Inglesa Formation Research Articles

Exceptional morphological and taxonomic diversity of early seals (Phocidae) from the Atacama Region, Chile

ABSTRACT Contrasting with their current ranges in the Antarctic and subantarctic zones, the fossil record reveals that phocids (true and elephant seals) inhabited widespread subtropical regions across the Southern Hemisphere in the geologic past. At least four extinct phocid taxa have been described from Miocene and Pliocene fossiliferous levels in Chile and Peru, constituting two of the taxonomically richest phocid assemblages known. Still, some Chilean remains morphologically differ from those recovered from Peru, suggesting an unprecedented phocid diversity. We examined phocid mandibular remains from the Bahía Inglesa Formation in northern Chile. We identified the occurrence of the long-snouted seal Acrophoca longirostris, a morphologically distinguishable and undescribed form of Acrophoca, and Hadrokirus martini, an extinct phocid with a robust feeding morphology, constituting the first record of this taxon outside Peru. We also recognised four other indeterminate phocids with considerable morphological differences from contemporaneous taxa. Moreover, one of these specimens uniquely combines morphological attributes distinct from all known extant and extinct phocids, likely corresponding to a new taxon. These reports significantly increase the taxonomic and morphological diversities of fossil seals from the eastern South Pacific and emphasise the substantial transformations of phocid assemblages over geologic time.

The fossil distribution of two pelagic lamniform sharks Alopias vulpinus and Lamna nasus, from South America

ABSTRACT The fossil record of the southeastern Pacific Ocean has been scarcely studied compared to other regions. We present the detailed description of two pelagic shark species, Alopias vulpinus (common thresher) and Lamna nasus (porbeagle) (Elasmobranchii: Lamniformes), from the Neogene of South America. The fossil teeth described here were recovered from the Bahia Inglesa Formation in Caldera, northern Chile. Our study provides the first comprehensive descriptions of fossil remains of A. vulpinus from Chile and L. nasus from the Americas. The occurrence of the common thresher shark represents the first published record and description of a representative from the family Alopiidae in northern Chile, whereas the fossil remains of the porbeagle shark are recorded for the first time in Chile. This study contributes to the understanding of the past distribution of shark species in the Eastern Pacific of South America during the Neogene period. It further confirms the particular abundance of lamniform sharks in the Neogene of Chile.

A small penguin cranium (Aves, Spheniscidae) from the Late Miocene of Bahía Inglesa Formation, Atacama Desert, Northern Chile

A new cranium of penguin from the Late Miocene of the Bahía Inglesa Formation (Northern Chile) is described here. Specimen SGO.PV.22245 exhibits a unique combination of characters that suggests it belongs to a new species of either Eudypula Bonaparte, 1856, Spheniscus Brisson, 1760, or more probably to a more basal taxon related to them. The specimen is notably smaller than the fossil species of Spheniscus and more similar in size to the extant Spheniscus. The fossa glandulae nasalis narrows caudally, the crista nuchalis transversa and the crista temporalis are expanded like short wings, and a short crista nuchalis sagittalis connects with the rounded and cranially projected eminentia cerebellaris. The fossa temporalis is subtriangular and deeper caudally and the cranial roof is widely expanded. All these features approach the condition to some species of Spheniscus and Eudyptula. However, because of the incompleteness of the material and the fact that it cannot be compared with some fossil species of Spheniscus only known through postcranial material, we are not able to provide a more accurate assignment.

Anatomy and phylogeny of a new small macraucheniid (Mammalia: Litopterna) from the Bahía Inglesa Formation (late Miocene), Atacama Region, Northern Chile

We describe a new macraucheniine macraucheniid, Micrauchenia saladensis gen. et sp. nov., from the late Miocene (Huayquerian SALMA). This is the first litoptern from Bahía Inglesa Formation, Chile. The specimen includes a partial mandible, cervical and thoracic vertebrae fragments, and portions of the forelimbs (a scapula fragment, an ulna-radius fragment, seven carpals, three metapodials, two proximal phalanges and four intermediate phalanges). The postcranial anatomy of Micrauchenia saladensis is consistent with terrestrial and cursorial locomotion, which suggests an allochthonous position of this specimen within the marine Bahía Inglesa Formation. The fusion of the ulna and radius and the presence of a radial aliform expansion align Micrauchenia with other macraucheniines, with which it shares these features. We interpret the fusion of the ulna and radius as a cursorial specialization and the aliform expansion as an adaptation for strong flexion movements and to resist higher transverse stresses during locomotion. In addition, Micrauchenia saladensis is the smallest member of the subfamily Macraucheniinae. To test the systematics and phylogenetics of this specimen, we expanded previous morphological matrices of macraucheniids by adding one dental and eight postcranial characters and scoring Micrauchenia saladensis. We performed maximum parsimony and Bayesian phylogenetic analyses, the latter applied for the first time to macraucheniid phylogeny. Our analyses confirm Micrauchenia saladensis as a member of the subfamily Macraucheniinae, although with uncertain affinities within this subfamily.

