Lepidopteran caterpillars in the Cretaceous: were they a good food source for early birds?

Caterpillars are an omnipresent component in modern terrestrial faunas. Not surprisingly, they represent an important food source for larger animals. The oldest fossils of caterpillars are known from the Cretaceous. Yet, so far, only nine possible Cretaceous specimens have been reported. Here we expand the known record by four new specimens of caterpillars preserved in 99 million-year-old Kachin amber from Myanmar. The specimens cannot easily be interpreted in a taxonomic or phylogenetic frame. A simple morphometric comparison reveals that the new specimens differ in their relative body dimensions from those of the previously known specimens, expanding the morphological diversity of Cretaceous caterpillars. All caterpillars from the Cretaceous of which sizes are known are rather small, the largest definite one being only about 5 mm. Comparison to younger ambers reveals no clear directed preservation bias towards preserving only small caterpillars. In addition, the sizes of known adult lepidopterans from the Cretaceous are compatible with rather small caterpillars, although possibly slightly larger than the known ones. While small, the observed size range appears still to be within the size range of food items known to be consumed by modern birds. It therefore seems likely that also in the Cretaceous caterpillars were adequate food items for early birds.