Birds set foot near South Pole in Early Cretaceous, Australian tracks show

The discovery of 27 avian footprints on the southern Australia coast -- dating back to the Early Cretaceous when Australia was still connected to Antarctica -- opens another window onto early avian evolution and possible migratory behavior.

PLOS ONE published the discovery of some of the oldest, positively identified bird tracks in the Southern Hemisphere, dated to between 120 million and 128 million years ago.

"Most of the bird tracks and body fossils dating as far back as the Early Cretaceous are from the Northern Hemisphere, particularly from Asia," says Anthony Martin, first author of the study and a professor in Emory University's Department of Environmental Sciences. "Our discovery shows that there were many birds, and a variety of them, near the South Pole about 125 million years ago."

Martin is a geologist and paleontologist focused primarily on ichnology -- the study of traces of life such as tracks, burrows, nests and tooth marks.

The international team of co-authors also includes researchers from Monash University and the Museums Victoria Research Institute in Australia; the Benemérita Normal School of Coahuila in Mexico and the Smithsonian Institution.

A possible migratory route

The 27 bird tracks vary in form and size and are among the largest known from the Early Cretaceous. They range from seven to 14 centimeters wide, which is similar to tracks of modern-day shorebirds, such as small herons and oystercatchers.

The tracks were found in the Wonthaggi Formation south of Melbourne. The rocky coastal strata mark where the ancient supercontinent Gondwana began to break up around 100 million years ago when Australia separated from Antarctica.

The polar environment at that time was a rift valley with braided rivers. Although the mean annual air temperature was higher during the Cretaceous than today, during the polar winters the ecosystem experienced deep, freezing temperatures and months of darkness.

The Wonthaggi avian tracks occurred on multiple stratigraphic levels, indicating a recurrent presence of a variety of birds. It also suggests seasonal formation of the tracks during polar summers, perhaps on a migratory route.

"The birds would likely have been stepping on soft sand or mud," Martin says. "Then the tracks may have been buried by a gentle river flow that deposited more sand or mud on top of them."

A scarcity of bird fossils

The Wonthaggi Formation is famous for its variety of polar dinosaur bones, although bird-fossil finds are extremely rare. The Cretaceous strata of the formation has yielded only one tiny bird bone -- a wishbone -- and a few feathers.

"Birds have such thin and tiny bones," Martin says. "Think of the likelihood of a sparrow being preserved in the geologic record as opposed to an elephant."

Birds are also lightweight and don't leave much of a foot impression, he adds.

Martin and colleagues discovered two 105-million-year-old bird tracks in Australia's Eumeralla Formation in 2013, making them the oldest from Australia at the time.

An eagle eye

Co-author Melissa Lowery, a local volunteer fossil hunter, first spotted some of the tracks in the current discovery in 2020. Dubbed "the doyenne of dinosaur discovery," Lowery has found hundreds of bones and more than 100 dinosaur footprints.

"Melissa is incredibly skilled at finding fossil tracks," Martin says. "Some of these tracks are subtle even for me, and I have lots of experience and training."

Most of the tracks were only exposed at low tide and some of them were encrusted by marine life such as algae, barnacles and mollusks.

Due to international travel restrictions in Australia during the COVID-19 pandemic, Martin had to wait until 2022 before he could travel to the site to lead the analyses of the tracks.

He was joined in the field by co-authors Patricia Vickers-Rich, professor of paleontology at Monash University, and Thomas Rich, curator of vertebrate aleontology at Museums Victoria Research Institute. The couple have led a major effort since the 1970s to uncover fossils in the Australian state of Victoria and to interpret the biota of Gondwana.

Also assisting in the field analyses were co-authors Mike Hall, a geologist at Monash University, and Peter Swinkels, a taxidermist at Museums Victoria Research Institute and an expert at preserving specimens through moldings and casts.

The thinness of the toes relative to the track lengths, the wide angles between the toes and the thin sharp claws and rear toes on some of the tracks helped Martin to verify their avian identity.

Co-author Claudia Serrano-Brañas, a paleontologist at the Benemérita Normal School of Coahuila and the National Museum of Natural History, Smithsonian Institution, verified similarities between the Australian bird footprints and ancient bird footprints from other parts of the world.

Swinkels created resin casts of the Australian tracks that brought into greater relief some of the nuances of the impressions. The casts provide a tool for further study. They also serve to preserve the finds. The silty, sandstone beds containing the footprints are rapidly eroding under the coastal tides and waves.

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New species of mosasaur named for Norse sea serpent

Scientists have discovered a new species of mosasaur, large, carnivorous aquatic lizards that lived during the late Cretaceous. With "transitional" traits that place it between two well-known mosasaurs, the new species is named after a sea serpent in Norse mythology, Jormungandr, and the small North Dakota city Walhalla near to where the fossil was found. Details describing Jormungandr walhallaensis are published today in the Bulletin of the American Museum of Natural History.

"If you put flippers on a Komodo dragon and made it really big, that's basically what it would have looked like," said the study's lead author Amelia Zietlow, a Ph.D. student in comparative biology at the American Museum of Natural History's Richard Gilder Graduate School.

