Return to the Tomb of Zootoca

One of my recent posts took a close look at the mummified corpse of a juvenile common lizard (Zootoca vivipara). Apart from noting that the fungus on it suggested it hadn't mummified too well, I also made the point (aided by a friend who knows about those strange tetrapod thingies) that there was surprisingly little written about lizard teeth/dentition. While mammalian dentition commands many pages of diagrams showing the different types of teeth, lizards - at least in the books and websites I could find - tend to simply be described as 'homodont' i.e. having all teeth of the same form. While the variation isn't as striking as in mammals (canines, incisors, molars etc), this is an oversimplification, so I decided to stay well outside my invertebrate comfort zone and delve further. First of all, an overview of the upper and lower jaws.

Fig. 1. Dorsal view of the lower jaw.

Fig. 2. Ventral view of the upper jaw.

Fig. 3. Side view of the upper jaw.

Fig. 4. Side view of the lower jaw (the red line parallels the curve of the jaw).

Comparing Figs. 1 & 2, the outline shapes of the jaws are clear and it can be seen that they match well, widening behind the snout - unsurprising as they wouldn't work if they didn't fit together. In Fig. 1, the dark central structure is taken to be the tongue which has mummified and appears to match the shape of the upper palate in Fig. 2. Looking at Figs. 3 & 4, the upper jawline is approximately straight in side view, while there is a slight curve in the lower jawline. However, the front section of the lower jaw (where the majority of teeth can be seen) is quite straight and so still fits well with the upper jaw, and I imagine that there could be some flexing when biting, especially as this is a juvenile with small bones. This is somewhat speculative however, and I'm more than happy for anyone who knows more about such things to send me info on errors or omissions! Now, zooming in on the jaws...

Fig. 5. Lower jaw - curved tooth arrowed.

Fig. 6. Lower jaw - 'appendiculate' teeth arrowed.

Fig. 7. Lower jaw - apparently serrated tooth arrowed.

Fig. 8. Upper jaw - three apparently fused teeth indicated by the position of the scale bar.

The homodont description of lizard teeth where they are all considered to be 'conical' is clearly not the whole story when looking at Fig. 5 which shows backwards-curving teeth at the front of the lower jaw - presumably for holding on to prey when it is initially captured. While some of the cheek-teeth do have simple conical points on a cylindrical shaft, others are again more complex as in Fig. 6 (you may need to enlarge it) which shows that some are 'appendiculate' or at least asymmetrical with a protrusion on the forward side. I don't know what the function of this might be - maybe a closer fit is ensured with the upper jaw, and/or there could be some element of shearing'cutting which a simple conical point would not achieve. To me, the latter idea is possibly supported by Fig. 7 which (as well as the asymmetrical shape) shows what appears to be a serrated edge. Given that Z. vivipara feeds on prey such as invertebrates with tough exoskeletons, such dentition may be useful.

Lastly, Fig. 8 shows a small section of the upper jaw where three teeth appeared to be fused. Again, the function is not clear (to me, anyway), but I can imagine the 'inter-tooth' sections acting like blades and/or providing a close fit against teeth in the lower jaw. As you can see from the scale bar, the structures here are small and were distinctly difficult to dissect but I hope that the key features are clear. As I say, I particularly welcome comments on this topic and fully expect this to get updated as I learn more.

2012 on the Spot

It's that time of year - the dribbly brained devotees of Mayan stonework-paranoia were wrong and we're still here on New Year's Eve, which means it's time for a run-down of some of my favourite Ecology Spot posts of the last twelve months.

January included a series of four posts about my pet Macleays's Spectre stick insects - I'm not sure I have a favourite as such, though part 2 (the males) does include a shot of one of the boys taking off which was seriously tricky to capture, plus one of my wife's head while she was being used as a launchpad for their aeronautical adventures.

February shifted from tropical-terrestrial to polar-marine with a look at gigantism in Antarctic sea-spiders, inspired by a visit to the Oxford Uni Museum of Natural History.

March was unusually warm and this got me out in the field (well, a churchyard) looking at the bees of a grassy bank, and very pleasant it was too.

In April, more fieldwork led to an unusual aphid/gall find and needed consultation with an aphid specialist to work out - quality collaboration!

May included a variety of invertebrates, including more collaboration, this time in order to identify a tricky pseudoscorpion specimen - a group I've never looked at before.

June saw a rare example of my use of video, looking at the leaf-mining fly larvae in Solomon's-seal.

Into July, and despite the horribly wet summer, I continued to record bee species in our garden (despite the weather, a range of bee-friendly features still attracted them), and reached the grand total of twenty species and counting.

As the summer finally dried out a bit in August, I shifted briefly away from British invertebrates and looked at a poison-arrow frog - you'll see why when you get to the end...

September saw me get a bit speculative (or odd, depending on your point of view) as I looked at why Smurfs are like slipper limpets. Yes, really...

