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It Came From The Wastebasket #07: Carnosaur Carnage

Carnosauria was originally named in the 1920s as a grouping for all of the large-bodied theropod dinosaurs known at the time.

For much of the 20^th century it was used as a general wastebasket taxon collecting together all big carnivorous forms – including allosaurids, carcharodontosaurids, megalosaurids, spinosaurids, ceratosaurids, abelisauroids, and tyrannosaurids – and for a while it even included a species that later turned out to be closer related to crocodiles than to dinosaurs.

An illustration showing four different carnosaurs: Asfaltovenator, Torvosaurus, Giganotosaurus, and Baryonyx. They're all bipedal carnivorous dinosaurs with small three-clawed arms, bird-like legs, and long counterbalancing tails, but they vary in size, coloration, and most notably head shape. Asfaltovenator and Giganotosaurus have fairly typical boxy theropod heads, while Torvosaurus has a longer snout and Baryonyx has slender crocodile-like jaws. — From left to right: *Asfaltovenator vialidadi*, *Torvosaurus tanneri*, *Giganotosaurus carolinii*, & *Baryonyx walkeri*

But then cladistic analysis in the 1980s and 1990s revealed that some of these theropods weren’t actually closely related at all. Carnosaurs weren’t a natural lineage but instead were highly polyphyletic, with the physical similarities between them seeming to be more due to convergent evolution than direct shared ancestry.

Some carnosaurs were split off and reclassified as more “primitive” types of theropod, while the tyrannosaurs were placed much closer to birds with the coelurosaurs. The remaining “carnosaurs” were just the allosaurids, carcharodontosaurs, and their closest relatives, and some paleontologists now prefer to use the name Allosauroidea for this group to distance it from the previous wastebasket mess.

…But Carnosauria might not be done just yet.

A screenshot from "Phineas and Ferb", with the two main characters in a room lit up by an offscreen disco ball, with one grabbing the arm of the other. Text below them reads "Dude, we're getting the band back together!" Both of their heads have been photoshopped into those of Megalosaurus and Asfaltovenator.

The discovery of Asfaltovenator in 2019 complicated matters once again, with a mixture of anatomical features linking it to both the allosauroids and the megalosauroids (megalosaurids, spinosaurids, and their relatives) – suggesting that these two groups might actually have been closely related to each other in a single lineage after all.

This would potentially return Carnosauria back to something surprisingly close to its original definition, with the various megalosauroids now forming an evolutionary grade leading to the allosauroids.

It Came From The Wastebasket #05: The Trouble With Troodon

Troodontids were small bird-like theropod dinosaurs, lightly built with slender legs and sickle-shaped “raptor” claws on the second toes of their feet. They had fairly big brains proportional to their body size, rather like modern birds, and their large forward-facing eyes had good depth perception. Owl-like asymmetrical ears in some species gave them a very keen sense of hearing, suggesting they may have been nocturnal hunters using sound to pinpoint the location of small prey.

The original specimen of the namesake of the group, Troodon formosus, was a serrated tooth discovered in the 1850s, about 77 million years old and originating from the Late Cretaceous Judith River Formation fossil beds in Montana, USA. It was so little to work with that it was initially mistaken for a lizard tooth, then during the 20^th century it was recognized as belonging to a dinosaur and spent time classified as a megalosaurid, then a pachycephalosaur, then finally as a small theropod similar to the Mongolian Saurornithoides.

In the late 1980s it was merged together with multiple other troodontids (including Stenonychosaurus of speculative “dinosauroid” fame), and since Troodon had been the first of all of them to be named it took priority as the genus name.

And then for a while every single Late Cretaceous troodontid specimen from North America was also lumped into Troodon, turning it into a wastebasket taxon.

An illustration of five troodontids standing in a circle facing each other. They're all very bird-like feathered dinosaurs with vaguely owl-like faces, reddish-orange and dark brown plumage, and white spots and bars on their longer wing and tail feathers. There are minor variations in their color shades and markings, but otherwise they all look incredibly similar to each other. The overall composition of the image is similar to that of the "Spider-man pointing at Spider-man" memes.

The problem was that all these troodontids came from locations separated by thousands of kilometers and millions of years of time, and it’s unlikely that they all actually represented just one single species. But they were only known from rare fragmentary remains, making distinguishing them from each other difficult, and the original Troodon tooth didn’t really have any distinctive features either – it turns out most troodontid teeth all look exactly the same!

It was becmoning increasingly dubious whether Troodon was even a valid name at all, and during the 2010s several paleontologists began trying to sort the mess out. The old names Pectinodon and Stenonychosaurus were revived, and some ‘Troodon’ fossils were also split off and given completely new names, becoming Albertavenator and Latenivenatrix*.

* Although Latenivenatrix might not actually be distinct enough from Stenonychosaurus to justify having a separate name.

