excellent snoots – Nix Illustration

Falcatacaris

The enigmatic thylacocephalans were a group of bizarre little arthropods, found in marine deposits all over the world from the late Ordovician (~435 million years ago) to the late Cretaceous (~85 million years ago). They had shield-like bivalved carapaces, large compound eyes, three pairs of spiny grasping limbs, and multiple pairs of small paddle-like swimming limbs, but details of their internal anatomy are poorly known and their evolutionary relationships to other arthropods are still very uncertain.

Traditionally they’ve been classified as crustaceans, possibly as close relatives of remipedes or malacostracans – but they’ve also recently been proposed as instead being part of a much more ancient branch of arthropods, potentially related to stem–mandibulates like Acheronauta.

Falcatacaris bastelbergeri was a thylacocephalan living during the late Jurassic, about 150 million years ago, in what is now Germany. Around 2.5cm long (~1″), its carapace had tiny interlocking square “teeth” resembling a zipper along the hinge line between the two valves, a ridge along each side, and a long pointed knife-shaped spine at the front.

Like other thylacocephalans it was probably a swimming predator, likely nocturnal or hunting in murky conditions based on its enlarged eyes, and would have captured smaller aquatic prey using its raptorial limbs.

Cadurcodon

Cadurcodon ardynensis was an odd-toed ungulate that lived in what is now Mongolia during the late Eocene, about 37-34 million years ago.

It was around 2m long (6’6″) and, despite its very tapir-like appearance and lack of horns, it was actually closer related to modern rhinoceroses – it was part of a group of early rhino-cousins known as amynodontids, which convergently evolved both hippo-like and tapir-like lifestyles.

Cadurcodon was the most tapir-like of the tapir-like amynodontids, with a short deep skull and retracted nasal bones that indicate it had a well-developed prehensile trunk. Males also had large tusks formed from their upper and lower canine teeth, which may have been used for fighting each other.

Maghriboselache

Maghriboselache mohamezanei was a cartilaginous fish from the late Devonian Period, about 369 million years ago, living in the shallow marine waters that covered what is now the Anti-Atlas mountain range of Morocco in northwest Africa.

Up to around 2.5m long (~8′), it’s known from several exceptionally well-preserved and near-complete skeletons.

It had a streamlined body with large pectoral fins, small pelvic fins, and a strongly keeled crescent-shaped tail fin. And although it was superficially shark-like in appearance, it was actually part of a lineage known as cladoselachids, which were much closer related to modern chimaeras than to sharks.

It’s unclear if Maghriboselache had two dorsal fins like its close relative Cladoselache, but some specimens preserve evidence of a chunky spine where the front dorsal fin would have been. Others show no sign of a front dorsal fin or spine at all, suggesting there may have been some sexual dimorphism going on in this species, with males having a spine (and possibly also an associated front dorsal fin) and females only having a rear dorsal fin.

But the most unusual feature of Maghriboselache was its nose.

It had a very broad snout with large and unusually widely-spaced nostrils, which would have given it the ability to “smell in stereo” and determine the direction of scents carried through the water much more precisely – making it the earliest known example of that sort of sensory specialization.

Strange Symmetries #15: Serrated Saw-Snoots

Long flattened snouts lined with pointy tooth-like denticles have convergently evolved at least three separate times in cartilaginous fish: in modern sawsharks and sawfish, and in the extinct sawskates.

This repeated “pristification” suggests that saws are just incredibly useful and relatively “easy to evolve” structures for these types of fish, being both highly sensitive to bioelectric fields and able to physically slash and stab to kill prey.

Onchopristis numida was a sawskate known from what is now Northern and Western Africa during the mid-Cretaceous, about 95 million years ago. Up to about 3m long (~10′), it lived in both saltwater and freshwater, and was probably a bottom-dwelling ambush predator similar to modern angelsharks.

Whenever a denticle was lost from its saw, a larger one would grow to replace it, and over the life of an Onchopristis this resulted in an increasingly extreme amount of saw asymmetry.

Modern pristified fish also have rather asymmetrical saws. Sawfish are commonly born with a different number of denticles on each side, while sawsharks add extra denticles of varying sizes as they age, with the ongoing replacement of lost denticles resulting in more uneven arrangements over their course of their lives.

It’s not clear if the asymmetry gives any sort of advantage to these fish – but if nothing else it probably doesn’t cause them any disadvantage, so there’s no evolutionary pressure to stay more symmetrical.

Strange Symmetries #06: Trilobite Tridents

The genus Walliserops was one of the weirdest-looking trilobites, covered in numerous pointy spines and sporting a large three-pronged “trident” on the front of its face.

They also had some degree of asymmetry in their bodies. Their tridents often didn’t fork evenly, and their long forehead spines curved off to one side – possibly so they could lift their heads up without stabbing themselves in the back.

Walliserops hammii lived in what is now Morocco during the early-to-mid Devonian, about 403-392 million years ago. Around 5cm long (~2″) It was one of the “short trident” species of Walliserops, and its chunky forehead spine curved particularly strongly to the right.

