I have to give a talk about prehistoric birds to the members of the local bird watchers club, in November! So I'm preparing a bunch of illustrations ... you are favoured to be able to see them first! To start things off: Diatryma giganteus (left) and Kelenken guillermoi (right). Diatryma lived in North America, about 55-45 million years ago. A very similar species was described from Europe and classified as Gastornis. Some people think Diatryma and Gastornis were one and the same ... but this is not yet clear-cut. Diatryma have been considered a relative of the ducks and geese but was much larger, reaching over 2 m in height! Some people thought it was a predator but there are more signs that it was a herbivore and used its huge beak to crack open nuts or to crush tough leaves.
Kelenken, however, was clearly a predatory bird. It lived abut 15 million years ago in South America. It was one of the Phorusracidae, the family of 'terror birds'. It was one of the largest, perhaps reaching 3 m in height. Only its relative Brontornis was heavier. It had the largest known skull of any bird, 71 cm/28" in length! Terror birds might have been able to run fast and kill their prey with quick strikes of their massive beaks. Their closest living relatives are the much smaller Seriemas, which are long-legged stalking-hunters of the grasslands. Only two species of Seriema survive today. There are many known terror-bird species, ranging from slightly larger than the seriemas, up to these huge ones.
Also for a while there were people who thought terror birds had re-evolved clawed fingers on their arms, because of having unusual joints in their wrists. But seriemas have similar joints, and no fingers or claws on their wings. Terror birds being flightless had very small wings, probably with no actual function.
Pencil drawing, coloured with Photoshop.