A new study uses carbon isotope dating to determine the first precise age for this bed, and ties the western coast of Africa to 30 million years of global geologic records

Paleontologists at Southern Methodist University have measured the carbon isotopes in marine fossils to precisely date for the first time 30 million years of sediments along Africa’s South Atlantic shoreline.
The researchers matched the pattern of ratios of carbon-13 and carbon-12 isotopes in marine fossils from Africa’s South Atlantic shoreline to known patterns of carbon ratios in fossils found elsewhere in the world. From that they determined the age of the coastal sediments at a fossil locality near the southern Angolan village of Bentiaba, said paleontologist Christopher Strganac, lead author on the study.

The analysis focused on a sequence of shoreline sediments totaling 140 meters thick. Their age spans a timeline of nearly 30 million years, from 95 million years ago to 68 million years ago. That period was about 40 million years after Africa and South America split, allowing the South Atlantic Ocean to slowly emerge.

The analysis revealed that the richest marine reptile fossil bed on Africa’s South Atlantic dated to 71.5 million years ago, he said. This new date at the Bentiaba locality is more than 2 million years older than the estimated date of about 69 million years previously assigned to those marine beds by earlier researchers.

Africa’s South Atlantic coast is remarkable in plate tectonics as the place where part of the prehistoric supercontinent Gondwana split 130 million years ago into what we now call Africa and South America.

“The precise age for these rocks allows better understanding of the ancient life and environments at Bentiaba by placing them accurately within the history of the ancient South Atlantic,” said Strganac, a doctoral student in SMU’s Roy M. Huffington Department of Earth Sciences. “It’s a benchmark now from the Southern Hemisphere with which we can better understand ancient life at that time.”

The precise dating was made possible by new scientific dating techniques. The age of the rocks hadn’t previously been assessed because Africa’s South Atlantic shore — noted for its puzzle-like fit with South America — has few localities with well-exposed rocks of this age. Also, it has been essentially unexplored by scientific expeditions since the 1960s largely because war and unrest prevented exploration in the previous century.

The new measurements stem from the work of Projecto PaleoAngola, an international team of scientists who in recent years have explored Angola and discovered an abundance of fossils. Their discoveries include the bones of dinosaurs, whales, mosasaurs and other ancient life from what is the richest marine reptile fossil bed along the South Atlantic coast.

Strganac and his co-authors report their findings in the Journal of African Earth Sciences.

“This improvement in understanding the ages of the rocks along the shore is a great first step in trying to understand the climatic and evolutionary events that accompanied the growth of this ocean,” said vertebrate paleontologist Louis L. Jacobs, also a co-author on the study and co-leader of Projecto PaleoAngola. Jacobs describes Angola as “an untapped frontier” for fossil hunters.

Aids in new knowledge of climate, temperature and vegetation

Scientists have recognized since the 1960s that ancient supercontinents split apart and their remnants drifted to the current positions of today’s continents over the course of millions of years. One of the results was the creation of vast new oceans. Little is known of the vertebrate life that lived during that time along the eastern and western margins of the emerging South Atlantic Ocean.

Fossils being discovered now by Projecto PaleoAngola hold the key to understanding the South Atlantic Ocean’s ancient past. Analysis of the fossils sheds light on the paleoenvironment, including changes in climate, temperature, vegetation and ecology.

The geologic time period covered by the 30-million-year sequence represents the Late Cretaceous. Studies have shown it was a period of dramatic change in climate, beginning with one of the warmest periods on Earth, then starting to transition to cooler climates, Strganac said.

Determining carbon ratios allowed comparison with global geologic events

To discover the age of the sediments, Strganac tested 55 fossil shells of ancient oysters and clams from 40 different rock layers on the coast. Testing determined the ratio of stable carbon isotopes, carbon-13 and carbon-12, in each shell. Because these isotopes do not decay with time, the relative abundance of each relates to the ocean when the shells formed. These isotope ratios can be compiled as a sequence with the rock layers, producing a pattern of carbon isotope change in the ancient oceans through millions of years. To accurately date the rocks, Strganac matched the pattern in isotope ratios in the shell record at Angola with the pattern known from ancient geologic events that occurred elsewhere in the world.

Specifically, the red rift-valley layers at Bentiaba were deposited as Africa and South America began to split. Also observed in the layers are a reversal in Earth’s magnetic polarity at 71.4 million to 71.64 million years to delimit the age of marine fossils; rocks deposited in the South Atlantic Ocean 93.9 million years ago during an oceanic anoxic event; and rocks south of Bentiaba that bracket the mass extinction of dinosaurs at 66 million years.

Besides comparing the stable carbon isotopes, other measuring techniques included: magnetostratigraphy, which measures the ancient polarity of Earth’s magnetic field when various sedimentary layers were deposited; and argon-argon radiometric dating of a volcanic basalt layer at the site, which measures the radioactive decay of potassium to argon and dates the cooling of the volcanic lava to 85 million years ago.

“Adding a new ocean to the globe, in this case the South Atlantic, has many long-lasting effects,” said SMU’s Jacobs. “One obvious example is the formation of energy resources found along the coasts of Brazil and Angola.”

Note : The above story is based on materials provided by Southern Methodist University. The original article was written by Margaret Allen.

Preserved giant sperm from tiny shrimps that lived at least 17 million years ago have been discovered at the Riversleigh World Heritage Fossil Site by a team including UNSW Australia researchers.

The giant sperm are thought to have been longer than the male’s entire body, but are tightly coiled up inside the sexual organs of the fossilised freshwater crustaceans, which are known as ostracods.

“These are the oldest fossilised sperm ever found in the geological record,” says Professor Mike Archer, of the UNSW School of Biological, Earth and Environmental Sciences, who has been excavating at Riversleigh for more than 35 years.

