Saturday, June 17, 2023

[Paleontology • 2023] Gonkoken nanoi • Relict Duck-billed Dinosaurs (Ornithopoda: Hadrosauroidea) survived into the last age of the Dinosaurs in Subantarctic Chile


Gonkoken nanoi  
Alarcón-Muñoz, Vargas, Püschel, Soto-Acuña, Manríquez, Leppe, Kaluza, Milla, Simon-Gutstein, Palma-Liberona, Stinnesbeck, Frey, Pino, Bajor, Núñez, Ortiz, Mansilla, Rubilar-Rogers & Cruzado-Caballero, 2023

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.

Stratigraphic location of Gonkoken nanoi and geographic distribution of South American duck-billed dinosaurs.
(A) Stratigraphic section of the Dorotea Formation, indicating the location of the bones of Gonkoken nanoi.
(B) Location of the duck-billed dinosaurs from South America: 1, Lapampasaurus cholinoi (Islas Malvinas locality, La Pampa Province, late Campanian to early Maastrichtian, Allen Formation); 2, Kelumapusaura machi (Matadero Hill, General Roca city, Río Negro Province, middle Campanian to early Maastrichtian, Allen Formation); 3, Bonapartesaurus rionegrensis (Salitral Moreno, General Roca Department, Río Negro Province, middle Campanian to early Maastrichtian, Allen Formation); 4, Huallasaurus australis (Arroyo Verde Puelén Department, Río Negro Province, late Campanian to early Maastrichtian, Los Alamitos Formation); 5, Secernosaurus koerneri (Río Chico, east of Lake Colhué Huapi, Chubut Province, Maastrichtian, Lago Colhué Huapi Formation); and 6, Gonkoken nanoi (Río de las Chinas Valley, Magallanes Region, late Campanian to early Maastrichtian, Dorotea Formation).
(C) The quarry from which Gonkoken nanoi bones were excavated (bonebed level).
(D) Detail of a nearly complete tibia.

Gonkoken nanoi gen. et sp. nov., skeletal anatomy. (A) Bones described in this work (white). Some elements are indicated specularly to facilitate their representation. (B) CPAP 5337, right premaxilla in lateral view. (C) CPAP 5341, incomplete left postorbital in lateral view. (D) CPAP 5340, incomplete right maxilla in lateral view. (E) CPAP 5370, left dentary in medial view. (F) CPAP 5343, right quadrate in lateral view. (G) CPAP 5344, cervical vertebra in anterior view. (H) CPAP 5346, dorsal vertebra in anterior view. (I) CPAP 5371, right scapula in lateral view. (J) CPAP 5352, left sternum in ventral view. (K) CPAP 5400, incomplete right rib in anterior view. (L) CPAP 5379, proximal portion of right radius in posterior view. (M) CPAP 5355, incomplete left ulna in anterolateral view. (N) CPAP 5353, left humerus in posterolateral view. (O) CPAP 3054 (holotype), right ilium in lateral view. (P) CPAP 5356, left postacetabular process in lateral view. (Q) CPAP 5357, proximal portion of right ischium in medial view. (R) CPAP 5363, proximal portion of left fibula in lateral view. (S) CPAP 5360, incomplete right femur in distal view. (T) CPAP 5358, left femur in anterior view. (U) CPAP 5362, left tibia in lateral view. (V and W) CPAP 5349, caudal vertebra in anterior and lateral views. (X) CPAP 5364, right metatarsal III in anterior view. Skeleton modified from (31).
 Scale bars, 50 mm [(B) to (G), (J), (K) to (N), (Q), (S), and (V) to (X)] and 100 mm [(H), (I), (O), (P), (R), (T), and (U)].

Systematic paleontology
 Dinosauria Owen, 1842
Ornithischia Seeley, 1887

Ornithopoda Marsh, 1881
Hadrosauroidea Cope, 1870, sensu Madzia et al. (16)

Gonkoken nanoi gen. et sp. nov.

Etymology: The words “gon” (same as, similar to) and “koken” (wild duck or swan) are in the language of the Aónik’enk, the indigenous people that inhabited the region where this species was found (Fernández Garay, 2004). The specific name nanoi is in honor of Mario NanoUlloa, who first found dinosaur bones at Río de las Chinas Valley and provided key logistic help during our expeditions.

Type locality and horizon: Loma Koken (50°42′42″S and 72°32′29″W), El Puesto area, Río de las Chinas Valley, Estancia Cerro Guido, Magallanes Region, Chilean Patagonia (51°S). Upper section of the Dorotea Formation (lower Maastrichtian), between 71.7 ± 1.2 and 70.5 ± 5.0 million years (Ma) (21, 22) (see Materials and Methods).

Diagnosis: Small-sized hadrosauroid dinosaur (total body length ~4 m) presenting the following autapomorphies: a scapula with an anteroventrally curved pseudoacromion process and an ilium with a medioventrally and anteroposteriorly well-developed sacral crest extending posterior to the base of the postacetabular process. Gonkoken also differs from all other members of Hadrosauroidea in its unique combination of characters. Unlike the Hadrosauridae, it shows a maxilla with a jugal articular surface showing a prominent and caudally projecting dorsal tubercle; a dentary with a short diastema, mandibular symphysis oblique relative to its long axis, and tooth rows with less than 30 tooth positions that do not extend beyond the coronoid process and converge anteriorly with the lateral surface of the dentary; quadrate with a medial condyle that is not markedly elevated dorsally compared with the lateral condyle; a deltopectoral crest ...


Jhonatan Alarcón-Muñoz, Alexander O. Vargas, Hans Püschel, Sergio SotoAcuña, Leslie Manríquez, Marcelo Leppe, Jonatan Kaluza, Verónica Milla, Carolina Simon-Gutstein, José Palma-Liberona, Wolfgang Stinnesbeck, Eberhard Frey, Juan Pablo Pino, Dániel Bajor, Elaine Núñez, Héctor Ortiz, Héctor Mansilla, David Rubilar-Rogers and Penélope Cruzado-Caballero. 2023. Relict Duck-billed Dinosaurs survived into the last age of the Dinosaurs in Subantarctic Chile. SCIENCE ADVANCES. 9(24); DOI: 10.1126/sciadv.adg2456