Phylogeny, classification and character polarity of the Osteostraci (Vertebrata)


Sansom, R. S., 2009. Phylogeny, classification and character polarity of the Osteostraci (Vertebrata). Journal of Systematic Palaeontology, 7 (1), pp. 95-115.

Related documents:

This repository does not currently have the full-text of this item.
You may be able to access a copy if URLs are provided below. (Contact Author)

Official URL:

Related URLs:


The jawless Osteostraci are the sister taxon to jawed vertebrates and, thus, are integral to understanding the evolution of gnathostomes from a jawless ancestor. Our understanding of this episode is currently hampered by incomplete knowledge of osteostracan phylogenetics and character polarity. Previous hypotheses of osteostracan intrarelations are reviewed and synthesised into two conflicting hypotheses ‐ ’Tremataspis‐basal’ versus ’Ateleaspis‐basal’ models, both related to the ancestral morphotype of the group. Previous analyses are shown to be limited in three main regards ‐ taxonomic scope, phylogenetic methodology and character polarity. To address this problem, direct observations and reconstructions were made for every osteostracan genus. This enabled a taxonomically comprehensive analysis, utilising global parsimony and out‐group analysis. The inclusion of a morphological range of taxa from both extant and extinct osteostracan‐related clades (pteraspidomorphs, galeaspids, placoderms and gnathostomes), enables a test of osteostracan polarity and character evolution. A new phylogeny and classification for the Osteostraci is proposed, identifying three main orders ‐ Benneviaspidida, Zenaspidida and Thyestiida. The ’Ateleaspis‐basal’ model is supported along with the homology of paired pectoral fins of Osteostraci and jawed vertebrates.


Item Type Articles
CreatorsSansom, R. S.
Related URLs
DepartmentsFaculty of Science > Biology & Biochemistry
ID Code27209


Actions (login required)

View Item