A new paleontological site from the (Upper Triassic- Lower Jurassic) Santo Domingo Formation in Northern Precordillera, San Juan Province.

COLOMBI, C.E.; KRAPOVICKAS, V. ; MARTÍNEZ, R.; ALCOBER, O.; SANTI MALNIS, PAULA; LUCERO M.; DROVANDI, JUAN; ABELIN, DIEGO; PEYRE DE FABREGUES, C.

Congreso; 36 Jornadas Argentina de Paleontología de Vertebrados. La Rioja, Argentina; 2023

Herein we present a new vertebrate paleontology quarry, located in the Santo Domingo Formation,producing both body and trace fossils. It consists of a red bed sequence composed of sandstones,mudstones, and minor conglomerates exposed in Northern Precordillera area, San Juan Province. Theunit is dated as Upper Triassic to Lower Jurassic based on the xyloflora (Taxaceoxylon sp. andRhexoxylon sp. cf. Rhexoxylon piatnitzkyi) and a radiometric datation (Ar40/Ar39 de 212,5 ± 7,0 Ma;Norian) in the type locality. At the Baños de la Bolsa area, along the Blanco River, the Santo Domingosuccession is 250 m thick, formed by five facies associations which paleoenvironments are single tomultistorey fluvial systems of high lateral mobility. Towards the top of the unit, the systems areinterbedded with facies of thin laminated sandy mudflats of a playa lake deposit. The body fossilrecord corresponds to the distal end of a humerus, probably belonging to a dinosaur due to thegracefulness that characterizes it, preserved in the middle portion of the succession. The fossilfootprints are preserved in the upper part of the succession, where the dominant facies are laminatedsheets and lobulated sandstones that characterize the outer sandy mudflat of a playa lake deposit. Twotrack-bearing surfaces are identified, both located in the lower bedding surfaces, as casts embeddedin a thin (mm to cm) plastic tuffaceous accumulation interlayered in a sandy-mudstone lobule. Allfootprints are deep and produced on soft to soupy grounds preserved as positive hyporelief. The lowtrack-bearing level records fourteen large quadrupedal pentadactyl tracks, possibly produced bydicynodonts: one trackway (Tw1), composed of 3 manus-pes sets, and eleven isolated tracks. Pesimpressions are, on average, 29 cm long and 37 cm wide, while manus impressions are about 16 cmlong and 42 cm wide. The upper track-bearing level exhibits two long trackways (Tw2 and Tw3) withlittle morphological resolution. Tw2 has 16 foot impressions and Tw3 has 18. Manus and pesimpressions are superimposed and cannot be clearly differentiated. Feet impressions are, on average,13 cm long and 10 cm wide. The same level also records one isolated, and clearly impressed,chirotheroid track (9 cm long, 5 cm wide) attributed to a crurotarsan archosauriform. Consideringthis, the low-resolution trackways may represent deeply impressed chirotheroid tracks. However, thishypothesis needs further analysis.