The Litopterns: Macrauchenia and More

Much has been made of the "splendid isolation" of South America for a large part of the Cenozoic. Finding itself girt by sea, South America became home to a number of endemic groups of animals: the 'terror-birds' of the Phorusrhacidae, notoungulates that were something like a rhino and something like a rabbit, and giant armadillos and anteaters. Among these uniquely South American animals were the subjects of today's post, the litopterns.

Digital reconstruction of Macrauchenia by Deskridge.

Litopterns are one of those groups of animals that tend to be represented in recent popular media by a single example, which many of you may recognise in the picture above. This was Macrauchenia patachonica, one of the latest surviving litopterns (like many other South American taxa, litopterns did not fare well during the so-called Great Faunal Interchange when South and North America became connected). But as with so many other under-represented groups, the popular exemplar is not necessarily a prime example. Macrauchenia was not only one of the last litopterns, it was also one of the largest, and the litopterns came in a whole range of appearances.

The earliest litopterns are known from the late Palaeocene. The basalmost members of the group are classified as the Protolipternidae, but the members of this family are united by primitive characters only. It is generally accepted that litopterns were closely related to two Palaeocene families of South American 'condylarths', the Didolodontidae and Sparnotheriodontidae, and there is a certain degree of arbitrariness about whether or not these families should also be treated as litopterns. Those who would exclude the didolodontoids from the litopterns do so on the basis of the latter's tarsal morphology, which has become adapted for a more cursorial lifestyle. The protolipternids bridge the gap between didolodontoids and other litopterns in that they possessed a litoptern-like tarsus, but retained teeth more like the didolodontoids. Protolipterna also retained five toes on the feet, while this number was reduced in later litopterns (Bastos & Bergqvist 2007). The other noteworthy feature of protolipternids was that they were not very big. Rose (2009) includes an illustration of partial upper and lower jaws of the protolipternid Asmithwoodwardia whose scale bar indicates that the complete skull must have been less than five centimetres in length, or about the size of a brown rat. Cifelli (1983) suggested on the basis of their small size that these animals may have been more leapers than runners, a suggestion not directly supported but not entirely ruled out by Bastos & Bergqvist (2003).

Reconstruction of Thoatherium minusculum by Charles R. Knight.

The remaining litopterns mostly belong to the families Proterotheriidae, Adianthidae and Macraucheniidae, united by specialisations of the dentition and reduction of the number of toes to three (a fifth family, the late Palaeocene Notonychopidae, are represented by dental remains only). The Palaeocene to Pleistocene Proterotheriidae have attracted a reasonable amount of interest in the past because of their convergences with the horses in the Northern Hemisphere. Like horses, proterotheriids centred locomotion on the middle toe only, with the toes on either side being reduced. In the Miocene proterotheriid Thoatherium, the side toes were almost completely lost, reduced to splints even smaller than those of the modern horse (being by this measure more horse-like than an actual horse, Thoatherium has also been a popular subject for books on evolution). In other respects, however, proterotheriids were not so horse-like. With relatively low-crowned teeth, proterotheriids and other litopterns were browsers rather than grazers, and they may have preferred more wooded terrain rather than grasslands. Ecologically, proterotheriids were probably more like deer or small antelopes than horses, and they resembled small antelopes in size. Only one proterotheriid survived into the Pleistocene, Neolicaphrium recens, and only in Uruguay and northern Argentina (Ubilla et al. 2011).

The Adianthidae were small litopterns (though not as small as the protolipternids) known from the Eocene to the Miocene. Most adianthids are known only from dental remains and/or jaw fragments, though some limb bones are known from the Miocene Adianthus godoyi (Cifelli 1991). These indicate a gracile form, probably more similar to proterotheriids than to macraucheniids, though Cifelli noted the similarities to the former were likely related to size rather than indicative of any deeper affinity.

Reconstruction of the cramaucheniine macraucheniid Theosodon garretorum, with the carnivorous metatherian Borhyaena tuberata, by Charles R. Knight.

The Macraucheniidae retained three functional toes, with the middle toe not substantially larger than the two side ones. They also differed from the proterotheriids in the development of a longer neck, and have usually been compared to camels in appearance (the name 'Macrauchenia' was originally coined to effectively mean 'big llama', in the mistaken belief that it represented an ancestor of that animal). They have been divided between to subfamilies, the Oligocene to Miocene Cramaucheniinae and the late Miocene to Pleistocene Macraucheniinae, though the latter are undoubtedly descended from the former. The cramaucheniines retain a plesiomorphic anterior nasal opening, but in the Macraucheniinae the nasal bones are reduced and the nasal opening has moved posteriad on the skull (Dozo & Vera 2010). It is this dorsal position of the nasal opening that has lead to the interpretation of Macrauchenia as having some form of proboscis, like that of a tapir. The combination of a long neck and a proboscis is, however, an unusual one, and I've wondered if it may have been more of a prehensile upper lip. The macraucheniids did better in the Pleistocene than the proterotheriids, with three species described from a large chunk of the continent, but eventually they two went the way of the toxodont.

REFERENCES

Bastos, A. C. F., & L. P. Bergqvist. 2007. A postura locomotora de Protolipterna ellipsodontoides Cifelli, 1983 (Mammalia: Litopterna: Protolipternidae) da Bacia de São José de Itaboraí, Rio de Janeiro (Paleoceno superior). Anuário do Instituto de Geociências 30 (1): 58-66.

Cifelli, R. L. 1983. Eutherian tarsals from the Late Paleocene of Brazil. American Museum Novitates 2761: 1-31.

Cifelli, R. L. 1991. A new adianthid litoptern (Mammalia) from the Miocene of Chile. Revista Chilena de Historia Natural 64: 119-125.

Dozo, M. T., & B. Vera. 2010. First skull and associated postcranial bones of Macraucheniidae (Mammalia, Litopterna) from the Deseadan Salma (late Oligocene) of Cabeza Blanca (Chubut, Argentina). Journal of Vertebrate Paleontology 30 (6): 1818-1826.

Rose, K. D. 2009. The Beginning of the Age of Mammals. JHU Press.

