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quinta-feira, 1 de outubro de 2015

[Paleo-Cetology / Behaviour • 2015] 

No Deep Diving: Evidence of Predation on Epipelagic Fish for A Stem Beaked Whale Messapicetus gregarius from the Late Miocene of Peru

Life reconstruction of three individuals of the extinct beaked whale Messapicetus gregarius preying upon a school of aged sardines Sardinops sp. (average body length 38.8 cm) in the upper part of the water column along the coast of nowadays Peru. The front individual is an adult male, whereas the last in the background is a female.
Illustration by A. Gennari.  DOI: 10.1098/rspb.2015.1530
Abstract
Although modern beaked whales (Ziphiidae) are known to be highly specialized toothed whales that predominantly feed at great depths upon benthic and benthopelagic prey, only limited palaeontological data document this major ecological shift. We report on a ziphiid–fish assemblage from the Late Miocene of Peru that we interpret as the first direct evidence of a predator–prey relationship between a ziphiid and epipelagic fish. 
 
Preserved in a dolomite concretion, a skeleton of the stem ziphiid Messapicetus gregarius was discovered together with numerous skeletons of a clupeiform fish closely related to the epipelagic extant Pacific sardine (Sardinops sagax). Based on the position of fish individuals along the head and chest regions of the ziphiid, the lack of digestion marks on fish remains and the homogeneous size of individuals, we propose that this assemblage results from the death of the whale (possibly via toxin poisoning) shortly after the capture of prey from a single school. Together with morphological data and the frequent discovery of fossil crown ziphiids in deep-sea deposits, this exceptional record supports the hypothesis that only more derived ziphiids were regular deep divers and that the extinction of epipelagic forms may coincide with the radiation of true dolphins.
KEYWORDS: feeding, fossil, Odontoceti, pacific sardine, Sardinops, Ziphiidae
Figure 2. Fossil remains of the extinct beaked whale Messapicetus gregarius and associated clupeid fish Sardinops sp. cf. S. sagax found in Cerro Colorado.
(a) Photograph and line drawing of the articulated caudal portion of a skeleton of Sardinops sp. in left lateral view (note the typically clupeid urostyle supporting the caudal fin complex), with a complete skeleton of the modern sardine S. sagax for comparison. (b) Imbricated large cycloid scales of Sardinops sp. in right lateral view showing tubercular protuberances in their central region and curved radii-like lines in their lateral fields, with a body of S. sagax for comparison reporting the putative collocation of the scale set. (c) Dolomite concretion with the skull and mandibles of M. gregarius in ventral view; occipital region, hamular processes of the pterygoids, posteroventral and apical regions of the mandibles emerge from the concretion. bv, articulated bivalve shells; mda, apex of mandibles; mdp, posteroventral part of mandibles; ph, hamular processes; wd, fragment of fossilized wood. (d) Line drawing of the skull of M. gregarius inside the concretion with a reconstructed outline of its body. Multiple individuals of Sardinops sp. found around the head and in the chest region are schematically represented. Stippled line marks the outline of the concretion.

Figure 1. Map and corresponding composite stratigraphic section of the locality of Cerro Colorado, Pisco Basin, southern coast of Peru, showing the distribution of 12 skeletons of the extinct beaked whale Messapicetus gregarius in the outcropping Pisco Formation. Note the concentration of specimens (including specimen O38 associated with fish remains, coloured in red), in a few layers of the lower allomember.

Figure 4. Phylogenetic tree illustrating the relationships between extant and part of the extinct ziphiids. The outgroup is the eurhinodelphinid Xiphiacetus. Grey (red) lines indicate stratigraphic ranges. Dotted lines indicate uncertainty for the age of some members of a genus. Separation between epipelagic and deep-diving taxa is based on morphology, platform versus deep-sea deposits for fossil taxa, stomach content analysis for Messapicetus, and optimization of the deep-diving ecology of most extant genera on the phylogenetic tree.
Olivier Lambert, Alberto Collareta, Walter Landini, Klaas Post, Benjamin Ramassamy, Claudio Di Celma, Mario Urbina and Giovanni Bianucci. 2015. No Deep Diving: Evidence of Predation on Epipelagic Fish for A Stem Beaked Whale from the Late Miocene of Peru. Proc. R. Soc. B. DOI: 10.1098/rspb.2015.1530
Fossilised Meal Illustrates Habitat Shift of Beaked Whales
Olivier Lambert, Giovanni Bianucci and Klaas Post. 2010. High concentration of long-snouted beaked whales (genus Messapicetus) from the Miocene of Peru.
Palaeontology. 53(5); 1077–1098. DOI: 10.1111/j.1475-4983.2010.00995.x

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