In October, normal service was resumed and I wrote a series of three posts about tarantula anatomy, the third of which looked at their various appendanges (e.g. feet and fangs) - not one for arachnophobes!

November was a busy month - not only did I go on holiday and come back full of ideas realting to things I'd seen during an unseasonally warm week in Devon, but my key to leaf beetles of the British Isles was also published, oh yes :)

And finally onto December where a rather unusual Christmas-party gift led to some unexpected microscope work and a specimen from an unexpected kingdom...

That's all from me for 2012 - back after the New Year celebrations which should involve a ridiculous hat of some sort...

Yup, that's me in a splendid hat with a gun of rum...

Into the Tomb of Zootoca

The title of a lost H.P. Lovecraft tale? Nope, though it isn't every Christmas party that you get handed a box containing a mummified corpse...

A mummified common lizard, Zootoca vivipara

Actually, this isn't as odd as it sounds - the lizard was found by friends while taking up an old carpet, and might be a casualty of one of their cats that subsequently dried out. As you'll see later, it isn't perfectly preserved... Anyhow, the first thing I did was measure it - at approximately 40mm in length including tail, it was newly born as the common (or viviparous) lizard (Zootoca vivipara, previously Lacerta) is 37-44mm long at birth with the tail no more than about half the overall length (Beebee & Griffiths 2000, Inns 2009). Then, as ever, I took a closer look...

Dorsal view of the Z. vivipara specimen

As you can see, the skin/scales of the head is largely intact and the scale pattern remains clearly visible, a feature that can be useful for identification, especially in areas (unlike the UK) with a wide range of superficially similar species. As is typical for young common lizards, the colour is dark, though this could be an artefact of death and drying, and zooming in on the abdominal scales gives a hint of the colour that develops after a few weeks. The dense, overlapping arrangement of dorsal scales (with 'keels') is typical of lacertids.

Dorsal abdominal scales of young Z. vivipara - dark but with a hint of the metallic greenish-brown-bronze colour (including some gold flecks) that typically develops after a few weeks (Beebee & Griffiths 2000)

Turning the specimen over, further structures can be seen. As well as skeletal features such as the ribs, some of the ventral scales (or 'plates') are intact (though not the collar area beneath the neck, nor the femoral pores beneath the thigh), and show the development of an iridescent greenish colour. The scales are not simple plates of keratin like the 'scutes' of crocodilians, but are outfoldings of the skin itself that are each covered in a tough waterproof layer and contain both an osteoderm (internal bony plate) for structural integrity and a layer of chromatophores - cells that produce colour - just below the outer epidermis.

Ventral view of young Z. vivipara

Ventral scales/plates of young Z. vivipara

Turning the specimen on its side then allows the skull to be investigated as the skin is missing. You can immediately see the teeth (more below on this) - as is usual for lizards, they are conical and all approximately the same size - and show that the young common lizard is well equipped to begin feeding (on anything small enough to catch, including aphids!) as soon as it is born. It's also worth taking note of the overall structure as lizard skulls are rarely represented in books on animal signs (unlike mammal skulls, a range of which tend to be illustrated) or other resources such as guides to the contents of owl pellets (presumably owls rarely if ever eat them).

Side view of the head of young Z. vivipara.

However, I did notice something towards the rear of the skull - you can just see it in the photo above as a pair of little white dots in the left-most of the three main cavities. Time to switch to a higher magnification...

Small Fungi growing on the head of Z. vivipara

...and another kingdom of organisms as these are clearly Fungi. These structures are around 0.5mm long, with the white 'blob' around 0.1mm in diameter. I can't begin to describe how fiddly it was removing these to make a slide, but I did (tiny tweezers) and decided to see if I could identify the fungus.

Fungus from Z. vivipara (the arrows indicate the length of one of the stalk cells)

This is clearly a spore-mass on a stalk (one cell thick, cell walls indicated by arrows). The white colour of the spore-mass in the first photo is an artefect of lighting and my camera; it is actually a pale yellowish-brown - darker in the second photo where it has been compressed. Consulting Ellis & Ellis (1998) it soon became clear this wasn't a specialised 'bone-eating' fungus but was more likely to be one of the moulds (Ascomycetes) that can be found on a wide range of organic matter. Given the overall form/size and the more-or-less round and transparent spores (some of which appear slightly warty), this is probably Eurotium and/or Aspergillus, although the faint equatorial groove of Eurotium isn't visible in the photos. 'And/or'? you may ask... well...

Cleistothecium (spore mass) of Eurotium /Aspergillus

Warty spores of Eurotium/Aspergillus indicated by arrows. Others are not in focus.

The taxonomy of some fungal groups is complex because different (asexual 'anamorph' and sexual 'teleomorph') stages have been given different names, and in some cases there are several anamorphs, all with separate names. This is case here with Eurotium being the teleomorph and Aspergillus the anamorph - both of which may be found together, and often are. I could expand on this, but fortunately don't need to - as of January 1st 2013, any one fungus will have a single name covering all stages/'morphs', and details of how this will work are given in Hawksworth (2011). As far as this specimen is concerned, taxonomic considerations aside, it does mean that it is mouldy and therefore not perfectly mummified. I have it in a dry container so it may surrvive, or I might find it turns into a clean skeleton. Certainly this eruption from the scales shows it's still active.

