Lecture 8 Tetrapods Marine Monsters PDF

14/10/2012 Lecture 8 Tetrapods Part 2: Marine Monsters of the Triassic, Jurassic and Cretaceous 1  14/10/2012 Permian Triassic J...

14/10/2012 Lecture 8 Tetrapods Part 2: Marine Monsters of the Triassic, Jurassic and Cretaceous 1  14/10/2012 Permian Triassic Jurassic Cretaceous Cenozoic Squamates Tuatara Lepidosauromorpha Mosasaurs Plesiosaurs ? Ichthyosaurs Marine Diapsids ? Thalatosaurs Champsosaurs Archosauromorpha Trilophosaurs Archosaurs Squamate Phylogeny Mesosaurs are though to be related to monitor lizards and thus represent a clade of squamates that adapted to marine environments Montor Lizard Mosasaur Monitor lizard Mosasaur 2  14/10/2012 5) Diapsids c) Marine Diapsids i) Mosasaurs These are marine relatives of monitor lizards and are thus a part of the Squamate radiation Fossils of mesosaurs are known from a short time window towards the end of the Cretaceaus (85 to 65 mya) when they were the dominant marine predators, eating large fish, mulluscs, etc. They ranged in size from 3 to 17.5 meters. Propulsion came from moving body and tail like a crocodile Skeletal drawings of three types of mosasaur 3  14/10/2012 Mosasaurs Platecarpus < 2 meters 4.3 meters Taniwhasaurus 6 meters Tylosaurus 17.5 meters A mesosaur in the late Cretaceus 4  14/10/2012 ERA Period mya Marine reptile timeline Quaternary 5 Tertiary CENOZOIC Mesosaurs 66 Cretaceous 145 MESOZOIC Jurassic 200 Triassic 251 Permian 299 Carboniferous 359 Devonian PAEOZOIC 416 Silurian 444 Ordovician 488 Cambrian 542 Permian Triassic Jurassic Cretaceous Cenozoic Squamates Tuatara Lepidosauromorpha Mosasaurs Plesiosaurs ? Ichthyosaurs Marine Diapsids ? Thalatosaurs Champsosaurs Archosauromorpha Trilophosaurs Archosaurs 5  14/10/2012 Permian Triassic Jurassic Cretaceous Cenozoic Squamates Tuatara Lepidosauromorpha Mosasaurs Plesiosaurs ? Ichthyosaurs Marine Diapsids ? Thalatosaurs Champsosaurs Archosauromorpha Trilophosaurs Archosaurs 5) Diapsids c) Marine Diapsids ii) Ichthyosaurs Have a shape similar to dolphins, but tail is vertical like a fish while a dolphin tail is horizontal. Limbs modified back to fins similar to those in dolphins. Ichthyosaur dolphin 6  14/10/2012 5) Diapsids c) Marine Diapsids ii) Ichthyosaurs Have a shape similar to dolphins, but tail is vertical like a fish while a dolphin tail is horizontal Main propulsion is side to side body motion like a fish, whereas a dolphin has an up down body motion The tail fin is generally very deep, characteristic of swimmers that use fast acceleration in hunting prey. Powerful jaw Good eyesight Ichthyosaurus modern dolphin 5) Diapsids c) Marine Diapsids ii) Ichthyosaurs Some early Ichthyosaurs had blunt, shell-crushing teeth for hunting ammonites and other shelled cephalopods Most ichthyosaurs ate fish ammonite 7  14/10/2012 5) Diapsids c) Marine Diapsids ii) Ichthyosaurs A spectacular ichthyosaur, Eurhinosaurus, was probably the ecological equivalent of the modern swordfish Upper jaw used to slash its way through a school of fish, the spinning around to catch its crippled victims Modern swordfish Eurhinosaurus 5) Diapsids c) Marine Diapsids ii) Ichthyosaurs Some morphological phylogenies suggest a close relationship to Thalatosaurs, another group of Triassic marine reptiles Two genera of Thalatosaurs 8  14/10/2012 5) Diapsids c) Marine Diapsids ii) Ichthyosaurs Some morphological phylogenies suggest a close relationship to Thalatosaurs, another group of Triassic marine reptiles The earliest ichthyosaur fossils were less than 2 meters in length, and had a long eel like tails, but fully formed flippers Two genera of Thalatosaurs Early Icthyosaurs Grippia Utatsusaurus Cymbospondylus 5) Diapsids c) Marine Diapsids ii) Ichthyosaurs Some morphological phylogenies suggest a close relationship to Thalatosaurs, another group of Triassic marine reptiles The earliest ichthyosaur fossils were less than 2 meters in length, and had a long eel like tails, but fully formed flippers Latter icthyosaurs evolved the more specialized tails. Two genera of Thalatosaurs Early Icthyosaurs Latter Icthyosaurs Grippia Stenopterygius Utatsusaurus Ichthyosaurus 9  14/10/2012 5) Diapsids c) Marine Diapsids ii) Ichthyosaurs Size: less than 1 meter (3 feet) to 21 meters (70 ft) in the recently discovered Shonisaurus sikanniensis from British Columbia, the largest marine reptile to have ever lived (in comparison, the great blue whale is 33 meters) 21 meters < 2 meters 10  14/10/2012 ERA Period mya Marine reptile timeline Quaternary 5 Tertiary CENOZOIC Mesosaurs Ichthyosaurs Only 3 genera from Cretaceous during 66 which time they go extinct Cretaceous 145 Greatest abundance in Late Triassic MESOZOIC Jurassic and Early Jurassic, with mass 200 Triassic extinction event at end of Triassic 251 Permian Originated early Triassic 299 Carboniferous 359 Devonian PAEOZOIC 416 Silurian 444 Ordovician 488 Cambrian 542 