paleoart – Page 26 – Nix Illustration

Elsornis

The enantiornitheans (“opposite-birds”) were the most diverse and widespread group of Mesozoic birds, existing all around the world throughout the Cretaceous period. They retained claws on their wings and had toothy snouts instead of beaks, and while most of them lacked the lift-generating tail fans of modern birds they appear to have still been very adept fliers.

But Elsornis keni here was doing something different.

Known from the Late Cretaceous of Mongolia, about 80 million years ago, this opposite-bird lived alongside famous dinosaurs like Velociraptor and Protoceratops in what is now the Gobi Desert. Only a single partial specimen has ever been found, so its full life appearance is unknown and this reconstruction is somewhat speculative, but it would have been around the size of a pigeon at 25cm long (10″) – not including any decorative tail feathers it may have had, similar to other enantiornitheans.

It wing and shoulder bones were very odd for an opposite-bird, with proportions that don’t match anything capable of competent flight. Instead Elsornis appears to have been a flightless enantiornithean, a representative of a previously unknown terrestrial lineage.

Heckerites

While most modern echinoderms display the group’s characteristic five-way symmetry, there were plenty of much much stranger-looking forms back during the Paleozoic.

And some of the most confusing of them were the paracrinoids, which evolved an incredibly diverse range of body shapes during their group’s relatively short 40 million year existence during the Ordovician.

Despite the name these echinoderms weren’t particularly closely related to true crinoids, instead being part of a completely extinct lineage known as the blastozoans. Their ancestors had been radially symmetric, but paracrinoids largely abandoned that body plan, instead developing irregularly shaped and often asymmetric bodies ranging from round to flattened. They had between two and five “food grooves” on their upper surfaces, derived from the ambulacra, lined with numerous feeding appendages along only the left side of each.

They were shallow-water animals, living either attached to the seafloor by a long stem or anchored into the sediment by a shorter one, suspension feeding with their appendages and transporting the food particles towards the mouth located between the bases of the food grooves.

(…And speaking of mouths, some paracrinoid species appear to have had two of them.)

Heckerites multistellatus here lived around 458-445 million years ago, during the Late Ordovician. It inhabited the then-subtropical seas of the Baltica region, with fossil material known from what is now Estonia, southeastern Norway, and northwest Russia.

About 10cm tall (4″), it lived on the seafloor in sheltered waters protected from strong waves by large reefs, and is unusual even among its weirdo relatives for features such as retaining feeding appendages on both sides of its food grooves – although irregularly arranged and with fewer on one side than the other. Its body was shaped rather like a flattened bean, with two food grooves diverging from roughly the centre of the top margin, chunky skeletal plates forming a border around its edges, and a short stem at is base.

It also had an unusually large “anal pyramid” on the opposite side of its body from its mouth, and this may have been used for respiration as well as waste expulsion, similar to modern sea cucumbers.

Brachydectes

The lysorophians were a group of Carboniferous and Permian tetrapods with highly elongated bodies and tiny limbs, usually thought to be part of the lepospondyl amphibians – but some recent studies have instead placed them and some of their close relatives as possibly being very early members of the reptile branch of amniotes.

Brachydectes newberryi here is one of the best-known lysorophians, represented by a good amount of fossil material compared to many of its relatives. Living in the Midwestern United States during the late Carboniferous and early Permian, around 310-290 million years ago, it had a proportionally tiny head and reached lengths of around 60-70cm (2′-2’4″).

Its wide shovel-shaped snout and thickened reinforced bones around its braincase suggest it was adapted for headfirst digging, and some specimens have actually been found preserved inside their burrows. The roof of its skull also developed extensive “sculpturing” as individuals aged, with juveniles having smooth bone surfaces and larger adults having a distinct rough bumpy texture.

So I’ve depicted it here with a speculative keratinous “head shield”.

Aegicetus

The protocetids were some of the first oceanic cetaceans, occupying a transitional position in the evolution of whales, with four paddle-like limbs and nostrils only partway up their snouts.

