August 2024 – Nix Illustration

Eons Roundup 14

It’s been a while, but let’s catch up with some more work I’ve done for PBS Eons:

An illustration of both a fossil example and the reconstructed internal structure of the enigmatic Paleodictyon, a hexagonal network of tunnels in seafloor sediment created by an unknown organism. — *Paleodictyon nodosum*

The enigmatic Paleodictyon, from “Something Has Been Making This Mark For 500 Million Years”

An illustration of Loxolophus, an extinct mammal related to early ungulates. It somewhat resembles a modern coatimundi, with a slender snout, long legs with plantigrade feet and claw-like hooves, and a long bushy tail. It's reconstructed with a mottled and striped camouflage pattern of brown and cream fur. — *Loxolophus hyattianus*

An illustration of Arctocyon, an extinct mammal related to early ungulates. It has a dog-like head with large canine teeth, a stocky bear-like body with plantigrade legs and claw-like hooves, and a long tail. It's reconstructed with an orange-brown pelt with white stripes along its limbs. — *Loxolophus hyattianus*

The archaic ungulates Loxolophus, Arctocyon, and Eoconodon, from “How a Mass Extinction Changed Our Brains”

An illustration of Aturia, an extinct relative of modern nautiluses. It's reconstructed with an orange-brown shell patterned with zigzagging darker stripes. — *Aturia sp.*

And the nautilid Aturia, from “When Nautiloids Met Their Match”

Allenypterus

Allenypterus montanus was an unusual early coelacanth that lived during the late Carboniferous, around 324 million years ago, in a tropical bay covering what is now central Montana, USA.

Up to about 15cm long (~6″), its tapering tadpole-like body plan somewhat resembled that of modern knifefishes and featherbacks, with the top part of its tail fin highly elongated into a ribbon-like shape and the rest of its tail fins being vestigial. The distinctive humped shape of its back was also much more pronounced in larger, more mature individuals.

It was probably a fairly slow swimmer, and preserved gut contents suggest it mainly ate small soft-bodied prey.

Its closest known relative seems to have been the eel-like Holopterygius – but since around 60 million years and different continents separated them both, this suggests the existence of a whole ghost lineage of other tapering coelacanths yet to be discovered.

Schoenesmahl

Schoenesmahl dyspepsia was a lizard that lived in what is now Europe during the late Jurassic, about 150 million years ago. Around 30cm long (~1′), it had a fairly small head, elongated hind limbs, and a very long tail – proportions that suggest it was an agile animal capable of fast running.

Only one specimen is known, most notable for being preserved inside the stomach of the dinosaur Compsognathus. For a long time it was classified as an example of Bavarisaurus, but it was finally recognized as representing a distinct type of lizard in 2018, with recent studies placing it as an early member of the gecko lineage closely related to ardeosaurids and eichstaettisaurids.

Compsognathus

First discovered in the 1850s, Compsognathus longipes was the first theropod dinosaur known from a fairly complete skeleton, and also the smallest known non-avian dinosaur for over 130 years.

(A second specimen was also, briefly, the “first” aquatic non-avian dinosaur, but that’s another story.)

Living in what is now Europe during the late Jurassic, about 150 million years ago, it was a lightly built animal with long legs and a long tail, growing to around 1.2m long (~4′). Its hands seem to have had only two functional fingers, with the third being vestigial and possibly not even having a claw.

Skin impressions from about a third of the way along its tail show small bumpy scales – but since other compsognathids like Sinosauropteryx are known to have been covered in fur-like feathers, this likely means that just that particular region of Compsognathus’ body wasn’t fluffy.

Some of Compsognathus‘ diet is known for certain, since preserved gut contents show it fed on smaller vertebrates like lizards and rhynchocephalians. The remains of a lizard in the stomach of one specimen were even identified as belonging to a previously-unknown species, Schoenesmahl dyspepsia, with the dismembered nature of the skeleton suggesting Compsognathus tore its prey into bite-sized chunks in a similar manner to modern predatory birds.