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Summary 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 characterized by a self-similar branching architecture that was most likely optimized 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 neighbors (the norm). Their locations indicate exceptional growth at existing loci, rather than insertion at new sites. Analogous overcompensatory 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 toward optimum morphology (e.g., [ 5–7 ]). Its presence in rangeomorphs indicates a hitherto unappreciated level of control to their growth plan, a previously unrecognized 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. Highlights • A new multifoliate rangeomorph from Charnwood Forest, Hylaecullulus fordi , is described • Hylaecullulus shows eccentric branches, interpreted as overcompensatory growth • This growth shows that Hylaecullulus was modular and able to recover from damage • Modularity in rangeomorphs enabled them to achieve large body sizes Charlotte et al. describe a new rangeomorph (Hylaecullulus fordi) from the Ediacaran of Charnwood Forest, UK. These fossils show evidence of overcompensatory growth, demonstrating that H. fordi was able to recover from damage. It is evidence of biological modularity in rangeomorphs, a construction shared by the first clades to achieve large size. [ABSTRACT FROM AUTHOR]