The Litiopids: Small Sea-Snails among the Weeds

I may have commented before that biodiversity tends to increase as one moves to a smaller scale. If I haven't, I certainly should have. The number of small representatives of a group will almost always be greater than the number of large ones. And if one considers the molluscs, for instance, the diversity of large, eye-catching species is considerably smaller is considerably smaller than the diversity of the micro-mollusks that usually go unnoticed.

Litiopids Alaba virgata crawling about on seagrass, copyright Ria Tan.

The Litiopidae are a group of marine gastropods that are found living among and feeding on seaweeds and seagrasses; though little recognised, they can be very abundant. They have high-spired, conical, translucent shells that reach about an inch in length in the largest species, but seem to be more commonly less than a centimetre. They belong among the larger gastropod clade known as the Cerithioidea and can be difficult to distinguish from other members of this clade by their shells alone. Most members of the Litiopidae are placed within the genera Litiopa and Alaba.

The soft anatomy of the family is more distinctive (Houbrick 1987). Litiopids have a long, narrow foot with a median slit in the rear part of the underside marking the opening of a large mesopodial mucous gland. The sides of the foot carry several epipodial tentacles; in other gastropods with such tentacles, they provide a sensory function. A pair of long tentacles is also present on the head, which is produced into an extensible bilobed snout. A pair of small eyes is present at the base of the tentacles.

Soft anatomy of Alaba incerta, from Houbrick (1987).

Litiopids glide about on the underwater vegetation at some speed; they are also able to glide upside-down on the water surface, hanging from the surface tension. The trail of mucus laid down by the mesopodial mucous gland functions like the drag-line laid down by a spider. If the animal finds itself torn away from its substrate, the mucous strand tethers it in place, and it can then haul itself back into place.

REFERENCES

Houbrick, R. S. 1987. Anatomy of Alaba and Litiopa (Prosobranchia: Litiopidae): systematic implications. Nautilus 101 (1): 9–18.

The Arms of an Ammonite

The ammonoids are one of the most characteristic animal groups of the late Palaeozoic and Mesozoic. During their time on this earth, they were one of the most diverse and abundant groups of mollusks around. But as with other mollusks, their fossil record is overwhelmingly dominated by the hard shells, with little direct evidence of the softer parts of the animal. So what did the rest of an ammonoid look like?

A typical ammonite Asteroceras obtusum, copyright Dlloyd.

Ammonoids belong to the cephalopods, and hence to the same group of mollusks as modern octopods, squids and nautilus. Indeed, it is generally accepted that ammonoids were more closely related to octopods and squid than nautilus. As such, we can safely take as a starting assumption that those features shared by modern cephalopods were also present in ammonoids, such as a muscular siphon for propelling the animal, and an array of arms or tentacles surrounding a central mouth. But how many tentacles did ammonoids have? Squid and octopods have eight or ten arms, but nautilus have many more, about ninety. Because nautilus bear a superficial resemblance to early cephalopods in retaining an external shell, it has been tempting to assume that they are more primitive than octopods and squid, but there are good reasons to believe that the supernumerary tentacles of nautilus are a derived peculiarity of that group. Arm development in cephalopod embryos begins from ten original buds in both nautilus and squid, with these buds becoming divided in nautilus (Klug & Lehmann 2015), suggesting that the lower number could be the more primitive. With ammonoids on the squid line rather than the nautilus line as mentioned above, it seems likely that they retained the primitive arm number like their sister group. In their review of preserved ammonoid soft-tissue remains, Klug & Lehmann (2015) noted that there is only a single known fossil ammonoid (going by the memorable name of GSUB [Geosciences Collection, University of Bremen] C5836) that might include preserved arm tissue, but the area in question shows little more than a tarry smear. Trace fossils have been used to argue for a low tentacle number in orthocerids, a group of Palaeozoic cephalopods commonly believed to include the ancestors of both ammonoids and squid, but again the evidence is not enough to be conclusive.

