Modularity and overcompensatory growth in Ediacaran rangeomorphs demonstrate early adaptations for coping with environmental pressures

Kenchington, Charlotte G. and Dunn, Frances S. and Wilby, Philip R. (2018) Modularity and overcompensatory growth in Ediacaran rangeomorphs demonstrate early adaptations for coping with environmental pressures. Current Biology, 28 (20). 3330-3336.e2. ISSN 0960-9822

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The first known diverse, complex, macroscopic benthic marine ecosystems (late Ediacaran, ca. 571-541 Ma) were dominated by the Rangeomorpha, an enigmatic group of extinct frondose eukaryotes that are candidate early metazoans[1,2]. The group is characterised by a self-similar branching architecture that was likely optimised for exchange, but nearly every other aspect of their biology is contentious[2-4]. We report locally-enhanced, aberrant growth ("eccentric branching") in a stalked, multifoliate rangeomorph - Hylaecullulus fordi n. gen., n. sp. - from Charnwood Forest (UK), confirming the presence of true biological modularity within the group. Random branches achieve unusually large proportions and mimic the architecture of their parent branch, rather than that of their neighbours (the norm). Their locations indicate exceptional growth at existing loci, rather than insertion at new sites. Analogous over- compensatory branching in extant modular organisms requires the capacity to orchestrate growth at specific sites, and occurs most frequently in response to damage or environmental stress, allowing regeneration towards optimum morphology[e.g. 5-7]. Its presence in rangeomorphs indicates a hitherto unappreciated level of control to their growth plan, a previously unrecognised form of morphological plasticity within the group, and an ability to actively respond to external physical stimuli. The trait would have afforded rangeomorphs resilience to fouling and abrasion, partially accounting for their wide environmental tolerance, and may have pre-adapted them to withstand predation, weakening this argument for their extinction. Our findings highlight that multiple, phylogenetically disparate, clades first achieved large size through modularity.

Item Type: Article
Uncontrolled Keywords: 2018AREP; IA73
Subjects: 04 - Palaeobiology
Divisions: 04 - Palaeobiology
08 - Green Open Access
Journal or Publication Title: Current Biology
Volume: 28
Page Range: 3330-3336.e2
Depositing User: Sarah Humbert
Date Deposited: 04 Oct 2018 22:33
Last Modified: 09 Feb 2021 18:17

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