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Gonkoken
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Gonkoken
Temporal range: Late Cretaceous (Maastrichtian), ~71.7–66 Ma[1][2]
Skeletal diagram and known bones
Scientific classification Edit this classification
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Clade: Dinosauria
Clade: †Ornithischia
Clade: †Ornithopoda
Superfamily: †Hadrosauroidea
Genus: †Gonkoken
Alarcón-Muñoz et al., 2023
Species:
†G. nanoi
Binomial name
†Gonkoken nanoi
Alarcón-Muñoz et al., 2023

Gonkoken (meaning "similar to a wild duck or swan") is an extinct genus of hadrosauroid ornithopod dinosaur from the Late Cretaceous Dorotea Formation of Chilean Patagonia. The genus contains a single species, Gonkoken nanoi, known from disarticulated bones of multiple individuals.[1]

Discovery and naming

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The Gonkoken fossil specimens were discovered beginning in 2013 in sediments of the Dorotea Formation in the Río de las Chinas Valley, Estancia Cerro Guido, in Magallanes Region, Chile. The holotype specimen, CPAP 3054, consists of a right ilium. Additional material assigned as paratype includes the disarticulated bones of at least three individuals. These bones include skull material, cervical, dorsal, and caudal vertebrae, ribs, partial pectoral and pelvic girdles, and arm and leg bones.[1]

In 2023, Alarcón-Muñoz et al. described Gonkoken nanoi as a new genus and species of hadrosauroid ornithopod based on these fossil remains. The generic name, "Gonkoken", combines the Aónik'enk words "gon", meaning "same as" or "similar to" and "koken", meaning "wild duck" or "swan". The specific name, "nanoi", honors Mario "Nano" Ulloa.[1]

Description

[edit]
Life restoration

Gonkoken was a relatively small hadrosauroid, with an approximate body length of 4 metres (13 ft). It exhibits a blend of derived hadrosaurid traits and ancestral hadrosauroid traits.[1]

Classification

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Alarcón-Muñoz et al. (2023) recovered Gonkoken as a derived, non-hadrosaurid hadrosauroid, proving that these taxa survived until the very end of the Cretaceous in southern South America. It was thus unrelated to other the South American hadrosaurids, Bonapartesaurus, Huallasaurus, Kelumapusaura, and Secernosaurus, which were found to belong to their own group of saurolophine hadrosaurids called Austrokritosauria. Both groups likely dispersed to South America from North America. The results of their phylogenetic analyses are shown in the cladogram below, with South American taxa highlighted:[1]

Paleoenvironment

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Gonkoken was discovered in layers of the Dorotea Formation, which dates to the lower Maastrichtian, between 71.7 ± 1.2 and 70.5 ± 5.0 million years ago.[1] The parankylosaur Stegouros has also been described from the formation.[3] Fossils belonging to amphibians, mammals, fish, reptiles, and several invertebrates have also been discovered there, along with material belonging to indeterminate sauropod, theropod, and ornithischian dinosaurs.[4]

References

[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Gonkoken

View on Grokipedia
from Grokipedia
Gonkoken is an extinct of hadrosauroid ornithopod that lived during the period, approximately 72 million years ago, in what is now southern . The type and only known species, Gonkoken nanoi, was a medium-sized measuring about 4 meters (13 feet) in length and weighing up to one metric ton, characterized by its duck-like bill and adaptations for grazing on vegetation. Named after a Tehuelche word meaning "similar to a wild duck or swan," it represents the first non-hadrosaurid duck-billed discovered in the southern of , challenging previous understandings of ornithopod distribution. Fossils of G. nanoi were unearthed from the Dorotea Formation in Chilean , dating to the early stage of the . This relict species survived as a transitional form between earlier ornithopods and more advanced hadrosaurids, retaining primitive traits like a less specialized while exhibiting some derived features shared with duckbills. Its discovery indicates that duck-billed dispersed southward earlier than previously thought, persisting in isolated southern populations until near the end of the dinosaur era. As a basal hadrosauroid, Gonkoken likely lived in herds and foraged on low-lying in a temperate, forested environment, contributing to our knowledge of in high-latitude Gondwanan ecosystems. The specimens include partial skeletons that preserve elements of the , vertebrae, and limbs, allowing paleontologists to reconstruct its and phylogenetic position within . This find underscores the role of southern continents in preserving evolutionary "living fossils" of northern migrant lineages during the final stages of the .

