Tag: dinosaur

Strange Symmetries #23: Convergent Earvolution

Although it’s not visible externally, owls have one of the most striking modern examples of asymmetry. The ears of many species are uneven, with the right ear opening positioned higher up than the left, giving them the ability to pinpoint the sounds of their prey much more accurately.

But surprisingly this isn’t a unique anatomical trait that only ever evolved once in their common ancestor.

Instead, multiple different lineages of owls have actually convergently evolved wonky ears somewhere between four and seven separate times.

The boreal owl (Aegolius funereus), also known as Tengmalm’s owl, is a small 25cm long (~10″) true owl found across much of the northern parts of both Eurasia and North America. While most other owls’ asymmetrical ear openings are formed just by soft tissue, the boreal owl’s lopsided ears are actually visible in the bones of its skull.

But despite how many times owls have convergently evolved asymmetrical ears, and how successful this adaptation has been for them, for a long time it seemed to be something that no other animals have ever mimicked.

In the early 2000s asymmetric ears were reported in the skulls of some troodontid dinosaurs, which seem to have been nocturnal hearing-based hunters similar to owls, but proper details on this feature still haven’t been formally published.

Then, just a couple of weeks ago, another example was finally announced.

The night parrot (Pezoporus occidentalis) is a small ground-dwelling parrot found in Australia, close to the same size as the boreal owl at around 22cm long (~9″). Critically endangered and very elusive, it’s rarely seen and little is known about it – and it was presumed extinct for much of the 20th century, until more recent sightings of living individuals confirmed that the species is still hanging on.

Recent studies of preserved museum specimens have revealed that it seems to have poor night vision but excellent hearing, and that its right ear opening is noticeably asymmetrical, bulging out sideways from its skull. Much like owls the night parrot relies on acute directional hearing to navigate in darkness, but since its diet consists mainly of seeds it’s probably not using this ability to locate food sources. Instead it may be listening out to keep track of the precise locations of other parrots, and for the approach of predators – so its sharp sense of hearing may be the reason this unique bird has so far just barely managed to survive the presence of invasive cats and foxes.

Strange Symmetries #17: Spiky Surprise

Styracosaurus albertensis was a ceratopsid dinosaur living during the late Cretaceous about 75 million years ago, in what is now Alberta, Canada. Around 5m long (~16′), it was one of the most elaborately ornamented horned dinosaurs, with a long nose horn and multiple elongated spikes on its frill.

There was actually quite a lot of variation in the frills of Styracosaurus, with varying numbers of long spikes and extra hook-like projections present on some individuals. But one recently-discovered specimen nicknamed “Hannah” is especially surprising – it had a noticeable amount of asymmetry in its skull. The left and right sides show different numbers and arrangements of spikes, so much so that if the two halves had been discovered separately they might have been identified as belonging to two completely different species.

Frill arrangements are often used to define different ceratopsids, so if this level of individual variation and asymmetry existed in other species, too, then we may need to reevaluate some of them.

Strange Symmetries #14: The Tooth About Baryonyx

Almost all toothed theropod dinosaurs had exactly four teeth on each of their premaxillary bones, the paired bones at the very tip of the upper snout.

A diagram of the various bones in the skull of Spinosaurus.
Spinosaurus skull by AS | Public domain

The semi-aquatic spinosaurids were an unusual exception to this with six or seven teeth per premaxilla – and one particular member of this lineage seems to have been just a little bit weirder.

Baryonyx walkeri lived during the early Cretaceous, around 130-125 million years ago, in what is now southeast England. About 9m long (~30′), it had distinctive enlarged curving claws on the first fingers of its hands, along with a long narrow snout with a “rosette” at the tip followed by a notch (a shape convergent with the jaws of modern pike conger eels).

And that premaxillary rosette had a strangely asymmetrical arrangement of teeth.

A closer view of the lineart for Baryonyx's premaxillary rosette. The six left teeth are indicated in pink, and the seven right teeth in dark green.

