When the fossil primate known as “Ida” was catapulted into the public consciousness in 2009, her backers pushed only one angle of her story. This primate, they said, was “THE LINK” – not a link to our prehistoric roots, but the single point in evolutionary history that connected us to our deeper primate past.
Not surprisingly, the Ida hype misconstrued our connection to her. This 47 million year old primate, known to paleontologists as Darwinius masillae, was more closely related to ancient lemurs and lorises than to our own lineage. Darwinius was about as distantly related to our ancestors as possible while still being a primate.
The kerfuffle over Ida truly was a shame. Even though the initial interpretation of her evolutionary relationships was wide of the mark, Ida is the most spectacular prehistoric primate specimen ever found. For the most part, the record of fossil primates is one of teeth, isolated bits of skeleton, and bone fragments. Complete specimens are exceptionally rare, and to find an intact skeleton with gut contents and remnants of hair is a paleoprimatologist’s dream come true. The ballyhooed Darwinius skeleton contains a wealth of information about the lemur-like primate’s biology, but these considerations were overshadowed during the initial mass media push. Now that’s starting to change.
Every now and then, I run a search for “Darwinius” on Google Scholar, just to see if there’s any news. The archaic lemur cousin is mostly mentioned in papers about other fossil primates. But late last night, a new result popped right up at the top: “Palaeopathology and fate of Ida (Darwinius masillae, Primates, Mammalia).”
When Jens Lorenz Franzen and colleagues described Darwinius in 2009, the paleontologists said little about how the young primate actually lived. The paper’s section on paleobiology had more to do with taphonomy – the science of what happens between the death of an organism and its discovery – than natural history . “Shortly after death,” the researchers hypothesized, “it appears that the body sank to the lake bottom, landing on its back before coming to rest on its side.” Now, in the new paper, Frazen and a different set of collaborators examine an injury Ida sustained long before she drifted to the bottom of an Eocene lake.
The focus of the new Palaeobiodiversity and Palaeoenvironments paper is a lump of bone on Ida’s right wrist. Franzen spotted the callus while studying the fossil prior to the 2009 description – the lump is called an “excrescence” in that paper. After examining the pathology anew through micro-CT analyses, Franzen and co-authors suggest that Ida suffered an early injury that stayed with her for the rest of her ancient life.
Ida’s left arm looks normal. The bones of the lower arm – the radius and ulna – are articulated with the carpals of the wrist and the metacarpals of the palm. But the carpals of Ida’s right arm can’t be seen. There is just a bump of spongy bone between the lower arm and the hand. This undoubtedly affected Ida’s ability to grasp branches as she moved through the forest. While Ida could probably still rotate her forearm and move her fingers, the bone callus limited the flexibility of her wrist and the movement of her palm. Even though the development of the bone shows that Ida was still healing when she died, Frazen and colleagues hypothesize that “the healing process led to a crippled, rather immovable hand.”
The researchers behind the new study suspect that Ida may have broken her wrist while falling out of the prehistoric canopy. “When hitting the ground, she tried to protect herself, cushioning her fall with her front legs,” they write. (I feel for Ida – I broke my right wrist in a similar way when I fell off a skateboard as a child.) This is only one possible scenario, though. The fact of the matter is that we’ll probably never know exactly how Ida injured her arm. All we know is that she sustained such an injury.
Regardless of how it happened, though, Frazen and collaborators propose that Ida suffered her injury at an especially vulnerable time. The young primate wasn’t yet full grown – she is thought to have been about 10 months old, and 60% the size of an adult when she perished – but she was too old to have been carried by her mother, as modern lemurs do. She had to climb trees and scamper over branches on her own, yet she had a painful, debilitating injury. I don’t agree with Frazen’s idea that Ida therefore must have spent her last weeks entirely on the ground, but Ida’s ability to climb and escape predators was undoubtedly hindered.
That’s all the more reason why Ida’s eventual preservation in the Messel oil shale is so wonderful – she beat the odds to become an exquisite articulated skeleton rather than a coprolite. Indeed, Franzen and colleagues point out that Ida is truly exceptional because the primates of the Messel oil shale are usually only found as rare fragments that have been damaged by predators. At least three Messel primate fossils exhibit bite marks, and part of a primate jaw was even found inside fossil feces (possibly left behind by an Eocene otter). This means that amphibious carnivores were often responsible for transporting primate bodies to a part of the lake where the remains had a chance of preservation, but it also makes Ida even more of an outlier. If most Messel primate fossils are scraps left over from amphibious predator meals, then why was Ida left untouched?
Ida’s initiation into the fossil record is just as mysterious as the trauma that crippled her. We know that she wasn’t dragged to the depths by a crocodile or an otter. But that’s all that’s certain. The new study suggests that Ida might have succumbed to poisonous gases that sometimes burped from the lake where she was interred, but, sadly, the primate's case has been cold too long to know if this actually happened.
After surviving a traumatic fall, Ida ultimately perished and somehow her body wash ushered past the carnivores and scavengers that sculled through the lake where she was buried. It was an ancient tragedy, now told in rock and bone. But the fact that we can even know this much about Ida is a testament to the many stories fossils have to tell, and the somber beauty of the fossil record.
References:
Franzen JL, Gingerich PD, Habersetzer J, Hurum JH, von Koenigswald W, & Smith BH (2009). Complete primate skeleton from the Middle Eocene of Messel in Germany: morphology and paleobiology. PloS one, 4 (5) PMID: 19492084
Jens Lorenz Franzen, Jörg Habersetzer, Evelyn Schlosser-Sturm and Erik Lorenz Franzen (2012). Palaeopathology and fate of Ida (Darwinius masillae,
Primates, Mammalia) Palaeobiodiversity and Palaeoenvironments DOI: 10.1007/s12549-012-0102-8
Switek, B. (2010). Ancestor or Adapiform? Darwinius and the Search for Our Early Primate Ancestors Evolution: Education and Outreach, 3 (3), 468-476 DOI: 10.1007/s12052-010-0261-x
