Microstructural defects and enamel hypoplasia in teeth of Toxodon Owen, 1837 from the Pleistocene of Southern Brazil

Abstract

Enamel hypoplasia is characterized by reduction in the enamel thickness, resulting from a disruption of ameloblast activity due to systemic physiological stress. The euhypsodont teeth of Toxodon, a notoungulate from the Pleistocene of South America, often exhibit signs of enamel hypoplasia, in the form of continuous grooves or a series of pits where the enamel is thinner than in normal areas. These defects alternate with areas of normal enamel, and sometimes more than one form of enamel hypoplasia is present on the same tooth. This study analysed teeth of Toxodon from the Pleistocene Touro Passo Formation and the coastal plain of State of Rio Grande do Sul, Southern Brazil. Six types of enamel hypoplasia were observed. Upper teeth present mainly superficial grooves on the buccal surface, and the defects are less severe than those observed in the lower teeth. In the lower incisors, deep grooves with mesiodistal rows of pits were observed, showing clearly cyclical changes, which to a lesser degree, exist in all teeth. These changes are likely related to the continuous growth of euhypsodont teeth. Seven specimens were analysed under scanning electron microscopy and optical microscopy, which showed the occurrence of microstructural changes associated with the macroscopic enamel defects. Enamel underlying in the vicinity of hypoplastic defects was aprismatic and associated with prominent pathologic striae. These pathological findings might indicate that toxodonts were exposed to some stressing conditions or that their teeth were more easily abraded due to a change in diet items, related to shifting climatic conditions.

Dental paleopathology in fossil rhinoceroses: etiology and implications

“…An environmental stress‐induced enamel hypoplasia appears reasonable in the case of P. germanicus because the seasonality might have caused recurrent droughts that contributed to nutritional stress in the extinct rhinoceros. Similar incidences of enamel hypoplasia in deciduous and permanent teeth have been reported in a number of studies including extinct rhinoceroses (Mead, ; Roohi et al ., ), giraffids (Franz‐Odendaal, Chinsamy & Lee‐Thorp, ), pigs (Dobney, ), sheeps and goats (Kierdorf et al ., ), bisons (Niven, Egeland & Todd, ), notoungluates (Braunn, Ribeiro & Ferigolo, ), and primates (Skinner, ; Lukacs, ).…”

Evolução dos Toxodontia da América do Sul durante o Cenozoico: aspectos dentários, paleoclimáticos e paleoambientais

“…Mudanças na morfologia da coroa dos Toxodontia associadas ao desenvolvimento da hipsodontia também podem ser observadas na morfologia microestrutural do esmalte dentário, que se torna adaptado ao consumo de dietas mais abrasivas (Fortelius 1985, Maas 1997, Braunn et al 2014.…”

“…Ao Centro de Microscopia e Microanálise da Universidade Federal do Rio Grande do Sul pela oportunidade de realizar proto e eu-hipsodontes, é possível observar três tipos de esmalte: uma camada interna com o esmalte radial modificado, sucedida pelas bandas de Hunter-Schreger, e, pelo esmalte radial na porção mais externa do esmalte (Lindenau 2005, Braunn et al 2014.…”

Enamel hypoplasia and dental wear of North American late Pleistocene horses and bison: an assessment of nutritionally based extinction models

“…These tooth defects have been extensively used in anthropological and archaeological studies to infer the health of past and present primate populations, including humans (e.g., Goodman and Rose 1990; Moggi-Cecchi and Crovella 1991; Skinner and Goodman 1992; Hillson 1996, 2005; Guatelli-Steinberg 1998, 2000, 2003; Lukacs 2001, 2009; Skinner and Hopwood 2004; King et al 2005; Schwartz et al 2006; Witzel et al 2008; Guatelli-Steinberg et al 2012; Smith and Boesch 2015). In contrast, fewer studies have been conducted on archaeological and paleontological non-primate mammals, including Neogene rhinoceroses (Mead 1999; Roohi et al 2015), domestic pigs and wild boar (Dobney and Ervynck 2000; Dobney et al 2004; Witzel et al 2006), late Pleistocene and Holocene bison (Niven 2002; Niven et al 2004; Byerly 2007), Pliocene giraffids (Franz-Odendaal et al 2004), cattle (Kierdorf et al 2006), Pleistocene equids (Timperley and Lundelius 2008), domestic sheep and goats (Kierdorf et al 2012; Upex et al 2014), and the Pleistocene notungulate Toxodon (Braunn et al 2014).…”