Early members of this group swam like otters, using a combination of undulating their bodies and paddling with large hind limbs, but somewhere in the Late Eocene they switched over to propelling themselves entirely with their tails and gave rise to even more whale-like forms like the basilosaurids.

And Aegicetus gehennae was right in the middle of that switch.

Discovered in the Wadi Al-Hitan (“Valley of the Whales”) fossil site in Egypt, Aegicetus lived around 37-35 million years ago. It was similarly-sized to earlier protocetids like Georgiacetus, measuring about 3.5m long (11’6″), but its hind limbs were proportionally smaller. Its hips were also completely disconnected from its vertebrae, giving it much more flexibility to undulate its body and tail – and preventing it from supporting its weight on land, suggesting that it spent its entire life in the water.

It wasn’t a direct ancestor to more “advanced” cetaceans, since it lived alongside several species of basilosaurids. Instead it seems to represent a late-surviving example of what the earlier protocetid-basilosaurid transitional forms would have looked like.

Spectrovenator

(This is a couple of days late for Halloween, but since this October saw the description of a new dinosaur species with a particularly spooky name, I couldn’t resist putting it into the schedule anyway.)

Spectrovenator ragei was an early member of the abelisaurid lineage, living in southeastern Brazil during the Early Cretaceous, about 120 million years ago. It was one of the smallest known abelisaurids, measuring just 2m long (6’6″), and lacked a lot of the skull specializations seen in larger-bodied Late Cretaceous forms like Carnotaurus, suggesting it was more of a generalist predator.

Its genus name translates to “ghost hunter” due to it being found underneath the fossil remains of another dinosaur entirely – a “ghost” unexpectedly appearing when the specimen was being prepared – but it’s extra appropriate since it also helps to fill in a rather sizeable ghost lineage in the fossil record of abelisaurids.

Anzu

Named after the mythological bird-like Anzû – and also nicknamed “the chicken from hell” – Anzu wyliei was one of the larger known oviraptorosaurs, measuring about 3m long (9’10”).

Its fossils are some of the most complete for a North American member of this dinosaur group, with four different specimens representing about 80% of the whole skeleton.

Living right at the end of the Cretaceous, about 66 million years ago in North Dakota and South Dakota, USA, Anzu inhabited the ancient floodplains of Hell Creek and appears to have been a fairly fast-moving omnivorous generalist. It had a large crest on its head made of rather fragile thin-walled bone, which may have been used for display or sound amplification similar to the casque of modern cassowaries.

Some of the fossil specimens also show evidence of healed injuries, including a broken rib and an arthritic toe.

Kerberos

Named after the mythical dog Cerberus, Kerberos langebadreae was a member of an early group of carnivorous placental mammals known as hyainailourids.

These large-headed predators were part of the hyaenodont lineage, evolutionary cousins to modern carnivorans that convergently developed similar shearing carnassial teeth in their jaws. Hyainailourids originated in Africa during the late Paleocene or early Eocene, and repeatedly dispersed into Eurasia and North America before eventually going extinct in the mid-Miocene.

Kerberos was one of the earliest of its kind known from Europe, living in Southern France during the mid-Eocene about 41-38 million years ago. It was close in size to a small American black bear, standing around 65cm tall at the shoulder (2’2″), not nearly as large as some of its later relatives but still making it one of the biggest carnivorous mammals in Europe at the time.

It was a heavily-built animal with a fully plantigrade posture, and would have been an active apex predator hunting similarly-sized early ungulates. While it wasn’t anatomically specialized for fast running it didn’t really need to be – it’s important to remember that modern bears have a similar chunky flat-footed build and yet can move surprisingly quickly.

Its incredibly powerful jaw muscles and premolar teeth adapted for bone-cracking also suggest it ate like a hyena, efficiently consuming entire carcasses.

Tanystropheus hydroides

Tanystropheus is one of the classic Triassic weirdos, a bizarre archosauromorph easily recognizable with its ridiculously long neck.

Mainly known from mid-Triassic deposits on the Swiss-Italian border, dating around 247–235 million years ago, fossils of the species Tanystropheus longobardicus have been found in two different “morphs” – small forms less than 2m long (6’6″), and larger ones up to 6m long (19’8″).

