Alien Species, a Natural Experiment in Actualistic Taphonomy

Martínez, Sérgio; Rojas, Alejandra; Cabrera, Fernanda; Antuña, Diego

doi:10.1007/978-3-030-20625-3_4

Cited by 3 publications

(3 citation statements)

References 18 publications

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“…As a recent introduction, M. tuberculata cannot be derived from reworked deposits, meaning all observed degradation occurred in the fluvial channels of the modern river within the last five decades, at most. Similar patterns of rapid alteration for invasive and exotic taxa have been noted in marine settings, where dead shells of recently introduced species may appear taphonomically similar to shells of much older, native species (Martínez et al 2020). This interpretation, however, relies on the two species having similar taphonomic pathways, such that TT scores of fossil and live E. floridensis can be applied a posteriori to M. tuberculata for classification, an assumption that is not unreasonable given the similarity in size, shape, and ecology of the two compared species.…”

Section: Death Assemblage Taphonomic Provenance and Pathwayssupporting

confidence: 54%

Live, dead, and fossil mollusks in Florida freshwater springs and spring-fed rivers: Taphonomic pathways and the formation of multisourced, time-averaged death assemblages

et al. 2020

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Taphonomic processes are informative about the magnitude and timing of paleoecological changes but remain poorly understood with respect to freshwater invertebrates in spring-fed rivers and streams. We compared taphonomic alteration among freshwater gastropods in live, dead (surficial shell accumulations), and fossil (late Pleistocene–early Holocene in situ sediments) assemblages from two Florida spring-fed systems, the Wakulla and Silver/Ocklawaha Rivers. We assessed taphonomy of two gastropod species: the native Elimia floridensis (n = 2504) and introduced Melanoides tuberculata (n = 168). We quantified seven taphonomic attributes (aperture condition, color, fragmentation, abrasion, juvenile spire condition, dissolution, and exterior luster) and combined those attributes into a total taphonomic score (TT). Fossil E. floridensis specimens exhibited the greatest degradation (highest TT scores), whereas live specimens of both species were least degraded. Specimens of E. floridensis from death assemblages were less altered than fossil specimens of the same species. Within death assemblages, specimens of M. tuberculata were significantly less altered than specimens of E. floridensis, but highly degraded specimens dominated in both species. Radiocarbon dates on fossils clustered between 9792 and 7087 cal BP, whereas death assemblage ages ranged from 10,692 to 1173 cal BP. Possible explanations for the observed taphonomic patterns include: (1) rapid taphonomic shell alteration, (2) prolonged near-surface exposure to moderate alteration rates, and/or (3) introduction of reworked fossil shells into surficial assemblages. Combined radiocarbon dates and taphonomic analyses suggest that all these processes may have played a role in death assemblage formation. In these fluvial settings, shell accumulations develop as a complex mixture of specimens derived from multiple sources and characterized by multimillennial time-averaging. These findings suggest that, when available, fossil assemblages may be more appropriate than death assemblages for assessing preindustrial faunal associations and recent anthropogenic changes in freshwater ecosystems.

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Section: Death Assemblage Taphonomic Provenance and Pathwayssupporting

confidence: 54%

Live, dead, and fossil mollusks in Florida freshwater springs and spring-fed rivers: Taphonomic pathways and the formation of multisourced, time-averaged death assemblages

et al. 2020

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“…It is an approximately 8 km straight to gently concave wave-dominated beach, oriented at a direction NE, and has a slope of approximately 9%. It is composed of fine, medium, and coarse quartz sands (Etchichury and Remiro 1971; Spoturno et al 2012; S. Martínez, personal observations 2020).…”

