8/19/2013 Topic 4: The Origin of Tetrapods Topic 4: The Origin of Tetrapods Next two lectures will deal with: What is the geological time scale and why is it important? Origin of Tetrapods, transition from Where do herps fit in the vertebrate water to land. phylogeny? What are the evolutionary origins of Origin of Amniotes, transition to dry tetrapods? habitats. What changes were involved in the transition from water to land? The geological time scale The geological time scale Organizes the history of the earth Eon Era MYA Precambrian accounts for Cenozoic 0-65 ~88% of Earth Based on geological and biological/fossil criteria history Phanerozoic Mesozoic 65-245 We will Allows us to consider “________________” concentrate on Phanerozoic Paleozoic 245-570 Time scale over which geological and ___________________ phenomena occur st Proterozoic 570-2500 1 multicellular organisms Organized into hierarchical ________, ________, Precambrian Archaen 2500-3800 1st unicellular organisms ______________, and ______________ Age of oldest rocks Hadean 3800-4600 The Paleozoic Era The Mesozoic Era Period MYA Events Period MYA Events - Mass extinction at end of 1st _________________ Permian 245-286 Cretaceous Cretaceous 65-144 - 1st modern Squamata 1st reptiles, amphibians Carboniferous 286-320 specialize st st Devonian 360-408 1 amphibians - 1 Urodela, Anura - 1st Rynchocephalia st Jurassic 144-208 Silurian 408-438 1 jawed fishes - High reptile diversity - 1st birds 1st jawless fishes & st Ordovician 438-505 land plants -1 Angiosperms, dinosaurs, mammals 1st vertebrates Cambrian 505-570 Triassic 208-245 - 1st Testudines, ___________ 1 8/19/2013 The Cenozoic Era What are stem and crown groups? Period Epoch MYA Comments _________________ – smallest Modern humans Holocene Recent monophyletic group to contain the last common ancestor of all extant members Quanternary Evolution of humans Pleistocene 0.01-1.5 of a taxon 1st hominines Pliocene 1.5-5 _________________ – contains crown Miocene 5-24 group plus closely related extinct taxa. Last common ancestor is older than that Tertiary Oligocene 24-37 for its extant members Eocene 37-58 -1st Gymnophiona 58-65 Paleocene - 1st pacental mammals Where do herps fit into the What are stem and crown groups? vertebrate phylogeny? Crown groups: Stem groups: Phylogeny of jawed Are monophyletic Are also monophyletic vertebrates Contain all extant taxa Contain all extant & What are outgroups of Tetrapoda (3)? Can contain extinct taxa extinct taxa Actinopterygii (6) Actinistia (7) Dipnoi (8) ____________________ (6) are ray-finned fishes Extremely diverse (~25,000 spp.) Highly derived Fins have extrinsic muscle Benton Fig 9.11 Pough et al 2004, Fig 2-1 Where do herps fit into the vertebrate phylogeny? Sarcopterygian lineages ________________ (2) _________________ Lobe-finned fishes Coelacanth, Latimeria Contain Actinistia (7), 2 extant species Dipnoi (8), Tetrapoda Symmetrical, 3-lobed (3) ________ “living fossil” Benton Fig 9.11 Fins/limbs are supported by bone and _________________ contain ___________ Lung fishes muscle 3 extant genera Teeth have enamel Gondwanan distribution What kind of characters 1 in S. America, 1 in are these? Africa, 1 in Australia Pough et al 2004, Fig 2-1 Vertebrate Life Fig 8-35 2 8/19/2013 Where do herps fit into the Sarcopterygian lineages vertebrate phylogeny? Tetrapoda This phylogeny includes Includes all modern only extant taxa amphibians and amniotes, and their Many species of early last common ancestor. tetrapods and _________________ stegocephalians are _________________ extinct Fully developed _____________ girdle Pectoral girdle free Therefore, must look at from the skull (not the both stem and crown case in non-tetrapods) Amphibia Discrete shaft of ______________ Pough et al 2004, Fig 2-1 Stem and Crown Amphibia Most groups of Amphibians and all early tetrapods are ____________ Benton 1997, Fig 4-21 3 8/19/2013 Early tetrapod relationships are contentious How do these two hypotheses differ? How are they the same? Why might we prefer one over the other? Stegocephali Tetrapoda Lepospondyls Temnospondyls Laurin & Reisz 1997 Traditional hypothesis No a priori assumptions, many more taxa included Inclusion of only some taxa, assumption of Temnospondyl-Lissamphibian association Pough et al. 2004 Fig 2-8 1 8/19/2013 What are the evolutionary origins of tetrapods? What are the evolutionary origins of tetrapods? Elpistostegidae (Panderichthys) Outgroup to Stegocephalia but closer than Dipnoi Laurin & Reisz 1997 Dorsoventrally _____________, no dorsal fin, dorsal eyes Lepospondyls are: _________________ water __________________ Tetrapod-like body but with fins Sister to Lissamphibia Developed frontal