Phylum Chordata Classification

Classification of Phylum Chordata

• Phylum Chordata is divided into Group Protochordata (Acrania) and Group Craniata.
• Subphylum Urochordata (Tunicata) features the notochord and nerve cord only in the free-swimming larva, with ascidian adults being sessile and encased in a tunic.
• Subphylum Cephalochordata includes lancelets with a notochord and nerve cord along the entire body length, persisting throughout life and fishlike in form.
• Subphylum Vertebrata has bony or cartilaginous vertebrae surrounding the spinal cord, with the notochord only in embryonic stages, persisting in some fishes and may be separated into two superclasses based on the presence of jaws.
• Superclass Agnatha includes hagfishes and lampreys, lacking true jaws or paired appendages and is potentially a paraphyletic group.
• Class Myxini consists of hagfishes with a terminal mouth with tentacles, lacking a buccal funnel, and having five to 15 pairs of gill pouches and are partially hermaphroditic.
• Class Cephalaspidomorphi includes lampreys with a suctorial mouth with horny teeth, a nasal sac not connected to the mouth, and seven pairs of gill pouches.
• Superclass Gnathostomata encompasses jawed fishes and all tetrapods, with jaws and paired appendages.
• Class Chondrichthyes consists of cartilaginous fishes with a cartilaginous skeleton and teeth not fused to jaws and usually replaced, along with five to seven gills with separate openings, no operculum, and no swim bladder.
• Class Actinopterygii contains ray-finned bony fishes with an ossified skeleton, a single gill opening covered by the operculum paired fins supported primarily by dermal rays, limb musculature within the body, and a swim bladder mainly as a hydrostatic organ, if present.
• Class Sarcopterygii consists of lobe-finned bony fishes with an ossified skeleton, a single gill opening covered by an operculum, paired fins with a sturdy internal skeleton and musculature within the limb, a diphycercal tail, and lunglike swim bladder.
• Class Amphibia consists of ectothermic tetrapods, respiration by lungs, gills, or skin, development through a larval stage, and moist skin with mucous glands and lacking scales.
• Class Reptilia consists of ectothermic tetrapods possessing lungs, embryo develops in a shelled egg, no larval stage, dry skin without mucous glands, and covered by epidermal scales.
• Class Aves consists of endothermic vertebrates with front limbs modified for flight, bodies covered with feathers, and scales on the feet.
• Class Mammalia consists of endothermic vertebrates possessing mammary glands, bodies more or less covered with hair, and well-developed neocerebrum.

Vertebrate Classifications

• There are five general groups which are fishes, amphibians, reptiles, birds, and mammals
• There are nine major vertebrate classes, two of which are extinct and seven are extant

Osteichthyans

• Osteichthyes have fins which are largely supported by long flexible rays.
• Osteichthyes have bones in their fins like a tetrapod forelimb.

Tetrapods

• Tetrapods are gnathostomes that have limbs
• One of the most significant events in vertebrate history was when the fins of some lobe-fins evolved into the limbs and feet of tetrapods.

Origin of Tetrapods

• Tiktaalik, found on Ellesmere Island (Nunavut, Canada), demonstrates how the transition from fins to limbs occurred partially in water-residing organisms.
• Tiktaalik is considered a missing link.
• Eusthenopteron, Tiktaalik and Acanthostega represent the evolution of tetrapods.
• Tiktaalik is a close relative of the direct ancestors of tetrapods.
• Acanthostega was the first lobe-finned fish that climbed out of the water and onto dry land.
• Tetrapods show fish characters such as scales fins gills and lungs.
• Tetrapods show tetrapod characteristics such as a neck, ribs a fin skeleton, a flat skull, eyes on top of its skull.

Move to Land

• Movement to land was influenced by unexploited food resources and aquatic habitat niches being occupied.
• A lack of terrestrial predators led to largely primitive plants and invertebrates, such as arthropods.
• Low oxygen levels in warm waters prompted the move, with unlimited land-based oxygen.

Derived Tetrapod Characteristics

• Life on land resulted in the fusion of the pelvic girdle to the backbone, which assists it in supporting the force exerted by hind legs against the ground.
• The head separated from the body by the neck, allowing it to swing up and down and side by side
• The gill slits/arches are lost in the embryo, forming parts of the ears and lower skull.
• They developed the ability to detect airborne sounds via detectable external ears
• Progressive evolutionary adaptations emerged such as improved respiration, protective and insulating body coverings, more efficient reproduction on land,a nd paired muscular appendages

