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.
At the time this region was a river plain with a tropical climate, experiencing seasonal floods that turned the whole area into what’s known as “viesses” (a name based on the abbreviation “V.S.S.” standing for “very shallow sea”), vast shallow lake-seas that persisted for weeks or months at a time.
So this little animal has been interpreted as being semi-aquatic, swimming around and feeding on aquatic invertebrates and tiny fish and amphibians. Its skull had numerous pits around the front of its face, suggesting that it had a highly sensitive snout – probably whiskery, allowing it to hunt entirely by touch in dark murky water, but it’s also been proposed to have possibly had an electroreceptive sense similar to modern platypuses.
But Brontornis might not actually have been a terror bird at all – it may have instead been a giant cousin of ducks and geese.
The known fossil material is fragmentary enough that it’s still hard to tell for certain, but there’s some evidence that links it to the gastornithiformes, a group of huge herbivorous birds related to modern waterfowl.
If it was a gastornithiform, that would mean it represents a previously completely unknown lineage of South American giant flightless galloanserans. And, along with the gastornithids and the mihirungs, it would represent a third time that group of birds convergently evolved this sort of body plan and ecological role on entirely different continents during the Cenozoic.
Non-tetrapod vertebrates like fish have spines that are much less differentiated, with just body and tail segments. So for a long time multiple distinct spine regions were thought to be something completely unique to tetrapods – a specialization developed early in their evolutionary history that served to better support their weight when moving around on land.
But one little fossil fish makes this idea… problematic.
Tarrasius problematicus lived during the early Carboniferous, about 345 million years ago, in shallow tropical marine waters in what is now southern Scotland. Around 9cm long (3.5″), it was an early type of ray-finned fish with a scaleless body and a long scaled eel-like tail with a single continuous dorsal fin.
Its spine shows five different regions all corresponding to those seen in tetrapods, despite it not being closely related to them. But unlike early tetrapods Tarrasius was no land-walker, with its lack of hind fins indicating it was instead a streamlined fully aquatic fast swimmer.
It’s not clear why this fish developed such an incredibly convergent backbone, but it may have helped to stiffen its body so its more flexible tail could provide more efficient thrust, swimming like a modern tadpole.
It also suggests that a pre-existing genetic basis for regionalization – specific patterns of Hox gene expression – was actually an ancestral trait for all bony fish or jawed vertebrates. Tarrasius and early tetrapods may have just happened to specialize their spines in the same way for different purposes, with only the tetrapods going on to see long-term evolutionary success with it.
They were previously known mainly from isolated teeth and jaw fragments, with some rare full skull material, but Adalatherium is remarkable for being represented by a complete skeleton.
And it’s turned out to be far stranger than anyone expected.
Living in northwestern Madagascar during the Late Cretaceous, about 70-66 million years ago, Adalatherium was one of the larger known Mesozoic mammals at around 60cm long (2′) – although the one known specimen seems to have been a juvenile, so mature individuals were probably slightly larger.
It was probably a marmot-like digging animal, excavating burrows with its large claws and powerful limbs, and since it likely evolved from ancestors that had become isolated on Madagascar over 20 million years earlier it had developed a very unusual mixture of both “primitive” and highly specialized anatomical features. It had more back vertebrae than any other known Mesozoic mammal, upright forelimbs, sprawling hind legs with bowed-out tibias, strong back and leg musculature, and a therian-like pelvis with epipubic bones.
And then there’s the snoot.
The snout region of Adalatherium‘s skull was pockmarked with a large number of foramina, holes that allow the passage of nerves and blood vessels through the bone. It had more of these than any other known mammal, and their presence suggests that it probably had a very sensitive upper lip and whiskery snout. Most mammals with a lot of whiskers just have one very big foramina, but Adalatherium seems to have evolved a different solution to the same problem.
