New australopithecine described

April 8, 2010 • 11:26 am

by Greg Mayer

Lee Berger of the University of the Witwatersrand and several colleagues will be describing a new species of Australopithecus, A. sediba, from 1.78 to 1.95 million-year-old deposits in South Africa, in tomorrow’s issue of Science. The issue will also have a geological article on the find by Paul H.G.M. Dirks of James Cook University, Queensland, and colleagues, and a news item, all available now at Science‘s website (plus a podcast and video). The description is based on two partial skeletons, including a well preserved juvenile skull, most of the right arm and shoulder girdle, parts of the hip and leg, and various other bits.

Skull of juvenile Australopithecus sediba. Image from University of the Witwatersrand.

The new species has a long arm, but the pelvis and leg indicate that it was bipedal (i.e. it could both climb and walk upright). The general evolutionary conclusion the authors draw is the mosaic nature of the origin of Homo features: some Homo-like characters evolved before others, e.g. bipedality preceding cranial enlargement. They find specific features linking the new species to Homo, and posit it to be intermediate between earlier australopithecines and Homo:

The age and overall morphology of Au. sediba imply that it is most likely descended from Au. africanus, and appears more derived toward Homo than do Au. afarensis, Au. garhi, and Au. africanus.

Something I rather liked about the paper is that it is quite data rich, having tables of comparison of traits and measurements of the new find and several other fossil hominids. Such data-richness is unusual for papers in Science, which prefers short papers, with data often being relegated to electronic appendices or other papers; the Berger et al. paper is an unusual ten pages long.

The news has already reached media websites (e.g. the New York Times, the BBC and the Telegraph). Unlike the case of Darwinius masillae, however, in which premature press coverage, which included the name and its diagnostic characters, and web posting of the description, led to questions about the proper authorship and publication of the name, the authors and journalists in this case have done everything right. The news accounts are appearing coincident with the name being published (i.e. printed on paper), not prior to its publication. (The newspaper pieces linked to above are online now, but they won’t be published in the sense of the International Code of Zoological Nomenclature until tomorrow, when the scientific paper itself will be published.) There will thus be no questions about the publication of the name; the authors have made sure that, as the ICZN recommends, Australopithecus sediba is “self-evidently published within the meaning of the Code” (ICZN, Rec. 8B)

News from the “hobbit conference” in New York

April 28, 2009 • 5:56 am

The hobbit continues to be a mystery: perhaps the deepest mystery about human evolution. Today’s New York Times has a longish and interesting report on the status of the “hobbit,” Homo floresiensis, that I’ve posted about several times.  This is a diminutive (3-foot-tall) human skeleton found on the island of Flores, in Indonesia, that has a brain case not much larger than those of modern chimps.  It is, however, modern in time, going back only about 18,000 years ago (see chapter 8 of WEIT).  Based on its wrist bones and other skeletal characteristics, scientists are now beginning to think it was not an aberrant or diseased individual, but a representative of a distinct species, perhaps an earlier species of hominin that became isolated on Flores hundreds of thousands or even millions of years ago:

Scientists who reviewed hobbit research at a symposium here last week said that a consensus had emerged among experts in support of the initial interpretation that H. floresiensis is a distinct hominid species much more primitive than H. sapiens. On display for the first time at the meeting was a cast of the skull and bones of a H. floresiensis, probably an adult female. . . . .

. . . Some prominent paleoanthropologists are reserving judgment, among them Richard Leakey, the noted hominid fossil hunter who is chairman of the Turkana Basin Institute at Stony Brook University. Like other undecided scientists, he cited the need to find more skeletons at other sites, especially a few more skulls. Mr. Leakey conceded, however, that the recent research “greatly strengthened the possibility” that the Flores specimens represented a new species.

It’s possible that hobbits represented a much earlier migration out of Africa than previously thought, earlier than the migration that gave rise to the widespread Homo erectus.  It could even represent a migration of the very early australopithecines!   As John Noble Wilford, the writer, says, lots of puzzles remain:

Indeed, the more scientists study the specimens and their implications, the more they are drawn to heretical speculation.

¶Were these primitive survivors of even earlier hominid migrations out of Africa, before Homo erectus migrated about 1.8 million years ago? Could some of the earliest African toolmakers, around 2.5 million years ago, have made their way across Asia?

¶Did some of these migrants evolve into new species in Asia, which moved back to Africa? Two-way traffic is not unheard of in other mammals.

¶Or could the hobbits be an example of reverse evolution? That would seem even more bizarre; there are no known cases in primate evolution of a wholesale reversion to some ancestor in its lineage.

Stay tuned; I’ll provide further information on this strange branch of our family tree as more research is published.  Be sure to listen to the 20-minute podcast on the Times website.  Meanwhile, courtesy of the NYT, here is the hobbit’s tiny foot (notice that the ruler is 5 cm long: about 2 in., which makes the foot about 6 inches long).


Homo footprints from Kenya

February 27, 2009 • 10:00 am

by Greg Mayer

In today’s issue of Science, Matthew Bennett and eleven colleagues from Britain, America, Kenya and South Africa report on the discovery of ancient footprints:

Here, we report hominin footprints in two sedimentary layers dated at 1.51 to 1.53 million years ago (Ma) at Ileret, Kenya, providing the oldest evidence of an essentially modern human–like foot anatomy, … The Ileret prints show that by 1.5 Ma, hominins had evolved an essentially modern human foot function and style of bipedal locomotion.

Although there were no directly associated fossils, the most likely maker of the prints was Homo erectus.  In WEIT, Jerry discussed the famous 3.75 million year old Laetoli, Tanzania footprints, which established that our ancestors had walked bipedally since at least that time.  The Laetoli prints, however were made by Australopithecus afarensis, and the newly announced prints are the oldest known for our genus, Homo (we are Homo sapiens), and Bennett et al. discuss the ways in which the Ileret prints indicate their makers had a more modern foot morphology than the makers of the Laetoli prints.  Homo erectus had a smaller brain than we do, so we see a general pattern in the fossil record exemplified: mosaic evolution–  different characters evolving at different rates.  In this instance, we see an essentially modern foot, with a brain that is intermediate between Australopithecus and modern Homo.  And, we see, once again, that intermediate forms occur at the times, and in the places, we expect them to on the hypothesis of descent with modification.

Update: A reader asks are the new prints from Homo erectus or Homo ergaster, two very closely related fossil species of Homo.  Bennett et al. don’t claim one or the other, writing:

The large stature and mass estimates derived from the Ileret prints compare well with those of Homo ergaster/erectus on the basis of postcranial remains and are significantly larger than postcrania-based stature and mass estimates for Paranthropus boisei and Homo habilis (table S3) (1921), suggesting that the prints at FwJj14E were made by Homo ergaster/erectus individuals.

In media reports, other scientists, for example Daniel Lieberman of Harvard (quoted in the New York Times), have referred to the prints as from erectus.  My own view is that the species taxonomy of fossil hominids is probably oversplit; if there is to be one name, it would, by priority, be erectus. The great Ernst Mayr wrote a paper in 1951 entitled ‘Taxonomic categories in fossil hominids’ (Cold Spring Harbor Symposia on Quantitative Biology 15:109-118), and it’s worth rereading; see also what Jerry had to say in chapter 8 of WEIT.