In situ cranium of 'Karabo' the Australopithecus sediba.
Credit: Wikimedia
1. Gasping for air
It's not much to look at, but a 375 million-year-old fossil lungfish (Rhinodipterus) could be evidence of one of the most important developments in the evolution of early life: the first air-breathing vertebrates. Australian palaeontologists John Long, now at the Natural History Museum of Los Angeles, and Alice Clement from Museum Victoria, who described the fossil in 2010, noted that Rhinodipterus had large ribs that helped anchor the fish's shoulder girdle, letting it lift its head up out of the water to gulp air. This adaptation was crucial as, during this time, atmospheric oxygen levels had dipped much lower than the 21% we enjoy today. Both fish and our tetrapod (four-limbed) ancestors would have been forced to rise to the surface and gulp oxygen in order to survive.
2. Death of an icon
The discovery of a 155-million-year-old feathered dinosaur, Xiaotingia zhengi, in China earlier this year threatened to knock 'first bird' Archaeopteryx off its proverbial perch. When scientists led by Xing Xu, from the Chinese Academy of Sciences' Institute of Vertebrate Palaeontology and Palaeoanthropology in Beijing, ran the new species through a phylogenetic analysis, it caused a slight shuffling of the dinosaur family tree. Archaeopteryx was yanked out of the Avialae group of dinosaur-like birds to join the new fossil in the Deinonychosauria group of bird-like dinosaurs. The reclassification "seems subtle," says Lawrence Witmer of Ohio University in a commentary in the journal Nature, "but it changes how we view the evolution of birds."
3. Breathing sulphur, not oxygen
Found among sand grains in a block of sandstone from the Strelley Pool in the remote Pilbara region of Western Australia, a group of 3.4 billion-year-old fossilised microbes are the oldest well-preserved fossils ever found, a team reported in August 2011 in Nature Geoscience. And the scientists who discovered them, led by David Wacey from the University of Western Australia in Perth, say the fossils hint at a time when Earth was so poor in oxygen, life had to metabolise sulphur instead. The primitive microbes were found alongside the mineral pyrite (also known as 'fool's gold'), which Wacey says is a by-product of their consumption of sulphur compounds.
4. Soft bits
In 2005 and 2009, scientists led by Mary Schweitzer from North Carolina State University were able to extract collagen and blood vessels from 68-million-year-old fossilised Tyrannosaurus rex and 80-million-year-old Brachylophosaurus canadensis femurs from the Judith River Formation in Montana. While the team failed to use the cells for a Jurassic Park-style cloning experiment, they were able to sequence the dinosaurs' proteins to construct new family trees, and found that both the dinosaurs belonged to the same group as chickens and ostriches, strengthening the case for the close relationship between dinosaurs and modern birds.
5. New human ancestor
This 1.98-million-year-old fossilised skull (pictured) belongs to a juvenile Australopithecus sediba, a primate that may be our earliest ancestor. The skull was unearthed in a South African cave along with another A. sediba skeleton of an individual believed to be the boy's mother. The team, including Paul Dirks from Queensland's James Cook University, thinks the boy was around 13 years old when he died. "It's the opinion of my colleagues and I that [A. sediba] may very well be the Rosetta stone that unlocks our understanding of the genus Homo," says the lead author, Lee Berger of the University of Witwatersrand in Johannesburg. In a September 2011 paper in Science, the researchers narrowed down the age of the specimens to 1.98 million years old, strengthening the case that this is the earliest ancestor of the Homo genus.
6. The mother fish
Unearthed from one of the Gogo fossil sites in north Western Australia in 2005, a 380-million-year-old armoured fish is the oldest vertebrate mother ever found. Not only have tiny embryonic bones been preserved inside the female's complete skeleton, but so too have her yolk sac and umbilical cord (above). She embodies the earliest evidence of vertebrate sexual reproduction, and her discoverers, led by John Long, named her Materpiscis attenboroughi, which means 'mother fish' and tips the hat to David Attenborough, who in 1979 first drew attention to the importance of the Gogo sites in his television series, Life on Earth.
7. Eyeing off predators
Fossilised eyes found in 515-million-year-old rocks on Kangaroo Island off South Australia push back the date of complex eye development to the Early Cambrian Period. The eyes belong to an unknown arthropod, a group that today includes crustaceans and insects, says a team led by Michael Lee from the South Australian Museum and University of Adelaide in Nature in June. Seven eyes were found with arrays of more than 3,000 lenses. "These eyes point to an active, highly mobile predator capable of seeing in low light conditions, suggesting that complex predator-prey relationships were already in place during the Early Cambrian," says co-author John Paterson from the University of New England in eastern Australia.
8. Colour change
In 2008, Derek Briggs and Jakob Vinther from Yale University in the U.S. uncovered a small, broadly striped fossilised feather from a 100-million-year-old bird in rocks from the Lower Cretaceous Crato Formation site in northeast Brazil. Using an electron microscope, the team examined the microscopic sausage-shaped structures within the dark bands to discover that they were pigment-producing structures called melanosomes. Differently shaped melanosomes represent different colour pigments, so the scientists were able to create a 'colour map' to reconstruct the appearance of the ancient black and white-striped bird. It's the first indication that microscopic analysis can reveal this kind of colour detail in fossils.
