Chordata Chordates are Deuterostomes that are bilaterally symmetrical coelomates with segmented bodies. Chordates share many features of embryonic development with echinoderms, but have evolved separately for at least 500 million years. Chordates comprise all vertebrates and two groups of invertebrates, the urochordates and cephalochordates.

Four key characters of chordates: Fig. 34-3 Four key characters of chordates: Dorsal, hollow nerve cord Muscle segments Notochord Mouth Anus Pharyngeal slits or clefts Muscular, post-anal tail *Some species have some of these traits only during embryonic development

Notochord It provides skeletal support throughout most of the length of a chordate In most vertebrates, a more complex, jointed skeleton develops, and the adult retains only remnants of the embryonic notochord

Dorsal, Hollow Nerve Cord The nerve cord of a chordate embryo develops from a plate of ectoderm that rolls into a tube dorsal to the notochord The nerve cord develops into the central nervous system: the brain and the spinal cord In arthropods, nematodes and annelids there is a ventral nerve cord

Pharyngeal clefts or slits In most chordates, grooves in the pharynx called pharyngeal clefts develop into slits that open to the outside of the body Functions of pharyngeal slits Suspension-feeding structures in many invertebrate chordates Gas exchange in vertebrates (except vertebrates with limbs, the tetrapods) Develop into parts of the ear, head, and neck in tetrapods

Muscular, post-anal tail Chordates have a tail posterior to the anus In many species, the tail is greatly reduced during embryonic development The tail contains skeletal elements and muscles It provides a propelling force in many aquatic species

Cephalochordata Urochordata Myxini Petromyzontida Chondrichthyes Actinopterygii Actinistia Dipnoi Amphibia Reptilia Mammalia 10

Cephalochordata Lancelets (Cephalochordata) are named for their bladelike shape They are marine suspension feeders that retain characteristics of the chordate body plan as adults

Cephalochordata

Chordate evolution Ancestral chordates may have resembled lancelets The same Hox genes that organize the vertebrate brain are expressed in the lancelet’s simple nerve cord tip Genome sequencing suggests that Genes associated with the heart and thyroid are common to all chordates Genes associated with transmission of nerve impulses are unique to vertebrates

Cephalochordata Urochordata Myxini Petromyzontida Chondrichthyes Actinopterygii Actinistia Dipnoi Amphibia Reptilia Mammalia 15

Urochordata Tunicates (Urochordata) are more closely related to other chordates than are lancelets Trunicates most resemble chordates during their larval stage, which may last only a few minutes As an adult, a tunicate draws in water through an incurrent siphon, filtering food particles When attacked, trunicates, or “sea squirts,” shoot water through their excurrent siphon

Urochordata

Tunicates are highly derived and have fewer Hox genes than other vertebrates

Craniates The origin of a head enabled chordates to coordinate more complex movement and feeding behaviors Craniates share some characteristics: a skull, brain, eyes, and other sensory organs Other animal phyla have evolved a head independently. They also evolved a more complex digestive system, a heart with at least 2 chambers, RBCs and kidneys.

Craniates One feature unique to craniates is the neural crest, a collection of cells near the dorsal margins of the closing neural tube in an embryo Neural crest cells give rise to a variety of structures, including some of the bones and cartilage of the skull.

Myxini The most basal group of craniates is Myxini, the hagfishes Hagfishes have a cartilaginous skull and axial rod of cartilage derived from the notochord, but lack jaws and vertebrae Only animals with a skull but no vertebrae Hagfishes are marine; most are bottom-dwelling scavengers Fossil hagfish as old as 300my are largely unchanged from modern hagfish

Myxini Hagfishes secrete “slime” composed of proteins. This slime can be produced in large amounts when attacked and will coat the gills of predators. http://www.youtube.com/watch?feature=player_embedded&v=F8aVgSIDJjM

Vertebrates are craniates with a backbone During the Cambrian period, a lineage of craniates evolved into vertebrates Vertebrates became more efficient at capturing food and avoiding being eaten

Vertebrates are craniates with a backbone There are about 52,000 species of vertebrates, including the largest organisms ever to live on the Earth. Vertebrates are highly diverse.

