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Of vole plagues and hip glands

The views expressed are those of the author and are not necessarily those of Scientific American.


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Bank vole, aka Red vole, Wood vole or Red-backed vole. Image by soebe, licensed under Creative Commons Attribution-Share Alike 3.0 Unported license.

You’ll already know what voles are. They’re blunt-nosed, comparatively short-tailed rodents with chunky bodies and rounded ears that are mostly concealed by fur. They often have open-rooted (or near open-rooted) teeth and perform well as grass-eaters (as you know, the silica crystals embedded in grass blades make them nasty, abrasive things to eat on a regular basis). There are a lot of voles: about 155 living species included within about 20 genera, the taxonomy, biogeography and phylogeny of which is hugely complex. There are several different ways of classifying voles: some authors put them together in a group (a ‘family’), along with lemmings and muskrats, termed Arvicolidae whereas others group them together with hamsters and some other muroid rodent groups within Cricetidae. [Adjacent image by Soebe.]

Arvicola amphibius, giant of European voles. Image by Rabensteiner, in public domain.

Here in the UK we generally have three voles, though things are made more complicated by the fact that there are several island endemics that have usually been regarded as distinct subspecies (and sometimes as distinct species). Anyway, the three are the Bank vole Myodes glareolus* (also known as the Red vole, Wood vole and Red-backed vole), Water vole Arvicola amphibius and Field vole Microtus agrestis (also known as the Short-tailed field vole, Short-tailed vole and, confusingly, as Field mouse or Meadow mouse). We also have the Orkney or Guernsey vole M. arvalis, though there are suspicions that this species was introduced to the UK from the Iberian Peninsula some time within the last 5000 years. Actually, though, the fact that the British Bank vole record only goes back to Roman times means that doubts have occasionally been cast about its presence as a native too (Flowerdew 1993). [Bank vole image below by Photopippo.]

German Bank vole in woodland habitat. Image by Photopippo, licensed under Creative Commons Attribution-Share Alike 3.0 Unported license.

* Like me, you might better know this vole as Clethrionomys. That generic name is still in widespread use, but it’s becoming more accepted that Clethrionomys Tilesius, 1850 should actually be included within the older Myodes Pallas, 1811 (Carleton et al. 2003).

I want to say a few things about voles, and all stem from my familiarity with these British species. My personal encounters with voles have been few and far between, and have always involved single individuals. I assume that this is true of most non-specialists. In view of this, it’s perhaps hard to appreciate that voles are famous for occasionally erupting into vast swarms or plagues where they cover the countryside in their millions and eat everything in sight. Lemming plagues are reasonably well known (it having given rise to the infamous tales of lemming mass suicide and so on)… but vole plagues?

Field voles caught per 100 traps in a Scottish study area, showing an obvious peak marking the 2011 ‘plague’ event. Image from BBC News, data from Aberdeen University.

Plagues of Field voles occurred in the New Forest and Forest of Dean (both here in southern England) in 1813 and 1814 and caused “considerable alarm lest the whole of the young trees in those extensive woods should be destroyed by them” (according to Thomas Bell’s 1837 A History of British Quadrupeds). Another epic vole event occurred in Scotland in 1891 and 1892 and other rodent plagues that were almost certainly of Field voles occurred in Kent and Essex in 1580 and 1581 and 1648, and in Norfolk in 1754 (Freethy 1983).

The animals forming these plagues were often only vaguely described (in the ones from the 1580s, the rodents were described as “sore plagues of strange mice”), meaning that it’s difficult to be absolutely sure about their identity. Take the account from Brut y Tywysogion of AD 893 which describes the following: “vermin of a strange species were seen in Ireland, similar to moles, with two long teeth each; and they ate all the corn, all the pasture, and the roots of grasses, and the hay ground, causing a famine in the country, and it is suppose the Pagans took them there, and wished likewise to introduce them into the isle of Britain; but by prayer to God, alms to the poor, and righteous life, God sent a sharp frost during the summer weather, which destroyed those insects” (Matthews 1989).

This sure sounds like a vole plague, the problem being that voles didn’t – historically – live on Ireland. Bank voles occur there now. They were discovered in County Kerry in the south-west in 1964, and have been spreading ever since (Fairley 1969, 1971). It’s thought that these Irish voles were introduced during the 1920s. The fact that voles can be accidentally introduced and then missed for decades probably explains that 9th century plague.

Bank vole and Field vole compared: the former has more obviously ears, a longer tail (about half of its body length) and is reddish-brown dorsally. The latter is greyish-brown, short-tailed and its ears are mostly invisible. Image by Darren Naish.

Why fluctuations in vole populations occur and why vole plagues erupt has been the subject of much speculation, as has the sudden cessation of the same events. Declines in the numbers of predatory birds and mammals, rainfall patterns and other climatic events have all been suggested. Within recent decades, mustelid predators have been outed as the probable controlling factor (Hanski et al. 1993) – in other words, the vole booms have been interpreted as part of a top-down-controlled trophic cascade – but this remains contested and environmental factors have also been shown to have a likely role in some habitats (Huitu et al. 2003).

Aww, cute wittle Field vole. Again, note near-absence of visible pinnae. Image by Neil Phillips, used with permission.

Lest we think that massive eruptions of Field voles only occurred in the past, a recent surge – occurring in 2011, again in Scotland – was termed a plague (though, I’m not wholly sure that it was a plague in the same sense as those events of centuries past). The voles were said to number in the hundreds of millions, their extraordinarily successful population increase apparently being due to snow cover resulting from an unusually cold winter. You can read more about the 2011 ‘plague’ in this BBC News article. [Adjacent Field vole image by Neil Phillips of UK Wildlife.]

Crashes in rabbit numbers have sometimes been linked to vole population surges, and weasels are known to increase in numbers when Field voles have good years. Owls move in and have an easy life when vole numbers surge (especially Short-eared owls Asio flammeus), and domestic cats and dogs are said to become so satiated with vole during plague events that they simply lose interest in eating them. Voles themselves become cannibalistic when their numbers are unusually high: they quarrel a lot, kill each other in fights, and seem not to like wasting the opportunity to eat a deceased neighbour.

Intuitively, it seems most likely that a combination of factors come together to give the population an ideal season. The Scottish events of the 1870s and 90s were severe enough that sheep had to be given supplementary feed since the voles had eaten most available grass (Matthews 1989); their burrows had also made the ground treacherous underfoot in places. Even in places where Field voles have not erupted in plagues but are simply highly numerous, considerable damage can be incurred – the British forestry industry is thought to be responsible for massively increasing the vole population, and it is in these forests that the voles bite the bark away from young trees, thereby deforming or killing them (Matthews 1989).

Field vole teeth have open roots: Bank voles have closed ones. Images composited from Lawrence & Brown (1963).