Ubilla, M., D. Perea, M. Bond & A. Rinderknecht. 2011. The first cranial remains of the Pleistocene proterotheriid Neolicaphrium Frenguelli, 1921 (Mammalia, Litopterna): a comparative approach. Journal of Vertebrate Paleontology 31 (1): 193-201.

The Wolf in Time

Black-backed jackal pup Canis mesomelas, photographed by Blake Matheson.
The dogs of the genus Canis include some of the most familiar of all mammals: the wolf Canis lupus, the coyote C. latrans, and of course the domestic dog Canis familiaris. I have already discussed in an earlier post how these three, together with the golden (Canis aureus) and the Simien (C. simensis) jackals, form a cluster of closely related species (that I'll refer to as the 'wolf group') that are not always clearly separated. Today, I'll take things a bit further and look at the fossil history of the genus Canis.

Coyote Canis latrans, from Ryan Photographic.
The earliest taxa assigned to the genus Canis are known from the late Miocene, about six million years ago (Tedford et al. 2009). Early Canis have been identified in both Europe (C. cipio) and North America (C. ferox), though there is some uncertainty about whether the European C. cipio should be treated as Canis or assigned to the related, slightly earlier fossil genus Eucyon. Whatever the case, it doesn't appear to have been long before Canis populations were well and truly established on both continents. The North American Canis ferox was, as far as I can tell, probably not dissimilar to a modern coyote in appearance, and early Canis species probably also resembled coyotes in being fairly generalist predators. In the evolutionary analysis by Tedford et al. (2009), C. ferox was suggested to have begat C. lepophagus at the beginning of the Pliocene, which in turn begat two lineages: one leading to the modern wolf group, the other leading to three North American Plio-Pleistocene species (C. thooides, C. feneus and C. cedazoensis) that were smaller than their ancestor and probably similar in appearance to modern jackals. It is somewhat unfortunate that Tedford et al.'s analysis did not include the African side-striped (C. adustus) and black-backed (C. mesomelas) jackals, which molecular and morphological analyses have generally agreed lie outside the wolf group. Biogeography alone suggests that the North American 'jackals' were probably convergent rather than directly related to the modern African species, but it would be nice to know.

Mounted skeleton of dire wolf Canis dirus, from lora_313. This species probably weighed between 50 to 80 kg, which is comparable in size to a very large dog such as a bullmastiff or great dane.
The modern wolf group diversified in the late Pliocene, including a number of fossil species as well as the modern. The rate of diversification and spread of wolf-group Canis was such that palaeontologists refer to their appearance in the fossil record as the 'wolf event', and use it as a marker of the development of the colder tundra climate of the Pleistocene ice ages. Higher diversity in Eurasia suggests that it was probably the centre of diversification, with North American species derived from repeated colonisation. Significant among these was the relatively large C. armbrusteri, a close relative of the grey wolf C. lupus. Canis armbrusteri is notable as the probable ancestor of the late Pleistocene dire wolf C. dirus, made famous by its appearances in the works of Robert E. Howard* and similar authors. As well as being a dominant predator in North America, the dire wolf spread into northwestern South America. A similar large Canis species, C. nehringi, is also known from the same time in Argentina, but the analysis of South American canids by Prevosti (2010) was unable to clearly determine whether C. nehringi was a southern relative of C. dirus or a convergent relative of the Xenocyon lineage.

*A man who spent far too much time thinking about oiled chests if ever there was one.

Dholes Cuon alpinus, from Rajnish Pradhan.
Xenocyon is itself relevant to the history of Canis: first appearing in the late Pliocene, Xenocyon lycaonoides is probably the ancestor of the modern African hunting dog Lycaon pictus and the Asian dhole Cuon alpinus, forming a hypercarnivorous lineage specialised for collaborative hunting of large prey. Phylogenetic analyses of modern taxa have varied as to whether Lycaon and Cuon are the sister group of modern Canis, or whether they are in fact more closely related to the wolf group than are C. adustus or C. mesomelas, rendering Canis paraphyletic. Removal of the latter two species from Canis into separate genera as Schaeffia adusta and Lupulella mesomelas to preserve monophyly has been suggested, but almost universally ignored (as well as failing to resolve the status of the non-wolf-group fossil Canis species). Tedford et al. (2009) even nested the Xenocyon lineage within the wolf group itself, as sister to the Canis lupus-C. dirus group, but one might suspect the influence of convergences to large size and hypercarnivory. Prevosti (2010) placed Lycaon and Cuon in a more standard position just outside the wolf group, but did not consider as many fossil Canis species as Tedford et al.

Remains of Cynotherium sardous (plus some smaller mammal), from here.
The Xenocyon lineage was undoubtedly Eurasian in origin, but the primarily Eurasian X. lycaonoides did spread into northern North America, and a second species X. texanus was found in the Pleistocene of (surprisingly) Texas. The modern dhole Cuon alpinus was also present in North America in the latest Pleistocene, with remains of at least four individuals found in a cave in northeastern Mexico, as well as being found in Europe (Tedford et al. 2009). Also a member of the Xenocyon lineage was the Pleistocene Cynotherium sardous, found on the Mediterranean islands of Sardinia and Corsica (which were a single island when the Mediterranean sea level was lower). Though descended from hypercarnivorous ancestors, Cynotherium became adapted in its island habitat to hunting smaller prey (such as the Sardinian lagomorph Prolagus sardus). Though it retained the simplified dentition of a hypercarnivore, it became smaller and the skull became less reinforced, as befits an animal no longer wrestling down large ungulates (Lyras et al. 2006).

REFERENCES

Lyras, G. A., A. A. E. Van Der Geer, M. D. Dermitzakis & J. De Vos. 2006. Cynotherium sardous, an insular canid (Mammalia: Carnivora) from the Pleistocene of Sardinia (Italy), and its origin. Journal of Vertebrate Paleontology 26 (3): 735-745.

Prevosti, F. J. 2010. Phylogeny of the large extinct South American canids (Mammalia, Carnivora, Canidae) using a "total evidence" approach. Cladistics 26: 456-481.

Tedford, R. H., X. Wang & B. E. Taylor. 2009. Phylogenetic systematics of the North American fossil Caninae (Carnivora: Canidae). Bulletin of the American Museum of Natural History 325: 1-218.