The left side had six teeth, and the right side had seven.

Why? We don’t know!

Baryonyx skull material is rare and fragmentary, so it’s unclear if this was actually a characteristic feature of the species or if the known asymmetric rosette just represents an unusual individual.

Strange Symmetries #11: Step Up To The Plate

Stegosaurs are some of the most popular and recognizable dinosaurs thanks to their unique appearances, with small heads, elaborate back plates, and spiky thagomizer tails.

Closely related to the ankylosaurs, they first appeared in the mid-Jurassic about 170 million years ago. While they lasted until at least the mid-Cretaceous (~100 milion years ago), their heyday was in the latter half of the Jurassic, ranging all across Asia, Europe, Africa, and North America – and the North American species like the eponymous Stegosaurus developed especially elaborate plates in a distinctive asymmetrical pattern, not arranged in pairs like most other stegosaurs but in alternating rows along each side of the midline of their backs.

Hesperosaurus mjosi lived around 156 million years ago during the late Jurassic, in what is now Wyoming and Montana in the Western United States. It was closely related to Stegosaurus but was a little older and a little smaller, about 5-6m long (~16-20′).

Much like its more famous relative its plates seem to have alternated along its back, which may have been an adaptation to maximize visible surface area while minimizing the number of plates, saving on the energy needed to grow such large elaborate ornamentation.

Hesperosaurus might also represent a rare case of possible sexual dimorphism in non-avian dinosaurs, with wider more rounded plates potentially interpreted as belonging to males and taller pointed plates belonging to females.

Natovenator

Halszkaraptorines were a group of small dromaeosaurids known only from the Late Cretaceous of Mongolia. They were odd little raptors with flattened snouts, long necks, and flipper-like arms – features that suggest they were specialized for swimming, making them the second known lineage of semi-aquatic non-avian dinosaurs after the spinosaurids.

This “duck-raptor” interpretation has been a little controversial since it was first proposed in 2017, but we’ve just gotten some more evidence for it in the form of an entirely new halszkaraptorine.

Natovenator polydontus lived in what is now the Gobi Desert in southern Mongolia, around 72 million years ago. The size of a small duck, about 45cm long (18″), it had jaws full of many needle-like teeth, a long flexible goose-like neck, and a streamlined body with a wide flattened ribcage convergently shaped like those of modern diving birds.

Although it had long strong legs, these don’t show much in the way of aquatic specializations and would have been used more for walking and running on land. Instead it may have used its flipper-like arms to propel itself through the water, like modern penguins or auks.

It probably had a lifestyle similar to modern mergansers, swimming and diving in lakes and rivers, and preying on fish, amphibians, and aquatic invertebrates.

It Came From The Trash Heap (We Don’t Talk About Kholumolumo)

A wastebasket taxon is what happens when species can’t be easily classified and instead get hurled into a “catch-all” category.

…But that’s not the only kind of taxonomic tangle that can befall a new discovery.

When a scientific name is assigned to a new species, but it isn’t given a corresponding formal description and type specimen, it becomes a nomen nudum – a “naked name”. Without a proper description and assigned holotype the name isn’t valid, and the new species isn’t technically accepted by the wider scientific community.

This has even happened to some surprisingly famous names. In the 1920s Velociraptor mongoliensis was briefly given the nomen nudum “Ovoraptor djadochtari” before getting its much more familiar name when it was officially described. Meanwhile the giant pterosaur Quetzalcoatlus northropi was stuck as a nomen nudum for decades, only finally getting a proper published description in 2021.

And there’s another particular long-standing nomen nudum that became mildly infamous – “Thotobolosaurus”, the “trash heap lizard”.

