Jurassic sea creatures

I am an amateur naturalist trying to identify everything living in my garden.

Hello, and welcome to my 100th creature posting!

I started my blog three years ago almost to the day. My motivation then as now, was simple curiosity. When I began I was almost completely ignorant of the identity of many of the insects, plants, mosses and lichens in my garden.I wanted to learn a little more. I am still learning! It has been a revelation to come to realise just how rich a diversity of life there is on my doorstep, and to discover the incredible variety and subtlety of form, function and behaviour that exists just outside my window. I have encountered flies with larvae that invade the nests of bees, cup-shaped fungi that close the 'roof' in the dry weather, hoverflies that can regulate their body temperature and spiderlings whose first meal is their own mother. It has been a further revelation for me to learn what an enormously detailed body of knowledge exists regarding the natural world (sixty years' worth of data on a Scarlet Tiger moth population in a woodland in Oxfordshire; a study of the behaviour of the Greyling butterflies taking in a staggering 50,000 experimental tests; an online database of 125,000 species of algae...) and yet at the same time, what a mass of unanswered questions exist that that any sufficiently motivated amateur could answer, thereby make a lasting contribution to human knowledge. I find it an inspiration to keep looking and learning about the countryside when I read that of 265 British species of hoverfly, a staggering 40% of larvae are simply unknown (that at least was the status in 1993 according to the Colour Guide to Hoverfly Lavae, G.E.Rotheray) ; or that there are 235 sub-species of British dandelion whose distribution and ecology in the UK in only sketchily understood; or that with changing climate patterns, the amateur has every chance of spotting some immigrant creature (a ladybird, say) new to their environment.

On to today's posting. This being my centennial posting it seemed appropriate to pick something a little different, and what better than to discuss the rarest of all the creatures in my garden, so rare in fact that they have been extinct hereabouts for around 150 million years, when my garden was last a submerged mass of Jurassic oyster beds and coral reefs.

What I know about the geology of my garden I have got from reading the splendid The Geology of Oxfordshire (Philip Powell, 2005, The Dovecote Press):

For those unfamiliar with the UK, Oxfordshire is a county located towards the centre of England. Layers of strata have built up over the eons and at some point the stack of layers has been tilted, so that as you travel across the county from North to South the layer exposed at the surface beneath your feet changes from a youngest (~100 MY-old) chalk layer in the South to an oldest (~200MY-old) ironstone and clay 'lias' layer in the North. Some of these layers are softer than others and have eroded more over time, given Oxfordshire its gently undulating landscape of hills and valleys. (These are the surface-exposed rocks, were you to drill down you would hit much older rocks; 490MY-old rocks from the 'Ordovician' period are known in the neighbouring county of Buckinghamshire). The splendid people at the British Geological Survey have recently put their maps online for free viewing so you can see some of this for yourself.

The rocks in photo 1 are known as 'Wheatley Coral Rag' limestone, Wheatley being a town in Oxfordshire where they're common, although outcrops of the rocks are also found at other locations in the county including Headington (where it was extensively quarried from the 14th to the 19th century), Cowley (where, apropos of nothing, the BMW 'Mini' car is manufactured) and the hill-top village of Beckley. Probably the most magnificent example of the use of Wheatley limestone in Oxfordshire is my garden wall...although I suppose the Radcliffe Camera building (built in the 1740's) in central Oxford isn't bad either! (Photo 2 - was taken by Tom MurphyVII and I understand I can use it here under the terms of the GNU free licence). The lower 3rd of the building is the Wheatley limestone.

The material that went into making Wheatly rag was laid down in shallow seas in the Upper Jurassic period (145-161 MY-ago) when my garden would have been at a latitude of 35-40 deg. North (the latitude of Southern Spain today). The rocks are composed of masses of shards of mollusc shells, bits of sea urchin and fragments of coral. In photo 2 I've zoomed in on the rock at the rear of photo 1. I'm not a skilled photographer but I hope you get an impression of this.

I have not attempted to identify the species of my fossils. Indeed I would hardly know where to start. If one finds a fossilised Jurassic mollusc shell, is it a relatively simple matter of keying out the find from amongst a handful of known and easily distinguished species, or is exhaustive analysis needed to separate it from hundreds or even thousands of candidate Jurassic molluscs? (Can anyone comment?). Part of me would love to throw myself into a study of this, but logic tells me that with limited time to devote to my hobby, and around 750 UK species of moss, 800 larger moths, 3500 larger fungi, a similar number of lichens, 4000 species of beetle, 7000 flies, heaven only knows how many mites and nematodes...I have more than enough living species to occupy my time without embarking on a study of the extinct ones.

I am left with one lead as to species. In discussing locally discovered Corallian fossials, the book above shows images of fossil oysters of the species Nanogyra nana, corals of the species Isastrea explanata and Thecosmilia annularis and sea urchins of the species Nucleolites scutatus. Whether any of these were truely present in my garden I do not know, and even if they were they're not living there now and so strictly I shouldn't count them in my species tally. Since this is 'my party' however, I am going to flagrantly break the rules, assume at least one of them did once live in my garden, and chalk up one more species to my blog count. Complaints should be addressed to my lawyer!