Jakapil kaniukura. Image credit: Pepe Mateos/Agencia Telam
The Late Cretaceous of Argentina is represented by a high diversity and abundance of Theropoda and Sauropoda, while ornithischian remains are scarce and are mainly represented by hadrosaurids. Thyreophora is a clade of ornithischian dinosaurs that includes stegosaurs, ankylosaurs and basal forms as Emausaurus ernsti, Scutellosaurus lawleri, and Scelidosaurus harrisonii. The group is characterized by the presence of a postcranial dermal armour extending from the neck to the tip of the tail. Their fossil record is mainly known from the northern hemisphere, and its presence in the Gondwanan continents remains poorly known with some skeletal remains and tracks in South America, Africa, Madagascar, Australia, New Zealand and Antarctica. Basal thyreophorans could be bipedal or combine bipedal and quadrupedal locomotion, while stegosaurs and ankylosaurs were obligate quadrupeds.
Jakapil kaniukura is the first definitive thyreophoran species from Argentina. The first remains were found in 2014, in the upper beds of the Candeleros Formation at the ‘Rinconada de la Piedra Blanca’ in Rio Negro Province, Argentina. The genus name Jakapil (Ja-Kapïl: shield bearer), comes from the ‘gananah iahish’, Puelchean or northern Tehuelchean language. The specific epithet, comprising kaniu (crest) and kura (stone), comes from the Mapudungun language and refers to the diagnostic ventral crest of the mandible.
Holotype of Jakapil kaniukura. From Riguetti et al., 2022.
The holotype (MPCA-PV-630), with an estimated living mass of 4-7kg (9-15lb), is a partial skeleton of a subadult individual that includes fragmentary cranial bones, a nearly complete left lower jaw, partial vertebral elements, a complete dorsal rib, a partial coracoid, a nearly complete left scapula, a partial right scapula, two partial humeri, a possible partial right ulna, and more than forty osteoderms.
The skull of Jakapil is incomplete. The premaxilla, maxilla and mandible reveal a short skull in comparison with most non-ankylosaurid thyreophorans. The mandible resembles that of heterodontosaurids and basal ceratopsians. The basipterygoid processes are not close to the midline. The ventral process is small and carries a foramen. The predentary is pyramidal-shaped with a rounded apex, and two large and rounded lateral processes. The most striking feature is the presence of a ventral crest of the mandible. The axial elements are similar to those of Scelidosaurus. The humeri are strongly reduced in size. The femoral fragments also resemble those of basal ornithischians. Despite the incompleteness of the material, the overall limb dimensions and estimations suggest a bipedal stance in Jakapil.
References:
Facundo J. Riguetti, Sebastián Apesteguía & Xabier Pereda-Suberbiola (2022) A new Cretaceous thyreophoran from Patagonia supports a South American lineage of armoured dinosaurs. https://doi.org/10.1038/s41598-022-15535-6
Letters from Gondwana. 