bones a Amniotes (including reptiles) are: synapomorphy with Sister group to stegocephalia Lissamphibia+Lepospondyls Stegocephali Tetrapoda Lepospondyls Stegocephali Lepospondyls Temnospondyls Pough et al. 2004 Fig 2-8 Tetrapoda Temnospondyls Pough et al. 2004 Fig 2-3 What are the evolutionary origins of tetrapods? What are the evolutionary origins of tetrapods? Acanthostega & Ichthyostega Acanthostega & Ichthyostega ___________ from Devonian _______________ (360mya) of Greenland and 6-8 digits per limb Russia What does this mean for Four limbs with digits, but also a ancestral number of digits? branchial apparatus with gills ________________ Stegocephali Lepospondyls Stegocephali Lepospondyls Tetrapoda Temnospondyls Pough et al. 2004 Fig 2-2 Tetrapoda Temnospondyls Vertebrate Life Fig 10-3 What are the evolutionary origins of tetrapods? What are the evolutionary origins of tetrapods? Temnospondyls Amniota Carboniferous We will come back to these Few centimeters to over 1m Mammals, birds, snakes & Limbed, posture more upright lizards, turtles, crocidilians than Acanthostega/Ichthyostega Some aquatic, others (below) terrestrial Typically ________________ Next slide Stegocephali Lepospondyls Stegocephali Lepospondyls Tetrapoda Temnospondyls Pough et al. 2004 Fig 2-7 Tetrapoda Temnospondyls 1 8/19/2013 What are the evolutionary origins of tetrapods? What are the evolutionary origins of tetrapods? Lepospondyls Lissamphibia Carboniferous & Permian Urodela, Anura, Gymnophiona Diverse Extant (finally) Microsauria – _________ & small Aisopoda – ___________ Nectridea – _________ & newt-like Stegocephali Lepospondyls Pough et al. 2004 Fig 2-4b,c; 4-14, 4-15 Tetrapoda Temnospondyls Photos: KP Bergmann, Pough et al. Fig 3-8 What changes were involved in the transition What changes were involved in the from water to land? transition from water to land? This transition involved aspects Obligate Aquatic of structure and function associated with: What is involved in ____________________ this major ____________________ evolutionary ____________________ transition? ____________________ ____________________ ____________________ ____________________ Terrestrial ____________________ 2 8/19/2013 What changes were involved in the What changes were involved in the transition from water to land? transition from water to land? Body support Ground reaction forces Moving onto land means coping Pectoral girdle became with _____________ ____________ from the head In the water, the body is Minimizes forces exerted on supported by the water, on skull and brain, increases head land by limbs Actinopterygii ____________ Coping with ______________ __________________ Small in water Large on land Ichthyostega Panderichthys Benton 1997 pg 183; Benton Fig 4-2a; Pough et al 2004 Fig 2-2 What changes were involved in the What changes were involved in the transition from water to land? transition from water to land? Ground reaction forces Locomotion Limb girdles became more ______________ to the A switch from ____________ vertebral column to walking and running Allows limbs to become support structures and transfer Terrestrial locomotion is much forces to the axis harder on the ___________ Fin-based swimming is replaced by pushing off a substrate with the limbs Lateral undulation plays a role in both ________________ less of an Protopterus issue on land (African lungfish) Acanthostega Benton 1997 Fig 3.22; Pough et al 2004 Fig 2-2a What changes were involved in the What changes were involved in the transition from water to land? transition from water to land? Locomotion Locomotion Limbs change dramatically: Vertebral morphology becomes more ______________ More ____________ Zygapophyses limit excessive intervertebral forces, More ________________ especially _____________ Switch from extrinsic to intrinsic limb musculature Panderichthys & Acanthostega Acanthostega Vertebrate Life Fig 10-3 Kardong & Zalisko 2002: Fig 5.8c, 5.11b 1 8/19/2013 What changes were involved in the What changes were involved in the transition from water to land? transition from water to land? Respiration Body shape Gills only to gills & lungs to Very _________________ in fishes lungs only Streamline but dorsoventrally flattened in Panderichthys Both gills and lungs are Allows invasion of shallow ancestral because lungs water arose from ____________ Also dorsal eyes, no dorsal fin Decrease in hydrodynamics in Acanthostega still had gills terrestrial forms Ventilation increasingly powered by __________ of the ______________ What changes were involved in the What changes were involved in the transition from water to land? transition from water to land? Excretion Water balance Trend from excreting ammonia Fishes