As of 2022, Troodon itself is now in a sort of taxonomic limbo, with some paleontologists abandoning it as a dubious name while others are still arguing in favor of continuing to use it. The name could potentially be properly rescued if the original tooth can be clearly linked to better fossil material, letting Troodon take over priority again from one of the other better-established troodontids, or by defining a new type species similar to what happened with Iguanodon.

…But with how incredibly generic that tooth is, both of those options would be very difficult.

It Came From The Wastebasket #02: What Makes A Monoclonius?

The first fossil remains of Monoclonius crassus were discovered in the Late Cretaceous Judith River fossil beds (~75 million years old) in 1876 in Montana, USA. It was one of the many dinosaur species hurriedly named as part of the Bone Wars, and was described based on a mixture of bones from several different sites.

At first much of this dinosaur’s anatomy was poorly understood, and at first it was misidentified as a hadrosaur. The skull remains were fragmentary and ceratopsians hadn’t yet been identified as a group, so Monoclonius‘ horns weren’t even recognized as being horns and a piece of the frill was initially misinterpreted as part of a breastbone.

Once the much better-preserved Triceratops was discovered in 1889, and the existence of ceratopsians was recognized, Monoclonius was re-examined and identified as a similar dinosaur – and three more species were quickly described within the genus, also based on very fragmentary fossils.

An illustration of Monoclonius, a dubious species of horned ceratopsian dinosaur. It has a parrot-like beak, a long straight nose horn, and a pair of small stubby brow horns. Its large bony neck frill is rimmed with small spikes, with a pair at the very top being longer and curling sharply downwards against the front of the frill. Its body is bulks and quadrupedal with a a thick tapering tail, and there are bumpy scales and sparse short quill-like spines on its back. It's colored mottled orange-and-brown, and there are hints of bright blue on its frill. — *Monoclonius crassus*

Then for a while afterwards every ceratopsid fossil that wasn’t clearly a Triceratops was then just dumped into Monoclonius, quickly turning the genus into a wastebasket full of dubious indistinct remains.

But then…

The new challenger screen from Super Smash Bros Ultimate, with the character silhouette replaced by that of Centrosaurus, a horned ceratopsian dinosaur. Text on the image reads "A new foe has appeared! Challenger approaching!"

Centrosaurus apertus was named in 1904, from the similarly-aged Dinosaur Park Formation in southern Alberta, Canada. It had originally been one of the various species of Monoclonius, but was now claimed to be different enough to deserve its own separate genus name – and this started a decades-long controversy between several paleontologists.

Over the new few decades arguments went back and forth over whether Centrosaurus was actually valid or if it was just a junior synonym of Monoclonius. As more and better ceratopsid fossil material was discovered several other Monoclonius species were eventually split off into their own separate genera, too, creating Styracosaurus, Chasmosaurus, and the somewhat dubious Brachyceratops. But other new species also continued to be lumped into Monoclonius up until 1990, meaning that over its century of existence this wastebasket taxon had at one point or another contained at least 16 different species.

During the 1990s opinion began to turn against Monoclonius, increasingly regarding it as a dubious name. Its original type specimen was a chimera of multiple different individuals (and possibly multiple different species), and it just didn’t have any distinct enough anatomical features to distinguish it from other ceratopsids.

Centrosaurus, meanwhile, was further validated by the discovery of huge bonebeds containing thousands of individuals, making it into one of the best-known of all ceratopsians.

Today Monoclonius‘ name remains attached to a few fossil specimens, but only the ones that are too indistinct to classify as anything else. Some “Monoclonius” have also turned out to actually be juveniles and subadults of other ceratopsians – it seems many young centrosaurines had a Monoclonius-like stage in their growth, before they went on to develop their own species’ distinctive horn and frill shapes.

So Monoclonius may never have been a distinct genus at all – it was just a bunch of different ceratopsian teenagers!

Spectember 2022 #01: Arboreal Ornithopod

Despite some minor delays, it’s time once again for #Spectember – when I dive back into the big pile of speculative evolution concepts that you all submitted to me in 2020, and try to get through a few more of the backlog.

(…There’s still over 50 of them left. This is going to take a while.)

So today’s concept comes from an anonymous submitter, who requested an arboreal ornithopod dinosaur:

Jakapil

The thyreophorans were heavily armored ornithischian dinosaurs, with their most famous representatives being the stegosaurs and the ankylosaurs. Earlier members of the group were all small bipedal animals covered in rows of prickly osteoderms, and until now these “primitive” forms were known only from the early-to-mid Jurassic, around 200-165 million years ago.

But now the recent discovery of Jakapil kaniukura is suggesting a lineage of early thyreophorans actually survived for much much longer than previously thought – all the way into the Late Cretaceous, about 97-94 million years ago.

