Abstract Detail

Paleobotany

Nibbelink, Megan [1], Tomescu, Alexandru [2].

What does a broader sampling of character space reveal about zosterophyll relationships?

Zosterophylls made up a significant portion of Silurian and Devonian floras, and gave rise to the lycophytes. Despite their importance in tracheophyte evolution, their taxonomy is still poorly understood. To address this issue, we analyzed a matrix of 20 genera and 40 characters. These taxa span the Lochkovian-Eifelian interval and were selected to maximize sampling of zosterophyll anatomy. We used parsimony-based phylogenetic analyses and phenetic methods to (1) explore phylogenetic relationships among zosterophylls with a more completely sampled dataset; (2) look at the influence of tree rooting and taxon sampling, and of morphological vs anatomical characters on the stability of relationships; and (3) examine how phylogenetic and phenetic methods compare in the taxonomic relationships recovered. Phenetic analyses (clustering) showed high sensitivity to taxon sampling. Nevertheless, they recovered Huia and Nothia as most similar to each other and least similar to the other zosterophylls, consistent with results of the phylogenetic analyses; and provided support for placement of Renalia among the zosterophylls. The phylogenetic analyses demonstrated that both taxon sampling and tree rooting influence resolution significantly. Trees rooted with Renalia showed higher resolution than trees rooted with our other outgroup, Psilophyton. Inclusion of Sengelia, an early lycophyte, and exclusion of the taxon with the highest percentage of missing data (Stolbergia), also yielded higher resolution. We consistently recovered three major clades: a Huia + Nothia clade sister to the rest of the ingroup, wherein a large clade includes taxa previously recovered in a sawdonialean clade, and another clade corresponds to the previously defined “nonterminate” group. The fact that the latter clade includes Sengelia, supports earlier ideas that the zosterophyll ancestor of lycophytes had nonterminate fertile axes. Whereas exclusion of morphological characters greatly diminished phylogenetic resolution, morphology-only analyses recovered a fully resolved tree that differed from that obtained using morphology + anatomy primarily in the membership of sawdonialean and “nonterminate” clades. These differences highlight the importance of broadening the sampling of morphological character space. Because both anatomy and morphology are part of the identity and evolutionary history of a species, the relationships recovered by inclusion of both morphological and anatomical characters are more likely to reflect natural evolutionary relationships. Thus, the breadth of character sampling and not the amount of phylogenetic resolution should be the primary criterion for selecting between alternative hypotheses of relationships.

1 - Humboldt State University, Biology, 1 Harpst St. , Arcata, CA, 95521, United States
2 - Humboldt State University, Department Of Biological Sciences, 1 Harpst Street, Arcata, CA, 95521, United States

Keywords:
Devonian
Paleobotany
Fossil
phylogeny
phenetics
zosterophyll.

Presentation Type: Oral Paper
Session: PL3, Paleobotany: Honoring Fran Hueber - Session 1
Location: /
Date: Tuesday, July 20th, 2021
Time: 11:15 AM(EDT)
Number: PL3003
Abstract ID:101
Candidate for Awards:Isabel Cookson Award,Maynard F. Moseley Award