Chapter 4-5 notes vertebrate zooology

The teleost or Teleostei

are by far the largest infraclass in the class Actinopterygii, the ray-finned fishes,[a] and make up 96% of all extant species of fish. Teleosts are arranged into about 40 orders and 448 families. Over 26,000 species have been described. Teleosts range from giant oarfish measuring 7.6 m (25 ft) or more, and ocean sunfish weighing over 2 t (2.0 long tons; 2.2 short tons), to the minute male anglerfish Photocorynus spiniceps, just 6.2 mm (0.24 in) long. Including not only torpedo-shaped fish built for speed, teleosts can be flattened vertically or horizontally, be elongated cylinders or take specialised shapes as in anglerfish and seahorses. Teleosts dominate the seas from pole to pole and inhabit the ocean depths, estuaries, rivers, lakes and even swamps. The difference between teleosts and other bony fish lies mainly in their jaw bones; teleosts have a movable premaxilla and corresponding modifications in the jaw musculature which make it possible for them to protrude their jaws outwards from the mouth. This is of great advantage, enabling them to grab prey and draw it into the mouth. In more derived teleosts, the enlarged premaxilla is the main tooth-bearing bone, and the maxilla, which is attached to the lower jaw, acts as a lever, pushing and pulling the premaxilla as the mouth is opened and closed. Other bones further back in the mouth serve to grind and swallow food. Another difference is that the upper and lower lobes of the tail (caudal) fin are about equal in size. The spine ends at the caudal peduncle, distinguishing this group from other fish in which the spine extends into the upper lobe of the tail fin. Teleosts have adopted a range of reproductive strategies. Most use external fertilisation: the female lays a batch of eggs, the male fertilises them and the larvae develop without any further parental involvement. A fair proportion of teleosts are sequential hermaphrodites, starting life as females and transitioning to males at some stage, with a few species reversing this process. A small percentage of teleosts are viviparous and some provide parental care with typically the male fish guarding a nest and fanning the eggs to keep them well-oxygenated. Teleosts are economically important to humans, as is shown by their depiction in art over the centuries. The fishing industry harvests them for food, and anglers attempt to capture them for sport. Some species are farmed commercially, and this method of production is likely to be increasingly important in the future. Others are kept in aquariums or used in research, especially in the fields of genetics and developmental biology.

Batrachomorpha

("frog form") is a name traditionally given to recent and extinct amphibians that are more closely related to modern amphibians than they are to reptiles. It most often includes the extinct groups Temnospondyli and Lepospondyli. The first tetrapods were all amphibians in the physiological sense that they laid their eggs in water, and are colloquially sometimes refereed to as labyrinthodonts or stegocephalians. In this scheme, batrachomorphs composed one branch of these early amphibians, while the reptiliomorphs composed the other. While the actual phylogeny of the modern amphibians is not well understood, their ancestors are descended from one line of batrachomorphs.[1] All other living tetrapods (reptiles, birds and mammals) are descended from one branch of reptiliomorphs, the amniotes. Amniotes achieved dominance, while all other reptiliomorphs and most batrachomorphs have gone extinct.

Osteolepis

('bone scale') is an extinct genus of lobe-finned fish from the Devonian period. It lived in the Lake Orcadie of northern Scotland. Osteolepis was about 20 centimetres (7.9 in) long, and covered with large, square scales. The scales and plates on its head were covered in a thin layer of spongy, bony material called cosmine. This layer contained canals which were connected to sensory cells deeper in the skin. These canals ended in pores on the surface, and were probably for sensing vibrations in the water.[1] Osteolepis was a rhipidistian, having a number of features in common with the tetrapods (land-dwelling vertebrates and their descendants), and was probably close to the base of the tetrapod family tree.

coelocanth

constitute a now-rare order of fish that includes two extant species in the genus Latimeria: the West Indian Ocean coelacanth (Latimeria chalumnae) primarily found near the Comoro Islands off the east coast of Africa and the Indonesian coelacanth. They follow the oldest-known living lineage of Sarcopterygii (lobe-finned fish and tetrapods), which means they are more closely related to lungfish and tetrapods than to ray-finned fishes. They are found along the coastlines of the Indian Ocean and Indonesia The West Indian Ocean coelacanth is a critically endangered species. Coelacanths belong to the subclass Actinistia, a group of lobed-finned fish related to lungfish and certain extinct Devonian fish such as osteolepiforms, porolepiforms, rhizodonts, and Panderichthys.[5] Coelacanths were thought to have become extinct in the Late Cretaceous, around 66 million years ago, but were rediscovered in 1938 off the coast of South Africa.[6][7] The coelacanth was long considered a "living fossil" because scientists thought it was the sole remaining member of a taxon otherwise known only from fossils, with no close relations alive,[5] and that it evolved into roughly its current form approximately 400 million years ago.[1] However, several recent studies have shown that coelacanth body shapes are much more diverse than previously thought

Elopomorpha

contains a variety of types of fishes that range from typical silvery-colored species, such as the tarpons and ladyfishes of the Elopiformes and the bonefishes of the Albuliformes, to the long and slender, smooth-bodied eels of the Anguilliformes. The one characteristic uniting this group of fishes is they all have leptocephalus larvae, which are unique to the Elopomorpha. No other fishes have this type of larvae.

Bowfin

(Amia calva) are bony fishes related to gars in the infraclass Holostei. Common names include mudfish, mud pike, dogfish, griddle, grinnel, swamp trout and choupique. They are regarded as taxonomic relicts, being the sole surviving species of the order Amiiformes which dates from the Jurassic to the Eocene, persisting to the present. Although bowfin are highly evolved, they are often referred to as "primitive fishes" because they have retained some morphological characteristics of their early ancestors. Bowfin are demersal freshwater piscivores native to North America, and commonly found throughout much of the eastern United States, and in southern Ontario and Quebec. Fossil deposits indicate Amiiformes were once widespread in both freshwater and marine environments with a range that spanned across North and South America, Europe, Asia and Africa. Now their range is limited to much of the eastern United States and adjacent southern Canada, including the drainage basins of the Mississippi River, Great Lakes and various rivers exiting in the Eastern Seaboard or Gulf of Mexico. Their preferred habitat includes vegetated sloughs, lowland rivers and lakes, swamps and backwater areas; they are also occasionally found in brackish water. They are stalking, ambush predators known to move into the shallows at night to prey on fish and aquatic invertebrates such as crawfish, mollusks, and aquatic insects. Like gars, bowfin are bimodal breathers which means they have the capacity to breathe both water and air. Their gills exchange gases in the water allowing them to exploit oxygen for breathing, but they also have a gas bladder that serves to maintain buoyancy, and also allows them to breathe air by means of a small pneumatic duct connected from the foregut to the gas bladder. They can break the surface to gulp air, which allows them to survive conditions of aquatic hypoxia that would be lethal to most other species