If we do presume that ammonoids had a squid- or octopus-like number of tentacles, can we then interpret ammonoids as basically a squid in a coiled shell? This may be the most common representation of such animals:

Unfortunately for Akane's purposes, ammonites may not have provided much in the way of good eating. Whereas the fossil record of ammonoid tentacles themselves is next to nonexistent, we do have a bit more evidence about the arrangement of an ammonoid's mouthparts. Living cephalopods usually have a hardened beak at the opening of the mouth, with the ribbon-like radula sitting directly behind it. The majority of tearing and crushing of food is done by the beak; the radula mostly functions to pull food particles back into the gullet. In basal ammonoids, the beak was more or less similar to that of a recent cephalopod, but in the derived ammonites* it became quite modified. Ammonites possessed a broad structure near the opening of the body chamber that is called an anaptychus or aptychus according to its configuration (though just to confuse matters, the term 'aptychus' seems to sometimes be used to cover both types). An 'anaptychus' was a single chitinous, semi-circular plate; an 'aptychus' was a calcified, bivalved arrangement. The aptychi were not directly attached to the main shell and may commonly be found as isolated fossils. Examination of aptychi that have been preserved still in their original body chamber has lead to the widely held conclusion that they represent a modification of the original lower jaw of the beak. Meanwhile, the upper jaw became reduced and weakened in ammonites with aptychi (Tanabe et al. 2015).

*A quick explanation about 'ammonoid' versus 'ammonite': 'ammonoids' are a particular group of shelled cephalopods that first appeared during the Devonian. 'Ammonites' are a particular clade within the ammonoids including most of the Mesozoic species (a small number of non-ammonite ammonoids survived into the Triassic). So all ammonites are ammonoids, but not all ammonoids are ammonites.

Specimen of Neochetoceras with aptychus in place, from here.

Because they often have a similar configuration to the opening of the ammonite's shell, the aptychi have often been interpreted as functioning as an operculum for when the animal retracted itself into the body cavity, presenting a tough barrier to any would-be predator. Certainly the reduced upper jaw meant that they could not function as a beak to bite into food (though some Late Cretaceous ammonites did exhibit a re-enlargement of the upper jaw and may have regained their bite). However, if aptychi functioned as opercula then the tentacles of ammonites could not have sat in quite same arrangement as in modern cephalopods. They could not have completely surrounded the mouth because then they would have prevented the operculum from closing. Perhaps some of the lower tentacles were lost, or perhaps the base of the circle became divided. Some authors have argued that aptychi were jaw structures only, with no operculum function, but I confess I find it difficult to understand their purpose in that case.

That most ammonoids were not subjecting their food to strenuous chewing is also indicated by the structure of the radula: where known, the majority of ammonoids had radulae with high, slender teeth more suited to grasping than rasping (Keupp et al. 2016). The overall indication is that most ammonoids were probably micropredators, feeding on small plankton such as crustaceans; where possible stomach contents have been identified in ammonoid fossils, they have also supported this conclusion. The modern nautilus has a similar diet, and ammonoid arms possibly did resemble nautilus tentacles in being short and slender rather than long and muscular (though at least one author has discussed the possibility of ammonoid arms being expanded into broad fans for the capture of plankton). The Late Jurassic ammonite Aspidoceras had a much more robust, powerful radula than is known for other ammonoids but may provide something of an exception to prove the rule: its stomach contents are dominated by the pelagic crinoid Saccocoma, suggesting that it was still a planktivore even if it was tackling tougher prey than its relatives (Keupp et al. 2016).

A speculative reconstruction of an ammonite with filter-feeding arms, copyright sethd2725. Despite its highly conjectural elements, in some ways this is one of the better ammonite reconstructions I've seen. Most have too many arms, too robust arms, or (arguably worst of all) show the aptychus articulating dorsally in the manner of a nautilus' hood (Edit: Turns out I made an error here; see the bottom of this post for an explanation).

So to sum up, ammonoids probably had only a small number of tentacles, no more than ten at the most. They were probably slight affairs, suited for sweeping small or poorly motile food objects out of the water rather than grabbing and manipulating struggling prey. A planktivorous habit for ammonoids would also seem to fit with their predominance when they were around; after all, there's no shortage of plankton in the sea.

REFERENCES

Keupp, H., R. Hoffmann, K. Stevens & R. Albersdörfer. 2016. Key innovations in Mesozoic ammonoids: the multicuspidate radula and the calcified aptychus. Palaeontology 59 (6): 775–791.

Klug, C., & J. Lehmann. 2015. Soft part anatomy of ammonoids: reconstructing the animal based on exceptionally preserved specimens and actualistic comparisons. In: Klug, C., et al. (eds) Ammonoid Paleobiology: From Anatomy to Ecology pp. 507–529. Springer Science.

Tanabe, K., I. Kruta & N. H. Landman. 2015. Ammonoid buccal mass and jaw apparatus. In: Klug, C., et al. (eds) Ammonoid Paleobiology: From Anatomy to Ecology pp. 429–484. Springer Science.

