Meeting Abstract
P1.62 Monday, Jan. 4 Development of the Sacrum in Land Mammals and Cetaceans MORAN, Meghan M.*; GEORGE, Craig; THEWISSEN, JGM; Department of Anatomy and Neurobiology, Northeastern Ohio Universities College of Medicine and Pharmacy; Department of Wildlife Management, North Slope Borough, Barrow, Alaska; Department of Anatomy and Neurobiology, Northeastern Ohio Universities College of Medicine and Pharmacy mmoran1@neoucom.edu
The sacrum of mammals consists of up to 13 fused vertebrae that form part of the bony pelvis and provide support for the hind limb. In some marine mammals the hindlimb and innominate are absent and the synostoses between sacral vertebrae are absent. The evolution of the bony pelvis in cetaceans is well documented by morphological intermediates and includes the reduction of the innominate (loss of acetabulum, loss of obturator foramen) and the reduction of synostoses between the four sacral vertebrae. Interestingly, whereas vertebral synostoses of the sacrum are absent in modern cetaceans, they do occur in the cervical vertebrae of many taxa (Delphinidae, Balaena). To understand the developmental mechanisms associated with sacral evolution in cetaceans we examine developmental controls of sacral synostoses in mouse vertebrae and compare this to protein signaling in the sacrum of cetaceans. We first determine the timing and location of signaling proteins using an ontogenetic series of CD-1 mice ranging from postnatal Day 1 to Day 60. Histological sections of the cervical, lumbar and sacral regions in each murine ontogenetic stage were investigated for expression of Wnt, β Catenin, FGF8, Shh, BMP4, and Pax1. To further understand cervical and sacral fusion in cetaceans, we undertook a morphological study of the intervertebral area in cetaceans. Preliminary CT-scan data indicate that fusion of cetacean vertebral epiphyses begins in the neck and tail, and proceeds toward the thoracolumbar area from these regions. Unlike most large land mammals, several cetaceans undergo vertebral epiphyseal fusion only long after sexual maturity, or forego it altogether.