The Neogene record of cartilaginous fishes (Chondrichthyes: Holocephali, Elasmobranchii) from northern Chile: A review and identification guide

The abundance of fossil sharks and other cartilaginous fishes in northern Chile is widely known. Fossil sites such as the Bahia Inglesa Formation were affected by intense exploitation by fossil traffickers, which caused the departure of numerous specimens that are currently in foreign collections. Fortunately, this has decreased in the last decade and the study of Chilean specimens has been increasing. This study seeks to synthesize and update our knowledge about fossil chondrichthyans from northern Chile, specifically during the Neogene, offering a review of the species mentioned in the literature, along with key characters that can help in their identification. In this way, we seek to generate a guide for the classification of dental elements, and outline future works that can validate some of these records. This is important if we take into account that a third of the records mentioned in the literature remain unconfirmed, due to the lack of adequate descriptions or images to validate the assignments. Furthermore, most confirmed records can only be validated at the genus level. Despite these difficulties, we identified 42 chondrichthyan taxa for the region and discuss their reliability. Of these only 28 can be confirmed based on the current evidence which, based on a rarefaction analysis, we estimate could represent 76% of the potential taxa to be discovered for the Neogene of northern Chile. This highlight the need for more studies on all unconfirmed taxa and to continue exploring these basins.

Neogene Bony Fishes from the Bahía Inglesa Formation, Northern Chile

Despite being one of the richest Neogene deposits of marine fossil vertebrates along the Pacific coast of South America, no detailed study of bony fishes from the Bahía Inglesa Formation has been carried out. Through the revision of historical collections of the Caldera Paleontological Museum, we describe 27 fossil remains of bony fishes. Fossils described here are distributed in 13 taxa. Among these, Sardinops sp. cf. S. sagax (Clupeidae) represents the first fossil record of the genus for Chile, Labrodon sp. (Labridae) and Stelliferinae (Sciaenidae) are the first respective records for the southeast Pacific Ocean, Sarda sp. (Scombridae) represents the first fossil record for South America, Semicossyphus sp. (Labridae) and Anisotremus sp. (Haemulidae) are the first respective records for the Southern Hemisphere. Gymnosarda sp. (Scombridae) is described for the first time for the Neogene. We performed a paleobathymetric analysis of fossil fishes, including elasmobranchs, to understand the paleoenvironment followed by a similarity analysis that compares the faunal composition of the Bahía Inglesa Fm. with other fossil assemblages for the Pacific of South America. Our results show that the fish fauna from the Bahía Inglesa Fm. likely represents a depth range of 98 to 382 m with a mean depth range of 252 m in an uppermost bathyal environment. The assemblage from the Bahía Inglesa Fm. shows low taxonomic similarity levels with other Neogene geological units from the southeast Pacific Ocean. The study represents the first paleoecological and paleobiogeographic analysis of the fossil fish fauna from the Southeast Pacific.

THE FIRST FOSSIL RECORD OF THE SAWSHARK PLIOTREMA (PRISTIOPHORIDAE) FROM THE NEOGENE OF THE SOUTH-EASTERN PACIFIC (CHILE)

We present the first fossil record of the sawshark genus Pliotrema from the south-eastern Pacific Ocean. The examined material was obtained from a little-known fossil locality named “Arenas de Caldera” in the Atacama Region of Chile. The fossiliferous deposits belong to the Bahía Inglesa Formation, which is most likely middle Miocene–early Pliocene in age. There are no extant species of this sawfish in the eastern Pacific, probably due to the onset of cooling conditions during the Neogene. The type of environment for the elasmobranchs reported in this study is interpreted as demersal, based on the bathymetric affinities of extant species. Our results show that future studies are needed to better understand the evolutionary history and past distributions of this sawshark genus and their implications on current biogeographic patterns.