Derived characteristics of vertebrates Vertebrates underwent a gene duplication involving the Dlx family of transcription factors Vertebrates have the following derived characters Vertebrae enclosing a spinal cord has replaced the notochord (which has become intervertebral discs) An elaborate skull Jawed vertebrates exhibit paired appendages

Petromyzontida Lampreys (Petromyzontida) represent the earliest living lineage of vertebrates. They are jawless vertebrates that feed by attaching to a live fish. They inhabit various marine and freshwater habitats. They have cartilaginous segments surrounding the notochord and arching partly over the nerve cord.

Gnathostomes Today, jawed vertebrates, or gnathostomes, outnumber jawless vertebrates Gnathostomes include sharks and their relatives, ray-finned fishes, lobe-finned fishes, amphibians, reptiles (including birds), and mammals

Gnathostomes Gnathostomes have jaws that have evolved from the pharyngeal slits

Gnathostomes Other characters common to gnathostomes: Genome duplication, including duplication of Hox genes to include 4 sets. An enlarged forebrain associated with enhanced smell and vision

Chondrichthyes have a skeleton composed primarily of cartilage The largest and most diverse group of chondrichthyes includes the sharks, rays, skates and chimeras

Chondrichthyes The largest are suspension feeders, but most are carnivores. Most have a relatively short digestive tract but add a structure called the spiral valve to increase the digestive time. Sharks have acute senses including sight, smell, and the ability to detect electrical fields from nearby animals

Chondrichthyes Shark eggs are fertilized internally but embryos can develop in different ways: Oviparous: eggs hatch outside the mother’s body (horn shark, cat shark) Ovoviviparous: the embryo develops within the uterus and is nourished by the egg yolk (most) Viviparous: the embryo develops within the uterus and is nourished through a yolk sac placenta from the mother’s blood (hammerheads, requiem sharks)

Digestion Scales Bouyancy Osmoregulation Highly developed smell – hammerheads Might be able to hear well 2 chambered heart - lancelets have expanded, contractile blood vessel - hagfish – 3 chambers (sinus venosus, 1 atrium, 1 ventricle)with valves - no nerves to heart to regulate heart rate - lamprey – 4 chambers (1 atrium, 1 ventricle) – nerve regulated - boney fish – similar to lamprey but more well developed and more innervation - lung fish – atrium and ventricle have partial septa (not seen in amphibians)

Osteichthyes The vast majority of vertebrates belong to a clade of gnathostomes called Osteichthyes Nearly all living osteichthyes have a bony endoskeleton Osteichthyes traditionally were the bony fish – however a strict interpretation of taxonomy required inclusion of all tetrapods

“Bony Fish” – - Actinopterygii - Actinistia - Dipnoi Most fish breathe by drawing water over gills protected by an operculum Fish control their buoyancy with an air sac known as a swim bladder Fish have a lateral line system Most species are oviparous, but some have internal fertilization and live birth

Osteichthyes

Actinopterygii Composed of the ray-finned fishes. Ray-finned fishes originated during the Silurian period (444 to 416 million years ago) The fins, supported mainly by long, flexible rays, are modified for maneuvering, defense, and other functions Actinopterygii Chondrichthyes Vertebrates

Lobe-finned fishes have muscular pelvic and pectoral fins Lobe-fins also originated in the Silurian period They include the extant coelacanths (Actinistia) and lungfishes (Dipnoi).

Lobe-finned fishes Lobe-finned fishes have muscular pelvic and pectoral fins Lobe-fins also originated in the Silurian period They include the extant coelacanths (Actinistia) and lungfishes (Dipnoi). Strictly speaking they include tetrapods

Tetrapods One of the most significant events in vertebrate history was the evolution of muscular limbs The first tetrapods appeared ~365 million years ago. Actinopterygii Chondrichthyes Vertebrates Tetrapods

Tetrapods Tetrapods have some specific adaptations Four limbs, and feet with digits A neck, which allows separate movement of the head Fusion of the pelvic girdle to the backbone The absence of gills (with a few exceptions) Ears for detecting airborne sounds

Tiktaalik

https://www.youtube.com/watch?v=mKxRe0hAQmg https://www.youtube.com/watch?v=zK8XGEDcTfo https://www.youtube.com/watch?v=NP01qomd-kM https://www.youtube.com/watch?v=yvDQCa7rleI

Amphibians Amphibian means “both ways of life,” referring to the metamorphosis of an aquatic larva into a terrestrial adult Amphibians (class Amphibia) are represented by about 6,150 species Most amphibians have moist skin that complements the lungs in gas exchange

Amphibians Order Urodela includes salamanders, which have tails. Order Anura includes frogs, which lack tails as an adult. Order Apoda includes caecilians, are legless.

