Bird-like footprints from mysterious animals from the Triassic predate the first bird fossils by 60 million years

Abrahams et al. 2023; One plus

New analysis shows that fossil bird-like three-toed footprints dating back more than 210 million years were created by bipedal reptiles. Shown are fossilized Trisauropodiscus tracks (left) and modern bird tracks (right).

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A new analysis of the tracks has revealed that fossil three-toed footprints dating back more than 210 million years were pressed into soft mud by bipedal reptiles with feet like those of birds.

The footprints, found at several sites in South Africa, have recently been identified as the oldest bird footprints ever found, predating the oldest known footprints. Skeletal fossils of birds about 60 million years old.

“Given its age, it was probably made by dinosaurs,” he said. Dr. Minja AbrahamsLecturer in Geological Sciences at the University of Cape Town, South Africa. Abrahams is the lead author of the new study describing the pathways, which was published Tuesday in the journal One plus.

Theropods, including Tyrannosaurus rex, were a diverse group of bipedal, three-toed carnivores. But among these dinosaurs are the most recently examined Some of the tracks were different from typical theropod prints. The outliers had a shorter extension of the central toe, a much wider span and “significantly narrower toes,” making them look more like bird footprints, Abrahams told CNN in an email.

However, since the animals that made the tracks are unknown, their relationship to birds is unclear. The prints could represent a missing clue about the evolution of birds, or they could belong to reptiles that are not close to the bird lineage but independently evolved with bird-like feet, the researchers report.

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The footprints were discovered in the mid-20th century and were given the scientific name Trisauropodiscus by French paleontologist Paul Ellenberger. The name is ichnogenus, which means it describes a genus based on trace fossils, or fossilized impressions left behind by the animal, rather than fossils of its body.

Seven phyla are thought to be related to the Trisauropodiscus tracks, and paleontologists have debated for decades about the affinity of birds in the group. Some described the tracks as bird-like, but others weren’t so sure. Ellenberger may have muddied the waters by assigning several different-shaped tracks to generated creatures, “and not all of them bird-like,” Abrahams said.

Furthermore, the shape of a footprint can vary greatly, depending on the type of material the animal is stepping into. This can make it difficult to determine the physical features of extinct animals when fossilized tracks are the only evidence they left behind, he said. Dr. Julia ClarkProfessor of Vertebrates Excavations at the University of Texas at Austin, who was not involved in the study.

“The footprints are this really unique record,” Clark told CNN. “But there will always be an area of ​​uncertainty, just in terms of the nature of the data that we have.”

She added that at a time when Trisauropodecus tracks were etched in clay, evolutionary adaptations were thriving in archosaurs – the ancient reptile group that includes dinosaurs, pterosaurs and crocodiles – so it is interesting to find evidence of bird-like feet in a little-known member of this group. .

“The footprints are not a direct match to any known fossil animals from this region and this time period. They could belong to other reptiles or cousins ​​of dinosaurs that evolved with bird-like feet,” Clark said. “It adds to our understanding of the morphological diversity in these “The really important time period in Archosauria.”

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Abrahams et al. 2023; One plus

A diagram of the fossil bird-like footprints (top right) and close-ups of two individual tracks (far left and front center) help depict their position and structure. Abbreviations: TL is path length; TW is the path width; II^IV indicates the spread of numbers.

The researchers’ investigation began in 2016: Abrahams said the UCT team was “following in the footsteps of Paul Ellenberger, documenting his sites using modern technological standards.”

During a trip to Mafutseng, a fossil locality in Lesotho, the team found a number of bird-like tracks from the Triassic period. “It took us a minute to realize we were looking at a Trisauropodiscus,” she said. “Our initial impression was that these tracks were indeed very bird-like, and we knew we needed to investigate them further.” This entailed visits to fossil sites; Analysis of archival photographs, drawings, and templates; And create 3D digital models of footprints.

The scientists reviewed 163 tracks and divided them into two categories, or morphotypes, based on their shapes. Tracks classified as Morphotype I were classified as non-birds. These prints were slightly longer than they were wide, and the toes were rounder, stronger, and narrowly splayed. “They also have a distinctive heel made from the third and fourth toes,” Abrahams said.

In comparison, Morphotype II trajectories were smaller. They were wider than they were tall, and their toes were thinner. In their shape and in the wide span of their toes, this second set of tracks closely resembled those of a bird from the Cretaceous period (145 to 66 million years ago): the wading bird Gruipeda, another bird known only by footprints. Overall, the scientists report that Morphotype II tracks closely resemble those of modern birds.

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The oldest fossil evidence of parapheids—the group of dinosaurs that includes the oldest birds and their closest relatives—appears around the mid-Jurassic period (201.3 million to 145 million years ago); Morphotype II Trisauropodiscus tracks, dating back at least 210 million years, suggest bird-like feet are even older.

“Trisauropodiscus shows a much older bird-like foot shape, a trait shared by modern birds and other late Mesozoic archosaurs,” Abrahams said. “This research contributes to our collective ongoing understanding of the evolution of dinosaurs and birds.”

Mindy Weisberger is a science writer and media producer whose work has appeared in Live Science, Scientific American, and How It Works.

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