How many species of the aquatic sloth Thalassocnus (Xenarthra: Megatheriidae) were in Chile?: new evidences from the Bahía Inglesa Formation, with a reappraisal of their biochronological affinities

The aquatic sloth, Thalassocnus, is one of the most intriguing lineage of mammal known from the southern pacific coast of South America during the late Neogene. It was initially recognized in Perú, but recent paleontological surveys also recorded its presence in Chile. However, the determination of how many species of Thalassocnus were actually present in Chile remains as an open question. Here, we provide a detailed morphological description of an isolated distal fragment of humerus recovered at the Mina Fosforita member (ca. 7 Ma), Bahía Inglesa Formation (Atacama Region, northern Chile), which is referred to Thalassocnus. Morphological comparisons with others forms from Chile and Perú allow us to attribute the CPUC/C/557 specimen to Thalassocnus cf. T. natans, though some degree of intraspecific variation is acknowledged. The assessment of the stratigraphic provenance of the materials with previously assigned to Thalassocnus from the Bahía Inglesa, Horcón and Coquimbo formations, permits us to propose that the taxonomic diversity of Thalassocnus in Chile is unequivocal conformed by T. carolomartini, and T. natans. We also admitted the likely presence of T. antiquus and probably T. yaucensis. Futures discoveries of more complete specimens, and/or the detailed analysis of undescribed specimens from Chile will undoubtedly contribute to illustrate the evolutionary history of the Thalassocnus radiation in Chile.

The Southernmost Occurrence of the Aquatic SlothThalassocnus(Mammalia, Tardigrada) in Two New Pliocene Localities in Chile

Abstract. Thalassocnus is a sloth (Mammalia, Tardigrada) adapted to an aquatic lifestyle. It was first described from the Neogene deposits of the Pisco Formation of Peru, from where most of the specimens come. The genus is represented by five species ranging from the late Miocene to the late Pliocene, occupying successive stratigraphic levels. Morpho-functional studies of the cranial and postcranial skeleton of Thalassocnus have demonstrated the progressive adaptation of these sloths to a marine environment, establishing gradual differences from from the geologically oldest to the youngest species of the genus. The first records of Thalassocnus outside the Pisco Formation have been referred to the Neogene Bahia Inglesa Formation, in northern Chile, where older species were recovered. In this paper, we describe materials from two new Pliocene localities in Chile: the Coquimbo and the Horcon formations, in northern and central Chile, respectively. The Coquimbo Formation material was collected from the Lomas...

Oroclinal bending of the Juan Fernández Ridge suggested by geohistory analysis of the Bahía Inglesa Formation, north-central Chile

The stratigraphy of the Bahía Inglesa Formation in the Caldera Basin west of Copiapó, (north-central Chile) is revised, based on hitherto unpublished stratigraphic sections and 87Sr/86Sr dating. The depositional environment varied from a rocky shoreline to the upper continental slope, with sea-level oscillations and tectonic movements causing numerous local unconformities as well as lateral and vertical facies changes. Geohistory and sedimentological analyses show that the area was close to the concurrent sea level at about 15.3Ma, but at the same time being elevated about 100m above the present sea level. Although the basin then subsided at least 350m until around 6Ma, marine deposition was only recorded after 10.4Ma. This suggests that the sea level initially dropped faster than the rate of subsidence so that subaerial erosion occurred. The period of subaerial exposure before 10.4Ma can be attributed to the presence of a NE-trending branch of the Juan Fernández Ridge below the continental crust at this time, whereas the ensuing subsidence was due to subduction erosion and crustal accommodation in its wake as it migrated south along the South American coastline. The subsequent uplift of at least 250m can be explained by an acceleration in plate expansion and isostatic rebound of the continental crust after being partially submerged in the upper mantle. The uplift–subsidence–uplift pattern mirrors those recorded around the Nazca Ridge in Peru, as well as in similar basins to the south of Caldera. However, a higher southward migration rate of the Juan Fernández Ridge against the edge of the South American Plate and less intense uplift–subsidence–uplift cycles are recorded in the latter basins. This can possibly be attributed to oroclinal bending of the ridge due to friction with the overlying continental plate, which diminished the angle of incidence and the intensity of the stress field, but increased the migration velocity of the ridge relative to the coastline.

