Sunday, 31 May 2009

100th post special: Darwinius masillae, or Ida

Darwinius masillae Franzen et al., 2009
Notharctidae; Primates; Mammalia; Chordata

Above photograph:
Cast of the original specimen in Natural History Museum
May 2009

Above illustration:
Pen drawing of the cast
May 2009

As my humble contribution to the Ida carnival, I thought I’d offer two original illustrations and a documentary review, and also a summary about Ida, her provenance, her significance and some other thoughts. You may have heard much of this before, so I apologise in advance.

Ida is the name given to the first, and so far only, specimen of the notharctid primate Darwinius masillae. Obviously, her generic name comes from the man who celebrated his 200th birthday posthumously earlier this year, Mr. Charles Robert Darwin. It is no surprise, then, that the species was formally described this year of all years. The ‘masillae’ epithet is more obscure and less obvious. This relates to its origins: it was found some 25 years ago by an anonymous collector in the Messel pits in Germany. The name is Latinised, but instead of ending in the more usual ‘-ensis’, which normally ends names named after locations (i.e. canadensis, mississippiensis, sinensis), it ends in the genitive ending usually reserved for female people, although is sometimes used for place names (i.e. novaehollandiae, novaeangliae, terraesanctae).

The Messel pits are renowned for their status as a Lagerstätte. Roughly translated as ‘place of storage’, Lagerstätten are known for yielding truly well-preserved fossils. As well as Messel, there is Solnhofen, also in Germany, with perfectly preserved Pterodactylus, Rhamphorhynchus, Compsognathus and Archaeopteryx specimens (Solnhofen scene depicted here). The Burgess Shale of British Columbia, Canada, is another example of a Lagerstätte from much earlier (Cambrian period), and the La Brea tar pits in Los Angeles, California, much more recent (Pleistocene epoch). All share in common a veritable bonanza of fossils not found anywhere else, or in such quantities or of such quality. Messel itself contains beautifully preserved examples of, for example, insects, fish, amphibians, snakes, birds, bats, primitive horses, and of course, primates. The reason for such a high diversity of life forms is the basis behind why Lagerstätten exist. In Messel, a crater formed by geophysical forces from the mantle, deep under the crust. The crater filled with water and became a deep lake mostly devoid of life. This is because the bottom of the lake was still exposed to the same geophysical forces that created the crater in the first place, but this time in the form of gases such as carbon dioxide. From time to time, big ‘burps’ of gas would escape from the vents at the lake bottom, and to some extent the lake margins, releasing large amounts of gases into the lake environment. This is key to explaining how Ida might have died.

Ida (pronounced ‘ee-da’, not ‘eye-da’, as I was saying it for a while!) was female and approximately 9 months old when she died. The evidence for both of these factors comes from the skeleton itself, which is 95% complete: a lack of a baculum (penis bone, or os penis) indicates it is not male; hidden teeth high up in the jaw which have yet to emerge indicate she is not fully grown. The preserved skeleton also reveals a pathology which most likely contributed to her death. The right metacarpals (wrist bones) are fused and form a risen lump. This indicates that the bones broke early in Ida’s life, possibly from a fall from a tree. Although Ida survived long enough for the bones to heal, she would have had a hard life to her conspecifics; her tree-climbing abilities would have been greatly impaired and probably couldn’t have found food in the usual way. This resorted Ida to foraging for fallen fruit, foliage and the occasional invertebrate on the ground. She would have been drawn to the lake for a drink, and may have fallen prey to the toxic gases burping out of the muddy margins. Ida was knocked out by the sudden intake of carbon dioxide, and fell in the lake, indisputably drowning. Her lifeless body found itself in its famous pose as it hit the bed.

I mentioned earlier that Ida is a notharctid primate, but what does that mean exactly? The notharctids are a family of extinct primates, placed in the infraorder Adapiformes. It has remained unclear as to where exactly within the Primates the Adapiformes and hence the Notharctidae belong. Much of the focus of the original description (referenced and linked at the end of this post) and the documentary reviewed shortly was on the phylogenetic placement of Darwinius related to two suborders of Primates: the prosimians (lemurs, lorises and their kin), and the anthropoids (monkeys and apes, including humans, which are apes of course). Neither are true monophyletic groups: the prosimians also include the tarsiers, which are actually on the same ‘branch’ as humans, the haplorhines. The original paper uses the more correct terms Strepsirhini and Haplorhini to indicate the true groupings. It occurs to me that the Adapiformes make up a third group.

