The first Ichneumonid fossil from the Early Pleistocene of Madeira Island (Portugal)

In oceanic islands, well age-constrained deposits containing arthropod somatofossils (body fossils) are rare. However, when available, these are important for providing empirical and independent minimum ages for molecular phylogenetic dating and complementary data on taxonomy, evolution and palaeobiogeography information of the biological groups found as fossils. This is especially important for taxa that speciated within oceanic islands, many becoming single island endemics (SIE). Recently, associated with a 1.3 Ma (Calabrian) fluvial and lacustrine sedimentary deposit from Porto da Cruz in Madeira Island (Fig. 1), a wing, putatively identified as Hymenoptera, was found. Here we describe this wing fossil as belonging to Ichneumonidae, a group with ca. 30% of SIE in Madeira Island. Moreover, this is the first somatofossil of ichneumonid parasitic wasps found in Madeira Island and in Macaronesian islands (i.e. Azores, Madeira, Canaries and Cabo Verde). Since the 19th century, oceanic island attracted several naturalists due to the high probability of finding taxonomical novelties (e.g. Vieira, 2005). Darwin (1859) amplified this interest, as oceanic islands biota presented a central role to explain evolution. Today oceanic islands became the ideal locations to study evolution, biogeography and ecology (e.g. Whittaker et al., 2017). Madeira Island (Central Atlantic Ocean; Fig. 1), geologically a shield volcano of 7 Ma (Ramalho et al., 2015 and references therein), is considered an insect diversity hotspot where 3019 species and subspecies are known, of which 665 are SIE (Borges et al., 2008). This diversity is most probably explained by stepping-stone through palaeo-Macaronesian islands and isolation (Triantis et al., 2010; Fernández-Palacios et al., 2011). Palaeoentomological records are rare in Madeira. The only known record is from the Mio-Pleistocene deposit of São Jorge (see Góis-Marques et al., 2018), where Heer (1857) described an extinct coleopteran, Laparocerus wollastoni, based on fossilized elytra. Machado (2006) in a taxonomic review of Laparocerus considers this taxon as nomen dubium, due to the missing holotype and the impossibility of reapraising its taxonomy. On other Macaronesian archipelagos, especially in the Canaries Islands, several deposits with insect ichnofossils have been described (e.g. Edwards & Meco, 2000; Meco et al., 2011; La Roche et al., 2014). In Azores only xylophagous ichnoentomological traces in charcoal wood are known (Góis-Marques et al., 2019b). The fossil wing was found within laminated lacustrine fine sandstone, associated with plant fossils. The sediments are constrained by two 40Ar-39Ar dates to 1.3 Ma, Calabrian stage (Góis-Marques et al., 2019a). Fossils are kept in the palaeobotanical collection at the Madeira University herbarium (UMad-P) with the numbers UMad-P500a (part) and UMad-P500b (counter-part). The wing fossil was studied under a stereo microscope, and its identification was performed through several sources (e.g. Goulet & Huber, 1993) and specific guidebooks (Prehn & Raper, 2016). Wing description follows the Comstock-Needham system as described by Quicke (2015)