Give Plateosaurus Its Due

You could make a fascinating study (and many have) just looking at the history of which dinosaurs have held the foreground of popular culture when. The Iguanodon and Megalosaurus of the late 1800s, the Trachodon and Palaeoscincus of the earlier 1900s, the stratospheric rise of Velociraptor (sensu lato) with the release of Jurassic Park. And then there are those that never quite seem to get their dues. I've commented before on the odd relegation of Camarasaurus to the status of also-ran among famous sauropods. But perhaps the ultimate example of a dinosaur forced unfairly to the background is the should-be darling of the Late Triassic, Plateosaurus.

Plateosaurus 'engelhardti' in the Sauriermuseum at Frick, copyright Ghedoghedo.

Plateosaurus should, by all rights, be a superstar of dinosaur pop-culture. It was one of the first dinosaurs to reach massive size, extending up to nine metres in length and probably standing about as high (or slightly higher) than a tall man at the withers (Yates 2003). It is known from literally hundreds of specimens, many of them with large parts of the skeleton preserved, representing ages from juvenile to full maturity. Some of the bonebeds where it is found contain little but Plateosaurus and may have been formed in dramatic mass mortality events. Plateosaurus is easily the best known of the basal Sauropodomorpha, the 'prosauropods'. And yet, though Plateosaurus regularly appears in popular depictions, it rarely seems to make much more than a brief cameo. Why is this the dinosaur that gets no respect?

In part, it may be because it comes from a time period that gets less attention as a whole. The Triassic tends to get seen as a meer prelude to later, more 'exciting' parts of the Mesozoic. Plateosaurus itself, together with the other 'prosauropods', tends to also get overshadowed by its later, more eye-catching relatives, the sauropods. And when you get down to it, Plateosaurus may also be let down by the fact that it is perhaps the single most average dinosaur you could possibly imagine. Honestly, if you asked someone to depict a truly generic dinosaur, I don't think it would come out looking too different from Plateosaurus.

Reconstructed Plateosaurus, albeit in a now-obsolescent quadrupedal pose, copyright Elekes Andor.

All these criticisms aside, Plateosaurus is still a fascinating genus. Its remains have been found across central Europe, in Germany, Switzerland and France. The exact number of species in the genus has long been uncertain. As with other early-named dinosaur genera, 19^th Century palaeontologists named several species whose application has been subject to debate. Yates (2003) recognised two species in the genus, the earlier and smaller P. gracilis, and a larger, later species that Yates labelled P. engelhardti but which, due to various taxonomic shenanigans, should probably now be called P. trossingensis. Plateosaurus trossingensis is the better known of the two species, known from extensive bone-beds found at Trossingen and Halberstadt in Germany, and Frick in Switzerland (Lallensack et al. 2021). Some have questioned whether all these bone-beds represent a single species but Lallensack et al. found that examination of skulls from different locations failed to identify specific distinctions. Both Plateosaurus species would have been among the largest land animals of their times; even the smaller P. gracilis may have still reached lengths of five or six metres. Plateosaurus had a relatively long, narrow head though comparison of this feature with other prosauropods may be complicated by post-mortem distortion.

The life posture of Plateosaurus has historically been the subject of much dispute, whether it was bipedal, quadrupedal, or shifted freely between the two. However, recent models of the range of movement of the Plateosaurus hand and fore-arm have concluded that it was incapable of turning its hands palm-downwards, so it could not have supported itself comfortably on its fore limbs (Reiss & Mallison 2014). Obviously, the capacity for quadrupedal locomotion would evolve at some point in sauropodomorph evolution (in this day and age, I don't think anyone is proposing bipedal sauropods) but it was not before Plateosaurus.

Skeletal reconstruction of Unaysaurus talentinoi, copyright Maurissauro.

The phylogenetic relationships of Plateosaurus to other sauropods have been similarly disputed. Plateosaurus is, of course, the type genus of the family Plateosauridae but the concept of that family has varied significantly over time. For a large part of the twentieth century, 'Plateosauridae' was kind of a catch-all for all moderately large prosauropods, with Anchisauridae for the smaller species and Melanorosauridae for the giants. Redefinition of Plateosauridae to include only close relatives of Plateosaurus have significantly winnowed its contents. The current closest known relative of Plateosaurus is the recently described Issi saaneq, based on a pair of near-complete skulls from Greenland (Beccari et al. 2021). This species is close enough to Plateosaurus that its remains were previously assigned to P. englehardti. Offhand, "issi saaneq" is translated by the species' authors as "cold bone" in the local Kalaallisut language, but this looks to be another situation like "mei long" where a phrase was converted into a species name without considering that noun and descriptor order is reversed in biological names.

