Nothrotheriops shastensis (Hansen, 1978)

Green, Jeremy L., 2009, Dental microwear in the orthodentine of the Xenarthra (Mammalia) and its use in reconstructing the palaeodiet of extinct taxa: the case study of Nothrotheriops shastensis (Xenarthra, Tardigrada, Nothrotheriidae), Zoological Journal of the Linnean Society 156 (1), pp. 201-222 : 216-217

MICROWEAR IN NOTHROTHERIOPS SHASTENSIS :

PALAEODIETARY IMPLICATIONS

Taphonomic processes, e.g. sedimentary transport, weathering, can result in the loss of ecologically significant information in fossilized remains ( Behrensmeyer, Kidwell & Gastaldo, 2000), and possible taphonomic alteration of microwear patterns should be accounted for when examining fossil teeth ( Teaford, 1991). Actualistic studies demonstrate that post-mortem physical weathering or abrasion of enamel results in total obliteration of the original microwear signature, as opposed to creating additional features that might be mistaken for food scars ( King, Andrews & Boz, 1999). Although no comparable actualistic studies are currently available for orthodentine, a similar, yet enhanced, obliteration of microwear features as a result of taphonomic weathering is expected for orthodentine because of its less mineralized state compared to enamel, but this hypothesis remains to be tested. Based on the presence of features that are similar in appearance and distribution with those in extant taxa, this study assumes that the N. shastensis microwear patterns analysed herein are original.

Nothrotheriops shastensis has a high mean number of scratches most consistent with that of extant folivores ( Bradypus ) ( Tables 1, 2; Fig. 5). Scratch texture is more consistently mixed (coarse and fine) relative to the folivore category ( Tables 1, 2), and scratches are visible on a smooth, slightly polished surface which reflects attritional wear through consumption of soft food (browser), similar to Bradypus ( Fig. 1E, F). When N. shastensis is clustered among extant taxa, the microwear signature of this taxon is statistically more similar to Bradypus tridactylus and all other folivores than any other extant species or dietary group ( Fig. 6 ), which strongly advocates an herbivorous diet. Qualitative and quantitative comparison of microwear patterns between N. shastensis and the anomalous cingulate C. centralis reveals overall similarities, yet cluster analysis failed to group these two species together and instead favoured assignment of N. shastensis among extant folivores ( Fig. 6 ). The current data fail to reject the hypothesis that N. shastensis microwear patterns are most similar to extant xenarthran herbivores, implicating orthodentine microwear analysis as a tool for palaeodietary reconstruction within Xenarthra .

Although the high scratch values for this species are most consistent with a herbivorous lifestyle ( Tables 1, 2; Fig. 1E, F), the predominance of a mixed scratch texture (indicating that coarse scratches are present) and the presence of gouges in this animal relative to Bradypus demonstrates that the diet of N.

Rescaled Distance Cluster Combine

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shastensis consisted of more abrasive food than extant arboreal folivores ( Tables 1, 2). Nothrotheriops shastensis fed at or near the ground surface ( Naples, 1987, 1990), where grit is still likely to enter the oral cavity incidentally, and could account for the presence of the coarse features. Consumption of grasses ( Poaceae ) could also explain a more abrasive diet; grass material has been recovered from N. shastensis dung ( Poinar et al., 1998). A combination of these variables is likely to contribute to the coarse features noted in N. shastensis microwear.

A larger, more geographically inclusive sample of N. shastensis teeth should be analysed for microwear patterns in order to provide a statistically more robust definition of N. shastensis microwear patterns, which would allow further dietary reconstruction. Examination of microwear in other extinct members of Tardigrada, including Megatherioidea (i.e. megalonychid and megathere sloths) and the outgroup Mylodontidae (sensu Gaudin, 2004) , would also provide microwear patterns for comparison to elucidate further the feeding habits and diet of N. shastensis .

Figures

Figure 6. Hierarchical cluster dendrogram (same method as Fig. 3) including Nothrotheriops shastensis among all extant xenarthran taxa. Note that N. shastensis clusters with extant folivores (Bradypus).