But I’m not talking about the dubious claims of non-avian dinosaur fossils found in places they shouldn’t be. This is about something else entirely: an unassuming little bird known as Qinornis paleocenica.
Living in Northwest China during the mid-Paleocene, about 61 million years ago, Qinornis was roughly pigeon-sized at around 30cm long (12″). It’s known only from a few bones from its legs and feet, but those bones are unusual enough to hint that it might have been something very special.
Uniquely for a Cenozoic bird, some of its foot bones weren’t fully fused together. This sort of incomplete fusion is seen in both juvenile modern birds and in adults of non-avian ornithurine birds from the Cretaceous – and the Qinornis specimen seems to have come from an adult animal.
If it was fully grown with unfused feet, then that would suggest it was actually part of a “relic” lineage living 5 million years after the mass extinction, surviving for quite some time longer than previously thought.
Remarkably similar-looking gliding reptiles have appeared multipledifferenttimes over the group’s evolutionary history, including the modern Draco – and despite being unrelated to each other almost all of them have achieved this in the exact same way, supporting their wing membranes on extremely elongated rib bones.
These early members of the neodiapsid lineage were the very first vertebrates known to have experimented with gliding, all the way back in the late Permian period 260-252 million years ago. And while they superficially resembled all the later rib-gliders, their wings were actually something never seen before or since in a gliding reptile.
Basically, these animals were the closest that Earth life ever came to legitimately evolving a dragon.
Coelurosauravus elivensis here was a weigeltisaurid living in what is now Madagascar, which at the time was part of southern Pangaea. About 40cm long (1’4″), its body was adapted for a life climbing and gliding around in the treetops, with pneumatized air spaces lightening its bones and long slender limbs similar to those of modern tree-climbing lizards.
Its large wings were formed from around 30 pairs of long hollow rod-shaped bones extending out from the sides of its belly. These flexible structures could furl and unfurl with a motion like a foldable fan, and are thought to have been highly modified from osteoderms in the skin, creating an entirely new part of its skeleton.
Towards the front of the wing the rods were arranged in several closely-packed “bundles”, and one specimen of Coelurosauravus preserves an impression of what seems to be the outline of the wing membrane’s leading edge – showing a stiffened pointed shape resembling the alula of a bird wing, which may have served a similar aerodynamic stabilization function.
From fig 2 in Schaumberg, G. et al (2007). New information on the anatomy of the Late Permian gliding reptile Coelurosauravus. Paläontologische Zeitschrift 81, 160–173. https://doi.org/10.1007/BF02988390
But aside from the wings, the most striking feature of weigeltisaurids were their heads. Their skulls featured large crest-like frills resembling those of chameleons and ceratopsid dinosaurs, and their edges were adorned with prominent bumps and spikes. These were probably used for visual display and might have been a sexually dimorphic feature, with males having larger spikier crests than females. The crests may also have anchored large powerful jaw muscles, giving weigeltisaurids a wider gape and faster bite speed, helping them to snap up their fast-moving insect prey.
Desmatophocids were a group of seal-like pinnipeds that appeared very early in the group’s evolution, around 23 million years ago. They were found across the northern Pacific from the west coast of North America to Japan, and were the first pinnipeds to get big, with some species reaching sizes comparable to modern northern elephant seals.
They had a mixture of anatomical features similar to true seals, sea lions, and walruses, but weren’t actually the ancestors of any of those modern groups. Instead they seem to have just been their own separate thing, a very early diverging “cousin” lineage of pinnipeds that convergently developed close resemblances to their later relatives.
Allodesmus demerei here was one of the last known desmatophocids, living in the late Miocene (~9 million years ago) in what is now southwest Washington, USA.
It would have been a sea lion-like animal, able to walk on all fours when hauled out on land, and showed distinct sexual dimorphism, with males growing to sizes of around 4m long (13′) and females being somewhat smaller. It powered its swimming using its front flippers, and may have mostly foraged in deep dark waters, using both keen vision and sensitive whiskers to locate prey.
The nasal region of its skull also shows some similarities to modern elephant seals, and some reconstructions depict males with the same sort of large proboscis.
Bipedal running has convergently evolved multiple times in squamate reptiles, known in over 50 modern species – and fossil evidence shows this is nothing new, with lizards repeatedly developing the ability to sprint on their hind legs for well over 100 million years.