The Sad, Sad Story of Physeter

Original drawing of the sperm whale stranded near Berkhey, the Netherlands, in 1598. Reproduction from Husson & Holthuis (1974).

In yesterday's post on the sperm whales, I alluded to the long and reprehensible debate over the name of the great sperm whale Physeter macrocephalus. Reprehensible because for at least the last hundred years there has been absolutely no disagreement over the nature of the animal concerned; the conflict has purely been concerned with what to call it.

When Linnaeus discussed the genus Physeter in the 1758 Systema Naturae, he referred to four species: P. macrocephalus, P. catodon, P. tursio and P. microps. Most authors now treat these names as synonyms of the great sperm whale*. Normally, when two or more names are available for the one species, the oldest name automatically becomes the correct one. However, because Linnaeus' 1758 publication is the official starting point for zoological nomenclature, none of these names count as the oldest. In such a case, the general rule is that the first person to treat the names as synonymous and pick one of them to be the correct name establishes which has priority (the principle of the First Reviser).

*Physeter tursio and P. microps were both described as having high dorsal fins, something the great sperm whale completely lacks, leading to considerable confusion over the identity of the animals concerned. Modern authors tend to assume they were based on distorted or mistaken accounts of ordinary sperm whales; this is not really a satisfactory explanation, but the true identity will probably never be establishable (killer or pilot whales seem not entirely unlikely to me), and there would be little to be gained from trying.

During the 19th Century, most authors knew the great sperm whale as Physeter macrocephalus while the name P. catodon was less often referred to (and sometimes thought to refer to something like the beluga or pilot whale). It wasn't until the beginning of the 20th Century that Oldfield Thomas (1911) asserted the synonymy of the species and selected P. catodon as the correct name. However, in 1938 Hilbrand Boschma noted that Murray had treated the names as synonymous in 1866 and selected P. macrocephalus, pre-dating Thomas' selection. This was countered in 1966 by Philip Hershkovitz who claimed that Murray's selection was invalid.

The most detailed discussion of the matter was by Husson & Holthuis (1974) who discussed each of the records cited by Linnaeus for the names Physeter catodon and P. macrocephalus, selecting a lectotype for the former and a neotype for the latter that confirmed both as sperm whales. They also established that Blasius had treated the names as synonyms in 1857 and selected P. macrocephalus as the valid name, meaning that P. macrocephalus had priority even if Murray was disqualified as an authority.

However, the validity of Physeter catodon was again championed by Schevill (1986) on the basis that P. macrocephalus was supposedly invalid from the get-go. Linnaeus had distinguished the two species on the basis that P. macrocephalus supposedly had its blowhole on its neck while P. catodon had it at the front of the head; the correct position in the sperm whale is, of course, the latter. Schevill claimed that Husson & Holthuis' examination of the earlier records to correct Linnaeus' description was invalid as the concept of type specimens did not exist in Linnaeus' time, making the printed description the only judge of the species identity. Because the description of P. macrocephalus did not agree with a real sperm whale, it could not be used as the valid name.

As pointed out by Holthuis (1987), Schevill's latter argument was simply wrong. If the original author did not explicitly nominate a type specimen for a new species, then all specimens considered in the original description automatically become the type series*. To claim that the concept of types is inapplicable to Linnaeus is to ignore a fundamental aspect of the nature of the Systema Naturae, which did not spring ex nihilo but was in many places an index to the work of earlier naturalists, tying their descriptions into Linnaeus' new nomenclatural system. In the case of the sperm whale, Linnaeus was mislead by the faulty descriptions provided by others (Linnaeus himself had never seen a sperm whale). Examination of these earlier records allows the error to be recognised. Husson & Holthuis (1974) chose as lectotype of P. macrocephalus a specimen stranded in the Netherlands in 1598; while the specimen has not been preserved anywhere, illustrations of it leave no doubt that it was a sperm whale.

*Though it is true that the type specimen did not exist as a formal concept in 1758, it was not long afterwards that naturalists were finding it useful to examine earlier authors' specimens to determine their intention. Exactly when the type concept became formalised, I'm not sure.

So, in summary, both P. catodon and P. macrocephalus are available names for the great sperm whale; Blasius as First Reviser established the priority of the latter in 1857. The correct name for the great sperm whale is therefore Physeter macrocephalus.

REFERENCES

Holthuis, L. B. 1987. The scientific name of the sperm whale. Marine Mammal Science 3 (1): 87-88 (reply by W. E. Schevill, pp. 89-90).

Husson, A. M., & L. B. Holthuis. 1974. Physeter macrocephalus Linnaeus, 1758, the valid name for the sperm whale. Zoologische Mededelingen 48 (19): 205-217, pl. 1-3.

Schevill, W. E. 1986. The International Code of Zoological Nomenclature and a paradigm: the name Physeter catodon Linnaeus 1758. Marine Mammal Science 2 (2): 153-157.

More than Just Moby (Taxon of the Week: Physeteridae)

Not surprisingly, it did not take readers long to reach a consensus about the identity of yesterday's ID challenge: the lower jaw of Kogia breviceps, the pygmy sperm whale. Kogia is distinguished from other toothed whales by its relatively small number of noticeably slender teeth; K. breviceps is usually distinguishable from the other species in the genus, the dwarf sperm whale K. sima, by having 12-16 pairs of teeth in the lower jaw (K. sima usually has 8-11).


Dwarf sperm whale, Kogia sima. The two Kogia species are externally very similar; indeed, Watson (1981) noted that their status as separate species had not yet gained universal acceptance. Photo by Robert Pitman.

The family Physeteridae as used in this post includes just three living species, the great sperm whale Physeter macrocephalus* and the two Kogia species (alternatively, many authors refer to this groups as the superfamily Physeteroidea, separating the living genera and their respective stem groups between families Physeteridae and Kogiidae). Though superficially distinct in appearance, the two genera share a number of unusual characteristics including enamel-less teeth (that are restricted to the lower jaw) and an externally squared head with anteriorly placed blowhole. The distinctive profile is due to the spermaceti organ, a pair of gigantic oil-filled sacs that fill the inside of the head. The upper sac, the spermaceti, contains a less dense oil than the lower sac, the junk. Just exactly what the spermaceti organ does is still uncertain; proposed uses (which are not all mutually exclusive) include vocalisation, echolocation, use as a battering ram (Carrier et al., 2002) and for buoyancy control (with the whale controlling the temperature of the organ by controlling the bloodflow to it and hence controlling the specific gravity of the contained oil) (Clarke, 1978). All living species feed primarily on squid though the Kogia species eat more fish than does P. macrocephalus**.

