Subphylum Vertebrata

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subphylum Vertebrata (/ˌvɜːrtəˈbreɪtə/) (chordates with backbones), including all mammals, birds, reptiles, amphibians and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, with currently about 69,963 species described. Although there are significant differences in the characteristics of each class, the organ systems and functions that make up the body are basically the same.

Any vertebrate, classified under subphylum Vertebrata, is an animal with a backbone. This group consists of several broad classes: fish, amphibians, birds, reptiles, and mammals. The word vertebrate refers to the bony vertebral column. All classes of vertebrate have developed brains, internal skeletons to which muscles can attach, two eyes, closed circulatory systems, and muscular mouths.

Primitive aquatic animals breathe with gills, secondary aquatic animals and terrestrial animals only have gill slits in the embryonic stage, and adults breathe with lungs.

There are 3 types of reproduction: oviparous, oviparous or viviparous.

A distinct head appears, the central nervous system becomes tubular, the front end expands into the brain, and the back differentiates into the spinal cord. In most species the notochord is seen only in the early stages of development (the exceptions are Cystophthora, Chondrichthyes, and Teleostichthyes), and is later replaced by the spine, which is joined by individual vertebrae. All have upper and lower jaws except round mouths. The circulatory system is relatively complete, and the heart that can contract appears, which promotes blood circulation and is conducive to improving physiological functions. Replace the simple renal tubes with complex kidneys to improve the excretion function, and the large amount of waste produced by metabolism can be excreted more effectively. In addition to Cyclostomum, aquatic animals have even fins, and terrestrial animals have paired appendages.

External relationships

Originally, the "Notochordata hypothesis" suggested that the Cephalochordata is the sister taxon to Craniata (Vertebrata). This group, called the Notochordata, was placed as sister group to the Tunicata (Urochordata). Although this was once the leading hypothesis, studies since 2006 analyzing large sequencing datasets strongly support Olfactores (tunicates + vertebrates) as a monophyletic clade, and the placement of Cephalochordata as sister-group to Olfactores (known as the "Olfactores hypothesis"). As chordates, they all share the presence of a notochord, at least during a stage of their life cycle.

First vertebrates

Vertebrates originated during the Cambrian explosion, which saw a rise in organism diversity. The earliest known vertebrates belongs to the Chengjiang biota and lived about 518 million years ago. These include Haikouichthys, Myllokunmingia, Zhongjianichthys, and probably Haikouella. Unlike the other fauna that dominated the Cambrian, these groups had the basic vertebrate body plan: a notochord, rudimentary vertebrae, and a well-defined head and tail. All of these early vertebrates lacked jaws in the common sense and relied on filter feeding close to the seabed.[page needed] A vertebrate group of uncertain phylogeny, small eel-like conodonts, are known from microfossils of their paired tooth segments from the late Cambrian to the end of the Triassic.

From fish to amphibians

The first jawed vertebrates may have appeared in the late Ordovician (~445 mya) and became common in the Devonian period, often known as the "Age of Fishes". The two groups of bony fishes, the actinopterygii and sarcopterygii, evolved and became common. The Devonian also saw the demise of virtually all jawless fishes save for lampreys and hagfish, as well as the Placodermi, a group of armoured fish that dominated the entirety of that period since the late Silurian as well as the eurypterids, dominant animals of the preceding Silurian, and the anomalocarids. By the middle of the Devonian, several droughts, anoxic events and oceanic competition lead a lineage of sarcopterygii to leave water, eventually establishing themselves as terrestrial tetrapods in the succeeding Carboniferous.

Mesozoic vertebrates

Amniotes branched from amphibious tetrapods early in the Carboniferous period. The synapsid amniotes were dominant during the late Paleozoic, the Permian, while diapsid amniotes became dominant during the Mesozoic. In the sea, the teleosts and sharks became dominant. Mesothermic synapsids called cynodonts gave rise to endothermic mammals and diapsids called dinosaurs eventually gave rise to endothermic birds, both in the Jurassic. After all dinosaurs except birds went extinct by the end of the Cretaceous, birds and mammals diversified and filled their niches.

After the Mesozoic

The Cenozoic world saw great diversification of bony fishes, amphibians, reptiles, birds and mammals.