Field voles are predominantly grassland voles, though they also occur in moorland, forests and dunes where sufficient grass cover is available. The weaving runway/burrow systems made by these voles – concealed by tall grass stems and going beneath tussocks, leaf litter and metal sheets – are often marked with small piles of cut, shredded grass fragments and droppings. Indeed, the numbers and whereabouts of voles can be easily tracked in some areas by counting their droppings (it’s much easier than trapping live animals in marked-off areas, or studying burrows or feeding piles). Field voles produce an obscene number of dropping – more than 1050 per day according to some counts. Bank voles are mostly woodland animals, sometimes associated with hedgerows. Field voles have an especially distinctive cheek dentition: the edges of the crowns form sharp, zig-zagging margins and the teeth are rootless. Bank vole cheek teeth have rounded edges and two roots are present on each tooth.

Bank and Field vole cheek dentitions compared. Note the obvious angular edges to the Field vole teeth. Images composited from originals in Lawrence & Brown (1963).

Like many rodents, voles possess an impressive number of scent glands. Their bodies are covered in them, meaning that they have the chance to deposit scent whenever they walk over an object or brush against one. Bank and Field voles both have anal glands and preputial glands (located on either side of the penis or clitoris). In addition, Bank voles have glands on the lips and corners of the mouth, on the pads on the soles of their feet, and on their hips. The hip glands become much enlarged during the breeding season. Field voles have flank glands as well (these are more anteriorly positioned than hip glands) – you might be familiar with those if you keep (or ever kept) pet hamsters.

Schematic depiction of most (but not all) rodent scent glands, depicted on a generic muroid. Image by Darren Naish, based on diagrams in Flowerdew (1993).

I was hoping to say more about voles, but it’ll have to wait to another time. I’ve covered some very familiar, extensively studied species here, but there’s a huge number of obscure ones. The UK’s island-endemic voles are also interesting and worthy of discussion, as is the evolution, diversity and systematics of the Water vole(s). Well, more on voles some other time. Tet Zoo needs more on rodents.

For previous Tet Zoo rodent articles, see…

Refs – -

Carleton, M. D., Musser, G. G. & Pavlinov, LYa. 2003. Myodes Pallas, 1811, is the valid name for the genus of red-backed voles. In Averianov, A. & Abramson, N. (eds) Systematics, Phylogeny and Paleontology of Small Mammals. Russian Academy of Sciences (Saint Petersburg), pp. 96-98.

Fairley, J. S. 1969. Bank voles Clethrionomys glareolus Schr. in Co. Cork. The Irish Naturalists’ Journal 16, 209.

- . 1971. Bank voles Clethrionomys glareolus Schreber in Cos. Clare and Tipperary. The Irish Naturalists’ Journal 17, 23-24.

Flowerdew, J. 1993. Mice & Voles. Whittet Books, London.

Freethy, R. 1983. Man & Beast: The Natural and Unnatural History of British Mammals. Blandford Press, Poole.

Hanski, I., Turchin, P., Korpimäki, E. & Henttonen, H. 1993. Population oscillations of boreal rodents: regulation by mustelid predators leads to chaos. Nature 364, 232-235.

Huitu, O., Norrdahl, K. & Korpimäki, E. 2003. Landscape effects on temporal and spatial properties of vole population fluctuations. Oecologia 135, 209-220.

Lawrence, M. J. & Brown, R. W. 1963. Mammals of Britain: Their Tracks, Trails and Signs. Blandford Press, Poole.

Matthews, L. H. 1989. British Mammals. Bloomsbury Books, London.

Darren Naish About the Author: Darren Naish is a science writer, technical editor and palaeozoologist (affiliated with the University of Southampton, UK). He mostly works on Cretaceous dinosaurs and pterosaurs but has an avid interest in all things tetrapod. His publications can be downloaded at darrennaish.wordpress.com. He has been blogging at Tetrapod Zoology since 2006. Check out the Tet Zoo podcast at tetzoo.com! Follow on Twitter @TetZoo.

The views expressed are those of the author and are not necessarily those of Scientific American.





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  1. 1. SciaticPain 2:17 am 01/2/2014

    What no comments yet on super-sexy voles?

    What can be said about vole social behavior? Is their any indication of voles forming multigenerational colonies or anything approaching the social order of naked mole rats? All of those scent marking glands are very suggestive to me for use in intricate social interactions but I have never looked at vole social behavior much. Furthermore I can imagine a strong evolutionary impetus for cooperative social behavior in the voles that live under snow.

    Speaking of little rodents under the snow I just learned about a theory suggesting foxes can use the earth’s magnetic field as a “range finder” of sorts to help pinpoint rodents under the snow.
    http://earthsky.org/earth/foxes-use-earths-magnetic-field-to-jump-on-prey
    I would not be surprised if the idea has been covered here before but I thought it was interesting when I learned of it watching a nature documentary last night.

    Whenever I walk by vacant lots or fields I always keep an eye out for little voles and such but hardly ever see them. But I am sure that there are a lot more rodents than are visible because of all the raptors/herons/feral cats/ other predators I see in the same fields.

    Duane Nash

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  2. 2. Dartian 3:00 am 01/2/2014

    Darren:
    Arvicola amphibius, giant of European voles

    Giant of native European voles, to be precise; the largest vole found in Europe nowadays is the muskrat Ondatra zibethicus – although it has, of course, been introduced there from North America.

    the fact that the British Bank vole record only goes back to Roman times means that doubts have occasionally been cast about its presence as a native too

    Are there any genetic data that also suggest the bank vole’s recent introduction to Britain?

    As for vole eruptions, they occur, as you mention, also outside of the UK. They are a well-known (although not necessarily a well-understood) phenomenon especially in the Holarctic boreal zone, where these population fluctuations are typically more pronounced than they are at lower latitudes.

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  3. 3. Tayo Bethel 3:42 am 01/2/2014

    That was informative … I live in a place where voleswould be considered exotic. Speaking of which, why have voles not inaded tropical and subtropical regions? And just out of curiosity, have field voles ever been consumed as food?

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  4. 4. David Marjanović 5:49 am 01/2/2014

    Huh. I didn’t know about the plagues at all.

    as you know, the silica crystals embedded in grass blades make them nasty, abrasive things to eat on a regular basis

    A few years ago I read that phytoliths are actually pasty affairs that are softer than enamel. Instead, sand abrades teeth, so high-crowned and rootless teeth are found in mammals that eat at ground level or of course below. This explains the gondwanatheres, in whose times grass wasn’t common enough to be staple food.

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  5. 5. Dartian 6:37 am 01/2/2014

    Darren:
    Water vole Arvicola amphibius”

    Oh, I only now noticed. No comment on the fairly recent name change of this species (formerly known as A. terrestris)?

    voles can be accidentally introduced

    I can attest from personal experience that this is indeed the case! I once transported a vole in my pants for at least half an hour without noticing. True story! For various reasons I’d rather not share it here, but remind me at some suitable RL occasion and I’ll recount it. The story works better while drinking a few beers anyway… ;)

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  6. 6. Yodelling Cyclist 7:14 am 01/2/2014

    Has it ever been suggested to have David Marjanović and/or Dartian, maybe Gigantala on the Tetzoo podcast?

