Scale microfossils from the mid-Neoproterozoic Fifteenmile Group, Yukon Territory

Abstract

Microscopic phosphatic scales are found in limestones and cherts from the 812–717 million year old Fifteenmile Group of the Yukon Territory. These enigmatic microfossils, which to date have not been identified in any other locality, display a diversity of intricate morphologies. Here we describe six new genera containing 17 new species of scale microfossils obtained from macerated limestone. We also revise existing taxa described originally from chert thin sections and now additionally freed from limestone by acid dissolution. New taxa described here are: Archaeoxybaphon serratacapacis n. sp., Archeoxybaphon serratapusilla n. sp., Paleoscutula inornata n. gen. n. sp., Paleoscutula serrata n. gen. n. sp., Paleoscutula convocationis n. gen n. sp., Hexacatillus allmonii n. gen. n. sp., Hexacatillus retetantillus n. sp., Quadrireticulum allisoniae n. gen. n. sp., Quadrireticulum palmaspinosum n. gen. n. sp., Circidentatus pistricis n. gen. n. sp., Circidentatus variodentatus n. gen. n. sp., Ospercapatera awramikii n. gen. n. sp., Circitorquis soccus n. gen. n. sp., Paleohexadictyon alexandrae n. sp., Paleomegasquama arctoa n. sp., Petasisquama petasus n. sp., and Thorakidictyon circireticulum n. gen. n. sp. Taxa described or amended here are Characodictyon skolopium Allison and Hilgert, 1986, Paleohexadictyon myriotrematum Allison and Hilgert, 1986, Archeoxybaphon polykeramoides (Allison and Hilgert, 1986) emend., Paleohexadictyon litosum (Allison and Hilgert, 1986) emend., and Thorakidictyon myriocanthum (Allison and Hilgert, 1986) n. comb. Many eukaryotic clades include species with surficial scales but none provides a close morphological analog to the Fifteenmile scales. Nonetheless, comparative and functional morphology suggest that the diversification of heavily armored and morphologically complex cell-coverings records a changing ecological landscape in Neoproterozoic seas.