Welcome to Unsolved Paleo Mysteries Month!
There’s a lot of things we now know about the distant past that seemed impossible only a few decades ago – discovering the colors of fossilized animals, fragments of collagen in dinosaur bones, and even finding near-complete remains of previously enigmatic animals like Deinocheirus.
But there’s also still a lot of things we don’t know. The fossil record is spotty and very incomplete, and even as we answer some questions others remain frustratingly unanswered.
So, every weekday during March I’ll be featuring a different paleontological mystery. Starting with…
We don’t really know where pterosaurs came from.
They appeared suddenly in the Late Triassic (~228 mya) with their anatomy already fully adapted for flight, and there are no traces of transitional forms before that point.
We at least know they were members of the archosaurs, and the sister group to dinosaurs, and their closest known relative seems to have been a small hopping creature named Scleromochlus. The complete lack of any other potential ancestors suggests that proto-pterosaurs must have evolved incredibly rapidly in an environment that just didn’t favor fossilizing their tiny fragile remains.
We might get lucky one day and finally find a pterosaur equivalent of Archaeopteryx, but for now all we have are hypothetical ideas of what such animals might have looked like.
Montealtosuchus arrudacamposi, a crocodyliform from the Late Cretaceous of Brazil (~93-83 mya). About 1.8m in length (6′), it had slightly forward-facing eyes, giving it binocular vision, and long upright limbs – adaptations for active hunting on land.
Basically, it would have looked a little like a “crocodile dog”.
Edestus, a holocephalan fish from the Late Carboniferous (~315-299 mya) of Eurasia and North America. A relative of the “spiral-saw-mouthed” Helicoprion, it continuously grew a single row of teeth in each jaw, creating an arrangement often compared to a pair of pinking shears.
Multiple species of this genus have been named, with varying degrees of tooth bracket curvature, and the largest may have had body sizes similar to modern white sharks – about 6m long (19′8″).
Since Edestus is only known from fossilized tooth brackets, how exactly its jaws worked and what it ate with them is still a mystery. Many reconstructions end up either goofy or horrifying as a result, and so I’ve attempted to make this one look a bit more “normal”. And capable of closing its own mouth.
Edit: This reconstruction was based more on chimaeras than on other eugeneodontids, and is therefore probably very inaccurate. When I originally did this image I wasn’t aware body outlines were known for the group. For a much more accurate version see my 2020 version in the “Weird Heads” series.
Homalodotherium, a South American notoungulate mammal from the Early-to-Middle Miocene of Patagonia (~20-15 mya). Standing about 1.4m tall at the shoulder (4′7″), it seems to have convergently evolved to fill the same selective browsing niche as the North American chalicotheres and the later giant ground sloths.
Despite being an ungulate it had claws rather than hooves, and walked plantigrade on its hind feet but digitigrade on its front feet. It would have been capable of rearing up bipedally to pull down branches with its long forelimbs, with the shape of its nasal bones suggesting it may have also had a prehensile upper lip to help it strip off vegetation while feeding.
Spinoaequalis schultzei, an early diapsid reptile from the late Carboniferous of Kansas, USA (~300 mya). Measuring about 30cm long (1′), it appears to have been semi-aquatic, with limbs like a typical terrestrial reptile but also possessing a long flexible paddle-like tail to aid in swimming – making it one of the earliest amniotes to experiment with “returning to the water”.
Bathornis grallator, a flightless bird about 75cm tall (2′6″) from the Late Eocene and Early Oligocene of Midwestern USA (~37-34 mya).
It was originally mistaken for a long-legged vulture (under the name Neocathartes) when first discovered in the 1940s, but later studies have shown it was actually one of the smaller members of the bathornithids – close cousins of the more well-known South American “terror birds”, successfully occupying terrestrial predator niches alongside large carnivorous mammals.
Lycopsis longirostrus*, a sparassodont mammal from the Middle Miocene of Colombia, South America (~14-12 mya). About 35cm tall at the shoulder (1′2″), it was originally thought to be a dog-like or thylacine-like animal, but studies of a well-preserved specimen have shown that it had an unusual mix of anatomic features in its limb bones, with adaptations for both climbing and running.
It was probably a terrestrial ambush hunter, preying on rodents and other small animals, but also had the ability to grasp and climb trees in its densely forested environment – especially useful for avoiding the land crocodiles that shared its habitat.
( * Often seen misspelled as L. longirostris )
Aaand we’re back to normal updates with a fully working computer again!
Let’s properly start off this year’s art pieces with a particularly weird sauropod dinosaur. This is Brachytrachelopan, known from Argentina at the very end of the Jurassic (~152-145 mya).
A member of the dicraeosaurids, it was a close relative of the spiky-necked Amargasaurus and was roughly the same size at about 10m long (32′9″) – but it also had the shortest neck of any known sauropod, suggesting it was specialized for a completely different diet. It may have been a sort of “iguanodont-mimic”, adapted to a low browsing niche, since actual iguanodonts were absent from its ecosystem.
I’ve given this one a little bit of speculative bristly fuzz, because I can. While all currently known sauropod skin impressions show scales, we don’t have full-body coverage and fuzz was almost certainly present in their ancestors – and both types of integument can also exist on the same animal in the same places.
Also I just like the idea of sauropods with manes and beards.
Myllokunmingia, from the Early Cambrian of China (~530 mya).
Just under 3cm long (or just over 1″), this tiny animal seems to have been a very close relative of the true vertebrates – almost a vertebrate itself but not quite there yet. A single known fossil specimen shows evidence of a cartilage skull and skeletal elements, five or six gill pouches, a large sail-like dorsal fin, and paired finfolds on its underside.
One of my favorite palaeontological discoveries of 2016 also involved one of my favorite extinct animals: the odd little “monkey lizard” Drepanosaurus.
Living during the Late Triassic of Europe and North America (~218-212 mya), this reptile measured about 50cm long (20″). It was already known to have some particularly weird anatomy, featuring a humped back, grasping feet, a prehensile tail ending in vertebrae modified into a pseudo-claw, enormous claws on the second finger on each hand, and a bizarre arrangement of its forearm bones.
In 2016, new fossils gave us a better look at those arm bones, and they turned out to be even stranger than previously thought. As well as the radius and ulna being unusual, several wrist bones were also heavily modified and elongated, creating an arm setup unique among all known tetrapods. This may have been a specialization for “hook-and-pull” digging, ripping up tree bark to get at burrowing insects – but now the real mystery is why no other tetrapods have ever managed to modify their limb bones to this sort of extreme.