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  7. 7. Dartian 7:25 am 01/2/2014

    Yodelling Cyclist:
    Has it ever been suggested to have David Marjanović and/or Dartian, maybe Gigantala on the Tetzoo podcast?

    As a matter of fact, I have once been mentioned – by my real name – on a Tet Zoo podcast. I think that I lack the necessary personal charisma to pull off an actual appearance in one – but thank you for suggesting it anyway. ;)

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  8. 8. naishd 7:34 am 01/2/2014

    Thanks for comments. Yes, of course Muskrats are enormous compared to native European voles – I will add the word ‘native’ somewhere to the text. As for the altered nomenclature of the Water vole, I’m saving all that for another article.

    TetZoopodcats: we’re rarely organised enough to book guests ahead of schedule (making time for podcasting is really, really difficult), but we’ll definitely feature more guests in future. Whether David and Dartian will be among them is a question I cannot answer right now.

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  9. 9. naishd 7:37 am 01/2/2014

    Oh yeah, and I forgot that it’s the sand particles ingested with grasses – not the silica particles embedded within the blades – that causes abrasion to teeth. I’ve definitely heard this too.

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  10. 10. Yodelling Cyclist 9:04 am 01/2/2014

    I feel I should name check vdinets as well.

    Is the year of murids being considered seriously?

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  11. 11. naishd 9:13 am 01/2/2014

    Murids no, rodents as a whole, hmmm…. wait and see…

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  12. 12. Heteromeles 10:45 am 01/2/2014

    Hmmm. So teeth go through lignin like it’s butter? I don’t think so.

    Actually, I’m not so sure that phytoliths are as soft as you think. They’re the primary tool for archeologists and paleoecologists, because they tend to be the only thing left after even the lignin is gone, which doesn’t suggest a friable structure at all.

    Moreover, in live plants, they tend to concentrate in parts of the plant most likely to be attacked by herbivores or pathogens, and there’s some nice research showing that plants engineered to not express phytoliths are much more vulnerable to both pathogens and herbivores. They also tend to cluster in the outer tissues of seeds and fruits.

    Finally, we use phytoliths fairly routinely. The scouring part of the “scouring rush” (Equisetum) are its phytoliths, and silicified hairs are the injection needles in nettles. Moreover, diatomaceous earth is made from the phytoliths created by diatoms (their silicon shells).

    I’d go so far as to say that the only place I’ve heard that phytoliths are soft and pasty is on this blog. References please, gentlemen?

    Ref: Piperno (2006) Phytoliths: A Comprehensive Guide for Archaeologists and Paleoecologists.

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  13. 13. naishd 12:46 pm 01/2/2014

    I certainly ain’t saying that phytoliths are soft – rather, that it’s the sediment particles stuck to foliage that have driven the evolution of tooth toughness in herbivores. I took this from various studies on tooth microwear by Janis, Sanson and others – there are numerous studies testing or reviewing this, including…

    Hummel, J., Findeisen, E., Südekum, K. H., Ruf, I., Kaiser, T. M., Bucher, M., Clauss, M. & Codron, D. 2011. Another one bites the dust: faecal silica levels in large herbivores correlate with high-crowned teeth. Proceedings of the Royal Society B: Biological Sciences 278, 1742-1747.

    Lucas P. W. & Teaford M. F. 1995. Significance of silica in leaves eaten by long-tailed macaques (Macaca fascicularis). Folia Primatologica 64, 30–36.

    Sanson G. D., Kerr S. A. & Gross K. A. 2007. Do silica phytoliths really wear mammalian teeth? Journal of Archaeological Science 34, 526–531.

    However, the issue of whether phytoliths or ingested grit are the main driver of tooth toughness remains contested – the more recent studies suggest that both might be involved, as might the longevity of the animal species you’re examining and other factors too.

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  14. 14. vdinets 1:08 pm 01/2/2014

    The issue of plagues and cycles in voles and lemmings is, indeed, an interesting mystery. Lemming cycles on large near-shore islands often don’t match those on the adjacent mainland; some island populations never cycle; there is some indication that lemmings continue to cycle in captivity; where many species of voles and lemmings co-occur, they usually cycle in unison; in the sagebrush uplands of western USA, some populations of Montane and Long-tailed voles cycle periodically, others produce irregular plagues, and yet others are always low, with no obvious ecological differences between them… try to make sense of all this :-)

    Yod: Thanks for checking my name! There is this old format where a simpleton asks all kinds of naive questions and the scientists answer them; would be fitting if I was invited.

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  15. 15. Yodelling Cyclist 1:47 pm 01/2/2014

    Vdinets: I’m familiar with the format. It’s essentially the approach around here!

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  16. 16. AlHazen 9:41 pm 01/2/2014

    Re David Marjanovi´c (#4):
    I think I remember reading somewhere that grass showed up significantly in South America quite a while before it hit the rest of the world in a big way… so maybe Gondwanatheres DIDhave to cope with it?

    (I think I’ve lost track– is it the current orthodoxy that Gondwanatheres were not Multituberculates… but that there were also genuine mutis in South America?)

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  17. 17. Chabier G. 2:50 am 01/3/2014

    Tayo, I’ve never heard of people eating field voles here in Spain, but the Southern Water Vole (Arvicola sapidus)was the original meat of the famous “paella”, a speciality born in the once swampy SE coast (Valencia). Consumption of this species would be more widespread,I think, as the latin name “sapidus” means “tasty”.
    Vole cycles are really mysterious, here we have Pitymys voles in the dry mediterranean regions, they can be more or less abundant following the year climate, but they never erupt forming plagues (yet more peasants wouldn’t agree).Otherwise, in the endless corn fields of North Castile, Microtus arvalis cycles and its demographic booms turn into enviromental disasters, thanks to the stupid reaction of Spanish authorities (sowing huge amounts of rodenticides over the whole region)as hapened some years ago. In Aragon, Microtus arvalis lives in cold mountain environments, where crop fields are similar to those of Castile but the whole extension is much smaller, I think this prevents vole popoulation booms.

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  18. 18. naishd 5:21 am 01/3/2014

    AlHazen (comment # 16): yes, what appear to be real multis are now known from South America. Kielan−Jaworowska et al. (2007) described Argentodites coloniensis for an Upper Cretaceous premolar. Together with Australia’s Corriebaatar marywaltersae (Rich et al. 2009) and possible Madagascan records, it now seems that multis were essentially cosmopolitan during the Cretaceous.

    Refs – -

    Kielan−Jaworowska, Z., Ortiz−Jaureguizar, E., Vieytes, C., Pascual, R. & Goin, F. 2007. First ?cimolodontan multituberculate mammal from South America. Acta Palaeontologica Polonica 52, 257–262.

