Chinese Puzzle: New Primate Fossil Raises Eyebrows

A new fossil primate skull from China, alleged to be 55 million years old, provides “much-needed substantial evidence of early primates in Asia,” says Robert Martin (Field Museum, Chicago), reporting in the Jan. 1 issue of Nature.¹  But “interpretation of the creature’s eye size and activity pattern,” he says, “will spark debate.”  (This is code for, “This find throws a monkey wrench into previous theories.”)
    Martin admits immediately that “The first fossil evidence for ‘primates of modern aspect’ – the euprimates – appears abruptly in the northern continents at the beginning of the Eocene, about 55 million years ago.”  He also points to a chart that depicts “the widely accepted view that there is a basic dichotomy in the primate evolutionary tree – one lineage leading to modern lemurs and lorises (strepsirrhines), the other to tarsiers, monkeys, apes and humans (haplorhines).”
    This new fossil, named Teilhardina asiatica, a kind of tarsier on the haplorhine side of the tree, casts into doubt the classification of the American genera with the Belgian and Chinese individuals.  It also creates a biogeography puzzle.  It was formerly assumed that European primates could have only reached Asia by crossing North America and then the Bering Strait, because a transcontinental marine barrier assumed to exist 55 million years ago would have prevented them migrating in the Eastern direction.  But if the American primates are not related, was there a way around the barrier after all?
    Martin takes issue with the discoverers’ interpretation that eye socket size relative to skull size indicates the animals were nocturnal.  “Biologically, one cannot assume that early primates (particularly if unusually small in size) showed the same functional patterns as modern primates – which themselves are very variable,” he states.  He gives some examples of features in modern animals that show skull size and eye socket size do not necessarily correlate to behavior habits.  His remarks are summarized on the publicly-available AAAS website EurekAlert.
    The primate evolution chart in Martin’s article is striking in its lack of connections.  Six lineages are shown without any obvious family relationships: lemurs and lorises (the strepsirrhines), lemuroids and tarsioids farther back in time, and then tarsiers and higher primates (the haplorhines).  The bottoms of these separate lineages are all dashed lines leading to inferred relationships unsupported by fossil evidence, with question marks at the bottom.

¹Robert D. Martin, “Palaeontology: Chinese lantern for early primates,” Nature 427, 22 – 23 (01 January 2004); doi:10.1038/427022a.

This sounds strikingly similar to the tale about mammal evolution in Africa (12/03/2003).  The criticisms there similarly apply here.