The First Fossil Evidence of the Denisovans
Several posts have been made on this blog regarding the Denisovans and what I want to do in this post is to begin to make some possible connections between the Denisovans and other hominids along with considering some possibilities. Denisova Cave is located in the Altai Mountains in Southwestern Siberia, Russia and this was the site where the first evidence of the Denisovans was discovered in 2010. This cave was originally investigated in the 1970’s by a Russian anthropologist by the name of Nikolai Ovodov looking for fossil remains of canids (dogs, wolves, jackals, dingoes, etc.). In 2008 the cave was once again investigated by the Russian Academy of Sciences. That exploration was led by Michael Shunkov and also involved other Russian scientists. It was this 2008 investigative team that found the first evidence of the Denisovans which consisted of a finger bone believed to be from a juvenile hominin that came to be known as the “X woman.” Associated artifacts found in the cave included a bracelet found at the same level as the finger bone which was dated at around 40 kyr (thousand years old) using radiocarbon dating and oxygen isotope dating. Since 2008 other investigations in the cave have established that hominins occupied the cave at various times as far back as 125 kya (thousand years ago) and possibly longer.
A team led by Johannes Krause and Svante Paabo from the Max Plank Institute of Evolutionary Anthropology sequenced mtDNA from the finger fragment and that indicated humans, Neanderthals, and the mysterious Denisovans shared a common ancestor about 1 mya. Their analysis also indicated that the Denisovans came from an earlier migration out of Africa distinct from a later migration which brought modern humans into the region. And it also indicated that the Denisovan migration was at a different time than when Homo erectus first migrated out of Africa. Additionally, their research also suggested that the Denisovans were a “sister group” of the Neanderthals that branched off from the human lineage about 600 kya and that the Denisovans likely branched off from Neanderthals in the Levant some 200,000 years later.
In 2010 Svante Paabo’s group reported a previous find found in 2000 in a second research paper which consisted of a third molar from a young adult Denisovan. It was dated the same as the tooth. The tooth was different from those found in Neanderthals. For one thing it was much larger and for another it also had archaic features seen in early Homo erectus specimens.
Analysis of the finger bone using mtDNA showed it was genetically distinct from both Neanderthals and modern humans. Analysis of nuclear DNA from the finger bone showed that the elusive Denisovans shared a common origin with Neanderthals and that they possibly ranged from Siberia to Southeastern Asia and that they lived alongside and interbred with the ancestors of modern humans in the area. Subsequent DNA analysis of Melanesians and Aboriginal Australians has shown that their DNA contains between 3-5% Denisovan DNA. Additionally, further DNA analysis from finds at Denisova Cave revealed that there was significant interbreeding among Neanderthals living in the region AND that there was also significant interbreeding with an UNIDENTIFIED ancient human lineage!
A Denisovan toe bone was found in 2011 along with two more teeth. These specimens were found in different layers than the original finger bone fragment. Then in 2013 something unexpected took place which was a bit of a shock to the paleoanthropology world. It was in that year that researchers sequenced mtDNA from a 400,000 year old femur bone found in Spain which was believed to be from a Neanderthal or H. heidelbergensis. To their amazement the mtDNA results indicated that the femur bone’s mtDNA was more closely related to DENISOVANS than to either the Neanderthals or Heidelberg Man!! So it appears that the Denisovans actually ranged from Siberia west into Spain and east into Southeast Asia which is a very large range.
So, in a nutshell here is the first evidence of the Denisovans found:
Denisova 2, a molar tooth found in 1984 at Denisova Cave dated to more than 100 kya.
Denisova 4, a molar tooth 30-50 kyr found in 2000 at Denisova Cave. This molar is larger than those found in Neanderthals or archaic modern human ancestors.
Denisova 3 (“X Woman”), a finger bone (phalanx) 30-50 kyr found at Denisova Cave in 2008 and unfortunately this specimen was destroyed to obtain its mtDNA.
Denisova 8, a molar tooth found in 2010 at Denisova Cave and not dated.
Toe Bone found in Denisova Cave.
Possibly the femur bone found in Spain.
So What Did the Denisovans Look Like?
The fossil evidence for the Denisovans is extremely small and limited and it is impossible to say exactly what this species classified as “Homo sapiens” looked like. What was determined based on the above fossil evidence was that the Denisovan’s fingers were unusually broad (big) and robust and much bigger than finger bones seen in modern humans. This, to me, suggests that the Denisovans were large hominins. Larger than modern humans and larger than Neanderthals. This finger bone belonging to “X woman” a female suggested that the build of the Denisovans may have been similar to Neanderthals but much more robust. The molars suggest no similar features with Neanderthals or modern humans as it is much bigger than molars found in either of those hominins. It’s been suggested that the toe bone may have belonged to a Neanderthal-Denisovan Hybrid but evidence for this hybridization has remained inconclusive. Incidentally, Paabo and his team along with other researchers took a very close look at the full Denisovan genome and noted and CONFIRMED that humans did interbreed with Denisovans and produced hybrid offspring!!
Older Denisovan Finds
There actually are some older finds believed to possibly be Denisovan fossil remains. These include remains of skulls from “Dali Man” found in Dali, China in 1978 and “Maba Man” found in Maba near Shaoguan city in northern China. Other possible fossil evidence includes several bone fragments found around Asia. Some researchers believe these older remains may be from Asian Neanderthals and not Denisovans.
