Scutarx is an extinct genus of Aetosauriformes, most commonly regarded by its species name Scutarx deltatylus (Scutarx Latin for “shield fortress” -scutum meaning “shield” and -arx meaning “fortress”; deltatylus Greek for “triangular protuberance” -delta meaning triangle and -tylos meaning “knob, knot, swelling, callous, protuberance”).[1] Scutarx lived around 230 million years ago during the Carnian and Norian stage of the Late Triassic.[2][3] Scutarx are “medium sized” paramedian osteoderms belonging to the clade Aetosauria, a heavily armored and more herbivorous cousin of crocodiles.[4]
The presence of a large, triangular boss in the posteromedial corner of the dorsal surface of the dorsal paramedian osteoderms is the primary morphological characteristic that distinguishes Scutarx from other aetosaurs.[2][5] Both morphologically and stratigraphically, Scutarx can be distinguished from the closely related taxas Calyptosuchus wellesi and Adamanasuchus eisenhardtae. Because of this, Scutarx is prevalent in the fossil record because it may be an indicator taxon for the late Adamanian biozone.[2]
Fossils of Scutarx have been found in the Triassic Chinle Formation of Petrified Forest National Park of Arizona and the Cooper Canyon Formation of Texas. Four partial skeletons including much of the carapace, vertebral column as well as the shoulder and pelvic girdles have been collected from PEFO between 2002 and 2009.[4] The locations where the Scutarx fossils were gathered are all found in the lower Sonsela Member of the Chinle Formation.[4][1] The Camp Butte, Lot's Wife, Jasper Forest, Jim Camp Wash, and Martha's Butte beds may be found in the PEFO area of the Sonsela Member. Lot's Wife, Jasper Forest, and Martha's Butte beds form cliffs, whereas the Lot's Wife and Marthas Butte beds are slope-forming units with a larger proportion of mudrocks than sandstones.[4][1] These locations all show neighboring floodplain facies connected to a braided river system.[4][1]
In Texas, the Cooper Canyon Formation's uppermost and the majority of its middle part are Revueltian in age. While the Scutarx fossils were found at around the same level as the lowest recorded occurrence of Machaeroprosopus, which indicates the local base of the Revueltian, this finding of Scutarx deltatylus is notable because it is from the lowermost Revueltian teilzone. With the sole other record being a reported specimen of Desmatosuchus smalli from the early Revueltian of Arizona, this significantly increases the record of non-desmatosuchin aetosaurs in the Revueltian.[5]
One of the most often discovered vertebrate fossils in the Petrified Forest National Park (PEFO), Arizona's Upper Triassic Chinle Formation are aetosaurians.[4] Four fragmentary skeletons that were believed to be a new taxon were discovered during paleontological research in the park between 2001 and 2009.[4] This genoholotype was later named in 2016 by William G. Parker as Scutarx.[4]
Scutarx belong to the family of Stagonolepididae of the clade Aetosauriformes.[4] The Late Triassic (Carnian/Norian) aetosaurs were armored archosaurian reptiles. They are commonly found in India, North Africa, North America, and South America. These rare, highly derived archosaurs are easily distinguished from other Triassic archosaurs by the presence of an elongated, occasionally spiky, premaxilla and substantial dermal armor.[3]