Discovery and Naming

History of Discovery

The fossils of Gonkoken nanoi were first encountered during paleontological excavations initiated in in the Río de las Chinas Valley of the , southern , led by Jhonatan Alarcón-Muñoz of the Universidad de Chile. These efforts uncovered a monodominant bonebed within the Dorotea Formation, spanning approximately 28 m² and an 80 cm-thick layer, from which 45 skeletal elements belonging to at least three individuals were recovered over subsequent field seasons. The site, part of a larger extending about 5 km, yielded a partial comprising elements such as portions of the , vertebrae, ribs, and limb bones, preserved in early strata dated to roughly 71.7 ± 1.2 to 70.5 ± 5.0 million years ago. The excavation faced logistical difficulties inherent to the remote Patagonian terrain, including its subantarctic location at 51°S , which limited access and required ongoing annual campaigns to fully document the bonebed. Additionally, the fossils' disarticulated and fragmentary state posed preservation challenges, complicating initial identification and necessitating extensive preparation and analysis over the following decade. Mario "Nano" Ulloa, a local collaborator, played a key role by first spotting bones in the valley and providing logistical support during the fieldwork. In 2023, Alarcón-Muñoz and colleagues formally described and named the Gonkoken nanoi ( CPAP 3054, a right ilium) in a comprehensive study published in Science Advances, marking it as the first non-hadrosaurid hadrosauroid from a Gondwanan locality. This description highlighted the specimen's significance in revising understandings of duck-billed dispersal, based on the accumulated material from the 2013 onward excavations.

Etymology

The genus name Gonkoken is derived from the Aónik'enk language, spoken by the indigenous people of Patagonia, combining the words "gon," meaning "same as" or "similar to," and "koken," meaning "wild duck" or "swan." This etymology alludes to the dinosaur's distinctive duck-billed morphology, characteristic of hadrosauroids, with a broad, flattened rostrum resembling the beak of waterfowl. The species epithet nanoi honors Mario "Nano" Ulloa, a local collaborator who first discovered the bones in the Río de las Chinas Valley and provided essential logistical support for subsequent paleontological expeditions in the region. The use of Aónik'enk (also known as Tehuelche) terminology in the naming of Gonkoken nanoi underscores the of the indigenous Aónikenk people, the original inhabitants of southern and subantarctic , integrating regional linguistic traditions into scientific to acknowledge their historical connection to the land where the fossils were found.

Description

Cranial Anatomy

The cranial anatomy of Gonkoken nanoi is represented by disarticulated elements from a monospecific bonebed, providing insights into its hadrosauroid affinities through preserved portions of the , jaws, and jaw articulation. These features highlight a combination of basal ornithopod traits and derived hadrosauroid specializations adapted for herbivory. The rostrum exhibits a flattened profile typical of ornithopods, with the (specimen CPAP 5337) featuring a convex, anteroventrally deflected oral margin and a double-layered denticulate margin suitable for cropping . An , deep circumnarial fossa surrounds the narial opening, positioned anteriorly without accessory fossae or foramina, contributing to a broad, oreinirostral snout configuration. The (CPAP 5340) is subtriangular in lateral view, with a robust subquadrangular articular surface for the jugal that includes a prominent dorsal , indicating a strong jugal-squamosal contact for enhanced rigidity, though the squamosal itself is not preserved. A rostral maxillary opens on the lateral surface. The lower jaw includes dentaries (CPAP 5342 and CPAP 5370) with a short comprising less than 20% of the alveolar row length, an oblique , and a row that converges anteriorly without extending beyond the coronoid . Approximately 25 positions are present, forming a dental battery with leaf-shaped teeth indicative of a herbivorous diet involving grinding of material; a predentary is inferred to articulate rostrally, completing the beak-like structure. Teeth are poorly preserved in the , but the dentary battery aligns with hadrosauroid patterns for efficient mastication. The size is moderately proportioned relative to the , supporting in a terrestrial , though exact dimensions are not quantifiable from available material. The quadrate (CPAP 5343) demonstrates derived hadrosauroid morphology, being dorsoventrally elongated with the dorsal half curving slightly posteriorly; the lateral condyle shows minimal ventral offset relative to the medial condyle, facilitating a stable without the pronounced offset seen in more basal ornithopods. Frontal bones lack expanded domes or a full hadrosaurid crest, distinguishing G. nanoi from advanced hadrosaurids while retaining transitional features like the reinforced temporal region. These cranial traits from the holotype bonebed (designated holotype CPAP 3054 for the ilium, with cranials as paratypes) underscore Gonkoken's position as a non-hadrosaurid hadrosauroid.

