Chronostratigraphic distribution of cetaceans in the Pliocene of Northern Apennines (Italy): palaeoecological implications

The awkward record of fossil whales

“…One yet unresolved mystery is the advent of gigantism among whales (Deméré et al, 2005;Lambert et al, 2010Lambert et al, , 2013Slater et al, 2017), given that the unexpectedly very limited Pleistocene global record of the mysticetes fails to document critical evolutionary steps that lead to the modern fauna, while single findings suddenly set the clock back with respect to previous generalisations (Bianucci et al, 2019). The hypothesis that Pleistocene glacial cycles are responsible for an increased exposure and erosion of shelf area, limiting the preservation potential of Pleistocene cetacean fossils (Deméré et al, 2005;Slater et al, 2017), has not been tested, nor it is sustained by the Mediterranean geological record, where a large volume of Pleistocene shelf and bathyal sediments has been available for collecting (e.g., Benvenuti et al, 2006;Dominici et al, 2011;Zecchin et al, 2012;Regione Emilia-Romagna, 2019), with small results with respect to what is found in the Pliocene (Freschi et al, 2019).…”

“…Think Pleistocene marine successions are also found in other regions (Van Couvering, 2004;Bianucci et al 2006). Local and regional studies are invoked as means to unravel relationships between productivity and cetacean diversity (Pyenson et al, 2010;Marx and Uhen, 2010b), much insight on ecosystem structure being gained by studying the taphonomy (e.g., Dominici et al, 2009;Gariboldi et al, 2015;Gioncada et al, 2018) and the high-resolution stratigraphic framework of fossil cetaceans (Peters et al, 2009;Pyenson et al, 2009Pyenson et al, , 2014Danise et al, 2010;Bianucci et al, 2016b;Dominici et al, 2018;Freschi et al, 2019;Cutiño et al, 2019;Gee et al, 2019). From two different perspectives, stratigraphic paleobiology (Holland and Pazkowski, 2012) and cetacean actuopalaeontology (Schäfer 1972;Smith et al, 2015) Available evidence suggests that the quality and quantity of fossil whales depends on position along the bathymetric paleoprofile.…”

“…From two different perspectives, stratigraphic paleobiology (Holland and Pazkowski, 2012) and cetacean actuopalaeontology (Schäfer 1972;Smith et al, 2015) Available evidence suggests that the quality and quantity of fossil whales depends on position along the bathymetric paleoprofile. Complete or partially articulated skeletons are particularly abundant in offshore shelf marine sediments in the late transgressive and highstand systems tracts of depositional sequences (basal Cetacea: Peters et al, 2009;crown Cetacea: Di Celma et al, 2018;Dominici et al, 2018;Freschi et al, 2019). Isolated and reworked bones are often found in condensed deposits and shell lags at maximum flooding intervals (Pyenson et al, 2009;Dominici et al, 2018), or in fluvial deposits above sequence boundaries (Peters et al, 2009).…”

“…Isolated and reworked bones are often found in condensed deposits and shell lags at maximum flooding intervals (Pyenson et al, 2009;Dominici et al, 2018), or in fluvial deposits above sequence boundaries (Peters et al, 2009). When comparisons are made, slope deposits provide a small fraction of the total record of a given region (Dominici et al, 2018;Freschi et al, 2019). Articulated whale skeletons in beach deposits are rare (Pyenson et al, 2014; if present at all, the association with cross-bedded sandstones belonging to the category of delta front paleoenvironments, where sudden sediment inputs eventually cover carcasses and allow for the preservation of pristine skeletons: e.g., Dominici et al, 2018).…”

“…This is expected to occur during forced regressions, when high-density turbidity currents become the main depositional mechanism seaward of river mouths (Catuneanu 2019). The best fossil record so far is associated with shelf and bathyal deposits, increasing in thickness during transgressive pulses, at maximum flooding intervals, and during highstands of sea level (Peters, 2009;Di Celma et al, 2018;Dominici et al, 2018;Freschi et al, 2019). Alongside a recurring, sequence-stratigraphic control on the quality and abundance of fossil whales, bone-eating worms could constitute a long-term unidirectional biotic driver in what has been called "Osedax effect" (Kiel et al, 2010, see also Higgs et al, 2012).…”