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Cited by 262Evolution and Paleontology StudiesMorphological variations and asymmetryPaleontology and Evolutionary Biology

Clades reach highest morphological disparity early in their evolution

Open access
Hughes, Martin, Gerber, Sylvain, Wills, Matthew Albion·2013·Proceedings of the National Academy of Sciences
DOI 10.1073/pnas.1302642110PMC PMC3752257
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Abstract

There are few putative macroevolutionary trends or rules that withstand scrutiny. Here, we test and verify the purported tendency for animal clades to reach their maximum morphological variety relatively early in their evolutionary histories (early high disparity). We present a meta-analysis of 98 metazoan clades radiating throughout the Phanerozoic. The disparity profiles of groups through time are summarized in terms of their center of gravity (CG), with values above and below 0.50 indicating top- and bottom-heaviness, respectively. Clades that terminate at one of the “big five” mass extinction events tend to have truncated trajectories, with a significantly top-heavy CG distribution overall. The remaining 63 clades show the opposite tendency, with a significantly bottom-heavy mean CG (relatively early high disparity). Resampling tests are used to identify groups with a CG significantly above or below 0.50; clades not terminating at a mass extinction are three times more likely to be significantly bottom-heavy than top-heavy. Overall, there is no clear temporal trend in disparity profile shapes from the Cambrian to the Recent, and early high disparity is the predominant pattern throughout the Phanerozoic. Our results do not allow us to distinguish between ecological and developmental explanations for this phenomenon. To the extent that ecology has a role, however, the paucity of bottom-heavy clades radiating in the immediate wake of mass extinctions suggests that early high disparity more probably results from the evolution of key apomorphies at the base of clades rather than from physical drivers or catastrophic ecospace clearing.

Integrity signals

Registry

Crossref · 10.1073/pnas.1302642110

Cites

76 of 76 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Claims the paper makes

0 of 27 cited sources checked · 0 supported · 0 flagged

  • Findingown data

    The relative frequencies of top-heavy and bottom-heavy clades differed between clades terminating at mass extinctions and those terminating at other times, whether all clades or only significantly skewed clades were included.

    “Likelihood ratio tests also confirmed that the relative frequencies of top-and bottom-heavy clades terminating at mass extinctions and at other times were different, whether including all clades (G = 7.648, P = 0.006) or only those with significant skew (G = 13.022,P < 0.001).”
    Quote in the paperSubstantial claim
  • Findingown data

    The only temporal pattern in disparity profile shapes detected in the data was a significant tendency toward top-heaviness in clades terminating coincident with a mass extinction.

    “The only temporal pattern in disparity profile shapes detected in our data was the significant tendency toward top-heaviness in those clades terminating coincident with a mass extinction [which predominantly result from physical drivers (59)].”
    Quote in the paperSubstantial claim
  • Findingown data

    More than half of the study clades had disparity profiles that were neither significantly top-heavy nor significantly bottom-heavy.

    “Over half of our study clades had disparity profiles that were neither significantly top-nor bottom-heavy.”
    Quote in the paperNot a substantial claim
  • Findingown data
    § Clades reach highest morphological disparity early in their evolution

    In the meta-analysis of 98 metazoan clades, clades that did not end at a mass extinction tended to reach their maximum morphological disparity relatively early in their evolutionary histories.

    “The remaining 63 clades show the opposite tendency, with a significantly bottom-heavy mean CG (relatively early high disparity).”
    • Also stated in: § Results and Discussion · plain
      “Therefore, clades that do not terminate at a mass extinction do indeed tend to reach their highest levels of disparity relatively early in their evolutionary histories (20).”
    • Also stated in: § Results and Discussion · plain
      “Of these, the proportion (two-thirds) that were either significantly bottom-heavy or showed early saturation (two mutually compatible conceptions of early high disparity) was significantly greater than the proportion that were either significantly top-heavy or showed late saturation (late high disparity) (two-sample test for equality of proportions; χ 2 = 4.613, P = 0.016).”
    Quote in the paperSubstantial claim
    • Rests on an assumption: The 98 sampled clades are representative of metazoan clades across the Phanerozoic.
    • Rests on an assumption: The 63 clades not terminating at a mass extinction were free-evolving and not otherwise truncated.
  • Findingown data

    For 29 of the 54 symmetrical clades, the null hypothesis that initial disparity did not differ from the maximum disparity achieved by the clade could not be rejected.