    Rich, T. H., Vickers−Rich, P., Flannery, T. F., Kear, B. P., Cantrill, D. J., Komarower, P., Kool, L., Pickering, D., Trusler, P., Morton, S., Klaveren, N. van, & Fitzgerald E. M. G. 2009. An Australian multituberculate and its palaeobiogeographic implications. Acta Palaeolontologica Polonica 54: 1–6.

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  19. 19. David Marjanović 6:05 am 01/3/2014

    Hmmm. So teeth go through lignin like it’s butter?

    Nobody has mentioned lignin. Lignin is an organic substance that doesn’t contain any silicon. Tough as it is, it can break teeth that aren’t chisel-shaped enough; but it’s not hard enough to scratch enamel.

    tend to be the only thing left after even the lignin is gone, which doesn’t suggest a friable structure at all.

    Depending on the conditions of deposition, this doesn’t necessarily have an influence on fossilization. Lignin can rot. Phytoliths can’t – as long as they’re not physically damaged, they’re preserved like any other rock.

    Moreover, in live plants, they tend to concentrate in parts of the plant most likely to be attacked by herbivores or pathogens, and there’s some nice research showing that plants engineered to not express phytoliths are much more vulnerable to both pathogens and herbivores. They also tend to cluster in the outer tissues of seeds and fruits.

    Which herbivores? The lumping with pathogens suggests insects; and I definitely expect silica to be harder than chitin.

    The scouring part of the “scouring rush” (Equisetum) are its phytoliths,

    Harder than lots of things, not necessarily harder than enamel.

    and silicified hairs are the injection needles in nettles.

    Much harder than skin; and able to maintain a sharp tip.

    Moreover, diatomaceous earth is made from the phytoliths created by diatoms (their silicon shells).

    Diatom shells are very different from phytoliths. They’re continuous monoliths (two per cell).

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  20. 20. David Marjanović 6:08 am 01/3/2014

    I think I remember reading somewhere that grass showed up significantly in South America quite a while before it hit the rest of the world in a big way… so maybe Gondwanatheres DIDhave to cope with it?

    Grasslands showed up earlier in the Eocene than elsewhere. That’s the age of the last known gondwanatheres. (And IIRC, the only known Eocene one is from Antarctica, though close to South America – on Seymour Island.)

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  21. 21. vdinets 12:00 pm 01/3/2014

    In the book Never Cry Wolf by Farley Mowat there is a good recipe for cooking voles; the author calls it Souris a la Creme.

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  22. 22. vdinets 12:06 pm 01/3/2014

    Here it is online: http://rationalwiki.org/wiki/Recipe:Souris_a_la_Creme

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  23. 23. barndad 12:37 pm 01/3/2014

    Although the Orkney and Guernsey voles are sometimes lumped together as aberrant, large, UK island forms, they appear to have very different histories. Recent ancient DNA work shows that the Orkney vole was likely a Neolithic transfer from the Belgian region, and that for whatever reason, quite a few were taken across. So many that the diversity now found in Orkney voles is sometimes greater than that found in large parts of the European mainland. The Guernsey voles are genetically depauperate and likely follow from a simple, recent colonisation. What is interesting is that it seems these boom-bust cycles in Mainland voles (Microtus arvalis in this instance) have the effect of wiping the genetic slate clean. The expansion and contraction appears to favour only a few lineages with the result that the majority of diversity is lost during each cycle. However, in regions like Orkney where these cycles do not occur, the “ancient” lineages can still be found. More in this recent paper.

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  24. 24. naishd 2:29 pm 01/3/2014

    Awesome – 23 comments, thank you, barndad. I’m planning to talk about Orkney and Guernsey voles (and the others) in a later article – we can consider this an interesting teaser…

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  25. 25. Andreas Johansson 3:13 pm 01/3/2014

    Someone remind me what’s magical about 23 comments?

    If phytoliths are softer than enamel, is there anything preventing grasses from evolving tougher ones?

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  26. 26. Heteromeles 3:18 pm 01/3/2014

    @David: phytoliths do include diatom shells, at least according to the people who study phytoliths. I should note that, of the papers listed by Darren (and it’s not a definitive list, only the Sanson paper tests tooth hardness, and it’s compared against papers from 1959 and 1978 that found the opposite. The Sanson et al. paper uses Vickers Hardness, which is a standard test of plastic deformation of materials under pressure. They also tested four species of grasses and sheep teeth, so it’s not a big test.

    Can a softer material damage a harder material? Absolutely. One formerly common method should be well-known: flintknapping. You can easily knap flint (which has a Mohs hardness of 7) with copper (Mohs hardness of 2) if you apply the pressure in the right direction. Vickers hardness only tests deformation under perpendicular pressure. Enamel is hard, but like flint, it’s pretty brittle. Can tooth enamel spall? According to that cap on my incisor, it certainly can. While two enamel surfaces crashing straight into each other may be able to crush some phytoliths between them, if there’s any angle in the forces, all bets are off, and(oddly enough) angled forces don’t appear to have been tested by anyone yet. I wouldn’t rate enamel’s relative hardness as prima facie evidence of its ability not to be damaged by silica.

    Another paper (on locusts, rather than vertebrates) suggests that silica in leaves reduces digestibility, and the best explanation is that increased silica content decreases mechanical degradation of plant cells, thereby reducing the digestion of the leaves containing the silica. The link is to the entire paper, so you can see links to other papers on the literature of herbivores chewing silica in plants.

    Do I believe in grit? Not really. Sand is a particle size, not a mineral, and the minerals composing dust, sand, and grit vary widely in hardness. The Hummel et al paper cited by Darren above notes that there’s no difference in the silica in herbivore poop in the Serengeti between the wet season and dry season, but there is difference in fecal silica content between species with low-crowned teeth and those with high-crowned teeth across seasons. Of course I don’t know objectively whether the dry-season Serengeti has more dust on the leaves than the wet-season Serengeti (sarcasm), but it does appear that high-crowned grazers have more silica in their poop, and this suggests a correlation (causation, even) between tooth characteristics and the amount of silica in the diet.

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  27. 27. naishd 3:26 pm 01/3/2014

    I don’t have a phytolith in this fight, or a sedimentary particle. All I’m saying is that people are arguing over whether phytoliths or grit particles are more important in shaping tooth toughness/hypsodonty, with different studies producing different results for different taxa, and with some studies suggesting that other factors – longevity and growth rates of the organism and so on – might have an impact as well. Do silica particles in leaves drive dental adaptations in herbivores? Well, maybe they do. Do we know this for sure? No, we’re still talking about it.

    As for 23 comments… it’s the magic number Tet Zoo articles have to reach before we can move on.

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  28. 28. Jerzy v. 3.0. 3:29 pm 01/3/2014

    There was lots of ecological research on rodent cycles, Darren, you barely scratched the surface! I committed a publication on voles once, and really there are layers and layers on why cycles, why not, who affects what etc.

