Enamel thickness and enamel growth in Oreopithecus: Combining microtomographic and histological evidence

Abstract

a b s t r a c tOreopithecus bambolii, a large-bodied fossil ape, lived in the Tusco-Sardinian archipelago during the Late Miocene, until ca. 6.7 Ma. Its dentition, an apparent blend of hominoid and cercopithecoid-like features, has been a matter of discussion since its first description, in 1872. While the height and sharpness of its molar cusps recall some Cercopithecidae, Oreopithecus is currently considered by many as more likely related to dryopithecines. Here, we use microtomographic-based quantitative imaging and histological evidence to link outer and inner tooth structural morphology with enamel development in Oreopithecus permanent teeth. The material consists of 14 teeth/crowns from the sites of Baccinello and Casteani, in Tuscany, and Fiume Santo, in Sardinia. In particular, we add to the record of 2-3D of molar enamel thickness topographic variation and enamel-dentine junction morphology, and using high-resolution replicas of the outer crown and ground sections, comparatively assess molar growth trajectory (crown formation times and enamel extension rates). Our results shed new light on dental development of this "enigmatic anthropoid" and provide additional evidence concerning the still debated question of its evolutionary history.

Dental development and age at death of the holotype of Anapithecus hernyaki (RUD 9) using synchrotron virtual histology

“…Oreopithecus (Zanolli et al, 2016) and Anapithecus show faster rates of crown and root extension than Pan M 2 s and more closely resemble those of Gorilla.…”

“…When considering tooth growth as a whole, figures 5 and 6 show that the CFTs of hominoid teeth vary greatly but those with absolutely taller crowns and longer roots appear to achieve this primarily by having faster extension rates in both enamel and root dentine (Zanolli et al, 2016).…”

Is the deciduous/permanent molar enamel thickness ratio a taxon-specific indicator in extant and extinct hominids?

“…We have used the X-ray microtomographic record available to us of specimens which have been previously scanned at: the University of Poitiers, France, by a Viscom X8050-16 system (all extant taxa; original data); the ID 17 beam line of the European Synchrotron Radiation Facility of Grenoble, France (Neanderthals and Oreopithecus; Bayle, 2008;Bayle et al, 2009;Macchiarelli et al, 2006;NESPOS Database, 2017;Zanolli et al, 2010bZanolli et al, , 2016a; the South African Nuclear Energy Corporation (Necsa), Pelindaba, by a Nikon XTH 225 ST equipment (Paranthropus and Australopithecus; original data); and the analytical platform set at the Bundesanstalt für Materialforschung und -prüfung (BAM) of Berlin, Germany (Ouranopithecus; Macchiarelli et al, 2008Macchiarelli et al, , 2009.…”

“…Martin for measurement procedure and standardization (Martin, 1985), the bi-three-dimensional assessment of tooth enamel thickness has become routine in taxonomic and adaptive/evolutionary studies of fossil and extant primates (e.g., Alba et al, 2013;Kono, 2004;Kono et al, 2014;Macchiarelli et al, 2004Macchiarelli et al, , 2009Macchiarelli et al, , 2013Olejniczak et al, 2008aOlejniczak et al, , 2008bOlejniczak et al, , 2008cOlejniczak et al, , 2008dPan et al, 2016;Skinner et al, 2015;Smith et al, 2003Smith et al, , 2005Smith et al, , 2011Smith et al, , 2012Suwa et al, 2009;Zanolli et al, 2015Zanolli et al, , 2016a. Commonly used to infer durophagy and considered as a proxy of the dietary niches exploited by extinct species (e.g., Constantino et al, 2011Constantino et al, , 2012Lucas et al, 2008;Martin et al, 2003;Schwartz, 2000a;Teaford, 2007;Teaford and Ungar, 2015;Vogel et al, 2008), occlusal enamel thickness is seen as intimately related to dietary abrasiveness and selectively responsive to lifetime dental wear resistance (Pampush et al, 2013;Rabenold and Pearson, 2011).…”

Isotopic reconstructions of habitat change surrounding the extinction of Oreopithecus, the last European ape

“…Living under insular conditions, Oreopithecus exhibits morphology strikingly different from other hominoids. In particular, its dentition differs due to its highly cuspidate molars (Zanolli et al, 2015), whose adaptive significance has been a matter of debate since early descriptions by Gervais (1872) and Schlosser (1887) with subsequent reassessments by H€ urzeler (1949, 1958), Bulter and Mills (1959), and Szalay and Delson (1979). Because of its peculiar postcranial features, researchers have alternatively reconstructed Oreopithecus as being slow-moving (Schultz, 1960), an agile suspensory/climber (Harrison, 1986;Jungers, 1987;Sarmiento, 1987;Harrison, 1991), or even a bipedal ape (Straus, 1963; K€ ohler and Moy a-Sol a, 1997; Moy a-Sol a and K€ ohler, 1997; Rook et al, 1999bRook et al, , 2004.…”