Eons Roundup 7

It’s another PBS Eons commission roundup day!

The metatherian mammals Pucadelphysand Khasia, and lineart of the sparassodont Paraborhyaena, from “How South America Made the Marsupials”
https://www.youtube.com/watch?v=l5doyrUWFbE

The dyrosaurid crocodyliform Acherontisuchus and the bothremydid turtle Puentemys, from “How a Hot Planet Created the World’s Biggest Snake”
https://www.youtube.com/watch?v=T-hDNbM-WLk

The early penguin Waimanu and the giant penguin Anthropornis, from “When Penguins Went From The Sky To The Sea”
https://www.youtube.com/watch?v=HMArjGQwLvY

Qianshanornis

Many modern predatory birds have enlarged claws on their second toes, similar to those of their paravian dinosaur ancestors – with seriemas being a particularly good example.

Seriemas are part of a lineage known as cariamiformes, highly terrestrial birds that were widespread across most of the world but are today represented today by only two living species in South America. During the Cenozoic this group repeatedly evolved into large predatory flightless forms like the the phorusrhacids and bathornithids, and were probably the closest avians ever got to recreating the “carnivorous theropod” body plan and ecological niche.

And yet none of them ever seem to have experimented with more dromaeosaurid-like claws.

…With one known exception.

Qianshanornis rapax here lived in East China during the mid-Paleocene, about 63 million years ago. It was a small cariamiform, probably around 30cm tall (1″), and is only known from fragmentary fossil material – but part of those fragments was a fairly well-preserved foot. And the bones of its second toe were unlike any other known Cenozoic bird, shaped incredibly similarly to those of dromaeosaurids and suggesting it may have had the same sort of big hyperextendible “sickle claw”.

While it had sturdy legs and short wings, and probably spent a lot of time walking on the ground like other cariamiformes, it was probably also still a fairly strong flier based on the known anatomy of its arms and shoulders.

Unfortunately, though, its head and claws were entirely missing, so without more fossil discoveries it’s hard to say anything definite about its ecology. I’ve restored it here based on other predatory cariamiformes, but since it was also closely related to a herbivorous species it’s not clear whether Qianshanornis was truly a dromaeosaur-mimic or if something else was going on with that unique second toe.

Prenoceratops

Although much less famous than their larger horned and frilled relatives, the leptoceratopsids were a widespread and successful group of ceratopsian dinosaurs during the Late Cretaceous, with fossils known from North America, Asia, and Europe (and, dubiously, Australia).

They were fairly small stocky quadrupedal dinosaurs, sort of pig-like, with short deep jaws and powerful beaks adapted for eating fibrous low-level plants like ferns and cycads – and to process such tough food they even evolved a chewing style similar to mammals like rodents.

Prenoceratops pieganensis here is known from the Two Medicine Formation bone beds in Montana, USA, dating to about 74 million years ago. Around 1.5-2m long (~5′-6’6″), it was very similar to its later relative Leptoceratops, but had a slightly lower, more sloping shape to its skull.

Weird Heads Month #29: Giant Saw-Toothed Birds

The pelagornithids, or “pseudotooth birds”, were a group of large seabirds that were found around the world for almost the entire Cenozoic, existing for at least 60 million years and only going completely extinct just 2.5 million years ago.

Their evolutionary relationships are uncertain and in the past they’ve been considered as relatives of pelicaniformes, albatrosses and petrels, or storks, but more recently they’ve been proposed to have been closer related to ducks and geese instead.

Whatever they were, they were some of the largest birds to ever fly, and many of the “smaller” species still had wingspans comparable to the largest modern flying birds.

But their most notable feature was their beaks. Although at first glance they look like they were lined with pointy teeth, these structures were actually outgrowths of their jaw bones covered with keratinous beak tissue. While these bony spikes would have been useful for holding onto slippery aquatic animals like fish and squid, they were actually hollow and relatively fragile so pelagornithids must have mainly caught smaller prey that couldn’t thrash around hard enough to break anything.

The serrations also only developed towards full maturity, and the “toothless” juveniles may have had a completely different ecology to adults.

Pelagornis chilensis here was one of the larger species of pelagornithid, with a wingspan of 5-6m (16’4″-19’8″), known from the western and northern coasts of South America during the late Miocene about 11-5 million years ago.