*The scientific name of the sperm whale is renowned for being one of the most prolonged, contentious and utterly pointless conflicts in zoological nomenclature. The needless complexity of this argument is such that I'm going to farm it out to a separate post rather than try to stuff it into this one.

**I've come across a number of references to the sperm whale as the largest ever carnivore. This isn't actually true. Even if one excludes the blue whale Balaenoptera musculus as a 'carnivore' due to its diet of planktic crustaceans (still technically animals), P. macrocephalus is just edged out of the top spot by the fin whale Balaenoptera physalus which, in at least some parts of its range, feeds primarily on fish (Watson, 1981).


The great sperm whale, Physeter macrocephalus. Source of image uncertain: I got it via Google Images from here, but the actual link appears to be broken.

However, as is not uncommon in the world of biology, the most familiar members of this family are far from being the most typical. The fossil record of Physeteridae sensu lato extends back to the Oligocene; for most of that time, fossil sperm whales had teeth far more intimidating than those possessed by any living species, indicating diets potentially more rapacious* (take a look at the gnashers in the specimen pictured at the top of a Tet Zoo post on the subject). Just this year, of course, we saw the publication of 'Livyatan', the largest of these killer sperm whales, with a skull some 3 m in length (Lambert et al., 2010; unfortunately, the original name bestowed on this animal, Leviathan, has turned out to be preoccupied, admittedly under pretty goofy circumstances). Bianucci & Landini (2006) suggested that the raptorial sperm whales may have been edged out by the evolution of large predatory delphinids (the lineage including the modern killer whale Orcinus orca) during the Pliocene, leaving only the squid-eaters behind.

*Interestingly, while both genera of living sperm whales lack teeth in their upper jaws, the loss of upper teeth seems to have happened independently; the stem lineages for both genera include taxa with teeth in both upper and lower jaws (Lambert et al., 2010).


Rather than the usual reconstruction of 'Leviathan' melvillei, I thought I'd show you this one by Hodari Nundu. The shark is supposed to be a juvenile.

REFERENCES

Bianucci, G., & W. Landini. 2006. Killer sperm whale: a new basal physeteroid (Mammalia, Cetacea) from the Late Miocene of Italy. Zoological Journal of the Linnean Society 148 (1): 103-131.

Carrier, D. R., S. M. Deban & J. Otterstrom. 2002. The face that sank the Essex: potential function of the spermaceti organ in aggression. Journal of Experimental Biology 205: 1755-1763.

Clarke, M. R. 1978. Buoyancy control as a function of the spermaceti organ in the sperm whale. Journal of the Marine Biological Association of the United Kingdom 58: 27-71.

Lambert, O., G. Bianucci, K. Post, C. de Muizon, R. Salas-Gismondi, M. Urbina & J. Reumer. 2010. The giant bite of a new raptorial sperm whale from the Miocene epoch of Peru. Nature 466: 105-108.

Watson, L. 1981. Sea Guide to Whales of the World. Hutchinson.

How the Badger Became (Taxon of the Week: Meles thorali)

Reconstruction of Meles thorali from Lyras & van der Geer (2007).

Badgers of the genus Meles are found throughout temperate Eurasia. They are burrowing omnivores, primarily feeding on worms, insects and other invertebrates but also quite willing to take plant matter and small vertebrates (the proportion of the diet made up by each varies from place to place). Badger lifestyles are also varied - badgers in England may live in groups of up to thirty individuals, but in other parts of their range they are much more reclusive. Many authors recognise only a single modern species in the genus, Meles meles, but based on characters of the dentition, coloration and baculum morphology some authors have argued for the recognition of three species - M. meles in Europe and Russia west of the Volga river, M. leucurus in Asia east of the Volga (with M. meles and M. leucurus marginally overlapping in central Asia east of the Caspian), and M. anakuma (the smallest species) in Japan (Abramov & Puzachenko, 2005). However, both the two continental species include a number of subspecies, while genetic divergence overall is low, so this is an area that requires further investigation (Marmi et al., 2005).

The genus Meles probably divided from the ancestors of its current living sister taxon, the hog badger Arctonyx collaris of south-east Asia, some time around the beginning of the Pliocene* (Tedford & Harington, 2003). Meles gennevauxi from Montpellier in France is known from the Lower Pliocene, but opinions differ as to whether this should be included in Meles or Arctomeles (a fossil genus related to Arctonyx; Tedford & Harington, 2003; Arribas & Garrido, 2007). If M. gennevauxi loses its spot, the runner-up is the late Pliocene Meles thorali.

*Offhand, Meles and Arctonyx are now the only living members of the mustelid subfamily Melinae, which used to contain all the "badgers" except the honey badger Mellivora capensis. Recent studies have shown that "badgers" are a polyphyletic group, and they have been divided up accordingly (Koepfli et al., 2008). The south-east Asian stink badgers of the genus Mydaus are related to the American skunks (which have been excluded from the Mustelidae as a separate family, Mephitidae), the American badger Taxidea taxus is sister to all other mustelids, while the ferret badgers (Melogale) are closer to Mustela and otters.


Upper jaw of Meles thorali spelaeus, seen from below. Photo from the Museo de Prehistòria de València.

Meles thorali was described from Saint-Vallier in France by Viret (1950; I haven't seen the original description), and has since been recorded from Bulgaria and Lesbos (Lyras & van der Geer, 2007). A subspecies, Meles thorali spelaeus, has been described from the south of France (Bonifay, 1971), but again I haven't seen the original description. Meles thorali was similar in size to modern Meles meles, but was distinguished by features such as the lesser lateral projection of the zygomatic arches (the cheekbones) and the presence of only two instead of three or more roots on the lower second molar (Arribas & Garrido, 2007).

