The Evolution of Chordates

1. The Evolution of Chordates

2. Phylum Chordata belongs to clade Deuterostomata. Deuterostomes have events of development in common with one another. 1. Coelom from archenteron surrounded by mesodermal tissue. 2. Anus develops from the blastopore with the mouth at the opposite end of the tube formed during gastrulation.

3. 3. Radial cleavage during embryonic development. *There are some deuterostomes that have been removed from the clade due to DNA analysis. This includes ectoprocts and brachiopods. These two phyla have been moved over to the Clade Lophotorchozoan.

4. Characteristics of Chordates (At sometime during their life) -Notochord-longitudinal rod of cartilage between digestive tube and nerve cord. Used for support. Many only possess this in the embryonic stage. -Dorsal hollow nerve cord derived from ectoderm during neuralation. Other animals have a solid cord on the ventral side -Pharyngeal cleft (slits) grooves posterior to the mouth. Develops into gills, ears, head neck etc. -Post-anal tails that extend beyond digestive tract (sometime during their life). Can be reduced in embryonic stage. Used for movement.

5. Three subphyla I. Subphylum Cephalochordata-Lancelets keeps all 4 characteristics of chordates through adulthood. Has series of muscles on trunk used for swimming. Does not have cranium.

6. II. Subphylum Urochordata-has 4 characteristics of chordates in larval stage but loses 3 (retains gill slits) as a sessile adult that undergoes extreme metamorphosis. Does not have a cranium III. Subphylum Craniates-has a cranium or head with a brain with sense organ evolving. Has two sets of Hox genes.

7. Vertebrates and tunicates share A) jaws adapted for feeding. B) a high degree of cephalization. C) the formation of structures from the neural crest. D) an endoskeleton that includes a skull. E) a notochord and a dorsal, hollow nerve cord.

8. ANS: E Both of these clades belong to Clade Chordata. All animals in this clade at some point in their life have 1. A notochord 2. Dorsal hollow nerve cord 3. Pharyngeal slits or pharyngeal clefts 4.Muscular, Post-anal tail

9. -Evolution of neural crests forming between the neural tube and ectoderm. These cells give rise to some structures unique to vertebrate skull and jaw. • -The pharyngeal slits may become gill slits associated with breathing. Terrestrial craniates’ pharyngeal slits become other structures.

10. Phylum Chordata belongs to clade Deuterostomata. Deutrostomes have events of development in common with one another. 1. Coelom from archenteron surrounded by mesodermal tissue. 2. Formation of the anus from the embryonic blastopore; the mouth develops at the opposite end of the embryo.

11. Classes in III Subphylum Craniates 1. Class Myxini (hagfishes) skull of cartilage, no vertebrae, no jaw, retains notochord into adulthood. Swims with segmented muscles attached to notochord. Produce slime as protection.

12. The animal above lacks the following: A) skull B) notochord C) vertebrae D) gill slits

13. ANS: C The hagfish belongs to the Phylum Myxini. It does not have any vertebrae but belongs to the Clade Craniates which means it has a skull. It also belongs to the Clade Chordata so it also has a notochord and gill slits.

14. 2. Class Petromyzontida (lampreys)are primitive vertebrates with a skull of cartilage, it also retains notochord into adulthood. The notochord is surrounded by a cartilage like pipe with primitive vertebrate-like extensions enclosing nerve cord, no jaw. Mouth is sucker like.

15. Which if the following is NOT found in lampreys like the one above? A) vertebrae B) notochord C) jaws D) dorsal nerve cord

16. ANS: A Lampreys are jawless fish. They have a primitive vertebrae, notocords and a dorsal nerve cord.

17. These are the classes that are found in the clade vertebrata.

19. The next important evolutionary development was jaws. This developed from the rods in the pharyngeal gill slits. Vertebrates 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. Intermediate fossilized animals between jawless and jawed vertebrates have been found. Jawed vertebrates also have larger cranium.

20. 3. Class Chondrichthyes- Include sharks and rays. The skeleton is composed of cartilage not bone. (Evidence suggests once it was bone). Evolution of fins increased swimming efficiency. Dorsal fin stabilizes shark, pectoral and pelvic fins allows for lift and forward movement. Oil in liver provide buoyancy, no swim bladder or lungs. Intestine with spiral valve. Reproduction: Oviparous-Eggs laid outside the body Ovoviviparous-Eggs retained in oviduct and develop there Viviparous-Eggs develop in the uterus with yolk sac placenta

22. Next evolutionary advance was a bony skeleton. Fish with a bony skeleton are in the clade Osteichthyes 4. Class Actinopterygil- Ray-finned fish have bony endoskeleton of calcium phosphate. Gills are covered with an operculum. Buoyancy controlled swim bladder (was once ancient lung) gas goes in and out by blood. Covered by scales covered by mucus. 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

23. Chondrichthyans can be distinguished from osteichthyans by the: A) presence in osteichthyans of a skull. B) presence in osteichthyans of a lateral line system. C) presence in condrichthyans of unpaired fins. D) absence in chondrichthyans of a swim bladder and lungs. E) absence in chondrichthyans of paired sensory organs.