Like other pelagornithids it was highly adapted for albatross-like dynamic soaring, with long narrow wings that allowed it to travel huge distances while expending very little energy – but with its proportionally short legs it would have been clumsy on the ground and probably spent the vast majority of its life on the wing, only returning to land to breed.

Weird Heads Month #21: Honking Hadrosaurs

The ceratopsians and pachycephalosaurs weren’t the only ornithischian dinosaurs to do weird things with their skulls.

The hadrosaurs are commonly referred to as “duck-bills” (despite how their beaks weren’t actually duck-like at all), and are famous for the elaborate crests seen on some of the group’s members, with shapes ranging from lobes to helmets to hatchets to spikes – and even some of the apparently crestless species are now known to have sported fleshy combs instead of the bony structures seen in their relatives.

But by far the most recognizable of the crested hadrosaurs is Parasaurolophus walkeri, with its long curved backwards-pointing tubular crest.

This particular species was mid-sized for the genus, growing up to around 10m long (32’10”) and is known from Western North America during the Late Cretaceous, about 76-73 million years ago.

Its crest was intermediate in size and shape between the other two known species. The larger Parasaurolophus tubicen had a longer and slightly straighter crest, while the smaller Parasaurolophus cyrtocristatus had a shorter more strongly curved one. Juveniles developed these crests as they matured, starting off with much smaller bumps on their snouts that gradually grew backwards and upwards.

Some hadrosaur crests were purely for visual display, but in the lambeosaurine lineage that Parasaurolophus belonged to they also incorporated complex looping nasal passages that were probably used as resonating chambers, allowing each species to make a unique-sounding loud bellowing call to communicate with each other.

There are also rumors of a currently-undescribed specimen of Parasaurolpphus that has preserved soft tissue around its crest, possibly a keratinous covering or skin flaps that made it appear even larger and more flamboyant in life than the underlying bone. So I’ve given this reconstruction a speculative structure like that, along with hoof-like claws on its hands similar to those recently revealed for Edmontosaurus.

Weird Heads Month #18: Boneheaded Dinosaurs

Pachycephalosaurs are highly recognizable dinosaurs with their thick spiky skulls, and it’s not hugely surprising that they were the evolutionary cousins of the equally weird-headed ceratopsians.

Much like their frilled relatives they had beaks at the tips of their snouts and large gut cavities for digesting plant matter, but they also had surprisingly sharp theropod-like teeth in front of their more standard herbivore teeth further back – suggesting they may also have been opportunistic omnivores, occasionally snacking on carrion or small animals similarly to modern pigs or bears.

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.

Recent discoveries of juvenile Pachycephalosaurus skulls confirmed a hypothesis proposed a few years earlier: these dinosaurs changed appearance drastically as they grew up, and younger individuals had been mistaken for separate species. They started off with domeless flat heads, bristling with long spikes (a form previously named Dracorex hogwartsia) then as they matured their domes began to grow (previously Stygimoloch spinifer) and by full maturity they had big domes with the spikes shrunk down to smaller stubbier knobs (the classic Pachycephalosaurus look).

This particular reconstruction depicts a Stygimoloch-like subadult individual, not quite fully mature and still sporting some longer spikes.

Weird Heads Month #14: Horns and Frills

We can’t go through this month without having an appearance from the most famous group of weird-headed dinosaurs: the ceratopsids!

Their distinctive-looking skulls were highly modified from those of their ancestors, with large bony frills extending from the back of their heads, various elaborate horns and spikes, enormous nasal cavities, large hooked beaks at the front of their snouts, and rows of slicing teeth further back.

And while typically depicted as purely herbivorous, ceratopsids’ powerful parrot-like beaks and lack of grinding teeth suggest they may actually have been somewhat more omnivorous – the Cretaceous equivalent of pigs – still feeding mainly on plant matter but also munching on carrion and opportunistically eating smaller animals when they got the chance.

Machairoceratops cronusi here lived during the late Cretaceous of Utah, USA, about 77 million years ago. Only one partial skull has ever been found belonging to an individual about 4.5m long (14’9″), but it wasn’t fully grown and so probably reached slightly larger sizes.

It had two long spikes at the top of its frill, similar to its close relative Diabloceratops but curving dramatically forward and downwards above its face. Whether they were purely for display or used in horn-locking shoving matches is unknown, but either way it was a unique arrangement compared to all other known ceratopsids.

