March 2025 – Nix Illustration

Incamys

Incamys bolivianus was a caviomorph rodent representing an early member of the chinchillid family, with its closest modern relatives being chinchillas and viscachas.

Living in what is now Bolivia and Argentina during the late Oligocene about 27 million years ago, it inhabited an arid open grassland at a time when the area’s climate had drastically cooled due to the formation of the Antarctic Circumpolar Current.

It’s estimated to have been similar in size to a large modern chinchilla – weighing around 700g (~1lb 8oz) and measuring about 25-30cm long not including the tail (~10-12″).

An endocast of the shape of its brain from a near-complete fossil skull shows that it had a well-developed sense of hearing, particularly in vocalization processing, suggesting it may have been a social animal living in groups communicating with complex calls similar to modern chinchillids. It was probably a ground-dweller less agile than its modern relatives, but still capable of fast movements.

Rhyniella

Rhyniella praecursor was an early springtail that lived during the early Devonian, about 410-400 million years ago, in what is now Scotland. Discovered in the exceptionally well-preserved Rhynie chert fossil site, it’s one of the earliest known hexapods.

It was around 2mm long (~0.08″) and closely resembled some of its modern relatives – with distinctive anatomical features like a collophore and a furca – showing that springtails were already well-established in such an early terrestrial ecosystem.

It probably had a similar sort of ecological role to modern springtails, too, being involved in the breaking down of organic matter and the formation of soils.

Greenwaltarachne

Greenwaltarachne pamelae was an orb-weaver spider that lived in what is now Montana, USA, during the mid-Eocene, around 46 million years ago.

Known from a single fossil of an adult female, it had a body length of about 2mm (~0.08″) and a legspan of around twice that. The specimen is even well-preserved enough to show banded markings on the legs resembling those of some modern orb-weaver species.

It would have lived in what was then a rift valley with a tropical climate, along the shoreline of the ancient 160km long (~100 miles) Lake Kishenehn. It was part of a highly diverse ecosystem full of numerous other invertebrates – including miniscule fairyflies, and even mosquitoes with evidence of blood preserved inside their bodies – and a wide variety of mammals ranging from tiny rodents to large brontotheres.

Hassianycteris

Hassianycteris messelensis was an early bat that lived in what is now Germany during the mid-Eocene, about 47 million years ago.

It’s generally considered to be very closely related to the common ancestry of modern bats – but a recent study suggests that the stem-bat evolutionary tree is actually quite a bit more complicated than previously thought.

It had a 35-40cm wingspan (~14″-16″), and thanks to the exceptional preservation of the Messel Pit fossil site we actually know some details about its external life appearance. One specimen preserves a soft-tissue impression of its ear shape, and fossilized melanosomes suggest that its fur was colored reddish-brown.

Its wing proportions indicate it was adapted to fly high and fast in open spaces, and its strong jaws and preserved gut contents show it mainly preyed on tough-shelled insects like beetles.

Miosiren

Miosiren kocki was a sirenian (sea cow) that lived during the early Miocene (~20-15 million years ago) in what is now the North Sea basin in northwestern Europe.

Similar in size to the very largest modern manatees, about 4-4.5m long (~13-14’10”), it has traditionally been classified as an early member of the manatee lineage – but a study in 2022 suggested it may instead represent a much earlier stem of the sirenian evolutionary tree, with its ancestors potentially having diverged around 34 million years ago.

It had unusually thickened bones in its skull, especially around the roof of its mouth, which would have given its jaws a very strong chewing force. Isotope analysis of its teeth show it was part of a marine algae-based food web, unlike the seagrass-based diets of other sirenians, so it may have been specialized to feed on a much tougher diet. Possibly it was eating something like calcareous algae, or more speculatively it might even have been crunching on hard-shelled algae-consuming marine invertebrates.