Lecture 4 Early Fishes 1. Chondrichthyes 2. Acanthodians 3. Sarcopterygians Chondrichthyes - Cartilaginous fishes Cartilaginous skeleton, calcified but not ossified Skull with no sutures Internal fertilization with claspers High blood concentration of urea Holocephali Elasmobranchii Gill cover over 4 gill openings 5 to 7 gill openings Top jaw fused to cranium Teeth serially replaced Chondrichthyes Classifications Class Subclass Cohort Subcohort Chondrichthyes Holocephali Elasmobranchii Palaeoselachii extinct Euselachii Protoselachii Neoselachii Elasmobranchii- (sharks & rays) A few morphological differences • gill slits on sides of sharks, ventral on rays • small lateral spiracles on sharks, large dorsal spiracles on rays • anterior edge of pectoral fin not attached to side of head in sharks Elasmobranchii- (sharks & rays) Elasmobranchii- (sharks & rays) • Teeth not fused to jaws • replaced serially • as a group, relatively large 90% > 30cm 50% > 1m 20% > 2m Chondrichthyes - Cartilaginous fishes Sharks Shark Orders Pristiophoriformes - (sawsharks) sensory barbels - use blade to laterally slash prey - relatively small ~ 1.8 meters - evolved independently of sawfishes (Pristiformes) Squatiniformes (Angel sharks) - benthic piscivores Squaliformes (dogfish) ovoviviparous dwarf lanternshark Etmopterus perryi Hexanchiformes (sixgill sharks) … not just a clever name Lamniformes (mackerel sharks) ovoviviparous Carcharhiniformes (ground sharks) oviparous, ovoviviparous, & viviparous >50% of shark spp. Orectolobiformes (Carpet & Nurse sharks) Heterodontiformes (bullhead sharks, hornsharks) spine on each dorsal fin oviparous Lamniformes Basking Sharks filter feeding has evolved three times in sharks Whales Sharks Orectolobiformes Ze Megamouth - Lamniformes mesopelagic animal Chondrichthyes - Cartilaginous fishes Rays & Skates Ray Orders and Families Torpediniformes (torpedo rays) generates electrical discharges Pristiformes (sawfish) rostrum loaded with electroreceptors get large ~ 7m Rajiformes: Rhinobatidae (guitarfishes) body intermediate between skate and shark feed mainly on inverts oviparous Rajiformes: Rajidae (skates) - fleshy tail lacks spine - dorsal fin present Myliobatioformes: Dasyatidae (stingrays) whip-like tail with stinging spine oviparous Myliobatioformes: Myliobatidae (eagle & mobula rays) ovoviviparous Acanthodians • oldest fossils of relatively advanced fishes • likely fed in the water column Acanthodians Synapomorphies: -5 gill arches - water column feeders - 440 - 280 Myrs ago Sarcopterygians (lobe finned vertebrates) Synapomorphies: • enamel on teeth • fins characterized by a thick, bony central axis and muscles contained within the fin itself Sarcopterygians (lobe-finned vertebrates) Two subclasses: Coelacanthimorpha - Coelacanths Dipnotetrapodomorpha - Lungfish & Tetrapods Coelacanthimorpha (coelacanths) First appeared 380 mybp Thought to have been extinct for 65 million years…. 1938 JLB Smith Genus is Latimeria after Majorie 2nd Coelacanth - 1952 Comoros Island – Latimeria chalumane Indonesian coelacanth Latimeria menadoensis Diverged from Comoros population millions of years ago South Africa - Sodwana Bay also Latimeria chalumnae Tanzania - Kenya Latimeria chalumnae Latimeria spp. distribution At least 24 other coelacanth genera in the fossil record highest coelacanth diversity was ~230 – 200 mybp Intracranial joint: allows the front part of the head to be lifted whilst feeding • unique to coelacanths • increases gape Coelacanth in Motion fins …..same motion as tetrapods Marjorie Courtenay Latimer 1907-2004 Dipnotetrapodomorpha (lungfishes & tetrapods) Lungfishes 1 spp. 1 spp. 4 spp. Estivation in Lungfish Devonian lungfish Devonian fish and amphibian comparisons Devonian fish and amphibian comparisons .