Animal Evolution – The Chordates Chapter 26 Part 1

Impacts, Issues Transitions Written in Stone  Fossils such as Archaeopteryx, an ancient winged dinosaur with feathers, are evolutionary evidence of transitions between species

26.1 The Chordate Heritage  Chordates Most diverse lineage of deuterostomes Some are invertebrates; most are vertebrates Bilateral and coelomate Cephalized and segmented Complete digestive system Closed circulatory system Classified by embryonic characteristics

Modern Chordate Groups

Embryonic Chordate Characteristics  Four characteristics of chordate embryos may not persist in adults Notochord of stiff connective tissue that extends the length of the body and supports it Dorsal, hollow nerve cord parallels the notochord Gill slits across the wall of the pharynx Tail that extends beyond the anus

Invertebrate Chordates  Lancelets are the only group of chordates that retains all chordate characteristics as adults

Fig. 26-2b, p. 434

a Dorsal, hollow nerve cord bNotochordc Pharynx with gill slits d Tail extends beyond anus eyespot tentacle-like structures around mouth segmented muscles (myomeres) midguthindgut aortagonadpore of atrial cavity anusepidermis

Animation: Lancelet body plan

Invertebrate Chordates  Tunicates have typical chordate larvae, but adults retain only the pharynx with gill slits

Fig. 26-3a, p. 435

nerve cord notochord gut pharynx with gill slits

Fig. 26-3b, p. 435

Fig. 26-3c, p. 435

pharynx with gill slits

Fig. 26-3d, p cm

Craniates  Craniates have a braincase of cartilage or bone (cranium) that encases the brain, paired eyes, and other sensory structures on the head  Craniates includes fishes, amphibians, reptiles, birds, and mammals  Hagfishes are the only modern craniates that are not vertebrates

Hagfishes  Soft bodied, boneless fishes

Fig. 26-4a, p. 435

tentaclesgill slits (twelve pairs)mucous glands

Fig. 26-4b, p. 435

Fig. 26-4c, p. 435

26.1 Key Concepts Characteristics of Chordates  Four traits characterizes the chordates: A supporting rod (notochord) A hollow, dorsal nerve cord A pharynx with gill slits in the wall A tail extending past an anus  Certain invertebrates and all vertebrates belong to this group

26.2 Vertebrate Traits and Trends  Vertebrates are chordates with an internal skeleton (endoskeleton) of cartilage or bone with a supportive backbone (vertebral column) made up of individual vertebrae  Modern vertebrates (except lampreys) have jaws derived from gill-supporting structures

Gill-Supporting Structures

Fig. 26-6a, p. 437 supporting structure for gill slits gill slits A In early jawless fishes, supporting elements reinforced a series of gill slits on both sides of the body.

Fig. 26-6b, p. 437 jaw, derived from support structure B In early jawed fishes (e.g., placoderms), the first elements were modified and served as jaws. Cartilage reinforced the mouth’s rim.

Fig. 26-6c, p. 437 location of spiracle (modified gill slit) jaw support jaw C Sharks and other modern jawed fishes have strong jaw supports.

Animation: Evolution of jaws

Evolution of Internal Skeleton  Fishes evolved appendages (fins) for swimming  Pelvic and pectoral fins gave rise to paired limbs in amphibians, which began the move to land

Evolution of Other Systems  Living in water (fish) Blood moves in a single circuit from heart to gills (respiratory organs that function in water)  Moving to land Modification of the respiratory system (lungs) and circulatory system (two circuits) Efficient kidneys to conserve water, and a system of internal fertilization

Chordate Family Tree

Fig. 26-5, p. 436 lancelets tunicates hagfishes lampreys cartilaginous fishes ray-finned fishes lobe-finned fishes lungfishes amphibians “reptiles” birds mammals amniotes tetrapods swim bladder or lungs jawed vertebrates vertebrates craniates ancestral chordates Origin of the first jawless fishes. Jawed fishes, including the placo- derms and sharks, evolve. Adaptive radiation of fishes, and the first amphibians move onto land. Diversification of fishes and amphibians. Armored fishes go extinct. Reptiles arise and start to diversify. Early amphibians in decline. Dinosaurs and marine reptiles evolve. Birds, mammals, and modern amphibians arise. Dinosaurs dominate. Dinosaur diversity peaks, then extinction by period’s end. Adaptive radiation of mammals. OrdovicianCarboniferousJurassicTertiary SilurianDevonianPermianTriassicCretaceous

Animation: Vertebrate evolution

26.2 Key Concepts Trends Among Vertebrates  In vertebrate lineages, a backbone replaced the notochord  Jaws and fins evolved in water  Fleshy fins with skeletal supports evolved into limbs that allowed vertebrates to walk onto land  On land, lungs replaced gills and circulation changed in concert