Over half of all living vertebrate species (about 32,000 species) are fish (non-tetrapod craniates), a diverse set of lineages that inhabit all the world's aquatic ecosystems, from snow minnows (Cypriniformes) in Himalayan lakes at elevations over 4,600 metres (15,100 feet) to flatfishes (order Pleuronectiformes) in the Challenger Deep, the deepest ocean trench at about 11,000 metres (36,000 feet). Many fish varieties are the main predators in most of the world's freshwater and marine water bodies . The rest of the vertebrate species are tetrapods, a single lineage that includes amphibians (with roughly 7,000 species); mammals (with approximately 5,500 species); and reptiles and birds (with about 20,000 species divided evenly between the two classes). Tetrapods comprise the dominant megafauna of most terrestrial environments and also include many partially or fully aquatic groups (e.g., sea snakes, penguins, cetaceans).

Cyclostomia

1. Skeletal system: only cartilage, no hard bone. (1) Skull: No upper and lower jaws. The skull is incomplete. (2) Pharyngeal bone (pharyngeal cranium): It is a cartilage basket made of braided cartilage strips, called gill cage, which has no homologous relationship with the pharyngeal arch of other vertebrates. , not segmented; and the pharyngeal arch is segmented, born in the inner wall of the pharynx.

2. Notochord: Notochord remains for life.

3. Fins: no paired fins. With odd fins.

4. The muscles keep the original segment, which is similar to amphioxus.

fish class

1. Body shape: Spindle shape: suitable for fast and long-lasting swimming; side flat shape: not much swimming but agile; flat shape: slow movement, bottom dwelling life; puffer fish type: poor swimming; eel type: cave life.

2. Fins: odd fins: dorsal fin, anal fin, caudal fin (cartilaginous fish crooked tail, bony fish regular tail) even fins: pectoral fin, pelvic fin.

3. Skin and scales: The skin is divided into epidermis and dermis. The epidermis has no stratum corneum and has a large number of mucous glands. There are scales in the dermis. There are few subcutaneous tissue. Hard scales, bony scales (divided into round scales and ctenoid scales). The latter two are unique to teleosts and are derived entirely from mesoderm.

4. Skeletal system: Axial bones: skull, spine, ribs (more developed in bony fish); appendage bones: girdle bones (shoulder girdle, girdle), fin bones (pectoral fin, pelvic fin), odd fin bones.

5. Muscular system: trunk muscles (upper and lower axis muscles), head muscles (gill muscles), and appendicular muscles.

Amphibians

1. Skull: The brain cavity is narrow, there is no orbital septum, and the brain is flat. Not high, few bone fragments. Caecilian osteoids are large, compactly arranged without large holes. Formed by the outer occipital bones. The brain-cranial connection is self-connecting. It loses the function of the suspension connecting the cranium and the pharyngeal cranium, enters the middle ear cavity, and forms the ear column bone that conducts sound waves. The other parts of the lingual arch and part of the gill arch become the tongue organ to support the tongue, the hyoid body is formed by the basal hyoid cartilage, the anterior horn is formed by the horn hyoid cartilage, and the posterior horn is evolved from the first pair of gill arch. Most of the adult branchial arches disappeared, and a small part evolved into spoon-shaped cartilage, cricoid cartilage and tracheal ring. Tadpoles have 4 pairs of gill arches.

2. Spine: 1 cervical vertebra, which is ring-shaped and called atlas. The vertebral bodies of the trunk are concave anteriorly, those of the Cynoglossidae are posteriorly concave, and those of the caudate amphibians are biconcave. The two types of vertebral bodies are called uneven vertebral bodies. One sacral vertebra, the front of the vertebral body is articulated with the trunk vertebrae, and the back is articulated with the coccyx. The transverse spur reaches and connects with the ilium. The caudal vertebrae of anurans unite into a single coccygeus bone. Caudal amphibians have more than 20 caudal vertebrae.

3. Bones and Appendicular Bones

Composed of scapula, coracoid, superior coracoid, and clavicle. In the middle of the abdomen, the sternum connects with the shoulder girdle to form the thorax, and the connection between the shoulder girdle and the forelimb forms the shoulder socket. The clavicle is a membranous bone. Breast-solid type: the left and right superior coracoids of the shoulder girdle are fused parallel to each other at the midline of the abdomen. Curved chest type: the upper black coracoids of the shoulder girdle on both sides overlap and heal together on the midline of the abdomen. sternum A structure unique to terrestrial vertebrates. The girdle consists of the ilium, ischium, and pubic bone. The joint of the three bones forms a socket called the acetabulum, which articulates with the femur. Frogs are adapted to jumping, and their ilium is particularly long.