24. ANS: D Chondrichthyes do not have swim bladders or lungs. They have oil in their liver which helps with buoyancy.

25. 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 species survive today and were thought to be extinct until a fisherman caught one in 1938 in the Indian Ocean.

26. 6. Class Dipnoi- lung fish have bony endoskeleton of calcium phosphate and lobbed-fins. These fish are freshwater fish living in stagnant water in the southern hemisphere. They gulp air that goes to the lungs. This oxygen is to supplement the oxygen that gills are extracting from the water. Lobe-fin fish are the closest living relative to amphibians or tetrapods.

27. The next development is the evolution of four limbs (Clade Tetrapod). Tetrapods have fours 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.

28. Which of the following could be considered the most recent common ancestor of living tetrapods? A) a sturdy-finned, shallow-water lobe-fin whose appendages had skeletal supports similar to those of terrestrial vertebrates B) an armored, jawed placoderm that had two sets of paired appendages C) an early ray-finned fish that developed bony skeletal supports in its paired fins D) a salamander that had legs supported by a bony skeleton but moved with the side-to-side bending typical of fishes E) an early terrestrial caecilian whose legless condition had evolved secondarily

29. ANS: A The most recent common ancestor of living tetrapods are thought to be a sturdy-finned, shallow-water lobe-fin whose appendages had skeletal supports similar to those of terrestrial vertebrates like the lobe-fin fish or lung fish.

30. The next develop-ment was the evolution of four limbs (Clade Tetrapod). The closest living tetra-pod to the lungfishes are the amphibians. The fossil record indicates that many other clades 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.

31. 7. Class Amphibia- Most amphibians reproduce in water. 3 chambered heart, lungs sac-like. Uses skin to help breath. 3 orders of amphibians. • Oder Urodela-salamanders retain tail as adults-legs out to. Walks side to side. • Order Anura-tadpoles 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.

34. Most amphibians reproduce in water, then live on land but some amphibians are entirely aquatic or entirely terrestrial. Most salamanders and caecilians do not undergo metamorphosis instead the juvenile form looks like the adult form.

35. Clade Amniotes- are tetrapods that have an amniotic egg which allowed tetrapods to be entirely terrestrial and not go back to the water to reproduce. Amniotic egg has extraembryonic membranes or membranes derived from the embryo but no longer a part of the embryo. • Membranes • Amnion-Contains fluid that surround the embryo. Cushions against mechanical shock. • Allantois-Garbage bag contains waste materials. Also aids in gas exchange with the chorion • Yolk sac-contains yolk or stockpile of nutrients for the embryo. The egg white stores protein and is a source of amino acids for the embryo • Chorion combines with the allantois and aids in gas exchange. Surrounds the embryo and all the membranes. • Albumen found outside the chorion but inside the shell as a source of amino acids.

38. Clade Amniotes- gave rise the two clades- reptiles and synapsids. The Class Reptiles gave rise to diapsids and anapsida. These clades are based on the structure of the skull. The Class Mammalia in the clade synapsid. 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 birds which are endothermic and have an extreme high metabolic rate.

39. The development that allowed reptiles and mammals to be entirely terrestrial is A) evolution of legs B) evolution of wings C) evolution of non-flagellated sperm D) evolution of the amniotic egg

40. ANS: D The amniotic egg is a self-contained egg with embryonic membranes that allows the embryo to develop and prevents the embryo from drying out.

41. Turtles are thought to have been anapsids but other molecular evidence have them more closely related to crocodiles. Snakes, lizards, and tuataras are diapsids belonging to the linage lipidosaurs. This group is greatly varied. Snakes evolved from tetrapods. Their scales are overlapping. Crocodiles and birds are diapsids belonging to the linage archosaurs. This linage also includes dinosaurs. Birds are adapted for flight -Hollow bones -4 chambered heart (crododiles also have 4 chambers) -Endotherms for high metabolic rate -Feathers which are modified scales and legs are covered with scales. -Beaks (adapted for food source) Once had teeth.

44. Class Mammals belong the clade synapsids which have one extra hole in the skull. -4 chambered heart -endotherms -mammary glands that produce milk Three clades -Monotremes-Egg laying mammals (only 5 species) no nipples but produce milk The other two clades do not produce shelled-eggs; all amniotic membranes are present and offspring undergo at least some development in the uterus -Marsupials- 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 convergent evolution occurred.

45. Mammals and living birds share all of the following characteristics except A) endothermy. B) descent from a common amniotic ancestor. C) a dorsal, hollow nerve cord. D) a hole behind the eye socket on each side of the skull. E) an amniotic egg.

46. ANS: D Birds are reptiles that are diapsids and have two holes in their skull behind the eye socket, whereas mammals are synapsids and only have one hole in their skull behind the eye socket.

47. Many of the marsu-pials in Australia fill the same niche as a placental mammal in North America. Case of convergent evolution due to the same selection pressures.

48. Unlike eutherians, both monotremes and marsupials A) lack nipples. B) have some embryonic development outside the mother's uterus. C) lay eggs. D) are found in Australia and Africa. E) include only insectivores and herbivores.

49. ANS: B In eutherians, there is a formation of a placenta during embryonic development. This structure allows for the embryo to develop longer in the uterus before birth..

50. This shows the relationship between the various orders mammals