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Abstract A fuller understanding of the role of developmental bias in shaping large‐scale evolutionary patterns requires integrating bias (the probability distribution of variation accessible to an ancestral phenotype) with clade dynamics (the differential survival and production of species and evolutionary lineages). This synthesis could proceed as a two‐way exchange between the developmental data available to neontologists and the strictly phenotypic but richly historical and dynamic data available to paleontologists. Analyses starting in extant populations could aim to predict macroevolution in the fossil record from observed developmental bias, while analyses starting in the fossil record, particularly the record of extant species and lineages, could aim to predict developmental bias from macroevolutionary patterns, including the broad range of extinct phenotypes. Analyses in multivariate morphospaces are especially effective when coupled with phylogeny, theoretical and developmental models, and diversity–disparity plots. This research program will also require assessing the “heritability” of an ancestral bias across phylogeny, and the tendency for bias change in strength and orientation over evolutionary time. Such analyses will help find a set of general rules for the macroevolutionary effects of developmental bias, including its impact on and interactions with the other intrinsic and extrinsic factors governing the movement, expansion, and contraction of clades in morphospace.
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GROWTH VARIATION AND DEVELOPMENTAL SEQUENCE POLYMORPHISM IN THE MIDDLE CAMBRIAN TRILOBITE ELRATHIA KINGII (MEEK)
Developmental sequence polymorphism (variation in the timing of developmental events) is a neglected form of variation, and whetherit is correlated with other forms of variation, what role it plays in shaping a species’ evolutionary trajectory, and the overall extent towhich it characterizes and can be measured in extinct species remain open questions. Intraspecific variation constitutes the rawmaterial with which natural selection shapes phenotypes over the course of evolutionary history. A complete understanding of themechanisms underpinning biological evolution therefore requires detailed knowledge of the different forms of variation by whichspecies are characterized. Intraspecific developmental variation is an important source of phenotypic variety because minordifferences in developmental pathways can result in significant differences among adult phenotypes. The fossil record provides representatives of past species, the most direct evidence we have of evolutionary change across geologictime. However, one limitation of studying fossils is that they are generally uncommon and sample sizes are often small. Intraspecificvariation of any kind is therefore rarely quantified for fossil species. Here, continuous growth and discrete developmental timing datafor the well-studied and abundant trilobite species Elrathia kingii are presented. 116 specimens representing a range of growth stageswere photographed, measured, and coded for the expression of discrete developmental transformations. The fossils are reposited atthe AMNH and were collected from a narrow stratigraphic interval in the Wheeler Formation of west central Utah. Linearmeasurements were plotted in multivariate space to construct growth series, a common practice in trilobite ontogenetic research. Inaddition to this, however, phenotypic characters associated with abrupt developmental transformations are documented for eachspecimen and coded into the growth series to illustrate the timing of these transformations relative to continuous changes in size andshape. The result is a series of plots in which overlap in developmental character states represents variation. This novel techniqueindicates that sequence polymorphism is present in E. kingii and future work will use this result as a starting point for the application ofOntogenetic Sequence Analysis.
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- Award ID(s):
- 1943082
- PAR ID:
- 10582988
- Publisher / Repository:
- Geological Society of America Abstracts with Programs
- Date Published:
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.1130/abs/2024AM-401222
