combination of visual and vocal display - a stationary shuttle display and dive display; when engaging in the stationary shuttle display, the male displays a flared gorget and hovers in front of the female, moving from side to side while rotating his body and tail.
The rhythmic movements of the male's wings produce a distinctive buzzing sound. When conducting a dive display, the male ascends 20–35 m in the air abruptly turns and descends in a dive-like fashion; as the male flies over the female, he rotates his body and spreads his tail feathers, which flutter and collide to produce a short, buzzing sound. In addition, some animals attempt to attract females through the construction and decoration of unique structures; this technique can be seen in Australia's satin bowerbirds, in which males build and decorate nest-like structures called "bowers". Bowers are decorated with colourful objects to attract and stimulate visiting females. Males who acquire the largest number of decorations tend to have greater success in mating. In some species, males initiate courtship rituals only after mounting the female. Courtship may continue after copulation has been completed. In this system, the ability of the female to choose her mate is limited; this process, known as copulatory courtship, is prevalent in many insect species.
In most species, the male sex initiates courtship displays in pre-copulatory sexual selection. Performing a display allows the male to present his traits or abilities to a female. Mate choice, in this context, is driven by females. Direct or indirect benefits to the female determine which males reproduce and which do not. Direct benefits may accrue to the female during male courtship behavior. Females can raise their own fitness if they respond to courtship behavior that signals benefits to the female rather than the fitness of the male. For example, choosing to mate with males that produce local signals would require less energy for a female as she searches for a mate. Males may compete by imposing lower mating costs on the female or providing material or offspring contributions to the female. Indirect benefits are benefits that may not directly affect the parents' fitness but instead increase the fitness of the offspring. Since the offspring of a female will inherit half of the genetic information from the male counterpart, those traits she saw as attractive will be passed on, producing fit offspring.
In this case, males may compete during courtship by displaying desirable traits to pass on to offspring. Female courtship display is less common in nature as a female would have to invest a lot of energy into both exaggerated traits and in their energetically expensive gametes. However, situations in which males are the sexually selective sex in a species do occur in nature. Male choice in reproduction can arise if males are the sex in a species that are in short supply, for example, if there is a female bias in the operational sex ratio; this could arise in mating systems. Such energy costs can include the effort associated in obtaining nuptial gifts for the female or performing long courtship or copulatory behaviors. An added cost from these time and energy investments may come in the form of increased male mortality rates, putting further strain on males attempting to reproduce. In pipefish, females use a temporary ornament, a striped pattern, to both attract males and intimidate rival females.
In this case, the female of a species developed a sexually selected signal which serves a dual function of being both attractive to mates and deterring rivals. Many species of animals engage in some type of courtship display to attract a mate, such as dancing, the creation of sounds and physical displays. However, many species are not limited to just one of these behaviors, it has been shown that the males of a multitude of species ranging many taxa create complex multi-component signals that have an effect on more than one sensory modality known as multi-modal signals. There are two leading hypotheses on the adaptive significance of multi-modal signal processing; the multiple message hypothesis states that each signal that a male exhibits will contribute to a possible mate's perception of the male. The redundant signal hypothesis states that the male exhibits multiple signals that portray the same'message' to the female, with each extra signal acting as a fall-back plan for the male should there be a signaling error.
The choosy sex may only evaluates one, or a couple, traits at a given time when interpreting complex signals from the opposite sex. Alternatively, the choosy sex may attempt to process all of the signals at once to facilitate the evaluation of the opposite sex; the process of multi-modal signaling is believed to help facilitate the cour
Chamaeleo
Chamaeleo is a genus of chameleons found in the mainland of sub-saharan Africa, but a few species are present in northern Africa, southern Europe and southern Asia east to India and Sri Lanka. They are slow moving with independently movable eyes, the ability to change skin colouration, long tongue a prehensile tail, special leg adaptations for grasping vegetation. Males are larger and more colorful than females. All species have a maximum snout-vent length between 15 and 40 centimetres; the vast majority are arboreal and found in trees or bushes, but a few species are or terrestrial. The genus includes only oviparous species. With few exceptions, the chameleons most seen in captivity are all members of Chamaeleo, notably the common and veiled chameleons, but they require special care. Chamaeleo is the type genus of the family Chamaeleonidae. All other genera of the subfamily Chamaeleoninae have at some point been included in the genus Chamaeleo, but are now regarded as separate by all authorities.
