Author: Sally Christine Reynolds, Associate Professor in Hominin Palaeoecology, Bournemouth University

Denisovans

The large Harbin skull from China has been linked to Denisovans through DNA and ancient proteins. Source: Wikimedia Commons

Take a walk in London’s Trafalgar Square this summer and wilting under the heat will be all sorts of body sizes, some tall, some short: a real mix of sizes.

Picking just two from the crowd to represent the whole human species would be a tall order. But that is exactly what we do when we find fossils of ancient hominins (human relatives).

Anthropologists can estimate a person’s height with reasonable accuracy from the long bones – your femur (thigh bone) works well. On average, the size of this bone
scales well with overall height, given a large samples of bones.

This is exactly what a group of scientists have done using fossils dredged from the seafloor off Taiwan. To add to the mystery, these bones are those of Denisovans, currently one of the most enigmatic species of hominins.

The Denisovans were a widespread species of Homo (the genus which encompasses our own species, as well as close relatives such as Neanderthals). They were initially known only from genetic sequences that had been extracted from isolated fragments of material, such as a small finger bone, at Denisova Cave in the Altai Mountains of Siberia.

The apparent absence of substantial fossil material from this species made them mysterious, although in recent years, fresh discoveries have added to our understanding. These include the Dragon Man (or Harbin) skull, recovered from a river in northeast China. DNA and protein analysis has now linked this large skull to the Denisovans.

The remarkable feature of the fossils analysed by Yousuke Kaifu, from the University of Tokyo, and colleagues, is that they were dredged from the Penghu Channel in the Taiwan Strait.

Most rare hominin fossils are carefully excavated, allowing researchers to record their exact position within layers of sediment and their relationship to associated animals, artefacts and environmental evidence.

These bones were instead recovered from the seabed among the fossilised remains of terrestrial ice age mammals, probably deposited when sea levels exposed the channel as dry land around the time when the ice age was at its height. Their precise discovery locations and geological contexts were not recorded.

This makes the fossils scientifically unusual: their anatomy and preserved proteins contain valuable evidence. However, much of the contextual information normally supplied by an archaeological excavation has been lost.

Recovered long bones

The bones – an incomplete femur (thigh bone) and tibia (the largest bone in the shin) – have been assigned to two Denisovans on the basis of analyses of their recovered ancient proteomes. A proteome is the collection of proteins preserved within a fossil. These proteins can retain evidence of evolutionary relationships, even when DNA has been lost.

These bones produced slightly different proteome signals, which is why the authors suggest that these represent two individuals. The newly described femur and tibia are likewise not directly dated.

Denisovans

A replica of the Turkana boy skeleton at the American Museum of Natural History in New York. Source: Wikimedia Commons

Because they were recovered by dredging and lack secure geological provenance, they can only be placed broadly within the Middle to Late Pleistocene, using the animal remains and preservation evidence. The Pleistocene epoch lasted from around 2.58 million years ago until 11,700 years ago.

Aside from assigning the bones to Denisovans, the researchers have used them to infer the stature of the two individuals. They are incomplete, which complicates matters somewhat, but skilled anatomists can be reasonably confident on the complete bone sizes.

The lack of context for the fossils – normally provided by the sediments in which they are recovered from – means we don’t know if the two individuals lived at the same time or at least a similar interval.

But the bones are long and when the other body elements are scaled based on the leg bones, it suggests that these individuals were tall. In the new paper, Yousuke Kaifu and colleagues say that the estimated height of Penghu 2 (one of the newly described specimens) was approximately 1.8 metres (5’11”), with a weight of around 83kg.

Their estimates for the other fossil, Penghu 3, give a height of about 1.9 metres (6’3″) and a weight of about 91kg. These estimates, the team writes in their study, “are comparable to the largest known Pleistocene Homo from Africa and Europe”.

Inferring tallness as a species-level trait based on two individuals is challenging, although it has not prevented some headlines from claiming that Denisovans were tall. Think back to our walk in Trafalgar Square.

Proceed with caution

The dangers of reconstructing stature are illustrated by the famous Turkana Boy or Nariokotome Boy, a remarkably complete Homo erectus skeleton discovered in Kenya in 1984. He was unusual because his skull, teeth and long bones were all complete and available for study.

He was already around 1.6 metres tall when he died, but estimates of his age have differed. Dentally, he appears younger than his skeleton suggests. His skeletal development appeared comparable to that of a modern human aged around 11-13, while microscopic growth increments in his teeth suggested that he was only about eight or nine.

The discrepancy reflects uncertainty over whether Homo erectus grew slowly like us, including an adolescent growth spurt, or matured more rapidly.

Different assumptions consequently produced different projections of his adult height, although more recent modelling suggests he would probably have reached approximately 1.76–1.80 metres.

He is the only example of such a complete Homo erectus skeleton, but does this mean that all members of his species would have been as tall? We should be sceptical – just as we should be about the height of Denisovans. The Conversation

This article is republished from The Conversation under a Creative Commons license. Original article.

The post Were Denisovans tall compared to other ancient humans? appeared first on Mapping Ignorance.