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