Conodont size, trophic level, and the evolution of platform elements

Abstract

Conodonts are among the first vertebrates to have evolved mineralized tooth-like structures. Among these, the so-called P1 elements are known to have been used to break down food and display a wide variety of morphologies. In particular, the repeated independent evolution of platform-like P1 elements have been suggested to correspond to similar functional constraints linked to diet. To test this hypothesis of convergence, we measured size (as element length) for various conodont taxa and used it as a proxy for trophic level. We then tested the correlation between size and platform presence/absence, both on raw data and in a phylogenetic context. Retaining or excluding the platform traits from the character matrix has limited impact on the resulting phylogeny. Contrary to platform presence/absence, size shows no phylogenetic signal. Using the raw data, size and platform presence appear positively correlated. That correlation, however, is no longer significant if one corrects for the phylogeny. We conclude that platform presence cannot be explained by an enlargement of the conodont element, be it via a trophic-level change or developmental constraints. This suggests that conodonts as a whole, and in particular platform-bearing conodonts, were an ecologically diverse group and that the various known platform types are likely to reflect different, rather than convergent, ecological niches.

Growth allometry and dental topography in Upper Triassic conodonts support trophic differentiation and molar-like element function

“…In M. communisti , as well as in E. rigoi , DNE values increased linearly with body size, where element length was used as a proxy for body size (Zhang et al, 2018; Ginot & Goudemand, 2019). This does not contradict the possible presence of a larval stage, during which conodonts had a different method of feeding (Shirley et al, 2018), because all specimens that are considered here were more mature.…”

“…The length of the element was used as a proxy for the size of the conodont animal, as has been done in previous studies (Purnell, 1993, 1994; Zhang et al, 2018; Ginot & Goudemand, 2019). The length of the element, as well as the length and the area of the platform, were measured using the 3D software MeshLab (Cignoni et al, 2008).…”

“…Conodonts changed their apparatus structure and disparity across their stratigraphic range (Dzik, 1991, 2015), possibly reflecting their evolving niches as marine ecosystems increased in complexity (Klug et al, 2010; Ginot & Goudemand, 2019). Their morphology also diversified (Martínez-Pérez et al, 2014a, 2015; Ginot & Goudemand, 2020).…”

“…Their morphology also diversified (Martínez-Pérez et al, 2014a, 2015; Ginot & Goudemand, 2020). This would suggest evolving trophic niches under the assumption that conodont element morphology is an adaptation to their diet (Jones et al, 2012a; Guenser et al, 2019; Ginot & Goudemand, 2019; Petryshen et al, 2020). There is, however, evidence from Ca isotope analysis, suggesting the existence of competition between some taxa, which indicates that trophic niches overlapped between them (Balter et al, 2019).…”

Evidence of parallel evolution in the dental elements ofSweetognathusconodonts

“…Broad, laterally expanded P 1 elements have been reconstructed to have repeatedly evolved to allow higher loads generated during mechanical food digestion [7], whereas sharp, laterally flattened elements were adapted to have a cutting function [34]. The morphological variation has been in all cases associated with expansion to new trophic niches [7,54].…”