A complete 1.8 million year old skull found from Dmanisi, Georgia could be evidence that early hominids are actually all members of a single species. Researchers published their analysis in Science today and argue that the skull’s combination of primitive and more evolved features, such as a small braincase (546 cubic cm) with a large prognathic face.., Similar morphological affinities with the earliest known Homo fossils from Africa, which make it difficult to classify by now accepted definitions of early hominid species.
This month in the Journal of Human Evolution, a new study on the teeth of the Dmanisi Homo erectus has been published. A site in the Republic of Georgia, Dmanisi has yielded a vast quantity of hominin fossils dating to approximately 1.8 million years ago—even an elderly individual without teeth. The discovered crania are remarkably well-preserved, and have given scientists the ability to look at our evolutionary history with higher resolution.
Based on the skeletal remains, how can we ascertain specifics about hominin diet? For this particular study, researchers used microwear analysis on two molars from Dmanisi. Microwear analysis observes the patterning left on teeth by components of specific diets. As one example, tough silicates in plants leave identifiable traces, as do other silica-based sands that end up being chewed.
Comparisons in wear patterns were made with Dmanisi H. erectus and African H. erectus as well as the genus Australopithecus and earlier Homo, to get an idea of where the Dmanisi hominins fit in on the spectrum of microwear diagnostic traits. These diagnostic traits include heterogeneity of the tooth surface, as well as complexity in the roughness of the tooth surface. To give you an idea of general evolutionary trends, Australopithecines typically had larger teeth and thicker enamel to break down tougher, lower quality foods. As later Homo emerged, teeth tended to get smaller and enamel thinner.
The results indicated that the molars of Dmanisi Homo erectus were very similar to African Homo erectus in general. However, there were also characteristics found to be consistent with other earlier hominin species. Overall the authors cautioned against drawing conclusions with such a small number of teeth, saying that meaningful statistical results are unattainable based on the sample size.
According to authors, the wear patterns on the Dmanisi teeth are indicative of hominins that exploited a range of foods. It seems then that versatility and not specialization is what defines H. erectus in both Africa and Europe. The ability to take advantage of a larger resource base is no doubt one of the factors that allowed the first hominins to spread out across such an expansive area.
By Matthew Magnani
Pontzer, H., Scott, J.R., Lordkipanidze, D., Ungar, P.S. 2011.“Dental microwear texture analysis and diet in the Dmanisi hominins.” Journal of Human Evolution 61:683-687.
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.
Tommorrow, Nature will be publishing a new study of the Dmanisi fossil specimens. In preparation, I’m gonna introduce you to the importance of the Dmanisi site, overview the human fossils that have come out of it, and the related debates.
Firstly, Dmanisi is a rich paleoanthropological and archaeological site in Georgia. Multiple lines of evidence date the human occupation at Dmanisi as early as 1.85 million years ago, putting it in the Pleistocene. You ask, “What sort of data?” Layers of ash and sandy sediment, which contain remains along with numerous crude stone tools and flakes, have been dated radiometrically at 1.7 to 1.85 million years old.
Other dating techniques, such as isotopic potassium-argon (K-Ar) and argon-argon (40Ar/39Ar) dating give an age of 1.8 million years ago. Paleomagnetic analysis of the units around the fossil layer, hold a record of change in magnetic polarity about 1.77 million year ago, which correlates to other dated sites, most notably Olduvai Gorge in Tanzania. All of these dating techniques help place Dmanisi as one of the most ancient human habitation sites in Eurasia. Dmanisi is approximately equivalent in age to the oldest H. erectus localities in eastern Africa. The remains found from Dmanisi have become crucial, and at the same time very controversial, to the study of human evolution.
The remains I want to segue into have consistently brought up a heated debate. And since we’re talking early Pleistocene, i.e. 1.8 mya, we are in the Homo lineage. For anyone not in the know, the fossils record for early Homo is spotty. Trying to make sense of the spottiness, many anthropologists have been butting heads about what has been happening to Homo erectus and Homo habilis during a 2 to 1 million year ago time frame. John Hawks reviewed Brown’s revised chronology in 2006. And the most recent debate, the Ilert hominids, have complicated our understandings of what was going with these two taxa in Africa. So to say that H. erectus has a problematical heritage is to grossly simplify matters.
