circa 284,000,000 BCE — Bolosaurid Eudibamus is the first known biped

The earliest known bipedal vertebrate, eudibamus cursoris was a small parareptile. The sole specimen that has been found (in Thuringia, Germany) measured about 25 cm long – about the size of a house cat. Reconstructions of it give it an appearance resembling a cross between a tiny velociraptor and a modern iguana.

The sole specimen of it known to science was discovered in 2000 by a paleontological team including David S. Berman, Robert R. Reisz, Diane Scott, Amy C. Henrici, Stuart S. Sumida and Thomas Martens. The species is believed to have existed for a span of about five million years or so.

circa 65,500,000 BCE — The Cretaceous–Tertiary extinction event wipes out the dinosaurs

Everyone loves the dinosaurs. A lot of people – if the Jurassic Park films are to be believed – would like to see them come back. But without their extinction, we wouldn’t be here today.

Even now, it’s still not clear what exactly caused the extinction event – but the best known hypothesis is that of Luis and Walter Alvarez, which states that a meteoric or cometary impact caused a nuclear winter-like effect that altered the climate drastically, wiping out something like 75% of all species alive at the time. The effects were particularly felt by larger species – which included most dinosaurs.

In the wake of the event, now open evolutionary niches were occupied by mammals and birds, including our own ancestors.

circa 28,400,000 BCE — the sub-Class Allotheria becomes extinct

Not actually true mammals, but instead mammaliformes, the members of the sub-class Allotheria are distinguished from other mammals chiefly by their dentition, which featured lower molariform teeth equipped with two longitudinal rows of cusps. Extant from the Late Triassic through to the Early Oligocene, the Allotheria were rodent-like animals in appearance.

They were widespread, found on all continents including Antarctica (which was considerably warmer in this era), and included in their ranks herbivores, carnivores and omnivores. Unfortunately for biodiversity, the last of them died out between 33.9 and 28.4 million years ago, give or take 100,000 years.

circa 3,900,000 BCE — Australopithecus evolves

Australopithecus was an early proto-hominid that evolved in Eastern Africa around 4 million years ago. It consisted of a number of sub-species: A. anamensis, A. afarensis, A. sediba, and A. africanus; and two more sub-species whose genus is disputed: A. robustus and A. boisei. Over the course of two million years or so, the various Australopithecenes ranged across Eastern and Southern Africa.

The Australopithecines evolved about 2 million years after the split between the ancestral roots of humanity and chimpanzees (our closest relative), and one or more of the various sub-species of Australopithecus is likely to have been the progenitor of the Homo Genus, to which modern humanity (homo sapiens sapiens) belongs.