An illustration of Kholumolumo (previously known as "Thotobolosaurus"), an extinct prosauropod dinosaur. It's a bipedal dinosaur with a small head, long neck, chunky arms, thick bird-like legs, and a long counterbalacing tail. It's colored dark blue, with lighter striping on its underside and a speckled red-and-orange pattern along its back. Its face is brighter teal-blue with a mask-like streak of orange than continues down onto a fleshy throat dewlap. There are also reddish quill-like filaments on the back of its neck and in a tuft at the tip of its tail.
Kholumolumo ellenbergerorum

Discovered next to a literal trash pile in the village of Maphutseng in Lesotho, a few scattered and broken bones of this “prosauropod” sauropodomorph dinosaur were first found in 1930. But it wasn’t until the mid-1950s that a more extensive bonebed began to be unearthed at the site, and over the next decade over 1000 fossil fragments were collected.

In the mid-1960s the remains were initially classified as belonging to Euskelosaurus browni (which is now considered to be a wastebasket taxon), but just a few years later in 1970 the “Maphutseng Beast” was re-evaluated as a species new to science. It was referred to as “Thotobolosaurus mabeatae” – based on the local name of the discovery site, “Thotobolo ea ‘Ma-Beata” (trash heap of Beata’s mother) – but this name was never actually formally published.

Despite “Thotobolosaurus” being an undescribed nomen nudum it nonetheless went on to be repeatedly referenced in scientific literature over the next few decades, and appeared in several popular dinosaur books (even as recently as 2020!).

In the mid-1990s it was alternatively named “Kholumolumosaurus ellenbergerorum” in a Ph.D. dissertation, with this name derived from the kholumolumo, a reptilian creature in Sotho mythology, and the Ellenberger brothers who worked on the site. But this also didn’t count as a formal publication and instead became a second nomen nudum for the species.

Eventually, 90 years after the first bones were found and 50 years after the debut of the name “Thotobolosaurus”, this long-neglected sauropodomorph was finally given a proper published full anatomical description in 2020.

And it also got a third name, this time officially valid, based on the second one from the 1990s: Kholumolumo ellenbergerorum.

For something associated with trash for so long, Kholumolumo is actually now one of the most completely-known prosauropods. At least five different individuals were present in the collected fossil material, possibly as many as ten, and between them most of the full skeleton is represented – with the exception of the skulls, which are only known from a couple of small fragments.

We now know Kholumolumo was rather heavily-built, with chunky limb bones and unusually short shinbones. It would have been one of the biggest animals around in the Late Triassic (~210 million years ago), measuring at least 9m long (~30′) and weighing around 1.7 tonnes (1.9 US tons), but despite its size it seems to have still been bipedal.

Due to the highly disarticulated nature of the bones the fossil site may have been a “bone accumulation area”, a place where dismembered bits and pieces of different carcasses were regularly carried to be eaten by a predator or scavenger  – essentially a trash heap, fittingly enough. A couple of “rauisuchian” teeth have actually been found among the remains, which might indicate what was chomping on these particular Kholumolumo.

It Came From The Wastebasket #17: Getting Ornithomimus In Order

The ostrich-like “bird-mimic” dinosaur Ornithomimus was named in 1890, based on some hand and foot bones from Late Cretaceous-aged fossil beds in Colorado, USA.

The first ornithomimid known to science, it was initially thought to be a ornithopod, but then a few years later more fossil material revealed it was actually a theropod – and then it spent some time classified as a “megalosaur” before ornithomimids were finally recognized as being coelurosaurs in the early 20th century.

And for nearly a century after its discovery it was treated as a wastebasket taxon for any similar-looking fossil material from North America and Asia, with around 17 different species named within the genus. One of these was split off into Struthiomimus in 1917, but it wasn’t until much later that the rest began to get sorted out.

A review of known Ornithomimus fossils in the early 1970s renamed a couple more species into the new genera Archaeornithomimus and Dromiceiomimus, and dismissed most of the remaining species as dubious or invalid. Just two valid species now remained: the original Ornithomimus velox from Colorado, and Ornithomimus edmontonicus from Alberta, Canada.

