It was one of the earliest known large-bodied members of the group, and shows that these animals must have increased in size very rapidly during their early evolution, going from rabbit-sized to pig-sized within just a couple of million years.
The cryptoclidids were fairly standard-looking plesiosaurs, with long necks and small heads – but those tiny skull bones were also rather fragile and so there’s very little good fossil material of their heads, making it difficult to figure out both their feeding ecology and their exact evolutionary relationships.
But a recently-discovered specimen from the Svalbard archipelago actually preserved a mostly-complete skeleton, including an unusually intact skull.
It measured around 5m long (16’5″) and had proportionally huge eyes that faced upwards on its head – an adaptation for seeing in low-light underwater conditions, maximizing the amount of light reaching it from above.
Those big dark-adapted eyes suggest it may have been nocturnal, or spent a lot of time diving into very deep waters in search of food. Its skull had weak jaw muscles and delicate teeth, and its gut region contained a lot of fine gravelly sediment, so it probably mainly grubbed around for small soft-bodied prey on the sea floor.
At that point in time Svalbard would have been a little further south than it is today, at a subarctic latitude, but the area would have still experienced particularly long nights during the winter. So it’s possible Ophthalmothule also developed such big sensitive eyes to help it survive through those darker seasons.
Their striking-looking dome heads were probably used for combat, headbutting or flank-butting each other, and many fossil skulls show evidence of injuries that would have been caused by that sort of behavior.
The eponymous Pachycephalosaurus wyomingensis lived in North America right at the end of the Cretaceous, about 70-66 million years ago. It was one of the largest of its kind, reaching lengths of around 4.5m (14’9″), and was characterized by a large bony dome-head surrounded by small blunt spikes.
But it turns out that was probably only what it looked like as a fully mature adult.
Living in Nova Scotia during the Late Triassic, around 235-221 million years ago, Teraterpeton (meaning “wonderful creeping thing”) was first named in the early 2000s based on a skull and partial skeleton, with some additional skeletal material being described recently in 2019.
Its head had a confusing mix of anatomical features, with a long beak-like toothless snout at the front of its jaws, small sharp interlocking cheek teeth further back, a huge nasal opening, and a closed-up fenestra at the back of its skull making it look more like the skulls of marine reptiles.
It also had a lizard-like body, perhaps up to 1.8m long (~6′), with rather long slender limbs and large blade-like claws, and more anatomical weirdness in the pelvic region convergently resembling those of distantly related groups like rhynchosaurs and tanystropheids. It had a sprawling posture, but its hind limb musculature suggests it might have been capable of getting up into a more erect stance when walking, somewhat similar to modern crocodilians’ “high walk” gait.
It was clearly quite an ecologically specialized animal, but quite what it was specialized for is still uncertain. It was presumably a herbivore like its close relatives, but it must have been eating a very different diet with its long beak, and its deep claws could have been used for scratch digging to get at roots and tubers.
Another possibility it that it could have been an insectivore with a diet similar to modern aardvarks or armadillos, probing with its beak and digging with its claws for insects, grubs, and other invertebrates. Since termite-like social insect nests do seem to have existed around the same time, it might even have been one the earliest known animals to specialize in myrmecophagy.
Fragmentary fossils of huge azhdarchidpterosaurs have been found in Canada since the early 1970s, and for a long time they were assumed to belong to Quetzalcoatlus. But more recently these remains were re-examined and shown to actually represent an entirely new genus and species.
Cryodrakon boreas – an excellent name meaning “icy dragon of the north wind” – was officially described in late 2019. With a wingspan of around 10m (32’10”) it was similar in size to its close relative Quetzalcoatlus, but it dates to about 10 million years earlier making it one of the oldest azhdarchids ever found in North America.
It lived about 76 million years ago in Alberta, with its fossils coming from the Dinosaur Park Formation, an area that at the time would have been a coastal plain near the northern parts of the Western Interior Seaway. Despite Alberta being located somewhat closer to the Arctic Circle than it is today, the climate was warm-temperate and temperatures rarely dipped below freezing, with short nights in the summers and only a few hours of daylight in the winters.
Ferrodraco lentoni (“Lenton‘s iron dragon”) is named after the ironstone that the fossils were found in, and while it’s known only from a partial skull, some pieces of its neck and wings, and various teeth, it’s still by far the best pterosaur specimen ever found in Australia.
Living during the mid-Cretaceous, somewhere between 94 and 90 million years ago, it had a 4m wingspan (~13′) and was also one of the very last of its kind. It was a member of the ornithocheirids, a group characterized by rounded crests at the tips of their long toothy jaws, which were previously thought to have all gone extinct by that time.
Many of Australia’s Cretaceous animals were close relatives of those found in South America, due to an earlier land connection via Antarctica, but surprisingly Ferrodraco wasn’t particularly closely related to any South American ornithocheirids. Instead it seems to have been part of a lineage known from halfway around the world in Europe, suggesting that these pterosaurs were capable of crossing long distances over oceans to disperse between continents.
Originating from Japanese monster movies like Godzilla, the word “kaiju” is now often used to refer to giant creatures in general – and so it was only a matter of time before a huge sauropod dinosaur was named after the concept.
Kaijutitan maui* was a titanosaur living in Argentina during the Late Cretaceous, about 89-86 million years ago. It’s only known from fragmentary remains, so its full size is difficult to estimate, but it was probably somewhere in the region of 20m long (66′). Nowhere close to the largestsauropod, but possibly one of the heaviest since it does seem to have been rather chunkily built, with stout limbs and an estimated weight of 40-60 tonnes (44-66 US tons).
* Not named for the Polynesian hero, apparently, but for the initials of the Museo Argentino Urquiza.
Named after the monster Grendel from the epic poem Beowulf, this 4m long (~13′) marine reptile had a big robust skull with large teeth, proportionally short flippers, and smaller eyes than some of its other relatives. It also had an unusual bony “hump” on its snout above its nostrils.
(About 20 years ago Grendelius was reassigned into Brachypterygius on the basis of the two not being distinct enough from each other to justify having separate genus names – but a more recent study suggests that that they actually were different after all, and the name may be valid again.)
Coelacanths are famous for being “living fossils”, completely disappearing from the fossil record at the end of the Cretaceous but then being rediscovered alive just 80 years ago. But although they’re often thought to have physically changed very little over the last 300 million years or so, more recent discoveries are starting to show that coelacanth body forms and lifestyles were actually more varied in the distant past.
Meet the wonderfully-named Rebellatrix divaricerca, from the Early Triassic of British Columbia, Canada (~251-247 mya). Measuring around 1.3m long (4′3″), its body shape and large symmetrical forked tail suggest it was adapted for fast swimming. Unlike its slow-moving deep-water modern relatives this coelacanth was a speedy oceanic active predator, convergently similar to tuna or some sharks.
Since it lived in the immediate wake of the end-Permian “Great Dying” mass extinction, Rebellatrix may have rapidly evolved from more standard-looking coelacanths to take advantage of a suddenly vacant ecological niche – or it might be part of a more extensive unusual lineage whose other members simply haven’t been discovered yet.