Other badger species present in Europe during the latest Pliocene and early Pleistocene were the Spanish M. iberica, M. dimitrius of Greece and M. hollitzeri of Germany. On purely phenetic grounds, M. iberica appears to be the most divergent of the European badgers, while M. dimitrius and M. hollitzeri were closer to M. thorali and M. meles. Genetic studies confirm the identity of modern Iberian badgers with M. meles (Marmi et al., 2005), and nearly one and a half millions years (not to mention a couple of ice ages) separate M. iberica from the earliest known Iberian M. meles (Arribas & Garrido, 2007). M. thorali has been suggested to be the ancestor to the modern Meles species (Baryshnikov et al., 2003), but it is notable that M. thorali spelaeus seems to be even closer morphologically to M. meles than M. thorali thorali - a fused root on the upper second premolar and a second lower molar wider than long are derived features of the first two not shared with the third (Arribas & Garrido, 2007). Moreover, if one considers M. thorali proper and not M. spelaeus, I don't see from the characters described by Arribas & Garrido (2007) why M. thorali is necessarily any closer to modern badgers than M. dimitrius or (particularly) M. hollitzeri - M. hollitzeri, for instance, is closer to modern badgers in molar morphology. While Baryshnikov et al. (2003) derive modern east Asian badgers as well as M. meles proper from M. thorali*, I don't know whether they considered the relatively little-mentioned early Pleistocene Chinese badgers M. chiai and M. teilhardi (Xue et al., 2006).

*That is, if I've understood the abstract correctly. Funnily enough, the Russian Journal of Theriology doesn't seem to be readily available here in Perth.

REFERENCES

Abramov, A. V., & A. Yu. Puzachenko. 2005. Sexual dimorphism of craniological characters in Eurasian badgers, Meles spp. (Carnivora, Mustelidae). Zoologischer Anzeiger 244 (1): 11-29.

Arribas, A., & G. Garrido. 2007. Meles iberica n. sp., a new Eurasian badger (Mammalia, Carnivora, Mustelidae) from Fonelas P-1 (Plio-Pleistocene boundary, Guadix Basin, Granada, Spain). Comptes Rendus Palevol 6: 545-555.

Baryshnikov, G. F., A. Yu. Puzachenko & A. V. Abramov. 2003. New analysis of variability of cheek teeth in badgers (Carnivora, Mustelidae, Meles). Russian J. Theriol. 1 (2): 133–149.

Bonifay, M. F. 1971. Carnivores quaternaires du Sud-Est de la France. Mem. Mus. natl Hist. nat., Paris, n.s., Ser. C 21 (2): 1–377.

Koepfli, K.-P., K. A. Deere, G. J. Slater, C. Begg, K. Begg, L. Grassman, M. Lucherini, G. Veron & R. K. Wayne. 2008. Multigene phylogeny of the Mustelidae: resolving relationships, tempo and biogeographic history of a mammalian adaptive radiation. BMC Biology 6: 10.

Lyras, G. A., & A. A. E. van der Geer. 2007. The Late Pliocene vertebrate fauna of Vatera (Lesvos Island, Greece). Cranium 24 (2): 11-24.

Marmi, J., A. V. Abramov, P. V. Chashchin, & X. Domingo-Roura. 2005. Filogenia, subespeciación y estructura genética del tejón (Meles meles) en la Península Ibérica y en el mundo. In Ecología y conservación del tejón en ecosistemas mediterráneos (E. Virgós, E. Revilla, J. G. Mangas & X. Domingo-Roura, eds) pp. 13-26. Sociedad Española para la Conservación y Estudio de los Mamíferos: Málaga (reproduced as part of Josep Marmi's thesis).

Tedford, R. H., & C. R. Harington. 2003. An Arctic mammal fauna from the Early Pliocene of North America. Nature 425: 388-390.

Viret, J. 1950. Meles thorali n. sp. du loess villafranchien de Saint-Vallier (Drôme). Eclogae Geologicae Helvetiae 43 (3): 274–287.

Xue X., Zhang Y. & Yue L. 2006. Paleoenvironments indicated by the fossil mammalian assemblages from red clay-loess sequence in the Chinese Loess Plateau since 8.0 Ma B.P. Science in China: Series D Earth Sciences 49 (5): 518—530.

"Creodonts": Carnivores by Association

"Karianne's Pet" by Carl Buell. The large animal in the painting is the hyaenodontid Megistotherium osteothlastes, a contender for the title of biggest terrestrial carnivorous mammal ever.

As explained in an earlier post (which you may be interested in reading as a bit of background to this one), the earlier part of the Caenozoic (the current era of the earth's history) was home to a number of mammalian lineages of very mysterious relationships. Very few of the familiar orders around us today had yet put in an appearance, and instead the world was home to such oddities as pantodonts, tillodonts and dinocerates. Among the prominent carnivorous mammals of the time were a group known as the creodonts. Creodonts ranged in size from that of a small cat to lion- or bear-size species, and often converged in appearance with those animals. But what were creodonts?

Current authors regard the Creodonta as including two families, the vaguely cat-like Oxyaenidae and the largely dog- or hyaena-like Hyaenodontidae. Oxyaenids were found in North America and Europe during the late Palaeocene and Eocene, while hyaenodontids were found in Africa, Eurasia and North America from the Late Palaeocene to near the end of the Miocene, though they disappeared from North America not long after the end of the Eocene (Gheerbrant et al., 2006). Many authors have suggested a relationship with modern carnivorans (cats, dogs, weasels, bears, etc.), and they have been included with the latter in a superorder Ferae. Popular as this arrangement has been, however, there's just one small problem - there's not a shred of evidence to support it.


The oxyaenid Patriofelis ferox, reconstructed by Dmitry Bogdanov.

Part of the problem is that creodonts are a good example of what might be called "taxonomic drift". Imagine that an author establishes a taxon, and presents a list of organisms that he thinks belong to that taxon. A few years pass by, and the taxon is revised by another author, who excludes some of the originally-included species that he thinks belong elsewhere, and substitutes a few more species that he believes to be related to the remainder. Carry this on through a few subsequent revisions, with species being taken out and put in, and you may end up with a situation where nearly all of the original members of the taxon have been taken out, and the taxon name has become associated with a very different concept from its original intent. This can be horrendously confusing for later readers, because if they don't realise that this taxonomic drift has taken place, they may read things into older publications that their authors never intended.