The best Dmanisi fossils from this time frame haven’t, as of yet, clarified the conundrum outside of Africa for us. The first hominid fossil from Dmanisi was a mandible, was found on the last day of the 1991 field season, by Antje Justus. This mandible was assigned as D211.
While the H. erectus versus H. ergaster debate is largely settled in favor of calling everything that was once ergaster synonymous with erectus, at the time, D211 opened a Pandora’s box of sorts because it differs from known H. erectus specimens. D211 has certain similarities to ER992 (pictured) and ER730, both assigned as H. ergaster from Africa. D211 shares the following similarities:
- General form and robustness of the jaw
- Anterior position of the ascending ramus, including the edge of the retromolar space
- The absence of a trigonum mentale
D211 differs from ER992 and ER730 because it has smaller molars and premolars as well as a less receding anterior surface of symphysis. Despite these differences in size, and Brauer and Schulz’s contention that D211 is a representative of H. erectus, D211 was placed closer to H. ergaster group.
Even though the debate over classifying D211 was between calling it H. ergaster and H. erectus, and not H. habilis vs. H. erectus, it did set the tone for agreeing about future hominid finds from Dmanisi.
Fast forward to 1999, when D2280 and D2282 surfaced from the same stratigraphic level as D221. D2280 is an almost complete calvaria. It includes most of the left mandibular fossa of the temporal, a partial cranial base with a damaged occipital, and parts of the greater wing of the sphenoid. It is pictured in the photographs to your right.
You can see it is rounded, and doesn’t have such an angular posterior side, traits seen in H. habilis. The endocranial volume for D2280 is about 775 cm3, making it small… closer to the size of H. habilis than H. erectus. But because D2280 included a supraorbital torus, and shared some proportional similarities to H. ergaster (like WT15000 and ER3733), it was assigned as such.
D2282 is a much more complete specimen. As you can see, it is a cranium with many of the bones of the face and cranial vault. The major problem with D2282 is that it has been kinda deformed throughout the ages, the occipital and temporal ares are crushed on the left side, as are the zygomatic bones making a lot of the measurements and proportions convoluted.
To complicate it, much of the median upper facial skeleton is missing including the supraorbital torus at glabella, nasal bones, and frontal processes of the maxillae. Which makes it even harder to compare feature to feature to D2280.
However, all hope was not lost with our friend D2280. With a well persevered maxillae that still holds the right P4-M2 and the left M1 and M2, as well as the alveoli of all other adult teeth including those of M3, a more thorough comparison was done. The comparison of the teeth lead to the conclusion that D2282 represents H. erectus. One example, the presence of singler roots in the upper premolar teeth is a H. erectus trait that.
D2282 is still small; the smaller of the two crania; 650 cm3 small; small like habilis.
Right above the tuff that locked away D211, D2280, and D2282, came another set of findings in 2001 and 2005, the D2700 cranium and the D2735 mandible, and the D3444 cranium and D3900 mandible.
The cool thing about D3444 cranium is that he was an old guy, completely toothless. His toothlessness was not something new, he had been toothless for several years before death, judging by the complete resorption of the tooth sockets. The implications of how he was cared for in his old age, were outstanding.
And about the D2700 cranium. It is even smaller than D2282, at 600 cm3. D2700 has many characteristics which resemble H. ergaster but also a handful that resembles the ER1813 H. habilis skull. Vekua et al., write in their 2002 paper that,
“In overall shape, D2700 is similar to D2280 and D2282, and D2735 resembles D211. Despite certain differences among these Dmanisi individuals, we do not see sufficient grounds for assigning them to more than one hominid taxon. We view the new specimen as a member of the same population as the other fossils, and we here assign the new skull provisionally to Homo erectus.”
So, other than showing you how bountiful Dmanisi has been in yielding Homo fossils, what else is going on here? We have a lot of small habilis-like skulls coming out from Dmanisi which have erectus-like features.
Do we go with size or do we go with morphology? As of right now, we’ve gone with morphology, but that’s problematic, especially dealing with heavily fragmented remains. Better yet, do the Dmanisi fossils represent a transitional species, one were humans were similar in size to habilis but similar in shape and form to erectus?
I think that will be answered in tomorrow’s Nature.
I don’t know really, but I’d like that to be answered because I’m pretty sure all you see right now is the great flaw in understanding evolutionary relationships and ancestors from fossil remains; when determining taxonomies with many traits, measurements, and damages to consider, it seems to be nothing more than a big pissing match between respective paleoanthropological groups.