26.3 The Jawless Lampreys  Lampreys have no jaws or paired fins; they undergo metamorphosis, and many are parasites of other fishes

26.4 The Jawed Fishes  Jawed fishes typically have paired fins and a body covered with scales  Cartilaginous fishes (Chondrichthyes) have a cartilage skeleton, gill slits, and teeth that shed Sharks and rays  Bony fishes (Osteichthyes) have a bony skeleton, gill covers, and a swim bladder Ray-finned fishes, lungfishes, coelacanth

Ray-Finned Bony Fishes

Fig. 26-9a, p. 439

swim bladderkidney ovarynerve cord brain cloacaintestinestomachliverheart gills

Fig. 26-9b, p. 439

Fig. 26-9c, p. 439

Fig. 26-9d, p. 439

Lungfish  Lungfishes have gills and lunglike sacs for breathing air

Coelacanth  The only modern lobe-finned fish; closely related to amphibians

26.5 Amphibians— First Tetrapods on Land  Tetrapods (four-legged walkers) Branched from lobe-finned fishes in Devonian  Amphibians Land-dwelling vertebrates that return to water to breed, undergo metamorphosis, and have a three-chambered heart

Adapting to Life on Land

Fig a, p. 440

Fig b, p. 440

Fig c, p. 440

Fig d, p. 440

Modern Amphibians  Salamanders and newts Body form most like early tetrapods, side-to-side walking motion  Caecilians Includes many limbless, blind burrowers  Frogs and toads Tailless adults with long, muscular hind legs

Salamander and Caecilian

Frog

26.6 Vanishing Acts  Amphibians depend on standing water to breed and have a thin skin unprotected by scales  These features make them vulnerable to habitat loss, disease, and pollution – causing deformities and threatening species

Frog Deformity

Key Concepts Transition from Water to Land  Vertebrates evolved in the seas, where cartilaginous and bony fishes still live  Of all vertebrates, modern bony fishes are most diverse  One group gave rise to aquatic tetrapods (four- legged walkers), the descendants of which moved onto dry land

26.7 The Rise of Amniotes  Amniotes are animals with embryos that develop inside a waterproof egg; their waterproof skin and highly efficient kidneys make them well adapted to dry habitats

Amniotes  Four branches of amniotes lead to synapsids (mammals), anapsids (turtles), lizards and snakes, and crocodiles and birds  Reptiles are an artificial group referring to amniotes other than bird or mammals  Dinosaurs are extinct amniotes; birds are their descendents

The Ruling Reptiles  For 125 million years, dinosaurs dominated the land and sea (Example: Ichthyosaurs)

Amniote Phylogeny

Fig c, p. 442 snakes lizards “stem” reptiles tuataras ichthyosaurs plesiosaurs birds therapod dinosaurs other dinosaurs pterosaurs archosaurs crocodilians turtles therapsids anapsids synapsids mammals PALEOZOIC ERAMESOZOIC ERA TERTIARY TO PRESENT CARBONIFEROUSPERMIANTRIASSICJURASSICCRETACEOUS

26.8 So Long, Dinosaurs  K-T asteroid impact hypothesis Asteroid impacts changed life on Earth, defining the Cretaceous-Tertiary (K-T) boundary Most dinosaurs became extinct

26.9 Diversity of Modern Reptiles  Reptile characteristics Scale-covered body Cloaca for waste disposal Four approximately equal limbs (except snakes) Internal fertilization Body temperature determined by surroundings (ectotherms)

Crocodile Body Plan

Fig , p. 444 kidney (control of water, solute levels in internal environment) olfactory lobe (sense of smell) hindbrain, midbrain, forebrain spinal cord vertebral column gonad snout unmatched rows of teeth on upper and lower jaws esophagus lung heart liver stomach intestinecloaca

Animation: Crocodile body plan

Turtles and Tortoises  Turtles and tortoises have a bony, scale- covered shell attached to the backbone

Fig b, p. 445 hard shellvertebral column

Lizards  Lizards, the most diverse reptiles, have many interesting defenses

Tuataras  The two remaining species of tuataras have a third eye under the skin of the forehead

Snakes  Snakes are legless, but some have bony remnants of hindlimbs

Fig f (1), p. 445 venom gland hollow fang

Crocodilians  Crocodilians, close relatives of birds, are the only reptiles with a four-chambered heart

Animation: Bony fish body plan

Animation: Cartilaginous fishes

Animation: Evolution of limb bones

Animation: Jawless fishes

Animation: Salamander locomotion

Animation: Tortoise shell and skeleton

Animation: Tunicate body plan