Other likely plateosaurids include two South American species, Unaysaurus tolentinoi and Macrocollum itaquii. The status of an Indian species Jaklapallisaurus asymmetrica is more uncertain. Beyond this, things become increasingly dodgy with little agreement over the details of prosauropod phylogeny. The overall conservative appearance of prosauropods means that phylogenetic studies are heavily reliant on fine details of the osteology that are debated between authors or not preserved in key taxa. Nevertheless, it does appear that the plateosaurids were widespread in the Norian epoch of the Triassic, and are bound to catch the attention of time travellers to the period.

REFERENCES

Beccari, V., O. Mateus, O. Wings, J. Milàn & L. B. Clemmensen. 2021. Issi saaneq gen. et sp. nov.—a new sauropodomorph dinosaur from the Late Triassic (Norian) of Jameson Land, central east Greenland. Diversity 13: 561.

Lallensack, J. N., E. M. Teschner, B. Pabst & P. M. Sander. 2021. New skulls of the basal sauropodomorph Plateosaurus trossingensis from Frick, Switzerland: is there more than one species? Acta Palaeontologica Polonica 66 (1): 1–28.
Reiss, S., & H. Mallison. 2014. Motion range of the manus of Plateosaurus engelhardti von Meyer, 1837. Palaeontologica Electronica 17 (1): 12A.

Yates, A. M. 2003. The species taxonomy of the sauropodomorph dinosaurs from the Löwenstein Formation (Norian, Late Triassic) of Germany. Palaeontology 46 (2): 317–337.

The Diversity of Neosauropods, or Pity Poor Camarasaurus

Articulated skeleton of juvenile Camarasaurus lentus in the Carnegie Museum of Natural History, photographed by Daderot.

Let me just get the obvious out of the way first: sauropods were huge. Mind-bendingly huge. In some cases, big enough to reduce a human to a sticky puddle under foot and not even break their stride. For close to 150 million years, they were the largest land animals anywhere in the world, and no other terrestrial animal at any time has come even close to rivalling their largest representatives in size. Being around for so long, it should also be no surprise that they were diverse: a large number of sauropod genera have been named, representing a wide variety of forms. Nevertheless, most people's idea of sauropods is encompassed within just four genera from the late Jurassic of North America: Diplodocus, Apatosaurus, Brachiosaurus and Camarasaurus.

These four genera all belong to the clade Neosauropoda, which has been defined as the smallest clade containing the genera Diplodocus and Saltasaurus (a late Cretaceous South American genus). Upchurch et al. (2004) diagnosed the neosauropods by a number of cranial features, together with a reduction in the fourth hind toe (part of a general trend towards toe reduction in sauropods as their feet became more columnar—see this article by Darren Naish for more on the subject). However, Upchurch et al. were writing before the recognition of the Turiasauria, a European clade that is probably the sister group of neosauropods (Royo-Torres et al. 2006), and I don't know how that clade would affect the synapomorphy distribution*. The neosauropods quickly became the dominant sauropod group after their appearance in the middle Jurassic, and the only non-neosauropod sauropods to make it into the early Cretaceous were the aforementioned turiasaurs and possibly Jobaria, an African genus that varying analyses place either just inside or just outside the Neosauropoda.

*There has been an annoying tendency in recent years for many papers featuring phylogenetic analyses to present us with the character data matrix and the final trees from the analysis, but not do anything to map character changes onto the tree. The only way to find that out would be by transcribing the entire matrix and re-running the analysis yourself.

Mounted skeleton of Amargasaurus cazaui in the Melbourne Museum.

The famed North American genera include representatives of each of the two main lineages within the Neosauropoda. Diplodocus and Apatosaurus belong the Diplodocoidea, and Brachiosaurus and Camarasaurus belong to the Macronaria. Diagnostic features of the diplodocoids according the Upchurch et al. (2004) include restriction of teeth to the front of the jaw and a subrectangular snout. This last feature reaches an extreme in the middle Cretaceous Nigersaurus, which was another of those animals that serves to remind us that, if God did indeed create all of nature, then he was taking the piss. Ludicrous diplodocoids also include the late Jurassic South American Brachytrachelopan, which took one look at the graceful, elongate necks of all the other sauropods and decided that it simply couldn't be having with all that.

