Nix Illustration – Page 17 – Paleontology and science illustration, and feathering ALL the dinosaurs

Rhenopyrgus

Despite looking more like some sort of scaly tubeworm, Rhenopyrgus viviani here was actually an echinoderm, distantly related to modern starfish, brittle stars, sea urchins, crinoids, and sea cucumbers.

It was part of an extinct Paleozoic echinoderm lineage known as edrioasteroids, which lived attached to the seabed or on hard surfaces like the shells of other marine animals, using the tube feet on their five arms to catch food particles from the water around them.

Living during the Silurian, about 435 million years ago, in what is now Quebec, Canada, it stood around 3-4cm tall (1.2-1.6″), firmly anchored into the seafloor sediment by a bulbous sac-shaped base. Its long stalked body was somewhat flexible, and it was able to partially contract the top feeding region down under a “collar” of large scale-like armor plates.

Sierraceratops

In the late 1990s a partial skeleton of a ceratopsian was discovered in New Mexico, USA. These remains were initially thought to belong to Torosaurus, but after more of the specimen was recovered in the mid-2010s it became clear the bones actually represented an entirely new species of horned dinosaur – officially named in 2022 as Sierraceratops turneri.

Sierraceratops lived during the Late Cretaceous, around 72 million years ago, in what at the time was the southern region of the island continent of Laramidia. About 4.6m long (~15′), it had fairly short chunky brow horns, long pointed cheek horns, and a relatively large frill.

It was part of a unique lineage of ceratopsians that were endemic to southern Laramidia, with its closest known relatives being Bravoceratops from western Texas and Coahuilaceratops from northern Mexico.

Casatia

Modern beluga whales and narwhals are the only living representatives of the monodontid lineage, found only in cold Arctic and sub-Arctic waters. But this whale family actually first evolved in much warmer climates – and some of them were downright tropical.

Casatia thermophila lived about 5 million years ago during the early Pliocene, in the Mediterranean Sea around Tuscany, Italy. Although known only from a couple of partial skulls and a few vertebrae it was probably similar in size to its modern relatives, around 5m long (16’4″).

It seems to have had a larger number of functional teeth than modern monodontids, and probably didn’t suction feed like its modern close relatives. Instead it may have fed more like most porpoises and dolphins, relying more on speed and snapping jaws to capture prey.

It inhabited the Mediterranean at a time not long after the sea there had mostly dried up and then been rapidly refilled. The presence of warm-water marine species such as bull sharks, tiger sharks, and dugongs in the same fossil beds as Casatia indicates the local climate at the time was hotter than it is today, with tropical temperatures – and suggests that this whale’s ancestors must have originally moved into the replenishing Mediterranean from lower latitudes alongside these other warmth-adapted animals.

This tropical monodontid was also much closer related to modern belugas than modern narwhals are, which raises the possibility that the two living monodontid species actually specialized for colder conditions completely independently of each other rather than descending from a cold-adapted common ancestor. Instead modern belugas and narwhals may have originated from separate warm-water monodontid ancestors who evolved similar cold-tolerant adaptations in parallel as the climate cooled during the onset of the Quaternary ice age, while the rest of their relatives all went extinct.

Calamostoma

Ghost pipefishes are close relatives of pipefish and seahorses, and today are represented by six different species found in shallow tropical waters of the Indo-Pacific. But while this lineage is estimated to have originated around 70 million years ago in the Late Cretaceous, their fossil record is very sparse – only three fossil representatives are currently known from the entire Cenozoic.

Calamostoma lesiniforme is one of the oldest of these, dating to the early Eocene around 50-48 million years ago. Known from the Monte Bolca fossil beds in northern Italy, it lived in a warm shallow reef environment during a time when that region of Europe was covered by the western Tethys Ocean.

Up to about 9cm long (3.5″), it was already very similar in appearance to modern ghost pipefishes, with a long tubular snout, star-shaped bony plates in its skin, two dorsal fins, and fairly large pelvic fins that formed an egg-brooding pouch in females. It probably had the same sort of lifestyle as its modern relatives, floating pointing downwards and camouflaging itself among seagrasses, algae, and corals.

One specimen preserves a small amount of color patterning, showing hints of dark banding on the pelvic and tail fins. But since modern ghost pipefish can change their coloration to better mimic their surroundings, it’s unclear whether these markings were common to all Calamostoma or were just part of this particular individual’s camouflage.

Falcatakely

Modern birds’ upper beaks are made up mostly from skull bones called the premaxilla, but the snouts of their earlier non-avian dinosaur ancestors were instead formed by large maxilla bones.

And Falcatakely forsterae here had a very unusual combination of these features.

Living in Madagascar during the Late Cretaceous, about 70-66 million years ago, it was around 40cm long (1’4″) and was part of a diverse lineage of Mesozoic birds known as enantiornitheans. These birds had claws on their wings and usually had toothy snouts instead of beaks, and many species also had ribbon-like display feathers on their tails instead of lift-generating fans.

Falcatakely had a long tall snout very similar in shape to a modern toucan, unlike any other known Mesozoic bird, with the surface texture of the bones indicating it was also covered by a keratinous beak. But despite this very “modern” face shape the bone arrangement was still much more similar to other enantiornitheans – there was a huge toothless maxilla making up the majority of the beak, with a small tooth-bearing premaxilla at the tip.