Its limb proportions indicate it would have been a bipedal runner, making it one of the earliest known examples of this type of locomotion in lizards. Its skull also had some features convergent with varanids, suggesting it may have had a similar sort of active-pursuit-hunting ecology.
Known from the Emu Bay Shale fossil deposits in Kangaroo Island, South Australia (~514 million years ago), Nesonektris was one of the larger known vetulicolians, growing to at least 17cm long (~6.5″). Like most of its relatives it had a large streamlined forebody with a mouth opening at the front, and no obvious appendages or sensory structures. A groove down each side may have housed gill openings, and a segmented flexible tail provided propulsion for swimming.
Very little is known about the ecology of these animals. They were clearly adapted for active swimming in the water column, and may have filter-fed on plankton – but some other vetulicolians have been found preserved with their guts full of seafloor sediment, suggesting some sort of detritivorous lifestyle instead.
Their evolutionary relationships are also still uncertain, but preservation of what appears to be a notochord in Nesonektris suggests that vetulicolians may have been part of the chordate lineage, possibly close relatives of tunicates.
This particular genus was very widespread for much of the Eocene, found across Europe, Asia, and North America, crossing back and forth between the continents via the North Atlantic land bridge.
The Jamaican Hyrachyus lived during the mid-Eocene, around 45 million years ago, and was very anatomically similar to the North American Hyrachyus affinis – with the known fossil material not being considered distinct enough to be assigned to a new species yet. It was also about 15-20% smaller than its mainland relative, standing only 25cm tall at the shoulder (10″), but it’s not yet clear if this was a case of insular dwarfism or not.
Its presence in ancient Jamaica suggests that there may have been some sort of land connection between the proto-island and Central America during the early Eocene, when a chunk of what would eventually become western Jamaica was located much closer to the coasts of Honduras and Nicaragua. It’s the only fossil ungulate known from the Caribbean, and one of only a few terrestrial mammals in the region with North American evolutionary roots (the others being the extinct rodents Caribeomys merzeraudi and Oryzomys antillarum, and modern solenodons).
Unfortunately these little rhinos didn’t get much time on their island home. Jamaica subsided fully underwater about 40 million years ago, drowning its unique Eocene ecosystem entirely, and wouldn’t re-emerge and be re-colonized until much later in the Cenozoic.
And back in the 1890s, a specimen of this species was discovered with soft tissue impressions showing a diamond-shaped tail fin.
But despite us knowing about plesiosaur tail flukes for such a long time, they’re surprisingly under-represented in reconstructions, never seeming to have become associated with the popular image of these animals in the same way that early pterosaur’s tail vanes did. It doesn’t help that no other direct impressions of plesiosaur tail fins have ever been found, or that the Seeleyosaurus specimen’s soft tissue got painted over at some point in the mid-1900s, making it incredibly difficult to study without causing further damage.
(Perhaps modern non-invasive scanning techniques could be able to see under the paintjob, but as far as I’m aware nobody’s tried that yet.)
These tail fins are usually assumed to have been vertically oriented like those of other aquatic reptiles, moving side-to-side and acting like a rudder. However, there’s also a hypothesis that their fins might have actually been horizontal more like those of modern cetaceans and sirenians, based on several anatomical quirks – such as their tail regions being very wide and flat at the base, and the vertebrae at the tip being unusually pygostyle-like, very different from the way the tail bones of vertically-finned reptiles look.
Silesaurus opolensis here was a type of dinosauriform – a reptile very closely related to the ancestors of true dinosaurs, but not quite actually a dinosaur itself.
Living in Poland during the Late Triassic (~230 million years ago), it was a quadrupedal animal roughly the size of a large modern dog, about 50cm tall at the shoulder (1’8″) and 2m long (6’6″). The front of its lower jaw was toothless and covered with a keratinous beak, and there may have been a corresponding much smaller beak at the very tip of its upper jaw, too.
Horseshoe crabs are famous examples of “living fossils“, having changed their external appearance very little over hundreds of millions of years. But some fossil species were much more varied in shape than their morphologically conservative modern relatives, such as Austrolimulus fletcheri here.
Living in freshwater environments in what is now New South Wales, Australia, during the Middle Triassic (~247-242 million years ago), Austrolimulus had incredibly long spines on each side of its head, reaching a span of around 18cm (7″) – wider than its total body length!
The function of these spines is unclear, but they may have acted like a hydrofoil in fast-moving currents, or they may have served a defensive purpose by making Austrolimulus‘ carapace too wide and unwieldy for some predators to deal with.
