# A New Genus and Species of Syspastoxyelidae (Hymenoptera) from Mid-Cretaceous Burmese Amber

## TL;DR

A new species of ancient wasp-like insect, Cilioxyela setosa, is discovered in Burmese amber, revealing new wing structures and evolutionary diversity in early hymenopterans.

## Contribution

The discovery introduces a new genus and species with unique wing features, expanding the morphological and evolutionary understanding of mid-Cretaceous hymenopterans.

## Key findings

- Cilioxyela setosa exhibits a smooth distal forewing membrane and elongated marginal setae, distinguishing it from other syspastoxyelid genera.
- The new genus supports the idea that distal forewing structures in Syspastoxyelidae are more variable than previously assumed.
- The discovery highlights evolutionary plasticity in wing architecture among early hymenopterans during the mid-Cretaceous.

## Abstract

Syspastoxyelidae is an extinct group of early hymenopterans known only from mid-Cretaceous Burmese amber. Although rare, these fossils provide important information on the early morphological diversification of basal Hymenoptera. In this study, we describe a new genus and species, †Cilioxyela setosa, based on a well-preserved amber inclusion from northern Myanmar. The new taxon can be clearly assigned to Syspastoxyelidae based on key family characters but differs from all previously known genera by the combination of a smooth distal forewing membrane and the presence of conspicuously elongated marginal setae. Comparison with other syspastoxyelid genera suggests that distal forewing structures were more variable than previously assumed. This discovery expands the known morphological diversity of the family and provides new insights into the early evolutionary experimentation in wing structure among basal hymenopterans during the mid-Cretaceous.

Syspastoxyelidae is an extinct basal hymenopteran lineage currently known only from mid-Cretaceous Burmese amber. Here, we describe a new genus and species, Cilioxyela setosa gen. et sp. nov., based on a well-preserved female specimen from the Hukawng Valley, northern Myanmar. The new taxon is assigned to Syspastoxyelidae based on diagnostic characters, including strongly proximally condensed forewing venation, a composite first flagellomere formed by fused ancestral segments, tibiae bearing dense robust spines, and segmented cerci. Cilioxyela gen. nov. differs from all previously described genera by a unique character combination, most notably, a distal forewing veinless membrane lacking longitudinal corrugation and conspicuously elongated marginal setae, together with a narrowed forewing, elongate pterostigma and anal cell, and distinctive antennal segmentation. These features support the establishment of a new genus. Comparative analysis indicates that distal forewing morphology in Syspastoxyelidae is more variable than previously recognized. The presence or absence of longitudinal corrugation in the distal forewing membrane likely reflects genus-level differentiation rather than a stable family-level synapomorphy. The new genus also supports a tentative division of Syspastoxyelidae into at least two morphologically cohesive groups, pending testing through additional fossil discoveries and quantitative phylogenetic analyses. The discovery of Cilioxyela setosa expands the known morphological disparity of Syspastoxyelidae and highlights evolutionary plasticity in distal forewing architecture among early Hymenoptera, contributing to a better understanding of morphological diversification in mid-Cretaceous forest ecosystems.