A Bayesian approach to dynamic homology of morphological characters and the ancestral phenotype of jawed vertebrates.

Martin Rücklin,Benedict King

doi:10.7554/elife.62374

Abstract

Phylogenetic analysis of morphological data proceeds from a fixed set of primary homology statements, the character-by-taxon matrix. However, there are cases where multiple conflicting homology statements can be justified from comparative anatomy. The upper jaw bones of placoderms have traditionally been considered homologous to the palatal vomer-dermopalatine series of osteichthyans. The discovery of 'maxillate' placoderms led to the alternative hypothesis that 'core' placoderm jaw bones are premaxillae and maxillae lacking external (facial) laminae. We introduce a BEAST2 package for simultaneous inference of homology and phylogeny, and find strong evidence for the latter hypothesis. Phenetic analysis of reconstructed ancestors suggests that maxillate placoderms are the most plesiomorphic known gnathostomes, and the shared cranial architecture of arthrodire placoderms, maxillate placoderms and osteichthyans is inherited. We suggest that the gnathostome ancestor possessed maxillae and premaxillae with facial and palatal laminae, and that these bones underwent divergent evolutionary trajectories in placoderms and osteichthyans.

Highlights

The concept of homology underpins the cladistic analysis of morphological data
Primary homologues are subjected to cladistic analysis, and those that correspond to synapomorphies are considered ‘secondary homologues’; this term corresponds to the vernacular use of the term homology
We find strong support for the hypothesis of Zhu et al, 2016, that placoderm supragnathal bones are homologous to the maxilla and premaxilla of osteichthyans and maxillate placoderms (Figure 5)

Summary

Introduction

The concept of homology underpins the cladistic analysis of morphological data. Testing of homology is usually considered a two-step process (Patterson, 1982a; Pinna, 1991). Primary homologues are subjected to cladistic analysis, and those that correspond to synapomorphies are considered ‘secondary homologues’; this term corresponds to the vernacular use of the term homology (similarity due to common ancestry). The starting point for a cladistic analysis, the character-by-taxon matrix, is a set of primary homology statements. Primary homology statements are based upon ‘homology criteria’ (Patterson, 1988; Rutishauser and Moline, 2005). Second is the test of conjunction: if two structures are found together on a single animal, they cannot be homologous (Patterson, 1988)

Methods

Results

Conclusion