The first mosasaur was discovered more than 200 years ago, and the word "mosasaur" predates the word "dinosaur." But many questions about these animals remain, including how many times they evolved flippers and became fully aquatic -- researchers think it was at least three times, and maybe four or more -- and whether they are more closely related to monitor lizards or snakes. Researchers are still trying to determine how the different groups of mosasaurs are related to each other, and the new study adds a new piece to that puzzle.

The fossil on which the study is based was discovered in 2015, when researchers excavating in the northeastern part of North Dakota found an impressive specimen: a nearly complete skull, jaws, and cervical spine, as well as a number of vertebrae.

After extensive analysis and surface scanning of the fossil material, Zietlow and her collaborators found that this animal is a new species with a mosaic of features seen in two iconic mosasaurs: Clidastes, a smaller and more primitive form of mosasaur; and Mosasaurus, a larger form that grew to be nearly 50 feet long and lived alongside Tyrannosaurus rex. The specimen is estimated to be about 24 feet long, and in addition to flippers and a shark-like tail, it would have had "angry eyebrows" caused by a bony ridge on the skull, and a slightly stumpy tail that would have been shorter than its body.

"As these animals evolved into these giant sea monsters, they were constantly making changes," Zietlow said. "This work gets us one step closer to understanding how all these different forms are related to one another."

The work suggests that Jormungandr was a precursor to Mosasaurus and that it would have lived about 80 million years ago.

"This fossil is coming from a geologic time in the United States that we don't really understand," said co-author Clint Boyd, from the North Dakota Geological Survey. "The more we can fill in the geographic and temporal timeline, the better we can understand these creatures."

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Newly discovered 'primitive cousins of T rex' shed light on the end of the age of dinosaurs in Africa

Fossils of primitive cousins of T. rex that had short, bulldog snouts and even shorter arms have been discovered by scientists in Morocco. The two new dinosaur species belong to the Abelisauridae, a family of carnivorous dinosaurs that were counterparts to the tyrannosaurs of the Northern Hemisphere. They lived at the end of the Cretaceous period and show that dinosaurs were diverse in Africa just before their mass extinction by an asteroid 66 million years ago.

Two new species of dinosaur have been found from the end of the Cretaceous in Morocco, just outside of Casablanca. One species, found near the town of Sidi Daoui, is represented by a foot bone from a predator about two and a half metres (eight feet) long. The other, from nearby Sidi Chennane, is the shin bone of a carnivore that grew to around five metres (15 feet) in length.

Both were part of a family of primitive carnivorous dinosaurs known as abelisaurs, and lived alongside the much larger abelisaur Chenanisaurus barbaricus, showing that Morocco was home to diverse dinosaur species just before a giant asteroid struck at the end of the Cretaceous, ending the age of dinosaurs.

Dr Nick Longrich, from the Milner Centre for Evolution at the University of Bath, led the study. He said: "What's surprising here is that these are marine beds.

"It's a shallow, tropical sea full of plesiosaurs, mosasaurs, and sharks. It's not exactly a place you'd expect to find a lot of dinosaurs. But we're finding them."

Even though dinosaurs account for a small proportion of the fossils, the region is so rich in fossils, it has produced the best picture of African dinosaurs from the end of the age of dinosaurs.

Rather than finding the same few species, palaeontologists often recover fossils from new species, suggesting the beds host an extremely diverse dinosaur fauna.

So far, the small number of dinosaur fossils that have been recovered represent five different species -- a small duckbill dinosaur named Ajnabia, a long-necked titanosaur, the giant abelisaur Chenanisaurus, and now the two new abelisaurs.

Dr Longrich said: "We have other fossils as well, but they're currently under study. So we can't say much about them at the moment, except that this was an amazingly diverse dinosaur fauna."

The last dinosaurs vanished around 66 million years ago, along with as much as 90% of all species on earth, including mosasaurs, plesiosaurs, pterosaurs and ammonites. The pattern of the end-Cretaceous extinction and its causes have been debated for over two hundred years.

A giant asteroid impact in the Yucatan peninsula has been linked to their demise, although it's been argued that dinosaurs were already in decline. The Moroccan dinosaurs suggest that they thrived in North Africa up to the very end.

"The end of the Cretaceous in western North America definitely seems to become less diverse at the end," said Longrich. "But that's just one small part of the world. It's not clear that you can generalise from the dinosaurs of Wyoming and Montana to the whole world.

"It also grew colder near the end, so it might not be surprising if dinosaurs at higher latitudes became less diverse. But we don't know much about dinosaurs from lower latitudes."

In Morocco at least, they seem to have remained diverse and successful up until the end.

"When T. rex reigned as a megapredator in North America, abelisaurs sat at the top of the food chains in North Africa," said Nour-Eddine Jalil, a professor at the Natural History Museum and a researcher at Universite Cadi Ayyad in Morocco, who was a co-author on the paper.

"The dinosaur remains, despite their rarity, give the same messages as the more abundant marine reptile remains.

"They tell us that, just before the Cretaceous-Paleogene crisis, biodiversity was not declining but on the contrary, was diverse."

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