Jakapil

''Jakapil'' (meaning "shield bearer" in Puelchean) is a genus of basal thyreophoran dinosaur from the Candeleros Formation of Argentina. The type species is ''Jakapil kaniukura''.

Discovery and naming

The holotype, MPCA-PV-630, is a partial skeleton including several osteoderms and a complete lower jaw, which were found on land owned by the Mariluan family in 2012 and excavated between 2014 and 2019/2020. The finds were prepared by L. Pazo and J. Kaluza. The generic name, "''Jakapil''", is derived from "Ja-Kapïl", a Puelchean word meaning "shield bearer". This is also the literal meaning of the clade name Thyreophora. The specific name, "''kaniukura''", means "crest stone" in Mapudungun, in reference to its uniquely deep jaw.

Description

''Jakapil'' represents a novel morphotype among thyreophorans, including, among other things, the presence of a predentary bone (absent or cartilaginous in other basal thyreophorans), large, low osteoderms, and a bipedal stance, similar to '' Scutellosaurus''. Its describers estimate it to be less than long and in weight, based on femoral circumference. While the holotype remains do not represent a juvenile individual, it was likely not fully grown and may not have been sexually mature.

Classification

Due to a combination of features seen in basal ornithischians, basal thyreophorans, and ankylosaurs, a phylogenetic analysis placed it, according to most data matrices, as a basal thyreophoran, outside the clade Eurypoda. Riguetti and colleagues (2022) suggested that ''Jakapil'' represents a member of a previously unknown thyreophoran clade. This clade may have diverged from the rest of the thyreophorans during the Sinemurian. Its discovery in the Late Cretaceous implies the existence of a long basal thyreophoran ghost lineage.

The status of ''Jakapil'' as a thyreophoran has been disputed by some researchers; a study focused on the phylogenetic relationships of the Thyreophora noted that the only thyreophoran characteristic it possessed was dermal armor, while presenting features not present in any other thyreophoran. The premaxilla of ''Jakapil'' had no teeth, a feature not known in any thyreophoran, while the shape and depth of the dentary are more similar to those of basal neoceratopsians. Additionally, the teeth of ''Jakapil'' have a morphology distinct from any other ornithischian. Therefore, the study concluded that ''Jakapil'' most likely represents an armored marginocephalian or a member of a yet to be known lineage of non-thyreophoran ornithischians.

In their 2024 analyses, Fonseca and colleagues recovered ''Jakapil'' as either the sister taxon to Eurypoda or as the basalmost member of Ankylosauria. They argued that ''Jakapil'' is likely not a ceratopsian or marginocephalian, since this would required 16 additional steps. However, a position within Parankylosauria only required four additional steps. As such, the authors suggested that this possibility should not be disregarded, even though it is not the most parsimonious position for the taxon.

Paleobiology

In light of its straight, narrow snout, Riguetti and colleagues (2022) suggested that ''Jakapil'' did not use its teeth and jaws to shear leaves, but instead likely processed tough plant material via mastication, as evidenced by the high amount of wear on the teeth.

Paleoenvironment

The Candeleros Formation is interpreted as an ancient desert known as the Kokorkom desert, with some oases represent a faunal assemblage typical of Middle Cretaceous ecosystems in the western remnants of Gondwana. Other animals from this formation include the rhynchocephalians '' Tika'' and '' Priosphenodon'', the snake '' Najash'', the mammal '' Cronopio dentiacutus'', the theropods '' Alnashetri'', ''Buitreraptor'', ''Ekrixinatosaurus,'' and ''Giganotosaurus'', as well as the sauropods ''Andesaurus'' and '' Limaysaurus''.

References

{{Taxonbar, from1=Q113494797

Thyreophora
Dinosaur genera
Cenomanian dinosaurs
Candeleros Formation
Fossil taxa described in 2022
Dinosaurs of Argentina