Thomas J. DeVries’s research while affiliated with Burke Museum of Natural History and Culture and other places

The East Pisco Basin, occupying the coastal plain of Peru between 13°S and 16°S, is widely known for its extensive Eocene to Quaternary biosiliceous deposits and excellent preservation of fossil marine vertebrates. Biochronologic studies published over the past 35 years record a hiatus of about 13 million years (*32–19 Ma) separating the youngest Paleogene deposits (Otuma Formation) from the oldest Neogene deposits (Chilcatay Formation). We describe a newly identified Lower Miocene depositional sequence that lies below documented Chilcatay strata, rich in diatoms and benthic foraminifers, which we name the Tunga Formation. A low-latitude diatom assemblage from the Tunga Formation indicates an age of 21.6 to 20.5 Ma age, whereas an ash within basal Tunga strata yields an 206Pb/238U weighted mean age of 20.58 ± 0.13 Ma. Benthic foraminifer paleodepth analysis and the diatom assemblage of the Tunga Formation indicate deposition took place along the continental margin at upper bathyal depths under hypoxic conditions beneath highly productive waters, a scenario also supported by the presence of abundant clupeoid fish scales and dolomitized horizons. The Tunga Formation is characterized by a profound scarcity of cetacean fossils, unlike the cetacean-rich neritic sediments of the overlying Chilcatay Formation.

The East Pisco Basin, occupying the coastal plain of Peru between 13°S and 16°S, is widely known for its extensive Eocene to Quaternary biosiliceous deposits and excellent preservation of fossil marine vertebrates. Biochronologic studies published over the past 35 years record a hiatus of about 13 million years (*32-19 Ma) separating the youngest Paleogene deposits (Otuma Formation) from the oldest Neogene deposits (Chilcatay Formation). We describe a newly identified Lower Miocene depositional sequence that lies below documented Chilcatay strata, rich in diatoms and benthic foraminifers, which we name the Tunga Formation. A low-latitude diatom assemblage from the Tunga Formation indicates an age of 21.6 to 20.5 Ma age, whereas an ash within basal Tunga strata yields an 206 Pb/ 238 U weighted mean age of 20.58 ± 0.13 Ma. Benthic foraminifer paleodepth analysis and the diatom assemblage of the Tunga Formation indicate deposition took place along the continental margin at upper bathyal depths under hypoxic conditions beneath highly productive waters, a scenario also supported by the presence of abundant clupeoid fish scales and dolomitized horizons. The Tunga Formation is characterized by a profound scarcity of cetacean fossils, unlike the cetacean-rich neritic sediments of the overlying Chilcatay Formation.

The calyptraphorine stromboid, Aulacodiscus lissoni (Douvillé, 1921), found in northern Peru in bioclastic sandstones of the lower Eocene Basal Salina Formation, is notable for its complete envelopment by calluses, including massive left-lateral callus knobs. Previous shell descriptions suffered from the absence of the anterior end. Newly reported specimens reveal an outer lip with a well-formed posterior notch and a short anterior spine, both unique to calyptraphorines. A suite of characters (inter alia, an extended posterior canal, notched outer lip, and dorsal callus knob) indicate A. lissoni burrowed just below the sediment surface in an environment where exhumation and overturning by waves or predators were a constant risk; more than half of the specimens exhibit ventral traces of predation that were likely lethal. The calyptraphorine taxon most similar to A. lissoni, the thickly callused Paleocene Veatchia carolinae (Maury, 1912), inhabited sandy carbonate platforms in Senegal, Trinidad, and Colombia. A calyptraphorine phylogeny that would include both thickly callused species is precluded at present by the scarcity and incompleteness of specimens of V. carolinae and the geographically and temporally isolated occurrence of A. lissoni in the eastern Pacific Ocean.

