Zygodontomys, Allen, 1897

Mistretta, Brittany A., Giovas, Christina M., Weksler, Marcelo & Turvey, Samuel T., 2021, Extinct insular oryzomyine rice rats (Rodentia: Sigmodontinae) from the Grenada Bank, southern Caribbean, Zootaxa 4951 (3), pp. 434-460 : 452

Grenada Bank Zygodontomys : natural or human-mediated dispersal?

Although genetic data are not available to determine the timing of divergence between Grenada Bank Zygodontomys and neighbouring populations ( Brace et al. 2015), conspecificity of these populations indicates that divergence must have been geologically recent. It is possible that arrival of Zygodontomys on the Grenada Bank represents a natural overwater dispersal event mediated by northward-flowing oceanic currents within the southern Caribbean basin ( Hedges 1996). The possibility of natural overwater dispersal is supported by the historical occurrence of the mainland Neotropical oryzomyine species Oryzomys gorgasi on Curaçao ( Voss & Weksler 2009), another southern Caribbean island that remained unconnected to the South American mainland during the Late Quaternary, and which also supported endemic oryzomyine taxa ( Hooijer 1959; Zijlstra 2012; Zijlstra et al. 2014). Conversely, the occurrence of this widespread species on the Grenada Bank might instead indicate deliberate or accidental human-mediated translocation (‘ethnophoresy’), suggesting that Megalomys might be the islands’ only native rice rat.

Numerous mammal species, including several rodents, are known to have been translocated around the insular Caribbean as food resources during prehistory, either between islands or from the South American mainland ( Hooijer 1963; Newsom & Wing 2004; Silva Taboada et al. 2007; Díaz-Franco & Jiménez Vásquez 2008; Giovas et al. 2012; Giovas 2019a; LeFebvre et al. 2019). In addition to guinea pigs ( Cavia porcellus ), which were domesticated between 5500 and 2500 BCE and were moved widely around the circum-Caribbean region, numerous non-native South American mammal taxa are also present in pre-Columbian midden contexts on Grenada and Carriacou ( Dasyprocta , Dasypus , Didelphis , Mazama , Odocoileus , Tayassu / Pecari ) ( Newsom & Wing 2004; Giovas et al. 2012, 2018b). Indeed, human movements continued between Grenada and northern South America throughout the Late Ceramic Age, and were associated with mainland-driven shifts in resource use and material culture on Grenada ( Hanna 2018). The arrival of Zygodontomys on the Grenada Bank might therefore represent deliberate translocation as a food resource. However, Zygodontomys is smaller than other oryzomyines that occur regularly in pre-Columbian middens in the Lesser Antilles ( Table 5 ), and is also much smaller than other non-native mammal species present in middens on the Grenada Bank ( Giovas 2019a). Small-bodied muroid rodents are now present on many islands worldwide as a result of widespread inadvertent human-mediated translocation during the historical period and recent prehistory (e.g. Yalden 1999; Searle et al. 2008; Bonhomme et al. 2010). The occurrence of Zygodontomys in archaeological contexts might therefore reflect commensalism rather than consumption, with its arrival on the Grenada Bank representing accidental rather than deliberate prehistoric introduction. Palaeontological investigation and/or ancient biomolecular research are required to test between these varying hypotheses concerning the colonisation pathway of Zygodontomys .