Teeth complexity, hypsodonty and body mass in Santacrucian (Early Miocene) notoungulates (Mammalia)

Abstract

Notoungulates, native South American fossil mammals, have been recently objective of several palaeoecological studies. Ecomorphology and biomechanics of the masticatory apparatus, together with micro and mesowear analyses on tooth enamel, were applied in order to understand their palaeobiology. In particular, the relationship between some dental traits (hypsodonty, occlusal surface area and complexity) and body mass is still poorly understood. These features were measured by means of the hypsodonty index (HI), occlusal surface area (OSA) and tooth area (OTA), enamel crest complexity (ECC) and length (OEL). The relationships between these indices were evaluated in five pan-contemporaneous Santacrucian Notoungulata genera from Patagonia: Adinotherium and Nesodon (Toxodontia), Interatherium, Protypotherium and Hegetotherium (Typotheria). While OSA, OTA and OEL were size dependent and strongly correlated, HI and ECC were size independent. All notoungulates analysed have very hypsodont teeth, indicating high rates of tooth wear in response to an increase of abrasives consumed with the food; their tooth occlusal area and complexity could be related to chewing efforts associated with the toughness of the plants consumed. HI, OSA and ECC were considered useful for palaeoecological reconstructions, but the results presented here show that these three features are integrated as a complex, so should not be evaluated separately.

The Allemann collection from the Santa Cruz Formation (late early Miocene), Argentina, in Zurich, Switzerland

“…For descriptions, the orientation of the teeth follows Smith and Dodson (2003). We follow Soria (2001) for the taxonomy of Litopterna; Billet (2011) and Cassini et al (2017) for Notoungulata, Scott (1905) for rodents, and Abello (2013) for Paucituberculata.…”

“…Comments The p3 and p4 are molariform, there is no labial sulcus, and they have a well-developed lingual sulcus forming the bridge between the trigonid and talonid on the labial side. The labial side of both trigonid and talonid is flat, whereas the lingual side of the trigonid is rounded and the talonid is triangular in cross section (Cassini et al 2017).…”

“…The lower dentition shows well-developed labial and lingual sulci. The bridge between the trigonid and talonid is formed close to the center of the teeth (Cassini et al 2017).…”

“…In the lower dentition, the talonid is bigger than the trigonid in the molars and this relationship is reversed in the premolars. The bridge between the trigonid and talonid is formed close to the labial side of the teeth, giving an asymmetrical occlusal view with a deep labial sulcus and a lingual groove (Cassini et al 2017).…”

Differential influences of allometry, phylogeny and environment on the rostral shape diversity of extinct South American notoungulates

“…specialized herbivory, fast growth; [ 11 ]), largely coincide with changing environments and climates starting by the end of the Palaeogene in South America ([ 12 , 13 ], figure 1 ). However, the relation of notoungulate dental morphology to ecological specializations remains to be explained [ 11 , 14 , 15 ], and its study should integrate the morphology of the whole masticatory apparatus for a better understanding of their evolution and function. A number of morphological traits of the masticatory apparatus were recently integrated into phylogenetic or ecomorphological analyses of notoungulates [ 8 , 16 , 17 ].…”