Reconstruction of Saltasaurus loricatus, by Lady of Hats.

The name of the other lineage, Macronaria, means 'big nostrils', and one of the notable features of this clade is, indeed, a great expansion in the size of the nares, the opening for the nostrils in the skull (though whether the size of the nares directly corresponds to the size of the actual nostrils is, I suppose, another question). As well as Brachiosaurus and Camarasaurus, this clade includes the Titanosauria, a very successful group that included the last surviving sauropods, but whose significance was overlooked for many years because they had the poor judgement not to achieve their main diversity in North America. At least some titanosaurs, such as Saltasaurus pictured above, sported a skin reinforced by nodules of bone.

Which brings us to Camarasaurus. For some reason, of the 'Big Four' genera, this is the one that gets the least love. While the other three have each in their turn enjoyed roles as stars of stage and screen, I'm not aware of a single film in which Camarasaurus has even been given a name-drop*. In John Sibbick's illustration of Brachiosaurus and Camarasaurus together (scroll down a bit at the link) in Norman's (1985) The Illustrated Encyclopedia of Dinosaurs, Brachiosaurus marches confidently towards the front bearing a goofy leer, while Camarasaurus is forced to sulk towards the back. It's all blatantly unfair. It's not as if Camarasaurus is rare: in fact, Camarasaurus may just be the best known of all sauropods, represented in the Morrison Formation by a whole whack of remains, including what is perhaps the single most beautiful sauropod specimen ever found (the one with which I opened this post). It was no slouch in the size department, either: its maximum length of about 23 metres is similar to that of Apatosaurus, despite it having proportionally shorter appendages than the latter. Nor does it lack distinctiveness: the short, bulldog-like face of Camarasaurus instantly stands out in any neosauropod line-up. So after all this time, doesn't Camarasaurus deserve to be given the spotlight?

*Though it is a pity that the name 'Camarasaurus' won out in the priority stakes over its competitor 'Morosaurus', which to those of us from a New Zealand background suggests a dinosaur made out of chocolate.

REFERENCES

Norman, D. 1985. The Illustrated Encyclopedia of Dinosaurs. Salamander Books: London.

Royo-Torres, R., A. Cobos & L. Alcalá. 2006. A giant European dinosaur and a new sauropod clade. Science 314: 1925-1927.

Upchurch, P., P. M. Barrett & P. Dodson. 2004. Sauropoda. In: Weishampel, D. B., P. Dodson & H. Osmólska (eds) The Dinosauria, 2nd ed., pp. 259-322. University of California Press: Berkeley.

The Anchisaurs: Near-lizards or Near-sauropods?

Reconstruction of Anchisaurus polyzelus by Brian Franczak.

The 'prosauropods' are one group of dinosaurs that seemingly don't get no respect. While most other groups have their swarms of enthusiasts, there are relatively few inclined to shout their enthusiasm for non-sauropod sauropodomorphs from the roof-tops. Pop culture has a tendency to gloss them over: in the 1990s TV series Walking with Dinosaurs, for instance, their appearance was limited to a brief cameo at the end of the first episode. Despite this, they are perhaps the most 'dinosaur-y' of all dinosaurs, if comparisons with generic 'dinosaur' depictions are to be made.

The name 'Anchisauria' was introduced by Galton & Upchurch (2004) for the most exclusive clade uniting the genera Anchisaurus and Melanorosaurus. Galton & Upchurch were working under the framework that prosauropods formed a monophyletic sister group to the sauropods, but subsequent phylogenetic analyses have placed sauropods close to Melanorosaurus and hence within Anchisauria (Yates 2010; Yates et al. 2010; Pol et al. 2011). The name 'Anchisauria' can be translated as 'near lizards', but they are more properly near sauropods. Still, because this is to be a prosauropod-centred post, I will ignore the sauropods from this point on unless they insist on pushing their way in (presumably not a difficult task for a sauropod).