Permian Triassic Jurassic Cretaceous Cenozoic Squamates Tuatara Lepidosauromorpha Mosasaurs Plesiosaurs ? Ichthyosaurs Marine Diapsids ? Thalatosaurs Champsosaurs Archosauromorpha Trilophosaurs Archosaurs 11  14/10/2012 5) Diapsids c) Marine Diapsids iii) Sauropterygians (Plesiosaurs and kin) 4 main groups of Sauropterygians Permian Triassic Jurassic Cretaceous Cenozoic Placodonts ? Pachypleurosaurs Nothosaurs Plesiosaurs 5) Diapsids c) Marine Diapsids iii) Sauropterygians (Plesiosaurs and kin) 1. Placodonts These lived from early Triassic to end of Triassic The earliest forms like looked like a marine iguana Latter forms evolved along two separate lines to independantly form shard shells Early forms Later forms with boney plates horeshoe crab Cyamodus Placodus Placochelys sea turtle 12  14/10/2012 ERA Period mya Marine reptile timeline Quaternary 5 Tertiary CENOZOIC Placodonts Mesosaurs Ichthyosaurs 66 Cretaceous 145 MESOZOIC Jurassic 200 Triassic 251 Permian 299 Carboniferous 359 Devonian PAEOZOIC 416 Silurian 444 Ordovician 488 Cambrian 542 5) Diapsids c) Marine Diapsids iii) Sauropterygians (Plesiosaurs and kin) 2. Pachypleurosaurs, Nothosaurs and Plesiosaurs The Pachypleurosaurs from the early Triassic were small (0.2 to 1 meter), lizard like diapsids with long limbs, and webbed toes. These evolved into slightly larger forms, the Notosaurs (less than 3 meters), from which the much larger Plesiosaurs are believed to have evolved (up to 20 meters). Pachypleurosaurs Notosaurs Plesiosaurs 13  14/10/2012 Notosaur (with digits) Plesiosaur Notosaurs have digits, probably with webbing. They probably reply heavily on tail movement for swimming The flippers become fully formed in Plesiosaurs and probably provide the main thrust when swimming 5) Diapsids c) Marine Diapsids iii) Sauropterygians (Plesiosaurs and kin) Plesiosaurs Two main body designs evolved in Plesiosaurs Plesiosaurs and pliosaurs were once though to represent two distinct clades but it is now thought that plesiosaurs may have evolved into pliosaurs multiple times and that some plesiosaurs may have evolved a pliosaur shape. Plesiosaur body shape Pliosaur body shape Pistosaurus Pliosaurus Thalassomedon Liopleurodon 14  14/10/2012 Plesiosaurs with a plesiosaur shape Slow swimmers Used long flexible necks to snap quickly at small prey such as fish and cephalopods Probably unable to leave water or even lift head above water As many as 76 neck vertebrae Giraffe has only 7 Styxosaurus Plesiosaurs with a plesiosaur shape < 2 meters Cryptocleidus Pistosaurus 8 meters 3 meters Dolichorhynchops Thalassomedon 3 meters 12 meters Mauisaurus 20 meters 15  14/10/2012 Elasmosaurus Plesiosaurs with a pliosaur shape Fast swimmers with shorter necks, giant elongated heads Probably ate fish, icthyosaurs and other plesioaurs These were the top predators of marine environments for most of the Triassic, Jurassic and Cretaceous 16  14/10/2012 Plesiosaurs with a pliosaur shape Kronosaurus 10 meters < 2 meters Pliosaurus macromerus ~ 15 meters Unassigned species Mexico ~ 15 to 18 meters Liopleurodon 17  14/10/2012 Liopleurodon ERA Period mya Marine reptile timeline Quaternary 5 Pachypleurosaurs Tertiary CENOZOIC Nothosaurs Placodonts Mesosaurs Ichthyosaurs Plesiosaurs 66 Cretaceous 145 MESOZOIC Jurassic 200 Triassic 251 Permian 299 Carboniferous 359 Devonian Sauroptrerygians PAEOZOIC 416 Silurian 444 Ordovician 488 Cambrian 542 18  14/10/2012 ERA Period mya Marine reptile timeline Legendary lochness and ogopogo Quaternary 5 Pachypleurosaurs Tertiary CENOZOIC Nothosaurs Placodonts Mesosaurs Ichthyosaurs Plesiosaurs 66 Cretaceous 145 MESOZOIC Jurassic 200 Triassic 251 Permian 299 Carboniferous 359 Devonian Sauroptrerygians PAEOZOIC 416 Silurian 444 Ordovician 488 Cambrian Ogopogo 542 QUESTION: What challenges might have marine amniotes of the Jurassic to Cretaceous faced in evolving back to the marine environment? 19  14/10/2012 5) Diapsids c) Marine Diapsids iv) Challenges to recolonizing the sea All marine reptiles are air breathers and must come to the surface to breath air. Amniote egg’s were adapted for terrestrial environments. Sea turtles and other small marine reptiles came ashore to lay eggs in nests. The strong limbs of plocodonts and small size of pachypleurosaurs suggest they may have come ashore to lay eggs. The large size and body design of most Plesiosaurs suggest they probably couldn’t come ashore to lay eggs and probably had live birth at sea Likewise, the Ichthysaurs gave live birth at sea with fossil Icthyosaurs with fetuses preserved inside them. Mesosaurs, no evidence one way or other whether they had live birth 30min 20  14/10/2012 QUESTION: Why might this sea turtle from the Cretaceous have grown to such monstrous sizes and why do turtles not grow to such sizes today? the giant Cretaceous sea turtle, Archelon For in depth review: Chapter 14 (pages 196 to 203) of Cown 35 min 21