Tetrapods, Amphibians, and Life on Land

Strolling through life Tetrapods, amphibians, and life on land

Tetrapods - the clade of four- limbed terrestrial vertebrates

Living tetrapod groups: * amphibians * mammals (including humans) * lizards and snakes * crocodilians * birds

Eurypos , early Permian temnospondyl (painting by Douglas Henderson, 1990) Department of Geological Sciences | Indiana University Dinosaurs and their relatives (c) 2015, P. David Polly Geology G114 Lobe-ﬁnned ﬁsh (Sarcopterygia)

Living coelacanth Fossil sarcopterygians

Late Cretaceous (ca. 65 mya)

Comparison of pectoral fins

Actinopterygian Sarcopterygian (ray finned) (lobe finned)

Scapulocoracoid Humerus Ulna

Ancestral characteristics of living tetrapods

• Pelvic and pectoral girdles • Forelimb with humerus, radius, and ulna bones • Hindlimb with femur, tibia, and ﬁbula bones • ﬁve digits on the feet • sprawling posture • undulating locomotion • skull with no fenestra Department of Geological Sciences | Indiana University Dinosaurs and their relatives (c) 2015, P. David Polly Geology G114 Tetrapoda: vertebrates more closely related to living Phylogeny of Bony Fish amphibians and amniotes than to their nearest living relatives

Fossil taxa coelocanths and Fish-like amphibian-like lung fish Tetrapods Tetrapods Actinopterygia Coelocanths Dipnoans (lungfish) Osteolepis Eusthenopteron Pandericthyes Acanthostega Icthyostega tetrapods Derived

Tetrapoda

Sarcopterygia Osteichthyes

Living amphibians • Begin life as larvae, metamorphose into adults • Larvae typically respire through gills, adults typically breath through lungs and moist skin Frogs Caecilians

Giant salamander walking

Ancestral vertebrate locomotion: Undulation

Fish

Salamander

Note “sprawling” posture

Early amphibian skull

Limb and skull evolution in tetrapods

Coates, M. I., M. Ruta, and M. Friedman. 2008. Ever since Owen: changing perspectives on the early evolutio of tetrapods. Annual Review of Ecology, Evolution, and Systematics, 39: 571-592. Department of Geological Sciences | Indiana University Dinosaurs and their relatives (c) 2015, P. David Polly Geology G114 Synapomorphies (homologies) Actinopterygia Coelocanths Dipnoans (lungfish) Osteolepis Eusthenopteron Pandericthyes Acanthostega Icthyostega tetrapods Derived

• reduction to five digits

Tetrapoda • flattened head • humerus with muscle attachment Sarcopterygia Osteichthyes • muscular pectoral and pelvic limbs with substantial bones Department of Geological Sciences | Indiana University Dinosaurs and their relatives (c) 2015, P. David Polly Geology G114 Challenges for a fish out of water Respiration. gills collapse in air, reducing surface area and inhibiting gas exchange. Solution: cutaneous respiration, lung respiration.

Support against gravity. Original vertebrate skeleton not able to support the body off the ground. Solution: limbs and vertebral column.

Sensory perception. Ever see a fish with ears? Solution: transformation of hyomandibula to stapes, reorganization of skull for forward sight, improvements to sense of smell.

Reproduction 1. Fish typically spawn. Solution: internal fertilization.

Reproduction 2. Fish eggs dry out. Solution: amniotic membrane surrounding embryo in egg to prevent desiccation.

Communication. Ever hear a fish scream? Solution: vocalizations come along with hearing, new sense of smell signals, and new visual signals.

Food. Fish are typically predatory and have prey capture strategies that often involve sucking prey into mouth with water. Solution: reorganization of jaws and differentiation of neck Department of Geological Sciences | Indiana University Dinosaurs and their relatives (c) 2015, P. David Polly Geology G114

Paleozoic amphibian trackway from Indiana