Reconstruction of Aardonyx celestae by Julius Csotonyi.
The two anchoring genera remain the most consistent non-sauropod members of the clade. The South American Riojasaurus, placed within Melanorosauridae by Galton & Upchurch (2004), has subsequently been placed outside Anchisauria. The Argentinian Lessemsaurus was also treated by those authors as a melanorosaurid, but may be a basal sauropod proper, while the status of the English Camelotia needs more work (Pol et al. 2011 were unable to resolve its position between Anchisauria and its close relatives). The Chinese Yunnanosaurus was placed within Anchisauria by Yates (2010), but other analyses have disagreed. Two recent genera, Aardonyx Yates et al. 2010 and Leonerasaurus Pol et al. 2011 are currently regarded as anchisaurians.

Mounted skeleton of Leonerasaurus taquetrensis, from here. Note that a large part of this skeleton is evidently reconstructed, as the described skeleton is much more fragmentary.

Anchisaurus polyzelus, from the early Jurassic of Connecticut, reached about four metres in length and is represented by the remains of a number of individuals. Some of these have been described as separate species such as Ammosaurus major and Yaleosaurus colurus, but Yates (2010) regarded them as representing a single species. This makes the '2.5 m' estimate of length given for this species by Galton & Upchurch (2004) too small, as based on a potential juvenile. Nevertheless, it was evidently such a good number that the fossil record apparently decided not to let it pass: the Argentinian anchisaur Leonerasaurus taquetrensis is about that size. The South African Aardonyx celestae was probably comparable to size to Anchisaurus* [Update: Spectacular reading fail on my part. A. celestae was about twice the size of Anchisaurus. See comments below].

*Actually, the scale bar given for the skeletal reconstruction of A. celestae by Yates et al. (2010) would seem to indicate that is must have been the smallest sauropodomorph ever. One can only assume that its size was meant to indicate 500 mm, not '500 µm' [Update: Ignore this. I am a twit. See comments below].

Reconstruction of Melanorosaurus readi, by Steveoc 86. Note that the four species illustrated in this post have been placed in order of increasing proximity to Sauropoda, as resolved by Pol et al. (2011).

Melanorosaurus readi was quite a bit larger, close to eight metres, and phylogenetic analyses have accordingly placed it as the closest relative to sauropods. Interestingly, M. readi was nevertheless quite a bit earlier than the other non-sauropod anchisaurs, being late Triassic rather than early Jurassic, and the smaller anchisaurs evidently survived the evolution of their larger cousins by some time. As well as its larger size, M. readi resembled sauropods in being an obligate quadruped. The other anchisaurs retained their plesiomorphic bipedality; the forelimbs of Aardonyx indicate that it was probably unable to adopt a comfortably quadrupedal stance (being unable to pronate its hands to a great degree, it would have had to rest them on their sides if it tried to do so). Pol et al. (2011) placed Leonerasaurus closer to the sauropods and Melanorosaurus than either Anchisaurus or Aardonyx, but the distal part of its forelimbs are unfortunately unknown.

REFERENCES

Galton, P. M., & P. Upchurch. 2004. Prosauropoda. In: Weishampel, D. B., P. Dodson & H. Osmólska (eds) The Dinosauria, 2nd ed., pp. 232-258. University of California Press.

Pol, D., A. Garrido & I. A. Cerda. 2011. A new sauropodomorph dinosaur from the Early Jurassic of Patagonia and the origin and evolution of the sauropod-type sacrum. PLoS One 6 (1): e14572.

Yates, A. M. 2010. A revision of the problematic sauropodomorph dinosaurs from Manchester, Connecticut and the status of Anchisaurus Marsh. Palaeontology 53 (4): 739-752.

Yates, A. M., M. F. Bonnan, J. Neveling, A. Chinsamy & M. G. Blackbeard. 2010. A new transitional sauropodomorph dinosaur from the Early Jurassic of South Africa and the evolution of sauropod feeding and quadrupedalism. Proceedings of the Royal Society of London Series B—Biological Sciences 277: 787-794.

Most Unbelievable Organisms Evah!

Last week I asked for nominations for the title of Most Incredible Organism Ever. Thank you very much to those of you who responded with your selections. Some of them were organisms I'd already selected myself, some of you reminded me of amazing organisms that were even better than the ones that I'd considered*. Certainly, getting the list down to ten top nominations was not easy, and I'm sure anyone else would have chosen differently from myself. Allen Hazen pointed out that, strictly speaking, "incredible" means "inspires disbelief", and certainly some of the things I have lined up do exactly that.