Spotless Ladybirds

Ladybirds are one of the first types of insect most children learn to recognise. Most people recognise these beetles straight away with their bright, contrasting colour patterns and shiny elytra. Many people are also aware of the beneficial role they may play in gardens and horticulture, feeding as both adults and larvae on plant-sucking insects such as aphids. However, ladybirds are a lot more diverse than many people realise. The great majority of species in the ladybird family Coccinellidae are not brightly coloured, and many of them do not feed on aphids.

Rhyzobius cf. chrysomeloides, a typical member of the Coccidulini, copyright Mick Talbot.

The ladybirds of the cosmopolitan tribe Coccidulini are mostly small species; many are dully coloured, though some are more distinctly patterned. As recognised by Ślipiński (2007) in his revision of the Australian Coccinellidae, the group is a diverse one and difficult to define; common features of its members include pubescent rather than shiny elytra, and certain features of the genitalia. A phylogenetic analysis of coccinellids by Seago et al. (2011) did not resolve the Coccidulini as a monophyletic clade, suggesting the possibility that they may represent a basal grade of unspecialised taxa, but no reclassification of the group appears to have been proposed as yet.

Stethorus punctillum, copyright Gilles San Martin.

The most familiar ladybirds are more or less hemispherical, but coccidulin species may vary in shape from rounded to oblong, with the body convex to flattened. The Tasmanian species Nat vandenbergae* particularly stands out in this regard, being oval and flattened with relatively long legs and antennae, and at first glance might be mistaken for a chrysomelid leaf beetle rather than a coccinellid. The rounded species of the genera Stethorus and Parastethorus include some of the smallest of all ladybirds, some being only a millimetre or so in length.

*Yes, the genus name for this species is Nat. Other coccidulin genera named by Ślipiński (2007) include Roger and Robert.

A mealybug destroyer Cryptolaemus montrouzieri engaged in destroying a mealybug, copyright Cynthia Bingham Keiser.

Being so small and easily overlooked, the life habits of many coccidulins remain poorly known. Many feed on aphids or scale insects in the usual ladybird manner. The orange-and-black Cryptolaemus montrouzieri was one of the first ladybirds to be deliberately used for biological control of pests; originally native to eastern Australia, it has been introduced to other parts of the world such as the United States to help control mealybugs. The tiny Stethorus and Parastethorus species feed on spider mites (Tetranychidae), species of which may similarly cause damage to crops. But other coccidulins have more unexpected diets. The larva of another Australian species, Bucolus fourneti, is a specialised predator of ants, lying in wait under the bark of Eucalyptus trees to ambush its prey as it passes by.

REFERENCES

Seago, A. E., J. A. Giorgi, J. Li & A. Ślipiński. 2011. Phylogeny, classification and evolution of ladybird beetles (Coleoptera: Coccinellidae) based on simultaneous analysis of molecular and morphological data. Molecular Phylogenetics and Evolution 60: 137–151.

Ślipiński, A. 2007. Australian Ladybird Beetles (Coleoptera: Coccinellidae): Their biology and classification. Australian Biological Resources Study: Canberra.

Perilampella acaciaediscoloris: An Australian Gall Wasp

The small but incredibly diverse chalcidoid wasps are mostly known as parasitoids, their larvae attacking the eggs and young of others insects. Some, however, have chosen the vegetarian option, inserting their eggs into plant rather than animal tissue. As the larva develops, it induces the host plant to develop an often bizarre-looking growth around it that provides both shelter and food; this growth is known as a gall.

Antenna, forewing venation and dorsum of Perilampella acaciaediscoloris, from Bouček (1988).

Perilampella acaciaediscoloris is an gall-forming wasp that was first described by Froggatt in 1892 from galls that he collected on the wattle Acacia discolor, a species now regarded as a synonym of the sunshine wattle A. terminalis of south-eastern Australia. Froggatt placed his species in the genus Cynips (which is not part of the Chalcidoidea but belongs to a different micro-wasp superfamily, the Cynipoidea) but it is now placed in the chalcid subfamily Ormocerinae in the (polyphyletic) Pteromalidae. Ormocerinae are fairly generalised 'pteromalids' that are non-metallic in colour and often finely sculpted. So far as is known, ormocerines are all associated with galls in one way or another, either as gall-causers themselves or as inquilines (species that lay their eggs in the galls caused by other insects). Another ormocerine species, Trichilogaster acaciaelongifoliae, has been introduced from Australia to South Africa to help control the Sydney golden wattle Acacia longifolia.

