# A New Species of Orthosyntexis (Hymenoptera: Anaxyelidae) from Mid-Cretaceous Burmese Amber

## TL;DR

A new species of ancient sawfly was discovered in 99-million-year-old Burmese amber, revealing more about their diversity and evolution during the Cretaceous period.

## Contribution

Description of a new fossil sawfly species and clarification of wing venation patterns to aid in understanding evolutionary relationships.

## Key findings

- A new species, Orthosyntexis mascula, was identified from mid-Cretaceous Burmese amber.
- The absence of a specific crossvein in the forewing correlates with hind wing venation differences.
- Re-examination of Kempendaja jacutensis corrected earlier misinterpretations of its wing structure.

## Abstract

Sawflies of the family Anaxyelidae are represented today by a single rare species in western North America, which lays its eggs in fire-damaged conifers. Fossils, however, show that these insects were far more diverse during the age of dinosaurs. In this study, we describe a new species from 99-million-year-old Burmese amber, providing fresh evidence of their Cretaceous diversity. We also re-examined an older fossil, Kempendaja jacutensis, and confirmed that an earlier interpretation of its wing venation was likely an error. Finally, we found that the presence or absence of a small crossvein in the forewing is consistently associated with differences in the hind wing: a pattern that may help future researchers untangle evolutionary relationships.

Anaxyelidae, a relict lineage of sawflies, are represented by a single extant species today but displayed remarkable Mesozoic diversity. Here, we describe the Orthosyntexis mascula sp. nov. from mid-Cretaceous Burmese amber. The new species can be readily distinguished by its forewing, with a normally sized, uniformly sclerotized pterostigma; 1-Rs shorter than 1-M; cell 1M more than twice as long as wide; absence of 1r-rs; 1-Cu, distinctly shorter than 2-Cu; 3-Cu shorter than 4-Cu; 2m-cu shorter than 1m-cu; and 3rs-m twice as short as 4-M. In the hind wing, abscissa 2-M+Cu present, 1-M shorter than 2-M, crossvein m-cu absent, and cell R1 closed. Mesotibia with two apical spurs. Examination of high-resolution photographs of Kempendaja jacutensis enables a revised interpretation of its venation, confirming its placement in Anaxyelinae. Comparative analysis of syntexine taxa further reveals that variation in the forewing crossvein 1r-rs consistently corresponds with hind wing venation, suggesting that multiple evolutionary trajectories may have existed within Syntexinae. These findings not only expand the known diversity of Cretaceous Anaxyelidae but also provide new evidence for reconstructing the evolutionary history and internal diversification of Anaxyelidae.