paleoart – Nix Illustration

Smilosuchus

Smilosuchus gregorii lived in what is now the Southwestern United States during the Late Triassic, about 218 million years ago.

Despite looking a lot like a crocodilian it wasn’t very closely related to modern crocs at all, instead being a phytosaur — a lineage of early pseudosuchians (or possibly earlier-branching archosauriformes) that convergently evolved a crocodile-like lifestyle and appearance.

Around 6m long (~20′), it was armored with bony osteoderms and had long toothy jaws with tusk-like teeth at the tip. But unlike the crocodiles it resembled its nostrils were set high on its snout up near its eyes, and it probably had scaly lizard-like lips.

The high-set position of its nose and a fossil specimen surviving for some time with both of its hind legs compromised by osteomyelitis suggest that Smilosuchus was semi-aquatic. Based on fossil bones of large terrestrial animals like rauisuchids with phytosaur teeth stuck in them it was probably a croc-like ambush predator lunging at prey at the water’s edge — but it may also have been capable of walking around on land with an upright “high walk” gait.

Chernyshevine

Cyclidans were an enigmatic group of crustaceans that first appeared in the Early Carboniferous (~358 million years ago) and survived all the way until the Late Cretaceous (~66 million years ago). They had body plans resembling crabs — making them an example of carcinization — with flattened round carapaces and pincer-like front appendages.

Their exact evolutionary relationships within Crustacea have been debated for a long time, but recent studies suggest they may have been most closely related to both malacostracans and the also-mysterious thylacocephalans.

Chernyshevine spinosus was an Early Carboniferous cyclidan, living about 340 million years ago in what is now Tajikistan in Central Asia. Around 2cm long (~0.8″), it had a rather domed carapace covered in small bumps — and also long pointed spines around its edges, a feature not seen in any other known cyclidan.

It inhabited shallow marine waters and probably had a similar lifestyle to the crabs it resembled, scuttling around in reefs and feeding omnivorously using its claws to manipulate food items.

Garamaudo

Garamaudo bauciensis was a mosasaur that lived during the Late Cretaceous, about 84 million years ago, inhabiting freshwater lakes and marshes in what is now southeastern France.

Its genus name comes from the Provençal expression “gara au maudo”, meaning “beware the cursed one”, referring to an aquatic serpentine monster of local legend.

Around 2.5m long (~8’2″), Garamaudo was a fairly “primitive” mosasaur, with limb anatomy closer to the legs of terrestrial lizards than the paddle-like flippers of later forms. It had increased bone density that would have helped control its buoyancy and aided it in diving — but this also would have made it unable to move around on land due to the increased fragility of its heavier bones.

It probably swam with an eel-like motion and may not have been particularly speedy or maneuverable, possibly relying on ambush predation to capture its prey.

It would have been one of the largest aquatic predators in its ecosystem, living alongside gars, turtles, small crocodilians, and some of the last known freshwater coelacanths.

Gargoyleosaurus

Gargoyleosaurus parkpinorum was a very early ankylosaur that lived in what is now Wyoming, USA, during the Late Jurassic, about 154-150 million years ago.

Known from a partial skeleton — including much of its armor preserved in place — it was a fairly small ankylosaur, around 3.5m long (~11’6″). Its head was proportionally small, its snout was rather narrow, and unlike later members of the group it still had teeth in the front of its jaws.

It would have inhabited the warm and semi-arid “Jurassic savanna” environment of western North America, feeding on vegetation along river flood plains and sharing its ecosystem with more famous dinosaurs such as Stegosaurus, Diplodocus, and Allosaurus.

Alienacanthus

Alienacanthus malkowskii was a placoderm armored fish that lived in the seas covering what is now Europe and northern Africa during the late Devonian, about 365 million years ago.

First discovered in the 1950s, this species was originally known only from some strange elongated bony elements that were interpreted as fin spines. But more recent finds of near-complete skull material revealed a surprise — the “spines” were actually this animal’s extremely elongated lower jaw!

