Vertebrate Evolution PDF
Document Details
Uploaded by ConciliatoryElder
Florida Gulf Coast University
Tags
Related
Summary
This document provides a comprehensive overview of vertebrate evolution, covering various lineages from early jawless fish to modern mammals and birds. It includes detailed diagrams, descriptions, and characteristics of different vertebrate groups.
Full Transcript
Ch 3 The Complete Vertebrate Story Fig. 3.1 Innovations Vertebral column Cranium and cephalization Pharyngeal pump Agnathostoma (Jawless Vertebrates) hagfish and lampreys Agnathans Cyclostomata Jawless Fish Agnathans Two extant lineages Petromyz...
Ch 3 The Complete Vertebrate Story Fig. 3.1 Innovations Vertebral column Cranium and cephalization Pharyngeal pump Agnathostoma (Jawless Vertebrates) hagfish and lampreys Agnathans Cyclostomata Jawless Fish Agnathans Two extant lineages Petromyzontiformes Myxiniformes Multiple extinct lineages Gnathostomata Myxiniformes - Hagfishes 75 species: all marine Two major genera Eptatretus and Myxine Elongated body form Scaleless Gray to purple in color Scavengers and predators Petromyzontiformes - Lampreys Diversity: 40 spp in two genera Petromyzon and Lamptera Range in size from about 10 cm to 1 m Found primarily in temperate northern regions Petromyzontiformes - Lampreys Structural Characteristics 7 pair of gill pouches Large well developed eye (possess color vision) Round mouth with keratinous teeth Parasites of fish Extinct Jawless Fish Multiple extinct lineages Appear late Cambrian Agnathans with radiations in the Silurian and Early Devonian Conodonts Gnathostomata Conodonts Mysterious early vertebrate Conodont elements widespread in fossil record from Cambrian to Triassic Spine or comb-like structures Calcified like vertebrate hard tissues Originally thought to be marine invertebrates But recent fossils suggest vertebrate synapomorphies Notochord Myomeres Complex pharynx formed with dentine and enamel Specifically vertebrate tissues Suggests they must be stem vertebrates Ostracoderms Extinct Jawless Fish “Ostracoderms” – Agnathans represents a paraphyletic group More derived than the extant agnathans Ordovician through Devonian Gnathostomata Ostracoderms Extinct Jawless Fish Structural Characteristics Possess true bone Mesoderm derived Collagen+Calcium matrix Dermal exoskeleton Large plate like scales 200 separate genera) Placoderms The hallmark characteristic of placoderms is the division between the bony head shield into distinct head and trunk portions with an articulating joint between them. Though they had jaws, most lacked teeth; instead had bony cutting or crushing plates around jaws (part of head armor) Plates not replaceable Placoderms Covered with a thick bony shield Exoskeleton - heavily armored like many ostracoderms Endoskeleton – mostly cartilaginous; some limited ossification beginning in cartilaginous elements→Endochondral Generally considered to be bottom-dwelling – why? Heavy armor would require considerable energy to maintain position in water column Placoderms Dunkleosteus Up to 10 m long – largest animal of the Devonian Upper cranium and lower jaw jointed to allow large gape Predator of other placoderms, sharks, etc. Chondrichthyans Many extant genera appeared as early as the Triassic Major extant diversity Elasmobranchi– sharks, skates, rays Holocephali – chimaeras Significant evolutionary changes Sub-terminal mouth Solid calcified cartilaginous vertebrae (Centrum will eventually replace notochord) Thicker, enamel-like coating on teeth Cartilaginous skeleton Distinctive Characters of Chondrichthyans Cartilaginous Skelton = poor fossilization What provides us with insight on the extinct diversity of Chondrichthyans? Teeth! Not embedded in jaw like bony fish. Composed of dentine and enameloid so they fossilize Presence of a tooth whorl Teeth are continuously replaced as they wear down and eventually fall out. Polyphyodont [many sets of teeth] Paleozoic holocephali Basal to Chimaeriformes Appear in the mid-Devonian Shark-like teeth Upper jaw not fused to the cranium unlike extant Chimaeras Helicoprion Elaborate teeth whorl Used like a circular saw Trap/saw prey Extant Chondrichthyans Neoselachii – sub-terminal mouths distinguish from earlier forms Squalomorphii Galeomorphii Batoidea Holocephali– Chimaeras – ghost shark Date to Jurassic and Cretaceous period Osteichthys Osteon- “bone” Ichthyes-”fish” Bony Fishes Sarcopterygians “fleshy-finned” fishes Actinopterygians “ray-finned” fishes Subclasses Cladistia Actinopteria Chondrostei (sturgeon and paddlefish Neopterygii Holostei (bowfins and ~32,000 species gars) Specialization of feeding mechanisms Teleostei prominent in evolution Exploitation of novel habitats and prey The origin of Bony Fishes Major Characteristics Bony fishes refer to their ossified endoskeleton Most endoskeletal bone is fundamentally different from dermal bone in that it has a cartilaginous precursor Major dermal bone elements retained in cranium Origins in ancient head shields of placoderms Dermal bone encases jaws The origin of Bony Fishes Major Characteristics True teeth are present and rooted in the dermal bone Contrast to tooth whorl of sharks Possess true enamel on outer layer of scales Dermal head bones extend to connect to pelvic girdle The origin of Bony Fishes Major Characteristics Gas Bladder derived from embryonic gut Used for buoyancy, breathing, or both