The evolution of falcons is rather poorly understood. Thanks to genetic evidence we know that they’re closely related to seriemas, parrots, and passerines, but their fossil record is patchy and little is known about the early members of their lineage.
But a group knows as masillaraptorids are giving us a rare glimpse at what some early falconiforms were up to. Known from the Eocene of Europe, these long-legged predatory birds seem to have been caracara-like terrestrial hunters specializing in chasing down prey on foot – although their wings and tails indicate they were also still strong fliers.
Danielsraptor phorusrhacoides lived during the early Eocene, about 55 million years ago, in what is now eastern England. Although only known from partial remains, it was probably around 45-60cm long (~1’6″-2′), and it had a large hooked beak with a surprising amount of convergent similarity to those of the flightless South American terror birds.
Its mixture of falcon-like and seriema-like features may indicate that the common ancestor of both of these bird groups was a similar sort of leggy ground-hunting predator.
Living during the Pliocene and Pleistocene in Florida and Texas, between about 5 and 1.8 million years ago, Titanis stood around 1.5-1.8m tall (~5-6′) and was heavily built, with long strong legs and a massive hooked beak. Remains of its small wings were incomplete and fragmentary but had seemingly unusual joints, with what looked like a stiffer wrist and more flexible “fingers” than other birds, which led paleontologist Robert Chandler to propose in 1994 that this terror bird species had modified its wings into clawed grasping arms similar to those of dromaeosaurs, used to restrain prey animals while its beak tore them apart.
But the idea of a giant murder-bird with added meathook-hands only lasted about a decade. Further investigation in 2005 showed that Titanis‘ arms weren’t that weird after all – the same sort of joints are found in terror birds’ closest living relatives, the seriemas, and so Titanis really had the same sort of small vestigial wings as many other large flightless birds.
…However, there still could have been some claws on there. Many modern birds actually have one or two small claws on their hands that aren’t visible under their feathers, and terror birds like Titanis having something like that going on is completely plausible – they just wouldn’t have been using them for any sort of specalized predatory function.
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.
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.
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.
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.
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.
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.
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.
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.
And there’s another particular long-standing nomen nudum that became mildly infamous – “Thotobolosaurus”, the “trash heap lizard”.
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.
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.
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.
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.
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.
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 speciesCetiosaurus 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.