HEADS AND TAILS: A CHORDATE PHYLOGENY

Area of Science:

• * Vertebrate Paleontology
• * Comparative Anatomy
• * Evolutionary Biology

Background:

• * Understanding the evolutionary history and relationships of major chordate groups is crucial for zoological classification.
• * Previous phylogenetic analyses have yielded varying results regarding the placement of extinct and extant taxa.
• * Integrating diverse data sources is key to resolving complex evolutionary trees.

Purpose of the Study:

• * To present a comprehensive cladistic analysis of chordate phylogeny.
• * To define higher chordate taxa using synapomorphies.
• * To investigate the phylogenetic positions of key fossil groups like acanthodians and placoderms.

Main Methods:

• * Cladistic analysis utilizing approximately 320 nested characters.
• * Data compilation from adult anatomy (osteology), embryology, physiology, and biochemistry.
• * Inclusion of both Recent and fossil taxa.

Main Results:

• * Established a conventional chordate higher taxon sequence: hemichordates, urochordates, cephalochordates, craniates.
• * Demonstrated cyclostomes as paraphyletic and gnathostomes as monophyletic.
• * Reclassified fossil

Conclusions:

• * The study provides a refined phylogenetic framework for chordates, clarifying relationships among major groups.
• * New interpretations of fossil taxa like acanthodians and placoderms challenge previous classifications.
• * The potential for a closer relationship between tetrapods and osteolepiform rhipidistians is re-evaluated based on new evidence.