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Taphonomy of marine vertebrates of the Pisco Formation (Miocene, Peru): Insights into the origin of an outstanding Fossil-Lagerstatte.

ABSTRACT: The Miocene Pisco Formation, broadly exposed in the Ica Desert of southern Peru, is among the most outstanding Cenozoic marine Fossil-Lagerstätten worldwide. It is renowned for its exceptional preservation and abundance of vertebrate fossils, including a rich assemblage of whales and dolphins (Cetacea). Here, we integrate taphonomic data on 890 marine vertebrate fossils, gathered through 16 different localities. Our observations range from the taxonomic distribution, articulation, completeness, disposition and orientation of skeletons, to the presence of bite marks, associations with shark teeth and macro-invertebrates, bone and soft tissue preservation, and the formation of attendant carbonate concretions and sedimentary structures. We propose that the exceptional preservation characterising many Pisco vertebrates, as well as their exceptionally high abundance, cannot be ascribed to a single cause like high sedimentation rates (as proposed in the past), but rather to the interplay of several favourable factors including: (i) low levels of dissolved oxygen at the seafloor (with the intervention of seasonal anoxic events); (ii) the early onset of mineralisation processes like apatite dissolution/recrystallisation and carbonate mineral precipitation; (iii) rapid burial of carcasses in a soupy substrate and/or a novel mechanism involving scour-induced self-burial; and (iv) original biological richness. Collectively, our observations provide a comprehensive overview of the taphonomic processes that shaped one of South America's most important fossil deposits, and suggest a model for the formation of other marine vertebrate Fossil-Lagerstätten.

SUBMITTER: Bosio G

PROVIDER: S-EPMC8282071 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:The Eocene electric ray †Titanonarke Carvalho, 2010 from the Bolca Konservat-Lagerstätte, north-eastern Italy, is redescribed in detail based upon new material from recent excavations. This taxon exhibits a combination of features (large voids between the pectoral and the axial skeleton filled in life by electric organs, anteriorly directed fan-shaped antorbital cartilages, lack of dermal denticles, long prepelvic processes, and rounded basibranchial copula with a small caudal tab) that clearly supports its assignment to the order Torpediniformes. The analysis of new material also demonstrates that the previous apparent absence of typical narcinoid characters used to diagnose †Titanonarke was the result of taphonomic biases. †Titanonarke shares at least three synapomorphies (presence of a rostral fontanelle, low number of ribs, and rostral cartilage connected to the antorbital cartilage through lateral appendices) with the extant genera Benthobatis, Diplobatis, Discopyge and Narcine, with which it forms a clade (family Narcinidae) recognized herein as unquestionably monophyletic. Moreover, based upon a single specimen of †Titanonarke that exhibits a unique combination of morphometric and meristic features, a new species of Eocene numbfish †T. megapterygia sp. nov., is recognized. The presence of several specimens representing different ontogenetic stages of at least two species of numbfishes suggests a close association of this taxon with shallow-water habitats corresponding to coral reefs as hypothesized for the Monte Postale palaeoenvironment. The occurrence of a fossilized marine batoid embryo is reported here for the first time. Moreover, the analysis of the gut contents suggests that the dietary adaptations of †Titanonarke can be related, at least in part, to an opportunistic strategy in the context of abundant larger foraminifera in the Monte Postale palaeobiotope, suggesting that this kind of feeding mode, known to occur in present-day reefs, already was realized 50 million years ago.

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Taphonomy of marine vertebrates of the Pisco Formation (Miocene, Peru): Insights into the origin of an outstanding Fossil-Lagerstatte.

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