The related ormocerine Trichilogaster acaciaelongifoliae, copyright Simon van Noort. Perilampella acaciaediscoloris most obviously differs from this species in its hairier and darker wings, and more shiny mesosoma.

The genus Perilampella differs from other ormocerines in being particularly shiny, with little clear setation. Bouček (1988) listed four Australian species in the genus, noting that P. acaciaediscoloris could be recognised by its very dark, long wings and shiny orange-yellow mesosoma. Froggatt (1892) described the galls of P. acaciaediscoloris as formed at the inception of a leaf bud or new shoot. Sometimes, they would be little more than swellings at the base of the shoot. More often, they would be oval with three irregular horns formed from aborted leaf buds. Sometimes, P. acaciaediscoloris galls would be the target of inquilines of their own that caused the gall to degrade to a shapeless mass.

REFERENCES

Bouček, Z. 1988. Australian Chalcidoidea (Hymenoptera): A biosystematic revision of genera of fourteen families, with a reclassification of species. CAB International.

Froggatt, W. W. 1892. Notes on Australian Cynipidae, with descriptions of several new species. Proceedings of the Linnean Society of New South Wales, second series 7: 152–156.

The Adaeines: South Africa's Cryptic Micro-Giants

Adaeulum sp., copyright Charles Haddad.

The Triaenonychidae are the family of Gondwanan harvestmen. While there are other families of harvestmen with a Gondwanan distribution (such as my own favoured family, the Neopilionidae), none of them are nearly as widespread and diverse as the triaenonychids. Despite their diversity, however, our understanding of triaenonychid relationships remains uncertain, and the family's classification poorly defined.

Within their range in Africa, Australasia and South America, triaenonychids can easily be distinguished from most other families of short-legged harvestmen by the structure of the claws on the hind two pairs of legs. Whereas members of other families bear a pair of simple claws on these legs, triaenonychids have a single claw with side branches on each leg. Branched claws are also found in the New Zealand genus Synthetonychia, which occupies its own distinct family, but that genus is easily recognised by its unusual body shape without a distinct eyemound. The Gondwanan Triaenonychidae were divided by Roewer into three subfamilies (Triaenonychinae, Triaenobuninae and Adaeinae) based on the shape of the sternum (the plate running along the underside of the body between the leg coxae). The significance of this feature was later questioned by Forster (1954) who recognised two subfamilies Triaenonychinae and Soerensenellinae on the basis of claw morphology (soerensenellines having longer side branches on the claws than triaenonychines) and reduced Roewer's subfamilies to tribes of Triaenonychinae. No large-scale analysis of triaenonychid phylogeny has been done so far, so it remains unestablished whether we should prefer one classification or the other (or possibly neither).

Typical triaenonychine (left) and adaeine (right) sternal shapes, from Forster (1954).

The Adaeinae or Adaeini may be one of the better defined of Roewer's original subgroups and recent authors have expressed the opinion that this may indeed turn out to be a natural clade. Whereas members of the Triaenonychinae sensu stricto and Triaenobuninae have a sternum that has a spearhead-shaped expansion at the front end and a broadened base at the back, members of the Adaeinae have a sternum that is a triangular or wedge shape without a posterior expansion. The adaeines are likely to be endemic to southern Africa; Kury et al. (2014) did list a single Australian species, Dingupa glauerti, in the Adaeinae but I would hazard a guess that future study proves this species to be misplaced (as has been found with other Australasian 'adaeines').

About forty species of adaeines are currently recognised, all from South Africa, but it is entirely likely that more remain to be described. The hard, granular body surface of adaeines inevitably picks up a covering of dirt and grit, making them exceedingly difficult to spot when not moving. Nevertheless, adaeines can be quite large as harvestmen go, with some being up to a centimetre in body length. Conversely, Micradaeum rugosum, a species found in the vicinity of Cape Town, is only about three-and-a-half millimetres in body length (Lawrence 1929). As with other species of Triaenonychidae, the large, raptorial pedipalps are larger and more robust in male adaeines than in females, and often have more pronounced spines. In some species of the genus Larifuga, nowever, spines or denticles may be more prominent on the female's pedipalps than on the male's, though the male's pedipalps are still larger and stronger overall (Lawrence 1937).

REFERENCES

Forster, R. R. 1954. The New Zealand harvestmen (sub-order Laniatores). Canterbury Museum Bulletin 2: 1–329.