    “For 29 of the 54 symmetrical groups, we were unable to reject this null.”
    Quote in the paperSubstantial claim
  • May combine two claims. 18
  • Classified as probably not a substantial claim. 14

  • May combine two claims.

    Findingown data

    Time-averaged indices masked some apparent differences in clade disparity profiles within and between eras; there were more bottom-heavy clades in the Late Paleozoic than top-heavy, with the opposite pattern in the Mesozoic.

    “Time-averaged indices masked some apparent differences in clade disparity profiles within and between eras; most notably, there were more bottom-heavy (CG <0.5) clades in the Late Paleozoic than top-heavy (CG >0.5) clades, with the opposite pattern in the Mesozoic.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data

    Extant clades truncated by the Recent had a median center of gravity significantly above 0.5, but this did not differ from fossil clades terminating at a mass extinction.

    “These extant clades (truncated by the present) had a median CG significantly greater than 0.500 (V = 1,150, P < 0.001) but indistinguishable from that for fossil clades terminating at a mass extinction (W = 924, P = 0.980).”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data

    Late saturation was observed in 32 symmetrical clades, and 12 of these also ended at a mass extinction.

    “Although late saturation was observed in 32 symmetrical clades, 12 of these also ended at a mass extinction (and were therefore likely to have been prematurely truncated).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    Across the 98-clade sample, the mean disparity profile center of gravity was 0.495 and the median was 0.501, which was indistinguishable from 0.5.

    “Across our sample of 98 clades (including those terminating coincident with a mass extinction), we found a mean disparity profile of CG of 0.495, with a median CG (0.501) indistinguishable from 0.5 (V = 2,429, P = 0.992).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data
    § Clades reach highest morphological disparity early in their evolution

    Clades that ended at one of the big five mass extinctions tended to have truncated trajectories and a significantly top-heavy center-of-gravity distribution overall.

    “Clades that terminate at one of the”
    • Also stated in: § Results and Discussion · plain
      “By contrast, the 35 clades ending at mass extinctions had a mean CG significantly greater than 0.500 (t = 3.901, P < 0.001).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Premisecitation

    Only one prior study focused on extinction selectivity itself; the others investigated the evolution of extinction survivors.

    “Moreover, only one of these studies (44) focused on extinction selectivity per se; all others investigated the subsequent evolution of extinction survivors.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [44] source

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  • May combine two claims.

    Interpretationreasoning

    Extant clades are more likely to have flat-topped disparity profiles, which would artifactually shift their center of gravity upward relative to a hypothetical complete clade history.

    “Extant clades are more likely to have”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Premisecitation

    New species arise only by fission of existing species, and extinctions can be random with respect to the phylogenetic tree.

    “New species can only arise from the fission of existing ones (clades initially diversify from a single species and therefore a single point in morphospace), whereas extinctions can be random with respect to this same tree (34).”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [34] source

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  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Premisecitation

    The manner in which these data have been analyzed is equally variable, although most studies implement some form of data reduction and ordination.

    “Second, the manner in which these data have been analyzed is equally variable, although most studies implement some form of data reduction and ordination (10,12).”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites [10] source

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  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Premisecitation

    There are many possible indices of morphological disparity, and these describe different aspects of morphospace occupation.

    “Third, there are many possible indices of morphological disparity, and these are known to describe different aspects of morphospace occupation (34).”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [34] source

      Not checked in the free run.

  • May combine two claims.

    Interpretationcitation

    Early high disparity patterns imply an unsampled period of cladogenesis or ghost ranges at the base of the clade, which either occurred too fast for stratigraphic resolution or was not fossilized.

