Effects of phylogenetic uncertainty on fossil identification illustrated by a new and enigmatic Eocene iguanian

Simon G Scarpetta

doi:10.1038/s41598-020-72509-2

Abstract

Fossil identifications made in a phylogenetic framework are beholden to specific tree hypotheses. Without phylogenetic consensus, the systematic provenance of any given fossil can be volatile. Paleobiogeographic and divergence time hypotheses are contingent on the accurate systematic placement of fossils. Thus, fossil diagnoses should consider multiple topologies when phylogenetic resolution or clear apomorphies are lacking. However, such analyses are infrequently performed. Pleurodonta (Squamata: Iguania) is an ancient and frequently-studied lizard clade for which phylogenetic resolution is notoriously elusive. I describe a skull fossil of a new pleurodontan lizard taxon from the Eocene deposits of the Willwood Formation, Wyoming, and use the new taxon as a case-study to explore the effects of phylogenetic uncertainty on fossil identification. The relationships of the new taxon differ considerably among analyses, and resulting interpretations are correspondingly disparate. These results illustrate generalizable and severe issues with fossil interpretations made without consideration of alternative phylogenetic hypotheses.

Highlights

Fossil identifications made in a phylogenetic framework are beholden to specific tree hypotheses
Identifications of fossils in a phylogenetic framework are entirely tree dependent; because there is no single consensus of the Tree of Life, systematic interpretations of most fossils are generally tied to individual tree topologies estimated by analyses of specific d atasets[1]
Because there are so many different hypotheses of pleurodontan relationships, and hypotheses are broadly inconsistent among morphological datasets and between morphological and molecular analyses[8, 9, 11], topological hypothesis choice is liable to change the phylogenetic placement of fossil pleurodontans

Summary

Introduction

Fossil identifications made in a phylogenetic framework are beholden to specific tree hypotheses. Fossil diagnoses should consider multiple topologies when phylogenetic resolution or clear apomorphies are lacking. The relationships of the new taxon differ considerably among analyses, and resulting interpretations are correspondingly disparate These results illustrate generalizable and severe issues with fossil interpretations made without consideration of alternative phylogenetic hypotheses. Identifications of fossils in a phylogenetic framework are entirely tree dependent; because there is no single consensus of the Tree of Life, systematic interpretations of most fossils are generally tied to individual tree topologies estimated by analyses of specific d atasets[1]. I use two phylogenetic matrices[14, 15] and both parsimony and Bayesian methods to validate my results, and perform Bayesian hypothesis testing to evaluate support for two alternative hypotheses of the phylogenetic relationships of the new taxon

Methods

Results

Conclusion