Lucy's Cousin

Nature news reports the finding of a new australopithecine in Ethiopia only 35km from the site where Lucy, Australopithecus afarensis, was discovered in 1974. Lucy marked one of the oldest examples of early hominins at that time, living as she did approximately 3.2 million years ago. She has a relatively small cranium, which means a small brain, but was clearly bipedal; thereby resolving the chicken and egg question in relation to large brain capacity and bipedalism. Her skeleton is 40% complete, which is remarkably intact for a specimen that old, and we have learnt an awful lot from her.

This new specimen is contemporaneous with A. afarensis, being 3.3-3.5 million years old, which throws up the scenario that there were possibly several early hominins all wondering around east Africa at the same period. But this shouldn't come as a surprise, it is only in very recent history that we became the only biped on the block when we finished off the last of the neanderthals; before then there had been as many as half a dozen species cohabiting in Africa and through into Asia. Part of the reason that this could happen is demonstrated in the new skeleton. It has a much sturdier and stronger jaw than Lucy does, this would imply that they had a different diet and therefore weren't competing for the same resources.

This new species has been dubbed Australopithecus deyiremeda which roughly translates as 'close relative' in the local Afar language. We shouldn't assume that she (I'm calling her a she) is our ancestor, however, many early hominins died out and weren't a part of the lineage that went on to become the Homo genus. That said, she does make for a wonderful transition fossil, which turns out to have been something of a theme on the blog this week. I shall try to transition into a new area next week.

Model of what Lucy, and possibly A. deyiremeda, may have looked like

Uprooting the Tree of Life

Yesterday I wrote a post about a cool new transition fossil. When writing it I was more than once tempted to make some kind of reference to the Tree of Life, but I resisted. Why? Put simply: because it would be wrong. There was a time when everyone, even people who were totally on board with evolution by natural selection, was under the impression that the species we see wriggling around today could be traced neatly back, branch by branch, to the ancestor that is common to all life and that those species that looked physically similar did so because they shared a branch on the tree. In the metaphor today's animals are represented by the fresh new shoots and buds on the mighty oak of life; each bud forms a neat ladder ever back to the base of the trunk that started everything, but this picture can lead to many misconceptions about evolution. A more modern understanding of the theory and the evidence we now have paints a different picture. The Tree of Life is dead, say hello to the Shrubbery of Life!

The traditional, misleading view of the Tree of Life

Actually, people generally say the Bush of Life but I saw a chance to use the word shrubbery and I ran with it. Instead of thinking of a perfect, archetypal tree that a 6 year old might draw, think of a tangled mess of thorns full of jagged twigs, thick and choking, jutting this way and that such that you can barely tell where one branch begins and another ends. This is the far better analogy. It allows for the possibility of animals arriving at the same physical niche via a variety of evolutionary paths. It also rules out the idea that as life evolves it moves ever upwards in an increasingly complicated and intricate manner, this isn't the case. Some species 'devolve', or lose features that they had previously evolved; some, like coelacanths or nautili, remain unchanged for millions of years.

Worry not, if you have a poster on your child's bedroom wall like the one on the right I'm not about to tear it down and set fire to it. But the next time you have a chat about it, as you undoubtedly do, use it as an opportunity to highlight that the reality is actually a lot more nuanced and complicated than we often like to think, just like every other single topic worth having a chat about.

I Love Transition Fossils

One of the many stupid arguments put forward by people trying to dispute the theory of evolution by natural selection is: if evolution is true then there should be fossils of missing links, if birds evolved from dinosaurs then show me a fossil that is half bird and half dinosaur. Now, asides from the fact that this shows a gross misunderstanding of the theory there are actually a great deal of 'missing links' out there; they're called transition fossils and there is now a quite beautiful catalogue of them. We have transition fossils for pretty much every major order of animals out there, the only exception I can think of is bats, we don't yet have a decent fossil record of their evolution - it's only a matter of time, though.

We have ambulocetus, a wonderful cetacean (whale and dolphin) precursor that could swim well and walk around on land too; we have tiktaalik, a transition fossil of a fish that had 4 primitive legs and was well on its way to being an amphibian; and we have the legendary archaeopteryx, which is quite literally half bird half dinosaur. The fossil record, by its very nature, will never be 100% complete, but it is now well stocked with a plethora of transition fossils all of which add support to the now invincible edifice that is evolution by natural selection, and, I'm pleased to say we can now welcome another strut to the structure.

Image used with permission

An article in Nature has given details of an awesome new transition fossil; it is quite clearly a snake but equally clearly it has four little legs. The legs would not have allowed it to walk, they're too small and it's body is too long, but they may have allowed it to grab prey a little easier or get a better grip when mating hence its name: Tetrapodophis amplectus which translates as four-legged hugging snake.

For a long time it was uncertain if snakes had evolved from land animals or aquatic animals. If the latter then we would expect to see a transition fossil with a tail adapted for swimming and vestigial fins; if the former then we would expect, well, we would expect exactly what this fossil shows. Another little gap in our knowledge has been filled in, leaving one less place for evolution deniers to hide.

Extinction by Fussiness

If there's one thing that really bugs me it's fussy eaters but a new paper from researchers at Oxford University may have found an example where the ramifications of a restrictive diet were more than just annoying me. Australopithecus bahrelghazali was a form of early hominid that forged west out of the rift valley some 4 million years ago; they settled in what is modern day Chad a long way from any other australopithecine yet found. The land was fertile and there were few predators and this allowed them to evolve into a niche that, when push came to shove a million years later, left them facing extinction in the face.

Although there were plenty of different things available to eat research has shown that the thin enamel of their teeth would have restricted their diet to soft, easily chewable plants like sedges. These are not a very nutritious food, which was fine when times were good, but as the climate changed and as predators moved into the territory they simply couldn't eat enough high quality food to survive the new difficult conditions and that, Science Fans, was the end of Australopithecus bahrelghazali.