Tuesday, 26 March 2013

Talk : The World in 10 Fossils

A recent UoN Public Science lecture featured a fascinating talk by Dr Susie Lydon entitled “The History of the World in 10 Fossils” in which she described a series of fossils that Dr Lydon felt had been important in the evolution of life on earth.

Dr Lydon pointed out that life had been present on earth well before the earliest fossils, but its presence could only be determined by the chemical effect that it had on the environment, and one of the rules Dr Lydon had set herself was that the fossils needed to be, well, fossils.

And the second key point that Dr Lydon made was that the period of time she was covering - the last 600million years or so - was much less than the 4,600million years that the earth has been around.

So, with that out of the way, let’s see what Dr Lydon’s 10 Fossils were…

1) Doushantuo Embryos
635-551 million years old, South China, Lagoonal Sea
The fossils in these sediments are so well preserved that they can be analyzed down to the cellular level, as shown in this image of animal embryos from the webpage of Geobiologist Prof Shuhai Xiao at Virginia Tech.

Doushantuo embryos (courtesy of Prof Xiao)

It is worth noting that this period in the earth’s history is just after the time when glaciers covered all, or almost all of the earth’s surface (the “Snowball Earth” hypothesis).

2) Pikaia
515 million years old, Burgess Shale, Rockies, Shallow Sea (no land life yet)
This two inch long sea creature is significant because it is one of the earliest to have had a primitive backbone (called a “Notocord”). Pikai also had other structures, such as segmented muscle blocks, that are characteristic of vertebrates.

Pikia

Incidentally, the Notocord is present in some modern day animals such as the Lancelot.

Lancelot structure, showing notocord (dark strip>

The Burgess Shale is a formation that is rich in fossils from the “Cambrian Explosion” when large numbers of, frankly plain weird, creatures swan in the oceans. NSB favourite, so far, is Opabinia.

Opainia - 5 eyes on stalks!

3) Rhymia
400 million years old, Aberdeen, silica rich hot springs
The silica rich water that covered these plants when they died diffused into the cells and resulted in fossils with unusually high levels of detail. Leaves had not evolved yet, so plants were still performing all their photosynthesis in the surface of their trunks, stems and branches

cells in a Rhymia stem

Impression of Rhymia

4) Tiktaalik
350million years ago, N Canada, Equatorial River system
Tiktaalik is an important transitional fossil that shows both fish-like and land animal(tetrapod)-like:
Fish-like features :scales,fins, half-fish,
In-between features :tetrapod like wrist joint but fish like fins instead of toes, half-tetrapod ear region
Tetrapod-like features : Rib bones, neck, lungs

Tiktalik

5) Lepidodendron
300million years, Europe, equatorial swamp forests
This plant, which grew to some 50m tall and lived in the Carboniferous period (the trees of which formed many of the worlds coal measures). Lepidodendron is in a similar classification to todays (very small) clubmosses

Lepidodendron

Impression of bark

6) Lystrosaurus
250million years, S Africa, river systems This is a mammal type creature, but from a different evolutionary path so it is not a direct ancestor of mammals. One surprising fact is that Lystrosaurus managed to survive the Permian extinction, and event that killed of many more species than the famous asteroid impact that gave the dinosaurs their exit ticket.

Lystrosaurus

While another is the the fossil distribution of Lystrosaurus was one of the pieces of evidence used to prove the existence of continental drift.

Range of Lystrosaurus consistent with continental drift
 

7) Iguanadon
125million years ago, Floodplain, lagoonal river system
With its spike famously placed first as horn before being given its correct location on the hand, Iguanadon is a well know dinosaur, but what is not so well known is that 38 Iguanadons were found in a Belgian coal face in 1878.

A condition known as “pyrite disease” was known to affect fossils and involved crystalline pyrite in the bones was being oxidized to iron sulphate, accompanied by an increase in volume that caused the remains to crack and crumble. Conservators tries to prevent this by impregnating the bones with gelatine and oil of cloves. Which didn’t work. So in 1935 conservators applied a mix of combination of alcohol, arsenic, and 390 kilograms of shellac. Which didn’t work. So in 2003 the previous preservatives were removed and replaced with polyvinyl acetate and cyanoacrylate and epoxy glues.

Iguanadon

8) Nymphaeales
120million year ago, Portugal, river lakes.
This is one of the first flowering plants, similar to todays water lillies

Waterlillies, not unlike Nymphaeales

9) Darwinius (Ida)
47 million years ago, Germany, lake surrounded by forests
This little fellow is a lemur like mammal, possibly an ancestor of modern primates. It’s relatively recent discovery, in 1983, was mired in controversy due to the speed at which findings were published (in an attempt to prevent leaks and speculation)

Darwinius

10) Lucy
3.2 million years ago, Ethiopia, lakeshore nr forests
Lucy (named after the famous Beatles song) is an early hominid who would have stood some 1.1 m, weighed 29 kg (64 lb) and looked somewhat like a Common Chimpanzee - but walked upright

Artists impression of Lucy


Errors
Any errors in this post are almost certainly due to NSB's inability to read its own, often unintelligible, notes.

Image Sources, by fossil number)
2, 2, 2, 3, 3, 4, 5, 5, 6, 6, 7, 8, 9, 10

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