Gonkoken

MEANING: Wild duck

PERIOD: Late Cretaceous

CONTINENT: South America

Gonkoken was fairly small for a hadrosauroid, at approximately 4 m in length, and exhibited a combination of basal and more derived traits. It is hypothesized that the ancestors of Gonkoken migrated south to fill herbivorous niches before being outcompeted by more advanced hadrosaurs in the northern continents.

Abstract from paper: In the dusk of the Mesozoic, advanced duck-billed dinosaurs (Hadrosauridae) were so successful that they likely outcompeted other herbivores, contributing to declines in dinosaur diversity. From Laurasia, hadrosaurids dispersed widely, colonizing Africa, South America, and, allegedly, Antarctica. Here, we present the first species of a duck-billed dinosaur from a subantarctic region, Gonkoken nanoi, of early Maastrichtian age in Magallanes, Chile. Unlike duckbills further north in Patagonia, Gonkoken descends from North American forms diverging shortly before the origin of Hadrosauridae. However, at the time, non-hadrosaurids in North America had become replaced by hadrosaurids. We propose that the ancestors of Gonkoken arrived earlier in South America and reached further south, into regions where hadrosaurids never arrived: All alleged subantarctic and Antarctic remains of hadrosaurids could belong to non-hadrosaurid duckbills like Gonkoken. Dinosaur faunas of the world underwent qualitatively different changes before the Cretaceous-Paleogene asteroid impact, which should be considered when discussing their possible vulnerability.

Gonkoken is from the Late Cretaceous. The Cretaceous is the third and final geological period of the Mesozoic Era, with the Late Cretaceous making up roughly the second half of it, lasting from about 100 to 66 million years ago. It was a time of significant evolutionary change, with dinosaurs reaching their greatest diversity before the mass extinction at the end of the Cretaceous.

The Cretaceous was a period with a relatively warm climate, though the Late Cretaceous experienced a global cooling trend, caused by falling levels of carbon dioxide in the atmosphere. The continents were nearing their present positions, but high sea levels flooded low-lying regions, turning Europe into an archipelago, and forming the Western Interior Seaway in North America. These seas were home to a variety of marine reptiles, including mosasaurs and plesiosaurs, while pterosaurs and birds shared the skies.

On land, dinosaurs continued to thrive and diversify during the Late Cretaceous, producing many of the most well-known goups, including tyrannosaurs, hadrosaurs, and pachycephalosaurs. Established Cretaceous dinosaur clades like the ceratopsians, ankylosaurs, and dromaeosaurs continued to flourish. Sauropod species consisted almost exclusively of titanosaurs, which seemed to be confined to the Southern Hemisphere for much of the Late Cretaceous. Flowering plants and grasses diversified and spread, becoming the dominant flora similar to what we see today.

The Cretaceous (along with the Mesozoic) ended with the Cretaceous-Paleogene (K-Pg) extinction event, a large mass extinction in which many groups, including non-avian dinosaurs, pterosaurs, and large marine reptiles, died out. This event, likely triggered by an asteroid impact, is marked by the abrupt K-Pg boundary, a distinct geologic layer separating the Mesozoic and Cenozoic Eras. In its aftermath, mammals and avian dinosaurs rapidly diversified, becoming the dominant land animals of the Cenozoic Era.

Gonkoken is an iguanodontian. Iguanodontia was an important branch of the ornithopoda, a group of herbivorous dinosaurs that would become one of the most successful clades of the Cretaceous. These dinosaurs first appeared in the Late Jurassic as small bipedal grazers, but diversified through the Early Cretaceous, gradually increasing into larger more robust forms. While the more derived hadrosaurs of the Late Cretaceous became highly specialized for chewing tough plant material, basal iguanodontians retained a mix of primitive and advanced traits. They were among the first large-bodied ornithopods to spread widely across the Northern Hemisphere, with fossils found in Europe, North Africa, and Asia.

Early iguanodontians possessed powerful hind limbs for efficient bipedal movement but could also walk on all fours when foraging. One of their most distinctive features was their unique hand structure, which included a stiff, spike-like thumb that may have been used for defense or breaking apart tough vegetation. Although they lacked the fully developed dental batteries of later hadrosaurs, their teeth were already adapted for efficient plant processing, giving them an evolutionary advantage as herbivores. These adaptations laid the groundwork for the eventual dominance of hadrosaurs, which would expand into even more diverse habitats and continue to thrive until the end of the Cretaceous.