    “Early high patterns inevitably imply an unsampled period of cladogenesis (or the existence of ghost ranges) at the base of the clade, but this either occurs too fast for the available stratigraphic resolution or is not fossilized (11,50).”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites [11] source

      Not checked in the free run.

    • cites [50] source

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  • Classified as probably not a substantial claim.

    Premisecitation

    Mass extinctions have influenced how clades explored morphospaces.

    “Mass extinctions have undoubtedly influenced the manner in which clades have explored morphospaces (42), but this phenomenon received little”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [42] source

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  • Classified as probably not a substantial claim. May combine two claims.

    Premisenone given

    The type of data used in published case studies is highly variable, as is the information these data convey.

    “First, the type of data used is highly variable (outlines, landmarks, and discrete characters), as is the information that these data are intended to convey (shape, form, or homologous characters of the entire organism or of particular organ systems).”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Premisecitation

    Global shifts in climate, sea level, and ocean chemistry, coupled with elevated extinction and turnover, affected ecospace availability throughout the Phanerozoic.

    “More generally it is likely that global shifts in climate, sea level, and ocean chemistry [coupled with the elevated rates of extinction and turnover that these phenomena engender (56-58)] affected the availability of ecospace throughout the Phanerozoic.”
    Quote in the paperNot a substantial claim0 of 3 sources checked
    • cites [56] source

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    • cites [58] source

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  • Classified as probably not a substantial claim.

    Study design and conductnone given

    The study avoided taxonomically overlapping cases or datasets obviously derivative of others.

    “We avoided taxonomically overlapping cases or datasets obviously derivative of others.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    Mass extinctions predominantly result from physical drivers.

    “which predominantly result from physical drivers (59)”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [59] source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based). May combine two claims.

    Interpretationreasoning

    Clades terminating at a mass extinction might be similarly truncated and likely have higher center-of-gravity values for similar reasons.

    “However, clades terminating at a mass extinction event might be similarly truncated and are likely to have higher CGs for similar reasons.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Premisecitation

    Mass extinctions need not increase subsequent ecospace availability and may cause its collapse.

    “However, mass extinctions need not increase the subsequent availability of ecospace but may actually cause its collapse (60).”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [60] source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Premisecitation

    Many recent studies followed similar protocols, and the authors adopted these methods as a unifying approach.

    “Many studies have recently followed similar protocols (27,(36)(37)(38), and we adopted these methods here as a unifying approach.”
    Quote in the paperNot a substantial claim0 of 3 sources checked
    • cites [27] source

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  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Premisecitation

    Morphological change during colonization of new ecospace may be rapid because transitions are unusually large or because cladogenesis rates are unusually high.

    “Morphological change under these circumstances may be rapid either because transitions are unusually large or because rates of cladogenesis are unusually high (even with”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [29]

      Not checked in the free run.

  • Classified as probably not a substantial claim. May combine two claims.

    Study design and conductreasoning

    The use of 0.5 as a null is slightly simplistic but biased against the principal finding that clades not terminating at a mass extinction are bottom-heavy on average.

    “Our use of 0.5 as a null is slightly simplistic, therefore, but biased against our principal finding (namely that clades not terminating at a mass extinction event are bottom-heavy on average).”
    Quote in the paperSubstantial claim

  • Classified as probably not a substantial claim.

    Study design and conductnone given

    Within datasets, strict rules were applied to ensure sampling was adequately uniform across known operational taxonomic units and through time, amalgamating taxa where necessary.

    “Within datasets, strict rules were applied to ensure that sampling was adequately uniform across known operational taxonomic units (OTUs) and through time, amalgamating taxa where necessary (Dataset S1).”
    Quote in the paperSubstantial claim

  • Classified as probably not a substantial claim.

    Premisenone given

    The manner in which trajectories of disparity through time are quantified and classified is variable.

    “Fourth, the manner in which trajectories of disparity through time are quantified and classified is also variable.”
    Quote in the paperSubstantial claim

  • Classified as probably not a substantial claim.