Postcranial Anatomy

The postcranial of Gonkoken nanoi is represented by elements including vertebrae, , scapulae, sternal plates, ilia, , humeri, femora, tibiae, fibulae, and partial metapodials, offering evidence of its structural adaptations for as a non-hadrosaurid hadrosauroid. These bones indicate a blend of primitive and derived features consistent with facultative bipedality or quadrupedality, differing from more specialized hadrosaurids in aspects such as crest proportions and limb robusticity. The vertebral column comprises cervical, dorsal, sacral, and caudal elements. Cervical are longer than dorsoventrally high, strongly opisthocoelous (convex anteriorly and concave posteriorly), and bear oval articular surfaces, contributing to flexibility. Dorsal are elongated, taller than wide, opisthocoelous, and feature heart-shaped anterior articular faces, supporting a robust . Caudal centra are amphiplatyan (flat on both ends) with hexagonal outlines, as seen in specimens such as CPAP 5347–5351 and 5397–5399, suggesting a moderately long tail for balance during movement. A partial indicates fusion typical of ornithopods, aiding weight transfer to the hindlimbs. The includes a with a dorsally curved blade, an anteroventrally directed pseudoacromion, and a narrow facet for the articulation, reflecting a compact pectoral structure suited for in quadrupedal postures. The features a deltopectoral crest that extends less than 48% of its total length, with a length-to-width of approximately 3.9 (specimen CPAP 5353), indicating relatively shorter forelimbs compared to the hindlimbs and reduced emphasis on manual manipulation. The pelvic girdle exhibits an ilium with a nearly straight dorsal margin, a prominent sacral crest, a laterally curved preacetabular process, and a supraacetabular process reaching about 82.6% of the iliac blade length (specimens CPAP 3054 and 5356), resembling iguanodontian ornithopods in its overall form for accommodating powerful hindlimb propulsion. The ischium has an iliac peduncle longer than the pubic peduncle (CPAP 5357), enhancing stability at the acetabulum. In the hindlimb, the femur is straight-shafted with a triangular fourth trochanter, deep grooves for flexor and extensor tendons, and posteriorly projecting distal condyles (CPAP 5358), optimized for extension during bipedal or quadrupedal strides. The tibia shows a cnemial crest under 50% of shaft length, about 45° of torsion between proximal and distal ends, and a robust posteromedial condyle (CPAP 5362), while the fibula has an enlarged proximal head (CPAP 5363) for enhanced lateral support. Metatarsal III possesses a triangular proximal articular surface and a length-to-width ratio of 4.5 (CPAP 5364), indicative of a subrectangular pes for efficient weight distribution on varied terrain. These limb and girdle traits collectively support a versatile locomotor repertoire, with the shorter forelimbs and robust hindlimbs facilitating both upright and sprawling gaits.

Size and Morphology

Gonkoken nanoi measured approximately 4 meters (13 feet) in total length, making it a relatively small representative among hadrosauroids. Body mass estimates, derived from limb bone scaling and comparisons to related ornithopods, suggest it weighed up to 1 metric ton. This dinosaur exhibited a transitional morphology characteristic of non-hadrosaurid hadrosauroids closely allied to Hadrosauridae, with a build adapted for facultative bipedalism and quadrupedalism as a herbivore. Its duck-like bill, formed by a premaxilla with a convex and anteroventrally deflected oral margin, facilitated low-level browsing on vegetation. In comparison to North American hadrosaurs such as , which reached lengths of 12–13 meters, G. nanoi was notably smaller and more slender, reflecting its status in southern . The specimen, comprising a right ilium (CPAP 3054), exhibits features indicative of an growth stage, including a "T"-shaped preacetabular process; however, the associated bonebed includes elements from subadult individuals, suggesting variability in ontogenetic stage across the assemblage.

