Final answer:
Orrorin tugenensis may not be considered a hominin due to uncertainty in its classification, the possibility of the australopithecines being part of the human lineage, and limited knowledge about its anatomical features.
Step-by-step explanation:
Orrorin tugenensis may not be considered a hominin due to several reasons. First, although Orrorin exhibits some anatomical traits that suggest bipedalism, there is still debate and uncertainty regarding its classification as a hominin. Additionally, the discovery of Orrorin does not necessarily exclude the possibility that the australopithecines are part of the direct human lineage. Finally, the scarcity of specimens and the limited knowledge about Orrorin's anatomical features make it challenging to determine its exact classification.