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BIGGER BIRTHS. "With their innominate decoupled from the vertebral column, the birth canal in basilosaurids may have been considerably larger than that in protocetids. This would have permitted birth of larger, more precocial infants, and we would predict that a near-term basilosaurid fetal skeleton, if found intact, would be positioned to be born tail-first as is seen in living whales." (Innominate are bones of the pelvis). http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0004366 View in LinkedIn

"BIRTH AT SEA was a prerequisite for the first fully-aquatic whales, the Basilosauridae (including Dorudon) which evolved from Protocetidae later in the Eocene. Basilosauridae have reduced hind limbs that no longer contact the vertebral column and could not support the weight of the body on land. Hence they could no longer come out of the sea onto land to give birth." http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0004366 View in LinkedIn

LAND BIRTH. "Preservation of an intact near-term fetal skull and partial skeleton indicates that birth in early archaeocetes involved a single calf that was born head-first as in land mammals, not tail-first as in living whales. This, in turn, indicates that birth almost certainly took place on land during this phase of early whale evolution." http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0004366 View in LinkedIn

BIRTH ORIENTATION. "Cephalic presentation at birth is generally held to be advantageous on land as it enables a newborn to breath during labor. Caudal presentation at birth, in contrast, is generally held to be advantageous at sea as it may reduce the risk of drowning. Caudal presentation may also hold an advantage in water, because it orients the newborn calf to swim parallel to the mother rather than away from her." http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0004366 View in LinkedIn

TRANSITIONAL WHALES. "Archaeoceti are basal cetaceans that document the evolutionary transition of whales from land to sea during the Eocene before the appearance of modern Mysticeti and Odontoceti." Wonderful figures of these transitional whale skeletons. http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0004366 View in LinkedIn