A revision of Prolimulus woodwardi Fritsch, 1899 with comparison to other highly paedomorphic belinurids.

Lorenzo Lustri,Lukáš Laibl,Russell D C Bicknell

doi:10.7717/peerj.10980

Lorenzo Lustri, Lukáš Laibl + Show 1 more

Open Access

https://doi.org/10.7717/peerj.10980

Copy DOI

Abstract

Xiphosurida is an ingroup of marine Euchelicerata often referred to as “living fossils”. However, this oxymoronic term is inapplicable for Paleozoic and early Mesozoic forms, as during these periods the group experienced notable evolutionary radiations; particularly the diverse late Palaeozoic clade Belinurina. Despite the iconic nature of the group, select species in this clade have been left undescribed in the light of recent geometric morphometric and phylogenetic considerations and methodologies. To this end, we re-describe Prolimulus woodwardi Fritsch, 1899 using new and type specimens to reveal more details on appendage anatomy and possible ecology. Furthermore, we present geometric morphometric and phylogenetic analyses that uncover relationships between P. woodwardi and other belinurids without genal spines. Both approaches highlight that a clade containing Prolimulus Fritsch, 1899, Liomesaspis Raymond, 1944, Alanops Racheboeuf, Vannier & Anderson, 2002 and Stilpnocephalus Selden, Simonetto & Marsiglio, 2019 may exist. While we do not erect a new group to contain these genera, we note that these genera exemplify the extreme limits of the Belinurina radiation and a peak in horseshoe crab diversity and disparity. This evidence also illustrates how changes in heterochronic timing are a key evolutionary phenomenon that can drive radiations among animals.

Highlights

Xiphosurida, are an extant group of euchelicerates with an extensive fossil record spanning most of the Phanerozoic (Van Roy, Briggs & Gaines, 2015)
They are often referred to as ‘‘living fossils’’ (Størmer, 1952), considered examples of stabilomorphism (Kin & Błażejowski, 2014) and morphological conservatism (Bicknell & Pates, 2020). Such statements are mostly applicable to the late Mesozoic and Cenozoic forms (Avise, Nelson & Sugita, 1994; Rudkin & Young, 2009; Kin & Błażejowski, 2014; Lamsdell & McKenzie, 2015; Błazejowski, Gieszcz & Tyborowski, 2016; Bicknell & Pates, 2019; Bicknell et al, 2019b; Bicknell & Pates, 2019)
We present a phylogenetic analysis including P. woodwardi and the morphologically comparable Stilpnocephalus pontebbanus Selden, Simonetto & Marsiglio, 2019, as well as a geometric morphometric analysis of species within Belinurina

Summary

Introduction

Xiphosurida, are an extant group of euchelicerates with an extensive fossil record spanning most of the Phanerozoic (Van Roy, Briggs & Gaines, 2015). They are often referred to as ‘‘living fossils’’ (Størmer, 1952), considered examples of stabilomorphism (Kin & Błażejowski, 2014) and morphological conservatism (Bicknell & Pates, 2020). Such statements are mostly applicable to the late Mesozoic and Cenozoic forms (Avise, Nelson & Sugita, 1994; Rudkin & Young, 2009; Kin & Błażejowski, 2014; Lamsdell & McKenzie, 2015; Błazejowski, Gieszcz & Tyborowski, 2016; Bicknell & Pates, 2019; Bicknell et al, 2019b; Bicknell & Pates, 2019).

Methods

Results

Discussion

Conclusion