Lecture 4 Early Fishes
2. Acanthodians
3. Sarcopterygians Chondrichthyes - Cartilaginous fishes
Cartilaginous skeleton, 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)
- viviparous
- benthic piscivores Squaliformes (dogfish)
ovoviviparous
two dorsal fins Hexanchiformes (sixgill sharks)
… not just a clever name Lamniformes (mackerel sharks) ovoviviparous -oophagous Carcharhiniformes (ground sharks)
oviparous, ovoviviparous, & viviparous
>50% of shark spp. Orectolobiformes (Carpet & Nurse sharks) oviparous & ovoviviparous 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
ovoviviparous Pristiformes (sawfish) rostrum loaded with electroreceptors get large ~ 7m Rajiformes: Rhinobatidae (guitarfishes) body intermediate between skate and shark feed mainly on inverts ovoviviparous Rhinopristiformes: guitarfishes & sawfishes
Batoids
Sharks
Pavan-Kumar etal 2014 Rajiformes: Arhynchobatidae & Rajidae (skates) - fleshy tail lacks spine ~ ¼ of all cartilaginous fishes
- dorsal fin present
- oviparous 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
• 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?? Indonesian coelacanth Latimeria menadoensis
Diverged from Comoros population ~ 30 mybp 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
…..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