Oldest evidence of life on land found in 3.48 billion-year-old Australian rocks

Fossils discovered by UNSW scientists in 3.48 billion year old hot spring deposits in the Pilbara region of Western Australia have pushed back by 580 million years the earliest known existence of microbial life on land. Previously, the world’s oldest evidence for microbial life on land came from 2.7- 2.9 billion-year-old deposits in South Africa containing organic matter-rich ancient soils.

— source newsroom.unsw.edu.au

400,000-year-old fossil human cranium is oldest ever found in Portugal

A large international research team, directed by the Portuguese archaeologist João Zilhão and including Binghamton University anthropologist Rolf Quam, has found the oldest fossil human cranium in Portugal, marking an important contribution to knowledge of human evolution during the middle Pleistocene in Europe and to the origin of the Neandertals.

The cranium represents the westernmost human fossil ever found in Europe during the middle Pleistocene epoch and one of the earliest on this continent to be associated with the Acheulean stone tool industry. In contrast to other fossils from this same time period, many of which are poorly dated or lack a clear archaeological context, the cranium discovered in the cave of Aroeira in Portugal is well-dated to 400,000 years ago and appeared in association with abundant faunal remains and stone tools, including numerous bifaces (handaxes).

— source binghamton.edu

280 Million-Year-Old Fossil Reveals Origins of Chimaeroid Fishes

High-definition CT scans of the fossilized skull of a 280 million-year-old fish reveal the origin of chimaeras, a group of cartilaginous fish related to sharks. Analysis of the brain case of Dwykaselachus oosthuizeni, a shark-like fossil from South Africa, shows telltale structures of the brain, major cranial nerves, nostrils and inner ear belonging to modern-day chimaeras.

This discovery, published early online in Nature on Jan. 4, allows scientists to firmly anchor chimaeroids—the last major surviving vertebrate group to be properly situated on the tree of life—in evolutionary history, and sheds light on the early development of these fish as they diverged from their deep, shared ancestry with sharks.

“Chimaeroids belong somewhere close to the sharks and rays, but there’s always been uncertainty when you search deeper in time for their evolutionary branching point,” said Michael Coates, PhD, professor of organismal biology and anatomy at the University of Chicago, who led the study.

“Chimaeras are unusual throughout the long span of their fossil record,” Coates said. “Because of this, it’s been difficult to understand how they got to be the way they are in the first place. This discovery sheds new light not only on the early evolution of shark-like fishes, but also on jawed vertebrates as a whole.”

Chimaeras include about 50 living species, known in various parts of the world as ratfish, rabbit fish, ghost sharks, St. Joseph sharks or elephant sharks. They represent one of four fundamental divisions of modern vertebrate biodiversity. With large eyes and tooth plates adapted for grinding prey, these deep-water dwelling fish are far from the bloodthirsty killer sharks of Hollywood.

For more than 100 years, they have fascinated biologists. “There are few of the marine animals that on account of structure and relationships to other forms living and extinct have as great interest for zoologists and palaeontologists as the Chimaeroids,” wrote Harvard naturalist Samuel Garman in 1904. More than a century later, the relationship between chimaeras, the earliest sharks, and other early jawed fishes in the fossil record continues to puzzle paleontologists.

Chimaeras—named for their similarities to a mythical creature described by Homer as “lion-fronted and snake behind, a goat in the middle”—are unusual. Their anatomy comprises features reminiscent of sharks, ray-finned fishes and tetrapods, and their form is shaped by hardened bits of cartilage rather than bone. Because they are found in deep water, they were long considered rare. But as scientists gained the technology to explore more of the ocean, they are now known to be widespread, but their numbers remain uncertain.

After a 2014 study detailing their extremely slow-evolving genomes was published in Nature, interest in chimaeras blossomed. Of all living vertebrates with jaws, chimaeras seemed to offer the best promise of finding an archive of information about conditions close to the last common ancestor of humans and a Great White.

Like sharks, also reliant on cartilage, chimaeras rarely fossilize. The few known early chimaera fossils closely resemble their living descendants. Until now, the chimaeroid evolutionary record consisted mostly of isolated specimens of their characteristic hyper-mineralized tooth plates.

The Dwykaselachus fossil resolves this issue. It was originally discovered by amateur paleontologist and farmer Roy Oosthuizen when he split open a nodule of rock on his farm in South Africa in the 1980s. An initial description named it based on material visible at the broken surface of the nodule. It was carefully archived in the South African Museum in Cape Town, where its splendor awaited technology able to unwrap its long-shrouded secrets.

In 2013, when the University of the Witwatersrand Evolutionary Studies Institute obtained a micro CT scanner, Dr. Robert Gess, a South African Centre of Excellence in Palaeosciences partner and co-author of this study, began scanning Devonian shark fossils while he was based at the Rhodes University Geology Department. Coates encouraged him to investigate Dwykaselachus.

At the surface, Dwykaselachus appeared to be a symmoriid shark, a bizarre group of 300+ million-year-old sharks, known for their unusual dorsal fin spines, some resembling boom-like prongs and others surreal ironing boards.