4. Appendicular bones Five-toed appendages.

Forelimb: upper arm, forearm (radius and ulna healed), carpal bone 6, metacarpal bone 5, phalanx 4 (first phalanx degenerates). Hind limb: femur, calf bone (tibia, fibula healed), tarsus 5, metatarsal 5, phalange 5.

5. Muscular system

Due to the complex movement after landing: jumping, crawling, flying, etc., amphibian muscles have the following characteristics: the original muscle segmentation phenomenon is no longer obvious, the muscle septum disappears, most of the sarcomeres are healed and displaced, and differentiate into many shapes and functions Different muscles. Only on the rectus abdominus can be seen several transverse tendons divided into myotome remnants. The axial muscles and septum on both sides of the trunk of salamanders are still developed. The appendicular muscles are more developed due to the variety of movements. Exogenous muscle: The origin of the muscle is on the trunk and the insertion point is on the appendage. When contracting, the appendages move as a whole according to the trunk (fish already have). Endogenous muscle: The starting and ending points of the muscle are on the appendage bone. When contracting, each part of the appendage can make corresponding local movements (around the elbow joint, wrist joint, knee joint, ankle joint). Frogs and toads have well-developed hind limbs. With the disappearance of the gills and the transformation of the branchial arches, the branchial muscles also changed, most of which degenerated; some turned into throat muscles.

The various movements of amphibians are seldom completed by one muscle, but by two or more groups of muscles with opposite effects.

Reptilia

1. Skin: The skin of animals in this class has no respiratory function, and rarely has skin glands, which can prevent water from evaporating in the body. The dermis is rich in pigment cells and is thin. Horny scales are different from fish scales, the former comes from the epidermis. Lizards and snakes have double horny scales that shed their skin.

2. Appearance: lizard type, snake type, turtle type. The body is divided into five parts: head, neck, trunk, tail, and limbs.

3. Skeletal system: The cartilaginous cranium of the skull, except for the nasal cartilage sac, is all ossified and covered with membranous bone. It is connected to the spine by an occipital condyle mainly formed by the occipital bone. The spine is divided into cervical, thoracolumbar, sacral, and coccyx. The neck is obvious. The first and second cervical vertebrae are specialized as the atlas and the axis respectively. The head can rotate flexibly. This is the first time a thorax has appeared in the animal kingdom. The lumbar spine is associated with two or more sacral vertebrae and connects to the hind limbs, just as the shoulder girdle connects to the forelimbs. Except for species with missing limbs (such as snakes), there are generally two pairs of palm-shaped limbs with 5 outs (a few forelimbs have 4 outs). Aquatic species have palms shaped like oars, with webs between fingers and toes for swimming, and foot joints It is not between the tibia and tarsus but between the two rows of tarsus, which is called the intertarsal joint. The limbs protrude from the side of the body, making it inconvenient to stand upright; the belly often touches the ground, and the movement is typical crawling; only a few light and agile ones can move fast. Tail docking is a phenomenon in which the self-mutilating part of the tailbone of some lizards is squeezed by external force and broken.

4. Muscle system: The original segmentation phenomenon disappears, and the trunk muscles and limb muscles are more complex, with intercostal muscles and skin muscles unique to terrestrial animals.

Aves

1. Muscles: The muscles are concentrated in the middle of the body, and the chest muscles are well developed. In addition, it has the habitat muscle and the song muscle, and the subcutaneous muscle is also relatively developed.

2. Skeletal system: Birds are adapted to flying and have significant specialization in the skeletal system, which is characterized by light and strong bones with gas-filled cavities. There is evidence of healing in the skull, spine, pelvis, and limb bones. The limb bones and girdle bones are greatly deformed, the skull is thin and light and healed, and the single occipital condyle (kē). The vertebrae are divided into five parts: cervical vertebrae, thoracic vertebrae, lumbar vertebrae, sacral vertebrae and coccygeal vertebrae. The cervical vertebrae are heteroconcave vertebrae, the first one is called the atlas, and the second one is called the axis. There are 5-6 thoracic vertebrae, which combine with the bony ribs and sternum to form the thorax. Flying birds have a well-developed sternum with a keel, and a few thoracic, lumbar, sacral and part of the tail vertebrae are healed. The sacrum is a unique structure of birds. With an open pelvis.

The bird's forelimbs are covered with primary and secondary flight feathers and covert feathers, which become the structure of flight, and the tail feathers can play a role in orientation and balance in flight. The skeletal system of modern birds is characterized by lightness and firmness, with no teeth, degenerated coccyx, and no bladder, which can reduce weight; the bone cavity is inflated, the skull, lower spine and pelvis are healed, and the bird body is solid and light to improve flight efficiency . The sternum of flying birds is extremely developed, and there is a keel protrusion to attach the pectoral muscles, which is convenient for quickly driving the wings.

