Beetle larvae with unusually large terminal ends and a fossil that beats them all (Scraptiidae, Coleoptera)

Abstract

Larvae, and especially fossil larvae, are challenging to deal with from a purely taxonomic view. Often one cannot determine which species the larvae belong to. Yet, larvae can still contribute to various scientific questions. Especially morphological traits of a fossil larva can be highly informative for reconstructing character evolution. Also the occurrence of specific larval types and larval characters in time and the disappearance of such forms can well be reconstructed also without being able to narrow down the phylogenetic relationship of a larva very far. Here, we report two new beetle larvae preserved in Baltic amber which are identified as representatives of Scraptiidae, based on an enlarged terminal end (‘9th abdomen segment’); this is only the third record of such larvae. In comparison to modern forms, the terminal ends of the two new fossil larvae is even larger in relation to the remaining body than in any known larva. Unfortunately, our knowledge of such larvae in the modern fauna is very limited. Still, one of the two already known fossil larvae of Scraptiidae also has a very long terminal end, but not as long as those of the two new fossils. These three fossil larvae therefore seem to possess a specific morphology not known from the modern fauna. This might either mean that they (1) represent a now extinct larval morphology, a phenomenon well known in other euarthropodan lineages, or that (2) these forms represent a part of the larval phase not known from modern day species as they have not been described yet; such cases occur in closely related lineages. In any case, the fossils expand the known diversity of larval morphologies.

Eco-morphological diversity of larvae of soldier flies and their closest relatives in deep time

“…An elongated metacephalic rod is in particular common in larvae of Mydidae, Xylophagidae, Thervidae and Scenopidae ( Hennig, 1952 ; James, 1981 ; Irwin & Leneborg, 1981 ; Kelsey, 1981 ; Wilcox, 1981 ). This makes the interpretation of morphotype 1 larvae relatively challenging, due to the “chimaera-like” combination of the traits, as a probable result of the “push of the past” effect ( Baranov, Schädel & Haug, 2019 ; Haug & Haug, 2019 ). This effect seems quite common among fossil representatives of Holometabola, representing phenomena occurring when initial diversification events in extant hyperdiverse groups lead to a number of “experimental” morphologies ( Budd & Mann, 2018 ; Haug & Haug, 2019 ).…”

“…This makes the interpretation of morphotype 1 larvae relatively challenging, due to the “chimaera-like” combination of the traits, as a probable result of the “push of the past” effect ( Baranov, Schädel & Haug, 2019 ; Haug & Haug, 2019 ). This effect seems quite common among fossil representatives of Holometabola, representing phenomena occurring when initial diversification events in extant hyperdiverse groups lead to a number of “experimental” morphologies ( Budd & Mann, 2018 ; Haug & Haug, 2019 ). In total we have found 13 larvae of this morphotype, with seven of them being preserved in just two amber pieces (four in PED-0031 and three in PED-0152).…”

Synchrotron-radiation computed tomography uncovers ecosystem functions of fly larvae in an Eocene forest

“…Yet, we demonstrate here the potential for insect larvae -long considered too poorly preserved and difficult to identify to provide useful palaeobiological data -to illuminate specific aspects of palaeodiversity, palaeoecology, and palaeoethology. Indeed, in recent years the utility of fossilized insect larvae has been documented repeatedly, with examples from diverse periods and deposits (e.g., Wang et al, 2016;Lohrmann and Engel, 2017;Badano et al, 2018;Baranov et al, 2019;Haug and Haug, 2019;Pérez-de la Fuente et al, 2012Haug et al, 2020). The exploration of fossil larvae has the potential to open those "dark" aspects of Eocene ecology and ecosystem functioning otherwise hidden.…”

“…The distinctness of larval and adult fly biology is one of the reasons for their evolutionary success (Grimaldi and Engel, 2005). Given this, it stands to reason that fossil fly larvae are perhaps better proxies for the reconstruction of palaeo-environments, as larval habitat and ecological preferences can be inferred more directly from their morphology (Haug and Haug, 2019;Baranov et al, 2019aBaranov et al, , 2020aBaranov et al, , 2020b. Therefore, studying immature and adult flies in concert provides additional and enhanced information about palaeoecosystems (Baranov et al, 2019b).…”

Peer Review #2 of "Eco-morphological diversity of larvae of soldier flies and their closest relatives in deep time (v0.1)"

“…An elongated metacephalic rod is in particular common in larvae of Mydidae, Xylophagidae, Thervidae and Scenopidae (Hennig 1968, James 1981Irwin and Leneborg 1981;Kelse 1981;Wilcox 1981). This makes the interpretation of morphotype 1 larvae relatively challenging, due to the "chimaera-like" combination of the traits, as a probable result of the "push of the past'' effect (Baranov, Schädel, and Haug 2019;Haug and Haug 2019). This effect seems quite common among fossil representatives of Holometabola, representing phenomena occurring when initial diversification events in extant hyper diverse groups lead to a number of "experimental" morphologies (Budd and Mann 2018; Haug and Haug 2019).…”