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The herpetological diversity recorded in the Santa Cruz Formation (late Early
Miocene) is low when compared with that of birds and mammals. It includes the
calyptocephalellid anuran Calyptocephalella,
an indeterminate “leptodactylid,” indeterminate pleurodont
iguanians (including those previously assigned to the extinct genus
tupinambine teiid Tupinambis, and
indeterminate “colubrids.” The presence of Calyptocephalella in the Estancia La Costa locality represents
its southernmost record and might indicate the occurrence of permanent lowland
lakes, ponds, and quiet streams, possibly developed in a forested area. The
presence of Tupinambis and
“colubrids” at around 50° S represents the southernmost
record in their respective evolutionary histories, suggesting warmer and
probably more humid conditions in the late Early Miocene than those prevailing
in southern Patagonia at present. Based upon the diets of extant Calyptocephalella and “colubrids” we
consider the Santacrucian Miocene representatives to be small carnivorous
vertebrates. Santacrucian pleurodont iguanians should be included in the
insectivorous and/or herbivorous groups, whereas Tupinambis would have been a generalist omnivorous reptile.
This chapter describes the paleobiology of Santacrucian cingulates (armadillos
and glyptodonts). At least five genera of armadillos and four genera of
glyptodonts were sympatric in the Santa Cruz Formation. Body masses were
calculated based on a variety of scaling models, allometric equations, multiple
regressions, and geometric similarity. The locomotor habits were inferred from
indices previously modeled in living dasypodids, using morphogeometric analyses
and the application of a strength indicator. Feeding habits were inferred from
jaw biomechanics, and the shape, arrangement, and wear patterns on teeth, and
from ecomorphological analyses. All armadillos fall in the range of medium-sized
living armadillos, and all glyptodonts are larger than any living armadillo,
slightly greater than 100 kg, but are smaller than Middle
Miocene–Pleistocene glyptodonts. All Santacrucian armadillos were good
diggers but none reached the degree of fossoriality found in some specialized
living taxa; all glyptodonts were ambulatory. The variation in the masticatory
apparatus of the armadillos exceeds that in the living species, denoting a
broader range of specializations and strong niche partitioning among the fossil
species. The degree of variation in the masticatory apparatus of glyptodonts
suggests differences in the selectivity of feeding and habitat preference. The
taxonomic richness of armadillos is similar to that recorded today in the
Chaqueña biogeographic province, supporting the environmental
interpretation of a mixture of open and relatively closed vegetation in
relatively dry conditions.