On Tuesday 26th May, Britain was hit by a double dose of Ida-goodness. I already knew that the documentary Uncovering Our Earliest Ancestors: The Link was scheduled for 9 pm on BBC1, but the other piece of news was bizarrely unknown to me. The Natural History Museum, the place where I work and have studied and worked for the past few years, was to host the REAL Ida specimen for just a few hours, of course, as luck would not have it, on a day I had chosen to take off for my sister’s birthday, dammit. I probably wouldn’t have had authority to see her anyway, as the event was restricted to the press, certain scientists and celebrities, including the revered Sir David Attenborough, who narrated and wrote the script for that night’s documentary. I’m a humble library shelving assistant, and have few, if any, links to the Palaeontology Department, as yet. I saw this on the lunchtime news, and was feeling an odd mixture of pride for my institution, and jealousy for not being there. Oh I’ve met Sir Dave already, twice in fact, so it’s not that. The news was announced, however, that a cast has been presented to the Museum that will be on display from the following day. So naturally, before I started my shift at work I gave Ida’s body double a visit. Oh my, I was blown away by her beauty, although it was a cast. From seeing her on TV the previous night, I expected her to be twice the size, but as with a lot of celebrities, she looked a lot smaller in person.

So onto my review. An overdramatic introduction (this truly was overdramatic... Jens Franzen was quoted as stating that the findings would be “just like an asteroid hitting the Earth”) led into the story of the fossil’s discovery by Jørn Hurum at a German fossil fair in 2006. The counterpart was not mentioned (the other half of the specimen which shows the imprints of the bones, rather than risen ones). An excited Hurum was shown seeing the fossil for the first time when he was filmed opening the crate containing Ida. Radiographic studies, including x-rays (which can be seen in the original paper), proved that the specimen, unlike Piltdown Man, is not a hoax. A quick overview of the skeletal features follows, focusing on the presence of nails on the digits. Three of the authors of the paper, Holly Smith, Jens Franzen and Philip Gingerich were introduced.

Deciphering the fossil’s age was due to the method of preservation. Before being found by Hurum and purchased by the Oslo Natural History Museum, somebody (conveniently anonymously) covered the front face of the fossil with a clear resin. This is, apparently, only done to fossils found at Messel; therefore Ida’s age could be pinpointed to approximately 47 million years old. Other Messel fossils were shown, including Propalaeotherium and Eurotamandua. These fossils date from the Eocene epoch, the second of the Cenozoic epochs, after the relatively ‘dead’ Palaeocene. This was the time when the first true carnivores (the miacids), horses, bats (like Palaeochiropteryx), whales (like Basilosaurus, but obviously not in Messel) and primates were evolving. No mention is made of why the lake was special in that the specimens were so perfectly preserved, of course due to the anoxic mud containing very little oxygen and thus few aerobic bacteria to break down the body. The black fuzz surrounding Ida’s body was not mentioned apart from stating that it is furry; it is not only fur, but also a bacterial slime, which I mentioned to interested passers by at the Museum.

The skeleton was scrutinised further by the quartet: ecological conclusions were being drawn, such as the relatively short limbs indicated an arboreal (tree-climbing) nature, as well as the fact that Darwinius would have been heavily muscular (try imagining a ripped Ida with huge pecs and abs – quite a laugh). The teeth were examined by Holly Smith, the dental anthropologist on the team. Externally they appear to be ‘all-purpose’, suggesting she would eat a variety of foods, but especially vegetation. This was confirmed by examination of the gut contents by Hurum and Franzen, having found leaves and seeds. A detailed CT scan was carried out in the Senckenberg Museum where Franzen is based, from which they were able to create a 3-D image of Ida’s skeleton. On this note, it is incredible that not a single whole animal reconstruction was shown. It took me half an hour to draw one (see end of this post), and I would’ve done it for free, so it can’t be to do with budget. A CGI reconstruction of more than just bones would’ve been greatly appreciated, if not just by me then by all viewers of the documentary who haven’t seen Darwinius reconstructed. This isn’t Night at the Museum, for crying out loud!

Comparisons were made between Ida and a 6 to 9 year old child (incidentally, this confused a few people I met at the Museum when I was answering casual questions – they had read that Ida was 9 months old, but had heard on the documentary that she was 6 years old, in comparative terms), and we see Ida’s namesake, Hurum’s daughter. There is a neat cut-scene where we see the human Ida playing and the notharctid Ida is superimposed over her, as they are in similar positions.

