Oh, for dendroid graptolites...

[Joe Botting]

Strange things, dendroids. They've basically not been studied at all from Builth (and barely from the rest of Wales, except for one monograph by Bulman that only covered the really good specimens. For those not in the know, graptolites are colonial hemichordates, probably very closely related to the modern pterobranchs, that you also won't have heard of. They build an organic, collagenous skeleton of linked tubes growing from an axis or axes (some are multi-branched, others single-branched, and some with two or more rows of tubes (thecae) per axis).
The planktic graptoloid graptolites have been very intensively studied (ask Lucy, who happens to be an expert on the things). The dendroids appear to have been the ancestral group, and lived as bushy, many-branched structures attached to the seafloor, or occasionally to floating objects like pumice or seaweed. The problem is that although they've hardly been examined at all, they're extremely diverse. We've been finding them everywhere from the blackest black mudstones to some very shallow-water sandstone. Even worse, it's unusual to find two specimens of the same thing. Where you find one, there are probably going to be a dozen species, even if specimens are actually very rare.
They can turn up as a single, perfect specimen in otherwise barren beds, or they can dominate the assemblage (although this is rare). Rather unlike graptoloids, we have yet to find a species from two different sites!

Ecologically, these are very interesting things, and they may also be of use for dating, if we can get a much more complete record of them. Because of their sporadic occurrence, they are something that anyone can find, and which are likely to be new if you do. So... now's your chance to be famous. How many have you found, in what environments and what age, and have you got any pictures? With your help, we can start to build up a picture of their ecology and real diversity. The ones we've found will be up on the main site shortly! (Honest! It's nearly there!)

Thanks,
Joe & Lucy

[dot]

Excuse my ignorance - what exactly are these dendroid things? How would I know one if I found it? You make it sound like they're really common, so why have I never heard of them before!

[hallucygenia]

Hi Dot - welcome to the forum!

Your questions would be a lot easier to answer if the old as the hills main website were up, because you could just look at some of the pictures on there. As it is, your best way of getting an idea of what they look like is to type dendroid into Google images - there are some nice pictures on there.

To give you some sort of idea before you do that, dendroids are mostly medium-sized fossils, between about a centimetre to ten centimetres high (although they can be bigger). When complete they're more-or-less conical, in the form of an open cone. The sides of the cone aren't solid, but are made of linear structures (each individual one is called a stipe) branching from a common origin at the bottom. The stipes repeatedly branch in two as they grow upwards. In some forms the stipes are joined together by horizontal branches called disseptiments. Dendroids are mostly found flattened, so their conical structure isn't necessarily obvious.

If you look closely at a dendroid (you'll need a hand lens or, preferably, a microscope) you'll see that there are little tubes sticking out of each stipe. These are called thecae (singular theca). Each theca contained an individual animal. Dendroids were colonial animals, the same sort of idea as corals.

As to why they're not better known - part of the problem is that they're not well studied. Bulman's 1922 work is the only publication on Welsh dendroid graptolites that I'm aware of. If fossil groups aren't well studied there are two possible reasons. One is that there isn't enough good material (not the case for dendroids). The other is that no-one has got around to working on them - this is what has happened with dendroids, and was also the case with sponges until Joe started studying them.

I think I should mention here that dendroids aren't found throughout the geological column. They're known from the Cambrian to the Carboniferous (roughly 500 million to 350 million years ago). That's another reason why they're not better known - they're simply not there in a lot of rocks.

As Joe mentioned, although they can be locally common, often within a locality they'll be quite rare. So even if they do occur at a site the chances of them being found can be quite low.

Hope this answers your question - please say if there's anything I haven't covered properly.

Lucy

[Joe Botting]

To add to Lucy's response (and hi also, Dot!)...

There are a whole host of fossils that aren't as common as trilobites, graptolites and brachiopods, but still turn up regularly if you spend a good amount of time looking. A lot of them haven't been well studied (or studied at all, in some cases!), and they're usually quite inconspicuous.
Dendroids look rather like bits of plant, and are often mistaken for them. The saw-tooth pattern is often difficult to see (look especially at the insides of the outermost branches, where they should be more-or-less in profile view), and they appear as simple black or silver markings. However, a good specimen is quite stunning, and not at all easy to miss.
Although we tend to think of them as moderately common, relative to the really rare things, we've still only found a few dozen specimens in our years collecting in the Builth Inlier, which I guess puts it into a more accurate perspective. There are lots of things out there that I've only ever seen one specimen of. You're likely to see a dendroid some time, but unless you find exactly the right bed, you won't find enough to get bored with them!
Most of the difficulty, though, is spotting that you've got something worth trying to identify in the first place!

Joe

[dot]

Thanks Hallucygenia and Joe. That makes more sense now. I tried looking on google for pictures, but most of what was there seemed to be plants. I think I found one or two pictures though. They seem to be fairly distinctive looking things.

[Joe Botting]

Hi Dot,
Yes, they're fairly distinctive, if you get a nicely preserved one... but a small grotty one is really quite difficult to see, sometimes!
Have a browse through the eccentric but highly authoritative
www.graptolite.net

for lots of information from Piotr Mierzejewski (a Polish Count and a top-class researcher) and others. (There are actually a fair number of other graptolite groups as well - the stolonoids, crustoids, camararoids, etc - but these really are obscure. Most palaeontologists have probably never heard of them.) Oh, and for the full effect, don't have you computer on 'mute...'

Joe

[Joe Botting]

Well, no-one's reported any discoveries here, but I thought I'd add something more, now that there are pictures to look at on: www.asoldasthehills.org/Graptolites.html

As you can see, there are quite a few species, and none of them are described. There's one (not up yet) that might possibly be Callograptus tenuis, but none of the others are identifiable. A lot of them we're struggling to put into genera. The 'dendroid gen et sp. nov.' is certainly new, and shares with Pseudocallograptus and a couple of others, what we call 'compound stipes.' The branches aren't a single row of tubes, but are built from loads of thecae all wrapping around each other. This looks like a really robust, strong structure.

It's theresore a little odd that these robust forms are mostly, as far as we've seen, in the finest-grained sediments, which indicate low turbulence and quiet, perhaps deep water. The ones we get in shallower, coarser deposits are slender, fragile-looking things, like Acanthograptus and the dendroid indet. sp A. There are are fair few Dendrograptus species in the relatively deep-water Llanfawr Mudstones as well, but they're mostly larger than the earlier ones. It's just not right.

We've been wondering if it's to do with flexibility - thin ones behave like elastic, thick ones crumple. It doesn't seem likely, though, and we've got one very shallow-water site with dendroid fragments that are just too small to do anything with. Someone was living there, and being slender didn't stop them falling to pieces.

It's an unsolved mystery at the moment, and we really need more data to get anywhere with it. Comments from anyone, in any area, would be useful for comparison. Otherwise I'll just keep talking to myself, in the hope that someone, somewhere is finding it interesting...

Joe