A new dwarf seal from the late Neogene of South America and the evolution of pinnipeds in the southern hemisphere

AbstractAlong the south‐western coast of South America, three genera of fossil phocids (true seals) have been formally described from the late Neogene:AcrophocaandPiscophocafrom Chile and Peru, and, more recently,Hadrokirusfrom Peru, which all represent medium‐ to large‐sized phocids. Here, we report the discovery ofAustralophoca changorumgen. et sp. nov., a diminutive phocid from the late Miocene of the Bahía Inglesa Formation (northern Chile) and Pisco Formation (southern Peru), comparable in size with the smallest species of modern phocids. This taxon is based on diagnostic postcranial material, including a humerus that has an elongated deltopectoral crest but lacks an entepicondylar foramen; a femur with a subtrochanteric fossa, among other characters; in combination with a relatively small body size. All these features together distinguishA. changorumfrom all other reported pinnipeds. This new taxon not only increases the taxonomic and morphological diversity of phocids of the late Neogene of the eastern South Pacific Ocean, but it also provides new insights about the evolutionary history of fossil pinniped assemblages in South America and, broadly, in the southern hemisphere.

Endocranial morphology of Pygoscelis calderensis (Aves, Spheniscidae) from the Neogene of Chile and remarks on brain morphology in modern Pygoscelis

The endocranial anatomy of Pygoscelis calderensis, a fossil species from the Bahía Inglesa Formation (Middle Miocene–Pliocene) of Chile, South America, was described through CT scans. Reconstructions of the fossil P. calderensis and endocasts for the living Pygoscelis adeliae, and Pygoscelis papua are provided here for the first time. Comparisons with the extant congeneric species P. adeliae, Pygoscelisantarctica and P. papua indicate that the morphological pattern of the brain and inner ear of the extant pygoscelids has been present already in the Middle Miocene. The neurological morphology suggests that the paleobiology of the extinct form would have been similar to the extant species. It was probably true for diet, feeding behaviour and diving kinematics.

Osteology of a new giant bony-toothed bird from the Miocene of Chile, with a revision of the taxonomy of Neogene Pelagornithidae

ABSTRACT Bony-toothed birds (Pelagornithidae) were among the largest volant birds, but their representatives from the upper size range have so far been known only from very fragmentary fossils. Here we report an exceptionally well-preserved giant species from the late Miocene of the Bahía Inglesa Formation in northern Chile, in which most major limb bones are complete and uncrushed. The fossil has the longest wing skeleton of any bird, and its wingspan in life was at least 5.2 m. Mass estimates of 16–29 kg are, however, surprisingly low and within the range of large extant volant birds, or only moderately above. The fossil constitutes the most substantial record of the Pelagornithidae (bony-toothed birds), and is assigned to a new species, Pelagornis chilensis. It is one of the largest known pelagornithids and the three-dimensionally preserved bones allow recognition of many previously unknown osteological features, especially concerning the vertebrae, pectoral girdle, and limb elements. We revise the taxonomy of Neogene pelagornithids and propose classification of all Miocene and Pliocene species into a single genus, Pelagornis. Osteological features are highlighted in which giant Neogene Pelagornithidae differ from their smaller Palaeogene relatives.

Fossil penguins (Pygoscelis calderensis sp. nov.) in the Bahía Inglesa Formation (Middle Miocene-Pliocene), Chile

Three new penguin skulls (Spheniscidae), assigned to the new species Pygoscelis calderensis sp. nov. from the Bahía Inglesa Formation of Middle Miocene-Pliocene age located south of Caldera on the coast of the III Región de Atacama, Chile (27°00'S, 70°45'W to 28°00', 71°00'W), are described. This finding broadens the geographic and chronologic distribution of the genus, constituting its most northern record. Before the present work, the genus was known from the Late Pliocene of New Zealand. This record, together with other faunistic evidences, suggests the existence of periods or cold oceanic currents during the Neogene.

Manganese nodules in the Miocene Bahía Inglesa Formation, north-central Chile: Petrography, geochemistry, genesis and palaeoceanographic significance

Manganese nodules recovered from two stratigraphic horizons of Tortonian–Messinian (late Miocene) age in the Bahía Inglesa Formation of north-central Chile were studied using XRD, SEM and geochemical analysis. The dominant mineral in the nodules is todorokite, which suggests a diagenetic, marine environment. This is supported by field observations of nodules replacing Ophiomorpha burrows. Preliminary, traditional statistical analysis of the nodule geochemistry, including single element, binary and ternary ratios, suggests that the nodules are of the supergene, deep marine type, as also indicated by the presence of foraminifers typical of the upper continental slope, as well as debris flow and turbidity current deposits in an associated submarine palaeocanyon. However, abnormally low Cu concentrations seem to contradict this interpretation, so that additional analyses were carried out. This included multiple discriminant analysis (MDA), as well as a new technique applied for the first time to manganese nodules, namely artificial neural network analysis (ANN). In both methods central log-ratio (CLR) normalization was applied to the raw data. The results, in particular those of the ANN analysis, suggest that the Bahia Inglesa nodules present a chemical signature distinct from that of nodules described to date. A new class is therefore proposed, namely supergene intermediate marine (partially restricted basin).

