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Chordates Chordates 1 Echinodermata

ANCESTRAL Cephalochordata Chordates • Origin of Chordates DEUTEROSTOME Urochordata Notochord

• Tunicates etc Craniates Common Myxini ancestor of • Sharks etc chordates Petromyzontida Vertebrates Head Chondrichthyes Gnathostomes • Bony “fish” Vertebral column Actinopterygii Osteichthyans – Osteichthans Jaws, mineralized skeleton Actinistia Lobe-fins – Lobe fins and lungfish Lungs or lung derivatives Dipnoi Lobed fins

Amphibia Tetrapods Amniotes Amniotes Limbs with digits Reptilia

Amniotic egg Mammalia Milk All Chordates have a notochord and a Feb 25, 2013 dorsal, hollow nerve cord

Figure 34.2a Derived features of Chordates

Echinodermata 2. Dorsal, Muscle hollow ANCESTRAL Cephalochordata segments nerve cord DEUTEROSTOME Urochordata 1.Notochord Notochord Common Myxini ancestor of chordates Petromyzontida Head Chondrichthyes Mouth Vertebral column Anus 3. Pharyngeal Jaws, mineralized skeleton 4. Muscular, slits or clefts Osteichthyes Bony fish & post-anal tail tetrapods

Figure 34.4

Cephalochordata- Lancets Cirri Urochordata Myxini Mouth Petromyzontida Pharyngeal slits Atrium Chondrichthyes Digestive tract Actinopterygii Notochord Actinistia Atriopore

Dorsal, 1 cm Segmental hollow Dipnoi muscles nerve cord Amphibia Anus Reptilia Tail Mammalia

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Figure 34.5

Cephalochordata

Urochordata Tunicates Incurrent Water flow Notochord siphon Myxini to mouth Dorsal, hollow Excurrent Petromyzontida nerve cord siphon Tail Excurrent Chondrichthyes siphon Excurrent siphon Atrium Incurrent Muscle Actinopterygii siphon Pharynx segments with Intestine Anus numerous Actinistia slits Stomach Intestine Tunic Dipnoi Atrium Esophagus Amphibia Pharynx with slits Stomach Reptilia (a) Tunicate larva (b) Adult tunicate (c) Adult tunicate Mammalia

Derived features of tunicates:

Figure 34.5a Figure 34.6

Incurrent Water flow Notochord siphon to mouth Dorsal, hollow BF1 Otx nerve cord Hox3 Tail Excurrent Nerve cord of lancelet embryo siphon Excurrent siphon Atrium Incurrent Muscle Pharynx BF1 siphon Otx Hox3 segments with numerous Intestine Anus slits Brain of vertebrate embryo Stomach Intestine (shown straightened) Tunic Atrium Esophagus Forebrain Midbrain Hindbrain Pharynx with slits Stomach (a) Tunicate larva (b) Adult tunicate

Figure 34.8

Cephalochordata Cambrian Urochordata Myxini Hagfish and | Petromyzontida Lampreys’ Head | Chondrichthyes Vertebrae Actinopterygii 5 mm Actinistia Dipnoi Segmented Only 3 cm long muscles Amphibia Reptilia Mammalia

Pharyngeal slits Had a well-formed brain, eyes, and muscular segments, but not a skull

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Figure 34.9 Figure 34.10

Slime glands

Gnathostomes have jaws that might have evolved from skeletal supports of the pharyngeal slits

Gill slits Cranium

Mouth Skeletal rods

Sea Lamprey parasitize fish in Lake Champlain

Gnathostome fossil Odovician 0.5 m Cephalochordata Urochordata Myxini Petromyzontida Chondrichthyes Sharks | Actinopterygii Jaws Actinistia Dipnoi Amphibia Reptilia Mammalia

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Figure 34.2b Sharks and Rays (about 470 species)

Actinopterygii

Actinistia Lungs or lung derivatives Dipnoi Lobed fins Amphibia

Limbs with digits Reptilia

Amniotic egg Mammalia Milk

“Fish” Ray-finned fish (about 30,000 species) Cephalochordata Urochordata Myxini Petromyzontida Chondrichthyes Actinopterygii Ray-finned fish | Actinistia Lobe fin fish Bony Dipnoi Lungfish endoskeleton Amphibia Reptilia Mammalia

Figure 34.16 Lobe Fins

Swim Dorsal fin Caudal Spinal cord bladder Adipose fin fin Brain

Nostril

5 cm

Lower Scaly Dorsal Cut Anal fin jaw covering edge of spine operculum Liver Anus Lateral Gills Gonad Stomach line Kidney Pelvic Intestine fin Urinary Heart bladder

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Coelocanth Derived Characters of 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 (except some aquatic species) – Ears for detecting airborne sounds

Figure 34.21 Tiktaalik: a fossil with both fish and tetrapod characteristics Lungfishes

Fish Tetrapod Characters Characters Eusthenopteron Scales Neck Fins Ribs Gills and Fin skeleton Panderichthys lungs Flat skull Eyes on top of skull Tiktaalik Shoulder bones Ribs Acanthostega Neck Scales Head Tulerpeton Eyes on top of skull Limbs Humerus with digits Flat Ulna Amphibians Key to skull limb bones Elbow “Wrist” Ulna Amniotes Radius Radius Humerus Fin Fin skeleton Silurian PALEOZOIC Devonian Carboniferous Permian 415 400 385 370 355 340 325 310 295 280 265 0 Time (millions of years ago)

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