The nine banded armadillo (Dasypus novemcinctus) is the only xenarthran mammal to have naturally expanded its range into the middle latitudes of the USA. It is not known to hibernate, but has been associated with unusually labile core body temperatures. Like some other xenarthrans (but unlike mammals in general), Dasypus also shows relatively frequent departures from species-typical thoracic and lumbar vertebral counts. If and how intrauterine temperature variation in xenarthrans might increase skeletal variation during development, and how xenarthran body temperature varies according to season, housing, and gestational status, are unknown. Here, we report temperatures recorded from 19 female armadillos over the course of three seasons (each for at least one month between November and July), tracking internal body temperatures recorded every 6 to 120 minutes. Average temperatures are similar regardless of housing inside or outside, gravid or nongravid. Nongravid individuals housed indoors show significantly higher daily fluctuations than other treatment groups, despite more stable ambient temperatures indoors than outdoors. Assuming that our estimates for implantation are accurate, gravid individuals show, on average, slightly lower daily fluctuations than nongravid, but the difference is not significant and some of our most extreme fluctuations (6-9C within 24 hours) took place in gravid animals. Compared to animals housed outdoors, lab-housed individuals less frequently exhibit body temperatures above their overall mean during typically dormant hours (e.g., afternoon), and body temperatures below their overall mean during typically active hours (e.g., early morning). Temperature periodicity as measured by discrete Fourier transforms shows strong 24 and 12 hour cycles in all individuals, reflecting circadian rhythms. CT scans of monozygotic quadruplets from dams with known body temperatures show a surprising range of phenotypic variation. While all offspring had seven cervicals, and most had ten thoracics, five lumbars, and three sacrals, three of twelve CT-scanned litters had nine rather than 10 thoracics and some offspring of one dam had two sacrals. Dams for two of these exhibited low average temperatures (<35C) early in their gestation. Two dams had offspring with a polymorphic axial skeleton, despite being genetically identical quadruplets. Our data demonstrate the thermal and phenotypic lability of D. novemcinctus but do not decisively link gestational temperatures with particular vertebral phenotypes.