Section: Geographical and Geological Settingmentioning

confidence: 99%

“…This problem also affects Holocene specimens, as the preservation grades of shells millennia or centuries old and very young shells may be nearly identical. For example, Martínez et al (2020) and Gómez Maduro et al (2023), using alien species, showed that over a few years (around two decades), very young shells can acquire a preservation grade typical of millennial-aged shells. On the other hand, at centennial-millennial scales, but concerning other taxa, Tomašových et al (2017) found that Nautilus shells from within-habitat time-averaged assemblages were altered differently than those from condensed assemblages, and Agiadi et al (2022) showed that in certain local circumstances, there is some support for a taphonomic clock in otoliths.…”

Section: Introductionmentioning

confidence: 99%

Millenial-Scale Time Averaging Inferred by Discolored Shells in Beach Death Assemblages

Martínez

Rojas

2023

Palaios

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Molluscan death assemblages occurring on present-day beaches frequently consist of secondary-colored shells, with yellow to brown and gray to black colors. It is hypothesized that this secondary coloration can be related to postmortem age and to conditions in the taphonomically active zone, altering shells to black and gray tones in reducing conditions, and then becoming yellowish or brownish in oxidizing settings. In this study, we assessed whether the variability in the degree of shell discoloration of two species of the infaunal bivalve Mactra collected in beach death assemblages from a temperate siliciclastic beach in Uruguay is a function of postmortem age, and whether this variability in discoloration can be linked to differences in their elemental composition, microstructure, and provenance. Although we did not detect any differences in mineralogy or elemental composition among shells differing in discoloration, we show that modern (younger than a century) beach shells are not secondary-colored, but have remained white, but some white shells are also old (millennial). In contrast, yellow and gray shells are consistently older than 1,000 years, indicating that this degree of discoloration requires millennial residence times in the taphonomically active zone and suggesting that discoloration can be used as an indicator of time averaging. Discolored shells are derived from subtidal death assemblages.

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TAPHONOMIC SIGNATURES IN DEAD SHELLS OF THE INVASIVE GASTROPOD RAPANA VENOSA (VALENCIENNES, 1846) AFTER TWO DECADES IN THE RÍO DE LA PLATA, URUGUAY

GÓMEZ-MADURO

Rojas

Martínez

2023

Palaios

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Rapana venosa (Valenciennes, 1846) is an invasive gastropod, the arrival of which in the Río de La Plata estuary 22 years ago is well-documented. Rapana venosa shells were collected during two sampling events from four beaches with different substrate types and wave energy regimes to compare the taphonomic attributes under different environmental conditions. We analyzed the samples by comparing frequencies of taphonomic attributes. Our results show that intermediate-reflective beaches with rocky substrates were dominated by intermediate- to highly fragmented specimens, with high corrasion, intermediate to high bioerosion, low bioencrustation, and medium to large sizes. In contrast, intermediate-dissipative beaches with sandy substrate, mobile stones, and occasional consolidated sediments were dominated by less fragmented shells, high to intermediate corrasion, scarcer bioerosion, low bioencrustation, and small- to medium-sized specimens. Results suggest that significant taphonomic differences arise within two decades under natural conditions. These findings imply that paleoenvironmental signals derived from the taphonomic attributes of fossil assemblages emerge much faster than the potential duration of time averaging of shelly fossils in shallow marine settings.

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Alien Species, a Natural Experiment in Actualistic Taphonomy

Cited by 3 publications

References 18 publications

Live, dead, and fossil mollusks in Florida freshwater springs and spring-fed rivers: Taphonomic pathways and the formation of multisourced, time-averaged death assemblages

Live, dead, and fossil mollusks in Florida freshwater springs and spring-fed rivers: Taphonomic pathways and the formation of multisourced, time-averaged death assemblages

Millenial-Scale Time Averaging Inferred by Discolored Shells in Beach Death Assemblages

TAPHONOMIC SIGNATURES IN DEAD SHELLS OF THE INVASIVE GASTROPOD RAPANA VENOSA (VALENCIENNES, 1846) AFTER TWO DECADES IN THE RÍO DE LA PLATA, URUGUAY

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