Terrestrial Isopods from Spanish Amber (Crustacea: Oniscidea): Insights into the Cretaceous Soil Biota

Abstract

Terrestrial isopods (Crustacea: Oniscidea) are a model group for studying the colonization of land. However, their fossil record is remarkably scarce and restricted to amber inclusions, and therefore amber deposits represent valuable windows to their past diversity and morphology. Here we present a new collection of 11 terrestrial isopod specimens preserved in Albian-aged amber from the Peñacerrada I outcrop, northern Spain, which collectively represent the most thoroughly documented fauna of Mesozoic Oniscidea. The three new genera and species identified belong to three of five major groups of the Oniscidea: Eoligiiscus tarraconensis, new genus and species (Ligiidae), Autrigoniscus resinicola, new genus and species (Synocheta: Trichoniscidae), and Heraclitus helenae, new genus and species (Crinocheta: Detonidae?). These taxa significantly expand the known fossil record of Oniscidea and demonstrate that considerable cladogenesis had already transpired by the Albian. The assemblage represents the earliest-known diversification of Oniscidea, extending direct evidence of terrestrialization in the group back to the late Early Cretaceous. These new taxa exhibit some characteristics that may inform hypotheses relating to general patterns of terrestrial isopod evolution. A discussion is provided about different aspects of the paleo-

First Fossil of Tylidae (Isopoda: Oniscidea) in Kachin Amber, Myanmar, with a List of All Oniscidea Fossil Records

“…The classification position of some groups is not clear due to the lack of detailed morphological characteristics [see list]. Among them, the earliest fossil records are from Spanish amber (Cretaceous Albian, 105 Ma) [29,92].…”

“…Regarding fossils, the earliest Oniscidea fossil record comes from the Cretaceous Albian (105 Ma), but some indications suggest that they could have already appeared on land in the Late Palaeozoic [14,29,30]. Fossil records of Oniscidea are quite scarce and mostly limited to preservation in amber [30]; until recently, they were almost entirely restricted to the Cenozoic.…”

Early detritivory and sedimentivory in insects based on in situ gut contents from Triassic aquatic nymphs

“…1c) and in terrestrial isopods preserved in Cretaceous amber (Sánchez‐García et al . 2021, figs 7B, 9B). The three‐dimensional (3D) cololites preserved in arthropods are usually present in body fossils, and not isolated as more commonly occurs in fossil vertebrates (Seilacher 2002).…”

“…Grimaldi 2000; Sánchez‐García et al . 2021). Even though the evolution of larval stages in insects has classically been one of the most neglected topics in (palaeo)entomology (Peñalver & Pérez‐de la Fuente 2014), compression deposits provide rich assemblages of aquatic preimaginal stages of insects, including egg lays, larvae, nymphs, or exuviae.…”