# Agathis vs. Hymenaea—trapping biases to interpret arthropod assemblages in ambers

## TL;DR

This study compares how two types of tree resins trap arthropods, showing differences in the kinds of fossils they preserve.

## Contribution

The study reveals distinct trapping biases between Agathis and Hymenaea resins, impacting interpretations of ancient arthropod ecosystems.

## Key findings

- Agathis resin traps fewer and less uniformly distributed arthropods compared to Hymenaea resin.
- Hymenaea resin captures arthropods similar to those in nearby traps, suggesting a closer ecological link.
- Agathis resin's rapid polymerization limits arthropod inclusions, affecting fossil record interpretations.

## Abstract

The genera Agathis (Coniferales: Araucariaceae) and Hymenaea (Fabales: Fabaceae) contain resin-producing tree species that are crucial for actuotaphonomic studies. While certain Cretaceous ambers likely originated from Agathis or Agathis-like trees, Hymenaea is the primary source of many Miocene ambers. Field studies were conducted in New Caledonia and Madagascar to collect Defaunation resin (resin produced after 1760 AD (Anno Domini)). Arthropods were collected with yellow sticky and Malaise traps in New Caledonia, Madagascar, and Mexico. Cretaceous and Miocene ambers, copals (2.58 Ma to 1760 AD), and Defaunation resins from various regions were analysed to compare arthropod trapping patterns.

Actuotaphonomic results show lower number of arthropods trapped in Agathis Defaunation resin, with a non-uniform distribution, compared to the abundant and uniformly distributed arthropods trapped in Hymenaea Defaunation resin. The lower number of arthropod inclusions in the trunk resin of the Agathis trees is attributed to the rapid polymerisation of that resin. Under the same experimental conditions, the arthropods in Agathis Defaunation resin plot far from the arthropods collected in the yellow sticky and Malaise traps, while the arthropods in Hymenaea Defaunation resin plot close to the arthropods in the yellow sticky traps.

These findings confirm different resin trapping patterns between Agathis and Hymenaea, with significant implications for interpreting the amber record. The fauna trapped by Hymenaea resin closely resembles the arthropod biocoenosis that live in and around the trunks, indicating autochthony and close relationship with the forest ecosystem, unlike Agathis resin. These results improve our understanding of arthropod trapping biases in resin and lead us to reconsider previously proposed interpretations of Cretaceous forest biocoenoses.

The online version contains supplementary material available at 10.1186/s12915-025-02453-y.