Abstract
BackgroundA novel physis in hominins modulates broadening and shortening of the ilium. We report analysis of a vascular canal system whose origin may be associated with this physis and which appears to be also unique to hominins. Its presence is potentially identifiable in the fossil record by its association with a highly enlarged foramen that is consistently present in modern humans and hominin fossils.MethodsWe measured the diameter of this foramen in humans, fossil hominins, and African great apes and corrected for body size.ResultsThe mean relative human foramen diameter is significantly greater than those of either Pan or Gorilla. Moreover, eight of the nine values of the Cohen’s d for these differences in ratios are highly significant and support the ordering of magnitudes: Pan < Gorilla < Homo. The relative foramen diameter of A.L. 288-1 is above the 75th percentile of all other hominoids and at the high end of humans. The foramen is also present in ARA-VP-6/500.ConclusionsWe posit that the presence and significant enlargement of this foramen in fossils can reasonably serve as an indicator that its anterior inferior iliac spine emerged via the unique hominin physis. The foramen can therefore serve as an indicator of hominin iliac ontogenetic specialization for bipedality in fossil taxa.
Highlights
The hominin ilium is strikingly superoinferiorly shorter than are the ilia of other primates, and its isthmus is mediolaterally much broader
We previously demonstrated that a unique physis, present only in hominins, likely guides these dimensional differences with other primates
Sirang’s Type III is a single canal that connects the most commonly identified nutrient foramen of the ilium (Ebraheim et al, 1997; Cunningham & Black, 2013; hereafter the NFI) to a solitary foramen lying close to the Anterior Inferior Iliac Spine (AIIS) (Fig. 1C), and which we have identified as the AIF
Summary
The hominin ilium is strikingly superoinferiorly shorter than are the ilia of other primates, and its isthmus is mediolaterally much broader. An unique structure occurring only in hominins, the Anterior Inferior Iliac Spine (AIIS), is formed by an epiphysis that partially covers this growth plate at time of fusion in late adolescence. It is a hominin synapomorphy (Zirkle & Lovejoy, 2019). Its presence is potentially identifiable in the fossil record by its association with a highly enlarged foramen that is consistently present in modern humans and hominin fossils. Conclusions: We posit that the presence and significant enlargement of this foramen in fossils can reasonably serve as an indicator that its anterior inferior iliac spine emerged via the unique hominin physis. The foramen can serve as an indicator of hominin iliac ontogenetic specialization for bipedality in fossil taxa
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