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The hyoid bulla is present in Chimpanzee hyoid bones, and not in Humans. Does A. afarensis have a hyoid bulla?

enter image description here

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Short answer:

Yes.

Longer but still short answer:

H. heidelbergensis and H. neanderthalensis have a modern human-like hyoid bone. A. afarensis has a hyoid bulla similar to modern chimpanzees.

The hyoid bone is thought by some to be important in human evolution because of its position in the throat and the possibility that morphological changes in the hyoid were important for the development of speech. However, this view is not without controversy, and it is probably not sufficient to use hyoid bone morphology as a definitive marker for development of speech similar to modern humans, though it may be suggestive.

Some quotes from two references on the morphology of the hyoid of A. afarensis:

Alemseged, et al. 2006:

[the hyoid of A. afarensis] "...is most similar to that of juvenile African apes, and unlike that of modern humans11,12. The exposed greater horn is slender, and the body is expanded anteriorly, forming a bulla that is deep relative to its breadth and height..."

Steele, et al. 2013:

"...the Dikika juvenile australopith hyoid is deep for its height (Figure 9) and width and is morphologically chimpanzee-like. This similarity applies both when comparing only subadults from the three extant species (Figure 9A), and when comparing across all observed age classes (Figure 9B..."


References:

Alemseged, Z., Spoor, F., Kimbel, W. H., Bobe, R., Geraads, D., Reed, D., & Wynn, J. G. (2006). A juvenile early hominin skeleton from Dikika, Ethiopia. Nature, 443(7109), 296-301.

Steele, J., Clegg, M., & Martelli, S. (2013). Comparative morphology of the hominin and african ape hyoid bone, a possible marker of the evolution of speech. Human biology, 85(5), 639-672.

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  • $\begingroup$ Is the A. afarensis hyoid bone in the Steele, Clegg, Martelli paper, from Selam (the 3 year old, aka "baby lucy") found in Dikika ? That's the only fossil remnant of an A. ararensis hyoid bone I've come across (nature.com/article-assets/npg/nature/journal/v443/n7109/images/…) From the image, it's difficult to make out a hyoid bulla, and the Steele, Clegg, Martelli paper mentions that they "interpret the morphology", would you happen to know if they go by indirect evidence, and if so, what? $\endgroup$ – homonidae Jul 6 '17 at 21:36
  • $\begingroup$ The Dikika specimen was a child also, 3 years old, and child hyoid bones have different proportions than adult ones (boneclones.com/images/store-product/…) $\endgroup$ – homonidae Jul 6 '17 at 21:36
  • $\begingroup$ I think that paper will be the best you get for an answer - as you say, if there are no other fossils, you aren't going to magically find one on Biology.SE. Steele et al. compare the Dikika sample to juveniles of the extant apes. The line about "interpret the morphology" has nothing to do with the type of evidence they used, they are just referring to comparison of all of the extinct samples with the extant species they studied. $\endgroup$ – Bryan Krause Jul 6 '17 at 21:46
  • $\begingroup$ A quote from the paper in case you cannot access it: "...the Dikika juvenile australopith hyoid is deep for its height (Figure 9) and width and is morphologically chimpanzee-like. This similarity applies both when comparing only subadults from the three extant species (Figure 9A), and when comparing across all observed age classes (Figure 9B..." $\endgroup$ – Bryan Krause Jul 6 '17 at 21:50
  • $\begingroup$ If the extinct sample is one, and its this one nature.com/article-assets/npg/nature/journal/v443/n7109/images/… are details, like the hyoid bulla, preserved? just by looking at it, it looks like its not protruding at the anterior end, i.imgur.com/BYdjvHx.jpg $\endgroup$ – homonidae Jul 6 '17 at 21:55

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