Taphonomy, new perspectives: a chapter in a book of sauropods.
Taphonomy: Overview and New Perspectives Related to the Paleobiology of Giants
Bernardo J. González Riga, Gabriel A. Casal, Anthony R. Fiorillo, and Leonardo D. Ortiz David
Abstract Most taphonomy studies of South American sauropodomorphs have addressed extrinsic factors such as sedimentary environments, bone dispersal, and mineralogical processes that occurred during fossil diagenesis. These studies provide important data on the taphonomic modes which are associated with bone accumulations in different paleoenvironmental contexts. However, these analyses have generally not considered intrinsic factors like the shape, size, and structural integrity of the skeletal elements, variables that can produce some taphonomic bias. Sauropodomorphs include dinosaurs of highly varied sizes, ranging from small (less than 8 m long) to remarkably giant forms (around 30 m long). In the largest sauropods, such as the huge titanosaurs, very incomplete skeletons are commonly found and most notably skull and articulated pedes rarely are preserved. We focus here on some intrinsic anatomical factors as they relate to articulation in some key parts of the skeletons. Further, this study suggests that the preservation of fragile portions of sauropodomorph skeletons was possible only under specific combinations of sedimentological and biological processes.
Keyword Taphonomy · Sauropoda · Extrinsic factors · Taphonomic modes · South America
Taphonomy is the study of all biotic and abiotic factors that influence the preservation of organismal remains after death (Behrensmeyer and Kidwell 1985; Behrensmeyer et al. 2000). Fiorillo and Eberth (2004) succinctly point out that ‘Taphonomic factors remove or modify information about living organisms and assemblages (e.g., soft tissue decomposition, bone dispersal) and therefore create a biased picture of their biology and environmental and ecological associations.’ Dinosaur taphonomy, then, is a multidisciplinary science with diverse aims and applications (Lyman 1994). In many regions of the world. taphonomy studies have had a relatively important multidisciplinary development. These studies typically include sedimentologists and paleontologists combining their expertise to understand the origin of fossil assemblages (Behrensmeyer and Kidwell 1985; Fastovsky et al. 1997; Eberth et al. 2001; Rogers et al. 2001; Fiorillo and Eberth 2004; Moore and Norman 2009; Csiki et al. 2010; Orr et al. 2016; Botfalvai et al. 2017). In South America, taphonomic studies have increased in recent years, incorporating new methods and techniques, but they fall short with respect to the growing and numerous discoveries of new species of sauropodomorphs. This is particularly unfortunate given that the last few decades have seen a tremendous growth in discoveries of new taxa of sauropods (Martínez et al. 2016; González Riga et al. 2016, 2019; Carballido et al. 2017). Further, given the enormous body size of many of these dinosaurs, in this chapter we explore how sauropods can provide unique insights into taphonomic processes that smaller-bodied vertebrates, including other dinosaurian clades, cannot offer. This is particularly evident in the examples of large, massive animals with skeletons 30 m long that cannot be covered by most fluvial sedimentary processes. This report will provide an overview that highlights the insights gained by studying such an unusual group of dinosaurs. In South America, most taphonomic studies of Triassic and Jurassic dinosaurs are focused on whole vertebrate assemblages, including some paleoecological aspects related to the increase of abundance, diversity, and body size of sauropodomorphs from the Late Triassic onwards (Martínez et al. 2011, 2013). Some taphonomic reviews focus on taphonomic modes (sensu Behrensmeyer 1988; Behrensmeyer and Hook 1992) and sedimentary environments (Colombi et al. 2012, 2017; Otero et al. 2019a). The Cretaceous fossil record from this continent includes 71 known and valid sauropod species, most of them titanosaurians. Recent studies on sauropod occurrences have included information about the preservational processes (i.e., biostratinomy, fossil diagenesis), and in some cases, the characterization of taphonomic modes, such as in the case of Mendozasaurus neguyelap (González Riga et al. 2007), Bonitasaura salgadoi (Pérez et al. 2009), Aeolosaurus colhuehuapensis (Casal et al. 2014a), and Pilmatueia faundezi (Pino et al. 2021). Additionally, important taphonomic studies of exceptionally preserved nest, eggs, and embryos have been made in Auca Mahuevo in northern Argentinean Patagonia (Chiappe et al. 1998, 2005; Salgado et al. 2005; García et al. 2010) as well as in Sanagasta in northwestern of Taphonomy: Overview and New Perspectives … 543 Argentina, shedding insights on both paleoenvironmental aspects and the gregarious behavior of sauropods (Fiorelli et al. 2012, 2013). The aim of this chapter is to bring forward primary taphonomic observations that focus specifically on South American Cretaceous sauropodomorphs, including the analysis of some intrinsic and extrinsic factors related to accumulation of large skeletal elements. Moreover, a new nomenclatural code is proposed in the analysis of taphonomic modes, to facilitate their description and understanding with respect to sauropods, and other relatively large no-avian dinosaurs. Lastly, it is important to point out that for the purposes of this study, as most of the case studies we cite are coincident with the now decades long growing appreciation of the value of taphonomic practices to an excavation, we make the assumption that all available bones were excavated, and removal of skeletal elements was not selective