Aïstopoda

(Greek for "[having] not-visible feet") is an order of highly specialised snake-like amphibians known from the Carboniferous and Early Permian of Europe and North America, ranging from tiny forms only 5 centimetres (2 in), to nearly 1 metre (3.3 ft) in length. The first appear in the fossil record in the Mississippian period and continue through to the Early Permian. The skull is small but very specialised, with large orbits, and large fenestrae. The primitive form Ophiderpeton has a pattern of dermal bones in the skull similar in respects to the temnospondyls. But in the advanced genus Phlegethontia the skull is very light and open, reduced to a series of struts supporting the braincase against the lower jaw, just as in snakes, and it is possible that the Aïstopods filled the same ecological niches in the Paleozoic that snakes do today

Protogyny

(female to male) Ex: bluehead wrasse

Protandry

(male to female) Ex: clown anemone fish

Diplocaulus

(meaning "double caul") is an extinct genus of lepospondyl amphibians which lived from the Late Carboniferous to Permian periods of North America and Africa. Diplocaulus are by far the largest and most well-known lepospondyls, characterized by a distinctive boomerang-shaped skull. Remains attributed to Diplocaulus have been found from the Late Permian of Morocco and represent the youngest known occurrence of a lepospondyl Diplocaulus had a stocky, salamander-like body, but was relatively large, reaching up to 1 m (3.3 ft) in length. Although a complete tail is unknown for the genus, a nearly complete articulated skeleton described in 1917 preserved a row of tail vertebrae near the head. This was construed as circumstantial evidence for a long, thin tail capable of reaching the head if the animal was curled up.[1] Most studies since this discovery have argued that anguiliform (eel-like) tail movement was the main force of locomotion utilized by Diplocaulus and its relatives The most distinctive features of this genus and its closest relatives were a pair of long protrusions or horns at the rear of the skull, giving the head a boomerang-like shape. Most of the outer/front edge of each horn was formed by the elongated, blade-like squamosal bone. The rear edge of the skull and horns, on the other hand, was formed by the postparietal bones, also known as dermosupraoccipitals in older publications. However, the primary component of each horn (including the tips) is a long bone with a historically controversial identification. Many early sources considered the bone to be a tabular, which in other early tetrapods is a small bone lying at the rear edge of the skull.[4][1] However, Olson (1951) doubted this, arguing that the bone's contact with the parietals excluded the possibility of it being a tabular. He argued that the bone was the supratemporal bone, which had enlarged and shifted towards the rear tip of the skull.[5] Beerbower (1963) countered Olson's reasoning by pointing out that Urocordylus, a newt-like relative of Diplocaulus, retained both a supratemporal and a tabular bone. In Urocordylus, the tabular lies closer to the back of the skull and even contacts the parietals, invalidating Olson's main point.[2] Based on this observation, it is more likely that the primary bone of the horns in Diplocaulus is a tabular. Many studies (even a later publication by Olson) now refer to Diplocaulus horns as tabular horns based on Beerbower's argument

Bichirs

/ˈbɪʃɪər/ and the reedfish comprise Polypteridae, a family of archaic-looking ray-finned fishes and the only family in the order Polypteriformes.[2] All species occur in freshwater habitats in tropical Africa and the Nile River system, mainly swampy, shallow floodplains and estuaries. Bichirs are considered the sister group to all other extant ray-finned fishes Bichirs are elongated fish with a unique series of dorsal finlets which vary in number from seven to 18, instead of a single dorsal fin. Each of the dorsal finlets has bifid (double-edged) tips, and are the only fins with spines; the rest of the fins are composed of soft rays. The body is covered in thick, bonelike, and rhombic (ganoid) scales. Their jaw structure more closely resembles that of the tetrapods than that of the teleost fishes. Bichirs have a number of other primitive characteristics, including fleshy pectoral fins superficially similar to those of lobe-finned fishes.[1] They also have a pair of slit-like spiracles on the top of their heads that are used to breathe air,[5] two gular plates, and paired ventral lungs (the left lung shorter than the right).[6] Four pairs of gill arches are present.[7] Bichirs have a maximum body length ranging from 25 cm (9.8 in) to over 100 cm (39 in) depending on specific species and morphology.[

Hermaphroditism:

20 families exhibit simultaneous hermaphroditism (both sex organs in one ind at same time) and have 3 mating patterns: Egg traders (alternate male and female role) Reciprocating monogamous pairs Harem polygynous species

sturgeon (Acipenseridae)

27 species of fish belonging to the family Acipenseridae. Their evolution dates back to the Triassic some 245 to 208 million years ago.[2] The family is grouped into four genera: Acipenser, Huso, Scaphirhynchus and Pseudoscaphirhynchus. Four species may now be extinct.[3] Two closely related species, Polyodon spathula (American paddlefish) and Psephurus gladius (Chinese paddlefish, possibly extinct) are of the same order, Acipenseriformes, but are in the family Polyodontidae and are not considered to be "true" sturgeons. Both sturgeons and paddlefish have been referred to as "primitive fishes" because their morphological characteristics have remained relatively unchanged since the earliest fossil record.[4][5] Sturgeons are native to subtropical, temperate and sub-Arctic rivers, lakes and coastlines of Eurasia and North America.[6] Sturgeons are long-lived, late-maturing fishes with distinctive characteristics, such as a heterocercal caudal fin similar to that of sharks, and an elongated spindle-like body that is smooth-skinned, scaleless and armored with 5 lateral rows of bony plates called scutes. Several species can grow quite large, typically ranging 7-12 feet (2-3½ m) in length. The largest sturgeon on record was a Beluga female captured in the Volga estuary in 1827, weighing 1,571 kg (3,463 lb) and 7.2 m (24 ft) long. Most sturgeons are anadromous bottom-feeders which migrate upstream to spawn but spend most of their lives feeding in river deltas and estuaries. Some species inhabit freshwater environments exclusively while others primarily inhabit marine environments near coastal areas, and are known to venture into open ocean. Several species of sturgeon are harvested for their roe which is processed into caviar—a luxury food and the reason why caviar-producing sturgeons are among the most valuable of all wildlife resources.[7] They are particularly vulnerable to overexploitation and other threats, including pollution and habitat fragmentation. Most species of sturgeon are considered to be at risk of extinction, making them more critically endangered than any other group of species.[8]