Kury, A., A. Mendes & D. Souza. 2014. World checklist of Opiliones species (Arachnida). Part 1: Laniatores—Travunioidea and Triaenonychoidea. Biodiversity Data Journal 2: e4094. doi: 10.3897/BDJ.2.e4094

Lawrence, R. F. 1929. The harvest-spiders (Opiliones) of South Africa. Annals of the South African Museum 29 (2): 341–508.

Lawrence, R. F. 1937. The external sexual characters of South African harvest-spiders. Transactions of the Royal Society of South Africa 24 (4): 331–337, pls 14–15.

Pines for the Sea

Black pine Neorhodomela larix growing alongside lighter-coloured Analipus japonicus on a beach in California, copyright Peter D. Tillman.

There aren't many types of algae that receive their own vernacular name. Despite the fact that thousands of different species of macroscopic algae exist in the world, the majority tend to get lumped under the catch-all term of 'seaweed'. Among those seaweeds that are visible enough to stand out from the general crowd is Neorhodomela larix, the 'black pine'.

Neorhodomela larix is a common seaweed species on the west coast of North America. It has also been recorded from the western side of the Pacific Ocean, but it should be noted that it might not always be readily distinguished from related species (indeed, N. larix was not distinguished at species level from the primarily western Pacific N. aculeata until the revision of this genus by Masuda, 1982). The name 'black pine' that has been bestowed on it reflects its overall appearance. Black pine grows as erect axes radiating from a small basal holdfast. These primary axes give rise to regular branches arranged in a spiral fashion; most of these side branches, at least in young individuals, only grow to a fixed, short length and remain unbranched or only bifurcate (in more mature individuals, some of the side branches become indeterminate in length and grow in a similar manner to the primary axes). The overall effect is to make the seaweed stems look like a bottlebrush or, with a bit of imagination, like a pine-tree branch (or at least like a plastic-Christmas-tree branch). Black pine is particularly common on horizontal, wave-exposed beaches about a foot above the mean low-tide mark; in some places it may form large, continuous stands. It is most abundant where said shorelines are swept by sand, probably because the action of the sand's movement keeps away grazers such as urchins (D'Antonio 1986).

Neorhodomela larix was previously included in the closely related genus Rhodomela, and some sources still refer to it as 'Rhodomela larix'. Masuda (1982) established Neorhodomela as a separate genus from Rhodomela due to differences in vegetative structure. Both genera possess hair-like branchlets known as trichoblasts, but in Rhodomela these arise from the main branches spirally whereas in Neorhodomela they are positioned dorsally and arise in a zig-zag arrangement. Spermatangia are produced from trichoblasts in Neorhodomela, whereas in Rhodomela the spermatangia are produced directly on the unspecialised branches and the trichoblasts are only vegetative structures. In N. larix, few vegetative trichoblasts are produced until shortly before the production of reproductive trichoblasts bearing spermatangia; other Neorhodomela species (such as N. aculeata) may start producing vegetative trichoblasts soon after germination.

Apart from the ecological role it presumably plays in providing food and shelter to other coastal lifeforms, Neorhodomela larix does not have much of a direct impact economically. Like many macroalgae, black pine produces chemical compounds known as bromophenols that have been subject to some investigation due to their potentially beneficial (such as anti-microbial or anti-oxidant) activities. However, to date no practical pharmaceutical products have been developed from algal bromophenols, in part because the amount of these compounds produced by the algae in vivo is fairly low (Liu et al. 2011). For now, there is little to disturb these little pine forests by the sea.

REFERENCES

D'Antonio, C. M. 1986. Role of sand in the domination of hard substrata by the intertidal alga Rhodomela larix. Marine Ecology—Progress Series 27: 263–275.

Liu, M., P. E. Hansen & X. Lin. 2011. Bromophenols in marine algae and their bioactivities. Marine Drugs 9: 1273–1292.

Masuda, M. 1982. A systematic study of the tribe Rhodomeleae (Rhodomelaceae,Rhodophyta). Journal of the Faculty of Science, Hokkaido University, Series 5: Botany 12 (4): 209–400.

Where Do You Put Your Camels?

A dromedary Camelus dromedarius dares you to say what you make of it. Copyright John O'Neill.