The tarsal bone heals with the tibia and the metatarsal bone respectively to form the tarsal tibia and the tarsal metatarsal bone, and the heel is off the ground, which increases the elasticity when taking off and landing. Most birds have 4 toes. The big toe is pointed backward, which is good for grasping the branches. Due to the special structure of the toe flexor tendon, the toe does not come loose when perched. The feeding, feather grooming, nesting and defense activities of birds are all completed by the mouth, so the neck is long, with multiple connected saddle-shaped neck bones, and the movement is extremely flexible.

Mammalia

1. Bones: The bone system of mammals is very developed, and the functions of support, protection and movement are further improved. The spine is clearly divided, and the structure is firm and flexible. The limbs move down to the ventral surface, where elbows and knees appear to prop up the body, suitable for rapid movement on land.

The evolution trend of the mammalian skeletal system is: ① Complete ossification, providing sufficient support for muscle attachment; ② Healing and simplification, increasing firmness and ensuring lightness; ③ Improving the toughness of the axial bone, enabling the limbs to Large speed and range (stride) activities; ④The growth of long bones is limited to the early stage, which is different from the lifelong growth of reptiles, which improves the firmness of the bones and is conducive to the perfection of skeletal muscles.

2. Muscle: Similar to reptiles, but more developed and complex. The limbs are muscular.

It has a unique diaphragm, which participates in the formation of the diaphragm that separates the thoracic cavity and the abdominal cavity, and its contraction and relaxation participate in breathing. The skin is muscular; expressive muscles appear on the face of primates. The head has powerful masticatory muscles attached to the zygomatic arch. The rectus abdominis of the abdomen still retains its original segmented state.

1. Round Mouth: No real teeth. Horny teeth. The anus is separated from the cloaca. A separate liver appears. Pancreatic cells are scattered throughout the intestinal wall.

2. Fish class

Digestive glands: gastric glands, intestinal glands, liver and pancreas (the latter two combined in most bony fishes). No salivary glands. Digestive tract: Mouth, oropharyngeal cavity, esophagus, stomach (some or not), intestine (some with pyloric caeca or spiral valve), cloaca. There are teeth in the mouth, and the differentiation of the digestive tract is not obvious.

3. Amphibians

Digestive tract: 1. The teeth in the oropharyngeal cavity are multiple and of the same type. Frogs have maxillary teeth (edge of the upper jaw), vomer teeth (oropharyngeal cavity roof, 2 tufts), toads have no teeth, and Cauraces have vomer teeth; caecilians have teeth in both the upper and lower jaws, vomers, and palates . Salamanders have 1-2 rows of jaw teeth. The function is to prevent food from slipping. The tongue is located at the floor of the oropharyngeal cavity and is muscular. The root of the tongue of anurous amphibians is located in front of the mandible, and the tip of the tongue is free. Frogs have forks of different shades, but toads have no forks. The salamander tongue is cushion-shaped and less mobile, with mucous glands and taste buds in the posterior mucosa. The intermandibular glands are located between the premaxilla and the nasal sac and open in the front of the oropharyngeal cavity. The internal nostrils are located lateral to the vomer. The orifice of the Eustachian tube is located in the roof of the oropharyngeal cavity near the corner of the mouth. The male black-spotted frog has a vocal sac hole near the corner of the mouth. The larynx is a longitudinal opening at the back of the oral cavity, the lower airway. The opening of the esophagus is behind the throat. 2. The esophagus is short, close to the subvertebral muscle, and communicates with the stomach. 3. The stomach is located on the left side of the body cavity. The end connected to the esophagus is called the cardia, and the end connected to the duodenum is called the pylorus. The mucosal layer of the gastric wall contains many tubular gastric glands that secrete gastric juice. The muscular layer of the stomach wall is very thick, and the muscles stretch and contract to move the stomach. 4. Small intestine, duodenum, and ileum. There is an opening for the common bile duct in the wall of the duodenum, which inputs bile and pancreatic juice to digest protein and fat. Small intestine has absorption function. 5. The large intestine is thick and short, also called the rectum. Its diameter is more than twice that of the small intestine, and it communicates with the vent cavity. The function is to absorb water, gather and discharge food residues. The inner wall of the alimentary canal has longitudinal folds and glands with different degrees of development and different numbers. The length of the intestine is related to feeding habits: short for carnivores and long for herbivores. The length of adult frog's intestines is twice the body length, and the length of tadpole intestines is nine times the body length. 6. The wall of the cloaca has openings for the anus, ureter, and reproductive duct, and the cloaca communicates with the outside world.