    The issue was often explained by imperfect population cotrol by specialist vole predators, who deplete vole population, die or disperse, and cannot prevent a new cycle, while dominance of generalist predators keeps vole populations stable. However, the cycles might be more likely caused by voles themselves overexploiting their food plant resources.

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  29. 29. Jerzy v. 3.0. 3:30 pm 01/3/2014

    However, I am in holiday mood, and voles remembered me of a little book you may find interesting: Chips Tardy “Each day a small victory”. The story is a year of life of Max the stoat, plus his animal neighbors, in English coutryside. The biology is solidly done: characters live, eat, get eaten, emerge from hibernation, mate, breed, migrate, hibernate and die at the appropriate seasons.

    The premise is that animals talk like in Beatrix Potter, but the biological reality is kept. The result is rather like Tarantino’s Pulp Fiction, where quests of several characters meet and overlap, and everybody is concentrated on sex and violence. Worth reading, or giving as a present to an annoying animal rights activist who believes nature is nice.

    Oswald the vole and several unnamed voles and mice appear there. The best scenes are when humans enjoy a relaxing day in the calm countryside, while around them, half a dozen unseen animals frantically try to steal their food, eat each other, or just survive.

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  30. 30. MattMiller 3:36 pm 01/3/2014

    Interesting post, Darrren. I live in the western United States, where we have periodic population explosions of montane voles. I witnessed this a few years ago and it was quite a sight to behold — voles everywhere, and a feeding frenzy among various predators (raptors, coyotes, weasels, rattlesnakes, etc). An impressive spectacle actually.

    I wrote a blog about large trout keying in on the “vole hatch”: http://blog.nature.org/science/2013/02/27/big-fish-rodent-eating-trout/

    Cheers,
    Matt Miller
    science writer
    The Nature Conservancy

    Link to this
  31. 31. naishd 3:36 pm 01/3/2014

    Jerzy: yes, I absolutely agree (re: comment # 28, on the tons of literature). It’s always the same problem – I aim to produce a short, concise review, and to just mention, most briefly, the interesting key points in passing… I usually aim not to get bogged down for ages and ages about the complex, much-studied phenomena. And thus it is with vole plagues and their apparent cyclicity… yes, you could write whole books on these things.

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  32. 32. morphospaceman 3:57 pm 01/3/2014

    In rodents hypsodonty and hypselodonty has, in my opinion, quite much to do with fossoriality and basically eating pure soil with food (eating at ground level, hoarding seeds underground). Phytoliths and other silica particles must be important as well, though. As silica contents seem to drive the local scale population cycles in voles in central europe. Also rodents eating aquatic plants often very high in phytolith contents usually have extreme dental adaptations while eating virtually no sediment.

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  33. 33. Yodelling Cyclist 4:25 pm 01/3/2014

    Dumb questions:

    In the rodent populations that cycle, why hasn’t repeated exposure to genetic bottlenecks not terminated these species? By now, after generations of dropping to small populations, surely the survivors are approaching clones, or do rodents mutate strangely rapidly?

    On phytoliths, to broaden the discussion, are there any fish (or other predators) which prey on siliceous sponges? I’m thinking of animals that would deliberately consume silica which could be an interesting point of comparison.

    I’d also point out that whilst all these structures may be chemically SiO2, the exact polymorph that is being generated will have a major impact on its toughness/hardness. Also the grain size, alignment, presence of impurities….all the fun of the materials chemistry faire! That’s before we get started on what may or may not be varying between the enamels of different species.

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  34. 34. naishd 6:06 pm 01/3/2014

    Sponge eating (= spongivory), you say? There are sea turtles that do it – that eat siliceous sponges and hence eat mouthfuls of silica fragments, but they’re a bit low on teeth…

    Meylan, A. 1988. Spongivory in hawksbill turtles: a diet of glass. Science 239, 393-395.

    And there are also spongivorous fish. I don’t know much about them – does anyone else?

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  35. 35. Yodelling Cyclist 6:42 pm 01/3/2014

    Well, turtles have beaks. What do we know about turtle beaks? Is that enamel/bone/keratin sheath?

    Various sea turtles (I don’t know about hawksbills) have been kept in captivity. Do their beaks need to be filed (lacking a siliceous sponge diet)? Certainly rabbits need their teeth filed, and I was told that this was because their teeth continuously grew to compensate for their grass diet.

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  36. 36. vdinets 7:28 pm 01/3/2014

    Yod (#33): rodents usually don’t cycle in unison in different parts of their ranges, so gene flow might compensate the loss of diversity… although some island populations (i.e. on Vrangel I.) also cycle and don’t seem to have trouble.

    It is also possible that repeated bottlenecks have removed all harmful alleles, like in those small island bird species that can bounce back after their population has been reduced to 2-3 individuals, and show no negative effects of inbreeding.

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  37. 37. vdinets 7:49 pm 01/3/2014

    Speaking of tooth wear, I once learned that the reason there is virtually no cattle in the Gran Sabana region of Venezuela is that all cows die from starvation by the age of three; their teeth become completely worn off. Locals said it’s something in the soil; I wonder if it’s iron-rich quartzite dust from eroding tepuis.

    As for voles and lemmings, one interesting thing about them is that they are the only tetrapods other than Sorex shrews, grouse and Lariform birds to have extensively diversified at very high latitudes. Their biogeography looks like there’s been no glaciations at all (the fact that ice age denialists sometimes mention).

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  38. 38. AlHazen 10:06 pm 01/3/2014

    Darren and David (#18 and #20)–
    Thanks for answers to my questions. I thought I remembered that there was Cretaceous grass in South America, but … my memory has more holes in it than the Gondwanathere fossil record!
    I **did** remember that there was a South American multi, but I think I’d missed the Australian one! (Hmm… do you suppose that multi’s emigrated from SA to Aus, or the other way, via Antarctica.)

    On, or at least tangential to, the topic of Australian multis: Burramys, the Mountain Pygmy Possum, has weird, multi-like, lower premolars. When Broom originally described it from fossils, he remarked on this. Anybody know whether he actually believed he HAD found an Australian Allotherian, or only something that remarkably converged on multituberculates?

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  39. 39. Dartian 3:02 am 01/4/2014

    Jerzy:
    an annoying animal rights activist who believes nature is nice

    Animal rights activists don’t think that wild animals live in peace and harmony with each other (at least no animal rights activist that I’ve ever met believes that). They are opposed to human mistreatment of animals, which is something quite different.

    Vladimir:
    As for voles and lemmings, one interesting thing about them is that they are the only tetrapods other than Sorex shrews, grouse and Lariform birds to have extensively diversified at very high latitudes.

    What do you mean by “extensively diverified” – how do you quantify that? What do you mean by “very high latitudes”? And what taxonomic level(s) are you operating with here?