CT scans showed that the Dwykaselachus skull was remarkably intact, one of a very few that had not been crushed during fossilization. The scans also provide an unprecedented view of the interior of the brain case.

“When I saw it for the first time, I was stunned,” Coates said. “The specimen is remarkable.”

The images, one reviewer commented, are “almost dripping with data.”

They show a series of telltale anatomical structures that mark the specimen as an early chimaera, not a shark. The braincase preserves details about the brain shape, the paths of major cranial nerves and the anatomy of the inner ear. All of which indicate that Dwyka belongs to modern-day chimaeras. The scans reveal clues about how these fish began to diverge from their common ancestry with sharks.

A large extinction of vertebrates at the end of the Devonian period, about 360 million years ago, gave rise to an explosion of cartilaginous fishes. Instead of what became modern-day sharks, Coates said, revelations from this study indicate that “much of this new biodiversity was, instead, early chimaeras.”

“We can now say that the first radiation of cartilaginous fishes after the end Devonian extinction was chimaeras, in abundance.” Coates said. “It’s the inverse of what we’ve got today, where sharks are far more common.”

The study, “A symmoriiform chondrichthyan braincase and the origin of chimaeroid fishes,” was supported by the National Science Foundation, the National Research Foundation (NRF) / Department of Science and Technology South African Centre of Excellence in Palaeosciences, and the NRF African Origins Programme. Additional authors include John Finarelli from the University College Dublin, Ireland, and Katharine Criswell and Kristen Tietjen from the University of Chicago.

— source newswise.com

The marine creatures evolved over 530 million years ago during the Cambrian period

A team of scientists led by University of Toronto undergraduate student Joseph Moysiuk has finally determined what a bizarre group of extinct cone-shaped animals actually are. Known as hyoliths, these marine creatures evolved over 530 million years ago during the Cambrian period and are among the first animals known to have produced mineralized external skeletons. Long believed to belong to the same family as snails, squid and other molluscs, a study published today in the prestigious scientific journal Nature shows that hyoliths are instead more closely related to brachiopods – a group of animals which has a rich fossil record, although few living species remain today.

— source utoronto.ca

Oxygen levels were key to early animal evolution

It has long puzzled scientists why, after 3 billion years of nothing more complex than algae, complex animals suddenly started to appear on Earth. Now, a team of researchers has put forward some of the strongest evidence yet to support the hypothesis that high levels of oxygen in the oceans were crucial for the emergence of skeletal animals 550 million years ago.

The new study is the first to distinguish between bodies of water with low and high levels of oxygen. It shows that poorly oxygenated waters did not support the complex life that evolved immediately prior to the Cambrian period, suggesting the presence of oxygen was a key factor in the appearance of these animals.

The research, based on fieldwork carried out in the Nama Group in Namibia, is published in the journal Nature Communications.

Lead author Dr Rosalie Tostevin completed the study analyses as part of her PhD with UCL Earth Sciences, and is now in the Department of Earth Sciences at Oxford University. She said: ‘The question of why it took so long for complex animal life to appear on Earth has puzzled scientists for a long time. One argument has been that evolution simply doesn’t happen very quickly, but another popular hypothesis suggests that a rise in the level of oxygen in the oceans gave simple life-forms the fuel they needed to evolve skeletons, mobility and other typical features of modern animals.

‘Although there is geochemical evidence for a rise in oxygen in the oceans around the time of the appearance of more complex animals, it has been really difficult to prove a causal link. By teasing apart waters with high and low levels of oxygen, and demonstrating that early skeletal animals were restricted to well-oxygenated waters, we have provided strong evidence that the availability of oxygen was a key requirement for the development of these animals. However, these well-oxygenated environments may have been in short supply, limiting habitat space in the ocean for the earliest animals.’

The team, which included other geochemists, palaeoecologists and geologists from UCL and the universities of Edinburgh, Leeds and Cambridge, as well as the Geological Survey of Namibia, analysed the chemical elemental composition of rock samples from the ancient seafloor in the Nama Group – a group of extremely well-preserved rocks in Namibia that are abundant with fossils of early Cloudina, Namacalathus and Namapoikia animals.

The researchers found that levels of elements such as cerium and iron detected in the rocks showed that low-oxygen conditions occurred between well-oxygenated surface waters and fully ‘anoxic’ deep waters. Although abundant in well-oxygenated environments, early skeletal animals did not occupy oxygen-impoverished regions of the shelf, demonstrating that oxygen availability (probably >10 micromolar) was a key requirement for the development of early animal-based ecosystems.

Professor Graham Shields-Zhou (UCL Earth Sciences), one of the co-authors and Dr Tostevin’s PhD supervisor, said: ‘We honed in on the last 10 million years of the Proterozoic Eon as the interval of Earth’s history when today’s major animal groups first grew shells and churned up the sediment, and found that oxygen levels were important to the relationship between environmental conditions and the early development of animals.’