For a long time the smaller fossils were thought to be juveniles, but while they certainly had juvenile-looking facial proportions they also had very different teeth compared to the larger forms. They had pointed teeth at the front of their mouths and multi-cusped cheek teeth further back, and the “adults” had jaws containing only the pointed teeth, suggesting very different diets and lifestyles between the two size classes.

Extreme changes in dentition and diet during maturation aren’t unheard of in fossil species, but something particularly odd was going on here. Larger forms over 2m long always had just the pointed teeth, and there were no signs of intermediate tooth arrangements at all.

And a new study using x-ray microtomography has given an answer: they weren’t actually the same species!

Turns out the smaller Tanystropheus longobardicus were all skeletally mature adults, already fully grown at that size. The larger ones were a completely separate species occupying a different ecological niche to their smaller relatives, and have been named Tanystropheus hydroides in reference to the mythical hydra.

Comparison of the skulls of *T. hydroides* and *T. longobardicus*

[ From fig 3 in Spiekman, S. N. *et al* (2020). Aquatic Habits and Niche Partitioning in the Extraordinarily Long-Necked Triassic Reptile *Tanystropheus*. *Current Biology*. https://doi.org/10.1016/j.cub.2020.07.025 ]

While the exact lifestyle of Tanystropheus is an ongoing paleontological argument, Tanystropheus hydroides at least appears to have been much more on the aquatic side of things, with nostrils positioned on the top of its snout and its pointed teeth forming a “fish trap” in its jaws.

Stomach contents suggest it mainly ate fast-moving aquatic prey like fish and cephalopods, but its body wasn’t really adapted for strong swimming and so it couldn’t have been catching them via active pursuit. Instead it was probably an ambush predator hunting in a similar manner to some plesiosaurs, using its incredibly long neck and relatively small head to carefully approach prey species without the rest of its body startling them, and then catching them with fast snapping sideways lunges.

Eons Roundup 8

Once again it’s a PBS Eons commission roundup day!

An illustration of an extinct baleen whale. It's looks very similar to modern rorquals, with pleated throat grooves. — Cerro Ballena rorqual

An illustration of an extinct seal. it has an unusually long neck. — Cerro Ballena rorqual

An unnamed Cerro Ballena rorqual whale and the long-necked seal Acrophoca, from “How the Andes Mountains Might Have Killed a Bunch of Whales”
https://www.youtube.com/watch?v=iNk6r5WljGc

An illustration of an extinct pseudosuchian, a relative of modern crocodiles. It resembles a dinosaur much more than a croc, standing bipedally, with a long neck, tiny arms, and a long counter-balancing tail. — Shuvosaurus inexpectatus

A skeletal diagram of an extinct pseudosuchian, a relative of modern crocodiles. It resembles a dinosaur much more than a croc, standing bipedally, with a long neck, tiny arms, and a long counter-balancing tail. — Shuvosaurus inexpectatus

The poposauroid pseudosuchians Shuvosaurus (life restoration) and Effigia (skeletal) from “When Dinosaur Look-Alikes Ruled the Earth”
https://www.youtube.com/watch?v=QsmV34Co32c

Thylacares

Thylacocephalans were a bizarre group of extinct marine arthropods that often looked like tiny alien creatures – and whose evolutionary relationships are still uncertain. Despite existing in oceans around the world for at least 350 million years, their fossil record is rather spotty and their internal anatomy is often poorly preserved, making it difficult to figure out anything more specific than “probably some sort of crustacean“.

Possible thylacocephalans are known from as far back as the Cambrian, but one of the earliest definite members of the group was Thylacares brandonensis.

Living during the early Silurian, around 436 million years ago, in the region that today is part of Wisconsin, USA (found in the same fossil formation as last week’s Venustulus), this species measured up to about 7.5cm long (3″). Its body was enclosed by a large bivalved carapace, with protruding stalked eyes and what may have been a pair of antennae, along with smaller raptorial limbs than its later relatives.

While it was less specialized than other thylacocephalans it was probably a similar sort of swimming predator, catching prey with its spiny limbs.