Is this one less link gone missing?

kw: book reviews, nonfiction, anthropology, paleontology, human origins

This little fossil monkey is changing some ideas about the way primates evolved. A juvenile female, she was dubbed "Ida" by scientist Jørn Hurum after his young daughter. Dr. Hurum arranged the purchase of the fossil from a dealer acting for a private collector, and assembled the first team to study and publish about this type specimen of the new species Darwinius masillae. "Massilae" honors the Messel quarry, where Ida was found.

In The Link: Uncovering Our Earliest Ancestor, by Colin Tudge (with substantial additions by Josh Young), I read with fascination the story, as well as we might know it, of Ida's discovery by a private collector 25 years ago, and the touch-and-go negotiations and dealings that had to occur for the specimen to be passed into the hands of the Oslo Museum of Natural History, there to be studied.

What is Ida's significance? Briefly, this "plate", together with its reverse, "plate B", form the most complete fossil primate ever recovered, and is particularly precious because of her age: 47 million years. Secondly, the fossil shows transitional features that indicate Darwinius masillae, or a species very like it, was the species ancestral to the Anthropoids, those primates that include Old World monkeys and all apes, including Homo sapiens.

Ida herself could not have been ancestral to anybody. Her teeth—about half her milk teeth were still in place, though adult teeth were right behind, soon to erupt—indicate she was less than a year old, comparable in development to a ten-year-old human or four-year-old chimp. Too young to give birth. But her species could well be the anthropoid "first ancestor" species, the one that forms the point of divergence with the Lemur group.

That is, if one believes that anthropoids and the lemurs are sister groups. There are other ways to interpret primate evolution, though the study of Ida is throwing most of them into doubt. As Dr. Hurum says, "Paleontology is the only science in which you can still shake up the whole field with a rock hammer." (I paraphrase)

Much of the book is a discussion of the Eocene and the Tertiary period of which it is an early section. Times were a bit different then. The planet was much warmer on average, due to much higher greenhouse gas amounts, and tropical forests reached almost to the Arctic and Antarctic Circles. Certain continents were connected that are separated today, so in substantially less than a million years, any slightly mobile species could spread to cover the globe. This is why, though much of primate evolution is thought to have occurred in Africa, particularly anthropoid evolution, a species such as Ida's could be found living in Germany.

If you look closely at the image above, you can see the brown outline around the bones. This is a "soft tissue" fossil, in which the skeleton is accompanied by cured and preserved flesh and hair. Even Ida's stomach content is visible (look at the dark mass just below her ribs), and shows she was mainly a fruit eater. The strength of her legs shows that she was a leaper, like the monkeys today that cling to branches and make spectacular leaps to nearby trees.

How did she wind up in a German oil shale quarry? Oil shale is formed in a specific way, in large lakes with deep oxygen-free water. Anything falling in and sinking will not decay, but be preserved in the thin mud that gradually accumulates. The pit at Messel has yielded spectacular fossils of many species, including more than a dozen specimens of small horses (the Eocene horse was a four-toed critter the size of a Spaniel) and two other primate species. Anoxic lakes have lots of carbon dioxide in their deep waters, often supplied from deeper magma bodies (Germany was a volcanic area in the Eocene), and the gas sometimes "burps", suffocating many creatures that happen to be nearby. Birds fall from the sky, animals taking a drink collapse and may fall into the water, and a monkey low in an overhanging tree can fall in also. This is apparently what happened to Ida.

I tried to locate a few cogent links, but the controversy following the publication is quite hot. A good survey can be found in this Wikipedia article. As the author predicted, some claim Ida is "just a Lemur", some that she in an Adapid (a completely extinct primate group), and there are few voices raised to support Drs. Hurum and Franzen and their coauthors. That is science for you. It takes years, and lots of heat before there is much light.