Antarctica yields oldest fossils of giant birds with 21-foot wingspans

Fossils recovered from Antarctica in the 1980s represent the oldest giant members of an extinct group of birds that patrolled the southern oceans with wingspans of up to 21 feet that would dwarf the 11½-foot wingspan of today's largest bird, the wandering albatross.

Artist's depiction of ancient albatrosses harassing a pelagornithid -- with its fearsome toothed
beak - as penguins frolic in the oceans around Antarctica 50 million years ago
[Credit: Brian Choo]

Called pelagornithids, the birds filled a niche much like that of today's albatrosses and traveled widely over Earth's oceans for at least 60 million years. Though a much smaller pelagornithid fossil dates from 62 million years ago, one of the newly described fossils -- a 50 million-year-old portion of a bird's foot -- shows that the larger pelagornithids arose just after life rebounded from the mass extinction 65 million years ago, when the relatives of birds, the dinosaurs, went extinct. A second pelagornithid fossil, part of a jaw bone, dates from about 40 million years ago.

"Our fossil discovery, with its estimate of a 5-to-6-meter wingspan -- nearly 20 feet -- shows that birds evolved to a truly gigantic size relatively quickly after the extinction of the dinosaurs and ruled over the oceans for millions of years," said Peter Kloess, a graduate student at the University of California, Berkeley.

The last known pelagornithid is from 2.5 million years ago, a time of changing climate as Earth cooled, and the ice ages began.

Kloess is the lead author of a paper describing the fossil that appears this week in the open access journal Scientific Reports. His co-authors are Ashley Poust of the San Diego Natural History Museum and Thomas Stidham of the Institute of Vertebrate Paleontology and Paleoanthropology at the Chinese Academy of Sciences in Beijing. Both Poust and Stidham received their Ph.Ds from UC Berkeley.

Birds with pseudoteeth

Pelagornithids are known as 'bony-toothed' birds because of the bony projections, or struts, on their jaws that resemble sharp-pointed teeth, though they are not true teeth, like those of humans and other mammals. The bony protrusions were covered by a horny material, keratin, which is like our fingernails. Called pseudoteeth, the struts helped the birds snag squid and fish from the sea as they soared for perhaps weeks at a time over much of Earth's oceans.

Large flying animals have periodically appeared on Earth, starting with the pterosaurs that flapped their leathery wings during the dinosaur era and reached wingspans of 33 feet. The pelagornithids came along to claim the wingspan record in the Cenozoic, after the mass extinction, and lived until about 2.5 million years ago. Around that same time, teratorns, now extinct, ruled the skies.

The birds, related to vultures, "evolved wingspans close to what we see in these bony-toothed birds (pelagornithids)," said Poust. "However, in terms of time, teratorns come in second place with their giant size, having evolved 40 million years after these pelagornithids lived. The extreme, giant size of these extinct birds is unsurpassed in ocean habitats,""

This five-inch segment of fossilized jaw, which was discovered in Antarctica in the 1980s, dates
 from 40 million years ago. The skull of the bird would have been about two feet long, while
 the pseudoteeth, which were originally covered with horny keratin, would have been up
to an inch long. At this scale, the bird's wingspan would have been 5 to 6 meters,
or some 20 feet [Credit: Peter Kloess/UC Berkeley]

The fossils that the paleontologists describe are among many collected in the mid-1980s from Seymour Island, off the northernmost tip of the Antarctic Peninsula, by teams led by UC Riverside paleontologists. These finds were subsequently moved to the UC Museum of Paleontology at UC Berkeley.

Kloess stumbled across the specimens while poking around the collections as a newly arrived graduate student in 2015. He had obtained his master's degree from Cal State-Fullerton with a thesis on coastal marine birds of the Miocene era, between 17 million and 5 million years ago, that was based on specimens he found in museum collections, including those in the UCMP.

"I love going to collections and just finding treasures there," he said. "Somebody has called me a museum rat, and I take that as a badge of honor. I love scurrying around, finding things that people overlook."

