1Lecture 8 – History of fishesRay Troll Picture = CARD SHARKSStructural Patterns and Trends in Diversification• Fish subsumed (since Cope (1889) proposed - Agnatha - jawless fishes and Gnathostome lines - hasn't really stood the test of time (explain later).• Consider Agnathan briefly.• Earliest fish-like vertebrates with reasonable fossil record - middle Ordovician (440-510 mya) of North America, Europe and Australia. • Many early vertebrate groups tried hard external armor (dermal bone) – this is preserved. ~ 500 mya dermal bone with structural complexity evolved. • Evolution of calcified tissues has had profound effect on vertebrate evolution - and the origin of vertebrate skeletal structure - considerable interest • All oldest fish-like vertebrates sometimes called ostracoderms (shell-like skin). • All (at least partly) encased in some bony armor, lacked jaws, paired lateral fins.• Mouth was slit or oval opening towards front of animal. • From tail structure - adapted to bottom dwelling existence, feeding probably by suction?? using flexible floor of oralobranchial chamber and associated ventral branchial muscles as a pump.Agnathans• Class – Pteraspidomorphi• Class – Myxini?? (living)• Class – Cephalaspidomorphi– Osteostraci– Anaspidiformes– Petromyzontiformes (living)Major Groups of Agnathans• 1. Osteostracida• 2. Anaspida• 3. Pteraspidomorphida• 1) Osteostracidanagnathans - include thumb sized cephalaspids (see Stensio) - characteristic anatomy = head shield, pair of openings (presumably for the eyes) and single aperture for naso-hypohyseal canal.2Major Groups of Agnathans1. Osteostracida2. Anaspida3. Pteraspidomorphida2 - Anaspidianagnathans - streamlined bodies and small scales suggest strong swimmers. Strange hypocercal tail probably raised anterior end of body in swimming. Immediately behind head is row of pores - thought to be gill openings.Major Groups of Agnathans• 1. Osteostracida, 2. Anaspida, 3. Pteraspidomorphida• 3) Pteraspidomorphidan agnathans - Most successful in abundance, taxonomic diversity and duration in fossil record – head, trunk enclosed in bony plates 2 living groups of agnathan fishes• Hagfish and Lamprey = Traditionally together in cyclostomata• Not a good group BUT many uncertainties surrounding evolutionary interrelationships of various agnathan groups (both fossil and living) Jaws = GNATHOSTOMES• Gnathostomes: the jawed fishes• While agnatha cannot be called good (monophyletic) group - there is very good evidence for gnathostome monophyly. • 4 major groups of jawed vertebrates:Extinct Acanthodii and Placodermi.Living Chondrichthyes and Osteichthyes3FOSSIL GNATHOSTOMES• Fossil gnathostome radiations:• 1) Placodermi - Most primitive – Diverse and bizarre group of heavily armored gnathostomes - Devonian (408-360 mya) -almost restricted to period.• Typically Placoderms are dorsoventrallycompressed. All = head shield articulated with trunk shield - cover anterior body.Placoderms – most primitive jawedGNATHOSTOMES• Living Chondrichthyans - usually divided into Selachii or Elasmobranchi (sharks and rays) and Holocephali (chimeroids). FOSSIL GNATHOSTOMES• Fossil gnathostome radiations:• 2) Acanthodians, or spiny-sharks = relatively conservative "fish-like" body form. Middle Silurian (440-408 mya) - disappear by middle Permian (290-245 mya).• Large eyes, active mid-water swimmers. Array of feeding specializations. • Teleostomi = Acanthodii + Osteicthyes4GNATHOSTOMES• Living Osteichthyans commonly regarded as forming two major groups -– Actinopterygii – Ray finned fish – Sarcopterygii (coelacanths, lungfish, Tetrapods).Gnathastome SummarySarcopterygians• Actinistia = Latimeria = Coelacanths• Dipnoi = Lung-fish• Osteolepimorphi = Tetrapod AncestorsCranial kinesis, internal choanae and labyrinthodont teeth. Famous –EusthenopteronClose to tetrapods - Panderichthys5Latimeria menadoensisLungfish - Dipnoi• Three genera•Africa• Australian• South AmericanLungfish - Dipnoi• Three genera•Africa• Australian• South AmericanA) Onychodontiformes - early to late DevonianB) Actinistia- middle Devonian to RecentC) Dipnoi- late Silurian or early Devonian to RecentD) Porolepiformes- early to late DevonianE) Rhizodontiformes- late Devonian to CarboniferousF+G) Osteolepiformes-middle Devonian to early Permian; G) Panderichthys-? –type of Osteolepiformes - middle to late DevonianH) Tetrapoda- late Devonian to Recent6Rhizodonts• Rhizodonts = extinct group of sarcopterygian fishes. Many areas of world - Upper Devonian to Upper Carboniferous - earliest known species = 377 Ma, latest around 310 Ma.Rhizodonts lived in tropical rivers and freshwater lakes. Dominant predators. Huge sizes - largest known species, Rhizodus hibberti from Europe and NA, estimated 7 meters, largest freshwater fish known. Osteolepimorphi = Tetrapod Ancestors– EusthenopteronAlso known as
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