On the value of Burmese amber for understanding insect evolution: Insights from †Heterobathmilla - an exceptional stem group genus of Strepsiptera (Insecta).

Hans Pohl,Benjamin Wipfler,Brendon Boudinot,Rolf Georg Beutel

doi:10.1111/cla.12433

Abstract

Burmese amber and amber from other periods and regions became a rich source of new extinct insect species and yielded important insights in insect evolution in the dimension of time. Amber fossils have contributed to the understanding of the phylogeny, biology, and biogeography of insects and other groups, and have also gained great importance for dating molecular trees. Another major potential is the documentation of faunal, floral and climatic shifts. Evolutionary transitions can be well-documented in amber fossils and can reveal anatomical transformations and the age of appearance of structural features. Here, using a new stem group species of Strepsiptera from Burmite, we evaluate this potential of amber insect fossils to assess the current phylogeny of Strepsiptera, with the main emphasis on the early splitting events in the stem group. Amber fossils have greatly contributed to the understanding of the evolution of Strepsiptera in the late Mesozoic and the Cenozoic. †Heterobathmilla kakopoios Pohl and Beutel gen. et sp. n. described here is placed in the stem group of the order, in a clade with †Kinzelbachilla (†Kinzelbachillidae) and †Phthanoxenos (†Phthanoxenidae). †Phthanoxenidae has priority over †Kinzelbachillidae, and the latter is synonymised. The superb details available from this new fossil allowed us to explore unique features of the antennae, mouthparts, and male copulatory apparatus, and to provide a phylogenetic hypothesis for the order. The younger †Protoxenos from Eocene Baltic amber was confirmed as sister to all remaining extinct and extant groups of Strepsiptera, whereas the position of the Cretaceous †Cretostylops in the stem group remains ambivalent. While the value of Burmite and amber from other periods has a recognized impact on our knowledge of the evolution in various lineages, this new fossil does not fundamentally change our picture of the phylogeny and evolution of early Strepsiptera. However, it offers new insights into the morphological diversity in the early evolution of the group.

Highlights

Burmese Cretaceous amber of the Albian/Cenomanian boundary (e.g. Zherikin and Ross, 2000; Grimaldi et al, 2002; Cruickshank and Ko, 2003; Shi et al, 2012), has turned out to be a very rich source of extinct species of insects and other groups, and the pace of studying amber fossils has distinctly accelerated since this fossil site was rediscovered
As in several other groups, the knowledge of the past diversity of Strepsiptera has been distinctly improved by amber fossils
20 species are from Miocene Dominican amber, 13 species from Eocene Baltic amber, two compression fossils from the Eocene Green River formation (USA), one species from Eocene Fushun Amber (China), one from Eocene Brown coal Geisel Valley (Germany), and one from Colombian copal (Holocene – Pleistocene)

Summary

Introduction

Burmese Cretaceous amber of the Albian/Cenomanian boundary (e.g. Zherikin and Ross, 2000; Grimaldi et al, 2002; Cruickshank and Ko, 2003; Shi et al, 2012), has turned out to be a very rich source of extinct species of insects and other groups, and the pace of studying amber fossils has distinctly accelerated since this fossil site was rediscovered (e.g.Grimaldi et al, 2002; Ross, 2019a, b, 2020). Zherikin and Ross, 2000; Grimaldi et al, 2002; Cruickshank and Ko, 2003; Shi et al, 2012), has turned out to be a very rich source of extinct species of insects and other groups, and the pace of studying amber fossils has distinctly accelerated since this fossil site was rediscovered Numerous new extinct species from 569 families of organisms (Ross, 2019a, b, 2020) have yielded important insights in insect evolution in the dimension of time Engel and Grimaldi, 2002; Liu et al, 2018; Mashimo et al, 2018, 2019; Yin et al, 2018), indicating a distinctly larger diversity in the past (Yin et al, 2018). New important beetle fossils were described, for instance from the suborder Myxophaga, which was previously largely (†Catiniidae?; Crowson, 1975; Beutel et al, 2008) or completely missing from the fossil record (e.g., Jałoszynski et al, 2017; see Fikacek et al, 2020)

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