Plottier Formation Research Articles

A new maniraptoran femur with alvarezsaurian affinities from the Plottier Formation (Coniacian-Santonian), northern Patagonia

ABSTRACT A new specimen, MAU-Pv-PH-453, comprising an isolated femur from the Plottier Formation (Coniacian-Santonian), northern Patagonia, is described here. Its characteristics, i.e., an anteriorly curved diaphysis; fused lesser and greater trochanters forming a trochanteric crest; a prominent medially directed head; and the absence of a fourth trochanter, allow us to identify it as belonging to a maniraptoran theropod. Among Patagonian maniraptorans, MAU-Pv-PH-453 shares similarities with alvarezsaurians, such as the absence of a posterior trochanter, a trochanteric shelf, and the fourth trochanter. However, in Patagonian alvarezsaurs, the lesser and greater trochanters are generally separated by a cleft. Notably, MAU-Pv-PH-453 exhibits some features seen in femora of parvicursorine alvarezsaurids, including a proximally projected trochanteric crest and an L-shaped profile in proximal view. However, MAU-Pv-PH-453 presents differences with parvicursorines, such as a knob partially separating the lesser and greater trochanters. Phylogenetically, MAU-Pv-PH-453 may have parvicursorine affinities, although its fragmentary nature might generate a bias in its phylogenetic position. Due to the lack of more diagnostic characters, MAU-Pv-PH-453 is assigned to Alvarezsauria indet. This material represents the second theropod record from the Plottier Formation and it could fill a temporal gap (between Coniacian and Santonian) in the record of Upper Cretaceous Patagonian alvarezsaurians.

Taphonomic analysis of saurischian dinosaurs from the Plottier Formation (Upper Cretaceous), Mendoza, Argentina

The uppermost Cretaceous continental deposits of the Neuquén Basin (west-central Argentina) have yielded a high diversity vertebrate assemblage, including numerous dinosaur species. The Neuquén Group is the richest unit in remains of dinosaur of the basin and comprises the Río Limay, the Río Neuquén and the Río Colorado subgroups. In this group, there is abundance of isolated, disarticulated or partially articulated sauropods and theropods. However, little is known about the taphonomic history of fossil assemblages. In this study, dinosaur remains from the Plottier Formation (late Coniacian-early Santonian) found in the Cerro Guillermo area in southern Mendoza are examined. The investigation of fossil occurrences within the study area revealed the existence of different taphonomic modes, from isolated bones until partially articulated skeletons preserved in deposits of floodplain and fluvial channel settings. SEM-EDS analysis showed the substitution of hydroxyapatite by francolite in the bone microstructure. The presence of fluorine-in one of the cases-suggested a link between the elemental composition and depositional environments: floodplain and fluvial channel. The survey of the vertebrate accumulation types and their sedimentary context allowed documenting a wide range of processes responsible for their genesis, operating within a meandering fluvial environment. This contribution represents a holistic approach about taphonomic history of Cretaceous dinosaurs for assessing the differential preservation of fossil assemblages in fluvial environments.

Bioeroded Dinosaur Bones: Novel Signatures of Necrophagous Activity in a Cretaceous Continental Environment

ABSTRACTWe describe a novel type of arthropod bioerosion trace fossil, Amphifaoichnus seilacheri new igen., new isp., associated with sauropod bones from the Upper Cretaceous (Coniacian–Early Santonian) Plottier Formation of western Argentina. The specimens are preserved in distal-floodplain deposits. The new ichnotaxon consists of predominantly horizontal, unbranched, unlined, elongated tubes, emplaced at the interface of bone and sediment, but penetrating the bone cortical tissue as well. Fill consists of unconsolidated sediment with evenly distributed bone chips in the infill sorted by size. The presence of bone fragments within the structures indicates prior bioerosion of the bone and their subsequent emplacement as part of the trace fill. A coleopteran with a heavily sclerotized body and well-developed biting mouthparts is tentatively inferred as a tracemaker. Amphifaoichnus seilacheri is interpreted as fodinichnion, reflecting the activity of scavengers able to decompose dinosaur carcasses. This ichnotaxon represents a novel ethology and ecological linkage previously undetected in continental ecosystems.

New record of ornithopod dinosaur from the Plottier Formation (Upper Cretaceous), Patagonia, Argentina

Ornithopods are the least known dinosaurs within the Upper Cretaceous record of Argentina. For this reason every new record is very important to know their evolution in South America. Here, we describe a new remain of an indeterminate ornithopod recovered in the Petrobrasaurus quarry of the Puesto Hernández area, northeastern Neuquén province (Argentina), late Coniacian–early Santonian in age. MAU-Pv-PH-458 is the northernmost bone record of an ornithopod in Argentina. This is a fragmentary neural arch from the middle section of the dorsal series of similar size to Macrogryphosaurus gondwanicus. MAU-Pv-PH-458 has typical ornithopod characters such as a lateromedial narrow neural spine and transverse processes dorsoposteriorly to posteriorly oriented. It shares with Macrogryphosaurus the presence of a deep channel between the bases of the postzygapophysis, which is a continuation of the channel that separates the postzygapophyses in posterior view. MAU-Pv-PH-458 increases the ornithopod record from the Plottier Formation.

