I switched on the radio this morning and fortuitously caught this morning’s edition of Science in Action.  The first item in the programme was Ida, the unlikely name given to Darwinius masillae, possibly the most over-hyped fossil in recent years (check my comments to my previous blog article for links to the growing controversy).

In the radio show, one of the authors of the paper speaks briefly, but is then followed by a series of contributors who basically say – while this is a spectacularly well-reserved fossil, no this isn’t quite as important as the media puffery would make out.  Steve Jones takes exception to the use of “missing link”.

You can listen to the show through BBC iPlayer (well, you can in the UK, and maybe elsewhere, given that this is the World Service) for the next week: Science in Action, Friday 22nd May (presumably I caught a repeat broadcast)..

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The news sites and blogs have reports of a new fossil found in Germany, a 47 million year old primate, named Darwinius masillae.  The quality of preservation of this fossil is extraordinary, and even reveals what its last meal was.  PZ Myers gives the lowdown at Pharyngula (Darwinius masillae).

Of course, there’s a major PR job going on about this – check out Ed Yong’s blog (Not Just Rocket Science – Darwinius changes everything) for a refreshing view.  John Wilkins (Evolving Thoughts -No, it’s not an ancestor either (probably)) questions statements that it’s the ancestor of all primates (he cites Science Daily).

The blogosphere’s pretty full of writing about Darwinius – some buys into the hype, others question it.  one thing’s for sure, it’s a damn fine fossil.  On the downside is the confusion the news coverage may engender in the public, with buzz-words/phrases like “missing link” and “oldest ancestor of humans” flying around.

I think the BBC News website (Scientists hail stunning fossil) strikes the correct balance with comments such as:

Dr Henry Gee, a senior editor at the journal Nature, said the term itself was misleading and that the scientific community would need to evaluate its significance.

The publication is accompanied by a David Attenborough fronted BBC TV programme!  (Makes my YouTube press release via the BBSRC look really rather puny!). If you’d like to read the paper, it is publishe din the open access journal PLoS One:

Franzen JL, Gingerich PD, Habersetzer J, Hurum JH, von Koenigswald W, et al. 2009 Complete Primate Skeleton from the Middle Eocene of Messel in Germany: Morphology and Paleobiology. PLoS ONE 4(5): e5723.doi:10.1371/journal.pone.0005723

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Ed Yong has a nice discussion of a recent paper about a feathered dinosaur over at his blog (Not Exactly Rocket Science -Tianyulong – a fuzzy dinosaur that makes the origin of feathers fuzzier).  The neat thing with this fossil is that it suggests that the evolution of feathers might have been a stepwise process, and indeed their origins may have predated the the last common ancestor of the Saurischian and Ornithiscian dinosaurs (see figure below).

Distribution of feather-like structures among dinosaur taxa

One more example of how we are gradually accumulating more and more supporting evidence for evolutionary explanations of the origins of birds.  You can clearly see the feathery “filamentous integumentary structures” in the fossil:

Primary citation: Zheng, X., You, H., Xu, X., & Dong, Z. (2009). An Early Cretaceous heterodontosaurid dinosaur with filamentous integumentary structures Nature, 458 (7236), 333-336 DOI: 10.1038/nature07856

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It’s often claimed that intermediary fossils representing stages in the divergence of extant taxa are absent from the fossil record.  Such claims are often made by those with a creationist bent, and in some cases on the back of spectacular ignorance of biology.  For example Adnan Oktar’s (he publishes bizarre anti-evolution tirades under the pen name Harun Yahya) stupid offer of several trillion Turkish Lira (apparently  many times the GDP of is home nation, Turkey) to anyone who can demonstrate an intemediary fossil.  Oktar’s concept of an intermediate fossil is of course quite bonkers (Richard Dawkins has an excellent demolition of this concept) in which intermediate forms are, for example, half starfish, half fish.  In reality, of course, intermediate fossils are known, though I suppose each gap filling fossil must generate two new gaps in the fossil record!

The evolution of birds from theropod reptiles is well established, from the fossil record (this being one of the great cases of transitional fossils), with many fossils notable for the presence of feathers.  This paper analyses fossilised footprint tracks, and interprets them as being made by reptiles of this type, and makes some interesting inferences on resting posture as well as the gait of these animals.  Trace fossils attributed to theropods are quite rare, and usually don’t include impressions made by resting animals.  In this case, the authors conclude that resting postures (which reflect the anatomical arrangements of limb and other joints) of theropods indicate avian characteristics much earlier that previously recognised.The 200 million year old traces that form the subject of this paper are found in southwest Utah, and are part of a longer trace that mostly comprises a record of a moving animal with impressions of hind feet with occasional tail drag impressions.  In the figure below, one of the studied strata is shown – you can see the footprints represented as little “crows feet”.  The set of impressions studied in the publications is indicated in red.  I think the tail impressions are the red lines, while the resting impression is to the bottom of the figure.  I have to confess that the technical terminology used in the paper can be a little opaque to non-specialists (such as me)!