*As an aside, something that never fails to amuse is looking up what Google search terms have brought people to Catalogue of Organisms. Trust me, "amazing organism" is bound to bring in the punters.

Honorable mentions should be given to those organisms that people nominated that I didn't end up using, because they're certainly all incredible. Allen Hazen suggested the platypus, while Alan nominated the aye-aye. Dave Coulter was all for the Osage orange, while Amie Roman asked me to "pick an onychophoran, any onychophoran".

But I'm afraid I ended up passing over these wonders. In no particular order, here are my nominations for "Most Incredible Organism" (click on the pictures to be taken to their source):



Homo sapiens Linnaeus, 1758: Both myself and Mike Keesey agreed on this one. As much as I hate to stoke this species' notoriously smug satisfaction, it has to be admitted that humans are pretty amazing. Douglas Adams once explained that "The History of every major Galactic Civilization tends to pass through three distinct and recognizable phases, those of Survival, Inquiry and Sophistication, otherwise known as the How, Why and Where phases. For instance, the first phase is characterized by the question How can we eat? the second by the question Why do we eat? and the third by the question Where shall we have lunch?" As far as we know, Homo sapiens is the only species on this planet to have reached Adam's second stage, let alone the third.



Polyascus polygenea (Lützen and Takahashi, 1997): Polyascus polygenea is a member of the Rhizocephala, notorious crustacean parasites of crabs. The larval rhizocephalan looks very similar to the larva of a barnacle (to which it is closely related), but when it finds a decapod host it burrows in and transforms into an almost fungus-like mass spreading through the hosts body. The only externally visible part of the parasite is its large egg-sac (the orange tube in the picture above, which does not show a Polyascus but another rhizocephalan species, Peltogaster paguri). The rhizocephalan egg-sac grows at the base of the crab's tail, where it would normally hold its own eggs. In order to make sure this spot is free, the rhizocephalan chemically castrates its host, preventing it from ever reproducing. It also affects its host's behaviour so that the crab lovingly tends the parasite's egg-sac as if it were its own. So powerful is the parasite's mental ju-ju that even male hosts that would not naturally produce eggs will tend the parasite just as a female would.

Vasha nominated the best-known rhizocephalan, Sacculina carcini, but I've decided to go with Polyascus polygenea because this species adds a further twist to the tale. A single Sacculina larva will give rise to a single egg-sac. But Polyascus reproduces within the host asexually by budding, so that one larva will give rise to multiple egg-sacs (Glenner et al., 2003).

Polyascus is also acting as the stand-in for all mind-controlling parasites. As we learn more about the natural history of parasitic organisms, it turns out that behavioral control of parasites over their hosts is not uncommon. Parasitic wasps make caterpillars guard the wasp's cocoons. Horsehair worms make crickets drown themselves so the aquatic adult worm can emerge. Tanya reminded me about Cordyceps unilateralis, a fungal parasite of ants that, when it's ready to produce spores, makes its host climb to the highest available point so that the spores will spread as far as possible. The ways of parasites are disturbing. And speaking of disturbing...



Acarophenax tribolii Newstead & Duvall, 1918: It is not uncommon for pregnant women to express delight at feeling their baby kick inside them. But what if it was doing more than just kicking? Mites of the genus Acarophenax are parasites of beetles that can claim to have perhaps the just-plain-ickiest life history of any animal. The sex ratio of this genus is highly skewed - depending on the species, a brood may contain up to thirty females, but usually only a single male. These offspring reach sexual maturity before they are even born, and the male proceeds to fertilise all of his sisters while still within their mother. In fact, the male doesn't even survive to become free-living - by the time the already-fertilised females emerge from their parent, the male has reached the end of his short (but extremely busy) lifespan. The advantage to the mite in this twisted incestuous life cycle? An exceedingly short generation time, of course - Acarophenax mahunkai, for instance, has a generation time of only three to five days (Steinkraus & Cross, 1993).



Mites of the closely related family Pyemotidae have a similar life cycle - the offspring reach full sexual maturity while in their mother, and begin copulating the instant that they emerge from their proud parent. Females of Pyemotes herfsi (shown in the picture above), known as "itch mites" and facultative biters of humans, can produce more than 250 fully mature offspring.



