Ancient Creatures with Avian-Like Feet Spotted Preceding Earliest Birds, Research Reveals
Millions of years ago, long before birds emerged, enigmatic creatures roamed the Earth on bird-like feet, as revealed by a study of ancient three-toed fossil footprints Uncovering bipedal reptiles that walked in the footsteps of birds, this analysis sheds light on a fascinating prehistoric era
Discover the universe with CNN's Wonder Theory science newsletter, featuring captivating news on groundbreaking discoveries and scientific progress. Uncover the story of three-toed fossil footprints, with a new study revealing that these imprints were left by bipedal reptiles with bird-like feet over 210 million years ago.
Footprints discovered at multiple locations in southern Africa have been identified as the oldest birdlike tracks ever found, predating the earliest known skeletal fossils of birds by approximately 60 million years. "Given their age, it is likely that they were made by dinosaurs," stated Dr. Miengah Abrahams, a lecturer in geological sciences at the University of Cape Town in South Africa and lead author of the study published in the journal PLOS One on Tuesday.
The recently analyzed dinosaur tracks revealed some outliers that were different from typical theropod prints. These outliers had shorter central digits with wider splay and "significantly narrower toes," resembling bird footprints, according to Abrahams. However, it is uncertain whether these tracks are related to birds, as the animals that made them are unidentified. The tracks could provide a missing link in avian evolution, or they could belong to reptiles that independently evolved birdlike feet, the researchers explained.
Footprints found in the mid-20th century were given the scientific name Trisauropodiscus by French paleontologist Paul Ellenberger. This name is an ichnogenus, which refers to a genus based on trace fossils rather than fossils of the animal's body.
There are seven ichnospecies associated with Trisauropodiscus tracks, and paleontologists have long debated whether the group has an avian connection. While some have described the tracks as birdlike, others have been less convinced. Ellenberger's assignment of variously shaped tracks to the ichnogenus has further complicated matters, with Abrahams remarking that "not all of them are birdlike."
In addition, the shape of a footprint can vary significantly depending on the type of material the animal stepped in. This variability can make it challenging to determine the physical characteristics of extinct animals when fossilized tracks are the only evidence they left behind, explained Dr. Julia Clarke, a professor of vertebrate paleontology at the University of Texas at Austin who was not part of the study.
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"Footprints are a truly remarkable record," Clarke shared with CNN. "But there will always be some degree of uncertainty due to the nature of our data."
During the time that the Trisauropodiscus tracks were imprinted in mud, evolutionary adaptations were flourishing in archosaurs - the ancient reptile group that includes dinosaurs, pterosaurs, and crocodilians. Therefore, it is fascinating to discover evidence of birdlike feet in an unknown member of this group," she added.
"The footprints are not a direct match for any fossil animals known from this region and time period. They could belong to other reptiles or cousins of dinosaurs that evolved birdlike feet," stated Clarke. "This adds to our understanding of morphological diversification in this really crucial time period in archosauria."
Figure 1 illustrates the birdlike fossil footprints, with close-ups of two individual tracks showing their placement and structure. Abbreviations used are TL for track length, TW for track width, and II^IV to indicate the spread of the digits. (Abrahams et al., 2023, PLOS ONE)
Starting in 2016, the researchers embarked on an investigation. According to Abrahams, the UCT team was "documenting Paul Ellenberger's sites with modern ichnological standards," as a way of following in his footsteps.
On a trip to Maphutseng, a fossil site in Lesotho, the team discovered several birdlike tracks from the Triassic Period. "It didn't take long for us to realize that these were Trisauropodiscus tracks," she explained. "At first, we thought they looked very similar to bird tracks and knew we had to investigate further." This involved visiting fossil sites, examining old photos, sketches, and casts, as well as creating 3D digital models of the footprints.
The scientists examined 163 tracks and grouped them into two categories, or morphotypes, based on their shapes. Tracks in Morphotype I were identified as non-avian. These prints were slightly longer than they were wide, with rounder, sturdier toes that were spread out narrowly. "They also have a distinctive heel, created by the pads of the third and fourth digits," Abrahams remarked.
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By contrast, the Morphotype II tracks were smaller and wider compared to their length, with slimmer toes. In their shape and the wide splay of their digits, this second group of tracks closely resembled those of an avian from the Cretaceous Period (145 million to 66 million years ago): the wading bird Gruipeda, another ichnogenus known only from footprints. The Morphotype II tracks were also found to closely resemble modern bird prints, as reported by scientists. The discovery of the Morphotype II Trisauropodiscus tracks, dating back at least 210 million years, suggests that birdlike features are even more ancient than previously thought, predating the oldest fossil evidence for paravians, the group that includes the earliest birds and their closest relatives from the middle of the Jurassic Period (201.3 million to 145 million years ago).
"Trisauropodiscus indicates that the birdlike foot structure dates back much earlier, representing a common characteristic between modern birds and other Late Mesozoic archosaurs," stated Abrahams. "This study adds to our ongoing knowledge of dinosaur and bird evolution."
Mindy Weisberger, a science writer and media producer, has contributed to publications such as Live Science, Scientific American and How It Works magazine.