Classification

Phylogenetic Position

Gonkoken is classified as a hadrosauroid ornithopod within the Hadrosauriformes, positioned outside of the more derived family . The is monotypic, represented solely by the Gonkoken nanoi, based on the specimen consisting of a partial including cranial and postcranial elements. Phylogenetic analyses conducted in a 2023 study utilized both parsimony and Bayesian methods on an expanded matrix of ornithopod taxa, recovering G. nanoi in a transitional position between basal iguanodontians and true hadrosaurs. Parsimony analysis yielded four most parsimonious trees of 1335 steps, placing Gonkoken as sister to or in a with other non-hadrosaurid hadrosauroids such as Lophorhothon and Huehuecanauhtlus, with moderate bootstrap support around 50% at key nodes. Bayesian tip-dated and undated analyses corroborated this placement, supporting a shortly before the origin of . Key synapomorphies supporting this position include moderately complex dental batteries with double-layer denticles on premaxillary teeth, indicative of advanced herbivory shared with hadrosaurs, and a well-developed pubic boot on the pubis, a derived pelvic feature typical of Hadrosauriformes. These traits, combined with retention of plesiomorphic features like fewer than 30 tooth positions per side, underscore Gonkoken's role as a basal member bridging earlier ornithopods and the duck-billed dinosaurs.

Evolutionary Significance

Gonkoken nanoi represents a population of non-hadrosaurid hadrosauroids that persisted into the early (~71.7–70.5 Ma) in subantarctic southern , long after such forms had been largely replaced by more derived hadrosaurids in . This survival highlights the endurance of basal lineages in isolated Gondwanan refugia, where ecological niches allowed these transitional duckbills to thrive despite global faunal shifts toward advanced hadrosaurs. The discovery of Gonkoken challenges traditional models of Laurasia-to-Gondwana dispersal for hadrosauroids, which posit a radiation of hadrosaurids southward via northern land bridges or island chains. Instead, phylogenetic and biogeographic analyses suggest its ancestors diverged from North American (Laramidian) forms around 91 Ma and dispersed earlier, potentially via island chains or across proto-Pacific seaways, granting them a temporal advantage to establish in southern continents before the arrival of competing hadrosaurids. This earlier migration implies a more complex, protracted history of hadrosauroid colonization in than previously envisioned. Morphologically, Gonkoken exhibits transitional features that bridge iguanodontian-grade ornithopods and advanced hadrosaurs, such as a combination of primitive postcranial elements and derived cranial traits indicative of a basal hadrosauroid position. As the first such non-hadrosaurid from , it fills critical gaps in the fossil record, illuminating the evolutionary continuum of duck-billed dinosaurs in regions long underrepresented in hadrosauroid studies. In the context of end-Cretaceous biodiversity, Gonkoken underscores how duck-billed dinosaurs could endure mass extinction pressures longer in isolated southern refugia, potentially evading the competitive exclusion faced by their northern counterparts. This persistence suggests that pre-K-Pg diversity declines may have been regionally variable, with Gondwanan hadrosauroids maintaining greater taxonomic depth into the latest than indicated by Laurasian records alone.

