TY - JOUR TI - Homeotic transformations reflect departure from the mammalian ‘rule of seven’ cervical vertebrae in sloths: inferences on the Hox code and morphological modularity of the mammalian neck AU - Böhmer, Christine AU - Amson, Eli AU - Arnold, Patrick AU - van Heteren, Anneke H. AU - Nyakatura, John A. T2 - BMC Evolutionary Biology AB - Sloths are one of only two exceptions to the mammalian ‘rule of seven’ vertebrae in the neck. As a striking case of breaking the evolutionary constraint, the explanation for the exceptional number of cervical vertebrae in sloths is still under debate. Two diverging hypotheses, both ultimately linked to the low metabolic rate of sloths, have been proposed: hypothesis 1 involves morphological transformation of vertebrae due to changes in the Hox gene expression pattern and hypothesis 2 assumes that the Hox gene expression pattern is not altered and the identity of the vertebrae is not changed. Direct evidence supporting either hypothesis would involve knowledge of the vertebral Hox code in sloths, but the realization of such studies is extremely limited. Here, on the basis of the previously established correlation between anterior Hox gene expression and the quantifiable vertebral shape, we present the morphological regionalization of the neck in three different species of sloths with aberrant cervical count providing indirect insight into the vertebral Hox code. DA - 2018/06/07/ PY - 2018 DO - 10.1186/s12862-018-1202-5 DP - BioMed Central VL - 18 SP - 84 J2 - BMC Evolutionary Biology SN - 1471-2148 ST - Homeotic transformations reflect departure from the mammalian ‘rule of seven’ cervical vertebrae in sloths UR - https://doi.org/10.1186/s12862-018-1202-5 Y2 - 2018/07/05/08:10:11 L1 - https://bmcevolbiol.biomedcentral.com/track/pdf/10.1186/s12862-018-1202-5 L2 - https://bmcevolbiol.biomedcentral.com/articles/10.1186/s12862-018-1202-5 N1 - Pages 84 in PDF KW - Axial patterning KW - Cervical vertebrae KW - Constraint KW - Evolution KW - Hox genes KW - Xenarthra ER -