    Their biogeography looks like there’s been no glaciations at all

    What? No! Holarctic microtine phylogeography is actually best explained by the effects of the Pleistocene glaciations. For example, the unusual distribution of the Norwegian lemming Lemmus lemmus – endemic to northern Europe – was already as early as in the 1920ies (Ekman, 1922) suggested to be the result of its local survival in ice-free refugia throughout the glacial periods. Later genetic studies (Fedorov & Stenseth, 2001) have supported Ekman’s hypothesis.

    Results of several studies on other microtine species also suggest strong effects of Pleistocene glaciations (e.g., Fedorov et al., 1999; Jaarola & Stearns, 2002; Cook et al., 2004; Galbreath & Cook, 2004; Brunhoff et al., 2006; Haring et al., 2011). In fact, it seems that everything we know about extant microtine phylogeography is quite compatible with what we think we know about Pleistocene glaciation history. So which, then, are the anomalous microtines whose distribution supposedly doesn’t fit into this pattern?

    Al:
    my memory has more holes in it than the Gondwanathere fossil record

    :) That’s the best Tet Zoo one-liner that I’ve read for quite some time!

    References:

    Brunhoff, C., Yoccoz, N.G., Ims, R.A. & Jaarola, M. 2006. Glacial survival or late glacial colonization? Phylogeography of the root vole (Microtus oeconomus) in north-west Norway. Journal of Biogeography 33, 2136-2144.

    Cook, J.A., Runck, A.M. & Conroy, C.J. 2004. Historical biogeography at the crossroads of the northern continents: molecular phylogenetics of red-backed voles (Rodentia: Arvicolinae). Molecular Phylogenetics and Evolution 30, 767-777.

    Ekman, S. 1922. Djurvärldens Utbredningshistoria på Skandinaviska Halvön. Albert Bonniers Förlag, Stockholm.

    Fedorov, V.B., Goropashnaya, A., Jarrell, G.H. & Fredga, K. 1999. Phylogeographic structure and mitochondrial DNA variation in true lemmings (Lemmus) from the Eurasian Arctic. Biological Journal of the Linnean Society 66, 357-371.

    Fedorov, V.B. & Stenseth, N.C. 2001. Glacial survival of the Norwegian lemming (Lemmus lemmus) in Scandinavia: inference from mitochondrial DNA variation. Proceedings of the Royal Society of London B 268, 809-814.

    Galbreath, K.E. & Cook, J.A. 2004. Genetic consequences of Pleistocene glaciations for the tundra vole (Microtus oeconomus) in Beringia. Molecular Ecology 13, 135-148.

    Haring, E., Sheremetyeva, I.N. & Kryukov, A.P. 2011. Phylogeny of Palearctic vole species (genus Microtus, Rodentia) based on mitochondrial sequences. Mammalian Biology 76, 258-267.

    Jaarola, M. & Searle, J.B. 2002. Phylogeography of field voles (Microtus agrestris) in Eurasia inferred from mitochondrial DNA sequences. Molecular Ecology 11, 2613-2621.

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  40. 40. David Marjanović 8:36 am 01/4/2014

    Someone remind me what’s magical about 23 comments?

    It’s the minimum number of comments every Tet Zoo post gets.

    phytoliths do include diatom shells, at least according to the people who study phytoliths.

    That’s silly, then. Diatoms aren’t plants and haven’t been mistaken for plants in 60 years. Their chloroplasts are derived from secondary endosymbiosis of red algae.

    Can a softer material damage a harder material? Absolutely. One formerly common method should be well-known: flintknapping.

    Sorry for the misunderstanding. A softer but tougher material can absolutely break a harder but more brittle one. I’m sure that’s why rodents & lagomorphs have ever-growing incisors: chisel-shaped teeth break rather easily.

    The molars (and premolars where present) of grass-eating placentals or gondwanatheres don’t have tall cusps or crests or suchlike, however. They can, I think, only be ground down; that requires scratching as far as I understand, and softer materials cannot scratch harder ones, right?

    I don’t understand how most microwear works, though.

    Another paper (on locusts, rather than vertebrates) suggests that silica in leaves reduces digestibility, and the best explanation is that increased silica content decreases mechanical degradation of plant cells, thereby reducing the digestion of the leaves containing the silica. The link is to the entire paper, so you can see links to other papers on the literature of herbivores chewing silica in plants.

    Phytoliths definitely make chewing harder. (So does lignin, just to a lesser extent.) The question is whether they grind down teeth in the process.

    there is difference in fecal silica content between species with low-crowned teeth and those with high-crowned teeth across seasons

    Not surprising: species with low-crowned teeth tend towards the browser end of the scale and get less dust in their food, those with high-crowned teeth have the entire range available to them (and many are rather specialist grazers).

    rodents eating aquatic plants often very high in phytolith contents usually have extreme dental adaptations while eating virtually no sediment.

    Now it gets interesting! Details, please! :-)

    Well, turtles have beaks. What do we know about turtle beaks? Is that enamel/bone/keratin sheath?

    All vertebrate beaks are ever-growing keratin sheaths supported by bone, just like claws/nails. Naked bone, to my knowledge, is entirely restricted to deer antlers.

    Parrotfish “beaks” consist of teeth.

    IIRC, cephalopod beaks are keratin, too.

    I **did** remember that there was a South American multi, but I think I’d missed the Australian one!

    I’m not sure if I remembered the Australian one either! :-)

    (Hmm… do you suppose that multi’s emigrated from SA to Aus, or the other way, via Antarctica.)

    Probably they simply had a Pangaean distribution in the Middle/Late Jurassic.

    Anybody know whether he actually believed he HAD found an Australian Allotherian, or only something that remarkably converged on multituberculates?

    Its molars, AFAIK, are unspectacular for a possum, so most likely the latter.

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  41. 41. Gigantala 9:53 am 01/4/2014

    “(I think I’ve lost track– is it the current orthodoxy that Gondwanatheres were not Multituberculates… but that there were also genuine mutis in South America?)”

    To the best of my underestanding, they’re usually considered non-cimolodont multituberculates (actual cimolodonts are known from Gondwanna, as pointed before)

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  42. 42. vdinets 11:48 am 01/4/2014

    Dartian: let’s say, more than ten species occurring mostly north of the tree line? Taxonomic levels are subjective ;-)

    Using glaciations to explain species’ distributions is a tricky thing, and it’s very easy to do it wrong. If a species is absent in some region, you can say it’s because of glaciations. If it’s present, you say it’s because of refugia. The funny thing about voles and lemmings is that many endemic taxa occur in places that were glaciated extensively, i. e. Scandinavia, Ogilvie Mountains, Labrador, the main range of Caucasus, etc. I can’t think of any other vertebrate group with such pattern of endemism, except Lagopus with their countless subspecies. Of course, the reason is probably their ability to survive on nunataks and in other small refugia, but at first glance it does look weird.