'Tuft' of Eurotium/Aspergillus growing from the skin of Z. vivipara

Now, back to the lizard... following a reader's comment, I returned to the specimen and had a better look at the teeth. I also Googled and was surprised to find few images showing lizard teeth in detail - presumably they exist, but not on my bookshelves. As mentioned above, the structure is fairly uniform (unlike us mammals with canines, incisors, molars with varying numbers of cusps and so on), but that is a slight oversimplification.

Cheek teeth of juvenile Z. vivipara

Front teeth of juvenile Z. vivipara

Ignoring the fungal structures this time, the cheek teeth are clearly more-or-less cylindrical with a conical point; they are also transparent showing what I presume is the pulp cavity as a whitish central mass. However, the front teeth are curved backwards and more 'fang-like' as might be expected in order to catch and hold prey. Although showing little obvious differentiation, a search of the literature online indicates (and I'm way out of my comfort zone here!) that lacertid teeth can be categorised as premaxillary (apparently of taxonomic and palaeontological importance with 7 in Zootoca), maxillary and dentary according to their position and associated jawbones (Arribas 1998). This is where I'll stop on dentition, but if any reader would like to expand on this in the comments (e.g. whether the different tooth groups differ structurally), please feel free!

Lastly, I can't finish this post without mentioning reptile conservation in the UK. The common lizard is widespread but has declined, especially in the south, due largely to development pressure and the loss of brownfield sites. Because of this it is now a UK BAP (Biodiversity Action Plan) species. It seems clear that habitat loss needs to be tackled (although with a government that seems to want to relax, rather than tighten, planning laws it is unclear how this will happen), but there is good advice in Gent & Gibson (2003) and Edgar et al. (2010). Rather than repeating what they have said, or putting my campaigning hat on, I'd just like to highlight the importance of collecting (and sending in to Biological Records Centres) reptile species records, especially as part of systematic surveys though ad hoc records are valuable too, and undertaking practical conservation work to improve habitat quality.


References

Arribas, O.J. (1998). Osteology of the Pyrenean Mountain Lizards and comparison with other species
of the collective genus Archaeolacerta Mertens, 1921 s. l. from Europe and Asia Minor (Squamata: Sauna: Lacertidae). Herpetozoa 11(1/2): 47-70.
Beebee, T. & Griffiths, R. (2000). Amphibians & Reptiles. HarperCollins, London.
Edgar, P., Foster, J. & Baker, J. (eds.) (2010). Reptile Habitat Management Handbook. ARC, Bournemouth.
Ellis, M.B. & Ellis, J.P. (1998). Microfungi on Miscellaneous Substrates (2nd ed.). Richmond, Slough.
Gent, T. & Gibson, S. (eds.) (2003). Herpetofauna Workers' Manual (revised reprint). JNCC, Peterborough.
Hawksworth, D. (2011). A new dawn for the naming of fungi: impacts of decisions made in Melbourne in July 2011 on the future publication and regulation of fungal names. Mycokeys 1: 7-20.
Inns, H. (2009). Britain's Reptiles and Amphibians. WildGuides, Old Basing.

Awww, ain't it scute... an Isle of Wight crocodile?

As well as yesterday's iridescent limpet, some other items of interest turned up during my visit to the Isle of Wight. Not least of these, found by my wife rather than me, was the series of fossils below, arranged in what appears to be a couple of rows along a large boulder fallen from the cliff...

Overview of boulderful of mystery fossils; each lump several cm across.

The initial cry of 'I've found a dinosaur' was followed by thoughts of 'yeah, right' and then 'er, well, actually...' and so a more careful look was needed. Now, I'm no palaeontologist, but dark pitted lumps in a pale matrix shout 'fossil bone' at me. Or maybe coral... The structure was pitted and compared favourably with a chunk of brontosaurus I've got on the shelf (the small holes and channels were visible, but I wasn't able to get a photo where they showed up clearly), but most interesting were the smaller (a few cm) volcano-like structures protruding from the boulder in a few places among the lumps of maybe-bone.

Above and below, two of the interesting 'volcano' structures (both about 5 x 2.5cm)

 

A bit of research online and even in books started nudging my thoughts away from coral and towards scutes (rectangular-ish armoured skin plates) from a crocodilian of some sort. Many images from these sources appear pitted (not unlike a crumpet in texture) but others are similar to the two photos above. Also, a well-known palaeontologist-blogger suggested the same, so I'm feeling cautiously vindicated at present - and of course, there could be coral, and other things, in the boulder too. However, thoughts on this are most welcome, and there will be an update if anything changes. Until then, my wife's feeling very pleased with herself...