Acanthostega

Acanthostega (meaning "spiny roof") is an extinct genus of stem-tetrapod, among the first vertebrate animals to have recognizable limbs. It appeared in the late Devonian period (Famennian age) about 365 million years ago, and was anatomically intermediate between lobe-finned fishes and those that were fully capable of coming onto land The 60 cm (24 in) Acanthostega had eight digits on each hand (the number of digits on the feet is unclear) linked by webbing, it lacked wrists, and was generally poorly adapted for walking on land. It also had a remarkably fish-like shoulder and forelimb.[2] The front foot of Acanthostega could not bend forward at the elbow, and thus could not be brought into a weight bearing position, appearing to be more suitable for paddling or for holding on to aquatic plants. Acanthostega is the earliest stem-tetrapod to show the shift in locomotory dominance from the pectoral girdle to the pelvic girdle. There are many morphological changes that allowed the pelvic girdle of Acanthostega to become a weight-bearing structure. In more ancestral states the two sides of the girdle were not attached. In Acanthostega there is contact between the two sides and fusion of the girdle with the sacral rib of the vertebral column. These fusions would have made the pelvic region more powerful and equipped to counter the force of gravity when not supported by the buoyancy of an aquatic environment.[3] It had internal gills that were covered like those of fish. It also had lungs, but its ribs were too short to support its chest cavity out of water.[1] It has been inferred that Acanthostega probably lived in shallow, weed-choked swamps, its legs being not an adaptation to walking on land. Jennifer A. Clack interprets this as showing that Acanthostega was primarily an aquatic animal descended from fish that never left the sea, and that the specializations in the tetrapod lineage developed features which would later be useful for terrestrial life. At that period, deciduous plants were flourishing and annually shedding leaves into the water, attracting small prey into warm oxygen-poor shallows that were difficult for larger fish to swim in; Clack remarks on how the lower jaw of Acanthostega shows a change from those of fish that have two rows of teeth, with a large number of small teeth in the outer row, and two large fangs and some smaller teeth in the inner row. This difference likely corresponds to a shift in stem-tetrapods from feeding exclusively in the water to feeding with the head above water or on land.[1] While normally considered more basal than Ichthyostega, it is possible that Acanthostega was actually more derived. Since Acanthostega resembles juvenile Ichthyostega and shows a lot less differences from juveniles to adults than the latter, it has been suggested that Acanthostega might be descended from a neotenic lineage. Although it appears to have spent its whole life in water, its humerus also exhibits traits that resemble those of later, fully terrestrial stem-tetrapods (the humerus in Ichthyostega being somewhat derived from, and homologous with the pectoral and pelvic fin bones of earlier fishes). This could indicate that vertebrates evolved terrestrial traits earlier than previously assumed, and numerous times independently from another.[4] Research based on analysis of the suture morphology in the skull of Acanthostega indicates that the species was able to bite prey at or near the water's edge. Markey and Marshall compared the skull with the skulls of fish, which use suction feeding as the primary method of prey capture, and creatures known to have used the direct biting on prey typical of terrestrial animals. Their results indicate that Acanthostega was adapted for what they call terrestrial-style feeding, strongly supporting the hypothesis that the terrestrial mode of feeding first emerged in aquatic animals. If correct, this shows an animal specialized for hunting and living in shallow waters in the line between land and water.[5] Newer research also indicates that it is possible Acanthostega evolved from an ancestor that had more terrestrial adaptations than itself

Protopterus

African lungfishes are elongated, eel-like fishes, with thread-like pectoral and pelvic fins. They have soft scales, and the dorsal and tail fins are fused into a single structure. They can either swim like eels, or crawl along the bottom, using their pectoral and pelvic fins.[4] The largest species reach about 200 cm (6.6 ft) long.[3] African lungfishes generally inhabit shallow waters, such as swamps and marshes. They are also found in larger lakes such as Lake Victoria. They can live out of water for many months in burrows of hardened mud beneath a dried stream bed. They are carnivorous, eating crustaceans, aquatic insect larvae, and molluscs.[4] The African lungfish is an example of how the evolutionary transition from breathing water to breathing air can happen. Lungfish are periodically exposed to water with low oxygen content or situations in which their aquatic environment dries up. Their adaptation for dealing with these conditions is an outpocketing of the gut, related to the swim bladder of other fishes, that serves as a lung.[4] The lung contains many thin-walled blood vessels, so blood flowing through those vessels can pick up oxygen from air gulped into the lung. The African lungfishes are obligate air breathers, with reduced gills in the adults. They have two anterior gill arches that retain gills, though they are too small to function as the sole respiratory apparatus. The lungfish heart has adaptations that partially separate the flow of blood into its pulmonary and systemic circuits. The atrium is partially divided, so that the left side receives oxygenated blood and the right side receives deoxygenated blood from the other tissues. These two blood streams remain mostly separate as they flow through the ventricle leading to the gill arches. As a result, oxygenated blood mostly goes to the anterior gill arches and the deoxygenated blood mostly goes to the posterior arches. African lungfishes breed at the beginning of the rainy season. They construct nests or burrows in the mud to hold their eggs, which they then guard against predators. When they hatch, the young resemble tadpoles, with external gills, and only later develop lungs and begin to breathe air.[

Gynogenesis -

Amazon molly: a unisexual hybrid of the bisexual sailfin and Mexican mollies

Amia

Bowfins

graviportal

Definition of graviportal. : having the body supports adapted to the bearing of great weights the elephant is a graviportal mammal.