Amphibians

Amphibians Fertilization is external in most species, and the eggs require a moist environment.

Amphibians Since 1980, it estimated that 9 amphibian species have become extinct and more than 100 species haven’t been seen in the past 20 years. Several causes are involved including habitat loss, climate change and pollution. http://www.youtube.com/watch?v=nBbkwlGM7X0

Amniotes Amniotes are named for the major derived character of the clade, the amniotic egg, which contains membranes that protect the embryo for terrestrial life. Members include reptiles (dinosaurs and birds) and mammals. The extraembryonic membranes are the amnion, chorion, yolk sac, and allantois. Amniotes also have a rib cage that is more efficient than having to breathe through the skin.

Cephalochordata Urochordata Myxini Petromyzontida Chondrichthyes Figure 34.UN04 Cephalochordata Urochordata Myxini Petromyzontida Chondrichthyes Actinopterygii Actinistia Dipnoi Amphibia Reptilia Mammalia 67

Reptiles The reptile clade includes the tuataras, lizards, snakes, turtles, crocodilians, birds, and the extinct dinosaurs. Reptiles have scales that create a waterproof barrier. They lay shelled eggs on land.

Reptiles Most reptiles are ectothermic, absorbing external heat as the main source of body heat. Birds are endothermic, capable of keeping the body warm through metabolism.

Reptiles The diapsids consists of two main lineages: the lepidosaurs and the archosaurs. The lepidosaurs include tuataras, lizards, snakes. The archosaur lineage produced the turtles, crocodilians, birds and the extinct pterosaurs and dinosaurs

Reptiles Pterosaurs (not dinos) were the first tetrapods to exhibit flight. The dinosaurs are archosaurs that diversified into a vast range of shapes and sizes and are seperated into 2 groups (ornithischians and saurischians). The saurischians included a subgroup of bipedal dinosaurs called theropods, the group from which birds are descended.

Birds Birds evolved from theropod dinosaurs to diversify into over 10,000 species.

Birds The oldest known feathered dinosaur, Anchornis, lived ~155 mya.

Avian Flight Flight enhances hunting and scavenging, escape from terrestrial predators, and migration. Many characters of birds are adaptations that facilitate flight. Flight requires a great expenditure of energy, acute vision or smell, and fine muscle control.

The avian genome and composition of feathers Flight may have accompanied the evolution of their genomes. The major adaptation of birds are wings with feathers comprised of β-keratin.

Loss of flight in birds evolved secondarily

Loss of flight in birds evolved for swimming

Cephalochordata Urochordata Myxini Petromyzontida Chondrichthyes Figure 34.UN04 Cephalochordata Urochordata Myxini Petromyzontida Chondrichthyes Actinopterygii Actinistia Dipnoi Amphibia Reptilia Mammalia 80

Mammals Mammals are organisms that produce milk and have hair. Mammals, class Mammalia, are represented by more than 5,300 species. They are endothermic like birds. Longer parental care relates to better survival skills and learning. They also have differentiated teeth.

Early Evolution of Mammals Mammals evolved from synapsids in the late Triassic period Two bones that formerly made up the jaw joint were incorporated into the mammalian middle ear.

Early Evolution of Mammals By the early Cretaceous three major lineages of mammals emerged: Monotremes (egg-laying mammals) Marsupials (mammals with a pouch) Eutherians (placental mammals)

Early Evolution of Mammals

Derived Characters of Primates Most primates have hands and feet adapted for grasping. Other derived characters of primates: A large brain and short jaws Forward-looking eyes close together on the face, providing depth perception Complex social behavior and parental care A fully opposable thumb (in monkeys and apes)

Derived Characters of Humans A number of characters distinguish humans from other apes: Upright posture and bipedal locomotion Larger brains Language capabilities and symbolic thought The manufacture and use of complex tools Shortened jaw Shorter digestive tract

Hominins The study of human origins is known as paleoanthropology Hominins (formerly called hominids) are more closely related to humans than to chimpanzees Paleoanthropologists have discovered fossils of about 20 species of extinct hominins

Hominins Since Homo sapiens arose, several other species of hominids cohabited earth. Homo neanderthalensis Homo floresiensis Denisova hominin – may be a subspecies of Homo sapiens

Hominin admixture