Reviewing the original notes by former UC Riverside student Judd Case, now a professor at Eastern Washington University near Spokane, Kloess realized that the fossil foot bone -- a so-called tarsometatarsus -- came from an older geological formation than originally thought. That meant that the fossil was about 50 million years old instead of 40 million years old. It is the largest specimen known for the entire extinct group of pelagornithids.

The other rediscovered fossil, the middle portion of the lower jaw, has parts of its pseudoteeth preserved; they would have been up to 3 cm (1 inch) tall when the bird was alive. The approximately 12-cm (5-inch-) long preserved section of jaw came from a very large skull that would have been up to 60 cm (2 feet) long. Using measurements of the size and spacing of those teeth and analytical comparisons to other fossils of pelagornithids, the authors are able to show that this fragment came from an individual bird as big, if not bigger, than the largest known skeletons of the bony-toothed bird group.

A warm Antarctica was a bird playground

Fifty million years ago, Antarctica had a much warmer climate during the time known as the Eocene and was not the forbidding, icy continent we know today, Stidham noted. Alongside extinct land mammals, like marsupials and distant relatives of sloths and anteaters, a diversity of Antarctic birds occupied the land, sea and air.

Seymour Island, near the northernmost point of the Antarctic peninsula, has yielded a wealth
of fossils, including parts of giant birds like the pelagornithids and the smaller ancestors
of today’s albatross, not to mention scads of penguins. The UCMP fossils described
in the new study came from points 1 and 6 [Credit: Peter A. Kloess et al. 2020]

The southern oceans were the playground for early penguin species, as well as extinct relatives of living ducks, ostriches, petrels and other bird groups, many of which lived on the islands of the Antarctic Peninsula. The new research documents that these extinct, predatory, large- and giant-sized bony-toothed birds were part of the Antarctic ecosystem for over 10 million years, flying side-by-side over the heads of swimming penguins.

"In a lifestyle likely similar to living albatrosses, the giant extinct pelagornithids, with their very long-pointed wings, would have flown widely over the ancient open seas, which had yet to be dominated by whales and seals, in search of squid, fish and other seafood to catch with their beaks lined with sharp pseudoteeth," said Stidham. "The big ones are nearly twice the size of albatrosses, and these bony-toothed birds would have been formidable predators that evolved to be at the top of their ecosystem."

Museum collections like those in the UCMP, and the people like Kloess, Poust and Stidham to mine them, are key to reconstructing these ancient habitats.

"Collections are vastly important, so making discoveries like this pelagornithid wouldn't have happened if we didn't have these specimens in the public trust, whether at UC Riverside or now at Berkeley," Kloess said. "The fact that they exist for researchers to look at and study has incredible value."

Author: Robert Sanders | Source: University of California - Berkeley [October 27, 2020]

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Irregular appearances of glacial and interglacial climate states

During the last 2.6 million years of Earth's climate has altered between glacial and interglacial states. As such, there have been times in which the transition between the two climate states appeared with either regular or irregular periodicity. AWI researcher Peter Kohler has now discovered that the irregular appearance of interglacials has been more frequent than previously thought. His study makes a significant contribution to our understanding of Earth's fundamental climate changes.

Credit: Pixabay

In order to understand human beings' role in the development of our current climate, we have to look back a long way, since there has always been climate change - albeit over vastly different timescales than the anthropogenic climate change, which is mainly due to the use of fossil fuels over the past 200 years. Without humans, for millions of years, climate altered between glacial and interglacial states over periods of many thousands of years, mainly because of the Earth's tilt which changes by a few degrees with a periodicity of 41,000 years. 

This in turn changes the angle at which the sun's rays strike Earth - and as such the energy that reaches the planet, especially at high latitudes in summer. However, there is strong evidence that during the course of the last 2.6 million years, interglacials have repeatedly been 'skipped'. The Northern Hemisphere - particularly North America - remained frozen for long periods, despite the angle of the axial tilt changing to such an extent that more solar energy once again reached Earth during the summer, which should have melted the inland ice masses. This means Earth's tilt can't be the sole reason for Earth's climate to alter between glacial and interglacial states.

