The of Chordata belongs to Deuterostomata. Deutrostomes have events of development in common with one another. 1. from archenteron surrounded by mesodermal tissue. 2. Formation of the at the opposite that of the which developed from blastopore.

3. Radial during . *There are some that have been removed from the clade due to DNA analysis. This includes ectoprocts and . These two phyla have been moved over to the Clade Lophotorchozoan. Characteristics of Chordates (At sometime during their ) --longitudinal rod of cartilage between digestive tube and nerve cord. Used for support. Many have only in the embryonic stage. -Dorsal hollow nerve cord derived from during neuralation. Other have a solid cord on the ventral side -Pharyngeal cleft (slits) grooves posterior to the mouth. Develops into , , etc. -Post-anal that extend beyond digestive tract (sometime during their life). Can be reduced in embryonic stage. Used for movement. Three subphyla I. Cephalochordata- Lancets keeps all 4 char- acteristics of chordates through adulthood. Has series of muscles on trunk used for swimming. Does not have cranium. II. Subphylum Urochordata -has 4 characteristics of chordates in larval stage but loses 3 (retains slits) as a sessile adult that undergoes extreme . Does not have a cranium III. Subphylum -has a cranium or head with a with sense evolving. Has two sets of Hox . -Evolution of neural crests forming between the and ectoderm. These cells give rise to some structures unique to and . -The pharyngeal gill slits become gill slits associated with . Terrestrial craniates pharyngeal gill slits become other structures.

Classes in III Subphylum Craniates 1. Myxini () skull of cartilage, no vertebrae, no jaw, retains notochord into adulthood. Swims with segmented muscles attached to notochord. Produce slime as protection. 2. Class Petromyzontida (lampreys)are primitive vertebrate with a skull of cartilage, it also retains notochord into adulthood. The notochord is surrounded by a cartilage like pipe with primitive like vertebrate extensions enclosing nerve cord, no jaw. Mouth is sucker like. These are the classes that are found in the clade vertebrata. The next important evolutionary development was . This developed from the rods in the pharyngeal gill slits. that have jaws are termed gnathostomes Jaws allowed vertebrates to eat larger and more varied types of food by shredding and tearing the food apart. Intermediates fossilized animals between jawless and jawed vertebrates have been found. Jawed vertebrates also have larger cranium. 3. Class Condrichthyes- Include and rays. The skele- ton is composed of cartilage not . (Evidence suggests once it was bone). Evolution of fins increased swimming efficiency. stabilizes , pectoral and pelvic fins allows for lift and forward movement. Oil in provide buoyancy, no or . Intestine with spiral valve. - Oviparous- laid outside the Ovovivparous-Eggs retained in oviduct and develop there Vivparous-Eggs develop in the uterus with yolk sac placenta

Next evolutionary advance was a bony . Animals with a bony skeleton are in the clade

4. Class Actinopterygil- Ray-finned have bony endoskeleton of calcium phosphate. Gills are covered with an . Buoyancy controlled swim bladder (was once ancient ) gas goes in and out by . Covered by scales covered by . Fins are supported by bony rays. Evolved first in freshwater and moved to marine environment. Some live in both environments during their life history. Reproduction mostly Oviparous-Eggs laid outside the body with external fertilization 5. Class Actinistia- lobe-finned fish have bony endoske-leton of calcium phosphate. Fins are supported by a single rod-shaped bone surrounded by a thick layer of muscle in their pectoral and pelvic fins. Allowed them to swim and “walk” underwater. Only two survive today and were thought to be extinct until a fisherman caught one in 1938 in the Indian Ocean. 6. Class Dipnoi- lung fish have bony endoskeleton of calcium phosphate and lobbed-fins. These fish are living in stagnant in the southern hemisphere. They gulp air that goes to the lungs. This is to supplement the oxygen that gills are extracting from the water. Lobe-fin fish are the closest living relative to or . The next development is the evolution of four limbs (Clade ). Tetrapods have four limbs. The neck has two veterbrae instead of one giving rise to side to side motion as well as up and down motion. Pelvic girdle fused to the backbone to reduce to force put on the legs. Pharyngeal clefts (no longer slits) give rise to the parts of the ears, glands and other structures. The next develop- ment was the evolution of four limbs (Clade Tetrapod). The closest living tetra- pod to the are the amphibians. The record indicates that many other evolved to give rise to the class Amphibia. The evolution of legs allowed the verte- brates to move on to land. Amphibia means dual life. 7. Class Amphibia- Most amphibians reproduce in water. 3 chambered , lungs sac-like. Uses to help breath. 3 orders of amphibians. A. Oder Urodela- retain as adults-legs out to. Walks side to side. B. Order Anuara- juvenile form “fish-like” with gills, coiled intestine, long tail. Later absorbs tails. Legs emerge. Digestive tract specializes. C. Order Apoda- legless nearly blind. Look like earthworms. Lost legs in the course of evolution.

Most amphibians reproduce in water, then live on land but there are some amphibians entirely aquatic or entirely terrestrial. Most salamanders and do not undergo metamorphosis instead the juvenile form looks like the adult form. Clade - are tetrapods that have an amniotic which allowed tetrapods to be entirely terrestrial and not go back to the water to reproduce. Amniotic egg has extraembryonic membranes or membranes derived the embryo but no longer a part of the embryo. Membranes within Eggs a. -Contains fluid that surround the embryo. Cushions against mechanical shock. b. -Garbage bag contains waste materials. Also aids in with the chorion c. Yolk sac- contains yolk or stockpile of nutrients for the embryo. The egg white stores and is a source of amino acids for the embryo d. Chorion combine with the allantois and aids in gas exchange.Surrounds the embryo and all the membranes. e. Albumen found outside the chorion but inside the shell as a source of amino acids.

Clade Amniotes- gave rise the two clades- and . The Class Reptiles gave rise to and anapsida. These clades are based on the structure of the skull. The Class Mammalia in the clade .

The holes in the skull are thought to provide better attachment for jaw muscles which allowed the animals to capture and digest a greater variety of prey.

The reptiles have scales, and internal fertilization. Most are ectothermic except for which are endothermic and have an extreme high metabolic rate. are thought to have been but other molecular evidence have them more closely related to .

Snakes, , and tuataras are diapsids belonging to the linage lipidosaurs. This group is greatly varied. evolved from tetrapods. Their scales are overlapping.

Crocodiles and birds are diapsids belonging to the linage . This linage also includes . Birds are adapted for flight -Hollow -4 chambered heart (crododiles also have 4 chambers) -Endotherms for high metabolic rate - which are modified scales and legs are covered with scales. -Beaks (adapted for food source) Once had teeth.

Class belong the clade synapsids which have two holes in the skull. -4 chambered heart -endotherms -mammary glands that produce milk Three clades --Egg layers (only 5 species) no nipples but produce milk The other two clades produce eggs and all amniotic membranes are present but offspring develop in the uterus forming a placenta -- Higher metabolic rate, nipples, young complete development in pouch (marsupium). -Eutherians- Higher metabolic rate, nipples, no pouch, development completed in the uterus. Embryo retained longer. Marsupials were isolated from Eutherians in Australia. Adaptive radiation and occurred. Many of the marsu- pials in Australia fill the same niche as a placental in North America. Case of convergent evolution due to the same selection pressures. This shows the relationship between the various orders mammals