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  43. 43. vdinets 11:50 am 01/4/2014

    Forgot the marmots… they also have a few endemics in recently glaciated places.

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  44. 44. Dartian 2:15 pm 01/4/2014

    Vladimir:
    let’s say, more than ten species occurring mostly north of the tree line?

    But is there any place in the world (north of the tree line) where more than ten microtine species actually live sympatrically? That’s certainly not the case in Europe/the Western Palaearctic, where you might perhaps get at most eight species (and even that’s a stretch).

    As for Europe/the Western Palaearctic as a whole, there are about 40 species (the taxonomy is a bit disputed) of native microtines (voles and lemmings). Almost 30 – or in any case, well over 20 – of these do not live north of the tree line; their distributions are restricted to Central and southern Europe (e.g., the species-rich Pitymys voles), the Caucasus, or even the Levant. Other species do reach far north but the main parts of their ranges cover the temperate regions of Europe. There are only a small handful of Western Palaearctic species that may be considered truly arctic or subarctic.

    So you see, I’m not at all sure that microtines are necessarily at their most diverse at “very high latitudes”. Their diversity seems rather to peak at slightly lower latitudes, in the Holarctic temperate zone. Arctic specialists they are not.

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  45. 45. vdinets 10:30 pm 01/4/2014

    Dartian: I never said they had most of their diversity at high latitudes, I just pointed out that they are one of very few lineages to have extensively diversified up there. Some tundra stretches of Dempster Hwy in Yukon do have 10 spp. of voles and lemmings (including common muskrat), but that’s not the point. What I find interesting is that the overall number of species occurring north of the tree line is so impressive (14-19 in North America and the same number in Eurasia, with just 3-5 spp. shared), in part because they have high levels of regional endemism there, which is also unusual for tetrapods other than Sorex and Lariformes.

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  46. 46. Dartian 2:25 am 01/5/2014

    Vladimir:
    I never said they had most of their diversity at high latitudes, I just pointed out that they are one of very few lineages to have extensively diversified up there.

    From what you originally wrote, it wasn’t really clear what you meant. That’s why I asked for clarifications. If you want to have a meaningful discussion about a topic such as this, you must first define the parameters of your argument more unambiguously. “Extensively diversified at very high latitudes” is a statement that requires both definitions (e.g., providing a cutoff point for “high” latitudes) and a context (e.g., a comparison with microtine diversity at lower latitudes).

    Speaking of clarifications: what do you mean by “Lariformes”? That is not a valid taxon name. Do you mean the ‘order’ Charadriiformes (which includes the various shorebirds, gulls and their kin, and alcids) or do you mean the ‘suborder’ Lari (which includes the gulls, terns, skuas, and a couple of other groups)?

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  47. 47. David Marjanović 8:19 am 01/5/2014

    To the best of my underestanding, they’re usually considered non-cimolodont multituberculates

    Not in the cladograms briefly shown in the SVP presentations on the complete skull from Madagascar, though they’re not very far away. Given the mess that the phylogenetic positions of Multituberculata and Haramiyida are even without gondwanatheres, we may have to wait for several more papers to find out.

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  48. 48. vdinets 1:16 pm 01/5/2014

    Dartian: yes, Chardriiformes, sorry.

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  49. 49. Jerzy v. 3.0. 4:11 pm 01/5/2014

    Anatiformes and Podicipediformes are also more common in high latitudes. There may be unique tropical clades, but flocks of diverse geese and ducks are a phenomenon of temperate climate.

    Waterbirds and wading birds are most common in seasonal environments, otherwise they are strongly limited by fish and crocodiles. Probably many pterosaurs were also migrants, visiting temporary floodplains and summer high-latitude habitats of the Mesozoic.

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  50. 50. Gigantala 7:52 pm 01/5/2014

    Not in the cladograms briefly shown in the SVP presentations on the complete skull from Madagascar, though they’re not very far away. Given the mess that the phylogenetic positions of Multituberculata and Haramiyida are even without gondwanatheres, we may have to wait for several more papers to find out.

    Mmm, I was under the impression they were. I think they’re still considered allotheres in any case, no?

    Haramiyidians are now allotheres too? Never heard of that before; if Allotheria is Multituberculata + Gondwanatheria + Haramiyida, then we have a clade that goes to the roots of the mammal phylogenetic tree. Or the Allotheria + Theria clade dates all the way to the Triassic, which seems to not be that far off given genetic studies that suggest therians existed all the way back in the Lower Jurassic.

    The atrocities I would commit in the name of a good genetic sampling of all of those clades…

    Waterbirds and wading birds are most common in seasonal environments, otherwise they are strongly limited by fish and crocodiles. Probably many pterosaurs were also migrants, visiting temporary floodplains and summer high-latitude habitats of the Mesozoic.

    We do have pterosaur remains in areas thought to have been quite cold (Liaoning, Dinosaur Cove, et cetera), so migratory species must have certainly existed. Of these, ctenochasmatoids and boreopterids, the two clades most certainly known to have had aquatic habits comparable to those of modern freshwater aquatic birds, are known from said places, so there’s that.

    Indeed, to the best of my knowledge the largest ctenochasmatoid and boreopterid samples come from Liaoning, which was cold enough to not have crocodylians in it (to give off perspective, Australia in the Lower Cretaceous, then subpolar, had one or two aquatic crocodylomorph genera), so it is possible that those pterosaurs were subjected to the same competitive pressures as aquatic birds. Particularly boreopterids, which seemed to have foraged pelagically on freshwater bodies.

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  51. 51. naishd 8:59 pm 01/5/2014

    The concept that haramiyids are allotherians, and close relatives of multituberculates, is – he says without checking the literature – more or less the ‘classic’ phylogenetic hypothesis, supported by Butler, Kielan-Jawaroska and others.

    The latest discoveries – Arboroharamiya (published 2013) and so on – seemingly support this view, showing that at least some haramiyids are more multi-like than was assumed before.

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  52. 52. David Marjanović 10:50 am 01/6/2014

    I think they’re still considered allotheres in any case, no?

    So few people have an opinion that it doesn’t make sense to say there’s a consensus. The term Allotheria may or may not be a synonym of Multituberculata.

    given genetic studies that suggest therians existed all the way back in the Lower Jurassic

    Calibrated how?

    The concept that haramiyids are allotherians, and close relatives of multituberculates, is – he says without checking the literature – more or less the ‘classic’ phylogenetic hypothesis, supported by Butler, Kielan-Jawaroska and others.

    Yes.

    The latest discoveries – Arboroharamiya (published 2013) and so on – seemingly support this view, showing that at least some haramiyids are more multi-like than was assumed before.

    Well. The analysis that comes with the description of A. does support that. The analysis that comes with the description of Megaconus in the same issue of Nature supports the other usual hypothesis, haramiyidans as pretty basal non-mammalian mammaliforms. Have you read their common News & Views article?