“The Riversleigh fossil deposits in remote northwestern Queensland have been the site of the discovery of many extraordinary prehistoric Australian animals, such as giant, toothed platypuses and flesh-eating kangaroos. So we have become used to delightfully unexpected surprises in what turns up there.

“But the discovery of fossil sperm, complete with sperm nuclei, was totally unexpected. It now makes us wonder what other types of extraordinary preservation await discovery in these deposits.”

The study is published in the journal Proceedings of the Royal Society B.

A UNSW research team led by Professor Archer, Associate Professor Suzanne Hand and Henk Godthelp collected the fossil ostracods from Bitesantennary Site at Riversleigh in 1988.

They were sent to John Neil, a specialist ostracod researcher at La Trobe University, who realised they contained fossilised soft tissues.

He drew this to the attention of European specialists, including the lead author on the paper, Dr Renate Matzke-Karasz, from Ludwig Maximilian University of Munich, Germany, who examined the specimens with Dr Paul Tafforeau at the European Synchrotron Radiation Facility in Grenoble, France.

The microscopic study revealed the fossils contain the preserved internal organs of the ostracods, including their sexual organs. Within these are the almost perfectly preserved giant sperm cells, and within them, the nuclei that once contained the animals’ chromosomes and DNA.

Also preserved are the Zenker organs – chitinous-muscular pumps used to transfer the giant sperm to the female. The researchers estimate the fossil sperm are about 1.3 millimetres long, about the same length or slightly longer than the ostracod itself.

“About 17 million years ago, Bitesantennary Site was a cave in the middle of a vast biologically diverse rainforest. Tiny ostracods thrived in a pool of water in the cave that was continually enriched by the droppings of thousands of bats,” says Professor Archer.

UNSW’s Associate Professor Suzanne Hand, who is a specialist in extinct bats and their ecological role in Riversleigh’s ancient environments, says the bats could have played a role in the extraordinary preservation of the ostracod sperm cells.

The steady rain of poo from thousands of bats in the cave would have led to high levels of phosphorous in the water, which could have aided mineralisation of the soft tissues.

“This amazing discovery at Riversleigh is echoed by a few examples of soft-tissue preservation in fossil bat-rich deposits in France. So the key to eternal preservation of soft tissues may indeed be some magic ingredient in bat droppings,” says Associate Professor Hand.

Previous discoveries of extraordinary preservation at Riversleigh include insects with internal muscles that have been preserved because bacteria became fossilised as they attempted to consume the soft tissues of these creatures.

Perfectly preserved cells of leaves have been found, as well as the preserved soft tissue of eyeballs in the eye sockets of some of the extinct marsupials.

Note : The above story is based on materials provided by University of New South Wales

A Case Western Reserve University student and his mentor have discovered an ancient kitten-sized predator that lived in Bolivia about 13 million years ago — one of the smallest species reported in the extinct order Sparassodonta.
Third-year undergraduate student Russell Engelman and Case Western Reserve anatomy professor Darin Croft made the finding by analyzing a partial skull that had been in a University of Florida collection more than three decades.

The researchers report their finding in the Journal of Vertebrate Paleontology.

“The animal would have been about the size of a marten, a catlike weasel found in the Northeastern United States and Canada, and probably filled the same ecological niche,” said Engelman, an evolutionary biology major from Russell Township, Ohio.

The researchers refrained from naming the new species mainly because the specimen lacks well-preserved teeth, which are the only parts preserved in many of its close relatives.

The skull, which would have been a little less than 3 inches long if complete, shows the animal had a very short snout. A socket, or alveolus, in the upper jaw shows it had large, canines, that were round in cross-section much like those of a meat-eating marsupial, called the spotted-tailed quoll, found in Australia today, the researchers said.

Although sparassodonts are more closely related to modern opossums than cats and dogs, the group included saber-toothed species that fed on large prey. This small Bolivian species probably fed on the ancient relatives of today’s guinea pigs and spiny rats, the researchers said.

“Most predators don’t go after animals of equal size, but these features indicate this small predator was a formidable hunter,” Croft said.

The specimen had not been studied in detail after being collected. It was provisionally identified as belonging to a particular group of extinct meat-eating opossums, due in part to its small size. Further adding to the identity challenge, almost all small sparassodonts have been identified by their teeth and lower jaws, which this skull lacks.

Croft wanted to study the skull because its age is nearly twice that of the oldest known species of meat-eating opossum. The specimen was found in a mountainous site known as Quebrada Honda, Bolivia, in 1978, in rock layers dated 12 million to 13 million years ago.

Structurally, extinct meat-eating opossums and sparassodont skulls share a number of similarities due to their similar meat-eating diet, Engelman said.

“No single feature found in the skull was so distinctive that we could say one way or the other what it was,” Croft said, “but the combination of features is unique and says this is a sparassodont.”

One key was that a particular bone of the orbit, the boney socket of the eye, does not touch the nasal bone in an opossum but does in a sparassodont.

The short snout was a kind of red herring. While jaguar-sized sparassodonts had them, the smaller members of the order had fox-like faces. And this species was smaller than most of those.

These smaller sparassodonts also have gaps between their teeth that are absent in most larger species. The skull shows no gaps.

Overall, the animal’s features are a mixture of those found in different species of sparassodonts, but are not characteristic of in any one subgroup within the order. That puts this species near the bottom of the family tree, the researchers said.

Croft, who regularly collects from the same site where the skull was found, will return there this summer to gather evidence he hopes will show whether this species lived in an open grassland, forest or mixed habitat.

He also hopes to find the lower jaw, which may enable direct comparisons with known species and provide enough foundation to name the animal.

Note : The above story is based on materials provided by Case Western Reserve University.