It also had one other bizarre feature – a hole in the top of its nose. A large “internasal vacuity” between its nasal bones is a unique feature not known in any other mammal, and its function is a total mystery.
Since this hole was also surrounded by many foramina it may have supported some sort of soft-tissue sensory structure on top of its nose. So I’ve speculatively depicted it here with a leathery horn-like “shield”.
The exact evolutionary relationships of cephalopods within the conchiferan family tree aren’t clear, but their closest relatives might be modern monoplacophorans and they probably descended from limpet-like “monoplacophoran-grade” ancestors in the early Cambrian. The current oldest potential cephalopod fossils come from about 522 million years ago, but the first definite cephalopods in the fossil record come from much later in the period.
Living in Scotland during the mid-Carboniferous period, about 326 million years ago, this 1.5m long (~5′) stem-tetrapod had an incredibly unusual head compared to its relatives – wide and flat, almost square in shape, with its jaws lined with hundreds of tiny chisel-like teeth.
Most other stem-tetrapods had deep skulls with large teeth, adapted for fish-eating, so clearly Spathicephalus was specialized for a very different diet. Some comparisons have been made to flat-headed ambush predator plagiosaurid temnospondyls like Gerrothorax, but a better ecological comparison might actually be filter-feeders like “pancake crocs“.
Fossils of at least a dozen different species of these predatory marine reptiles have been found in the area, and they seem to have all been occupying different ecological roles to avoid being in direct competition with each other. Many had conical piercing teeth adapted for gripping onto slippery soft-bodied prey, but others had rounded blunt teeth for crushing hard shells, and some even had sharp shark-like teeth for tearing flesh.
This 7m long (23′) mosasaur was part of the plioplatecarpine lineage, but it had uniquely long and narrow jaws with pointy interlocking teeth and highly retracted nostrils. Its snout shape resembled that of a crocodilians like modern gharials more than any of its short-skulled close relatives, and it was probably specialized for a similar diet of small fast-moving fish.
Despite having a genus name that sounds more like it should belong to a cartoon dinosaur mascot for dental hygiene, Smilesaurus ferox was actually a real gorgonopsian, a predatory synapsid distantly related to modern mammals.
Living in South Africa during the Late Permian, around 259-254 million years ago, Smilesaurus was comparable to a medium-sized dog at around 1m long (3’3″). It had some of the longest sabre-like canine teeth of any known gorgonopsian, proportionally comparable to those of sabertoothed cats – and it may have hunted in a similar manner, using powerful grasping limbs to pin down struggling prey and then dispatching it with slashing bites.
…And it also turns out that when you don’t horribly shrink-wrap a gorgonopsian, you end up with something that looks rather like a bear-hippo.
(For some similarly chonky gorgonopsians, check out Tas’ @i-draws-dinosaurs reconstructions here. Bullet Man was definitely a bit of an inspiration in this.)
Its fossil remains were found in the Kem Kem beds of Morocco – ancient river deposits famous for yielding some of the newer specimens of the bizarre aquatic dinosaur Spinosaurus – and consist of just a couple of small pieces of jaw bones.
But those fragments are rather weird for a pterosaur.
While it’s hard to tell for certain from such meagre remains, Leptostomia might have been part of the azhdarchoid lineage, related to both the elaborately-crested tapejarids and the terrestrial-stalking giants like Quetzalcoatlus. And if it was indded an azhdarchoid it was an especially tiny one, possibly the smallest known member of the whole group. Based on the proportions of its relatives it would have stood just 30cm tall (1′) with a wingspan of 60-70cm (2′-2’4″), roughly comparable in size to a modern pigeon.
And it had an incredibly long beak that tapered to a thin delicate tip, resembling the beaks of modern probe-feeding shorebirds more than any other known pterosaur. It may have been specialized for the same sort of ecological niche, poking around in mud and shallow water for small invertebrates and snapping them up, possibly detecting its hidden prey using super-sensitive nerve endings in the tip of its beak.