From this point onwards, the documentary dwells heavily on the phylogenetic placement of Ida in comparison to the prosimians and the anthropoids. My favourite part of the documentary follows: an examination of a slow loris (Nycticebus sp.) to show two of the salient features of most prosimians. Most primates have nails instead of claws (some notable exceptions include the needle-clawed galagos [Euoticus spp.] and the aye-aye [Daubentonia madagascariensis]), but a claw is present on the second digit of the hind foot (the toe next to the big toe). This is variously known as the grooming claw or the toilet claw (I prefer the latter term). It is used, fairly obviously, for grooming. The slow loris has a nice example of a toilet claw. The other feature which prosimians like lorises have is the tooth comb. This is made of the lower incisors and canines squished close together to form a comb-like structure, also used in grooming. The loris’ features are then contrasted with Ida’s, who lacks both the toilet claw and the tooth comb.

This immediately suggests that Ida is NOT a prosimian/strepsirhine. According to the documentary, this automatically places Ida on the anthropoid branch. Just because something does not belong in one category, it does not necessarily mean it has to belong in the other. This way of thinking has been criticised heavily by my fellow bloggers and other scientists, so I won’t add too much to that. Comparisons were then inevitably made to anthropoids, but why start and end with the chimpanzee? Obviously their hands and feet look similar, but doesn’t it make sense to look at an anthropoid with a longer fossil record? Clearly, they were trying to oversell the point that Ida is closer to apes than to lemurs.

In reference to Charles Darwin and his theory of evolution by natural selection, Attenborough can be heard saying that there are “billions of species” on the planet. Barely a million have been described, there’s a long way to a billion, let alone ‘billions’. The dependence on the term ‘missing link’ is clear, so of course the most famous link, Lucy, the Australopithecus afarensis specimen discovered in 1974, was featured. It was a nice opportunity, however, to see how Lucy’s reconstructed pelvis compares with bipedal primates, i.e. humans, and quadrupeds, like the chimpanzee.

The injury to the metacarpals was featured, and it was proposed that Ida’s mother may have dropped her. Ida’s death was mentioned in as much detail as I have already gone into. While watching though, I was reminded of how Archaeopteryx lithographica, of which a handful of specimens (such a strange term, how can you have a handful of giant slabs of limestone?) are known, had probably died of the same fate a hundred million years before. This then provoked another thought: other specimens of Darwinius may exist out there, but are lying in “some rich guy’s basement”, to use Hurum’s words. With any luck, Ida’s worldwide media exposure (family in a village in Cyprus have even heard) might motivate private collectors to sell their specimens to museums, obviously for a hugely elevated price which no museum can afford on today’s budgets.

The final nail in the coffin for me in this documentary was the end to the constant search for a trait to link Ida with the anthropoids, and by extension, to us. The authors noticed that the talus bone in the animal’s heel is of a similar shape to those of humans, who walk bipedally. Did it not occur to them that this could be a form of convergent evolution? Just like the opposable thumb and big toe which likens them to chimpanzees, the talus’ shape could have nothing to do with walking upright, or shared ancestry with us. Of course, it may still be true, but not enough analysis has been carried out. In the last minute of the documentary, Ida is declared as “part of our history” and that’s that. End of story. Had this documentary been made much later, as in not yet, the views of other scientists would have made an appearance and made it a much less biased argument. The documentary was, however, drawing upon the points made in the paper itself, which is also full of holes.

You can tell by the length of my review that this was a long documentary, but there was much repetition of ideas. Friends and colleagues with whom I have discussed the programme with have agreed that it could have easily been half as long with still as much detail. Despite this, the documentary is still worth watching, if only for the incredible footage of a sedated slow loris (even slower than usual!) being examined at Duke Lemur Center in Durham, North Carolina.

I leave you with my reconstruction of Ida. I based her on living lemurs and of course on the cast of the skeleton I have illustrated earlier.

Graphite pencil illustration
May 2009

Franzen, J. L., P. D. Gingerich, J. Habersetzer, J. H. Hurum; W. von Koenigswald & B. H. Smith (2009). Complete Primate Skeleton from the Middle Eocene of Messel in Germany: Morphology and Paleobiology. In: PLoS One 4(5), 27 pp. (link to PDF here)

1 comment:

Canidae Art said...

Great article, I found the documentary fascinating, and your article too, I love your artist's impressions of Ida...I did a couple myself because I just found it so inspiring that such a spectacular specimen of such great age was found in that condition.

Keep up the great writing! :)