<i>Globacrochordiceras</i>gen. nov. (Acrochordiceratidae, late Early Triassic) and its significance for stress-induced evolutionary jumps in ammonoid lineages (cephalopods)

Monnet, Claude; Bucher, Hugo; Brayard, Arnaud; Jenks, James F.

doi:10.1002/mmng.201300010

Cited by 9 publications

(1 citation statement)

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“…However, morphological variation in response to environmental stressors more broadly is a well-studied feature of the ammonoid fossil record. For example, spectacular morphological changes and evolutionary “jumps” within lineages occur during recoveries from carbon cycle perturbations and extinctions (e.g., Monnet et al 2013), and morphological changes are commonly seen coincident with sea-level fluctuations and faunal invasions in epeiric seaway basins, particularly within endemic lineages (Yacobucci 2003; Klug et al 2005; Witts et al 2020).…”

Section: Discussionmentioning

confidence: 99%

Geographic and temporal morphological stasis in the latest Cretaceous ammonoidDiscoscaphites irisfrom the U.S. Gulf and Atlantic Coastal Plains

Witts¹,

Myers²,

Garb³

et al. 2022

Paleobiology

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We examine temporal and spatial variation in morphology of the ammonoid cephalopod Discoscaphites iris using a large dataset from multiple localities in the Late Cretaceous (Maastrichtian) of the U.S. Gulf and Atlantic Coastal Plains, spanning a distance of 2000 km along the paleoshoreline. Our results suggest that the fossil record of D. iris is consistent with no within-species net accumulation of phyletic evolutionary change across morphological traits or the lifetime of this species. Correlations between some traits and paleoenvironmental conditions as well as changes in the coefficient of variation may support limited population-scale ecophenotypic plasticity; however, where stratigraphic data are available, no directional changes in morphology occur before the Cretaceous/Paleogene (K/Pg) boundary. This is consistent with models of “dynamic” evolutionary stasis. Combined with knowledge of life-history traits and paleoecology of scaphitid ammonoids, specifically a short planktonic phase after hatching followed by transition to a nektobenthic adult stage, these data suggest that scaphitids had significant potential for rapid morphological change in conjunction with limited dispersal capacity. It is therefore likely that evolutionary mode in the Scaphitidae (and potentially across the broader ammonoid clade) follows a model of cladogenesis wherein a dynamic morphological stasis is periodically interrupted by more substantial evolutionary change at speciation events. Finally, the lack of temporal changes in our data suggest that global environmental changes had a limited effect on the morphology of ammonoid faunas during the latest Cretaceous.

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