Digestive glands: 1. The liver is located in the front of the body cavity, with two left and right lobes and a smaller middle lobe. There is a notch in the left lobe that divides it into anterior and posterior parts. There is a green spherical gallbladder between the left and right lobes, and two tubes communicate with it, one communicates with the hepatic duct to send bile into the gallbladder, and the other communicates with the common bile duct to send bile from the gallbladder to the common bile duct. 2. Pancreas is an irregularly branched pale yellow gland located on the mesentery between the duodenum and the stomach. Pancreatic juice is secreted by pancreatic cells into the common bile duct and enters the duodenum with bile.

4. Reptiles

The teeth are divided into lateral teeth, terminal teeth, and alveolar teeth, and there are heteromorphic teeth differentiation (some are specially venomous teeth). The oral glands and muscular tongue are developed, and the embryonic form of the cecum appears.

5. Aves

Birds mainly rely on horny beaks and flexible tongues to ingest food, without teeth. In some birds, the lower end of the esophagus expands and becomes a crop for storing and softening food, but the crushing of food is mainly done by the well-developed gizzard. Grits are often present in the gizzard to aid in grinding. Birds have well-developed digestive glands, strong digestion, rapid digestion, short large intestines, and do not store feces.

6. Mammalia

1. Digestive canal

The basic functions of the alimentary canal are to transport chyme, complete mechanical and chemical digestion, and absorb nutrients. The rectum directly opens out of the body through the anus (the cloaca disappears) is a significant difference between mammals and lower vertebrates. Mammalian stomach shape is related to feeding habits. Most mammals are monogastric.

Ruminants among herbivores have a complex compound stomach (ruminant stomach). The ruminant stomach is generally composed of 4 compartments, namely rumen (rumen), reticulum (honeycomb stomach) (reticulum), omasum (omasum) and abomasum (abomasum). Among them, the first three gastric chambers are the deformation of the esophagus, and the abomasum is the stomach body, which has glandular epithelium and can secrete gastric juice.

The process of rumination is: when fibrous food (such as hay) mixed with a large amount of saliva enters the rumen, it is fermented and decomposed under the action of microorganisms (bacteria, ciliates and fungi) (sometimes it can also enter the reticulum). The rough food stored in the rumen and reticulum floats up, stimulating the rumen vestibule and esophageal groove, causing regurgitation reflex, and the rough food is chewed retrogradely through the entrance of the esophagus. After chewing, the finely divided and relatively heavy food passes through the bottom of the rumen and reticulum, and finally reaches the abomasum. This rumination process can be repeated until the food is fully decomposed.

The mammalian small intestine is highly differentiated, and the small intestinal mucosa is rich in villi, blood vessels and lymphatic vessels, which enhance the absorption of nutrients. The small intestine has a lactic duct (lacteal), a lymphatic vessel that transports fat, and its appearance is milky white. The junction of the small intestine and the large intestine is the cecum, which is particularly developed in herbivorous species. Under the action of bacteria, it is helpful for the digestion of plant fibers. The large intestine is divided into colon and rectum.

2. Digestive glands In addition to the salivary glands in the oral cavity, the digestive glands of mammals also have liver and pancreas near the small intestine, which secrete bile and pancreatic juice respectively and inject them into the duodenum.

A vertebrate is a member of the Animalia or Metazoa kingdom. The six-kingdom classification system is starting to look a little dated thanks to our growing knowledge of genetics; however, it is still used. Kingdom Animalia is composed of eukaryotic, multicellular, and heterotrophic (do not produce their own energy) organisms.

Vertebrate classification is complex due to the sheer numbers of animal traits. Kingdom Animalia is divided into two subphyla: invertebrates and vertebrates. Vertebrates make up less than 5% of all known animals. Invertebrates, without an internal skeleton (but often with an external skeleton or exoskeleton) comprise approximately 95% of all known animals.

Subphylum Vertebrata is further split into seven vertebrate classes:

Mammalia (mammals)Aves (birds)Reptilia (reptiles)Amphibia (amphibians)Agnatha (jawless fish)Osteichthyes (bony fish)Chondrichthyes (cartilaginous fish)