Creodonta was originally established by Edward Drinker Cope in 1875 as a suborder of the Insectivora*. In his new suborder, Cope included three families - Oxyaenidae, Ambloctonidae (now included in Oxyaenidae - Gunnell, 1998) and Arctocyonidae (another contemporary family of carnivorous placentals, within which Cope also included what are now regarded as the Miacidae). The Hyaenodontidae were not part of the original Creodonta - at the time, Hyaenodon was regarded as a genuine carnivoran. Cope distinguished creodonts from carnivorans by the former's lack of a fused scapholunar bone in the wrist, their ungrooved astragalus, and their less-developed and smoother cerebral hemispheres (Cope, 1884). These features, it should be noted, are all primitive for placentals, but to Cope indicated the creodonts' position in the insectivoran grade. He nevertheless regarded creodonts as ancestral to carnivorans, with cats descended from Oxyaenidae and dogs from Miacidae (Cope, 1880). Later, Cope (1883) included Insectivora and Creodonta as separate suborders of his order Bunotheria, which also included the tillodonts, taeniodonts and prosimians**. Cope (1883) also redefined creodonts to include mammals without continuously-growing incisors and with trituberculate molars, which meant that in addition to the Oxyaenidae and Miacidae, Creodonta now included Mesonychidae, Leptictidae, moles and tenrecs (Arctocyonidae were transferred to the Insectivora). The Hyaenodontidae wormed their way in a year later (Cope, 1884).

*This does not necessarily mean that he thought they were specifically related to modern insectivorans such as shrews and hedgehogs. Cope and most of his contemporaries would have regarded the "Insectivora" as representing the generalised basal form from which all other placental mammals were derived, and recent insectivorans would have been the remnants of that original grade.

**It is also notable that Cope regarded the aye-aye as forming a separate suborder from other prosimians, due to its rodent-like incisors. Cope (1884) held that the tillodonts were "intimately allied to the living Chiromys [aye-aye] of Madagascar, which is itself almost a lemur, by general consent" (emphasis mine).


Skull of the sabre-toothed creodont Machaeroides eothen. Gunnell (1998) places Machaeroides in Oxyaenidae. Photo by Ghedoghedo.

So right from the beginning, the question of what was a creodont was convoluted. Over the years, various families of "creodonts" were reassigned as their relationships became clearer. The Miacidae became regarded as true Carnivora. Arctocyonidae and Mesonychidae became included among the primitive ungulates (another confused mess, but that's a story for another year) and may be related to artiodactyls. Moles and tenrecs, of course, were reunited with their fellow modern insectivorans (though the tenrecs have recently had another falling-out). Eventually, the creodonts were whittled down to their modern content of oxyaenids and hyaenodontids, but, as pointed out by Polly (1996), "Hyaenodontidae and Oxyaenidae are currently grouped together in Creodonta because they are the only taxa that have not been removed from the group, not because there has been specific positive evidence proposed for their grouping". Those few characters the two families do share are also found in other, non-creodont mammals. As for their association with Carnivora, the two orders have been associated because they both possess shearing carnassial teeth. However, while the carnassials in Carnivora are formed by the last upper premolars and the first lower molars, those of Oxyaenidae are derived from the first upper and second lower molars, while hyaenodontids have two sets of carnassials formed by the first upper/second lower and second upper/third lower molars. Carnassials have also developed in other groups of mammals - notably the borhyaenoids, which are metatherians if not marsupials and so definitely not related to carnivorans. The only real reason creodonts have been associated with Carnivora for so long seems to be their prior inclusion of the genuinely carnivoran (or stem-carnivoran) miacids. It's a bit like when one of your friends brings an acquaintance of theirs to a party who just hangs around for hours with everybody being too polite to ask them to leave.

So, if they weren't related to Carnivora, can we say what creodonts were related to? Particularly in the case of Oxyaenidae, the answer is brief, simple and to the point: we really have not got a sodding clue. Whatever their ancestry might have been, oxyaenids were horribly derived little (or not so little) beggars - for instance, they had completely lost the third molars. Van Valen (1969) derived both oxyaenids and hyaenodontids from the Palaeoryctidae, particularly from the Cretaceous-Palaeocene Cimolestes, and other authors seem to have regarded the idea favourably, at least for the hyaenodontids (Polly, 1996; Gheerbrant et al., 2006). The main problem with this scenario, however, is that the Palaeoryctidae of Van Valen and other authors is itself polyphyletic. For instance, the phylogenetic analysis of Wible et al. (2007) included two "palaeoryctids", Cimolestes and Eoryctes (Eoryctes is more likely to represent the Palaeoryctidae proper),and while Cimolestes appeared outside the placental crown group, Eoryctes was placed among the insectivorans as the sister to Potamogale (Tenrecidae). If creodonts (either or both families) are closer to Cimolestes, they may be stem-eutherians. If they are closer to Palaeoryctidae proper, they may even be afrotheres (Wible et al. did not support placement of tenrecs among afrotheres, but it is notable that the earliest hyaenodontids are African). Placement of either the Oxyaenidae or the Hyaenodontidae still awaits proper analysis.

REFERENCES

Cope, E. D. 1880. On the genera of the Creodonta. Proceedings of the American Philosophical Society 19 (107): 76-82.

Cope, E. D. 1883. On the mutual relations of the bunotherian Mammalia. Proceedings of the Academy of Natural Sciences of Philadelphia 35: 77-83.

Cope, E. D. 1884. The Creodonta. American Naturalist 18 (3): 255-267.

Gheerbrant, E., M. Iarochene, M. Amaghzaz & B. Bouya. 2006. Early African hyaenodontid mammals and their bearing on the origin of the Creodonta. Geological Magazine 143 (4): 475-489.

