BIO 370 — Vertebrate Zoology
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Vertebrate Diversity
Class Sarcopterygii — Lobe-fined Fishes

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Sarcopterygii Characteristics

  • Muscular lobed paired fins joined to body by single bone
  • Two dorsal fins with separate bases
  • Has a pulmonary vein
  • Phylogenetically, this clade should also include tetrapods
  • Formerly treated as a subclass of the Osteichthyes (bony fishes)
See additional lobe-finned fish fossils here

Subclass Actinistia — Coelacanths

Characteristics

  • Large size (~2m)
  • In most, a distinctive 3-lobed caudal fin with fleshy central lobe
  • Fins muscular, limb-like ("lobed")
  • Skeleton mostly cartilagenous
  • Modern species are marine, in deep water
  • 2 extant species (first one discovered in 1938)
Coelacanth
Comorese Coelacanth, Latimeria chalumnae, model
PreservedCoelacanth
Comorese Coelacanth, Latimeria chalumnae, preserved specimen
Los Angeles Museum of Natural History
Axelrodichthys
Models of some extinct coelacanths (Actinistia). Note that the earlier forms were quite small and lacked the symmetric 3-lobed tail of more derived species.
Cardiosuctor Fossil
Fossil of the posterior portion of Caridosuctor populosum, a coelacanth of the Carboniferous Period; note the 3-lobed tail; Montana
Whiteia Fossil
Whiteia woodwardi fossil; Early Triassic Period, Madagascar
Coccoderma Fossil
Coccoderma barvaricum fossil; Late Jurassic Period, Europe

Subclass Dipnoi — Lungfishes

Characteristics

  • Elongated bodies
  • Dorsal, caudal, anal fins fused into single rear fin
  • Fins flipper-like or reduced to long filaments
  • Paired lungs
  • Live in tropical rivers or swamps prone to drying
  • 6 living species
West African Lungfish
West African Lungfish, Protopterus annectens; Order Lepidosireniformes
Marbled African Lungfish
Marbled African Lungfish, Protopterus aethiopicus; Order Lepidosireniformes
Australian Lungfish
Australian Lungfish, Neoceratodus forsteri; Order Ceratodontiformes
Scaumenacia Fossil Lungfish
Cast of Fossil Lungfish, Scaumenacia curta (Devonian Period, Quebec)
Dipnoi Models
Models of extinct lungfishes.
Lungfish toothplate
Fossil Lungfish Pterygopalatine Toothplate, Ceratodus africanus? (Cretaceous Period, Niger)

Stem Tetrapodamorpha & Tetrapod Origins

Characteristics

  • The following image depicts the earliest tetrapods (Acanthostega and Ichthyostega) with some closely related lobe-finned fishes
  • All date from the late Devonian Period
  • Osteolepiform fishes — e.g. Osteolepis (at right) and Hyneria, Mandageria & Eusthenopteron (below) — share with tetrapods various skull characteristics, internal nostrils and labyrinthodont teeth (with folded enamel)
  • They also have fins with distinct humerus, ulna, radius or femur, tibia, fibula
  • All of these species probably lived in fresh water (only Ichthyostega was probably partially terrestrial)
Osteolepis fossil
Osteolepis panderi fossi; Devonian Period, Scottland; Order Osteolepiformes

osteolepiforms
Models of basal tetrapodomorphs: the "osteolepiform" fishes.
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Tetrapods
Phylogenetic sequence for the origin of tetrapods.
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Acanthostega fossil Ichthyostega Skull
Cast of partial Acanthostega gunneri Fossil (Wyoming Dinosaur Center) Cast of Ichthyostega Skull
This page last updated 21 January 2024 by Udo M. Savalli ()
Images and text © Udo M. Savalli. All rights reserved.