The Peruvian Province, from 6° S in Peru to 42° S in Chile, is a highly productive coastal marine region whose biology and fossil record have long been studied separately but never integrated. To understand how past events and conditions affected today's species composition and interactions, we examined the role of extinction, colonization, geologic changes to explain previously unrecognized peculiar features of the biota and to compare the Peruvian Province's history to that of other climatically similar temperate coasts. We synthesized all available data on the benthic (or benthically feeding) biota, with emphasis on fossilizable taxa, for the interval from the Miocene (23–5.4 Ma) and Pliocene (5.4–2.5 Ma) to the present. We outline the history of ecological guilds including primary producers, herbivores, predators, and suspension‐feeders and document patterns of extinction, colonization, and geographic restriction. We identify twelve unusual attributes of the biota, most of which are the result of repeated episodes of extinction. Several guilds present during the Miocene and Pliocene are not represented in the province today, while groups such as kelps and perhaps intertidal predatory sea stars are relative newcomers. Guilds on soft bottoms and in sheltered habitats were severely affected by extinction, whereas those on hard bottoms were most affected by colonists and held their own in diversity. The Peruvian Province has not served as a biogeographic refuge, in contrast to the coasts of Australasia and Argentina, where lineages no longer present in the Peruvian Province survive. The loss of sheltered habitats since the Pliocene explains many of the present‐day peculiarities of the biota. The history of the province's biota explains its unique attributes. High productivity, a rich Southern Hemisphere heritage, and colonization from the north account for the present‐day composition and unusual characteristics of the biota.

Carbonate biomineralization normally occurs in three distinct types: controlled, induced and influenced, each with its peculiar characteristics. Building-reef species within the family Cirratulidae (Annelida, Polychaeta) constitute the first known example of “double-phased” biomineralization among marine invertebrates, as they combine controlled and influenced biomineralization types in the process of developing carbonate tube aggregates. The ultrastructure of the tubes, composed of thin calcareous lamellae with a spherulitic prismatic ultrastructure, as well as lamellae with a homogeneous structure, is produced directly by the worms living inside them and clearly indicates a controlled biomineralization, while the calcareous matrix with agglutinated xenolithic granules that fills the areas between the tubes of the same aggregate is the product of an influenced biomineralization. The reason why this biomineralization process occurs is yet unknown. This study is therefore aimed at describing in detail for the first time the biomineralization of Miocene (Diplochaetetes) and Recent (Dodecaceria) tubes of cirratulid aggregates from southern Peru via optical microscopy, epifluorescence, SEM and EDS analyses. Furthermore, a detailed morphometric and compositional study of tubes was performed and results were statistically evaluated. The comparison with recent cirratulids allowed the recognition of the double-phased biomineralized skeletons in the fossil specimens, despite the different degree of recrystallization which affected the studied Peruvian bioconstructions. This observation suggests that this type of biomineralization has not changed over the course of the entire Cenozoic and can be considered a unique evolutionary character which probably was developed by these polychaetes to be safer from predators, as well as generally more stable and more resistant to environmental stressing factors.

Global sea-level changes and substantial vertical displacement along the Monte Grande Fault (MGF) in the lower Río Ica Valley of south-central Peru influenced the accumulation of bioclast-bearing and diatom-bearing Miocene siliciclastic sediments in an area of the East Pisco forearc basin (EPB) colloquially known as Laberinto. Two depositional hiatuses in the Laberinto area (~17–14 Ma, ~12.5–10 Ma) manifest as sediment-filled erosional depressions a few kilometers in breadth. Erosion of the older depression was preceded by an ~18-Ma massive debris flow, possibly triggered by motion on the MGF causing lower Miocene lithoclastic olistoliths of up to two hundred meters length to spill off the footwall block. Sediment shed from the same footwall block may have formed previously recognized early Miocene deltas. From 14–13 Ma, the older depression filled with sediments herein assigned to the provisionally named Laberinto, Pampa, and Naranja members of the Pisco Formation, the latter member being characterized by marine delta foreset beds. The three members are at least partly correlative with the Pisco-0 sequence of the Pisco Formation. The younger depression was overrun at 10 Ma by debris flows of lithoclastic and granitic cobbles and boulders, then filled with diatomaceous silty sand with five-meter-sized lithoclastic olistoliths. The two lithologies constitute the provisionally named Mature Formation. Radiometric and newly revised biochronological data from throughout the EPB coupled with new diatom data from the Laberinto area have provided new insights into the correlation of sequences within the Chilcatay and Pisco formations and the interaction of local and basin-wide tectonism and global eustatic sea-level events across the basin.