Paddle fish anatomy

During the initial stages of development from embryo to fry, paddlefish have no rostrum (snout). It begins to form shortly after hatching.[11] The rostrum of a Chinese paddlefish is narrow and sword-like while the rostrum of the American paddlefish is broad and paddle-like. Some common morphological characteristics of paddlefish include a spindle-shaped, smooth skinned scaleless body, heterocercal tail, and small poorly developed eyes.[6][11] Unlike the filter-feeding American paddlefish, Chinese paddlefish are piscivores, and highly predaceous. Their jaws are more forward pointing which suggest they forage primarily on small fishes in the water column, and occasionally on shrimp, benthic fishes, and crabs.[6][12] The jaws of the American paddlefish are distinctly adapted for filter feeding only.[4] They are ram suspension filter feeders with a diet that consists primarily of zooplankton, and occasionally small insects, insect larvae, and small fish.[4] The largest Chinese paddlefish on record measured 23 ft (7.0 m) in length, and was estimated to weigh a few thousand pounds.[5] They commonly reach 9.8 ft (3.0 m) and 1,100 lb (500 kg).[5][6][13] Although the American paddlefish is one of the largest freshwater fishes in North America, their recorded lengths and weights fall short in comparison to the larger Chinese paddlefish. American paddlefish commonly reach 5 ft (1.5 m) or more in length and can weigh more than 60 lb (27 kg). The largest American paddlefish on record was caught in 1916 in Okoboji Lake, Iowa.[14] The fish was taken with a spear, and measured 7 ft 1 in (2.16 m) long and 45.5 in (1.16 m) in the girth.[14] A report published by J.R. Harlan and E.B. Speaker in Iowa Fish and Fishing (1969) said the fish weighed over 198 lb (90 kg).[15] The world record paddlefish caught on rod and reel weighed 144 lb (65 kg) and was 54.25 in (1.378 m) long. The fish was caught by Clinton Boldridge in a 5-acre pond in Atchison County, Kansas.[16][17] Scientists once believed paddlefish used their rostrums to excavate bottom substrate,[11][18] but have since determined with the aid of electron microscopy that paddlefish have electroreceptors on their rostrum's ampulla (hair cells) which are similar in structure to other Lorenzini.[19] The electroreceptors can detect weak electrical fields which not only signal the presence of prey items in the water column, such as zooplankton which is the primary diet of the American paddlefish, but they can also detect the individual feeding and swimming movements of zooplankton's appendages.[4][11] Paddlefish have poorly developed eyes, and rely on their electroreceptors for foraging. However, the rostrum is not the paddlefish's sole means of food detection. Some reports incorrectly suggest that a damaged rostrum would render paddlefish less capable of foraging efficiently to maintain good health. Laboratory experiments, and field research indicate otherwise. In addition to electroreceptors on the rostrum, paddlefish also have sensory pores covering nearly half of the skin surface extending from the rostrum to the top of the head down to the tips of the operculum (gill flaps). Therefore, paddlefish with damaged or abbreviated rostrums are still able to forage and maintain good health.[4][11]

ectotherm thermoregulation

Ectotherms use external sources of temperature to regulate their body temperatures. They are colloquially referred to as cold-blooded despite the fact that body temperatures often stay within the same temperature ranges as warm-blooded animals. Ectotherms are the opposite of endotherms when it comes to regulating internal temperatures. In ectotherms, the internal physiological sources of heat are of negligible importance; the biggest factor that enables them to maintain adequate body temperatures is due to environmental influences. Living in areas that maintain a constant temperature throughout the year, like the tropics or the ocean, have enabled ectotherms to develop a wide range of behavioral mechanisms that enable them to respond to external temperatures, such as sun-bathing to increase body temperature, or seeking the cover of shade to lower body temperature.[7][6]

anura

Frog

DISTINCT FEATURES OF OSTEICHTHYES

Fully ossified endoskeleton and endochondral bone Unique dermal bones around jaw and brain Covering of marginal mouth bones: maxilla and premaxilla in upper jaw and dentary in lower jaw Dermal bones extend into roof of mouth covering the palate Dermal head bones attach to pectoral girdle and also form operculum Branchiostegal rays form floor of gill chamber and aid in suction and respiration Gas-containing structure derived from embryonic gut (lost in some bottom-dwellers

gars

Gars (or garpike) are members of the Lepisosteiformes (or Semionotiformes), an ancient holosteian order of ray-finned fish; fossils from this order are known from the Late Jurassic onwards. The family Lepisosteidae includes seven living species of fish in two genera that inhabit fresh, brackish, and occasionally marine, waters of eastern North America, Central America and the Caribbean islands.[2][3] Gars have elongated bodies that are heavily armored with ganoid scales,[4] and fronted by similarly elongated jaws filled with long, sharp teeth. All of the gars are relatively large fish, but the alligator gar (Atractosteus spatula) is the largest, as specimens have been reported to be 3 m (9.8 ft) in length;[5] however, they typically grow to 2 m (6.5 ft) and weigh over 45 kg (100 lb).[6] Unusually, their vascularised swim bladders can function as lungs,[7] and most gars surface periodically to take a gulp of air. Gar flesh is edible and the hard skin and scales of gars are used by humans; however their eggs are highly toxic

Ichthyostega

Greek: "fish roof") is an early genus of tetrapodomorphs that lived at the end of the Late Devonian Period. It was one of the first four-limbed vertebrates in the fossil record. Ichthyostega possessed lungs and limbs that helped it navigate through shallow water in swamps. Although Ichthyostega is often labelled a "tetrapod" due to the possession of limbs and fingers, it was more basal ("primitive") than true crown-tetrapods, and could more accurately be referred to as a stegocephalian or stem tetrapod. Likewise, while undoubtedly of amphibian build and habit, it is not considered a true member of the group in the narrow sense, as the first modern amphibians (members of the group Lissamphibia) appeared in the Triassic Period. Until finds of other early stegocephalians and closely related fishes in the late 20th century, Ichthyostega stood alone as a transitional fossil between fish and tetrapods, combining fish- and tetrapod-like features. Newer research has shown that it had an unusual anatomy, functioning more akin to a seal than a salamander, as previously assumed.[3] Ichthyostega was a fairly large animal, broadly built and about 1.5 m (4.9 ft) long. The skull was flat with dorsally placed eyes and armed with large labyrinthodont teeth. The posterior margin of the skull formed an operculum covering the gills. The spiracle was situated in an otic notch behind each eye. The limbs were large compared to contemporary relatives, and it had seven digits on each hind limb. The exact number of digits on the forelimb is not yet known, since fossils of the manus (hand) have not been found.[4] It had a fin containing fin rays on its tail.

dipnoan (Dipnoi)

Lungfish

Lungfish

Lungfish are freshwater rhipidistian fish belonging to the subclass Dipnoi. Lungfish are best known for retaining characteristics primitive within the Osteichthyes, including the ability to breathe air, and structures primitive within Sarcopterygii, including the presence of lobed fins with a well-developed internal skeleton. Today there are only six known species of lungfish, living only in Africa, South America and Australia. The fossil record show that lungfish were abundant since the Triassic.[1] While vicariance would suggest this represents an ancient distribution limited to the Mesozoic supercontinent Gondwana, the fossil record suggests advanced lungfish had a widespread freshwater distribution and the current distribution of modern lungfish species reflects extinction of many lineages subsequent to the breakup of Pangaea, Gondwana and Laurasia. Lungfish have historically been referred to as salamanderfish,[2] but this term more often refers to Lepidogalaxias salamandroides.