14 species are recognized as being valid, subspecies are recognized for some species. Chamaeleo africanus Laurenti, 1768 – African chameleon Chamaeleo anchietae Bocage, 1872 – Angola double-scaled chameleon Chamaeleo arabicus Matschie, 1893 – Arabian chameleon Chamaeleo calcaricarens Böhme, 1985 – Awash spurless chameleon Chamaeleo calyptratus A. M. C. Duméril & A. H. A. Duméril, 1851 – veiled chameleon Chamaeleo calyptratus calyptratus A. M. C. Duméril & A. H. A. Duméril, 1851 – veiled chameleon Chamaeleo calyptratus calcarifer W. Peters, 1871 – short-casqued chameleon Chamaeleo chamaeleon – common chameleon Chamaeleo chamaeleon chamaeleon – European common chameleon Chamaeleo chamaeleon musae Steindachner, 1900 – Sinai Peninsula common chameleon Chamaeleo chamaeleon orientalis Parker, 1938 – Arabian common chameleon Chamaeleo chamaeleon rectricrista Boettger, 1880 – Middle East common chameleon Chamaeleo dilepis Leach, 1819 – flap-necked chameleon Chamaeleo dilepis dilepis Leach, 1819 – flap-necked chameleon Chamaeleo dilepis idjwiensis Loveridge, 1942 - Idjwi Island flap-necked chameleon Chamaeleo dilepis isabellinus Günther, 1893 - Isabelline flap-necked chameleon Chamaeleo dilepis martensi Mertens, 1964 – Pemba Island flap-necked chameleon Chamaeleo dilepis petersii Gray, 1865 – Peters' flap-necked chameleon Chamaeleo dilepis quilensis Bocage, 1866 - Quilo River flap-necked chameleon or Bocage's chameleon Chamaeleo dilepis roperi Boulenger, 1890 Chamaeleo dilepis ruspolii Boettger, 1893 – Ruspoli's flap-necked chameleon Chamaeleo gracilis Hallowell, 1844 – graceful chameleon Chamaeleo gracilis gracilis Hallowell, 1844 – graceful chameleon Chamaeleo gracilis etiennei K.
P. Schmidt, 1919 – Etienne's slender chameleon Chamaeleo laevigatus Gray, 1863 – smooth chameleon Chamaeleo monachus Gray, 1865 – Socotran chameleon Chamaeleo namaquensis A. Smith, 1831 – Namaqua chameleon Chamaeleo necasi Ullenbruch, P. Krause & Böhme, 2007 – Nečas' flap-necked chameleon Chamaeleo senegalensis Daudin, 1802 – Senegal chameleon Chamaeleo zeylanicus Laurenti, 1768 – Indian chameleonNota bene: A binomial authority or trinomial authority in parentheses indicates that the species or subspecies was described in a genus other than Chamaeleo. Branch, Bill. 2004. Field Guide to Snakes and Other Reptiles of Southern Africa. Third Revised edition, Second impression. Sanibel Island, Florida: Ralph Curtis Books. 399 pp. ISBN 0-88359-042-5.. Laurenti JN. 1768. Specimen medicum, exhibens synopsin reptilium emendatam cum experimentis circa venena et antidota reptilium austriacorum. Vienna: "Joan. Thom. Nob. de Trattnern". 214 pp. + Plates I-V... Spawls, S.. A Field Guide to the Reptiles of East Africa.
