lecture 6.pdf

EASC 103 The Rise and Fall of the Dinosaurs LECTURE 6 – DINOSAUR ANCESTRY 1 Lecture 6 Learning Goals: u Evolution and diversification of tetrapods u Building the tetrapod family tree...

EASC 103 The Rise and Fall of the Dinosaurs LECTURE 6 – DINOSAUR ANCESTRY 1 Lecture 6 Learning Goals: u Evolution and diversification of tetrapods u Building the tetrapod family tree u A closer look at the diapsid reptiles u Pterosaurs – sister clade to the dinosaurs  Evolutionary Steps to get to Dinosaurs 2 Recall that all animals can be divided into invertebrates and vertebrates. What are the evolutionary steps to get us to the first dinosaurs? The first animals with a true backbone were primitive fish…so that is near the start of our evolutionary story. We need to go back one further step. The Cambrian sees the earliest chordates Pikaia (~ 510 Ma) evolve. These were small (4 cm long) fish-like animals with a flexible notochord along their backs – the precursor to a vertebral column. The first true vertebrates came next – the primitive jawless fishes. Fish Diversification 3 Lobe-finned fish have articulated bones within their fins. They also had both gills and lungs. These fish ’walk’ along the river bed and during drought they could travel overland to nearby waterways, breathing air through their lungs. Tetrapod Ancestry 4 Amphibians were the earliest true tetrapods with relatively robust limb bones. Transitional species such as Tiktaalik.  Rise of Reptiles 5 — Reptiles evolved from amphibian ancestors. Key evolutionary novelties of the reptiles include skeletal modifications for terrestrial Mainly water dwelling and reproduce locomotion and development of by laying egg masses (in water). an amniotic egg. Salamander Early reptiles were mainly land dwelling and egg mass 4.1 Amniotic egg reproduce via an amniotic egg (laid on land). 4.2 Skeletons of amphibian and early reptile  Building the Tetrapod Family Tree 6 Pikaia jawless fishes placoderms cartilaginous fishes early spiny sharks chordates ray-finned fishes lobe-finned fishes amphibians Tiktaalik reptiles  Building the Tetrapod Family Tree 7 Pikaia jawless fishes placoderms cartilaginous fishes early spiny sharks chordates ray-finned fishes lobe-finned fishes amphibians Tiktaalik anapsids reptiles euryapsids synapsids mammal-like reptiles mammals diapsids  Diapsid Reptiles 8 — Diapsid reptiles are divided into: ¡ Lepidosaurs (the lineage that leads to modern lizards and snakes) ¡ Archosaurs (two lineages: the crocodilian line called pseudosuchia, and another called avemetatarsalia which includes the pterosaurs and dinosaurs) pseudosuchia Key evolutionary novelties of the archosaurs include changes to the ankle that allowed for semi-upright avemetatarsalia (pseudosuchia) and fully upright postures (avemetatarsalia). 4.6 Archosaur diversity  Tetrapod Family Tree 9 Pikaia jawless fishes placoderms cartilaginous fishes early spiny sharks chordates ray-finned fishes lobe-finned fishes amphibians Tiktaalik anapsids reptiles euryapsids synapsids tetrapods mammal-like reptiles mammals lepidosaurs diapsids pseudosuchia archosaurs pterosaurs avemetatarsalia Now let’s zoom in on diapsids dinosaurs and add our dinosaur groups birds  Diapsid Reptiles 10 Lastly, let’s take a look at the sister clade to the lepidosauria dinosaurs - the pterosaurs pseudosuchia diapsidae pterosauria archosauria sauropodomorpha (changes to avemetatarsalia saurischia the ankle) (fully upright dinosauria theropoda posture) aves ornithopoda ornithischia thyreophora marginocephalia  Pterosaurs 11 — Pterosaurs are the sister clade to the dinosaurs. These (“winged lizards”) are known from rare fossils in strata from the Late Triassic through to the end of the Cretaceous (228-66 m.y.a.). One well-known pterosaur is Pteranodon longiceps which means ‘winged, toothless, long-headed’. It lived in North American 85 Ma. It has a wingspan of over 6 metres (20 ft)  Pterosaurs 12 — Pterosaurs have incredibly odd body dimensions including many adaptations for powered flight. Let’s check them out.  Pterosaur Wings 13 A pterosaur wing is composed of a membrane of skin, tissues and muscles. View of the underside of the left forelimb National Geographic Pterosaurs 101 (3 min) https://www.youtube.com/watch?v=mfYuvlE78Nk  Azhdarchids Cessna 172 light aircraft 14 — Azhdarchid pterosaurs include some of the largest pterosaurs to ever exist. One of the very largest lived at the end of the Cretaceous in North America – meet Quetzalcoatlus with an 11-metre wingspan. We will watch many segments from Prehistoric Planet with David Attenborough Let’s begin by watching a 2-minute trailer https://www.youtube.com/watch?v=vnoNeMlNeD0 And then watch Tyrannosaurus rex vs Quetzalcoatlus (4 min) https://www.youtube.com/watch?v=zWGnlAQsRaE