56 million years ago.
As the birds made their advances beyond their primitive reptile brethren, one race stood tall and dominant; the Diatryma.
Diatryma, in their own eyes, were the only intelligent species to ever exist; like us, they had no evidence of past sapient life to prove otherwise. Mostly solitary, Diatryma eventually began to form societies, breaking down trees and using them to build large shelters from which they would emerge in large groups to hunt or to make war with other Diatryma cities. Largely carnivores, Diatryma made tools, which it could manipulate with its beak, for hunting and fighting purposes.
The Pierce was a large spear-like weapon, made from whittled tree branches and sharpened rocks, held in a firm grip by the beak, pointing straight forward. The Diatryma used it to charge into large prey, grievously piercing it. Due to it's barbed end, the Pierce couldn't be removed from it's victim. Pierces were also used in combat with other Diatryma, and could seriously wound if not outright kill an unguarded opponent.
The Rip was a large serrated blade-like weapon, also made from whittled down trees, but from the trunk instead of the branches. Each tooth on the serrated edges had a sharp stone attached to it; this complex design meant that a Rip was a very valuable and rare weapon, due to it taking so long to make with Diatryma's limited tools.
Those were the early days. Diatryma continued the idea that tools were meant to be an extension of the body; as they had no arms, many tools were held in the beak, or, as time went on, large constructs were made that could be mounted on the back of a Diatryma, with various tool-holding slots so that a Diatryma could change it's tools on the fly.
Eventually, mechanical limbs were created, using a system of wooden pulleys and string, that created "bionic arms" for the Diatryma, much as they witnessed other species having arms.
As Carnivores, they eventually learned not to kill prey on sight, but rather to capture it and farm it, so that they could have a more predictable food source; this allowed for less infighting amongst the Diatryma, and more peaceful relations between the various Diatryma settlements.
The dominating ideology amongst the Diatryma was one of superiority, and subjugation of weaker and more primitive species. They believed themselves to be the apex of life. As for life itself, it was not to be questioned, but to be taken and used advantageously. An aggressively opportunistic philosophy, but one that kept these apex predators alive for a long time.
As Diatryma did not have extremely large brains, however, they did not have the capacity for growth as we humans do; they couldn't fathom the concept of digging underground for minerals or ores, as they were very large and saw the underground as a place for the minuscule beasts of the earth. They did, however, tame and use fire to their advantage. Since Diatryma could not see well in the dark, fire not only was of an aid to them, but also a weapon against other less sapient beasts, who feared fire through natural instinct.
Tribes of Diatryma spread predominately across the Americas, Europe, And Africa; the Asian plains could not be conquered, as Diatryma was too large to hide and ambush prey in the plains, as it did in other places. Also, a new competitor to the Diatryma was arising in the plains of Asia, a proto-wolf, that used sheer speed and pack hunting to run down its prey.
Eventually, this proto-wolf spread across the globe and encouraged natural selection to favour speedy herbivores, and wild prey could easily outrun a Diatryma, leaving them only with the animals that they had domesticated. But Diatryma had no concept of genetics, and inbreeding led to weaker and weaker domestic animals, until they eventually died out.
The Diatryma were forced to once again go out and hunt actively, but by now, the world had changed... and Diatryma couldn't keep up. The Sapient species died a slow and painful death of starvation, and their wooden tools and structures barely lasted 100 years; and thus, a sapient species and civilization almost 4 million years old was wiped off the earth without a trace.