Weird Heads Month #12: Double-Crested Dinosaurs

Dilophosaurus wetherilli is a fairly recognizable dinosaur thanks to its memorable appearance in the Jurassic Park franchise – but unfortunately that also means the popular image of it is completely wrong.

Rather than a small frill-necked venom-spitting creature, this early theropod was actually rather large, reaching around 7m long (~23′), and along with its distinctive double crests it also had a narrow snout with large teeth and a distinctive notch at the front of its lower jaw.

It lived in North America during the early Jurassic, about 196-183 million years ago, and while it wasn’t venomous its notched jaws were probably capable of delivering powerful bites to small struggling prey, much like the similar-looking ornithosuchids in the Triassic. Some structural similarities to the skulls of spinosaurids suggest it may have primarily eaten fish.

Its two bony crests were probably used for visual display, with juveniles only having small crests that fully developed as they matured. They also may have had a more extensive keratinous covering, so it’s not clear what their actual shape and full extent was in life.

Bambolinetta

Between about 9 and 7 million years ago, the modern regions of Tuscany, Corsica, and Sardinia were once part of a single island in the ancient Mediterranean Sea.

And since evolution often goes in weird directions on isolated islands, it’s no surprise that some unusual species developed there.

One of which was a very odd duck.

A map of the Mediterranean region during the Late Miocene, showing the location of the Tusco-Sardinian island.
From fig 4 in Williams, M. F. (2008). Cranio-dental evidence of a hominin-like hyper-masticatory apparatus in Oreopithecus bambolii. Was the swamp ape a human ancestor?. Bioscience Hypotheses, 1(3), 127-137. https://doi.org/10.1016/j.bihy.2008.04.001

Bambolinetta lignitifila lived during the Late Miocene, about 7.5 million years ago. Known from a single partial skeleton discovered in the mid-1800s, it was initially thought to be a fairly normal dabbling duck and wasn’t properly re-examined until 2014, when its strange features were finally recognized.

It was a medium-sized duck, probably around 50cm long (1’8″), but it had much chunkier wing bones than its relatives, with noticeably shortened forearms – looking much more like the wings of an auk or penguin, and suggesting that it was a similar sort of wing propelled diver. This is incredibly weird for a duck, since every other known diving species uses feet for propulsion instead, and so Bambolinetta may be the only known waterfowl to ever develop this type of underwater locomotion.

It’s not clear whether it was still capable of flying or not. There were few predators in its habitat, so it may well have become completely flightless – and that could also be the reason it later went extinct. Sea levels in the region began to drop around 7 million years ago, reconnecting the Tusco-Sardinian island to the European mainland, and Bambolinetta‘s high level of ecological specialization and its potential island tameness would have given it little defence against an influx of new unfamiliar predators.

Atlasaurus

Sauropod dinosaurs were just generally weird animals, but there’s something… not quite right about Atlasaurus imelakei.

Named after the Atlas Mountains of Morocco where its fossil remains were discovered, Atlasaurus lived during the mid-Jurassic period, around 168-165 million years ago. While it wasn’t the strangestlooking sauropod by any means, compared to other species its body proportions still show a particularly bizarre combination of features, with a slightly bigger head, unusually short neck, and very long slender legs that made up nearly half of its 9m height (29’6″).

It’s sort of the uncanny valley of sauropods. Everything about it is just a tiny bit wrong.

A photograph of an Atlasaurus model. Its been reconstructed very skinny, which only serve to emphasize its weird proportions.
And more shrinkwrapped depictions really don’t help with that. [image source]

Its tall shoulders and sloping back resemble the body plan of brachiosaurids so closely that it was initially thought to be an early member of that group, but more recent studies suggest it may have been part of an earlier evolutionary branch of sauropods known as the turiasaurs – which would mean its brachiosaur-like shape was actually the result of convergent evolution.

But what was it doing with such weird proportions?

…We really don’t know. Other short-necked sauropods seem to have been adapted for feeding on lower vegetation only a couple of meters off the ground, but Atlasaurus’ leggy build would have made it a high browser like the brachiosaurids it was mimicking. Its long legs may also have allowed it to move faster, or given it some advantage navigating over rough terrain, but since no other sauropod ever seemed to evolve this way it must have been doing something particularly unique.

Or perhaps it was just an evolutionary fluke. Maybe part of a lineage that had started adapting to short-necked low browsing, then moved back towards the high browsing niche – and happened to end up lengthening their legs instead of their necks to get the necessary height back.