Definition

1. Noun:
   • A fish of the order Crossopterygii: A member of an ancient group of bony fishes, most of which are known only from fossils. This group is significant in evolutionary history as it includes the ancestors of tetrapods (four-limbed vertebrates). The coelacanth is a famous living example.

Examples of Usage

• Noun:
  • The fossilized fin of the crossopterygian provided clues about the evolution of limbs.
  • Scientists were amazed to discover a living crossopterygian, the coelacanth, in the 20th century.

Advanced Usage

• In evolutionary biology: The term is used to discuss transitional forms between fish and amphibians.
  • The study of crossopterygian anatomy is crucial for understanding the water-to-land transition in vertebrates.

Variants and Related Words

• Crossopterygii (noun): The taxonomic order to which crossopterygians belong.
  • The order Crossopterygii was once thought to be entirely extinct.
• Lobe-finned fish (noun): A common name for fish in the class Sarcopterygii, which includes crossopterygians.
  • Lobe-finned fish, like the crossopterygian, have fleshy, limb-like fins.

Synonyms

• Lobe-finned fish: A broader term encompassing crossopterygians and lungfish.
• Sarcopterygian: A member of the class Sarcopterygii, which includes crossopterygians and lungfish.

Noun

1. any fish of the order Crossopterygii; most known only in fossil form