Fossil evidence of elytra reduction in ship-timber beetles

Abstract

Beetles (Coleoptera) comprise about one quarter of all described animal species. One of the main contributors to their evolutionary success is the elytra, or hardened forewings, which have protective functions while maintaining their ability to fly. Unlike other beetles, some ship-timber beetles (Lymexylidae) have extremely small elytra and largely exposed functional hindwings. There is little fossil evidence illuminating the evolutionary history of short elytra in lymexylids. Here, I report five well-preserved lymexylid fossils in mid-Cretaceous and Cenozoic ambers from Myanmar (ca. 99 million years ago [Mya]), Russia (ca. 44 Mya), and the Dominican Republic (ca. 16 Mya). Three Cretaceous fossils have strongly reduced, shortened elytra, with unexpected variation in elytral size and shape, whereas very small, modified elytra are found only in much younger Dominican amber. These morphologically diverse extinct lymexylids shed new light on the early origin and evolutionary history of elytra reduction and its diverse variation in the ship-timber beetles. Based on the striking morphological similarities with extant lymexylids, these extinct taxa might have had the same, or similar, ecological, behavioural, and flight modes as the extant ship-timber beetles.

Origin and evolution of fungus farming in wood‐boring Coleoptera – a palaeontological perspective

“…Shin et al, 2017) excluded the Lebanese fossil scolytine, which may have led to an unrealistically recent estimation for Scolytinae. By contrast, the earliest Lymexylidae are described from the Aptian period, and these beetles are relatively abundant in Kachin amber of Cenomanian age (Yamamoto, 2019) but are also found in more modern Eocene Baltic and Miocene Dominican ambers (Wolf-Schwenninger, 2011;Yamamoto, 2019). A similar situation also occurs for Bostrichidae (Peris et al, 2014;Legalov & H ava, 2020).…”

“…None of these families are known from the Jurassic fossil record. Lymexylidae and Bostrichidae are abundant and diverse from the Cretaceous, mainly the late Cretaceous (Peris et al, 2014;Clarke et al, 2019;Yamamoto, 2019;Legalov & H ava, 2020), scolytine fossils are scarce in the Cretaceous (Cognato & Grimaldi, 2009;Kirejtshuk et al, 2009, but see Clarke et al, 2019) and not abundant until the Eocene (Hieke & Pietrezeniuk, 1984), and platypodines occurred in the Eocene (Peris et al, 2017;Legalov, 2020), but not abundantly until the Miocene (Bright & Poinar, 1994;Peris et al, 2015) (Fig. 3).…”

First fossil species of ship-timber beetles (Coleoptera, Lymexylidae) from Eocene Rovno amber (Ukraine)

“…The fossil records of Lymexylidae are relatively rare and scarce, mostly known from fossiliferous resins (e.g. Heer 1865 ;Wickham 1911;Kirejtshuk 2008;Wolf-Schwenninger 2011;Chen 2019;Yamamoto 2019;Chen and Zhang 2020;Nazarenko et al 2020). The earliest Lymexylidae fossil is known from the Lower Cretaceous Crato Formation in Brazil (Wolf-Schwenninger 2011).…”

“…The earliest Lymexylidae fossil is known from the Lower Cretaceous Crato Formation in Brazil (Wolf-Schwenninger 2011). Five species in four genera of the subfamily Atractocerinae have recently been described from mid-Cretaceous Burmese (Kachin) amber (Chen 2019;Yamamoto 2019;Chen and Zhang 2020), with some unstudied material (e.g. Peris 2020Peris , 2021Yamamoto, pers.…”

“…obs.). The family is relatively rare in Eocene Baltic amber and is represented definitively only by adults (Kirejtshuk 2008;Yamamoto 2019). So far, three extinct species of the recent atractocerine genus Raractocetus Kurosawa have been described from Kachin and Eocene Baltic ambers (Yamamoto 2019).…”