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

The fossil skull of a procellariid, Pachyptila sp., from Late Miocene marine sediments of the Bahia Inglesa Formation (Midde Miocene-Pliocene) of Northern Chile is described. The fossil is compared with extant species of the family Procellariidae. This discovery represents the first Neogene fossil record of the genus Pachyptila from South America.

The southernmost sirenian record in the eastern Pacific Ocean, from the Late Miocene of Chile

A tooth of a sirenian from the Late Miocene sediments of the Bahia Inglesa Formation (Chile) is described and referred to the Dugongidae. The fossil represents the first sirenian record from Chile and the southernmost record of the Sirenia in the eastern Pacific Ocean (latitude 27° S). The Chilean record extends the already wide geographical distribution of fossil sirenians along the Eastern Pacific coast. The presence of a sirenian during the Miocene on the Chilean coast is related to a globally warmer climatic condition and a still limited northern extension of the cold Humboldt Current. To cite this article: G. Bianucci, C. R. Palevol 5 (2006) .

A possible earthquake-triggered mega-boulder slide in a Chilean Mio-Pliocene marine sequence: evidence for rapid uplift and bonebed genesis

The type area of the Bahía Inglesa Formation (north–central Chile) is structurally complex as a result of active margin subduction at the Peru–Chile Trench. Inliers of subaerially exposed Mesozoic igneous basement are unconformably overlain by a mid-Miocene to late Pliocene marine siliciclastic sequence, which has become known for its abundance of fossil vertebrates found concentrated in a phosphatite on an omission surface. Mega-boulders derived from one of the largest inliers occur exclusively within this bonebed, which appears to have formed after major localized uplift caused removal of a significant thickness of unconsolidated sediment. The mega-boulders were probably dislodged by a high-magnitude earthquake event that accompanied tilting of the sea floor, and their emplacement was an integral part of the processes involved in genesis of the bonebed.

New penguin remains from the Pliocene of Northern Chile

Until recently, all described fossil penguin species from South America were recovered from the Atlantic coast. The description of three fossil species of Spheniscus from Peru and Chile now allows a clearer estimate of the historical diversity on the Pacific coast. Here we describe a further new species from a Pliocene level of the Bahía Inglesa Formation, northern Chile. This taxon, the first to be described from this sequence, is based on a partial skeleton lacking a skull. These remains are clearly referable to the living genus Pygoscelis, and share a mosaic of characters with extant species of the genus. Pygoscelis grandis sp. nov. was around the size of a King Penguin, and therefore much larger than any extant Pygoscelis species. Our cladistic analysis places P. grandis within the Pygoscelis clade as the sister taxon of living representatives. Living species of Pygoscelis have a sub-Antarctic distribution, and the presence of this species slightly south of the Tropics during the Pliocene may relate to end Neogene global cooling.

Primer registro de cráneos asignados a Palaeospheniscus (Aves, Spheniscidae) procedentes de la Formación Bahía Inglesa (Mioceno Medio-tardío), Chile

Although the skulls of the Spheniscidae are unusual in the paleontologic record, they show important features useful in the systematics of the group, as well as in the rest of the birds. Until now, fossil occurrences were restricted to six skulls: Paraptenodytes antarctica and one new species from the Gaiman Formation (Early Miocene) and Puerto Madryn Formation (Late Miocene) of Argentina, respectively; Spheniscus megaramphus and S. urbinai from the Pisco Formation (Late Miocene), Peru; Marplesornis novaezealandiae from New Zealand (Pliocene); and Spheniscidae cf. Spheniscus from the Bahia Inglesa Formation (Middle-Late Miocene), Chile. Five new materials have been exhumed from this last unit. These skulls, which come from the Caldera locality (Region of Atacama, Chile), have been preliminarily assigned to Palaeospheniscus (Aves, Spheniscidae), constituting the first skulls described for this species. We made an important contribution to the knowledge of the fossil avifauna of Chile and particularly of the Bahia Inglesa Formation.