Name two extant osteoglossomorphs

Osteoglossum - arawana (S AM) Mormyrus - elephant-nose (Afr)

Hybridogenesis -

Rio Fuerte topminnow: unisexual hybrids resulting from mating of female headwater topminnows with male clearfin topminnow

Shared derived characters of amphibians

Structure of the skin for gas exchange Papilla amphibiorum (inner ear specialty) Operculum-columnella complex - also a feature of the inner ear Green rods - distinct retinal cells (blue light sensitivity) Pedicellate teeth - teeth have narrow band of connective tissue Structure of levator bulbi muscle - results in characteristic bulging eyes of amphibians

vestibular apparatus (cerebellum)

The vestibular system, in most mammals, is the sensory system that provides the leading contribution to the sense of balance and spatial orientation for the purpose of coordinating movement with balance. Together with the cochlea, a part of the auditory system, it constitutes the labyrinth of the inner ear in most mammals. As movements consist of rotations and translations, the vestibular system comprises two components: the semicircular canals which indicate rotational movements; and the otoliths which indicate linear accelerations. The vestibular system sends signals primarily to the neural structures that control eye movements, and to the muscles that keep an animal upright and in general control posture. The projections to the former provide the anatomical basis of the vestibulo-ocular reflex, which is required for clear vision; while the projections to the latter provide the anatomical means required to enable an animal to maintain its desired position in space. The brain uses information from the vestibular system in the head and from proprioception throughout the body to enable the animal to understand its body's dynamics and kinematics (including its position and acceleration) from moment to moment. How these two perceptive sources are integrated to provide the underlying structure of the sensorium is unknown.

examples of teleosteans

giant oarfish measuring 7.6 m (25 ft) or more, and ocean sunfish weighing over 2 t (2.0 long tons; 2.2 short tons), to the minute male anglerfish Photocorynus spiniceps, just 6.2 mm (0.24 in) long. Including not only torpedo-shaped fish built for speed, teleosts can be flattened vertically or horizontally, be elongated cylinders or take specialised shapes as in anglerfish and seahorses

neopterygian

i are a group of fish. Neopterygii means "new fins" (from Greek νέος neos, new, and πτέρυξ pteryx, fin). Only a few changes occurred during their evolution from the earlier actinopterygians. They appeared sometime in the Late Permian, before the time of the dinosaurs. The Neopterygii were a very successful group of fish, because they could move more rapidly than their ancestors. Their scales and skeletons began to lighten during their evolution, and their jaws became more powerful and efficient. While electroreception and the ampullae of Lorenzini are present in all other groups of fish, with the exception of hagfish (although hagfish are not Actinopterygii, they are Agnathans), Neopterygii have lost this sense, even if it has later been re-evolved within Gymnotiformes and catfishes, which possess nonhomologous teleost ampullae.[2]

Diadectomorpha

are a clade of large reptile-like amphibians that lived in Euramerica during the Carboniferous and Early Permian periods and in Asia during Late Permian (Wuchiapingian),[1] and are very close to the ancestry of the Amniota. They include both large (up to 2 meters long) carnivorous and even larger (to 3 meters) herbivorous forms, some semi-aquatic and others fully terrestrial. The Diadectomorpha seem to have evolved during late Mississippian times, although they only became common after the Carboniferous rainforest collapse and flourished during the Late Pennsylvanian and Early Permian periods Diadectomorphs possess both amphibian and reptilian characteristics. Originally these animals were included under the order Cotylosauria, and were considered the most primitive and ancestral lineage of reptiles. More recently they have been reclassified as amphibian-grade tetrapods, closely related to the first true amniotes (though they have also been argued to be amniotes more closely related to synapsids than to sauropsids[2]). Contrary to other Reptiliomorph amphibians, the teeth of the Diadectomorpha lacked the infolding of the dentine and enamel that account for the name Labyrinthodontia for the non-amniote tetrapods

osteoglossomorpha

are a group of bony fish in the Teleostei. A notable member is the arapaima (Arapaima gigas), the largest freshwater fish in South America and one of the largest bony fishes alive. Other notable members include the bizarre freshwater elephantfishes of family Mormyridae, and the extinct predator, Xiphactinus.

caecilian

are a group of limbless, serpentine amphibians. They mostly live hidden in the ground and in stream substrates, making them the least familiar order of amphibians. All modern caecilians and their closest fossil relatives are grouped as a clade, Apoda, within the larger group Gymnophiona, which also includes more primitive extinct caecilian-like amphibians.[1] Caecilians are mostly distributed in the tropics of South and Central America, Africa, and southern Asia. Their diet consists of small subterranean creatures such as earthworms. Caecilians completely lack limbs, making the smaller species resemble worms, while the larger species, with lengths up to 1.5 m (5 ft), resemble snakes. Their tails are short or absent, and their cloacae are near the ends of their bodies.[2][3][4] Their skin is smooth and usually dark, but some species have colourful skins. Inside the skin are calcite scales. Because of these scales, the caecilians were once thought to be related to the fossil Stegocephalia, but they are now believed to be a secondary development, and the two groups are most likely unrelated.[4] The skin also has numerous ring-shaped folds, or annuli, that partially encircle the body, giving them a segmented appearance. Like some other living amphibians, the skin contains glands that secrete a toxin to deter predators.[5] The skin secretions of Siphonops paulensis have been shown to have hemolytic properties.[6] Caecilians' vision is limited to dark-light perception,[7] and their anatomy is highly adapted for a burrowing lifestyle. They have a strong skull, with a pointed snout used to force their way through soil or mud.[4] In most species, the bones in the skull are reduced in number and fused together, and the mouth is recessed under the head. Their muscles are adapted to pushing their way through the ground, with the skeleton and deep muscles acting as a piston inside the skin and outer muscles. This allows the animal to anchor its hind end in position, and force the head forwards, and then pull the rest of the body up to reach it in waves. In water or very loose mud, caecilians instead swim in an eel-like fashion.[5] Caecilians in the family Typhlonectidae are aquatic, and the largest of their kind. The representatives of this family have a fleshy fin running along the rear section of their bodies, which enhances propulsion in water.[8] All but the most primitive caecilians have two sets of muscles for closing the jaw, compared with the single pair found in other creatures. These are more highly developed in the most efficient burrowers among the caecilians, and appear to help keep the skull and jaw rigid.[5] All caecilians possess a pair of tentacles located between their eyes and nostrils. These are probably used for a second olfactory capability, in addition to the normal sense of smell based in the nose.[5] The middle ear consists of only the stapes and the oval window, which transfer vibration to the inner ear through a reentrant fluid circuit as seen in some reptiles. The species within the Scolecomorphidae lack both stapes and an oval window, making them the only known amphibians missing all the components of a middle ear apparatus.[9] Except for one lungless species, Atretochoana eiselti,[10] all caecilians have lungs, but also use their skin or mouths for oxygen absorption. Often, the left lung is much smaller than the right one, an adaptation to body shape that is also found in snakes