The highly productive waters of the Humboldt Current System (HCS) host a particular temperate ecosystem within the tropics, whose history is still largely unknown. The Pisco Formation, deposited during Mio-Pliocene times in the Peruvian continental margin has yielded an outstanding collection of coastal-marine fossils, providing an opportunity to understand the genesis of the HCS ecosystem. We present a comprehensive review, completed with new results, that integrates geological and paleontological data from the last 10 My, especially focusing on the southern East Pisco Basin (Sacaco area). We discuss the depositional settings of the Pisco Formation and integrate new U/Pb radiometric ages into the chronostratigraphic framework of the Sacaco sub-basin. The last preserved Pisco sediments at Sacaco were deposited ~ 4.5 Ma, while the overlying Caracoles Formation accumulated from ~ 2.7 Ma onwards. We identified a Pliocene angular unconformity encompassing 1.7 My between these formations, associated with a regional phase of uplift. Local and regional paleoenvironmental indicators suggest that shallow settings influenced by the offshore upwelling of ventilated and warm waters prevailed until the early Pliocene. We present an extensive synthesis of the late Miocene–Pleistocene vertebrate fossil record, which allows for an ecological characterization of the coastal-marine communities, an assessment of biodiversity trends, and changes in coastal-marine lineages in relation to modern HCS faunas. Our synthesis shows that: (i) typical endemic coastal Pisco vertebrates persisted up to ~ 4.5 Ma, (ii) first modern HCS toothed cetaceans appear at ~ 7–6 Ma, coinciding with a decline in genus diversity, and (iii) a vertebrate community closer to the current HCS was only reached after 2.7 Ma. The genesis of the Peruvian coastal ecosystem seems to be driven by a combination of stepwise transformations of the coastal geomorphology related to local tectonic pulses and by a global cooling trend leading to the modern oceanic circulation system.

A new megabalanine barnacle, Austromegabalanus carrioli sp. nov., is described from lower Miocene strata of the Chilcatay Formation (East Pisco Basin, southern Peru). An assessment of the value of interlaminate figures in distinguishing species within the tribe Austromegabalanini from thin sections is provided-a useful identification tool with fossil taxa such as the austromegabalanines, which are commonly found only as fragmented shells. The paper concludes with a reassessment of the palaeobiogeography and distribution patterns of the austromegabalanines, proposing a circum-equatorial origin for this tribe.

Shell beds from the Caballas Formation in the East Pisco Basin of southern Peru have yielded an assemblage of molluscs numerically dominated by oysters and cerithioid and eulimid gastropods, with lesser numbers of neritid, ampullinid, and pyramidelloid gastropods and noetiid, mytilid, anomiid, and cardiid bivalves. The shell beds mark a transition from continental to marine-influenced environments. Palaeontological evidence, including plant twig moulds on the attachment scars of oysters and a high diversity of potamidid gastropods, is consistent with an interpretation of a brackish-water setting. The majority of molluscan species from the Caballas Formation show a close affinity with Late Cretaceous species from northern Peru, but no unequivocally Cretaceous invertebrate taxa (e.g. ammonites, rudists) have been found. A morphologically distinctive bivalve species that occurs in the Caballas Formation, Carolia (Parinomya) parinensis, only occurs elsewhere in the upper lower Eocene Pariñas and Chacra formations of the Talara Basin of northern Peru. Moreover, several other Caballas Formation molluscan taxa closely resemble early Eocene species from the Talara Basin. These equivocal biostratigraphic data indicate an early Paleogene age as most likely for the Caballas Formation. http://www.zoobnk.org/urn:lsid:zoobank.org:author:25E21A31-0230-48C7-A2ED-A48A98A3F231