Paleoecology

Geological Setting

The Dorotea Formation, from which specimens of Gonkoken nanoi were recovered, represents a sedimentary unit in the Magallanes-Austral Basin of southernmost , specifically in the Patagonian region near the Río de las Chinas Valley. This formation is part of a broader system that developed along the western margin of southern during the . The Gonkoken fossils originate from the upper section of the Dorotea Formation, which spans the early stage of the . The age of the Dorotea Formation is constrained to approximately 71.7 ± 1.2 to 70.5 ± 5.0 million years ago, determined through U-Pb dating of detrital zircons from layers interbedded within the strata. Supporting biostratigraphic evidence comes from ammonite assemblages, which align with the early Neocrioceras , further refining the temporal framework. These dating methods indicate deposition during a period of tectonic stability in the basin, following earlier phases of . The of the upper Dorotea Formation reflects a continental setting dominated by fluvial and systems, with meandering rivers traversing low-energy floodplains and vegetated lowlands. This represents a distal progression from underlying shallow marine and tide-dominated deltaic , indicating a progradational shift toward terrestrial conditions as sea levels regressed. Sediments consist primarily of sandstones, mudstones, and conglomerates, recording episodic fluvial channel migration and overbank deposition in a humid, subtropical paleoclimate. Taphonomic analysis of the Gonkoken specimens reveals preservation in fine-grained, reddish-brown sandstones and sandy mudstones, with bones exhibiting three-dimensional articulation and minimal or abrasion. This suggests rapid burial in low-energy riverine or contexts, likely following short-distance transport from nearby death sites, which facilitated the exceptional retention of skeletal integrity. Such conditions are consistent with the formation's overall record of quick sediment accumulation in anastomosing fluvial networks.

Associated Fauna and Flora

The Dorotea Formation, where fossils of Gonkoken nanoi occur, preserves a diverse assemblage of vertebrates indicative of a dynamic terrestrial and marginal . Among the , indeterminate titanosaurs represent the dominant large herbivores, coexisting with smaller ornithopods like Gonkoken in and fluvial environments. Theropod remains, including those attributable to megaraptorids and unenlagiines, suggest the presence of mid-to-large carnivores capable of preying on herbivores such as Gonkoken. Smaller vertebrates, including pipid and calyptocephalellid frogs, chelid turtles, and early mammals, further populate this community, while marine influences are evident from sharks, plesiosaurs, mosasaurs, bivalves, gastropods, and ammonites in transitional . The of the Dorotea Formation reflects a humid subtropical paleoclimate, characterized by warm and wet conditions that supported lush vegetation along river systems and floodplains. Angiosperms dominate the macro- and record, accompanied by ferns (including aquatic and terrestrial species) and , as evidenced by leaf impressions, palynomorphs, and wood assemblages. This plant diversity provided ample low- to mid-level browse for herbivores, with Gonkoken likely occupying a niche for smaller, more maneuverable feeders distinct from the bulk-grazing titanosaurs, facilitating resource partitioning in the . Local theropods, such as megaraptorids, may have exerted predation pressure on these herbivores, contributing to balanced trophic dynamics without evidence of direct competitors for Gonkoken's ecological role.

Biogeographic Implications

The discovery of Gonkoken nanoi, the first non-hadrosaurid hadrosauroid documented from , indicates the persistence of archaic ornithopod lineages in southern high-latitude refugia during the . This from (51°S) suggests that basal hadrosauroids survived in isolated Gondwanan environments even as more derived hadrosaurids dominated northern continents. This finding challenges prevailing models of unidirectional northward migration for hadrosauroids during the , instead supporting earlier bidirectional dispersal or southward colonization from Laurasian landmasses like . Phylogenetic and biogeographic analyses estimate that Gonkoken's ancestors diverged from North American forms around 91 million years ago ( stage), potentially via island-hopping across widening seaways, allowing them to reach southern well before the proliferation of advanced hadrosaurids. In contrast to the hadrosaurid-dominated record of northern , where taxa such as and related Austrokritosauria represent later Campanian-Maastrichtian arrivals, Gonkoken highlights independent evolutionary trajectories for hadrosauroids in southern . As a transitional form outside the Austrokritosauria , it underscores how non-hadrosaurid lineages occupied herbivorous niches in temperate to polar ecosystems without direct from advanced duck-billed dinosaurs. Overall, Gonkoken reveals significant undersampling of dinosaur faunas in and Gondwanan regions, where fragmentary remains previously attributed to hadrosaurids may instead pertain to basal forms. This emphasizes the urgency for expanded excavations in these understudied areas to refine understanding of biogeographic patterns across southern supercontinents.
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