The species concept in a long-extinct fossil group, the conodonts

Girard, Catherine; Renaud, Sabrina

doi:10.1016/j.crpv.2010.10.009

Cited by 11 publications

(20 citation statements)

References 52 publications

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“…First, this element was the most robust within the former apparatus and therefore with the highest preservation potential. Second, P1 elements display very characteristic morphological traits that make them crucial for the description of the morphological and taxonomical diversity within Palmatolepis [26] . Many of these characteristics are expressed by variations of the platform shape that can be adequately described by a morphometric analysis [27] , [28] , [29] .…”

Section: Methodsmentioning

confidence: 99%

Disparity Changes in 370 Ma Devonian Fossils: The Signature of Ecological Dynamics?

Girard¹,

Renaud²

2012

PLoS ONE

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Early periods in Earth's history have seen a progressive increase in complexity of the ecosystems, but also dramatic crises decimating the biosphere. Such patterns are usually considered as large-scale changes among supra-specific groups, including morphological novelties, radiation, and extinctions. Nevertheless, in the same time, each species evolved by the way of micro-evolutionary processes, extended over millions of years into the evolution of lineages. How these two evolutionary scales interacted is a challenging issue because this requires bridging a gap between scales of observation and processes. The present study aims at transferring a typical macro-evolutionary approach, namely disparity analysis, to the study of fine-scale evolutionary variations in order to decipher what processes actually drove the dynamics of diversity at a micro-evolutionary level. The Late Frasnian to Late Famennian period was selected because it is punctuated by two major macro-evolutionary crises, as well as a progressive diversification of marine ecosystem. Disparity was estimated through this period on conodonts, tooth-like fossil remains of small eel-like predators that were part of the nektonic fauna. The study was focused on the emblematic genus of the period, Palmatolepis. Strikingly, both crises affected an already impoverished Palmatolepis disparity, increasing risks of random extinction. The major disparity signal rather emerged as a cycle of increase and decrease in disparity during the inter-crises period. The diversification shortly followed the first crisis and might correspond to an opportunistic occupation of empty ecological niche. The subsequent oriented shrinking in the morphospace occupation suggests that the ecological space available to Palmatolepis decreased through time, due to a combination of factors: deteriorating climate, expansion of competitors and predators. Disparity changes of Palmatolepis thus reflect changes in the structure of the ecological space itself, which was prone to evolve during this ancient period where modern ecosystems were progressively shaped.

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Section: Methodsmentioning

confidence: 99%

Disparity Changes in 370 Ma Devonian Fossils: The Signature of Ecological Dynamics?

Girard¹,

Renaud²

2012

PLoS ONE

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“…Quantitative studies on conodont elements are made difficult by their lifelong accretionary mode of growth (Donoghue 1998): growth lamellae are periodically added around the elements, resulting in an increase of the number of denticles and a modification of the length:height ratio of the element during ontogeny, thereby hindering definition and identification of homologous landmarks and complicating biologically relevant comparisons (Jones et al 2009). Previous quantitative analyses on conodont elements were based on classical and/or geometric morphometrics and quantified interspecific (Croll et al 1982; Murphy and Cebecioglu 1984; Klapper and Foster 1993; Girard et al 2004a; Chen et al 2009; Girard and Renaud 2011) or intraspecific variation (Murphy and Springer 1989; Ritter 1989; Jones et al 2009; Chen et al 2016). Some authors further described evolutionary trends (Barnett 1972; Roghi et al 1995; Girard and Renaud 2007; Jones 2009) or linked some morphological evolutions to paleoenvironmental changes (Barnett 1972; Renaud and Girard 1999; Girard et al 2004b; Girard and Renaud 2008), paleobiogeography (Tolmacheva and Löfgren 2000), or functional aspects (Purnell 1994; Martínez-Pérez et al 2014a, b, 2016).…”

Section: Introductionmentioning

confidence: 99%

Deciphering the roles of environment and development in the evolution of a Late Triassic assemblage of conodont elements

