Stepping back in time

Our extinct ancestors walked just like us, according to American scientists. By studying ancient fossilised tracks the researchers found that our way of walking, on two feet and taking long strides with each step, evolved long before we did.

Spot the ancestral gait... Image: Raichlen et al/PLOSone

Ancient hominims – the group of primates including ourselves – could have walked in one of two ways; either they walked just like us, with long, striding steps, or with bent legs like a chimpanzee. Different gaits leave different shaped footprints, so the researchers could compare fossilised trackways at Laetoli, Tanzania, to the footprints left by modern volunteers to see how some of our ancestors moved.

The fossil footprints found at Laetoli in Tanzania have courted controversy ever since they were discovered thirty years ago. At 3.6 million years old, the tracks are the oldest direct fossil evidence of bipedalism in any of our ancestors, and this presents a problem. They could only have been left by one of our distant ancestors called Australopithecus afarensis, but their skeletons suggest they used a bent-legged gait like chimps, well adapted to life in the trees.

To solve the puzzle, the researchers asked volunteers to walk through sand normally, or imitating a chimpanzee, with bent knees and back. A laser scanner mapped the footprints they left behind, and the results showed clear differences between the two gaits – bent-knee gaits leave much deeper toe-prints, for example. With this data the researchers could then look at the Laetoli tracks.

Their results were quite conclusive: Laetoli toe-prints were shallower than their heel-prints, and in the same range as our modern gait, strongly supporting the idea that they walked much like we do today. Our way of walking is the most energy efficient way to get around on two legs, so the results also suggest walking on the ground, rather than in the trees, was an important part of the Australopithecine lifestyle – an important step towards the plains-striding apes that went on to conquer the world.

Paper Reference: Raichlen DA,  Gordon AD,  Harcourt-Smith WEH,  Foster AD,  Haas WR Jr,. (2010) Laetoli Footprints Preserve Earliest Direct Evidence of Human-Like Bipedal Biomechanics. PLoS ONE 5(3). e9769. doi:10.1371/journal.pone.0009769

Fantastic Fish Fossils Found

Researchers have found several new species of gigantic extinct fish that fed solely on the tiniest of food-sources – plankton. The fossil fish fill a gaping hole in the fossil record: before now, large plankton-eating fish were missing from a 100million year chunk of prehistory.

A modern Basking Shark - such a big mouth for such tiny prey. Image: Wikimedia

Long before the evolution of filter-feeding whales and sharks the seas were home to nine-metre long fish, such as the newly-discovered Bonnerichthys, which took advantage of the same food source. Until recently, researchers believed the group to which these fish belonged, the pachycormids, went extinct around 172million years ago, in the Jurassic period.

The new discoveries, which included fossils from the USA, UK and Japan, show that the pachycormids actually went extinct at the same time as the dinosaurs, 65 million years ago. Only once they were gone was there an opportunity for modern ‘planktivorous’ groups, like baleen whales and basking sharks (Cetorhinus maximus), to evolve.

Plankton – the collection of microscopic marine creatures found in every sea and ocean around the world – today supports gigantic marine animals such as the blue whale (Balaenoptera musculus). These animals use comb-like structures called baleen plates to filter the tiny plants, animals and bacteria out of seawater.

The hole in the fossil record was a complete mystery. Plankton is so abundant, and supports such large animals today that researchers expected something to eat it. Bonnerichthys and friends are, it seems, just the massive fish required to plug such a massive hole.

Paper Reference: Friedman et al. 100-Million-Year Dynasty of Giant Planktivorous Bony Fishes in the Mesozoic Seas. (2010). Science, 327 (5968), p990-993 DOI: 10.1126/science.1184743

What makes a bird?

New findings could knock Archaeopteryx off its perch as the oldest-known bird. According to an international team of scientists, Archaeopteryx “…was simply a feathered and presumably volant [flying] dinosaur.”!

Is it a bird, is it a ... dinosaur?! Image: Wikimedia/Luidger

The scientists, from the USA, Germany and China, looked at the fossilised bones of Archaeopteryx under a microscope. The bones contained very few spaces for blood vessels, resembling instead the slow-growing bones of a reptile. In contrast, modern bird bones contain lots of spaces for blood vessels, as their rapid growth means their bones need a substantial supply of nutrients.

Young birds grow up very quickly; reaching their adult size in just a few weeks before they leave the nest (this is why you never see a ‘young’ pigeon in the flocks that crowd our cities). Scientists had thought the earliest birds, which evolved from dinosaurs 150 million years ago, grew up just as fast, but the new evidence suggests they grew up  slowly, just like the dinosaurs from which they evolved. Only later did they acquire the speedy metabolism needed to support the rapid growth we see in modern birds.

The dinosaur-like growth rates cast doubt over the theory that Archaeopteryx is the oldest known bird. It’s teeth, clawed hands and long bony tail show Archaeopteryx is closely related to dinosaurs, but the presence of well-developed feathers (which can be clearly seen as impressions in the rock surrounding fossil Archaeopteryx found at Solnhofen in Germany) has marked it out as a true bird. The new findings could overturn this, as the slow metabolism and un-bird-like growth rates suggest Archaeopteryx may be essentially just another feathered dinosaur.

Paper Reference: doi:10.1371/journal.pone.0007390

Section through an Archaeopteryx femur. Image: PLOS one