    Premisecitation
    § Clades reach highest morphological disparity early in their evolution

    The empty ecospace model predicts that clades will radiate and diversify more rapidly when colonizing a new environment.

    “The”
    Quote in the paperSubstantial claim0 of 3 sources checked
    • cites [52]

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    • cites [53] source

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24 of 24

  • The paper relies on this without support.

    The early high disparity model had not been tested systematically before this study.

    “However, the validity of this early high disparity model has never been tested systematically.”

  • The paper relies on this without support.

    The 98 sampled clades are representative of metazoan clades across the Phanerozoic.

    “We compiled published discrete morphological and stratigraphic data for 98 vertebrate and invertebrate clades radiating throughout the Phanerozoic (Dataset S2).”

  • The paper relies on this without support.

    Key innovations can arise at any time.

    “key innovations (which can evolve at any time)”

  • The paper relies on this without support.

    The 63 clades not terminating at a mass extinction were free-evolving and not otherwise truncated.

    “we again focused on the 63”
4 of 4

Claims other papers make about this one

Each is checked against this paper’s own text: does it say what the citing paper says it does?

  • Early bursts of morphological and taxonomic diversity should be associated with adaptive radiations, and many have been identified in the fossil record.

    “Early bursts of morphological and taxonomic diversity should be associated with adaptive radiations [5] and many have been identified in the fossil record, ranging from the Cambrian radiation [27] to many invertebrate [28,29] and vertebrate [30,31] clades.”

    From Novelty and Innovation in the History of Life (2015) · cites this paper as [29]

    The Results and Discussion report that fossil clades tend to reach their highest morphological disparity early, and Materials and Methods says the sample includes invertebrate clades. The paper distinguishes morphological disparity from taxonomic diversity; it does not establish an early burst of taxonomic diversity. The adaptive-radiation expectation is attached to a different citation in the citing sentence. (LLM, conf=0.85)

    Experimental — accuracy not yet measured

Cites

Flagged first, then by citations

2 of the 78 references couldn’t be matched to a known paper.

Research works printed but not linked: 2

  1. SJ Gould Wonderful Life (W. W. Norton, New York, 1989).
  2. ENK Clarkson Invertebrate Palaeontology & Evolution (Wiley, New York, 1998).

Cited by

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Related

Authors
Hughes, M., Gerber, S., & Wills, M. A.
Affiliations
University of Bath (GB)
ORCID
Venue
Proceedings of the National Academy of Sciences
Publisher
National Academy of Sciences
Published
2013-07-24
Volume
110
Issue
34
Pages
13875-13879
ISSN
  • 0027-8424 (ISSN-L)
  • 1091-6490
DOI
10.1073/pnas.1302642110
PMC
PMC3752257
OpenAlex
W2040344633
Cited by
262
References
78
Citations by year
2026: 14 · 2025: 18 · 2024: 10 · 2023: 19 · 2022: 13 · 2021: 23 · 2020: 24 · 2019: 38 · 2018: 26 · 2017: 24 · 2016: 23 · 2015: 17 · 2014: 11 · 2013: 2
FWCI
11.97
Type
journal article
Language
en
Open access
Locations
  • Proceedings of the National Academy of Sciences (publishedVersion)
  • Europe PMC (PubMed Central) (publishedVersion)
  • PubMed Central (publishedVersion)
  • PubMed (publishedVersion)
Funders
Leverhulme Trust (F/00 351/Z)
Topics
  • Physical Sciences › Earth and Planetary Sciences › Paleontology › Evolution and Paleontology Studies
  • Physical Sciences › Mathematics › Geometry and Topology › Morphological variations and asymmetry
  • Physical Sciences › Earth and Planetary Sciences › Paleontology › Paleontology and Evolutionary Biology
Keywords
morphological disparity, macroevolutionary trends, center of gravity, mass extinction, Phanerozoic, apomorphies, developmental constraints
MeSH terms
Anatomy, Comparative, Biological Evolution, Models, Biological, Phylogeny, Species Specificity

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