Paddlefish (family Polyodontidae)

are basal Chondrostean ray-finned fish.[2] They have been referred to as "primitive fish" because they have evolved with few morphological changes since the earliest fossil records of the Late Cretaceous, seventy to seventy-five million years ago.[3] Polyodontids are exclusively North American and Chinese.[4] There are six known species: four extinct species known only from fossil remains (three from western North America, one from China), and two extant species, including the American paddlefish (Polyodon spathula) which is native to the Mississippi River basin in the U.S. and the critically endangered Chinese paddlefish (Psephurus glades) which is endemic to the Yangtze River Basin in China.[5] Chinese paddlefish are also commonly referred to as "Chinese swordfish", or "elephant fish".[6][7] Paddlefish populations have declined dramatically throughout their historic range as a result of overfishing, pollution, and the encroachment of human development, including the construction of dams that have blocked their seasonal upward migration to ancestral spawning grounds.[8] Other detrimental effects include alterations of rivers which have changed natural flows resulting in the loss of spawning habitat and nursery areas. Chinese paddlefish have not been seen since 2007, and may now be extinct for many of the same reasons that have plagued the American species

Reptiliomorpha

is a clade containing the amniotes and those tetrapods that share a more recent common ancestor with amniotes than with living amphibians (lissamphibians). It was defined by Michel Laurin (2001) and Vallin and Laurin (2004) as the largest clade that includes Homo sapiens, but not Ascaphus truei (tailed frog).[1][2] The informal variant of the name, "reptiliomorphs", is also occasionally used to refer to stem-amniotes, i.e. a grade of reptile-like tetrapods that are more closely related to amniotes than they are to lissamphibians, but are not amniotes themselves; the name is used in this meaning e.g. by Ruta, Coates and Quicke (2003).[3] An alternative name, "Anthracosauria", is also commonly used for the group, but is confusingly also used for a more primitive grade of reptiliomorphs (Embolomeri) by Benton.[4] As the exact phylogenetic position of Lissamphibia within Tetrapoda remains uncertain, it also remains controversial which fossil tetrapods are more closely related to amniotes than to lissamphibians, and thus, which ones of them were reptiliomorphs in any meaning of the word. The two major hypotheses for lissamphibian origins are that they are either descendants of dissorophoid temnospondyls or microsaurian "lepospondyls". If the former (the "temnospondyl hypothesis") is true, then Reptiliomorpha includes all tetrapod groups that are closer to amniotes than to temnospondyls. These include the diadectomorphs, seymouriamorphs, most or all "lepospondyls", gephyrostegids, and possibly the embolomeres and chroniosuchians.[3] In addition, several "anthracosaur" genera of uncertain taxonomic placement would also probably qualify as reptiliomorphs, including Solenodonsaurus, Eldeceeon, Silvanerpeton, and Casineria. However, if lissamphibians originated among the lepospondyls according to the "lepospondyl hypothesis", then Reptiliomorpha refers to groups that are closer to amniotes than to lepospondyls. Few non-amniote groups would count as reptiliomorphs under this definition, although the diadectomorphs are among those that qualify.[5]

The Otocephala

is a clade of bony fishes within the Teleostei that evolved some 230 million years ago. It is named for the presence of a hearing (otophysic) link from the swimbladder to the inner ear. Other names proposed for the group include Ostarioclupeomorpha and Otomorpha. The clade contains the Clupeiformes (herrings) and the Ostariophysi, a group of other orders including the Cypriniformes (minnows and allies), Gymnotiformes (knifefish), and Siluriformes (catfish). The Otocephala may also contain the Alepocephaliformes (slickheads), but as yet (2016) without morphological evidence. The clade is sister to the Euteleostei which contains the majority of bony fish alive today.[1][2][3][4] In 2015, Benton and colleagues set a "plausible minimum" date for the origin of the crown Otocephala as about 228.4 million years ago. They argued that since the oldest locality for any diversity of stem teleosts is the Carnian of Polberg bei Lunz, Austria, whose base is 235 million years old, a rough estimate for the Otocephala can be made

The Euteleostei or euteleosts

is a clade of bony fishes within the Teleostei that evolved some 240 million years ago. It is divided into the Protacanthopterygii (including the salmon and dragonfish) and the Neoteleostei (including the lanternfish, lizardfish, oarfish, and the Acanthopterygii).[1][2][3]

