Professor Jørn Hurum was among the paleontologists to unveil Ida to the public in May 2009. His team, led by Professor Jens Franzen, contends that the newly discovered species was a human ancestor. Two studies from rival teams contend that the species was instead a lemur ancestor.  (Source: Jennifer Graylock/AFP)

Darwinius masillae was discovered in Germany and may be one of the oldest known ancestors of man.  (Source: PLoS ONE/Jens L. Franzen, Philip D. Gingerich, Jörg Habersetzer, Jørn H. Hurum, Wighart von Koenigswald, B. Holly Smith)
Original study labeled fossil as human predecessor, two later studies claimed it was a lemur ancestor

One of the most fascinating topics in science today is studying how humans evolved from scurrying rodent-like ancestors in the days of the dinosaurs to erect almost 2-meter tall masters of their modern domain.

Much focus has been put on recent hominid discoveries, such as newly discovered hominid "Ardie", a member of the newly discovered Ardipithecus ramidus species, and skeletons from the newly discovered Australopithecus sediba species.  While these hominids -- which are thought to have lived around 2 million years ago, provide essential insight into how mankind evolved, equally tantalizing are the fossil clues of much older ancestors which are slowly coming to light.

Among those is the 47-million-year-old remains of Ida, a 58 cm (23 in) primate-like creature.  Ida was discovered in 1983 at the Messel Pit, 35 miles southeast of Frankfurt, Germany.

The skeleton took 24 years to painstakingly fully assemble, finally being completed in 2007.  In 2009 Jens Franzen at the Research Institute and Natural History Museum of Senckenberg in Frankfurt, Germany published in the journal PLoS ONE the first detailed analysis of the resulting skeleton. 

Professor Franzen named the creature Darwinius masillae, in honor of the bicentenary of the birth of Charles Darwin, the father of modern evolutionary theory.

In that analysis he asserted that Ida was a haplorrhine, a precursor to the branch of modern day primates that includes monkeys, apes, and humans.

Two following studies [1] [2], published in Nature and the Journal of Human Evolution, respectively, dissented with the initial publication.  They contended that Ida was instead the precursor to the strepsirrhine branch of primates -- the branch that contains modern lemurs. 

Now a fourth study has come out tying the score, defending the assertion that Ida was a human ancestor.  Philip Gingerich, a professor of biology, anthropology, paleontology, and anthropology at the University of Michigan was the lead author of this most recent analysis.  His study was published in the Journal of Human Evolution.

The bone of contention so to speak is in minimally complete skeletons of prehistoric lemurs.  The new study claims that the dissenting studies used such sketchy skeletons to support their claims that Ida was a lemur ancestor.  It argues that using teeth and bone fragments to identify the phylogeny of Ida is a flawed approach. 

Professor Gingerich complains there's a lot of uncertainty about the phylogeny of these incomplete skeletons themselves.  He states, "There are almost no skeletons comparable to Darwinius ... our opponents are referring mostly to fragments of jaws and teeth."

Palaeontologist John Fleagle of the State University of New York in Stony Brook disagrees, commenting in Nature, "Why not include data from the many fossils from the past 54 million years?"

Blythe Williams, an evolutionary anthropologist at Duke University in Durham, North Carolina also does not agree with Professor Gingerich.  He comments, "I'd love to see an analysis like they're doing with a much broader [range of] taxa."

Professor Williams says that the most recent study fails to account for some "spectacularly preserved" fossil lemurs.

Palaeontologist Chris Beard of the Carnegie Museum of Natural History in Pittsburgh, Pennsylvania explains that part of the reason for the dissenting viewpoints is that the skeleton itself is still somewhat poor.  He comments, "If Darwinius were as beautiful and complete as we're led to believe, there would be less controversy.  Its ear would be definitive."

Ears and ankles are two of the most valuable features for classification of primates.  The ear was incomplete.  And the ankle was too crushed to be used in the first four studies, but that could soon change.  Professor Franzen says that his team has completed high-resolution computed tomography (CT) scans of Ida's hands and feet.  These scans could give him ammo to defend the hypothesis that Ida was a human precursor.

While at present the various paleontology experts agree to disagree on the topic of Ida's phylogeny, all of them are in resounding agreement that Ida is a product of natural selection, the force that drives evolution.  In that sense the disagreement here is on what species Ida evolved into, not the a critique on evolution by natural selection.  That critique (of the validity of evolutionary theory) is considered a non-debate among educated researchers in the biosciences, despite it being a lively topic of debate among the less-informed general public.

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