Around 2.5m long (~8’2″), it was probably a streamlined open ocean swimmer that may have used its bizarre underbite similarly to the snouts of modern billfish, slashing at and stunning soft-bodied prey.

Ogresuchus

Ogresuchus furatus was a small crocodyliform that lived during the Late Cretaceous, about 66 million years ago, in what is now Catalonia, Spain.

It was originally classified as a sebecid, which would have made it the earliest known member of that family, but a more recent analysis suggests it was probably instead an atoposaurid.

Around 1m long (~3’3″), it was a lightly-built generalist predator that would have fed on invertebrates and small vertebrates — possibly even including sauropod hatchlings, since its fossil remains were discovered in a titanosaur nesting site.

Mamenchisaurus

Although sauropod dinosaurs are famous for their long necks, one group known as mamenchisaurids took that particular feature to the extreme, with elongated necks that made up around half of their total body length.

And ‘Mamenchisaurus’ sinocanadorum* was one of the largest and longest. Living in what is now northwestern China during the Late Jurassic, about 160 million years ago, it had a 15m-long neck (~49′) and an estimated total length of 25-30m (~82-98′).

(*The whole Mamenchisaurus genus is a bit of a wastebasket and needs revision. Recent phylogenetic analyses suggest M. sinocanadorum was closer related to Xinjiangtitan than to other Mamenchisaurus species, but whether it actually belongs in that genus instead or merits its own new name has yet to be determined.)

Its enormous neck was ultralightly-built and highly pneumatic, with the vertebrae containing around 70% air sacs by volume. Extremely long cervical ribs served to stabilize the neck, but would also have limited flexibility along most of its length — it may have operated like a crane arm, sweeping around to feed on vegetation across a wide arc without having to move its body at all.

Bataspis

Bataspis crux was an armored jawless fish that lived during the early Devonian, around 419 million years ago, in coastal marine waters covering what is now southwestern China.

It was a member of the galeaspids, a group characterized by massive headshields covered in a pattern of sensory canals, with a large opening on the front top surface between the eyes. While this hole often looked like a comical mouth, it was actually a single nostril that took in water for the gills, while the real mouth was located on the animal’s underside.

Galeaspids also had scaly bodies with three dorsal fins, a tail fin, and long low ribbon-like fins along the sides that may have been the precursors to paired fins in jawed fish.

Bataspis’ headshield was unusually shaped compared to its relatives, with sweeping side projections forming a distinct “batwing”. Hydrodynamic simulations indicate that it functioned as a hydrofoil, generating lift while swimming and making Bataspis an efficient underwater glider — and suggesting that galeaspids were much more ecologically diverse than previously thought.

Ictitherium

Ictitherium ebu* was a hyena that lived in what is now Kenya during the late Miocene and early Pliocene, around 7-5 million years ago. It was part of an early branch of the hyaenids known as ictitheres, dog-like hyenas found across Miocene Africa and Eurasia that occupied similar ecological niches to modern canids.

(*alternatively classified as Hyaenictitherium ebu by some studies)

It was similar in size to the modern aardwolf, standing about 50cm tall at the shoulder (~1’8″) – but it had proportionally longer legs, giving it a build convergently similar to the present-day maned wolf. Despite these long limbs it wasn’t a fast runner, with its joint anatomy instead suggesting it was adapted for efficient walking, pouncing on prey, and looking over the tall grasses of its savanna woodland habitat.

Polysacos

Polysacos vickersianum was a marine mollusc that lived during the early Carboniferous, around 345 million years ago, in what is now Indiana, USA.

It was part of a group known as multiplacophorans, which are usually considered to be close relatives of modern chitons — but may instead represent a much earlier branch of the aculiferan lineage that convergently evolved chiton-like anatomical features.

About 2.5cm long (~1″), Polysacos had seventeen shell plates surrounded by a fringe of long spines with concave upper surfaces. Like the modern chitons it resembled it was probably a grazer that scraped up algae from hard rocky surfaces.