Welwitschia mirabilis Hook.f.: I also have to thank Tanya for reminding me of the wonder that is Welwitschia. Welwitschia mirabilis is unique to the Namib Desert in Angola and Namibia, and is a member of the gymnosperm order Gnetales along with the genera Ephedra and Gnetum. The Gnetales have received a lot of attention due to their much-debated phylogeny (morphological characters suggest they are the living sister group to angiosperms, while molecular analyses place them closer to conifers), but that's not what's so amazing about Welwitschia. It's not even the bright pink, insect-pollinated cones. What makes this plant so incredible is the way it grows. Welwitschia mirabilis only ever produces two adult leaves, followed by the death of the plant's apical meristem (growing tip). The two strap-like leaves, however, continue to grow indefinitely, and can reach lengths of over eight metres (most individuals look like they have more than two leaves, but this is only because of the leaves splitting as the ends get frayed). Welwitschia is very slow-growing, and individual specimens can live to be hundreds, if not thousands of years old.



Argentinosaurus huinculensis Bonaparte & Coria, 1993: There's no other way to say it - sauropods were just stupidly huge. And Argentinosaurus was one of the most ridiculous of all, being the largest well-characterised sauropod (potentially outdone only by such almost-apocryphal taxa as Amphicoelias fragillimus and Bruhathkayosaurus matleyi). With an estimated total length of nearly thirty metres, and potential weight of up to 80 tonnes... well, there's nothing much that can be said in response except "Whoa".

Sauropods are so huge that when a popular blog was set up dedicated to them, the site authors couldn't fit in the entire animal and were forced to dedicate themselves to a single section. I refer, of course, to the famed Sauropod Vertebra Picture Of the Week - SV-POW!. Rumour has it, however, that a second site is in the works devoted to sauropod crania, to be called "Sauropod Heads - Anatomy, Zoology And Morphology".



Rhizanthella slateri (Rupp) M. A. Clem. & P. J. Cribb, 1984: Rhizanthella is a small genus of three orchid species unique to Australia. What makes Rhizanthella so amazing is that its entire life cycle is spent underground. The plant is saprophytic, dependent on an associated fungus for nutrition, and its stems are entirely subterrean. Even the flowers do not have to break the surface - they are pollinated by minute gnats that can reach them through tiny cracks in the covering litter. The first known Rhizanthella specimens were discovered in 1928 when they were brought up by a farmer's plough, and only intermittent finds were made for a long time afterwards. Even today, their obscure habits mean that Rhizanthella species are poorly known. Sad to say, they are also all regarded as endangered. They are only known from restricted, scattered ranges, limited by the presence of their associated fungus and the tree of which it is in turn connected to mycorrhizally (in Rhizanthella gardneri, the tree is Melaleuca uncinata, but the associations of Rhizanthella slateri are still unknown).

Vasha reminded me of Rhizanthella by telling me of the American saprophytic plant Thismia americana, which also spends most of its life underground with only the minute flowers emerging above the surface. Thismia americana has not been recorded since 1916, and is feared to be extinct, though it is hard to know for certain. As described at the link, an intensive search in the early 1990s failed to find any specimens, but a concurrent dummy run using scattered white beads about the same size as T. americana flowers was also a failure.



Puccinia monoica Arthur, 1912: The object of the photo above is not a flower. It grew from a flowering plant, but it's not a flower. Puccinia monoica is a fungus parasitic on Brassicaceae (mustard) species. Like rhizocephalans on their crabs, Puccinia monoica changes the reproductive biology of its host, preventing it from growing its own flowers. Instead, it makes the host plant grow a tight whorl of leaves, which are covered by the bright yellow sporangia of the fungus. Not only does the fungus-induced 'false flower' look like a real flower, it even produces nectar and scent like a real flower, attracting insect pollinators just like a real flower would (Raguso & Roy, 1998). And just like pollen from a real flower, these pollinators carry spores from fungus to fungus, cross-fertilising the fungi as they do so.



