A 100 million-year-old armoured caterpillar supports the early diversification of moths and butterflies

Highlights

• A new Cretaceous caterpillar in amber is described, just the fifth from that period.

• It is the only Cretaceous caterpillar armoured with spines, probably for defense.

• This find supports an early diversification of moths and butterflies.

Abstract

The lepidopteran caterpillar is a ubiquitous type of larva with a significant impact on the modern ecosystem. Quite on the contrary, the fossil record of caterpillars is quite scarce, with four occurrences in Cretaceous ambers representing the oldest ones. Here we report a new specimen from 100 million-year-old Cretaceous Myanmar amber. The caterpillar has appendages on abdomen segments 3–6 and 10. Such an arrangement is today only known in caterpillars of the group Gracillariidae. These caterpillars are usually dorso-ventrally flattened, adapted for leaf mining. The fossil specimen does not appear flattened and is additionally armoured with spines dorsally on the trunk segments. All other known Cretaceous larvae are “naked”, lacking dorsal armature. The new specimen hence increases the diversity of Cretaceous caterpillars. This finding is congruent with recent phylogenetic reconstructions and hence supports an early diversification of the group Lepidoptera.

Introduction

The caterpillar is probably the most famous type of larva of the group Insecta. Some groups of scorpion flies and saw flies have caterpillar-type larvae (e.g. Williamson, 2009, p. 19901), but more commonly known are the larvae of moths and butterflies (Lepidoptera), not least due to the book of Eric Carle “The very hungry caterpillar”. The group Lepidoptera is one of the “big four”, lineages with more than 100,000 formally described species (the other lineages are Diptera, Coleoptera and Hymenoptera, the groups of flies, beetles and wasps). As the group Lepidoptera is so species-rich and due to the fact that butterflies and moths spend quite a large part of their life span in their larval form, caterpillars must represent quite a significant part of the biomass of modern-day terrestrial ecosystems. Caterpillars naturally are an important food source for many other organisms (e.g. Lin et al., 2019); as defoliaters, caterpillars have economic impact (e.g. Berti Filho, 1981; Dhir et al., 1992; Zanuncio et al., 1994), and some species occurring in high densities are even a factor in human health issues (e.g. Rosen, 1990; Gottschling et al., 2007; Gómez, 2014).

Given the importance of caterpillars in the modern fauna, it is surprising that the fossil record of caterpillars is quite scarce (Sohn et al., 2012, Sohn et al., 2015). In addition, most of the record is restricted to findings in amber and mostly to only 40 million years ago (Eocene) or even younger occurrences (Sohn et al., 2012). Due to the scarceness even from these rather young ambers, also single, relatively young specimens may represent quite significant findings (e.g. Fischer et al., 2019). Cretaceous ambers (c. 100 Ma), otherwise quite productive, have so far only provided very few caterpillar specimens, four of them were depicted. Older deposits lack caterpillars entirely.

The first of the Cretaceous caterpillar fossils is a broken head capsule from Canadian amber (MacKay, 1970, p.380 Fig. 1; Fig. 1A). A much better preserved specimen from Lebanese amber was depicted and discussed in several occasions (Grimaldi, 1996; Grimaldi, 1999, p. 405, fig. 12e; Grimaldi and Engel, 2005, p. 566, fig. 13.21; Fig. 1B), representing the oldest record of the group Glossata (embracing the major diversity of the group Lepidoptera). Xia et al. (2015, pp. 132, 133) figured two well-preserved caterpillar specimens from Myanmar amber (Fig. 1C, D), yet without further description or discussion. There was mentioning of additional specimens from Taimyr amber, yet we could not find any depictions of these specimens (Zherikhin and Sukacheva, 1973, p. 38; Skalski, 1979, p. 63)

All these finds appear to represent rather simple types of caterpillars, more or less appearing “naked”, while many modern caterpillars exhibit a wide range from similarly naked forms over very hairy ones to larvae with strong, defensive spines. Here we report a new lepidopteran caterpillar from 100 million-year-old Myanmar amber with an unusual combination of characters, most prominently it is armoured with numerous dorsal spines. We discuss the implications of this new finding.