Temnospondyli

is a diverse subclass of small to giant tetrapods—often considered primitive amphibians—that flourished worldwide during the Carboniferous, Permian, and Triassic periods. A few species continued into the Cretaceous. Fossils have been found on every continent. During about 210 million years of evolutionary history, they adapted to a wide range of habitats, including fresh water, terrestrial, and even coastal marine environments. Their life history is well understood, with fossils known from the larval stage, metamorphosis, and maturity. Most temnospondyls were semiaquatic, although some were almost fully terrestrial, returning to the water only to breed. These temnospondyls were some of the first vertebrates fully adapted to life on land. Although temnospondyls are considered amphibians, many had characteristics, such as scales, claws, and armour-like bony plates, that distinguish them from modern amphibians. Temnospondyls have been known since the early 19th century, and were initially thought to be reptiles. They were described at various times as batrachians, stegocephalians, and labyrinthodonts, although these names are now rarely used. Animals now grouped in Temnospondyli were spread out among several amphibian groups until the early 20th century, when they were found to belong to a distinct taxon based on the structure of their vertebrae. Temnospondyli means "cut vertebrae", as each vertebra is divided into several parts. Experts disagree over whether temnospondyls were ancestral to modern amphibians (frogs, salamanders, and caecilians), or whether the whole group died out without leaving any descendants. Different hypotheses have placed modern amphibians as the descendants of temnospondyls, another group of early tetrapods called lepospondyls, or even as descendants of both groups (with caecilians evolving from lepospondyls and frogs and salamanders evolving from temnospondyls). Recent studies place a family of temnospondyls called the amphibamids as the closest relatives of modern amphibians. Similarities in teeth, skulls, and hearing structures link the two groups. Many temnospondyls are much larger than living amphibians, and superficially resemble crocodiles. Others are smaller and resemble salamanders.[1] Most have broad, flat heads that are either blunt (brevirostrine) or elongated (longirostrine). The skulls are rounded or triangular in shape when viewed from above, and are usually covered in pits and ridges. The rugged surfaces of bones may have supported blood vessels, which could transfer carbon dioxide to the bones to neutralize acidic build up in the blood (early semiaquatic tetrapods would have had difficulty expelling carbon dioxide from their bodies while on land, and these dermal bones may have been an early solution to the problem).[2] Many temnospondyls also have canal-like grooves in their skulls called sensory sulci. The sulci, which usually run around the nostrils and eye sockets, are part of a lateral line system used to detect vibrations in water.[1] As semiaquatic animals, all known temnospondyls have small limbs with no more than four toes on each front foot and five on each hind foot.[3] Terrestrial temnospondyls have larger, thicker limbs, and some even have claws.[4] One unusual terrestrial temnospondyl, Fayella, has relatively long limbs for its body, and probably lived as an active runner able to chase prey.[5] Homologues of most of the bones of temnospondyls are also seen in other early tetrapods, aside from a few bones in the skull, such as interfrontals, internasals, and interparietals, that have developed in some temnospondyl taxa.[1] Most temnospondyls have tabular horns in the backs of their skulls, rounded projections of bone separated from the rest of the skull by indentations called otic notches; in some temnospondyls, such as Zatrachys, they are pointed and very prominent. Among the most distinguishing features of temnospondyls are the interpterygoid vacuities, two large holes in the back of the palate. Another pair of holes, choanae, are present in front of these vacuities, and connect the nasal passage with the mouth. Temnospondyls often have teeth on their palates, as well as in their jaws. Some of these teeth are so large, they are referred to as tusks. In some temnospondyls, such as Nigerpeton, tusks in the lower jaw pierce the palate and emerge through openings in the top of the skull.[6] Very little is known of the soft tissue of temnospondyls. A block of sandstone, described in 2007 from the Early Carboniferous Mauch Chunk Formation of Pennsylvania, included impressions of the bodies of three temnospondyls. These impressions show, when alive, they had smooth skin, robust limbs with webbed feet, and a ridge of skin on their undersides.[7] Trackways referable to small temnospondyls have also been found in Carboniferous and Permian rocks. The trackways, called batrachichni, are usually found in strata deposited around freshwater environments, suggesting the animals had some ties to the water

Lepospondyli

is a diverse taxon of reptiliomorph tetrapods. With the exception of one late-surviving lepospondyl from the Late Permian of Morocco (Diplocaulus minumus),[4] lepospondyls lived from the Early Carboniferous (Mississippian) to the Early Permian and were geographically restricted to what is now Europe and North America.[5] Five major groups of lepospondyls are known: Adelospondyli; Aïstopoda; Lysorophia; Microsauria; and Nectridea. Lepospondyls have a diverse range of body forms and include species with newt-like, eel- or snake-like, and lizard-like forms. Various species were aquatic, semiaquatic, or terrestrial. None were large (the biggest genus, the diplocaulid Diplocaulus, reached a meter in length, but most were much smaller), and they are assumed to have lived in specialized ecological niches not taken by the more numerous temnospondyl amphibians that coexisted with them in the Paleozoic. Lepospondyli was named in 1888 by Karl Alfred von Zittel, who coined the name to include some tetrapods from the Paleozoic, that shared some specific characteristics in the notochord and teeth. Lepospondyls have sometimes been considered to be either related or ancestral to modern amphibians[6][7][8] or to Amniota (the clade containing reptiles and mammals All lepospondyls are characterised by having simple, spool-shaped vertebrae that did not ossify from cartilage, but rather grew as bony cylinders around the notochord. In addition, the upper portion of the vertebra, the neural arch, is usually fused to the centrum (the main body of the vertebra).[10] The position of the Lepospondyli within the Tetrapoda is uncertain because the earliest lepospondyls were already highly specialized when they first appeared in the fossil record. Some lepospondyls were once thought to be related or perhaps ancestral to modern salamanders (Urodela), but not the other modern amphibians. This view is no longer held and all modern amphibians (frogs, salamanders, and caecilians) are now grouped within the clade Lissamphibia. For a long time, the Lepospondyli were considered one of the three subclasses of Amphibia, along with the Lissamphibia and the Labyrinthodontia.[10][11][12] However, the dissolution of "labyrinthodonts" into separate groups such as temnospondyls and anthracosaurs has cast doubt on these traditional amphibian subclasses Much like "Labyrinthodontia", some studies proposed that Lepospondyli is an artificial (polyphyletic) grouping with some members closely related to extinct stem tetrapod groups and others more closely related to modern amphibians or reptiles.[13] Early phylogenetic analyses conducted in the 1980s and 1990s often maintained the idea that lepospondyls were paraphyletic, with nectrideans close to colosteids and microsaurs close to temnospondyls, which were considered to be ancestral to modern amphibians. However, a 1995 paper by Robert Carroll argued that lepospondyls were actually a monophyletic group closer to reptiles. Carroll considered them closer to reptiles than the seymouriamorphs, but not as close as the diadectomorphs.[14] Many phylogenetic analyses since Carroll (1995) agreed with his interpretation, including Laurin & Reisz (1997),[15] Anderson (2001),[16] and Ruta et al. (2003).[9] A few have still considered lepospondyls ancestral to amphibians, but came to this conclusion without changing the position of lepospondyls compared to seymouriamorphs and diadectomorphs.[8] Lepospondyl and tetrapod classification is still controversial, and even recent studies have had doubts about lepospondyl monophyly. For example, a 2007 paper has suggested that adelospondyls are stem-tetrapods close to colosteids[3] and a 2017 paper on Lethiscus has Aïstopoda in the tetrapod stem based on their primitive braincase.[17] These studies differ in the internal and external relationships of the remaining lepospondyl taxa. The former places the remaining lepospondyls into a single clade along the amniote stem. The latter does not treat the relationships of nectrideans or adelospondyls, but finds microsaurs to be early amniotes, and places lysorophians within microsaurs.

Palaeoniscidae

is a family of fish who possessed a bony skeleton and operculum. This group of fish appeared in the Silurian, and died out in the Cretaceous.