Guenser¹,

Souquet²,

Dolédec³

et al. 2019

Paleobiology

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To assess evolutionary processes in deep time, it is essential to understand the roles of development and environment, both recorded through the morphological variability of fossil assemblages. Thanks to their great abundance and the high temporal resolution of their fossil record, conodont elements are ideal to address this issue. In this paper, we present the first quantitative study of a Carnian–Norian (Late Triassic) assemblage of closely related P1 conodont elements. Using geometric morphometrics (landmarks, sliding landmarks, and elliptic Fourier analysis), we explore the main axes of phenotypic variation and relate them to classically used taxonomic characters. We show that some important taxonomic features follow laws of covariation, hence highlighting developmental constraints. Furthermore, the intraspecific variation within all considered species, either Carnian or Norian forms, is similarly restricted, emphasizing, for the first time in conodont P1 elements, a common line of least resistance to evolution, which means that similar intrinsic (developmental) factors were acting on these taxa and likely biased the evolutionary trajectories of all these taxa in a similar way. Because the evolution between Carnian and Norian forms is known to have followed a trajectory that is significantly different from the line of least resistance, strong extrinsic pressures, such as environmental disturbances, were probably at play around the Carnian/Norian boundary to counteract the effects of these intrinsic, developmental constraints.

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“…The problems highlighted herein with regard to atypical Lochriea morphologies are significant to the extremely problematic concept of a ‘species’ in studies of conodonts and other extinct animal groups, where the morphology of their mineralized tissue is used as a proxy for distinct biological groupings (Girard & Renaud ). The practice of using the morphology of P 1 ‐elements to differentiate any conodont lineage is based on the assumption that the ornamentation is related directly to the biology of the organism (and is presumably functional) and that it gets faithfully inherited from generation to generation, with evolutionary forces dictating any morphological modification.…”

Section: Discussionmentioning

confidence: 99%

“…However, establishing what morphological characters would be testable within the Lochriea genus is no easy task given the somewhat subjective features currently used to define species. As discussed in Girard & Renaud (, and references therein), ‘cherry‐picking’ of convenient distinct morphologies for imaging or analyses creates a false impression of taxonomic robustness for species definitions within genera. The relative abundance of taxonomically difficult and unrecognized Lochriea specimens encountered herein raises important questions – are the current taxonomic definitions robust, and if so, why are the morphological features that currently define species given taxonomic significance while others are not?…”

Section: Discussionmentioning

confidence: 99%

Conodonts of the genus Lochriea in Ireland and the recognition of the Viséan–Serpukhovian (Carboniferous) boundary

Barham

Murray

Sevastopulo

et al. 2015

LET

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Conodonts of the genus Lochriea offer high‐resolution biostratigraphical differentiation of the upper Mississippian (Carboniferous). In particular, L. ziegleri is regarded as the most suitable index taxon for recognition of a revised Viséan–Serpukhovian boundary and selection of a Global Stratotype Section and Point. Mixed carbonate‐siliciclastic Carboniferous sections from western Ireland demonstrate that gradual morphological evolution is expressed within the Lochriea lineage, evidenced by P1‐elements with progressively more complex ornament appearing in a pulsed fashion in the Late Viséan. Significant diversification of the Lochriea conodonts occurs below the currently recognized base of the Namurian (identified by ammonoids), with which the basal Serpukhovian has been correlated in the past. The First Appearance Datum (FAD) of L. ziegleri in the Lugasnaghta Section of western Ireland is apparently coincident with the FAD's of other complexly ornamented Lochriea species (e.g. L. cruciformis) and corresponds with the Irish and British P2a ammonoid biozone and the lower part of the upper Cf6δ (MFZ15) foraminiferal biozone. The FAD of L. ziegleri in Ireland is closely related to other Lochriea morphotypes with complex ornament, which are difficult to identify to species level using current species definitions. These forms, recorded from the three sections examined (St Brendan's Well, Kilnamona and Lugasnaghta), may partly be explained as abnormal growth histories, evolutionary intermediate forms, etc. In some instances, however, the apparently consistent and novel morphotypes suggest that current Lochriea taxonomy needs to be re‐examined. Furthermore, given the close association of the morphologies with asymmetric complex ornament and L. ziegleri, these taxa may hold significance as biostratigraphical tools in their own right.

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The species concept in a long-extinct fossil group, the conodonts

Cited by 11 publications

References 52 publications

Disparity Changes in 370 Ma Devonian Fossils: The Signature of Ecological Dynamics?

Disparity Changes in 370 Ma Devonian Fossils: The Signature of Ecological Dynamics?

Deciphering the roles of environment and development in the evolution of a Late Triassic assemblage of conodont elements

Conodonts of the genus Lochriea in Ireland and the recognition of the Viséan–Serpukhovian (Carboniferous) boundary

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