This suggests that there was more than one potential way for early birds to evolve modern-style beaks, and there may have been much more diversity in these animals’ facial structures than previously thought.

Termonerpeton

During the Early Carboniferous, around 330 million years ago, the region that is now the East Kirkton Quarry in Scotland was located close to the equator, with a lush tropical climate and volcanic hot springs dotting the landscape. It preserves fossils of some of the earliest known fully terrestrial tetrapods, and a recent discovery shows how some of these animals were already experimenting with the shapes of their feet to better get around on land.

Termonerpeton makrydactylus is only known from a partial skeleton, and shows a mix of anatomical features that make identifying its exact evolutionary relationships rather difficult – but it was probably a very early reptilomorph, closer related to amniotes than to lissamphibians. It may also have been very closely related to the equally enigmatic Eldeceeon and Silvanerpeton from the same region, but was almsot twice their size with a estimated total length of around 70cm (2’4″).

It would have resembled a rather heavily-built lizard-like or salamander-like animal, with fairly stumpy legs and probably lacking claws on its digits. While it would have had spindle-shaped scales on its underside, and possibly small rounded scales along its sides and back, these were bony structures embedded in its skin and probably weren’t very visible externally in life.

But Termonerpeton‘s most surprising feature was its proportionally large feet with especially elongated fourth toes, which would have helped to extend its stride length for energy-efficient terrestrial locomotion and to stabilize its movement on unstable surfaces – a much more “advanced” amniote-like arrangement than expected in such an early reptilomorph, and convergently similar to to the foot shapes of some modern lizards. Its fourth toe was also unusually chunky, suggesting it may even have been bearing most of its weight on just that one digit when walking.

Antarcticarcinus

Euthycarcinoids were a group of arthropods that lived between the mid-Cambrian and the mid-Triassic – but despite existing for over 250 million years their fossil record is incredibly sparse, and it’s only within the last decade that they’ve been recognized as being close relatives of modern centipedes and millipedes.

The earliest members of this group were marine, living in shallow tidal waters, but they quickly specialized into brackish and freshwater habitats and were even some of the very first animals to walk on land. Fossil trackways show they were amphibious, venturing out onto mudflats to feed on microbial mats, avoid aquatic predators, and possibly lay their eggs in a similar manner to modern horseshoe crabs.

Most euthycarcinoid species are known from tropical and subtropical climates, but Antarcticarcinus pagoda here hints that these arthropods were much more widespread and diverse than previously thought. Discovered in fossil deposits in the Central Transantarctic Mountains of Antarctica, it lived in freshwater lakes during the Early Permian (~299-293 million years ago), at a time when the region was in similar polar latitudes to today with a cold icy subarctic climate.

About 8.5cm long (3.3″), it would have had a similar three-part body plan to other euthycarcinoids – with a head, a limb-bearing thorax, and a limbless abdomen ending in a tail spine – but its most distinctive feature was a pair of large wing-shaped projections on the sides of its carapace. These may have helped to stabilize its body when resting on soft muddy surfaces, spreading out its weight, or they might even have functioned as a hydrofoil generating lift while swimming.

Bathyergoides

Blesmols, or African mole-rats, are a group of rodents adapted for mole-like burrowing. Closely related to the more famous naked mole-rat, these little mammals have reduced eyes and ears along with incisors that protrude out even when their mouths are closed, allowing them to excavate tunnels primarily using their teeth.

One of the earliest known fossil blesmols is Bathyergoides neotertiarius here, from the early Miocene of Namibia about 20 million years ago. For almost a century this species was known only from teeth and partial skull remains, but recently a partial skeleton was described giving us a better idea of its overall appearance and lifestyle.

Bathyergoides was a fairly large blesmol, around 25cm long (~10″), and was already specialized for tooth-digging with a skull very similar to modern forms. It had powerful muscular forelimbs that would have been used to push back loose soil while burrowing, but unlike its living relatives it also had a long tail and relatively slender hindlimb bones – with anatomy suggesting its legs were used more for stabilizing its posture than for actively digging.

It may have had a less subterranean lifestyle than modern blesmols, digging out extensive burrows but still foraging for food above ground in a similar manner to modern semi-fossorial rodents like giant pouched rats.

Amargasaurus

Amargasaurus cazaui was a sauropod dinosaur with a very distinctive-looking skeleton, sporting a double row of long bony spines along its neck and back. It lived in what is now Argentina during the Early Cretaceous, about 129-122 million years ago, and was fairly small compared to many other sauropods, reaching about 10m in length (~33′) with a proportionally short neck compared to its body size.

And despite being known from fairly complete skeletal remains there’s still a lot we don’t know about this dinosaur – especially what was actually going on with those vertebral spines. While it’s sometimes been depicted with skin sails over the spines, for the last couple of decades the general opinion has trended towards them being more likely to have been covered by spiky keratinous horn-like sheaths.

But recently that’s been brought back into question. A detailed study of the microscopic bone structure of Amargasaurus‘ spines shows no evidence for keratin attachment and instead found textures associated with skin coverings, along with an extensive web of ligaments connecting the spines to each other along each row.

So maybe it had big flashy sails after all!