Beyond Bones – What we’re Learning from the Softer Parts of Dinosaurs (and Friends)

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Everyone loves a good bone, at least when it comes to fossils. If you ask someone leaving a major natural history museum about the coolest things they saw and they DON’T include the skeletal remains of something very old and probably very large, then they’re either lying or their opinion is wrong.

The right bones to the right people can reveal an incredible amount of information – this is how we know that that the three tiny bones of your inner ear were once part of the jaw, that whales evolved from an amphibious wolf-like ancestor and that many dinosaurs used large air sacs to complement the lungs like birds do today. But dinosaurs and other ancient species left more than just their skeletons.

Yup, this is what you think it is. The ruler represents 15 cm / 6 inches.

I suppose poop is a good a place as any to start. Fossilised feces are known as corprolites, meaning “stone dung”. If Jamie the Ankylosaurus drops a nice patty into prime fossilisation conditions, she is inadvertently gifting us a time capsule of life in her day and age. It contains a personal introduction including her rough size and favourite foods and perhaps a few secrets she wouldn’t want her friends to know.

In terms of information to be gained, the fresher the better. For the first few thousand years (with a few exceptions to be discussed!), complex organic molecules such as DNA and proteins may remain intact enough to be  extracted and studied. Yet even after millions of years, there’s plenty of discover – and far more than just what was served up for breakfast the day before.

A hardy cyst of Entamoeba hystolytica

Coprolites have revealed gut parasites from the age of dinosaurs which are not dissimilar from some of our own. Today around 50 million people are infected with a particularly unpleasant parasite called Entamoeba hystolitica. Some people get no symptoms at all but in many it causes stomach cramps, dysentery and liver abscesses. It kills 100,000 people each year. The parasite is transmitted through a fecal-oral route and converts into a tough inactive cyst just before it exits the current host. This allows it to survive in the outside world before being picked up by the next unfortunate person.

Cysts like these have proven incredibly hardy. In 2006, palaeontologists obtained coprolites from the early Cretaceous period and scrubbed (with a toothbrush and soap powder, no less!), ground down, treated with acid and centrifuged them. Among pollen, spores and other microfossils, they found cysts highly reminiscent of Entaemoeba hystolitica as well as tiny nematode worm eggs. Unfortunately we know neither the identity of the coprolite’s original “donor”, nor whether these gut parasites had any effect on the health of this individual or the population overall.

Oh and if you’ve ever wondered about dinosaur pee, there may even be evidence of that in the form of bathtub shaped depressions” which can’t be explained geologically.

So much for the inner workings, but what about the outside? The colouration of dinosaurs and their peers have historically been considered beyond the reach of science. Thankfully science didn’t like to be told “no” on this issue and bided its time, developing technology and waiting for better fossils to be unearthed. It is now tentatively touching at what was once claimed to be out of grasp.

An image from the 2013 paper from Field et al. The melanosomes are the rice shaped objects. Click to enlarge.

This gorgeous 55 million year old fossil feather is so well preserved that it clearly shows the individual barbs and an obvious gradation of colour from base to tip, but Daniel Field from Yale University and a team from across the USA and UK wanted to look closer. The colouration of modern animals including humans is partly determined by the type, arrangement and concentration of melanosomes – elongated sacs of pigment. More melanosomes generally mean darker colour, but were they also responsible for the patterning of this ancient feather?

They used electron microscopy to search for melanosomes – and the results were plain. It turns out melanosomes are super stable and withstood the fossilisation process well enough to indeed be responsible for the feather’s pattern. The darker the feather region, the more melanosomes were present. So even 55 million years ago individual feathers were not restricted to one hue and could take on complex patterning.

Some birds such as grackles and starlings find the matte look far too passé and sport feathers that sheen with copper and purple in the sunlight. This phenomenon is called iridescence, and it doesn’t seem to be a new trick.

Grackle feathers are highly iridescent

In fact it’s at least 120 million years old, according to a 2012 paper revealing a new fossil of a four-winged dinosaur called Microraptor (similar to the one at the top of this post). The melanosomes of iridescent feathers in living birds are very narrow and all aligned up, which is just what was found in the Microraptor feathers. This pigeon sized dinosaur also has tail feathers at least as long as its body which could well have been used in courtship rituals, and an iridescent sheen would certainly have added a special something to the display.

Feathers and poop are all well and good but squishy bits of real dinosaur have become an actual thing in the last decade. In a groundbreaking but controversial 2005 paper, Mary Schweitzer from North Carolina State University and her team managed to extract soft, elastic marrow remnants from an exquisitely preserved Tyrannosaurus Rex leg.

Soft tissue from inside the bones of a T rex
Soft tissue from inside the bones of a T rex. Image from Schweitzer et al, 2005.

This was an astounding find given that organic matter is generally given a maximum “sell-by date” of one million years and usually much less. Understandably there was a fair amount of scepticism from the scientific community including a 2008 paper which claimed that it must have come from infiltrating bacteria.

In 2009, Schweitzer’s team did it again, this time with a duck-billed Bracyhlophosaurus from 80 million years ago. Amazing shots of individual cells were taken, and her experiments were replicated successfully by no less than five independent labs. In summary: the tissues are legit dinosaurian and blood really can come from stone.

Just how this tissue could have been preserved for so many millions of years is still under debate, but in the last year evidence has come through demonstrating the likely involvement of iron and oxygen (two key components of haemoglobin in blood). When iron is let loose from red blood cells after death, it’s free to interact with oxygen in such a way that makes it able to cross-link protein together in a similar way to the common preservative formaldehyde. If this happens before degradation gets underway, then the tissue may keep indefinitely. To demonstrate this point, the group treated ostrich blood vessels with broken up red blood cells and found that even after two years sitting around at room temperature there was no sign of decay.

Fantastic new fossils are being found every year and as experimental techniques get increasingly precise, our connection with the Earth’s deep backstory will become more familiar through bones and beyond.

Thanks to Brian Switek, author of the Laelaps palaeontology blog for checking over this post. His fantastic book: “Written in Stone: The Hidden Secrets of Fossils” served as an inspiration and resource in my research.

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