Köln: Academic Press. ISBN 0-12-656470-1. Http://www.chameleoninfo.com/Species_Profiles.html
Iguanomorpha
Iguania is an infraorder of squamate reptiles that includes iguanas, chameleons and New World lizards like anoles and phrynosomatids. Using morphological features as a guide to evolutionary relationships, the Iguania are believed to form the sister group to the remainder of the Squamata. However, molecular information has placed Iguania well within the Squamata as sister taxa to the Anguimorpha and related to snakes. Iguanians are arboreal and have primitive fleshy, non-prehensile tongues, although the tongue is modified in chameleons; the group has a fossil record. The Iguania include these extant families: Clade Acrodonta Family Agamidae – agamid lizards, Old World arboreal lizards Family Chamaeleonidae – chameleons Clade Pleurodonta – American arboreal lizards, iguanas Family Leiocephalidae Genus Leiocephalus: curly-tailed lizards Family Corytophanidae – helmet lizards Family Crotaphytidae – collared lizards, leopard lizards Family Hoplocercidae – dwarf and spinytail iguanas Family Iguanidae – marine, Galapagos land, rock, desert and chuckwalla iguanas Family Tropiduridae – tropidurine lizards subclade of Tropiduridae Tropidurini – neotropical ground lizards Family Dactyloidae – anoles Family Polychrotidae subclade of Polychrotidae Polychrus Family Phrynosomatidae – North American spiny lizards Family Liolaemidae – South American swifts Family Opluridae – Malagasy iguanas Family Leiosauridae – leiosaurs subclade of Leiosaurini Leiosaurae subclade of Leiosaurini Anisolepae Below is a cladogram from the phylogenetic analysis of Daza et al. showing the interrelationships of extinct and living iguanians
Maui
The island of Maui is the second-largest of the Hawaiian Islands at 727.2 square miles and is the 17th largest island in the United States. Maui is part of the State of Hawaii and is the largest of Maui County's four islands, which include Molokaʻi, Lānaʻi, unpopulated Kahoʻolawe. In 2010, Maui had a population of 144,444, third-highest of the Hawaiian Islands, behind that of Oʻahu and Hawaiʻi Island. Kahului is the largest census-designated place on the island with a population of 26,337 as of 2010 and is the commercial and financial hub of the island. Wailuku is the seat of Maui County and is the third-largest CDP as of 2010. Other significant places include Kīhei, Makawao, Pukalani, Pāʻia, Kula, Haʻikū, Hāna. Native Hawaiian tradition gives the origin of the island's name in the legend of Hawaiʻiloa, the navigator credited with discovery of the Hawaiian Islands. According to it, Hawaiʻiloa named the island after his son, who in turn was named for the demigod Māui; the earlier name of Maui was ʻIhikapalaumaewa.
The Island of Maui is called the "Valley Isle" for the large isthmus separating its northwestern and southeastern volcanic masses. Maui's diverse landscapes are the result of a unique combination of geology and climate; each volcanic cone in the chain of the Hawaiian Islands is built of dark, iron-rich/quartz-poor rocks, which poured out of thousands of vents as fluid lava over a period of millions of years. Several of the volcanoes were close enough to each other that lava flows on their flanks overlapped one another, merging into a single island. Maui is such a "volcanic doublet," formed from two shield volcanoes that overlapped one another to form an isthmus between them; the older, western volcano has been eroded and is cut by numerous drainages, forming the peaks of the West Maui Mountains. Puʻu Kukui is the highest of the peaks at 5,788 feet; the larger, younger volcano to the east, Haleakalā, rises to more than 10,000 feet above sea level, measures 5 miles from seafloor to summit. The eastern flanks of both volcanoes are cut by incised valleys and steep-sided ravines that run downslope to the rocky, windswept shoreline.
The valley-like Isthmus of Maui that separates the two volcanic masses was formed by sandy erosional deposits. Maui's last eruption occurred around 1790. Although considered to be dormant by volcanologists, Haleakalā is capable of further eruptions. Maui is part of a much larger unit, Maui Nui, that includes the islands of Lānaʻi, Kahoʻolawe, Molokaʻi, the now submerged Penguin Bank. During periods of reduced sea level, including as as 20,000 years ago, they are joined together as a single island due to the shallowness of the channels between them; the climate of the Hawaiian Islands is characterized by a two-season year and uniform temperatures everywhere, marked geographic differences in rainfall, high relative humidity, extensive cloud formations, dominant trade-wind flow. Maui itself has a wide range of climatic conditions and weather patterns that are influenced by several different factors in the physical environment: Half of Maui is situated within 5 miles of the island's coastline. This, the extreme insularity of the Hawaiian Islands account for the strong marine influence on Maui's climate.
Gross weather patterns are determined by elevation and orientation towards the Trade winds. Maui's rugged, irregular topography produces marked variations in conditions. Air swept inland on the Trade winds is shunted one way or another by the mountains and vast open slopes; this complex three-dimensional flow of air results in striking variations in wind speed, cloud formation, rainfall. Maui displays a unique and diverse set of climatic conditions, each of, specific to a loosely defined sub-region of the island; these sub-regions are defined by major physiographic features and by location on the windward or leeward side of the island. Windward lowlands – Below 2,000 feet on north-to-northeast sides of an island. Perpendicular to direction of prevailing trade winds. Moderately rainy. Skies are cloudy to cloudy. Air temperatures are more uniform than those of other regions. Leeward lowlands – Daytime temperatures are a little higher and nighttime temperatures are lower than in windward locations. Dry weather is prevalent, with the exception of sporadic showers that drift over the mountains to windward and during short-duration storms.
