Abstract
The Triassic was a crucial period for the early evolution and diversification of insects, including Coleoptera1-3-the most diverse order of organisms on Earth. The study of Triassic beetles, however, relies almost exclusively on flattened fossils with limited character preservation. Using synchrotron microtomography, we investigated a fragmentary Upper Triassic coprolite, which contains a rich record of 3D-preserved minute beetle remains of Triamyxa coprolithica gen. et sp. nov. Some specimens are nearly complete, preserving delicate structures of the legs and antennae. Most of them are congruent morphologically, implying that they are conspecific. Phylogenetic analyses suggest that T. coprolithica is a member of Myxophaga, a small suborder of beetles with a sparse fossil record, and that it represents the only member of the extinct family Triamyxidae fam. nov. Our findings highlight that coprolites can contain insect remains, which are almost as well preserved as in amber. They are thus an important source of information for exploring insect evolution before the Cretaceous-Neogene "amber time window." Treated as food residues, insect remains preserved in coprolites also have important implications for the paleoecology of insectivores, in this case, likely the dinosauriform Silesaurus opolensis.
Highlights
Other types of 3D preservation of insects include specimens preserved as mineralized replicas, as voids, in chert, or within vertebrate coprolites
The definite fossil record dates back to the Permian,[4,5,6] and modern lineages started to diversify in the Triassic.[1,2,3]
But no beetles, have been described from amber older than that,[8] and the fossil record of beetles prior to the Early Cretaceous is entirely derived from non-amber deposits.[9]
Summary
Other types of 3D preservation of insects include specimens preserved as mineralized replicas (e.g., silicified, phosphatized, or pyritized), as voids, in chert, or within vertebrate coprolites (fossil excrement). It has become evident that coprolites may act as microenvironments in which organic inclusions can be better preserved than in the host rock.[10,11,12] Coprolites can contain inclusions that otherwise are rarely preserved as fossils (e.g., soft tissues), and these are preserved three-dimensionally, even when derived from highly compacted host sediments. The inclusions from coprolites can be used to infer character states of extinct animals,[13,14] and they carry important information on diets, digestive strategies, and trophic structures of past ecosystems.[11,]
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