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Paleobiology, 47(2), 2021, pp. 198–220 DOI: 10.1017/pab.2020.24 Article Estimating dispersal and evolutionary dynamics in diploporan blastozoans (Echinodermata) across the great Ordovician biodiversification event Adriane R. Lam†, Sarah L. Sheffield† , and Nicholas J. Matzke Abstract.—Echinoderms make up a substantial component of Ordovician marine invertebrates, yet their speciation and dispersal history as inferred within a rigorous phylogenetic and statistical framework is lacking. We use biogeographic stochastic mapping (BSM; implemented in the R package BioGeoBEARS) to infer ancestral area relationships and the number and type of dispersal events through the Ordovician for diploporan blastozoans and related species. The BSM analysis was divided into three time slices to ana- lyze how dispersal paths changed before and during the great Ordovician biodiversification event (GOBE) and within the Late Ordovician mass extinction intervals. The best-fit biogeographic model incorporated jump dispersal, indicating this was an important speciation strategy. Reconstructed areas within the phyl- ogeny indicate the first diploporan blastozoans likely originated within Baltica or Gondwana. Dispersal, jump dispersal, and sympatry dominated the BSM inference through the Ordovician, while dispersal paths varied in time. Long-distance dispersal events in the Early Ordovician indicate distance was not a significant predictor of dispersal, whereas increased dispersal events between Baltica and Laurentia are apparent during the GOBE, indicating these areas were important to blastozoan speciation. During the Late Ordovician, there is an increase in dispersal events among all paleocontinents. The drivers of disper- sal are attributed to oceanic and epicontinental currents. Speciation events plotted against geochemical data indicate that blastozoans may not have responded to climate cooling events and other geochemical perturbations, but additional data will continue to shed light on the drivers of early Paleozoic blastozoan speciation and dispersal patterns. Adriane R. Lam. *Department of Geological Sciences and Environmental Studies, Binghamton University, 4400 Vestal Parkway East, P.O. Box 6000, Binghamton, New York 13902, U.S.A.; and Department of Geosciences, University of Massachusetts Amherst, 627 North Pleasant Street, 233 Morrill Science Center, Amherst, Massachusetts 01003, U.S.A. E-mail: [email protected]. *Present address: Department of Geological Sciences and Environmental Studies, Binghamton University, 4400 Vestal Parkway East, P.O. Box 6000, Binghamton, New York 13902, U.S.A. Sarah L. Sheffield. School of Geosciences, University of South Florida, 4202 East Fowler Avenue NES 107, Tampa, Florida 33620, U.S.A. E-mail: ssheffi[email protected] Nicholas J. Matzke. School of Biological Sciences, University of Auckland, 3A Symonds Street, Auckland Central, Auckland 1010, New Zealand. E-mail: [email protected] Accepted: 13 May 2020 Data available from the Dryad Digital Repository: https://doi.org/10.5061/dryad.4tmpg4f6j † These authors contributed equally to this work and are therefore listed alphabetically by last name. Introduction 2009). The early Paleozoic experienced large shifts in geochemical cycles (Haq and Schutter Echinoderms show complex patterns of mor- 2008; Trotter et al. 2008; Rasmussen et al. phological disparity and taxonomic diversity 2016; Albanesi et al. 2019) that impacted micro- throughout their evolutionary history (Sumrall fossil and marine invertebrate groups (reviewed 1997; Deline 2015; Deline and Thomka 2017; in Stigall et al. 2019), suggesting that blastozoan Deline et al. 2020) and have been suggested to echinoderms would have been impacted. respond to long-term environmental and However, there are limited studies that have climatic patterns (Paul 1968; Clausen 2004; analyzed the paleobiogeography of extinct echi- Dickson 2004; Clausen and Smith 2005, 2008; noderms to infer how they evolved and dispersed Zamora and Smith 2008; Rahman and Zamora in response to major climatic perturbations. © 2020 The Paleontological Society. All rights reserved. This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution, and reproduction in any medium, provided the original work is properly cited. 