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<p>Sloths (Folivora) display remarkable morphological diversity yet share a highly conserved dental formula, whose occasional deviations offer key insights into their evolutionary history. Among nothrotheriids, Neogene species retained upper and lower caniniforms, whereas these teeth were lost in Pleistocene genera. Here we describe, for the first time, a poorly developed alveolus interpreted as an atavistic upper caniniform alveolus in an individual of <i>Nothrotherium maquinense</i> from the Late Pleistocene of Bahia, Brazil. Computed tomography and X-ray imaging confirm its internal anatomy and rule out taphonomic or pathological origins. The alveolus occupies the precise position of the caniniform in Neogene nothrotheriids and exhibits similar morphology, suggesting a partial re-expression of a lost ancestral trait. Beyond its developmental implications, this observation may offer additional context for interpreting the taxonomy of <i>Nothropus</i>, traditionally defined based on the presence of a lower caniniform alveolus. The occurrence of similar atavistic structures in related taxa indicates that this feature alone may be insufficient for diagnosis and warrants reevaluation within a broader evolutionary framework.</p>

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The presence of an atavistic caniniform alveolus in Nothrotherium maquinense (Xenarthra, Folivora, Nothrotheriidae)

  • 期刊论文

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  • 发表日期：

    2026年5月20日

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  • Daniel M. Casali,
  • Claudia G. Costa,
  • Fernando H. S. de Barbosa,
  • Fellipe P. Muniz,
  • Gabriel Mestriner,
  • Rodrigo Parisi Dutra,
  • Rachel E. Narducci,
  • H. Gregory McDonald,
  • Camille Fonseca Tostes,
  • Izabella Lucas de Abreu Lima,
  • Flávio Ricardo Manzi,
  • Luciano Vilaboim Santos

摘要

Sloths (Folivora) display remarkable morphological diversity yet share a highly conserved dental formula, whose occasional deviations offer key insights into their evolutionary history. Among nothrotheriids, Neogene species retained upper and lower caniniforms, whereas these teeth were lost in Pleistocene genera. Here we describe, for the first time, a poorly developed alveolus interpreted as an atavistic upper caniniform alveolus in an individual of Nothrotherium maquinense from the Late Pleistocene of Bahia, Brazil. Computed tomography and X-ray imaging confirm its internal anatomy and rule out taphonomic or pathological origins. The alveolus occupies the precise position of the caniniform in Neogene nothrotheriids and exhibits similar morphology, suggesting a partial re-expression of a lost ancestral trait. Beyond its developmental implications, this observation may offer additional context for interpreting the taxonomy of Nothropus, traditionally defined based on the presence of a lower caniniform alveolus. The occurrence of similar atavistic structures in related taxa indicates that this feature alone may be insufficient for diagnosis and warrants reevaluation within a broader evolutionary framework.