February 2025 – Nix Illustration

Eons Roundup 15

It’s time for a little bit more recent PBS Eons work this week:

An illustration of Arctodictis, an extinct predatory mammal related to modern marsupials. It's a vaguely wolverine-like animal with a boxy snout, a low-slung body, stout limbs, and a long tail. It's depicted in a crouched stalking pose, and it's colored grey-brown with darker spot and stripe markings. — Arctodictis sp.

An illustration of Thoatherium, an extinct hoofed mammal. It resembles a small horse or deer, with a long face, high-set pointed ears, a boxy body, a short tail, and long slender legs each ending in a single hoofed toe. It's depicted with its head lowered to browse on some leaves, and it's colored reddish-brown with a darker back and limbs and a lighter belly — Arctodictis sp.

• The metatherian predator Arctodictis and the litoptern ungulate Thoatherium from “The Mystery of South America’s False Horses”

Dorypterus

Dorypterus hoffmanni was a stem–actinopterygian fish that lived during the late Permian, around 259-254 million years ago, in shallow warm lagoons covering what is now northwestern Europe.

About 13cm long (~5″), it had a tall narrow disc-shaped body convergently similar to modern reef fish, and it was mostly scaleless with only a few scales on its underside, below its pectoral fins, and along the top of its tail. It also appears to have been toothless, and probably used its large scissor-like jaws to snip off mouthfuls of soft food such as algae.

But its most distinctive feature was its highly elongated pennant-like dorsal fin, which may be an example of sexual dimorphism – fossils of short-finned individuals have also been found, and although they were originally named as a separate species (Dorypterus althausi) they probably actually represent female D. hoffmani.

Albireo

Albireonids were an early branch of the delphinoid whales, with their closest living relatives being modern oceanic dolphins, narwhals and belugas, and porpoises. Known from temperate latitudes of the North Pacific Ocean between the late Miocene and the late Pliocene, about 9-2.5 million years ago, their fossil remains are very rare in coastal deposits and they seem to have primarily been offshore open ocean animals.

Albireo whistleri is the best known member of this family, represented by a near-complete skeleton from what is now Isla de Cedros in Baja California, Mexico, dating to the late Miocene between about 8 and 6 million years ago. It was a rather small dolphin, around 2.5m long (~8’2″), with a stocky body, fairly broad flippers, and skull anatomy with some convergent similarities with the modern Dall’s porpoise.

Interestingly these dolphins also seem to have frequently had pathological neck vertebrae, with both Albireo whisteri and the younger species Albireo savagei from California, USA, showing unusually asymmetrical atlas bones – but on opposite sides to each other. This might be due to illness or injury earlier in life, or possibly be evidence of some sort of “handedness” with individuals preferring to perform some actions more with one side of their body than the other.

Tardisia

Tardisia broedeae was a small arthropod recently discovered in the 308-million-year-old Late Carboniferous Mazon Creek fossil beds in Illinois, USA.

Its anatomy has distinctive features of vicissicaudatans (close relatives of the trilobites), but its presence in Mazon Creek makes it by far the youngest known member of this group – indicating a previously-unknown ghost lineage of around 100 million years, and inspiring its name based on the time-travelling TARDIS in Doctor Who.

About 1.5cm long (~0.6″), Tardisia had an oval segmented body ending in a pair of pointed “tail” appendages. It also appears to have been eyeless, although some vicissicaudatans had eyes on their undersides so this might just be an artifact of preservation.