Class Amphibia

• Class Amphibia is derived from the word "amphibious", which means "both ways or dual life"
• Amphibians spend part of their life in water and part on land.
• They are represented by about 6,150 species
• Order Urodela(Urodeles) have 300 species, have retained tails, have a long body and four walking legs. Examples are salamanders.
• Order Anura(Anurans) have 3,000 species and lack tails as adults. They have powerful legs body that contains poison glands for predators and camouflage. Examples include frogs.
• Order Apoda (Apodans) have 160 species where examples are caecilians. These are legless, resemble an earthworm, and usually have complete blind.
• Amphibians developed limbs to help them walk on land.
• Many species can respire using their lungs or skin, which is aided by mucus secretion
• Amphibians have a two-way blood circulation and partially divided heart
• Amphibians have a pulmonary and systemic circuit
• Amphibians have left and right atrium ventricles.
• Amphibians developed eyelids that can blink.
• They return to the water to provide a suitable wet enviornment for their eggs

Amniotes

• Amniotes are tetrapods that have a terrestrially adapted egg.
• Amniotes are a group of tetrapods where animals that are reptiles, including birds, and mammals.
• Reptiles is a group of amniotes, broken down into Diapsids and Synapsids.
• Anapsid, synapsid and diapsid skulls have varying post-orbital openings that allow muscles to expand and lengthen.

Class Reptilia

• Reptiles include tuataras, snakes, lizards, crocodiles, and turtles
• They have a dry scaly skin
• Reptiles lay amniotic eggs on land protected by the eggs calcareous or leathery shells with protection and allows gas exchange.
• The extra embryonic membranes facilitate gas exchange, provides nutrients and cushions and supports the embryo.
• Reptiles are Ectotherms (non-bird) and regulate body temp using external sources for example, large spiny lizard and turtle basking on the rocks to regulate their body temperature
• They have internal fertilization, examples Hemipenes (in males) are Hemipenes in lizards and snakes during copulation
• Examples of reptiles are, Tuatara, Australian thorny devil lizard , Wagler's pit viper, Eastern box turtle, and an American alligator

Class Aves

• Class Aves, or birds, descended from archosaurs.
• Features of their reptilian anatomy have undergone modification in their adaptation to flight.
• Birds are considered part of the reptile clade in evolution
• Birds evolved from theropod dinosaurs developing feathers, having hollow fused bones and teeth, having three forward facing toes, and teeth and Snouts turning to beaks. Archaeopteryx is the earliest bird with a toothed beak
• Derived characteristics include adaptations centered around flight. They have wings and feathers which are feathers are modified scales constructed of keratin
• Laced air cavities light weight bones
• Fused bones like Furcula, synsacrum and a pygostyle
• Bird's have Massive flight muscles
• Other adaptations to reduce weight include a lack of a urinary bladder, a single ovary and small gonads plus the loss of teeth, which is replaced by a beak _ Birds are endothermic
• Birds behavior and morphology has adapted to fulfill distinct niches (ie: Swimming like a King penguin Or Feeding like a Hummingbird) and they show adaptive behaviors in their beaks.

Concept 5: Mammals

• Mammals are amniotes that have hair and produce milk.
• Class Mammalia has over 5,300 species.
• Mammals have mammary glands and hair.
• They have a high metabolic rate due to endothermy
• Mammals have larger brains than other vertebrates, and differentiated teeth.
• Mammals include Prototheria, Metatheria and Eutheria
• Malleus/Incus = Articular/Quadrate which articulate bones and jaw
• Monotremes marsupials and eutherians are orders of mammals.

Prototheria

• A small group of egg-laying mammals.
• Consists of echidnas and platypus.

Metatheria

• Includes possums, kangaroos and Koalas
• The embryo develops a placental connection in the mothers uterus allowing for long gestation times and live birth
• A marsupial is born very early in its development and lives maternally in a marsupium for nutrients

Mammal Diversity

• There is convergent evolution throughout the groups of mammals especially with marsupials which may look like an eutherian version. Example: a sugar glider and flying squirrel.

Primates

• Primates are of the Eutheria subclass, with derived grasping hands and feet, flat finger nails, larger brains, and forward looking eyes to provide depth, complex social behavior, and fully opposable thumbs,
• Their are three groups of living primates, lemurs(Lemuroidea), tarsiers (Tarsioidea) and anthropoids (Plattyrhini and Catarrhini)

Concept 6: Humans

• Humans are mammals that have a large brain and bipedal locomotion.
• Humans have an upright posture and bipedal locomotion to stand erect and walk on two feet.
• A larger brain capable of language, symbolic thought, and the manufacturing and use of complex tools.
• Humans jawbones and jaw muscles are reduced, with a shorter digestive tract.
• Hominins originated in Africa about 6–7 million years ago and show evidence of small brains and increasing bipedalism.

Misconceptions

• It is a misconception that Early hominins were chimpanzees when in reality, hominins and chimpanzees shared a common ancestor.
• It is misunderstood that human evolution is like a ladder that directly leads to living Homo sapiens, when in reality it included many branched which may be extinct.
• The evidence suggest that hominins walked upright 3.5 million years ago.
• Homo sapiens appeared in Africa by 195,000 years ago, with all living humans descending from these African ancestors.
• Homo sapiens were the first group to show evidence of symbolic and sophisticated thought.
• In 2002, a 77,000-year-old artistic carving was found in South Africa.