The earliest known fossil footprints on land actually predate the earliest definitively land-based animals fossils by a considerable margin: 170 million years. It appears that our early ancestors may have explored the land before they moved there permanently. In fact, fossil records suggest that this exploration began before there were even terrestrial (as opposed to aquatic) plants – which may account for this peculiarity: no plants would have meant no food.
The first known animals to leave the ocean for good were members of the superclass Tetrapoda, a large group that includes all amphibians, reptiles, birds, and mammals, living and extinct. Including us.
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.
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.
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.
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.
The earliest species to evolve in the genus homo was Homo habilis, which is believed to have evolved in Africa from Australopithecene ancestors (although which of several species of australopithecus was the direct ancestor is not known). The genus homo would go on to become the most successful species in the entire history of the earth, until it created a global ecological catasprophe in the early to mid twenty first century, which destroyed all the members of that genus, and almost every other genus above the size of bacteria.
(By the way, if you’re reading this, you’re either a homo, or an extraterrestrial intelligence that’s very tolerant of our immaturity.)
(Man, I love that pun.)
The classic ‘caveman’, Neanderthals – homo neanderthalensis – were native to Europe, Western Asia and Central Asia. The earliest Neanderthal characteristics evolved at around this time – fossil evidence (admittedly incomplete) suggests that the full differentiation of the species had taken place by 130,000 BCE.
They were not, as is often thought, the ancestors of modern humanity, but rather a rival species that our ancestors wiped out in a competition for space and resources.
It’s unclear exactly how our nearest hominid relatives went extinct, but the leading candidates are our direct ancestors: whether fucking or fighting.
I mean that quite literally: some of them interbred with homo sapiens until they no longer existed as a separate species, or they just plain got killed by other homo sapiens. At their widest range, Neandertals occupied lands from Ireland and Spain in the west through to the southern Urals in the East. They did not go extinct everywhere at the same time, of course, but the precise details are somewhat obscured by the incompleteness of the fossil record.
It’s unclear exactly what killed the mammoths off, although there are two leading contenders: the end of the last Ice Age made climates generally warmer (although the last ice age ended several thousand years before the extinction was complete) and predation – the predator in question being, of course, us.
At one point, mammoths were found across most of the northern reaches of Europe, Asia and America, in several different species, but bit by bit, these were hunted to extinction. The shrinking of their optimal habitat as the ice retreated probably made the hunting easier, but their extinction was a certainty as soon as our ancestors developed a taste for mammoth-meat.
The last known population of mammoths, that on Wrangel Island in the Arctic Sea to the north of Chukotka (the easternmost part of Asia), became extinct in about 1650 BCE, having survived their relatives on St Paul Island, Alaska, by about 1100 years.
One of the most controversial books in the world, On the Origin of Species (often called Origin of the Species is one of the foundational texts of modern science. Not only is almost the entirety of modern biology built on its foundation, but it remains an excellent (if imperfect) example of the scientific method.
Charles Darwin had spent many years developing this theory, beginning with initial observations in 1835 during his voyage on the Beagle, and working on it in earnest for more than 15 years prior to publication. Darwin was entirely unprepared for the controversy he kicked off, although one suspects that he’d merely be saddened and confused by the low esteem in which a majority of Americans currently hold his theory.