Cretaceous Crato creature!

Last year, I was mooching around some fossil sites online and found some insects for sale. They were from an old collection and had originally been collected from the Crato Formation in Brazil. Many interesting specimens had already been sold, but among those remaining was a rather nice little beetle (according to the seller) around 12.5mm long excluding appendages. Such items are popular with collectors (including plenty with more money than me), but this one had been broken in half and neatly glued. So, still complete, but less popular with collectors and hence more affordable. Result! I bought it...

Here it is - my Cretaceous insect complete with crack, but otherwise in good condition.

...and so, it has sat in my curio cabinet for a while, until today I decided to find out more about it. First of all, the location. The Crato Formation is of Early Cretaceous age and is found in the Araripe Basin of NE Brazil. It is an important Lagerstätte (an undisturbed fossil accumulation, and today's first new word) which has yielded many important fossils - the decay conditions (or taphonomy - new word no.2) are unusual and mean that limestone accretions formed nodules around dead organisms, preserving more soft parts than is usually the case; there have even been Odonata specimens with preserved iridescence, and fish with their stomach contents preserved! The strata were mostly laid down mostly during the early Albian Age (approx 108 mya) in what was then a shallow inland sea. Crato has long been considered part of the Santana Formation (also important for palaeontology), but this is about 10 my younger and the two have now been formally separated.

Sadly, local mining activity damages the sites and a significant trade in illegally collected fossils has developed over the last decade or so. As such specimens are likely to be lost to science (not to mention incidental damage to the site), paleontologists are quite rightly calling for an urgent preservation programme - I'm glad that my specimen was legitimately collected and studied well before this became a problem; a reminder to check the provenance of anything like this, particularly for non-specialists like me who might otherwise not be aware of problems with particular sites, however well known to specialists.

So, I know it's a bit more than 100 my old, and it might be a beetle - what next? Well, as I've mentioned before, I'm no palaeontologist, but it's time to take a closer look...

The front half.

The two circular structures in the middle of this picture almost look like they could be eyes, but they are behind the sinuate line that I think must be the rear of the head or front of the pronotum. These, along with the yellowish 'figure-8' behind them, and the white subtriangular 'shield' behind that, appear to be the underlying attachments and musculature below the pronotum - possibly attachments between the prothorax and pronotum, and/or the attachment points of the elytra. The eyes appear quite bulbous and between them is a blunt protrusion - the mandibles or other appendages?

The thorax and abdomen.

Moving further back, there is a central division (about in line with the crack) and this looks very much like the rear of the pronotum. Behind this is a white area in the centre of the abdomen, surrounded by darker oblique abdominal segments; nothig too surprising there. The legs appear fairly simple and are all present - in front of the head is what might be a thickened front left femur, but I can't tell for sure - certainly the other femur looks somewhat thickened where it joins the tibia. Now, time to zoom in a bit more...

The tip of the front left leg.

The legs don't appear to have any major adaptations or obvious spines, and going by the above picture, terminate in a single straight to slightly curved claw. Moving onto the head, there seems at first to be few features, but closer examination provides a little more, at least tentatively:

Close-up of mouthparts.

Close-up of left eye (the circle is approx 0.3-0.5mm across).

 

An even closer look at the left eye.

The blunt protrusion at the front of the head does appear to be the mandibles, and they appear fairly simple (there's just a hint of a serrated join between the two halves, or is that wishful thinking aided by the handy placement of crystals of rock?); in any case there's little more to be seen here. However, zooming in on the left eye (the better preserved of the two), does reveal some interesting detail. Within the blue circle above is an area that, down the microscope, is not only shiny, but also has a few surviving ommatidia (lenses of the compound eye). At this point, my camera can do no better, but I hope that you can see some of these (six or so, faintly at the centre of the blue circle). They appear to be separated (unlike a mosaic arrangement), and thisis seen in some modern beetles (as well as the trilobite fossil that's also in my cabinet). Now moving rearwards again...

Close-up of part of the pronotum/thorax.

Close-up of abdominal segments.

 The pronotum shows layers of tissue in close-up; both what looks (to me) like chitinous material, and a small amount of what I think is soft tissue - the small folded purplish area just below the centre. The abdomen shows a similar mixture of textures, and I have to wonder whether the faint striation in the centre is the remains of muscle fibres, some other structure, or an artefact of preservation. Any thoughts on this are most welcome.

Close-up of the tip of the abdomen.

 Lastly, looking at the tip of the abdomen, what appears to be the pygidium (rear-most segment) is visible. This looks like a pair of curved 'pincers' but I expect is simply an artefact of preservation i.e. a gap left when the fossil formed. Still, some insects do have structures like this, so it could be something genuine - again, ideas are gratefully received and it would be great to be able to identify some reproductive apparatus...

So, after all that, what do I think I've got? Well, going by the general shape and simple legs, I thought it was probably a water beetle - something like the family Noteridae ('burrowing water beetles') which is already known from Crato/Santana. This example shows some similar features - leg form, overall shape, the round pronotal attachments behind the head. However, a message from Beetles In The Bush (see below) provided a quite different hypothesis. The eyes are where I think they are (the ommatidia are a good clue!), and the femurs are enlarged, and likely to be raptorial. The 'mandibles' appear to be the clypeus (so, the 'serrated join' mentioned above is an artefact/wishful thinking after all), and the revised ID is that it's a belostomatid hemipteran - a group still around and known at the 'giant water bugs' (which I've seen plenty of on my travels), although this one is less giant than many. The body shape is right, and having looked at some other images of fossil belostomatids (like this), the oblique abdominal segments are closer than seen in water beetles. Like the Noteridae, they've been found at Crato before and have one of the best fossil records of any insect group (presumably because of their large size and relatively frequent/rapid burial in shallow waters). So, I have a new (and better) ID, but I'm open to suggestions and further hypotheses. It's not the beetle I thought I'd bought, but it's still excellent and I remain fascinated by it - I'd love to learn more; I do have an 'Atlas of Macroinvertebrate Fossils', but it's only got two insects in it which are nothing like this.

Lastly lastly - for a brief extract from the 'insect' chapter of 'The Crato Fossil Beds of Brazil' (Martill, Bechly & Loveridge, 2007, Cambridge University Press), look here. For more about the whole book (it's not cheap though, RRP £92), look here (Amazon has a 'look inside' link for this title too). Soooo tempting...