Deinococcus radiodurans (ex Raj et al. 1960) Brooks and Murray 1981: A dose of radiation of 10 joules per kilogram will kill a human being. Sixty joules per kilogram will kill Escherichia coli. Deinococcus radiodurans may look like a fairly unremarkable bacterium at first glance, but it can withstand a radiactive dose of 5000 joules per kilogram and not even blink (that is, if it had eyes they wouldn't blink). It can withstand radiation so strong that its genome is simply blasted to pieces, stoically knitting the fragments back together again afterwards. Deinococcus can withstand extreme heat, extreme cold, and strong acidity. In a pun so bad that it demands to be repeated, this organism has been dubbed Conan the Bacterium. Pavlov et al. (2006) went so far as to suggest that Deinococcus' incredible resilience to radiation indicated an extraterrestrial origin, carried from Mars on an asteroid, but it seems more likely to be a by-product of resilience to other stressors such as desiccation (Cox & Battista, 2005). Still, one can't help wondering if, even if it didn't come from Mars in the first place, it has managed to make it over there on one of Earth's probes.

So resistant is Deinococcus to everything possibly imaginable, in fact, that we still have no idea where it lives naturally. It was first isolated from cans of irradiated beef, and has not yet been found to be abundant in any particular environment. Phylogenetically, Deinococcus forms a clade with the thermophilic bacterium Thermus (one species of which, Thermus aquaticus, is of enormous significance to molecular biology as the source of the Taq enzyme used in PCR). This clade is most commonly referred to (rather unimaginatively) as the Deinococcus-Thermus group, but I personally prefer the name given to them by Cavalier-Smith (2002) - Hadobacteria, the bacteria of Hades.



Proteus anguinus anguinus Laurenti, 1768: The white olm, the only truly cave-dwelling tetrapod (the closely related black olm, Proteus anguinus parkelj, is a surface-dweller). [Update: Much to my chagrinn, Nick Sly has reminded me that there are other cave-dwelling salamanders out there.] I've included the olm not only for its own sake, but as a representative of the entire world of troglobitic and stygobitic fauna (troglobitic animals are those that live in actual caves while stygobitic taxa live buried in the ground, usually in aquifers). In this strange, silent world, animals are almost entirely dependent on food particles washing down from the surface, so life underground is slow, and patient. Troglobites can go for incredible amounts of time without eating - Darren Naish informs us of an olm that was supposedly kept at the Faculty of Biotechnology in Ljubljana without food for twelve years! If that is what a large, complex vertebrate is capable of, imagine what is possible for the smaller invertebrates with their lower metabolic requirements.

And last, but certainly not least:



Wasmannia auropunctata (Roger, 1863): Commonly known as the little fire ant or electric ant (the latter name has been promoted in recent years to dissuade confusion with the larger, not closely related fire ants of the genus Solenopsis), Wasmannia auropunctata is regarded as one of the world's worst invasive organisms. It has been linked with decreases in biodiversity in locations to which it has been introduced, and has a painful sting to boot. It also has one of the world's most remarkable reproductive systems (Fournier et al., 2005). Like other ants, Wasmannia has both haploid males and diploid females, with the females divided between reproductive queens and non-reproductive workers. Genetically, though, Wasmannia is a little different from other ants. While males appear to mate with queens the normal way, only workers are produced by male fertilisation. Any new queens that are produced are genetically identical to their mothers. Still, the male lineage doesn't disappear - somehow, the male genes are able to eliminate the female genes from some of the eggs, and the resulting male Wasmannia are genetically identical to their fathers.

Wasmannia is one of very few organisms that exhibit androgenesis - clonally reproducing males. The only other known natural habitual cases are a cypress species, Cupressus dupreziana, and freshwater bivalves in the genus Corbicula, though odd cases of androgenesis have been recorded in laboratory and cultivated organisms (Hedtke et al., 2008). Effectively, the male and female Wasmannia are reproductively isolated from each other - they are separate species.

REFERENCES

Cox, M. M., & J. R. Battista. 2005. Deinococcus radiodurans — the consummate survivor. Nature Reviews: Microbiology 3 (11): 882–892.

Fournier, D., A. Estoup, J. Orivel, J. Foucaud, H. Jourdan, J. Le Breton & L. Keller. 2005. Clonal reproduction by males and females in the little fire ant. Nature 435: 1230-1234.

Glenner, H., J. Lützen & T. Takahashi. 2003. Molecular and morphological evidence for a monophyletic clade of asexually reproducing Rhizocephala: Polyascus, new genus (Cirripedia). Journal of Crustacean Biology 23: 548-557.

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