An illustration of Ornithomimus, an extinct feathered dinosaur. It has a a small beaked head atop a long slender neck, two wing-like arms with three clawed fingers, long ostrich-like legs, and a counterbalancing tail with longer feathers towards the tip.
Ornithomimus edmontonicus

Since then opinions have gone back and forth about some of the other Ornithomimus species. For a while Dromiceiomimus was merged back into Ornithomimus, but more recently it’s been found to have distinct limb proportions and was probably actually a separate genus after all. Another species that’s usually considered to be part of Struthiomimus is also sometimes instead classified as an Ornithomimus instead.

Really all of the North American ornithomimids are in need of a modern taxonomic revision – especially since Ornithomimus edmontonicus shows enough anatomical variation that it might actually represent a species complex of multiple very similar forms, which might get split apart in the future if anyone can figure out how to reliably distinguish them.

It Came From The Wastebasket #13: Certifying Cetiosaurus

Discovered in England in the early 1840s, Cetiosaurus was one of the first sauropod dinosaurs known to science – although its scrappy remains were initially mistaken for a massive crocodile-like marine reptile, hence its name meaning “whale lizard”.

It wasn’t even identified as being some sort of dinosaur until a couple of decades later, and then in the 1870s discoveries of much more complete sauropods like Brontosaurus and Diplodocus in North America led to it finally being recognized as a similar long-necked form.

Like some other early dinosaur discoveries it quickly became a wastebasket taxon, with vaguely-similar fragmentary fossils found in England, France, Switzerland, and Morocco all being lumped under its name. By the end of the 20th century nearly 20 different Cetiosaurus species had been created, most of them highly dubious and based on poor fossil material without any distinctive anatomical features.

An illustration of Cetiosaurus, a sauropod dinosaur. It has a small head atop a long neck, a chunky four-legged body with mitten-like forefeet and three-clawed hindfeet, and a long tapering tail. It's colored pale teal with darker red-brown stripes and a lighter underside, with brighter yellow-green towards its head. There are also speculative red quill-like structures on its throat, cheeks, neck, and tail tip.
Cetiosaurus oxoniensis

It wasn’t until the early 2000s that the mess was finally cleaned up. A major revision and redescription of Cetiosaurus determined that just one species was actually valid: Cetiosaurus oxoniensis from the mid-Jurassic of England, known from fairly complete remains and dating to about 170 million years ago.

But this did create a new problem – it meant that the original type species Cetiosaurus medius wasn’t actually based on anything distinctive. So, much like what happened with Iguanodon, the type species was officially changed to Cetiosaurus oxoniensis in 2014, ensuring that this historically significant genus was defined by decent fossil material rather than by dubious fragments.

It Came From The Wastebasket #12: Coelurosaur Confusion

Historically Coelurosauria was the counterpart to the Carnosauria, with both of them representing two major lineages of theropod dinosaurs.

Created as a group in the early 20th century, coelurosaurs quickly became a dumping ground for all small-bodied theropods – including coelophysoids, compsognathids, ornithomimids, oviraptorosaurs, dromaeosaurids, and troodontids– and for a while this wastebasket taxon also included the large-bodied ceratosaurids and tyrannosauroids, before they were moved over into the carnosaurs.

But during the 1960s and 1970s this arrangement began to break down. A better understanding of groups like dromaeosaurs revealed a confusing mixture of traditional “carnosaur” and “coelurosaur” anatomical features, and paleontologists struggled to figure out where these sorts of theropods actually fit in.

The development of cladistic methods from the 1970s onwards led to efforts to clean up the coelurosaur wastebasket, trying to figure out a more accurate version of these animals’ evolutionary relationships. After briefly collapsing Coelurosauria down to just coelophysoids and “coelurids“, the growing recognition of modern birds as living theropod dinosaurs eventually resulted in the group being properly redefined in the 1980s as “birds, and all theropods closer related to them than to carnosaurs“.