Schematic map of the “Top Surface” tracksite (SGDS.18). Beige shaded areas represent the “Top Surface” of the Main Track-bearing Sandstone Bed; gold shaded areas are unexcavated; brown areas represent areas removed after mapping to examine lower horizons. The Eubrontes trackway that includes the crouching trace is highlighted in red.

The authors describe the significant resting trace fossil as resulting from an animal which, when moving up a 10 degree slope

[...] then stopped, placing both feet parallel. It then lowered its body, bringing the metatarsals and ischial callosity into contact with the substrate, creating nearly symmetrical, elongate “heel” and circular ischial impressions.

Unusually, and because the animal was resting on a slope, there are impressions made by the fore-limbs.  These are uniqe, with medially-directed digits.  This argues for a joint arrangement in these animals inconsistent with reconstructions in which the fore-limb palms are oriented ventrally, and in favour of one in which the palms are medially oriented.  You can see this arrangement in the figure below, showing a reconstruction.

Restoration of Early Jurassic environment preserved at the SGDS, with the theropod Dilophosaurus wetherilli in bird-like resting pose

The authors conclude that these movement traces represent evidence of remarkably avian-like joint arrangements and posture in theropods, much earlier than previously thought.  It’s possible that the arrangement reflects a function in grabbing and holding prey.  In any case, in among the rather technical and anatomical descriptions in the paper, the description of the animal’s movements as it made the impressions in the substrate are really quite appealing.

Milner, A., Harris, J., Lockley, M., Kirkland, J., & Matthews, N. (2009). Bird-Like Anatomy, Posture, and Behavior Revealed by an Early Jurassic Theropod Dinosaur Resting Trace PLoS ONE, 4 (3) DOI: 10.1371/journal.pone.0004591

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Todays issue of Science contains a report on the identification of bipedal hominin footprints found at Ileret in Kenya.  Of course older hominid footprints, probably of Australopithecus arafensis, were found some years ago at Laetoli and have become iconic images.

The new discovery is of fossil footprints which are morphologically distinct from the much older Laetoli footprints, and are thought to have been left by Homo ergaster or Homo erectus. These footprints were found on two distinct strata at the site.  The authors have analysed the prints in detail using laser scanning.  Stride analysis of the tracks suggests the originators were about 1.75 to 1.76m tall (though there are some sequences of prints from a smaller individual), considerably larger than A.afarensis.  Some of the footprints (see panel B in the figure below) show well-preserved imprints of individual toes.

In normal walking of humans, the weight-bearing foot contacts the ground first via the heel, followed by the outside edge of the foot, the metatarsal heads, then finally the weight transfers to the ball of the foot, making the deepest impression on the substrate.  As the walker moves to make the next step, weight is transferred to the big toe (the hallux) – the deepest impressions left in the footprint are often made under the first and second metatarsal heads, along with the big toe impression.  This is distinct from that of great apes such as the chimp (which knuckle walks rather than walking properly bipedally) which have different foot morphology.  In the case of the chimpanzee, the heel and lateral mid-foot make contact with the ground first, followed by contact with the lateral toes and the big toe – though the imprints left by chimps are much less stereotyped than are those of humans.

The Ileret prints are far closer in the details of their impressions to modern humans than to the older Laetoli prints – most notably this is shown by the angle of the hallux – this is the angle between the big toe and the rest of the toes.  For footprints made by modern humans, this angle is around 8 degrees, while the Laetoli prints show an angle of 27 degrees.  The Ileret prints have an abduction angle of 14 degrees.  Most significant is the conclusion that the prints appear to have been made by individuals with a long stride and extended lower limbs.

The attribution of the prints to either Homo ergaster or Homo erectus is based upon estimates of body stature (height and weight) – data derived from post-cranial remains of Paranthropus boisei and Homo habilis indicate these were smaller than the animals responsible for the Ilerat tracks.  While there remains uncertainty about this assignment, the tracks do represent the earliest evidence of a relatively modern human–like foot, adding to evidence of a hominin transition to forms with longer stride length, conferring advantages of a lower energetic cost of locomotion and correlating with archaeological indications of activities in a variety of ecological settings and the transport of resources.

M. R. Bennett, J. W.K. Harris, B. G. Richmond, D. R. Braun, E. Mbua, P. Kiura, D. Olago, M. Kibunjia, C. Omuombo, A. K. Behrensmeyer, D. Huddart, S. Gonzalez (2009). Early Hominin Foot Morphology Based on 1.5-Million-Year-Old Footprints from Ileret, Kenya Science, 323 (5918), 1197-1201 DOI: 10.1126/science.1168132

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