Gunnell, G. F. 1998. Creodonta. In Evolution of Tertiary Mammals of North America vol. 1. Terrestrial Carnivores, Ungulates, and Ungulatelike Mammals (C. M. Janis, K. M. Scott & L. L. Jacobs, eds) pp. 91-109. Cambridge University Press.

Polly, P. D. 1996. The skeleton of Gazinocyon vulpeculus gen. et comb. nov. and the cladistic relationships of Hyaenodontidae (Eutheria, Mammalia). Journal of Vertebrate Paleontology 16 (2): 303-319.

Van Valen, L. 1969. The multiple origins of the placental carnivores. Evolution 23 (1): 118-130.

Wible, J. R., G. W. Rougier, M. J. Novacek & R. J. Asher. 2007. Cretaceous eutherians and Laurasian origin for placental mammals near the K/T boundary. Nature 447: 1003-1006.

Wolf and Wolf and Wolf and Wolf and Cub

Canis rufus, the controversial red wolf of North America. Photo from Steven Hoelzer.

Despite the fact that I've been posting on this site for nearly two years now, I think this is just about a first - I'm actually going to write about something I've said I was going to write about. I'd better not let it become a habit - people might begin to think that I'm reliable.

In the post just linked to, I considered writing on "the taxonomy of dingoes and singing dogs, and of the wolf complex in general, [and] the origins of the red wolf (and how the ICZN fumbles on hybrids)". This is that post. To write about the wolf complex, though, first I'll have to define it. The phylogenetic analysis of Bardeleben et al. (2005) found a primary division of the genus Canis between the side-striped (Canis adustus) and black-backed (Canis mesomelas) jackals on one hand, and a clade containing the golden jackal (Canis aureus), coyote (Canis latrans), wolf (Canis lupus) and domestic dog (Canis familiaris) on the other. This latter clade was also supported by Zrzavý & Řičánková (2004), who also included therein Canis simensis, the Simien jackal or Ethiopian wolf. These five species, therefore, can be referred to as the wolf complex (or Canis 'sensu stricto', if one were to accept Zrzavý & Řičánková's suggestion of moving the other two species to separate genera, but I don't know of anyone who has). Relationships within the clade are not yet clearly resolved.


The Indian wolf, Canis pallipes, one of the "subspecies" of Canis lupus that has been regarded as a separate species in recent years. Photo by Rajpal Singh.

Though the four main species of Canis aureus, C. lupus, C. latrans and C. simensis all seem to be safe enough, beyond this it all becomes hazy*. At their broadest circumscriptions, three of the four species are extremely polytypic. Mech (1974) listed thirty-two subspecies for Canis lupus, Bekoff (1977) gave nineteen for Canis latrans, and while I haven't found a full listing of subspecies for Canis aureus, I think it's safe to say that there's a few. Even C. simensis manages to fit in two subspecies (Sillero-Zubiri & Gottelli, 1994), despite having a distribution not much larger than a cereal box (the two subspecies are divided by a minor geographical hiccup known as the Rift Valley). Needless to say, a number of these "subspecies" have been recognised as distinct species at one time or another, particularly various wolf populations such as the eastern North American Canis lycaon, the Indian C. pallipes or the Japanese C. hodophilax. The North African C. lupaster doesn't seem to be clamouring for separate species status, but authors disagree whether it's a subspecies of C. aureus or C. lupus. And yes, this is one of those "species concept" things - all members of the wolf clade seem to be pretty much fully interfertile, though behavioral differences may slow down cross-breeding where species overlap.

*It occurs to me that this line is becoming something of a cliché for this site. Honestly, is there any group of organisms out there for which the taxonomy is not hazy?


The Egyptian Canis lupaster, the one that doesn't know if he's a wolf or a jackal. Photo by Thomas Krumenacker.

The most hotly contested issue of interfertility in the wolf clade is undoubtedly that involving 'Canis rufus', the red wolf. The name 'Canis rufus'* has been applied to a form of Canis once found over a large part of the south-eastern United States, from Texas to Florida (Paradiso & Nowak, 1972), but which became extinct in the wild by 1980, before a re-introduced population was established from captive animals in North Carolina in the late 1980s. However, numerous authors have made the suggestion that C. rufus is not a valid 'species', but represents a hybrid between C. lupus (or C. lycaon) and C. latrans (Brownlow, 1996). As 'pure' red wolves became fewer and further between, hybridisation with coyotes became common, further muddying the waters.

*Older references use the name Canis niger, originally applied to the now-extinct Florida red wolf (Canis rufus floridanus). While niger is the older name by some sixty years, the book that it was published in, the Travels of W. Bartram, was declared by the ICZN to be invalid for the purposes of nomenclature, so the next-oldest name swings into use.


The original Canis lupus lupus. The species status of this one, at least, is safe. Photo by Milan Kořínek.

The red wolf was perhaps the academic victim of two malign influences - an unjustified preconception about how speciation works, and the ability of politics to interfere with scientific inference. While no law explicitly states as much (Brownlow, 1996), the general policy for conservation in the United States (and, for that matter, most other places in the world) has been that "hybrids" aren't worth conserving. Instead, there is generally a focus on maintaining "pure" lineages that is sometimes at odds with reality. Also, hybridisation has generally been assumed to be of little importance in animal evolution. The stereotypical view that hybrids between species are infertile (not the case with members of the wolf clade) means that hybrids are assumed to be dead-end oddities. Even the ICZN previously regarded names based on hybrids as invalid, and while this rule was most likely introduced to prevent names based on one-off, individual hybrid specimens (such as a mule), it was also invoked to declare names for populations of hybrid origin to be invalid (the current Code has changed the rules somewhat to remove this ambiguity). This is in stark contrast to the situation in botany, where hybridisation has long been recognised as a major player in the origin of new species, and where the Botanical Code of Nomenclature even has a specific concept of "nothospecies" for taxa of hybrid origin. As a result, the debate over the red wolf became unnecessarily polarised into an argument over whether it was of hybrid origin or a valid species - the possibility that it could be both seems to have never entered consideration.

The taxonomy of the wolf clade is further confused, of course, by the question of how to deal with domestic dogs and their wild derivatives. I'll refer you to a post by Darren Naish from a couple of years ago on the question of domestic dog origins. Darren refers in that post to the pariah dogs - wild populations of generalised domestic dog-type that are found from southern Asia to Australia, where, of course, they are represented by the dingo.


