Mario E. Suárez

Repeated mass strandings of Miocene marine mammals from Atacama Region of Chile point to sudden death at sea

Marine mammal mass strandings have occurred for millions of years, but their origins defy singular explanations. Beyond human causes, mass strandings have been attributed to herding behaviour, large-scale oceanographic fronts and harmful algal blooms (HABs). Because algal toxins cause organ failure in marine mammals, HABs are the most common mass stranding agent with broad geographical and widespread taxonomic impact. Toxin-mediated mortalities in marine food webs have the potential to occur over geological timescales, but direct evidence for their antiquity has been lacking. Here, we describe an unusually dense accumulation of fossil marine vertebrates from Cerro Ballena, a Late Miocene locality in Atacama Region of Chile, preserving over 40 skeletons of rorqual whales, sperm whales, seals, aquatic sloths, walrus-whales and predatory bony fish. Marine mammal skeletons are distributed in four discrete horizons at the site, representing a recurring accumulation mechanism. Taphonomic analysis points to strong spatial focusing with a rapid death mechanism at sea, before being buried on a barrier-protected supratidal flat. In modern settings, HABs are the only known natural cause for such repeated, multispecies accumulations. This proposed agent suggests that upwelling zones elsewhere in the world should preserve fossil marine vertebrate accumulations in similar modes and densities.

Aristonectes quiriquinensis, sp. nov., A New Highly Derived Elasmosaurid from the Upper Maastrichtian of Central Chile

ABSTRACT This paper describes a new species of elasmosaurid plesiosaur, Aristonectes quiriquinensis, sp. nov., based on a partial skeleton recovered from upper Maastrichtian beds of the Quiriquina Formation of central Chile. The material described here consists of two skeletons, one collected near the village of Cocholgue, and a second juvenile specimen from Quiriquina Island. Prior to these finds, Aristonectes was viewed as a monospecific genus, including only the enigmatic Aristonectes parvidens, the holotype of which consists of an incomplete skull and incomplete postcranium. Other material referred to the genus includes an incomplete juvenile skull and other postcranial material from the upper Maastrichtian of Antarctica, as well as a partial skull from the Quiriquina Formation of central Chile. The relationships of Aristonectes have been controversial, with competing theories assigning the genus to Cryptoclididae, Elasmosauridae, and Aristonectidae; however, there is a developing consensus that Aristonectes is a derived elasmosaurid, and this paper gives strong evidence for this view. Comparison of the specimen here studied with the holotype of A. parvidens demonstrates that A. quiriquinensis is a distinct species. The completeness of the adult skeleton allows the first confident size estimates for adult Aristonectes. It is a large plesiosaurian with a relatively large skull with numerous homodont teeth, a moderately long and laterally compressed neck, and relatively narrow trunk, with slender and elongate forelimbs. The two specimens are restricted to the upper Maastrichtian of central Chile, posing questions concerning the austral circumpolar distribution of different elasmosaurids towards the end of the Cretaceous.

Pinniped Turnover in the South Pacific Ocean: New Evidence from the Plio-Pleistocene of the Atacama Desert, Chile

ABSTRACT Modern pinnipeds distributed along the coasts of continental South America consist almost entirely of otariids (sea lions and fur seals). In contrast, phocids (true seals) are present only on the southernmost extreme of Chile. This recent biogeographic pattern is consistent with the zooarchaeological record (∼8-2 ka), but it is incompatible with the pinniped fossil record during the Neogene. From the middle Miocene to the Pliocene, true seals exclusively dominated pinniped assemblages, and they were only replaced by the fur seals and sea lions sometime after the early Pliocene. Here, we describe pinniped material collected from two new localities in the Atacama Desert, northern Chile, that clarifies this marine mammal faunal turnover. Specifically, these finds provide records of the first occurrence of Otariidae (late Pleistocene) and the last occurrence of Phocidae (early Pliocene) in Chile, which in turn constrain the timing of this turnover to between the early Pliocene and late Pleistocene. The stratigraphic context of these findings provides new insights into hypotheses that explain this faunal turnover in South America, and we briefly discuss them in the context of turnover events involving other marine vertebrates throughout the Southern Hemisphere.

A new titanosaur sauropod from the Atacama Desert, Chile

Partial remains of a titanosaur sauropod collected in the Tolar Formation (Upper Cretaceous) at the Atacama Desert (Antofagasta Region), northern Chile, is described, and a new species, Atacamatitan chilensis gen. et sp. nov., is erected. The material consists mainly of dorsal and caudal vertebrae, part of a humerus and a femur. The presence of a titanosaur confirms the Cretaceous age for the outcrops of red sandstone of the Tolar Formation whose age was previously uncertain, ranging from the Upper Cretaceous to the Paleocene. The new specimen represents the most complete dinosaur reported for this region and one of the most complete titanosaur known from Chile and the pacific margin of South America so far.

Elephant Seal (Mirounga sp.) from The Pleistocene of the Antofagasta Region, Northern Chile

ABSTRACT The genus Mirounga is the largest living member of the Phocidae family (true seals) and includes two species: M. angustirostris and M. leonina. These species exhibit a noticeable antitropical distribution in the Northern and Southern hemispheres, respectively. The evolutionary history of elephant seals, especially in regard to establishing this antitropical pattern, is poorly known. Nearly all fossils of the genus are isolated remains from the Pleistocene of California (M. angustirostris) and South Africa (M. leonina). Here, we describe new fossil material of Mirounga sp. (incomplete maxilla, dentary, and humerus), from the middle to late Pleistocene of Antofagasta Region, northern Chile. This material constitutes the first fossil occurrence of this species in South America and suggests that during part of the Pleistocene, phocids coexisted with otariids along the eastern edge of the South Pacific Ocean, which contrasts with the current biogeographic pattern in this ocean basin, providing new information about the structure of the pinniped community during the Pleistocene of South America.

The skull of a fossil Prion (Aves: Procellariiformes) from the Neogene (Late Miocene) of northern Chile

Se describe un craneo fosil de un procellariido, Pachyptila sp., proveniente de sedimentos marinos del Mioceno Tardio de la Formacion Bahia Inglesa (Mioceno Medio-Plioceno) del norte de Chile. El fosil es comparado con especies actuales de la familia Procellariidae. Este hallazgo representa el primer registro fosil neogeno del genero Pachyptila en America del Sur.