— source ucl.ac.uk

Ancient brain area controls eye movements

An ancient area of the midbrain of all vertebrates called the corpora quadrigemina can independently contol and reorientate the eyes, researchers from Karolinska Institutet report in a study published in the journal eLIFE.

There is much going on around us all the time, phenomena that we perceive with our different senses, which send information to the brain. When we walk along the street, for example, we encounter other people that we have to avoid bumping into, or might find our attention drawn to an unexpected object. The brain then has the very difficult task of determining which of these multifarious events we need to respond to.
This problem is solved by an ancient part of the midbrain called the corpora quadrigemina, or tectum. This area is found in all vertebrates and [Neil Bett1] contains a complex network of neurons that control the movements of the head and eyes. Information from different parts of the retina project onto different parts of the tectum creating a retina-based map that reflects the information sent by the retina.

“You could say there’s a spatial sensory map in the tectum, where images from the eye are projected to create signals about where things happen,” says Professor Sten Grillner at Karolinska Institutet’s Department of Neuroscience.
Different parts of the retinal map can then activate nerve cells that control motor centres for eye and head movements in the brain stem. When a movement is triggered, other parts of the tectum network are disabled and thus other movements of the eyes and head.
The study also shows that if an event is registered by two senses (e.g. vision and hearing) from the same point the signals will be merged. If two senses thus supply the tectum with contradictory information, the neurons will become less active, thus reducing the likelihood of a triggered physical event such as eye-movement.

The study was conducted on the lamprey, a small, eel-like fish that represents the earliest form of vertebrate, by Sten Grillner along with visiting researchers Andreas Kardamakis and Juan Pérez-Fernández.

“It’s more primitive than normal fish, but important parts of its nerve system share all their basic features with the more advanced nerve systems of mammals,” says Professor Grillner.
Although the study was basic research, it can help scientists understand certain clinical phenomena, such as the morbid impairment of ocular movements caused by Parkinson’s disease.

The study was financed by the Swedish Research Council, KI’s Research Funds, EU FP7 and StratNeuro.

— source ki.se

Evolution of Darwin’s finches tracked at genetic level

Researchers are pinpointing the genes that lie behind the varied beaks of Darwin’s finches – the iconic birds whose facial variations have become a classic example of Charles Darwin’s theory of natural selection.

Last year, researchers identified a gene that helps to determine the shape of the birds’ beaks1. Today in Science, they report a different gene that controls beak size2. Shifts in this gene underlay an evolutionary change that researchers watched in 2004–05, during a drought that ravaged the Galapagos Islands, where the finches live. The beak sizes of one population of finches shrank, so as to avoid competing for food sources with a different kind of finch – and their genetics changed accordingly.

“A big question was, ‘Is it possible to identify genes underlying such evolution in action, even in a natural population?’,” says Leif Andersson, a geneticist at Uppsala University in Sweden and one of the study’s authors. “We were able to nail down genes that have directly played a role in this evolutionary change.”

The story begins about two million years ago, when the common ancestor of all Darwin’s finches arrived on the Galapagos Islands. By the time of Charles Darwin’s visit in 1835, the birds had diversified into more than a dozen species, each adapted to different ecological niches. Some had massive beaks for cracking seeds, some had delicate beaks for snatching insects, and some even had sharp beaks for feeding on blood.

To examine the genetic basis for this variation, the researchers compared the genomes of 60 birds representing six species of Darwin’s finches, along with 120 specimens from other species to help them tease out phylogenetic relationships. As expected, closely related species had the most similar genomes.

Gene for size

Beaks in Darwin’s finches range from small insect-crunchers to large seed-demolishers.

But in those six finch species one region of the genome correlated more with bird size than with relatedness. Small species had one variation of this genomic region, large species had another and medium-sized species had a mixture of the two, suggesting that at least one of the genes in this region affected size. The most likely candidate was HGMA2, which is known to affect size and face structure in other animals. Further analysis showed that in Darwin’s finches, the HGMA2 region is especially important in controlling the size of the beak.

The researchers then looked at the role of HGMA2 in a dramatic evolutionary event. After drought struck the Galapagos in 2003, many of the medium ground finches (Geospiza fortis) with larger-than-average beaks starved to death. They couldn’t compete with a bigger species (Geospiza magnirostris) that had recently colonized the island and was better at eating large seeds. After the drought, the medium ground finches that managed to survive had smaller beaks than those that had perished, probably because they were better suited to eating the small seeds that their competitors avoided.

By analysing DNA from medium ground finches that lived around the time of the drought, the researchers found that the large-beak HGMA2 variant was more common in birds that starved to death, while the small-beak variant was more common in birds that survived. This genetic shift is likely responsible for some of the reduction in beak size, the researchers say.

The discovery opens up new questions for biologists to explore, such as when gene variants arise and how they contribute to splits between species, says Dolph Schluter, an evolutionary biologist at the University of British Columbia in Vancouver, Canada.

“On the one hand it doesn’t change anything, in that we already knew there was an evolutionary response to competition during that drought,” says Schluter. “But on the other hand, it changes everything, because we can point to a physical, material basis for that change.”

— source nature.com By Nala Rogers