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Conodont affinity and chordate phylogeny.

P C Donoghue¹, P L Forey, R J Aldridge

¹School of Earth Sciences, University of Birmingham, Edgbaston, UK. p.c.j.donoghue@bham.ac.uk

Biological Reviews of the Cambridge Philosophical Society

|July 6, 2000

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Conodonts, ancient jawless vertebrates, are confirmed as the earliest jawed vertebrates (Gnathostomata). Their mineralized skeletons evolved before bone, with complex sensory systems arising multiple times.

Area of Science:

Paleontology
Vertebrate Evolution
Phylogenetics

Background:

Conodonts are extinct marine vertebrates known from fossilized tooth-like structures.
Previous interpretations of conodont relationships to vertebrates have varied.
Recent advances in understanding conodont hard tissues provide new data for phylogenetic analysis.

Purpose of the Study:

To re-evaluate the phylogenetic position of conodonts within the Chordata.
To investigate the evolution of vertebrate skeletal and sensory systems using conodonts as a model.
To establish the earliest origins of mineralized skeletons and jawed vertebrates.

Main Methods:

A comprehensive phylogenetic analysis using 17 chordate taxa and 103 morphological, physiological, and biochemical characters.

Related Experiment Videos

Inclusion of conodonts as a primary taxon in the analysis.

Experimental variations including character coding, taxon deletion, and constraint trees.

Main Results:

Conodonts are determined to be cladistically more derived than hagfishes and lampreys due to their mineralized dermal skeleton.
Conodonts represent the most primitive (plesiomorphic) member of the total group Gnathostomata (jawed vertebrates).
The evolution of neuromasts within canals appears to have occurred independently multiple times, and vertebrate mineralized skeletons originated as odontodes.

Conclusions:

Conodonts are basal gnathostomes, providing insights into early vertebrate evolution.
The evolution of the vertebrate skeleton and sensory systems was complex, involving multiple independent origins.
Phylogenetic analysis predicts the Cambrian existence of hagfishes and lampreys, consistent with fossil evidence.