Abstract
Analysis of ontogenetic changes in long bone microstructure aid in vertebrate life history reconstructions. Specifically, osteohistological examination of common fauna can be used to infer growth strategies of biologically uncommon, threatened, or extinct vertebrates. Although nine-banded armadillo biology has been studied extensively, work on growth history is limited. Here we describe long bone microstructure in tibiae and femora of a limited ontogenetic series of nine- banded armadillos (Dasypus novemcinctus) to elucidate patterns of bone growth. The cortex of the smallest individual is composed of compacted coarse cancellous bone (CCCB) and woven tissue. Extensive cortical drift is driven by periosteal erosion and further compaction of trabeculae resulting in an increase in the amount of CCCB. The cortex of the largest specimens is primarily CCCB with thickened endosteal bone and thin outer cortices of lamellar and parallel-fibered tissue. The outer cortices of the largest individuals are interpreted as an external fundamental system (EFS) indicating a cessation of appositional bone growth corresponding to skeletal maturity (i.e. asymptotic or adult size). The EFS forms in femora prior to tibiae, indicating femoral growth rates begin decreasing earlier than tibial in D. novemcinctus. Growth trends in common fauna like the nine-banded armadillo can be used as a foundation for understanding life histories of related, but uncommon or extinct, species of cingulates.
Highlights
Recent molecular work suggests that Xenarthra is one of the four original clades of placental mammals [1,2,3,4,5,6]
The epiphyses of UTCM 801, UTCM 802, and OMNH 39188 were unfused in both elements and we tentatively identify these individuals as juveniles
The femur of UTCM 802 has an endosteal layer of lamellar tissue of varying thickness
Summary
Recent molecular work suggests that Xenarthra is one of the four original clades of placental mammals [1,2,3,4,5,6]. Xenarthra is composed of sloths (Folivora), anteaters (Vermilingua), and armadillos (Cingulata).
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