Panderichthys

is a genus of extinct sarcopterygian (lobe-finned fish) from the late Devonian period, about 380 Mya. Panderichthys, which was recovered from Frasnian (early Late Devonian) deposits in Latvia, is represented by two species. P. stolbovi is known only from some snout fragments and an incomplete lower jaw. P. rhombolepis is known from several more complete specimens. Although it probably belongs to a sister group of the earliest tetrapods, Panderichthys exhibits a range of features transitional between tristichopterid lobe-fin fishes (e.g., Eusthenopteron) and early tetrapods.[1] It is named after the German-Baltic paleontologist Christian Heinrich Pander. A recent study uncovered tetrapod tracks dating back to before the appearance of Panderichthys in the fossil record, which suggests that Panderichthys is not a transitional fossil, but nonetheless shows the traits that evolved during the fish-tetrapod evolution

Eusthenopteron

is a genus of prehistoric sarcopterygian (often called lobe-finned fishes) which has attained an iconic status from its close relationships to tetrapods. The name derives from two Greek stems—eustheno- "strength" and -pteron "wing" and thus "strongly developed fins".[1] Early depictions of this animal show it emerging onto land; however, paleontologists now widely agree that it was a strictly aquatic animal.[2] The genus Eusthenopteron is known from several species that lived during the Late Devonian period, about 385 million years ago. Eusthenopteron was first described by J. F. Whiteaves in 1881, as part of a large collection of fishes from Miguasha, Quebec.[3] Some 2,000 Eusthenopteron specimens have been collected from Miguasha, one of which was the object of intensely detailed study and several papers from the 1940s to the 1990s by paleoichthyologist Erik Jarvik.[4]

Tiktaalik

is a monospecific genus of extinct sarcopterygian (lobe-finned fish) from the Late Devonian Period, about 375 Ma (million years ago), having many features akin to those of tetrapods (four-legged animals).[1] Unearthed in Arctic Canada, Tiktaalik is technically a fish, complete with scales and gills - but it has the flattened head of a crocodile and unusual fins. Its fins have thin ray bones for paddling like most fishes', but they also have sturdy interior bones that would have allowed Tiktaalik to prop itself up in shallow water and use its limbs for support as most four-legged animals do. Those fins and a suite of other characteristics set Tiktaalik apart as something special; it has a combination of features that show the evolutionary transition between swimming fish and their descendants, the four-legged vertebrates - a clade which includes amphibians, reptiles, birds, mammals and humans.[2] It and similar animals may possibly be the common ancestors of the broad swath of all vertebrate terrestrial fauna: amphibians, reptiles, birds, and mammals.[3] The first well-preserved Tiktaalik fossils were found in 2004 on Ellesmere Island in Nunavut, Canada.

Latimeria

is a rare genus of fish that includes two extant species: West Indian Ocean coelacanth (Latimeria chalumnae) and the Indonesian coelacanth (Latimeria menadoensis). They follow the oldest known living lineage of Sarcopterygii (lobe-finned fish and tetrapods), which means they are more closely related to lungfish, reptiles and mammals than to the common ray-finned fishes. They are found along the coastlines of the Indian Ocean and Indonesia.[2][3] Since there are only two species of coelacanth and both are threatened, it is one of the most endangered genus of animals in the world. The West Indian Ocean coelacanth is a critically endangered species.[4]

Aestivation

is a state of animal dormancy, similar to hibernation, although taking place in the summer rather than the winter. Aestivation is characterized by inactivity and a lowered metabolic rate, that is entered in response to high temperatures and arid conditions.[1] It takes place during times of heat and dryness, the hot dry season, which are often the summer months. Invertebrate and vertebrate animals are known to enter this state to avoid damage from high temperatures and the risk of desiccation. Both terrestrial and aquatic animals undergo aestivation. The fossil record suggests that aestivation may have evolved several hundred million years ago. Organisms that aestivate appear to be in a fairly "light" state of dormancy, as their physiological state can be rapidly reversed, and the organism can quickly return to a normal state. A study done on Otala lactea, a snail native to parts of Europe and Northern Africa, shows that they can wake from their dormant state within ten minutes of being introduced to a wetter environment. The primary physiological and biochemical concerns for an aestivating animal are to conserve energy, retain water in the body, ration the use of stored energy, handle the nitrogenous end products, and stabilize bodily organs, cells, and macromolecules. This can be quite a task as hot temperatures and arid conditions may last for months. The depression of metabolic rate during aestivation causes a reduction in macromolecule synthesis and degradation. To stabilize the macromolecules, aestivators will enhance antioxidant defenses and elevate chaperone proteins. This is a widely used strategy across all forms of hypometabolism. These physiological and biochemical concerns appear to be the core elements of hypometabolism throughout the animal kingdom. In other words, animals who aestivate appear to go through nearly the same physiological processes as animals that hibernate

actinistian

is a subclass of mostly fossil lobe-finned fishes. This subclass contains the coelacanths (Order Coelacanthiformes), including the two living species of coelacanths, both of the genus Latimeria: the West Indian Ocean coelacanth and the Indonesian coelacanth.

Sarcopterygii

lobe-finned fish sometimes considered synonymous with Crossopterygii. constitute a clade (traditionally a class or subclass) of the bony fish, though a strict cladistic view includes the terrestrial vertebrates. The living sarcopterygians include two species of coelacanths and six species of lungfish.

The articular processes or zygapophyses .

of a vertebra, are projections of the vertebra that serve the purpose of fitting with an adjacent vertebra. The actual region of contact is called the articular facet.[1] Articular processes spring from the junctions of the pedicles and laminæ, and there are two right and left, and two superior and inferior. These stick out of an end of a vertebra to lock with a zygapophysis on the next vertebra, to make the backbone more stable. The superior processes or prezygapophysis project upward from a lower vertebra, and their articular surfaces are directed more or less backward (oblique coronal plane). The inferior processes or postzygapophysis project downward from a higher vertebra, and their articular surfaces are directed more or less forward and outward. The articular surfaces are coated with hyaline cartilage. In the cervical vertebral column, the articular processes collectively form the articular pillars. These are the bony surfaces palpated just lateral to the spinous processes

actinopterygian

or the ray-finned fishes, constitute a class or subclass of the bony fishes.[1] The ray-finned fishes are so called because their fins are webs of skin supported by bony or horny spines ("rays"), as opposed to the fleshy, lobed fins that characterize the class Sarcopterygii (lobe-finned fish). These actinopterygian fin rays attach directly to the proximal or basal skeletal elements, the radials, which represent the link or connection between these fins and the internal skeleton (e.g., pelvic and pectoral girdles). Numerically, actinopterygians are the dominant class of vertebrates, comprising nearly 99% of the over 30,000 species of fish.[2] They are ubiquitous throughout freshwater and marine environments from the deep sea to the highest mountain streams. Extant species can range in size from Paedocypris, at 8 mm (0.3 in), to the massive ocean sunfish, at 2,300 kg (5,070 lb), and the long-bodied oarfish, at 11 m (36 ft).

caudata

salamanders