Just 1.5m long (5′), Jakapil lived in what is now southern Argentina, in an ancient desert with a braided river system. It was bipedal, with a short beak, small arms, and a body bristling with spiky armor, and its unusually deep lower jaw and heavily worn teeth indicate it fed on rather tough vegetation that required a lot of chewing to process.

It’s currently only known from somewhat fragmentary remains, so reconstructions of its full appearance are rather speculative and there’s already been some dispute about whether Jakapil actually was a thyreophoran. One proposal is that it shared a lot of anatomical features with early ceratopsians instead, which if true would make it an incredibly weird armored ceratopsian, and also the first definitive member of that group from South America. But the ceratopsian-like features could also just be due to convergent evolution – and a Jakapil-like dinosaur might actually help explain the only other known dubious South American “ceratopsian” Notoceratops, and the similarly-disputed Australian Serendipaceratops.

But whatever it was – late-surviving basal thyreophoran, southern armored ceratopsian, or even a previously unknown lineage of ornithishcians entirely new to science – it’s an exciting and unexpected discovery.

Rajasaurus

Abelisaurids were a group of theropod dinosaurs characterized by short snouts, bony ornamentation on their skulls, tiny stiff arms, and stocky legs. Known mostly from the southern continents of Gondwana, they were the dominant predators in these regions and are thought to have been specialized hunters of titanosaurian sauropods.

Rajasaurus narmadensis lived in what is now western India during the Late Cretaceous, about 67 million years ago. Around 7m long (23′), it had very rough-textured thickened bone on the top of its snout, along with a short rounded horn on its forehead that was probably used for display or headbutting behaviors.

India at this time was an isolated island continent located off the east coast of Africa, and Rajasaurus‘ ancestors probably island-hopped across from then-nearby Madagascar – where its closest known relative lived, the very similar-looking Majungasaurus.

Annakacygna

Around 11 million years ago, during the late Miocene, much of what is now northern Honshu in Japan was submerged under fairly deep ocean waters. This offshore environment was inhabited by a variety of ancient sea-going tetrapods such as turtles, desmostylians, seal-like allodesmines, archaic baleen whales, and early oceanic dolphins… and also one very unexpected bird.

Meet the flightless marine swan.

Annakacygna hajimei, also known as the Annaka short-winged swan, was the same size as a modern black swan at about 1.2m long (~4′), but had a combination of features unlike any of of its living close relatives. Its head was proportionally large, and it had a long spoon-shaped bill like a shoveler duck, lined with comb-like structures for filter-feeding on plankton. It also had widened hips that would have helped keep it stable floating in rough waters, its tail was highly mobile and muscular, and its feet resembled those of diving birds like loons.

With thickened heavy bones and shortened forearms it was clearly completely unable to fly, but its reduced wings appear to have been highly specialized rather than just vestigial. Its shoulders were extra flexible while its wrists had a more limited range of motion, allowing it to fold its wings into a distinctive half-raised position similar to modern mute swans.

It probably used its wings and tail to perform elaborate “busking” visual displays, and also to carry and protect its young on its back while out at sea – basically making itself into a living swan boat.

Sierraceratops

In the late 1990s a partial skeleton of a ceratopsian was discovered in New Mexico, USA. These remains were initially thought to belong to Torosaurus, but after more of the specimen was recovered in the mid-2010s it became clear the bones actually represented an entirely new species of horned dinosaur – officially named in 2022 as Sierraceratops turneri.

Sierraceratops lived during the Late Cretaceous, around 72 million years ago, in what at the time was the southern region of the island continent of Laramidia. About 4.6m long (~15′), it had fairly short chunky brow horns, long pointed cheek horns, and a relatively large frill.

It was part of a unique lineage of ceratopsians that were endemic to southern Laramidia, with its closest known relatives being Bravoceratops from western Texas and Coahuilaceratops from northern Mexico.

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.

Amargasaurus

Amargasaurus cazaui was a sauropod dinosaur with a very distinctive-looking skeleton, sporting a double row of long bony spines along its neck and back. It lived in what is now Argentina during the Early Cretaceous, about 129-122 million years ago, and was fairly small compared to many other sauropods, reaching about 10m in length (~33′) with a proportionally short neck compared to its body size.

And despite being known from fairly complete skeletal remains there’s still a lot we don’t know about this dinosaur – especially what was actually going on with those vertebral spines. While it’s sometimes been depicted with skin sails over the spines, for the last couple of decades the general opinion has trended towards them being more likely to have been covered by spiky keratinous horn-like sheaths.

But recently that’s been brought back into question. A detailed study of the microscopic bone structure of Amargasaurus‘ spines shows no evidence for keratin attachment and instead found textures associated with skin coverings, along with an extensive web of ligaments connecting the spines to each other along each row.

So maybe it had big flashy sails after all!