“Dali Man” as it is known consists of a complete fossilized skull thought to represent and early form of archaic Homo sapiens that lived during the Late Middle Pleistocene period. It was discovered in 1978 in Dali County, China by Liu Shuntang. The dating of the skull is an ongoing matter of debate. This fossil is considered to be the most complete skull from the 1970’s era found in China to date. Some anthropologists consider the Dali Skull to be the ideal specimen of archaic Homo sapiens as it is thought to have a mixture of traits similar to Homo erectus and Homo sapiens. The facial details and the skull itself are different from European Neanderthals and earlier hominins found in Europe such as those skulls found at Petralona, Greece and in the Alapuerca Mountains of Spain. This skull is low and long much like that seen in Homo erectus. The back of the skull is rounded and it has a rather prominent sagittal keel atop the skull. The brain appears to have been primarily sitting right behind the face which accounts for its extremely low forehead. The cranial capacity of Dali Man has been estimated to be about 1120 cc which puts it at the lower end of the modern human range for skull volume but also at the upper end range seen in H. erectus. The base of the Dali Skull is LESS robust than that seen in many H. erectus specimens. Further, the posterior margin lacks the heavy neck muscle attachment seen in H. erectus. Additionally, the “tympanic plate” is thin and foreshortened which is similar to that found in modern humans.
The face of Dali Man shows a massive brow ridge that curve over the eyes and is unlike the straight bar-type brow ridge seen in Peking Man (a H. erectus specimen) and others. In fact, the curvature seen in the brow ridges of Dali Man are similar to archaic human specimens found in Europe and Africa! The skull shows delicate cheek bones and a flattened nasal bone. Some anthropologists hold the view that Dali Man is a variation of Homo heidelbergensis while others believe it to be a specimen of archaic Homo sapiens and, still, some believe it to be a Denisovan specimen. The debate is ongoing.
“Maba Man” was discovered in 1958 in caves near the town of Maba which is near Shaoguan in northern China as well. The caves are also known as “Lion Caves.” This site has been turned into a tourist attraction with a museum. It is described (marketed) as the site of the “ape men.” However, the Maba people were not really ape-like and, in fact, more resemble European Neanderthals.
The fossil remains of Maba Man consist of skull fragments and this species is believed by some to be an intermediate (possibly hybrid) species between H. erectus and archaic H. sapiens. Others believe they are the remains of an Asian H. heidelbergensis while others consider it possible the fossils are those of the elusive Denisovans or a Denisovan-Archaic Human Hybrid. The fossil remains consist of a skullcap and fragments of the right upper face including bones of the nose. It has a pronounced browridge which forms an arch over the eyes and the braincase is low and thick. The brain volume was larger than that of H. erectus and the skull’s base is incomplete making an exact estimate of the size of the brain impossible.
The Maba Skull is interesting in another way because it also shows the earliest evidence we have to date of human aggression! The guy or gal took a really good knock on the right side of the head BUT they lived to see another day! The knock appears to have been from a blunt force that caused trauma but the wound is healed and that means the person lived although perhaps not at the level they did prior to the trauma. Evidence of the injury can be seen on CT scans of the Maba Skull along with healing of the bone. The blunt force object caused the skull to crack and the victim was likely clubbed with a stone weapon of some kind or one made out of heavy bone or wood. Likely the injury caused bleeding and a concussion too and it may have even caused this individual to have brain damage. In fact, even though the fracture healed and the individual lived to see another day he/she may have been helpless and dependent on others for food and survival. What this means is that since this person lived they were likely cared for by other members of their group and that shows compassion!
The Maba Skull fracture depressed the bone inward onto or perhaps into soft tissue (the brain). Even still this person survived apparently for several years after the injury and the injury was not the cause of this person’s eventual death as far as we can tell.
I also need to mention in regards to this skull that associated animal bones were found with it and those animal bones have been dated to 130 kyr. The skull has similarities to European and western Neanderthals but it lacks the characteristic features of Neanderthal skulls. This too MAY be a hybrid but at this point we are uncertain.
The Denisovan Molars
The Denisovan fossils show that this species of hominin had some very large molars. DNA evidence appears to suggest that the Denisovans coexisted alongside Neanderthals and archaic modern humans for tens of thousands of years. The fossil evidence suggests that the Denisovans were humanlike. At first when the first tooth was found it was thought to be from a cave bear but analysis showed it was not. Researchers thought the tooth was from a cave bear because of its features which included its size, and huge splayed roots. One thing we can be certain of is that huge teeth require huge jaws so the Denisovans must have had some rather large jaw bones! Also, new genetic studies on the Denisovan fossils have shown that they were NOT as closely related to Neanderthals like we first suspected.
Hidden Denisovan Evidence?
There may be other fossil evidence of the Denisovans elsewhere throughout Asia, Europe, and other places mislabeled in those dusty old museums as archaic modern humans or Homo erectus specimens. Recent finds in southern China have yielded teeth dated between 80-120 kyr that have both ancient and modern features which is much like those features seen in Denisovans. Some of these teeth may well belong to Denisovans. In other words, Denisovan evidence may well be hiding in plain sight!
In my next post on the Denisovans I’ll take a look at how modern humans may have polluted their gene pool by interbreeding with this elusive species resulting in infertility Should you worry? Also in posts over the next few weeks I’ll also look at a highly controversial theory that suggests either Denisovans themselves or their descendants might STILL be living in the American Pacific Northwest among other places!