Physotomous Pneumatic duct Physoclistous Rete Mirable Gas gland Homologous in all osteichthyans Actinistia – coelacanths & relatives †Onychodontiformes Rhipidistia Sarcopterygii Dipnomorpha – lungfish & relatives Tetrapodomorpha – four-limbed vertebrates & relatives Rhipidistia Dipnomorpha –lungish and relatives Tetrapodomorpha – four-limbed vertebrates and relatives Lissamphibia – descendants of the anamniotic tetrapods Amniota Tetrapoda Diversity of Extant Amphibians Monophyletic group – Lissamphibia Extant taxa date from the Triassic (not the same species but the same orders) General characteristics Moist, gas permeable, and essentially scale-less skin Important site for gas exchange Plethodontid salamanders have no lungs Rely upon cutaneous respiration instead Extant Amphibians Monophyletic group - Lissamphibia Modern orders differ from each other in terms of locomotor adaptations, reproduction, and defense Three sub-clades Caecilians – Gymnophiona Lack limbs Short tails Salamanders – Urodela Most with long tails and robust limbs Frogs – Anura (an, ura = without, tail) Lack tails Synapsids and Sauropsids Two major clades of amniotes Different Approaches to Terrestrial Life Amniotes split into two evolutionary lineages Synapsida “mammal-like reptiles”- mammals Sauropsida – turtles, lizards, snakes, crocodiles, dinosaurs, birds Split occurred relatively early and prior to appearance of many derived features among amniotes More than one way to succeed in terrestrial environment How did these two lineages take advantages of the opportunities presented in the terrestrial environment? Both lineages developed: Fast predators—sustained locomotion Fast prey Powered flight Parental care Social behavior Endothermy Efficient lung ventilation Anamniotes can’t get enough oxygen to muscles Some synapsids Some sauropsids pelycosaurs therapsids mammals Mesozoic Diaspids Characteristics of Diaspids Contains the crown group Reptilia that includes common ancestor to all Diaspids We’ll focus on extinct diaspids in this section Diaspid means two arches Upper and Lower fenestra Mesozoic Diaspids 2 major lineages Lepidosauromorphs Extant Squamata Sphenodon Extinct Several marine lineages Archosauromorphs Extant Turtles Crocodilians Birds Extinct Pterosaurs Dinosaurs Lepidosauromorphs Ichthyosaurs Basal form (A) → retained lizard like body Swam with lateral undulations Derived form (B)→ more stream lined Swam with lateral undulations of caudal fin (Carangiform) Retain form limbs and hind limbs Contrast to Cetaceans which retain only forelimbs Modified limbs as paddles Archosauromorpha Fig. 3.33 Bird lineage Crocodilians Modern crocodilians evolved from within a diverse group of crocodilomorphs Largest extant reptiles Greater than 6 m Greater than 1,000 kg Extinct forms range from Pakasuchus-50 cm Sarcosuchus-12 m Crocodilians Exant Diversity Gavialidae Long thin snouts specialized for feeding on fish using sideways snaps Alligatoridae Includes caimans Broad, blunt snouts Crocodylidae Only group to include marine forms though only coastal or estuarine; not pelagic Range of snout widths Differ in the way the teeth occlude Evolution of Birds Birds Birds are derived therapod dinosaurs Clearly recorded in the fossil record…classic example of macroevolution Thomas Huxley → ”Nothing more than glorified reptiles” Avian Characters in Nonavian Therapods Skeletal Characters of Extant Birds Trunk held in horizontal position Highly modified fore limbs Hindlimbs with extensive fusion of bones and digitigrade foot posture Walking on Toes Paedomorphic skull Retaining Juvenile Characteristics Synapsids – origins of mammals Earliest synapsids (“pelycosaurs”) emerged in the Paleozoic during the Carboniferous Carboniferous period immediately followed Devonian (earliest tetrapods) Synapsids represent a very early off-shoot of amniote diversity Pelycosaurs did not make it across end- Permian extinction Therapsids diversified in late Paleozoic and into Mesozoic but nonmammalian lineages vanished by early Cretaceous Various mammal lineages persisted through Cretaceous, but only three survived to the present Monotremata Theria Metatheria (Marsupials) Eutheria (Placentals) Mammal origins – synapsid evolution “Pelycosaurs” “Therapsids” Synapsida – one of the 2 major amniote lineages to Theria persist to present Mammalia Cynodontia Therapsida Synapsida Synapsids – origins of mammals Trends / sequence of synapsid evolution “Pelycosaurs” – basal synapsids; anatomical condition similar to basal amniotes Sprawling posture Ectothermic Some (not all) had “sails” Not sexually dimorphic, which indicates a function other than display Likely played a role in thermoregulation/basking Diversity of non- mammalian synapsids Three basal pelycosaur species Caseid Cotylorhynchus (herbivorous form) About size of cow Phiacodontid Ophiacodon (possibly a fish-eater) Varanopsid Varanops (a generalized carnivore). Synapsids – origins of mammals Trends / sequence of synapsid evolution “Therapsids” – more derived, but not true mammals Includes the dicynodonts and cynodonts Mostly carnivores or insectivores Numerous anatomical features that suggest more activity and greater metabolic rate than that seen in pelycosaurs Dicynodont – herbivorous therapsid …and then all the derived mammals we know today. In subsequent lectures we will look at how different organs and body systems evolved within all these groups.