A critique of the juvenile Dikika fossil publication

I have just returned from a presentation lead by UC Berkeley paleoanthropologist Tim White. Lil Lucy Long Bones I must say, even as the paper came out, I had reservations about it all. I was once taught by my physical anthropologist to always accept new finds in paleoanthropology with a skeptical eye. Suffice to say, after hearing what White has said, I have a lot to say about the public relation hurricane spun by the new Nature publication, “A juvenile early hominin skeleton from Dikika, Ethiopia.”

After reading the paper, I immediately had beef with the claims from Zeresenay Alemseged et al. that this specimen has a “gorilla-like scapula.” To me, I didn’t see why and how, an australopithecine would have a scapula that is more similar to a more primitive ape than say a chimpanzee. Australopithecines are well documented to be bipedal, with a restructed lower limb morphology to support walking on two feet. Even this specimen shows a robust calcaneus (bone on the lower left of the image to the right) and a buttressed tibia (bone on the lower right of the image to the right) to support the weight of the organism on two limbs. Why then would it have a scapula of a gorilla, who is so outrageously robust, and specialized for a different mode of locomotion and ecological context? What is the evolutionary signifance of carrying such a hefty upper body when you are primarily bipedal? Let me remind you gorillas live in dense rain forrest, for the most part and are often arboreal… whereas all australopithecine fossils have been found in stratigraphic layers that represent savannah mosiac and marshland like ecosystems.

As I continued to read the paper, the authors showed the scapula from multiple angles. They showed a comparative anatomical lineup of the Dikika scapula to a human, gorilla, and chimpanzee one. In their analysis they documented that the scapula is proportionally similar to a gorillas, based on the infraspinatus to supraspinatus regions. But you have a look for yourselves, the image to the right is the picture the authors provided in their paper.Lil Lucy Scapula To the top left (a) is Dikika, (b) in the top right is a gorilla’s scapula, and (c) and (d) are human and chimpanzee scapula respectively. Just eyeballing it, the regions above and below the spine of the scapula are equal in the gorilla. In contrast, Dikika’s portions looks similar to a humans… where the supraspinatus region looks about a third of the size of the infraspinatus region.

The authors specifically measured only an abstract angle and breadth of the infraspinatus region of the scapula and called it signfiicantly similar to African apes, specifically gorilla like. But! If you know anything about osteology, free floating bones such as the os penis (bacculum), hyoid, patellae, and scapula are highly variable. The shape and morphology of the bone is highly specialized to that particular inidividual’s life history. For example, as White pointed out, there are populations of native Americans on the Pacific coast, which have scapulae that are remarkably unlike modern humans. So how can you use this bone as a signficant marker of gorilla-ness?

I specifically noticed that the measurements of Dikika’s glenoid fossa do not quite match up with that of a gorillas, either. The glenoid fossa is the point of articulation of the scapula, the shoulder blade, and the humerus. In arboreal organisms, such as gorillas and other primates that spend some time up in the trees the glenoid fossa is a wide and deep joint. This is significant because a joint like that bears a lot of stress, force, and needs to be stable in order to support the organism. In humans, who are not arboreal as you may already know, the glenoid fossa is not as deep. It is a shallow joint that allows for flexibility at the cost of joint stability. That’s why people discolate their arms frequently and get so many rotator cuff injuries, while gorillas do not.

To me, the glenoid fossa is the most significant indicator on how gorilla-like the scapula is. I say that because the glenoid fossa is the point of interest in understanding how strongly the arm is connected to the body. While, I do not have an image of the glenoid fossa of Dikika, let me document that the supplementary information for the paper writes that the Dikika glenoid fossa size is 14mm which falls between roughly +/- 1mm standard deviation of human and chimpanzee scapula of the same age. In contrast a gorilla scapula is over 20mm in size! A 6mm difference is far too significant for me to call it only gorilla– so why then did Zeresenay Alemseged and Nature allow this to be published?

Listening to White, I was introduced to many other reasons as to why Alemseged, Nature, and the whole system behind this paper let a detail like this pass on by. I’m not a professional paleoanthropologist, to say the least, but I can smell a dupe just like anyone else… for example, what’s up with calling Dikika a female? Sexing a fossil is nearly impossible, especially with a immature juvenile, lacking the bones of the pelvic girdle. You need multiple specimens, erupted permanent molars… and this paper doesn’t even document the measurements of the “lower canine mesodistal diameter” that allowed them to define a sex.

Furthermore, A. afarensis is not a sexually dimorphic taxon… unlike A. boisei. And sexual dimorphism does not manifest in any primate skeleton, that I know of, until after puberty/maturation. A three year old, with unerupted permanent molars is too early to sex.

White also told us the tales meeting with other paleoanthropologists… like W. H. Kimbel and his research methods and ethics, in the 1990’s. I now wonder about the scientific authority of team Alemseged gathered up because of what I heard from White. See, Kimbel, is a famous paleoanthropologist, and worked with Donald Johanson ( “grandfather of Lucy”) back in the ’70’s, and he is a co-author for this new Nature paper. According to White, Kimbel was once criticsized, by him, on how he collected specimens from the various sites in Afar. Kimbel is known for his work in north (and some of south) Hadar, and that region is so prone to dramatic changes in geomorphology. After one rain, the run off from the sides of the hills really displaces fossils, but Kimbel seemed not to care when White told him he should pay attention to this detail… enough to become fairly hostile to him.

I now raise the question, influenced by White, “how much of this Dikika fossil is left in the field because of Kimbel’s sloppy collecting methods?” …One can assume, that as Alemseged’s mentor, and his past history of not being thorough in excavating they both neglected to fully search down stream for the rest of Dikika. Since the Dikika long bones clearly show post fossilization, 90 degree breaks, the specimen was not consumed by a predator; so the rest of the fossil is out there. Why then has such a rare spectacular specimen like this not be excavated with more care and attention? Could it be the nature of Kimbel’s researching, or was Alemseged pressured to excavated faster because of financial reasons?

White went through a lot more criticisms of this paper… but I want to clarify that he never questioned the impact and importance of Dikika. He only cited that there are a lot of details that are not well substantiated… and they, in his and my opinion, are not thorough enough be published in a paper like Nature as well as be marketed like a super-ultimate-fantastic paleoanthroloogical finding. In all reality, this finding has not taught us anything new about what we already know about australopithecines, for example we already knew that metacarpals of A. afarensis are curved less than apes but more than humans. That was established in the ’60’s! Alemseged could really have spent a lot more time teaching us more about what is signficantly different about this fossil!

If you take a look at the P.R. media blitz unleashed by this paper, and correlate it with the faulty scientific methods, I think you can begin to see that this Nature paper was released a little prematurely. Nature even devoted a damned video page for it, but overlooked key details! Perhaps pressure from the funders of the research, the National Geographic Society, who were itching for a find of the year, was a factor to consider. Last year we had the Hobbit, and so far this year we have had not a big paleanthropological finding. In my opinion, and should this be the case, I believe this is where big business has done a disservice to science and the scientific process.

This paper has been published in Nature, the cream of the crop of scientific publications, despite the gapping holes that I have outlined from Whites observations and my readings. Journals like this, set the standard for the whole discourse, and in all honesty this paper shows how flawed the peer review process is. It can be tainted and influenced to hastily publish papers that needed more time and in depth analysis, just for the sake of publicity.

If you want to read other criticisms of the paper, please check out Owen Lovejoy of Kent State University’s words in Kate Wong’s SCIAM OBSERVATIONS.

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