In preparation for today’s Nature paper on Dmanisi, yesterday I went over some of the hot Homo fossils that have come from Dmanisi. But I focused only on remains of the head. And of those remains, what I went over was a whole range of features, proportions, and sizes, that showed a lot of variation in early Homo cranium from Dmanisi. Size-wise, the fossils have been more in the range of H. habilis than erectus, but feature by feature each one seemed to have bits and pieces of what we acknowledge as H. erectus.
The paper that I’ve been waiting for, “Postcranial evidence from early Homo from Dmanisi, Georgia,” reminds me that there are other fossils than ones from the head, to analyze. Especially from such a rich site.
In this new paper, David Lordkipanidze and all the other authors, describe new fossils of the postcranial, of a teenager that is associated with D2700 cranium and 2735 mandible as well as three adults who are also associated with other fossils. The elements analyzed are pictured to the right. This last section of the abstract is the most important,
“This material shows that the postcranial anatomy of the Dmanisi hominins has a surprising mosaic of primitive and derived features. The primitive features include a small body size, a low encephalization quotient and absence of humeral torsion; the derived features include modern-human-like body proportions and lower limb morphology indicative of the capability for long-distance travel. Thus, the earliest known hominins to have lived outside of Africa in the temperate zones of Eurasia did not yet display the full set of derived skeletal features.”
So we’re looking at at least four people in this collection of bones. As I mentioned, the authors think they have the teenager’s skull and mandible. The other parts, such as a left clavicle, some ribs, a set of cervical and thoracic vertebrae with one lumbar vertebrae, both humeri but one is broken, a left femur, and several bones of the hands and feet, of this youngin’ are the seen in “a”, all the bones in the left half of the above image.
So how do they know that these are the bones from the same individual? Well, I’m pretty sure they don’t know for sure because they did say a minimum of four people… But because the bones were found in the same stratigraphic layer, in close proximity to one another…. And that the cranial and postcranial bones both show similar developmental stages, such as fusion patterns in the sutures of the skull and fusion patterns of the epiphysis (ends) of long bones to the shaft, or diaphysis, they can make this claim with some confidence.
The other three individuals, two small folk and one larger person, weren’t anywhere close to the teenager. The large adult is represented by a big right femur, whole tibia, and a patella… which all articulate snuggly. That’s how they figured out this was one individual. The other two small ones are represented by metatarsals and bones of the feet from different stratigraphic layers.
This is an impressive collection of bones. Having more than one individual from the same place and time helps paint a much better picture of what was going on with early Homo than would a single skeleton. In the following paragraphs, I’m gonna summarize the analysis of each element.
D4166 – The Adult Right Scapula
This element has a short and wide coracoid process and a narrow glenocoracoid angle, which are primitive, great-ape like traits. But the position of the glenoid to the spine as well as the breadth of the spine fall right at the bottom of modern human variation and resemble Turkana Boy.
D2724, D4161 & D4162 – The Clavicles
These clavicles represent the right and left sides. As you can see, both D4161 and D4162 are missing the sternal and acromial ends. D2724 is a bit better and is similar to modern day teenagers in shaft length. Since all of these clavicles have a middle portion, the cross sectional shape was analyzed. That feature resembles H. habilis.
D2680, D2715, D4507 – The Humeri
The Dmanisi have straight humeri but a lot of torsion and lateral epicondyles that are higher than the lateral condyles which are all seen in most great apes, and other ancient hominin humeri. Modern humans do not have as much torsion.
D2673, D2674, D26721, D2713, D2672 – The Vertebrae
These vertebrae, such as the slope of the articular processes, represent primitive australopithecine-like or even great-ape like form. But since the spinal process is short, narrow, and the canal shapes of all the vertebrae are wider side to side, these bones represent more modern traits.
D4167 – The Femur
This is the most complete femur of an early Homo individual. It has a defined linea aspera, a ridge on the femur that serves as an attachment for the adductors and the intermuscular septa. It is very robust, straight. The neck of the femur, where the leg is attached to the hip, is similar to the autralopithecines and the bicondylar angle, a measurement of how the femur rests on the tibia, is similar to australopithecines too.
D3901 – The Tibia
This is the first complete fossil hominin tibia, pretty cool. It too is robust, and the joint surfaces on the top and bottom are large. The mid-shaft, though, is less robust and the degree of torsion is similar to modern humans…. something not seen that much in other great apes.
There are other bones, such as the the patella, the talus, and metatarsals which I’m not gonna review for several reasons, one of which is that this post has gotten long enough already. The second reason is that I think you can see that Lordkipanidze et al., have been really thorough in documenting how these specimens are a hodgepodge of archaic and modern traits. Very indicative of some sort of transition going on.
In their conclusion, the authors say, the most definitive, ancestral trait is the torsion seen in the humerus. And since the Dmanisi postcranial remains and endocranial volumes are awfully close in size to H. habilis that suggests the first hominis out of Africa weren’t completely like the H. erectus originating in Africa. What does that mean really? That means a wave of more primitive Homo fled Africa, all the while African hominins were doing their own thing. Does this mean once the African H. erectus figured it out and moved out of Africa, that these primitive Homo were replaced? This study certainly suggests that.