The function of these trilobites’ elaborate tridents is still poorly understood. But an unusual individual of the long-tridented species Walliserops trifurcatushas been found with a lopsided four-pronged trident, and since it was able to grow to full maturity the shape of the structure probably wasn’t absolutely vital for survival, suggesting it wasn’t used for feeding or sensory purposes.

The tridents may instead have been used for combat with each other similar to the horns of some modern beetles. However, these sorts of features are usually only seen in males, and there’s currently no definite evidence for any significant sexual dimorphism in trilobites.

(Although perhaps like ceratopsid dinosaurs their ornaments were just present in both males and females, being also useful for species recognition, visual display, and defense against predators.)

Tsaidamotherium

Tsaidamotherium hedini was a ruminant ungulate living around 11 million years ago during the late Miocene, in the northeastern part of the Tibetan Plateau in what is now Northwestern China. Although it’s known only from partial skull remains it was probably similar in body size to a large sheep, about 80cm tall at the shoulder (2’7″).

Since its discovery in the 1930s it’s traditionally been classified as part of the muskox lineage, but in 2022 it was proposed to actually be a giraffoid very closely related to the newly-discovered Discokeryx.

Tsaidamotherium had some extremely unusual headgear, with highly asymmetrical “horns” (actually ossicones if was a giraffoid). The left one was small and positioned above the eye, while the right one was shifted back and towards the middle of the forehead, and was expanded out into a wide bony disk that would have supported a large helmet-like domed keratin covering.

Its skull also had a very large nasal cavity resembling that of the modern saiga antelope, suggesting it may have convergently evolved a similar sort of complex air-filtering snout to deal with dry cold air in its mountainous habitat.

Falcatakely

Modern birds’ upper beaks are made up mostly from skull bones called the premaxilla, but the snouts of their earlier non-avian dinosaur ancestors were instead formed by large maxilla bones.

And Falcatakely forsterae here had a very unusual combination of these features.

Living in Madagascar during the Late Cretaceous, about 70-66 million years ago, it was around 40cm long (1’4″) and was part of a diverse lineage of Mesozoic birds known as enantiornitheans. These birds had claws on their wings and usually had toothy snouts instead of beaks, and many species also had ribbon-like display feathers on their tails instead of lift-generating fans.

Falcatakely had a long tall snout very similar in shape to a modern toucan, unlike any other known Mesozoic bird, with the surface texture of the bones indicating it was also covered by a keratinous beak. But despite this very “modern” face shape the bone arrangement was still much more similar to other enantiornitheans – there was a huge toothless maxilla making up the majority of the beak, with a small tooth-bearing premaxilla at the tip.

This suggests that there was more than one potential way for early birds to evolve modern-style beaks, and there may have been much more diversity in these animals’ facial structures than previously thought.

Utaurora

Ever since the bizarre anatomy of Opabinia was first recognized in the 1970s, it’s been a persistently unique “weird wonder” of the Cambrian period. Over the decades we’ve figured out that it was an early type of arthropod in an evolutionary position between lobopodians and radiodonts, but this whole time it’s still been sitting there alone as the only known representative of a weird stem-lineage with no other known close relatives.

…Until now!

A fossil from the Wheeler Shale in Utah, USA (~507 million years ago) that was originally thought to be a tiny radiodont has been re-studied, and now we finally have another member of the opabiniid family: Utaurora comosa.

Only about 3cm long (1.2″), Utaurora had 15 pairs of swimming flaps along the sides of its body, and a tail region with a 7-part fan and a pair of serrated spines. Hair-like gill blades covered both its back and the bases of its swimming flaps, and although its head region was poorly preserved it probably had an arrangement of 5 eyes and a long flexible claw-tipped proboscis similar to that of Opabinia.

Its discovery extends both the geographical and temporal known range of opabiniids, and suggests that their continued scarcity in other Cambrian fossil sites compared to other soft-bodied arthropods may simply be because they were just incredibly rare animals in those habitats at the time.

Eons Roundup 11

It’s time for another batch of PBS Eons commission work!

An illustration of an extinct marine reptile. It has a lizard-like body and a long paddle-like tail, and a small head with an oddly-shaped wide mouth lined with many tiny teeth – the overall shape of its bizarre jaws resembles the head of a vacuum cleaner! — Atopodentatus unicus

An illustration of an extinct marine reptile. It resembles a turtle with a wide squared-off beak, small spikes on the back of its head, and a wide carapace shaped vaguely like a horseshoe crab. — Atopodentatus unicus

The marine reptiles Atopodentatus and Henodus, from “The Triassic Reptile With ‘Two Faces'”
https://www.youtube.com/watch?v=-8W26SiCylI

An illustration of an extinct giant marine turtle. it has a ridged shell like a leatherback, and a hooked eagle-like beak. — Archelon ischyros

An illustration of an extinct sea turtle. — Archelon ischyros

The marine turtles Archelon and Euclastes, from “The Return of Giant Skin-Shell Sea Turtles”
https://www.youtube.com/watch?v=Tmb8XCwb3FI

Leptostomia

Leptostomia begaaensis here is a recently-discovered pterosaur that lived during the mid-Cretaceous period, around 100 million years ago.

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.