Integrative systematics reveal an unusual species of pedunculate ground beetles lacking fossorial legs from Late Cretaceous Kachin amber (Coleoptera: Carabidae: Scaritinae)

Abstract

Context The subfamily Scaritinae (Coleoptera: Carabidae) is a speciose, cosmopolitan group of ground beetles characterised by a pedunculate body form and modified fossorial forelegs, adaptations associated with a burrowing lifestyle in soil or sandy substrates. The fossil record of Scaritinae is scarce and only one Mesozoic species has been described up to the present. Aims A new genus and species of scaritine ground beetles is described from Late Cretaceous amber in northern Myanmar. Its phylogenetic relationship with extant lineages of Scaritinae was investigated and divergence times among lineages of Scaritinae were estimated. Its palaeoecology is also discussed from the perspective of morphological adaptation. Taxon A Late Cretaceous pedunculate ground beetle (Insecta: Coleoptera: Carabidae: Scaritinae), Cretoscarites burmanicus gen. et sp. nov., aligns well with extant Scaritinae, yet it lacks the fossorial legs typically seen in modern scaritines. Methods Its relationship with extant Scaritinae was investigated based on two datasets using maximum parsimony, Bayesian inference and maximum likelihood: (i) 55 morphological characters belonging to 16 taxa (representing 6 of the 7 tribes and 13 of the 20 subtribes of modern Scaritinae); and (ii) a combined morphological and molecular dataset for 16 taxa, comprising a partitioned alignment of 2772 bp from COI and 18S sequences of seven taxa, representing 5 tribes and 6 subtribes. Divergence times within Scaritinae were estimated in a Bayesian tip-dating framework based on both datasets under a relaxed clock. Key results Phylogenetic analyses using various approaches and datasets consistently placed Cretoscarites burmanicus within Scaritini. Among Scaritini, the nominal subtribe was recovered as the most likely closest relative of Cretoscarites burmanicus. Results indicate that Scaritinae originated in the Middle Jurassic (ca. 167–168 Mya) and the major lineages started to differentiate during the Cretaceous. The overall body form and small eye size suggest that it was likely a nocturnal, olfactory-tactile hunter inhabiting restricted or confined environments, whereas its simple, unmodified forelegs indicate a non-fossorial lifestyle. Conclusions The newly described scaritine ground beetle from Kachin amber can be confidently assigned to Scaritini based on our integrative phylogenetic approach. This finding represents the oldest documented occurrence (ca. 99 Mya) of this tribe to date and its unique forelegs suggest that the lifestyles of Scaritinae may have been more diverse in their early evolution than they are today. ZooBank LSID: urn:lsid:zoobank.org:pub:7E489EEA-A5A2-422B-B3EA-45B9FF3600D9

The authors' abstract, as published at the source. Invertebrate Systematics, 2026 · DOI ↗