April Fools 2023: How Titanis Lost The Right To Bear Arms

Huge, flightless, and carnivorous, the phorusrhacids (or terror birds) were some of the largest apex predators in South America during its Cenozoicsplendid isolation” as an island continent – and they were possibly the closest that birds ever came to reclaiming the ecological roles of their extinct non-avian theropod dinosaur relatives. 

And for a while in the late 1990s and early 2000s there was a hypothesis that they’d even re-evolved clawed hands.

This idea was based on the wing bones of Titanis walleri, the only terror bird known to have dispersed northwards during the Great American Biotic Interchange when North and South America became connected via the Isthmus of Panama.

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.


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.


Bathornis grallator, a flightless bird about 75cm tall (2′6″) from the Late Eocene and Early Oligocene of Midwestern USA (~37-34 mya).

It was originally mistaken for a long-legged vulture (under the name Neocathartes) when first discovered in the 1940s, but later studies have shown it was actually one of the smaller members of the bathornithids – close cousins of the more well-known South American “terror birds”, successfully occupying terrestrial predator niches alongside large carnivorous mammals.