0094-8373/21 Downloaded from http://pubs.geoscienceworld.org/paleobiol/article-pdf/47/2/198/5304181/s009483732000024xa.pdf by guest on 01 October 2021 EVOLUTIONARY DYNAMICS OF DIPLOPORAN ECHINODERMS 199 Of the blastozoan echinoderms, we primarily et al. 2017; Stigall et al. 2017). The Ordovician is focus on the Diploporita in this study. Diplo- a critical time to investigate in order to under- poritan echinoderms (Ordovician– stand patterns of evolution and dispersal, as Devonian) appeared in the fossil record in two of the largest diversity booms and busts Lower Ordovician rocks in the Prague Basin, occur within this period: the great Ordovician and quickly gained high biogeographic diver- biodiversification event (GOBE) and the Late sity and morphological disparity (Lefebvre Ordovician mass extinction (LOME). To date, et al. 2013); all three large groupings within there is no information regarding the speciation Diploporita (i.e., Asteroblastida, Sphaeroni- types and dispersal patterns of diploporan tida, and Glyptosphaeronitida) are found in species, and few regarding echinoderms (a not- similarly aged strata within the Prague Basin. able exception being Bauer 2020) within a rigor- Diploporitans were originally placed in the ous phylogenetic and statistical framework same group by the presence of diplopore through the Ordovician Period. As diploporans (double-pore) respiratory structures, as all blas- were likely reevolving respiratory structures tozoan groups are traditionally classified by through their evolutionary history, it is critical their respiratory structures (Sprinkle 1973). to assess why this pattern occurred. During However, it is suspected that many groups of the Ordovician, organisms like diploporans blastozoans are not monophyletic and that and other blastozoans were likely responding respiratory structures might be convergent to changing conditions, such as increasing (Paul 1988; Sumrall 2010; Sheffield and Sumrall oxygen levels (e.g., Lenton et al. 2018), by 2017, 2019a). Sheffield and Sumrall (2019a), the evolving these respiratory structures and first study to place diplopore-bearing echino- other morphological features. derms within a phylogenetic framework, con- In this contribution, we use the R package cluded that Diploporita is likely polyphyletic BioGeoBEARS (Matzke 2013) to infer the bio- and diplopores have evolved more than once geographic history of the diploporans through in echinoderms. As Diploporita is not a real the entire Ordovician Period. Further analysis evolutionary grouping, we refer to diplopore- of the patterns of dispersal and speciation bearing blastozoans as diploporans herein. within the group is investigated using biogeo- While biogeographic patterns of blastozoan graphic stochastic mapping (BSM; Dupin et al. echinoderms have been explored to a degree 2017). These analyses are conducted to (1) inves- (e.g., Lefebvre 2007; Nardin and Lefebvre tigate the origin of the diploporan echinoderms; 2010; Lefebvre et al. 2013; Zamora et al. 2013), (2) assess the contribution of vicariance, disper- these studies have treated blastozoan groups sal, and founder-event speciation (or “jump as monophyletic, which can limit our under- dispersal”) that led to the early Paleozoic radi- standing of biogeographic and evolutionary ation of the diploporans; and (3) reconstruct patterns. Further, these studies have largely the source and directionality of dispersal events been conducted by analyzing the counts of before, during, and after the GOBE. echinoderm taxa within stratigraphic locations, not through phylogenetic methods. Similarly, Background many studies of diversity curves, origination, and extinction rates of Paleozoic echinoderms The Ordovician Earth System.—The Ordovi- have been conducted at the genus level, with- cian Period (485.4–443.8 Ma; Ogg et al. 2016)was out the context of evolution (e.g., Nardin and a time of increased tectonic activity, widely dis- Lefebvre 2010). Interpretation of such patterns persed continents, and major climatic shifts. of evolution within a phylogenetic framework Throughout the entire study interval, volcanic is important, because biogeographic processes island arcs fringed the major paleocontinents are critical for understanding large-scale pat- and terranes (e.g., Fitton and Hughes 1970;Ped- terns in biodiversity and paleoecology through ersen et al. 1992;Harperetal.1996; Glen et al. time, particularly through the Middle to Late 1998; Cocks and Torsvik 2011; Samygin 2019; Ordovician (e.g., Miller 1997; Wright and Sti- Zhang et al. 2019), especially within the Iapetus gall 2013; Trubovitz and Stigall 2016; Lamsdell Ocean (Rasmussen and Harper 2011; Liljeroth Downloaded from http://pubs.geoscienceworld.org/paleobiol/article-pdf/47/2/198/5304181/s009483732000024xa.pdf by guest on 01 October 2021 200 ADRIANE R. LAM ET AL. et al. 2017). These tectonic and climatic factors column characterized by oxygen-poor and undoubtedly had a large influence on the bio- phosphate-rich conditions that lasted until the geographic patterns and evolutionary history of earliest Katian Age (Wilde 1991; Kolata et al. blastozoan echinoderms. 2001; Young