Emerging Beasts - Bridger Formation

A valley in Wyoming, USA, during the Eocene. After the extinction event at the end of the Cretaceous and the decimation of non-avian dinosaurs, mammals experienced their great rise, occupying numerous niches with more varied forms and sizes than ever before. Bizarre beasts emerged, groups that left no living descendants, and creatures that offered a glimpse into what would become their prosperous and, for us, iconic lineages today.

In a forest surrounded by mountains and volcanoes, a lake gathers animals that are thirsty, hungry, or simply seeking a bit of refreshment. The central figure is a visitor: a large Tetheopsis sp., with a skull about 90 cm long and an overall length of around 4 m. This animal is known from the Washakie Formation, located further south and of equivalent (though more extensive) age to the Bridger Formation, and the illustration assumes this species might have passed through the “neighboring” formation. Its relatives definitely found in the region are also present, with a pair of Uintatherium anceps drinking at the lake. These animals were slightly smaller than Tetheopsis (skulls around 70 cm and also close to 4 m in length), and displayed clear sexual dimorphism, especially in their horns.

These beasts are dinoceratans, a group with relationships hard to decipher, but currently understood as part of Laurasiatheria, which includes ungulate mammals, bats, pangolins, and the order Carnivora. Dinoceratans were likely especially close to the extinct xenungulates, though this is debated.

Over 2.5 m from snout to tail, a Patriofelis ferox emerges from the water with a slain Chisternon undatum turtle, thus satisfying both its thirst and hunger. It was once believed this was a semi-aquatic predator due to its broad, paddle-like feet, but that idea is now dismissed - but, of course, that wouldn’t stop it from seizing the opportunity to hunt something in the water, as shown in the image.

Still at the lake, capturing mollusks, is a pair of small Aletornis gracilis, a highly varied genus with fossils (always quite fragmentary) indicating species that ranged in size from woodcocks, like those depicted, to nearly as large as a flamingo. These species have been the subject of dispute, and the genus may actually encompass birds from different groups. Further back, on the shore, the “four-eyed” lizard Saniwa ensidens (counting the usual pair of eyes, plus the pineal and parapineal eyes) drinks and warms itself in the sun.

Moving to the foreground of the scene, we see activity on the ground and in the treetops. In the upper left corner, a Vulpavus ovatus rests on a branch of a Lauraceae tree, unaware it is being watched from below by the hyaenodont Sinopa major . On the right, two female Notharctus tenebrosus, primates about 40 cm long (not including their long tails), feed on the leaves of a Sapindaceae tree. On nearby branches of the same tree, a pair of Zygodactylus sp. birds tries to stop giant Titanomyrma sp. ants (workers around 3 cm long) from advancing toward their nest with chicks. On the ground, a Boavus occidentalis, a snake about 2 m long, slithers among dry leaves, while a Chimaeroblattina sp., a wasp-mimicking insect, flies through the lower left corner.

In the background, to the left and entering the forest, appears a hunter rivaling Patriofelis in size: measuring almost 2 m (excluding the tail), a Mesonyx obtusidens, a basal ungulate predator with a superficially canid appearance, follows a herd of Orohippus pumilus, small equids just over half a meter long.

Completing the illustrated animals, another “visitor”: the large (~2 m tall) bird Gastornis sp., foraging among the plants at the center of the image, behind the lake. This animal is not directly known from the Bridger Formation, but its presence in the region is speculated based on its records in another nearby formation, the Green River Formation - just like the Zygodactylus, Titanomyrma, and Chimaeroblattina.

The flora includes distant sequoias, palms (Sabalites) near the lake's edge, and ferns scattered on the forest floor, part of the rare fossil plants known from the Bridger Formation. Green River also inspires the flora of this time and region depicted in the scene, expanding the variety of plants with a richer angiosperm forest made up of trees like oak, cinnamon, and maple, along with the previously mentioned Sapindaceae and Lauraceae, and some cucurbitaceae growing near the ground.

Among the rocks on the lake shore, erosion reveals a treasure that tells a bit of the story preceding this landscape: part of a Torosaurus skull.

New artwork for Tales from the Phanerozoic, a project by João Macêdo. Check out the Eocene chapter here, with the backstory of the scene and detailed information about its environment and creatures: https://sites.google.com/view/talesfromthephanerozoic/the-cenozoic/renewed-world