Bio310 – Fish Skeleton and Evolution

Fish Evolution

• Vertebrata includes all craniates; may or may not exclude Myxiniformes (hagfishes), which lack vertebrae.
• Craniata encompasses all organisms with a chondrocranium, including Myxiniformes.
• Gnathostomata excludes jawless fishes (Petromyzontiformes and Myxiniformes).
• Osteichthyes includes all jawed fishes, excluding Chondrichthyes (sharks and rays).
• Sarcopterygii refers to lobe-finned fishes, excluding Actinopterygii (ray-finned fishes).
• Jawless fishes include living hagfish and lampreys, as well as extinct ostracoderms.

Origin of Jaws

• Placoderms are the first vertebrates with true hinged jaws (extinct).
• Chondrichthyes comprises living sharks, skates, rays, and chimaeras.
• Acanthodii are an extinct group of fish noted for their spiny features.
• Actinopterygii are categorized into basal groups (e.g., bichirs, sturgeons, gars) and derived teleosts.

Synapomorphies of Vertebrata

• Key adaptations include predation, bone and cartilage structures, a developed head (including the brain), neural crest cells, a thyroid derived from endostyle, and specialized nephron structures instead of flame cells.
• Segmentation (metamerism) is a characteristic feature of the vertebrate body plan, allowing evolutionary adaptations.

Fish Development

• Gastrulation is crucial for embryo formation, impacting overall body structure.
• Splanchnopleur is the tissue layer giving rise to the gut and involved in feeding, while somatopleur gives rise to body structures and is involved in locomotion and defense.
• Evolutionarily, the ability to capture larger prey played a significant role in vertebrate emergence.

Skeletal Development

• Living bony fishes possess two bone types: cartilage replacement (endochondral) bones and dermal bones.
• The internal skeleton (e.g., ribs) is primarily composed of endochondral bone, while dermal bones provide armor or structural support.

Evolution of the Skull

• Evolution shows a trend toward the fusion and reduction of bony elements from ancient actinopterygians to modern teleosts.
• Hagfish exhibit a simple cranial structure, while lampreys lack dermal cranial components due to secondary loss.
• Jaw suspension types include amphistylic, hyostylic, and autostylic, varying in structural support and evolutionary implications.

Branchial Complex

• Structures associated with the gills and jaw function differ significantly between jawless fishes and gnathostomes in terms of element articulation and position.

Postcranial Skeleton

• The vertebral column includes two sections: trunk (precaudal) vertebrae and caudal vertebrae.
• Precaudal vertebrae feature neural arches, centra, and potential rib attachments, while caudal vertebrae have a focus on the tail structure.

Caudal Fin Types

• Protocercal tail: an undifferentiated tail found in ancient fishes and some modern forms.
• Heterocercal tail: characterized by an upward turn at the vertebral axis; typically seen in chondrichthyans and certain early actinopterygians.
• Homocercal tail: features symmetrical fin rays with a fused spike-like structure (urostyle) at the end, commonly present in many modern bony fishes.

This quiz covers essential topics in Bio310 regarding fish anatomy, including the evolution of their skeletons, skin, and scales. Students will explore both extant and extinct species, focusing on the cranial and postcranial structures, fins, and scales. Prepare to test your knowledge on the fascinating world of fish evolutionary biology.