In any discussion of the conflicts that may exist between morphological and molecular data in phylogenetic analysis, hippos and whales are bound to come up sooner or later. The claim in the late 1990s that these are each other's closest living relatives (and hence, that whales are nested fairly deeply within the artiodactyls, or even-toed hoofed mammals) was greeted with amazement, incredulity and more than a little skepticism. The story even caught the interest of the general public through news stories like this one, meaning that many people who are otherwise unfamiliar with the trivia of mammalian phylogeny may have picked up this detail. Since then, the whale-hippo relationship has been tested, re-tested and examined again, using every data source available. But the insertion of the whales was not the only way that molecular data mixed up the artiodactyl family tree. There was also the question of where one put the camels.

Based on anatomical data, it had previously been generally agreed that camelids (including camels and llamas) were most closely related to the ruminants, the group including such artiodactyls such as cattle, deer or giraffes. Both camelids and ruminants regurgitate cud pellets from the stomach back to the mouth in order to break their food more efficiently*, and both camelids and ruminants have a stomach divided into chambers with food only travelling to the rear section of the stomach after it has been re-chewed. They do differ in that whereas ruminants have the stomach divided into four distinct chambers, camelids only possess three; the rear two chambers (the abomasum and omasum) are not clearly differentiated in camelids. They were also united by features of the dentition, such as the presence of distinctly crescent-shaped cusps on the rear teeth. This latter feature lead the camelid+ruminant grouping to commonly be referred to as the Selenodontia (the 'moon-teeth').

*Yes, giraffes do chew cud. Yes, the cud does travel all the way between the stomach and the mouth each time.

However, the advent of molecular analyses cast doubt on this long-accepted arrangement. Instead of supporting the expected Selenodontia clade, molecular analyses placed camelids as the sister group to all other artiodactyls, with the ruminants instead being sister to the whales+hippos clade (with a pigs+peccaries clade the next clade out). This implied that the shared features of camelids and ruminants had arisen convergently (or else all other artiodactyls had reverted to a state considered more plesiomorphic for the group as a whole). In support for such a proposition, one might point to the ecological similarities in play. Camelids and ruminants are more specialist browsers than the non-selenodont artiodactyls, which are commonly more omnivorous (pigs and peccaries) or even carnivorous (whales).

Alternative phylogenies of artiodactyls, based on morphological (left) and molecular (right) data, from Spaulding et al (2009).
However, even if one is willing to credit that the 'selenodont' characters may have been the result of similar dietary pressures, one must also consider the issue that there are a number of fossil artiodactyl groups with selenodont or quasi-selenodont features. Examples of these include the Protoceratidae, a North American group that has commonly made some sort of appearance in popular books on fossil animals due to the weird home arrangements of some species, and the semi-bipedal Anoplotherium. In an influential morphological study of artiodactyl relationships, Gentry & Hooker (1988) referred to the possibility that some of these groups might be members of the selenodont stem, sitting outside the exclusive camelid+ruminant clade. Obviously, if selenodonts were not monophyletic, fossil 'selenodonts' might be aligned to either camelids or ruminants, but they couldn't be connected to both. Most studies that posited selenodont polyphyly, however, looked at living taxa only and did not consider extinct groups.

The most detailed study that I've found so far that considers the relationship between data from fossil taxa and from molecular sources in artiodactyl phylogeny is that published by Spaulding et al. (2009). This combined analysis of both morphological and molecular data produced results that were largely concordant with the latter, generally supporting placement of camelids as the sister group to all other artiodactyls (it's worth noting, mind you, that the size of the molecular data set used was considerably larger than that for the morphology, and an analysis of their morphological data only resulted in selenodont monophyly). The various 'proto-selenodonts' were scattered to the stems of various Recent clades. Protoceratids, for instance, were associated with ruminants rather than with camelids*. There are still a number of groups that remain yet to be analysed, but they've made a start.

*Another result of their analysis that is not directly relevant to the selenodont question, but cannot go unremarked upon, is that their tree indicates that Andrewsarchus, a lead contender for the title of largest terrestrial mammalian carnivore ever, might some sort of giant entelodont. I don't know how much I should read into this—not all of Andrewsarchus' potential relatives were included in Spaulding et al.'s analysis—but that's the sort of result that one just wants to be true.

REFERENCES

Gentry, A. W., & J. J. Hooker. 1988. The phylogeny of the Artiodactyla. In: Benton, M. J. (ed.) The Phylogeny and Classification of the Tetrapods vol 2. Mammals pp. 235–272. Clarendon Press: Oxford.

Spaulding, M., M. A. O’Leary & J. Gatesy. 2009. Relationships of Cetacea (Artiodactyla) among mammals: increased taxon sampling alters interpretations of key fossils and character evolution. PLoS ONE 4(9): e7062. doi:10.1371/journal.pone.0007062