Sedimentología y estratigrafía de alta resolución del subgrupo río Neuquén (Cretácico Superior) departamento confluencia, provincia de Neuquén, Argentina

The Upper Cretaceous exposid in the northeastern part of the Neuquen Basin, southeast of Neuquen, Argentina. Rio Neuquen Subgroup of continental origin, has been divided into two incomplete stratigraphic sequence units (SI y SII) on the basis of lithofacies assemblages and architectural elements. Parts of the succession (Portezuelo Formation SI) formed in northeasward-draining low and high sinuosity fluvial systems. Those are analyzed in detail in terms of macroformscale and stratigraphic-level architecture to assess fluvial styles and the evolution of non-marine depositional environments. Lateral and oblique accretion is a significant process of deposition in high-energy systems with mixed load. The overbank deposits dominate the floodplain stratigraphy; they contribute more than 45% of floodplain sediments. The Plottier Formation (SII) was accumulated from a low sinuosity perennial system with well developed deposits of alluvial plain with flood events. The unit was accumulated on topographic slopes dipping from west-southwest to east-northeast. The alluvial architecture and stacking patterns in the Rio Neuquen Subgroup were controlled by a combination of allogenic factors, most significantly tectonics followed by climate. The Upper Cretaceous succession in the Andean foreland basin, deposited in a backbulge zone, consists of tectonically-driven cycles comprising two components: strata deposited in an underfilled basin (Portezuelo Formation, AA-SI) and strata deposited in an overfilled basin lacking evidence of a forebulge (Plottier Formation, BA-SII).

Registro de un dinosaurio Aeolosaurini (Sauropoda, Titanosauria) en el Cretácico Superior (Formación Plottier) del norte de la Provincia de Neuquén, Argentina, y comentarios sobre los Aeolosaurini sudamericanos

RECORD OF AN AEOLOSAURINI DINOSAUR (SAUROPODA, TITANOSAURIA) IN THE UPPER CRETACEOUS (PLOTTIER FORMATION) OF NORTHERN NEUQUEN PROVINCE, ARGENTINA, AND COMMENTS ON THE SOUTH AMERICAN AEOLOSAURINI. The clade Aeolosaurini is represented by several specimens found, so far, only in Argentina and Brazil. The material reported here corresponds to a sauropod titanosaur consisting of four incomplete anterior caudal vertebrae, from the Narambuena Paleontological Site, Rincon de los Sauces, Neuquen Province, Argentina. The specimen comes from the Plottier Formation (late Coniacian-lower Santonian, Upper Cretaceous), Neuquen Group. The specimen has a combination of features that includes it into the clade Aeolosaurini: anterior caudal centra with anterodorsal margin bent forward; prezygapophyses elongated in anterior caudal, in correlation with the extreme displacement of the neural arch forward; and anteroposteriorly elongated articular facets of prezygapophyses, at least in the anterior caudals. However, it differs from other Aeolosaurini by having postzygapophysis with anteroposteriorly short articular facets, not as elongated in the prezygapophyses. This specimen corresponds not only to the fi rst discovery of an Aeolosaurini in the north of the Neuquen Basin (because Rinconsaurus caudamirus Calvo & Gonzalez Riga has been included in another clade, Rinconsauria), but also the oldest record of the group.

Upper Cretaceous vertebrates from El Anfiteatro area, Río Negro, Patagonia, Argentina

The first vertebrate remains from the Upper Cretaceous locality El Anfiteatro (northern Río Negro, Patagonia, Argentina) are described. Fossil remains were recovered in beds of Cerro Lisandro, Portezuelo, and Plottier formations. From the Cerro Lisandro Formation, remains of large fishes, dipnoans, titanosaur sauropod dinosaurs, and a variety of theropod dinosaurs (cf. Carcharodontosauridae, cf. Spinosauridae, cf. Abelisauria and Coelurosauria indet.) are reported. The Plottier Formation, in turn, has yielded remains of Chelidae turtles, crocodyliforms, titanosaur sauropods, theropods (cf. Carcharodontosauridae, Coelurosauria indet., cf. Unenlagiinae), and ornithopods. To date, the Portezuelo Formation has been the less prolific of all. Except for the record of a possible spinosaurid in the Cerro Lisandro Formation, the rest of the evidence obtained from El Anfiteatro is congruent with the record of other Patagonian sites where the Limayan and Neuquenian tetrapod associations were established.