Interior lowlands – Intermediate conditions sharing characteristics of other lowland sub-regions. Experience intense local afternoon showers from well-developed clouds that formed due to local daytime heating. Leeward side high-altitude mountain slopes with high rainfall – Extensive cloud cover and rainfall all year long. Mild temperatures are prevalent. Leeward side lower mountain slopes – Rainfall is higher than on the adjacent leeward lowlands, but much less than at similar altitudes on the windward side.
Binomial nomenclature
Binomial nomenclature called binominal nomenclature or binary nomenclature, is a formal system of naming species of living things by giving each a name composed of two parts, both of which use Latin grammatical forms, although they can be based on words from other languages. Such a name is called a binomen, binominal name or a scientific name; the first part of the name – the generic name – identifies the genus to which the species belongs, while the second part – the specific name or specific epithet – identifies the species within the genus. For example, humans belong within this genus to the species Homo sapiens. Tyrannosaurus rex is the most known binomial; the formal introduction of this system of naming species is credited to Carl Linnaeus beginning with his work Species Plantarum in 1753. But Gaspard Bauhin, in as early as 1623, had introduced in his book Pinax theatri botanici many names of genera that were adopted by Linnaeus; the application of binomial nomenclature is now governed by various internationally agreed codes of rules, of which the two most important are the International Code of Zoological Nomenclature for animals and the International Code of Nomenclature for algae and plants.
Although the general principles underlying binomial nomenclature are common to these two codes, there are some differences, both in the terminology they use and in their precise rules. In modern usage, the first letter of the first part of the name, the genus, is always capitalized in writing, while that of the second part is not when derived from a proper noun such as the name of a person or place. Both parts are italicized when a binomial name occurs in normal text, thus the binomial name of the annual phlox is now written as Phlox drummondii. In scientific works, the authority for a binomial name is given, at least when it is first mentioned, the date of publication may be specified. In zoology "Patella vulgata Linnaeus, 1758"; the name "Linnaeus" tells the reader who it was that first published a description and name for this species of limpet. "Passer domesticus". The original name given by Linnaeus was Fringilla domestica; the ICZN does not require that the name of the person who changed the genus be given, nor the date on which the change was made, although nomenclatorial catalogs include such information.
In botany "Amaranthus retroflexus L." – "L." is the standard abbreviation used in botany for "Linnaeus". "Hyacinthoides italica Rothm. – Linnaeus first named this bluebell species Scilla italica. The name is composed of two word-forming elements: "bi", a Latin prefix for two, "-nomial", relating to a term or terms; the word "binomium" was used in Medieval Latin to mean a two-term expression in mathematics. Prior to the adoption of the modern binomial system of naming species, a scientific name consisted of a generic name combined with a specific name, from one to several words long. Together they formed a system of polynomial nomenclature; these names had two separate functions. First, to designate or label the species, second, to be a diagnosis or description. In a simple genus, containing only two species, it was easy to tell them apart with a one-word genus and a one-word specific name; such "polynomial names" may sometimes look like binomials, but are different. For example, Gerard's herbal describes various kinds of spiderwort: "The first is called Phalangium ramosum, Branched Spiderwort.
The other... is aptly termed Phalangium Ephemerum Virginianum, Soon-Fading Spiderwort of Virginia". The Latin phrases are short descriptions, rather than identifying labels; the Bauhins, in particular Caspar Bauhin, took some important steps towards the binomial system, by pruning the Latin descriptions, in many cases to two words. The adoption by biologists of a system of binomial nomenclature is due to Swedish botanist and physician Carl von Linné, more known by his Latinized name Carl Linnaeus, it was in his 1753 Species Plantarum that he first began using a one-word "trivial name" together with a generic name in a system of binomial nomenclature. This trivial name is what is now known as specific name; the Bauhins' genus names were retained in many of these, but the descriptive part was reduced to a single word. Linnaeus's trivial names introduced an important new idea, namely that the function of a name could be to give a species a unique label; this meant. Thus Gerard's Phalangium ephemerum virginianum became Tradescantia virgi
Diapause
Diapause, when referencing animal dormancy, is the delay in development in response to and recurring periods of adverse environmental conditions. It is considered to be a physiological state of dormancy with specific initiating and inhibiting conditions. Diapause is a mechanism used as a means to survive predictable, unfavorable environmental conditions, such as temperature extremes, drought, or reduced food availability. Diapause is most observed in all the life stages of arthropods insects. Embryonic diapause, a somewhat similar phenomenon, occurs in over 130 species of mammals even in humans, in the embryos of many of the oviparous species of fish in the order Cyprinodontiformes. Activity levels of diapausing stages can vary among species. Diapause may occur in a immobile stage, such as the pupae and eggs, or it may occur in active stages that undergo extensive migrations, such as the adult monarch butterfly, Danaus plexippus. In cases where the insect remains active, feeding is reduced and reproductive development is slowed or halted.
