Horseshoe Crabs, Hox genes and Virtual Palaeontology

This blog is inspired by the first lecture I went to last week at the British Science Festival, about virtual palaeontology. It was given by two excellent speakers, Dr Russell Garwood and Dr Imran Rahman and I’ve now done a bit more research into what they spoke about, as well as found a video of some 3D fossils like I promised!

First of all, here is a video made by Dr Garwood about using Micro-CT to get 3D images of fossils. The crack you can see through all the scans is the break that was made that allowed the fossil to be discovered. It really shows how crude the old methods of simply breaking it open a fossil, or even grinding it down slowly to reveal its inner workings while destroying it (!) are compared to x-raying it.

Also if you notice at the end he has an Imperial email (:0) because he did his PhD (and I think still teaches) there which is so exciting! If you want to see some more awesome photos and details of his work you can go to his website.

As you can see in the video, he basically x-rays the fossils, giving you a 3D image of what the creatures looked like. From this you can see lots of details that were missed before, which can reveal so much more about how the creature lived, for example how would have been able to move.

However, researching something else he mentioned in the lecture about horseshoe crabs has taken me off on a huge tangent into evolutionary developmental biology…

As far as I can tell from reading his paper, modern day horseshoe crabs have some legs at the front for feeding and walking, and the back legs have evolved into gills, whereas one of its ancestors had branched legs, where one branch did the breathing and the other the feeding and walking. It was thought that the back legs turned into gills and then the front specialised and lost their breathing branches afterwards.

A new fossil he scanned, called ‘Dibasterium Durgae’ however, is some kind of weird in-between stage with branched legs like the old one, but coming from four different parts of the body like they had begun to separate already and only after they had divided the branches went away.

That is a pretty convoluted summary. I freely admit that this paper, and the other ones I tried to read for some background, might as well have been written in Hieroglyphs. I mean here is a typical sentence: ‘Offacoluscan also be considered a synziphosurine, albeit with an aberrant trunk morphology (the posterior part of the opisthosoma is fused) that may be paedomorphic.’

I tried looking those words up. Even Google was convinced I’d made some hideous spelling mistake. I thought that perhaps two years at university and reading a lot might have helped me, but apparently that was just me being an arrogant physicist because wow these papers are incomprehensible. Researching this blog was actually pretty frustrating and made me realise just how alien science can be to laypeople. It didn’t help that this being the first lecture I went to, meant I hadn’t realise that I would want to take notes, and ended up scribbling them on the back of a leaflet about the palaeontology society that was handed out.

Anyway, the reason these legs changed in this was apparently down to something called Hox genes which can tell legs and arms where and when to be generated. I thought Hox genes would turn out to be something pretty dull, but they are actually anything but, so now, several hours later, I now know lots about regulatory genes. If you are not a biologist, be excited, cos this stuff is interesting. If you are a biologist feel free to read on and feel smug/point out where I am wrong. A few hours probably doesn’t equate to years of study, after all, even if it is in Biology…

You might have heard all those statistics about how we are 97.5 % genetically identical to a mouse or whatever and have thought—hang on what? I am not 97.5 % like a mouse or 55% like a fruit tree. Oh Biology. It turns out these weird statistics can be explained by regulatory genes. These are genes that don’t code for a specific feature like a small bit of a human eye— they are vague overlord genes that say ‘A leg type thing should go here,’ and ‘I want eye-like thing should go over there,’ while the embryo is developing. It doesn’t matter to them if the peasant genes that they are ordering about have the instructions for a fruit fly eye or a human eye. They are just the visionaries, and this means that they can remain completely unchanged in organisms that have since gone down very different evolutionary paths.

This is why so much of our genetic material can be similar, though we are quite different. You can even transfer the genes between species—put a mouse regulatory eye gene in a fruit fly and it will grow a fruit fly eye as usual. Since they remain relatively unchanged, they can be brilliant things to track to see what evolution has been getting up to.

They also explains how some things like velociraptors at some point lost their teeth and became things like chickens with beaks without waiting for millions of individual genes coding for the enamel and the nerves and stuff to politely notice they are not needed anymore and turn off. One simple change in the regulatory gene responsible means that teeth as a whole are just ‘switched off’ in the embryo. This means that modern birds can still carry the genes for teeth and other crazy things, which can be weird if they accidentally switch back on and you literally get chickens with teeth again.

So cool.

Click here if you want to read more about chicken dinosaurs and here if you want a good website on Hox Genes 😀

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