In order to solve the puzzle, climate researchers are investigating more closely at what points in Earth's history irregularities occurred. Together with colleagues at Utrecht University, physicist Peter Kohler from the Alfred Wegener Institute (AWI) has now made a significant contribution towards providing a clearer picture of the sequence of glacial and interglacial periods over the last 2.6 million years. Until now, experts thought that, especially over the past 1.0 million years, glacial and interglacial periods deviated from their 41,000- year cycle, and that interglacial periods were skipped, as a result of which some glacial periods lasted for 80,0000 or even 120,000 years. "For the period between 2.6 and 1.0 million years ago, it was assumed that the rhythm was 41,000 years," says Peter Kohler. But as his study, which has now been published in the scientific journal Nature Communications, shows, there were also repeated irregularities during the period between 2.6 and 1.0 million years ago.

Kohler's study is particularly interesting because he re-evaluated a well-known dataset that researchers have been using for several years - the LR04 climate dataset - yet arrived at completely different conclusions. This dataset consists of a global evaluation of core samples from deep-sea sediments that are millions of years old, and includes measurements from the ancient shells of microscopic, single-celled marine organisms - foraminifera - that were deposited on the ocean floor. Foraminifera incorporate oxygen from the seawater into their calcium shells. But over millennia, the level of specific oxygen isotopes - oxygen atoms that have differing numbers of neutrons and therefore different masses - varies in seawater.

18O reveals what the world was like in the past

The LR04 dataset contains measurements of the ratio of the heavy oxygen isotope 18O to the lighter 16O. The ratio of 18O/16O stored in the foraminifera's shells depends on the water temperature. But there is also another effect that leads to relatively large amounts of 18O being found in the foraminifera's shells in glacial periods: when, during the course of a glacial period, there is heavy snowfall on land, which leads to the formation of thick ice sheets, the sea level falls - in the period studied, by as much as 120 m. Since 18O is heavier than 16O, water molecules containing this heavy isotope evaporate less readily than molecules containing the lighter isotope. As such, comparatively more 18O remains in the ocean and the 18O content of the foraminifera shells increases. 

Aerial view of the Beyond EPICA camp [Credit: Beyond EPICA]

"If you take the LR04 dataset at face value, it means you blur two effects - the influence of ocean temperature and that of land ice, or rather that of sea level change," says Peter Kohler. "This makes statements regarding the alternation of the glacial periods uncertain." And there is an additional factor: climate researchers mainly determine the sequence of glacial periods on the basis of glaciation in the Northern Hemisphere. But using 18O values doesn't allow us to say whether prehistoric glaciation chiefly occurred in the Northern Hemisphere or in Antarctica.

Computer model separates the influencing parameters

In an attempt to solve this problem, Kohler and his team evaluated the LR04 dataset in a completely different way. The data was fed into a computer model that simulates the growth and melting of the large continental ice sheets. What sets it apart: the model is capable of separating the influence of temperature and that of sea level change on the 18O concentration. Furthermore, it can accurately analyse where and when snow falls and the ice increases - more in the Northern Hemisphere or in Antarctica. "Mathematicians call this separation a deconvolution," Kohler explains, "which our model is capable of delivering." 

The results show that the sequence of glacials and interglacials was irregular even in the period 2.6 to 1.0 million years ago - a finding that could be crucial in the coming years. As part of the ongoing major EU project 'BE-OIC (Beyond EPICA Oldest Ice Core)', researchers are drilling deeper than ever before into the Antarctic ice. With the oldest ice core recovered to date, 'EPICA', they have 'only' travelled back roughly 800,000 years into the past. 

The ancient ice provides, among other things, information on how much carbon dioxide Earth's atmosphere contained at that time. With 'Beyond EPICA' they will delve circa 1.5 million years into the past. By combining the carbon dioxide measurements with Kohler's analyses, valuable insights can be gained into the relation between these two factors - the fluctuations in the sequence of glacials and the carbon dioxide content of the atmosphere. And this can help us understand the fundamental relationship between greenhouse gases and climate changes in Earth's glacial history.

Source: Alfred Wegener Institute for Polar and Marine Research [October 26, 2020]

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