Diapause in insects is a dynamic process consisting of several distinct phases. While diapause varies from one taxon of insects to another, these phases can be characterized by particular sets of metabolic processes and responsiveness of the insect to certain environmental stimuli. Diapause can occur during any stage of development in arthropods, but each species exhibits diapause in specific phases of development. Reduced oxygen consumption is typical as is feeding. In Polistes exclamans only the queen is said to be able to undergo diapause; the sensitive stage is the period. Examples of sensitive stage/diapause periods in various insects: The induction phase occurs at a genetically predetermined stage of life, occurs well in advance of the environmental stress; this sensitive stage may occur within the lifetime of the diapausing individual, or in preceding generations in egg diapause. During this phase, insects are responsive to external cues called token stimuli, which trigger the switch from direct development pathways to diapause pathways.
Token stimuli can consist of changes in photoperiod, thermoperiod, or allelochemicals from food plants. These stimuli are not in themselves favourable or unfavourable to development, but they herald an impending change in environmental conditions; the preparation phase follows the induction phase, though insects may go directly from induction to initiation without a preparation phase. During this phase, insects accumulate and store molecules such as lipids and carbohydrates; these molecules are used to maintain the insect throughout diapause and to provide fuel for development following diapause termination. Composition of the cuticle may be altered by changing hydrocarbon composition and by adding lipids to reduce water loss, making the organism resistant to desiccation. Diapausing puparia of the flesh fly, Sarcophaga crassipalpis, increase the amount of cuticular hydrocarbons lining the puparium reducing the ability of water to cross the cuticle. Photoperiod is the most important stimulus initiating diapause.
The initiation phase begins. In some cases, this change may be distinct and can involve moulting into a specific diapause stage, or be accompanied by color change. Enzymatic changes may take place in preparation for cold hardening. For example, only diapausing adults of the fire bug, Pyrrhocoris apterus, have the enzymatic complement that allows them to accumulate polyhydric alcohols, molecules that help to lower their freezing points and thus avoid freezing. Insects may undergo behavioural changes and begin to aggregate, migrate, or search for suitable overwintering sites. During the maintenance phase, insects experience lowered metabolism and developmental arrest is maintained. Sensitivity to certain stimuli which act to prevent termination of diapause, such as photoperiod and temperature, is increased. At this stage, insects are unresponsive to changes in the environment that will trigger the end of diapause, but they grow more sensitive to these stimuli as time progresses. In insects that undergo obligate diapause, termination may occur spontaneously, without any external stimuli.
In facultative diapausers, token stimuli must occur to terminate diapause. These stimuli may include chilling, freezing, or contact with water, depending on the environmental conditions being avoided; these stimuli are important in preventing the insect from terminating diapause too soon, for instance in response to warm weather in late fall. In the Edith's checkerspot butterfly, individuals must receive enough sunlight in order to terminate the diapause stage and become a grown butterfly. Termination may occur at the height such as in the middle of winter. Over time, depth of diapause decreases until direct development can resume, if conditions are favourable. Diapause ends prior to the end of unfavourable conditions and is followed by a state of quiescence from which the insect can arouse and begin direct development, should conditions change to become more favourable; this allows the insect to continue to withstand harsh conditions while being ready to take advantage of good conditions as as possible.
Diapause in insects is regulated at several levels. Environmental stimuli interact with genetic pre-programming to affect neuronal signalling, endocrine pathways, metabolic and enzymatic changes. Environmental regulators of diapause display a characteristic seasonal pattern. In temperate regions, photoperiod is the most reliable cues of seasonal change. Depending on
Chordate
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