    Cifelli, R. L. & Davis, B. M. (2013): Jurassic fossils and mammalian antiquity. Nature 500: 160–161.

    What needs to be done is to merge those two quite divergent analyses (they have different taxon samples, different character samples…).

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  53. 53. Gigantala 12:58 pm 01/6/2014

    Calibrated how?

    I’m going by Hugall, A.F. et al. (2007).

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  54. 54. AlHazen 11:25 pm 01/6/2014

    The Megaconus/Arboroharamiya issue was the best in Nature this year! (Possible bias: I am interested in paleomammalogy, and not in most of the other tipics Nature covers….)

    Takehome was that — IF A and M are both haramiyids — then Jurassic haramiyids show an exceptionally broad range of skull traits, ranging from a basal mammal (iaform) condition to a “definitive” mammalian jaw-ear arrangement: so there is an argument that one was a haramiyidan and the other a multi. Supporting the “anti-Allotheria” theory, that multis and harries have at best convergent resemblances and are not closely related. The argument for a monophyletic Allotheria (harries, with multis derived from them) is that they resemble each other VERY closely, particularly in molar morphology, so parsimony…

    Tooth form has obvious links to functional considerations: my own … gut feeling? … is that convergence should be EXPECTED in such matters. (I still shake my head over the apparent establishment of a monophyletic Glires: I felt, a priori, that it was to be expected that different lineages would have convergently evolved “gliriform” dentitions.) So my current … prejudice … is to be anti-Allo.

    The methodological issues are fascinating. I take it most people would admit that IN PRINCIPLE convergence can happen and that this complicates cladistic inference, but in practice it is so hard to make a rigorous link between morphology and function that nobody wants to adopt a policy of “correcting” cladistic analyses by reducing the value of synapomorphies that a priori seem likely to be candidates for convergent evolution.

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  55. 55. David Marjanović 9:52 am 01/7/2014

    I’m going by Hugall, A.F. et al. (2007).

    The sauropsid timetree paper that isn’t focused on mammals? I’ll check it out ASAP…

    I still shake my head over the apparent establishment of a monophyletic Glires: I felt, a priori, that it was to be expected that different lineages would have convergently evolved “gliriform” dentitions.

    Yeah, lots of people did for all of the 20th century if not more, and lots of mammals have indeed convergently evolved gliriform dentitions (that term really exists, and is used for ever-growing chisel-shaped incisors, AFAIK). It became a logical fallacy: “they have their gliriform dentition in common, which doesn’t count, because it might possibly have evolved convergently; I haven’t noticed that they have anything else in common; therefore, they can’t possibly be sister-groups”. The exact same thing happened with “raptors” and owls: “ooh, that’s too easy, so it can’t possibly be true”.

    The way convergence can mess up phylogenetic analysis is not by its mere existence. Halfway reasonably large cladograms derived from morphological data routinely have consistency indices of 0.3 or even less, meaning that each character state change happens not once, but on average three, four, five times. It’s just noise: as you add data, the signal adds up, and the noise cancels itself out.

    Convergence only becomes a problem when a matrix contains correlated characters, meaning that the same character state change is in effect counted several times. This way you get an artifical signal that adds up at least as fast as the real one. Well, overexpress ectodysplasin in the development of a mouse, and the mouse grows extra cusps on its molars and grows an atavistic premolar – several characters included in many phylogenetic analyses change states as the result of what would be one change to one gene. Underexpress ectodysplasin, and the mouse grows peg-like molars like the fish-eating rodents of Australia & New Guinea…

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  56. 56. AlHazen 1:19 am 01/8/2014

    Re: David Marjanoviç-
    Correlated characters are, of course, the big problem, but your example shows that it can be very hard to decide that two characters are correlated(*) in the appropriate way: what if we were wondering about premolars and molar cusps in a species that wasn’t conveniently extant to allow developmental experiments like the one described.
    The general strategy you describe — LOTS MORE DATA, so the signal will drown out the noise — is of course the right one, but frustratingly hard to follow with extinct taxa known from typically spotty remains! I suspect it will be a long time before we have enough specimens of Multituberculates and Haramiyidans to sort them out! (And more about the developmental pathways involved in things like the inner-ear/jaw joint would probably help too.)

    (*) “Correlated” is maybe a bit unfortunate as a word here, given the old saw about correlation not being causation: what is relevant is correlations that stem from a shared cause. Your example of the mouse cheek teeth is of characters that are correlated because of an ontogenetic cause, but I think similar problems can arise from (functionally important) characters that are correlated by being evolved in response to common environmental and “niche” causes. There is a very nice paper by Christine Janis and a co-worker (it’s in a volume put out by ??? Zoological Society of London ??? in the 1980s and I’ll see if I can find a reference) on the relationships of the numerous fossil groups of Pecoran Artiodactyls. Tree based on “straight” count of traits. Then discussion of how various tooth and jaw-shape traits “go with” different diets (grazing vs browsing– that sort of thing). New tree with traits correlated by this mechanism not “double counted”: topology changes.

    (And how does one get the right diacritic on the last letter of your surname again?)

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  57. 57. AlHazen 1:41 am 01/8/2014

    Ummm….
    I think the paper I was remembering was
    Scott, KM, and CM Janis, “Relationships of the Ruminantia (Artiodactyla, Mammalia), and an analysis of the characters used in ruminant taxonomy,” in Szalay, Novacek & McKenna, ads, Mammal Phylogeny: Volume II: Placentals (New York, Springer-Verlag, 1993), pp 282-302

    but from the bibliography at CMJ’s Brown U. web-page, she and Scott wrote several papers on related topics, and I have also read

    Janis & Scott (1988) “The Phylogeny of the Ruminants (Art, Mam),” in
    NJ Benton, ed, The Phylogeny and Classification of Tetrapods: Systematics Association Special Publication 35B (Oxford: Clarendon, 1988), pp. 273-282

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  58. 58. David Marjanović 9:13 am 01/8/2014

    Correlated characters are, of course, the big problem, but

    I agree with everything. :-)

    And how does one get the right diacritic on the last letter of your surname again?

    1) Copy & paste.
    2) Copy & paste from the character map. In Windows, that’s Start > All Programs > Accessories > System Programs > Character Map.
    3) Let’s see if the HTML entity works here: ć should give… ć.

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  59. 59. David Marjanović 9:15 am 01/8/2014

    …It works too well, even. :-) ć

    NJ Benton

    MJ. Michael is his first name.

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  60. 60. David Marjanović 9:16 am 01/8/2014

    So, the usual HTML trick that’s supposed to prevent “&” from being parsed somehow doesn’t work here. ~:-|

    & # 2 6 3 ; without the spaces.

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  61. 61. AlHazen 12:58 am 01/10/2014

    David Marjanović (#59)
    Sorry, typo: I knew his name was Michael.
    (And cut and paste seems to work… for some things. CMJ’s publication list is in a format I don’t seem to be able to copy efficiently.)

    Link to this

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