An illustration showing four examples of coelurosaurs, theropod dinosaurs closely related to birds. One the left is Citipati, a bird-like feathery oviraptorosaur that has a cassowary-like crest on its head, a short beak, a long neck, feathered wings, long slender legs, and a short tail with a feather fan at the end. It's mostly colored black and white, with bright blue and yellow face markings and small eyespots on its wing and tail feathers. At the top is Albertosaurus, a tyrannosaur with short bony crests above its eyes, tiny two-fingered hands, long bird-like legs, and a long thick counterbalancing tail. It's colored with a blotchy striped pattern of yellow, red, and dark brown, with bright blue on the crests over its eyes. On the right is Yi, a small bird-like scansoriopterygid with a fluffy feathery coat, four long tail feathers, and large membranous wings supported by a bony extension from its wrist that make it look like a dino-bat or a wyvern. It's colored brownish-grey with a yellow snout and striped markings on its neck, wings, and tail feathers. At the bottom is Sinosauropteryx, a compsognathid with a typical theropod body plan – triangular head, S-shaped neck, three-clawed hands, bird-like legs, and a long tail – but it's covered in fluffy feathers which are especially bushy on its tail. it's colored ginger-and-white, with a black raccoon-like mask marking over its eyes and a stripey tail.
Clockwise from the left (not to scale): Citipati osmolskae, Albertosaurus sarcophagus, Yi qi, Sinosauropteryx prima

The coelophysoids were finally removed entirely, reclassified as a much earlier branch of theropods – but quite a few of the other groups from earlier concepts of Coelurosauria survived this reshuffling, with the compsognathids, ornithomimids, oviraptorosaurs, dromaeosaurs, and troodontids all proving themselves to have really been closely related the whole time. Meanwhile the tyrannosauroids were brought back in, along with the therizinosaurs, alvarezsauroids, and a whole bunch of paravian and avialan lineages.

(Megaraptorans might belong somewhere in the coelurosaurs, too – possibly being tyrannosauroids – but their classification is currently being disputed.)

It Came From The Wastebasket #10: Struggling With Stegoceras

First described and named in the early 1900s, Stegoceras validum was a dog-sized small pachycephalosaur that lived in Alberta, Canada, during the Late Cretaceous (~77-74 million years ago).

Initially just known from its skull domes, it was one of the first pachycephalosaurs to be discovered and was very poorly understood until more complete remains were found in the 1920s. Then it spent a couple of decades being mixed up with Troodon due to similarities in tooth shape, until the discovery of Pachycephalosaurus led to pachycephalosaurs finally being recognized as a distinct group of ornithischian dinosaurs in the 1940s.

An illustration of Stegoceras, an extinct pachycephalosaur. It's a small bipedal dinosaur with tiny arms, bird-like legs, a speculative coat of fluffy protofeathers over most of its body, and a long tapering tail with speculative bristly quills. It has a large bony dome on its forehead, rimmed with short spikes, and a short snout with a stubby beak. It's mainly colored white and grey, with brighter red and yellow markings on its face and red towards the tip of its tail.
Stegoceras validum

For much of the 20th century Stegoceras was treated as a wastebasket taxon for any small-to-mid-sized North American (and one Asian) pachycephalosaur, and multiple different species were named based on what were often rather dubious fragmentary fossils. But towards the start of the 21st century this mess did start getting cleaned up, merging some dubious species into the original Stegoceras validum, and moving others to separate genera like Sphaerotholus, Colepiocephale, Hanssuesia, and Sinocephale.

By the early 2000s just the Canadian Stegoceras validum remained – but then in 2011 the new species Stegoceras novomexicanum was named based on specimens from New Mexico, USA. The validity of this second species has been debated, since the fossils are juveniles and might instead belong to Stegoceras validum or another genus like Sphaerotholus, but if it is some sort of Stegoceras then it significantly re-extends the known geographic range of this little pachycephalosaur.