67-million-year-old ants have shed light on the lives of the ancestors of modern species

Two partially preserved ants found in Canadian amber have helped to fill a gap in the history of these insects in the period immediately preceding the mass extinction that wiped out the non-avian dinosaurs. The fossils, dating back around 67 million years, have been identified as the oldest confirmed representatives of two subfamilies that still exist today.

Analysis also showed that one of the ants probably built its nests on the ground. Its later and modern relatives mainly live in trees, so the transition to a tree-dwelling lifestyle may have occurred after the extinction at the end of the Cretaceous period.

Details

The fossils were discovered at the Big Muddy amber deposit in the south of the Canadian province of Saskatchewan. Around 67 million years ago, the area was a swampy forest containing metasequoias, ferns and flowering plants. The insects became trapped in tree resin approximately one million years before the Cretaceous–Palaeogene extinction event.

Only part of one ant’s head has been preserved, whilst the other is an incomplete body. The specimens were embedded in epoxy resin, polished and scanned using bright X-rays from the Canadian Light Source. Microtomography with a voxel size of 1.5 micrometres enabled the researchers to construct detailed three-dimensional models of the body parts hidden within the amber.

Based on their morphology, the researchers classified the finds as belonging to the subfamilies Pseudomyrmecinae and Aneuretinae. These are the most ancient reliably identified representatives of both groups. Today, Pseudomyrmecinae are found mainly in the tropical regions of the Americas, Africa, Asia and Australia, whilst the subfamily Aneuretinae is represented by a single species living in Sri Lanka.

To infer the lifestyle of these ancient insects, Elyssa J. T. Loewen and her colleagues applied the Random Forest machine learning algorithm. It was trained using the morphology and ecology of 170 modern species from 114 genera and 15 subfamilies. The model correlated the shape of body parts with nest location, foraging behaviour and the functional role of the ants.

For the ant Pseudomyrmecinae, the model produced the most consistent result: it probably nested on the ground. Younger fossil representatives of this group and most of their modern relatives are associated with trees. The authors suggest that the colonisation of the tree canopy may have occurred following a mass extinction event and the restructuring of terrestrial ecosystems.

The results for Aneuretinae ants were less reliable due to incomplete fossil preservation. The researchers emphasise that the exclusion of certain characteristics, particularly those related to the senses, significantly reduces the accuracy of ecological predictions.

Why this is important

There is a significant gap in the ant fossil record between approximately 72 and 66 million years ago. The new specimens show that the ancestors of modern groups were already ecologically diverse shortly before the global catastrophe at the boundary between the Cretaceous and Palaeogene periods.

The findings support the hypothesis that modern ant lineages spread widely during the late Cretaceous period, coinciding with the expansion of flowering plants. Following the mass extinction, ancient ant groups disappeared, whilst lineages related to modern ones became significantly more diverse and numerous.

However, the study is based on just two incomplete fossils. The determination of their phylogenetic relationships relies on preserved anatomical features, whilst the reconstruction of their lifestyle is a probabilistic inference from a model rather than direct observation. Further finds from Big Muddy are needed to verify the proposed transition from ground-dwelling to arboreal life.

Source

Elyssa J. T. Loewen et al., ‘Ants (Hymenoptera: Formicidae) preserved in amber shed light on faunal turnover and ecological roles before the end-Cretaceous extinction’, Insect Systematics and Diversity, 2026. DOI: 10.1093/isd/ixag027. The article is published under a CC BY 4.0 licence.

A report on the research was published by Phys.org, citing the Canadian Light Source. Image: Loewen et al., Insect Systematics and Diversity, 2026, CC BY 4.0; a section of the original figure was used for the cover.