Lucy (Australopithecus)
Sacrum and spine

Although this was the case, in the mid-2010s studies came out with new theories as to why Lucy's fifth sacral segment is in that shape. Some researchers conclude that Lucy has only four sacral segments. Published in the American Journal of Physical Anthropology, researchers suggest that fossil damage did not shorten the transverse process and that Lucy's sacrum was in this state from the beginning. This specific study points to Lucy's sacrum having four sacral segments which researchers say conforms with the "long-back" model of hominoid vertebral evolution. There are some disagreements in the community about the fifth sacral segment and if fossil damage was enough to change the fifth segment or if it was originally in that state. Discussed in the Journal, researchers conclude that Lucy having only four sacral segments is consistent with other findings related to early Miocene hominoids.
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