Fossil Discovery in Mongolia Reveals Bizarre Two-Fingered Dinosaur
Paleontologists have announced the unearthing of remarkable fossils in Mongolia’s Gobi Desert, detailing a newly identified dinosaur species exhibiting an unusual anatomical feature: two-fingered hands equipped with formidable, curved claws. This peculiar creature, named Duonychus tsogtbaatari, represents an extraordinary addition to the therizinosaur group, already known for their unconventional characteristics among dinosaurs. The find sheds light on the diversity of life during the Cretaceous Period and provides crucial insights into dinosaur evolution and adaptation.
Unearthing Duonychus tsogtbaatari
The remains of Duonychus tsogtbaatari were discovered during the excavation for a water pipeline in the Gobi Desert region of Mongolia. Researchers estimate this dinosaur roamed the Earth approximately 90 to 95 million years ago during the Cretaceous Period. It is assessed to have been around 10 feet (3 meters) in length and weighed about 575 pounds (260 kg). Notably, its prominent claws measured an impressive foot (30 cm) in length.
Therizinosaurs: An Unusual Dinosaur Group
Duonychus is classified as a medium-sized member of therizinosaurs, a dinosaur family recognized for their peculiar physique. These dinosaurs typically featured a bulky body, elongated neck, small head, and a bipedal posture. They were also characterized by feathers and, most strikingly, substantial claws on their forelimbs. Although therizinosaurs belong to the theropod clade – the broader group including carnivorous dinosaurs like Tyrannosaurus and Spinosaurus – they were primarily herbivores.
Unique Two-Fingered Feature
A defining characteristic of therizinosaurs, previously found in both Asia and North America, is their prominent claws. Until the discovery of Duonychus, all known therizinosaurs possessed three clawed digits on each hand. In contrast, Duonychus presented a reduction to just two clawed fingers, a feature directly reflected in its name, which translates to “two claw.”
“Evolutionary Experiment” Unveiled
Paleontologist Yoshitsugu Kobayashi from Hokkaido University Museum in Japan, the lead scientist of the study published in iScience, described therizinosaurs as “some of the weirdest dinosaurs ever,” noting their theropod lineage juxtaposed with their “giant feathered sloth”-like appearance.
Kobayashi further elaborated on Duonychus, stating, “Duonychus amplifies that strangeness. It had a shortened hand with only two fingers, yet these fingers were tipped with raptor-like claws, despite being used for plant consumption. It’s as if evolution tested a completely novel approach, and it proved successful.”
Habitat and Coexistence
Researchers believe the discovered Duonychus specimen was not yet fully mature. It inhabited a semi-arid environment interspersed with river systems, living alongside other dinosaur groups including different therizinosaurs, armored dinosaurs, horned dinosaurs, duck-billed dinosaurs, and Alectrosaurus, an earlier, smaller relative of Tyrannosaurus.
Preservation and Claw Structure
While the uncovered skeleton was incomplete, lacking the skull and leg bones, the arms and hands were remarkably well-preserved. Significantly, one of the claws retained its keratin sheath – the outer layer composed of the same substance as human fingernails – in addition to the bone structure. This keratin sheath contributed over 40% to the total length of the claw.
Paleontologist Darla Zelenitsky of the University of Calgary in Canada, a co-author of the study, described these claws as “big, sharp, and nasty.”
Kobayashi emphasized the rarity of keratin fossilization, calling it an “extraordinary window” into the functional morphology of these dinosaurs’ hands. “The hands are exceptionally preserved, revealing extensive detail, including fused wrist elements, rigid joints, and the prominent pair of claws.”
Claw Functionality
The formidable claws likely served multiple purposes, with their primary function believed to be grasping and pulling down branches to access foliage for consumption.
Zelenitsky suggested broader potential uses: “They may have also employed the claws for grappling, self-defense, digging, and possibly even for species recognition – perhaps as a visual signal: ‘Notice me, I also possess only two fingers.'”
Evolutionary Digit Reduction
Duonychus exemplifies digit reduction—the evolutionary process of losing fingers or toes. Early land vertebrates possessed eight digits. While the earliest dinosaurs had five fingers, mirroring human hand structure, many dinosaur lineages underwent digit reduction over evolutionary time.
The discovery of Duonychus elevates the number of theropod lineages known to have independently evolved two-fingered hands to at least five. The most renowned example is T. rex, belonging to the tyrannosaur group characterized by disproportionately small arms relative to their massive size.
The Advantage of Fewer Digits?
Addressing the evolutionary advantage of reduced digits, Zelenitsky pondered, “For dinosaurs utilizing their hands to manipulate vegetation while foraging, one might assume more fingers would be advantageous. However, Duonychus demonstrates that a two-fingered hand construction was perfectly adequate, implying a potentially specialized feeding strategy or specific food source.”
Zelenitsky further explained the case of tyrannosaurs: “Tyrannosaurs were hypercarnivorous predators with massive skulls and jaws designed for capturing and dispatching prey. For them, the reduced fingers and arms were likely a consequence of their limited utility compared to their skull.”