The New Guinea singing dog, Canis hallstromi (sometimes). Photo by Patti McNeal.

There is no doubt that populations such as the dingo and the New Guinea singing dog are ultimately derived from dogs that arrived in Australasia with the original human settlers. On this basis, the majority of authors have tended to include them with with domestic dogs as Canis familiaris and Canis lupus familiaris. However, these dogs have been living wild in their respective countries for a very long time, and have become morphologically distinct from their ancestors, leading others to separate them as the species Canis dingo and Canis hallstromi (Koler-Matznick et al., 2003)*. Again, the difference seems to be more one of philosophical approaches to what should be regarded as a "species", with a soupçon of the artificial distinction between "natural" and "altered" conditions. How long does it take for a "feral" population to become a "wild" one?

*One further point (which I'm putting in a footnote because I couldn't work out how to integrate it into the paragraph) is that these dogs quite possibly became part of the "wild" environment very soon after their arrival with humans, if not immediately (and while there's a lot of disagreement about when exactly that was, it was at least many tens of thousands of years ago). After all, the modern intensive management of domestic animals did not always apply - in many cases, animals were largely left to roam free, dogs especially so, and their presence was more encouraged than controlled. The dogs that originally arrived in New Guinea and Australia could have been more commensals than domesticates of humans.

REFERENCES

Bardeleben, C., R. L. Moore & R. K. Wayne. 2005. A molecular phylogeny of the Canidae based on six nuclear loci. Molecular Phylogenetics and Evolution 37 (3): 815-831.

Bekoff, M. 1977. Canis latrans. Mammalian Species 79: 1-9.

Brownlow, C. A. 1996. Molecular taxonomy and the conservation of the red wolf and other endangered carnivores. Conservation Biology 10 (2): 390-396.

Koler-Matznick, J., I. L. Brisbin Jr, M. Feinstein & S. Bulmer. 2003. An updated description of the New Guinea singing dog (Canis hallstromi, Troughton 1957). Journal of Zoology 261: 109-118.

Mech, L. D. 1974. Canis lupus. Mammalian Species 37: 1-6.

Paradiso, J. L., & R. M. Nowak. 1972. Canis rufus. Mammalian Species 22: 1-4.

Sillero-Zubiri, C., & D. Gottelli. 1994. Canis simensis. Mammalian Species 485: 1-6.

Zrzavý, J., & V. Řičánková. 2004. Phylogeny of Recent Canidae (Mammalia, Carnivora): relative reliability and utility of morphological and molecular datasets. Zoologica Scripta 33 (4): 311-333.

The Uglier Side of the Family (Taxon of the Week: Ceratomorpha)

Lowland tapir, Tapirus terrestris, in a blatant attempt to exploit the cute factor. Photo by Antonio Pinheiro.

The modern perissodactyls are, sadly, but a shadow of their former glory. Once among the planet's dominant herbivores, the odd-toed hoofed mammals have become reduced to less than twenty living species (the majority of which are critically endangered to boot). Nevertheless, their secure position as charismatic megafauna means that they are familiar animals to most people (at least conceptually). One species in particular, the horse Equus caballus, has developed a close association with humanity and holds a high position in the human psyche (or at least the Eurasian and American psyche). But this post won't be dealing with horses - this is for the other side of the perissodactyls. The Ceratomorpha may not have been blessed with the aesthetic appeal of the horses, but they're not without their charms.


Skull of Tapirus terrestris. Note the severely recessed nasal bones, positioned above the eyes, that indicate the presence of the muscular trunk in life. Tapirs are often thought of as more "primitive" than other perissodactyls, but no other perissodactyl has a skull like that. Photo by Matthew Colbert.

The Ceratomorpha contains two living families, the Tapiridae (tapirs) and Rhinocerotidae (rhinoceroses). Most of the people reading this will, I'm guessing, probably be familiar with the appearance of both, though rhinos do get given a little more press than tapirs*. Rhinos are also marginally more diverse in the modern environment, with five species to the tapirs' four - but considering that at least two of the rhino species are hovering on the brink of extinction, that may yet change. As regards fossil taxa, the limits of Ceratomorpha are a little more hazy, mostly because different authors have applied slightly different concepts for 'Ceratomorpha' vs. the related name 'Tapiromorpha'. In my opinion, the most sensible definitions for both are those proposed by Holbrook (1999), who used 'Ceratomorpha' for the crown clade of tapirs + rhinos, and 'Tapiromorpha' for the total group of anything more closely related to tapirs and rhinos than to horses. These definitions are better than the alternatives proposed by Froehlich (1999) in being agnostic as to whether the extinct chalicotheres are tapiromorphs (as supported by Froehlich, 1999, among others) or not (as indicated by, e.g., Hooker & Dashzeveg, 2004, who placed chalicotheres outside the perissodactyl crown group).

*Completely unrelated aside to everything else - the Japanese name for 'tapir' is 'baku'. Originally, a baku was a trunked mythical creature that was supposed to feed on people's dreams (particularly nightmares), but living tapirs have a somewhat more material diet. This isn't the only example in Japanese of a living exotic animal being granted the name of a pre-'existing' mythical creature: giraffes are known as 'kirin'.

Within the Ceratomorpha, then, the primary division is between the Tapiroidea and the Rhinocerotoidea, each including (obviously) the taxa more closely related to one of the living families than the other*. The Rhinocerotoidea are far better understood that the Tapiroidea, which have a more spotty fossil record. Four families are generally assigned to the Tapiroidea - Helaletidae, Lophialetidae, Deperetellidae and Tapiridae. The mostly Eocene 'Helaletidae', small tapiroids of North America and Eurasia, however, are probably paraphyletic with regard to other tapiroids. Holbrook (1999), for instance, excluded the North American genus Heptodon from the Helaletidae as he found it to be sister to all other tapiroids. At least one 'helaletid' genus, the North American Oligocene Colodon, is of interest because it possessed significantly retracted narial opening, indicating the presence of a trunk as in modern tapirs. However, Colbert (2005) included Colodon within the Tapiridae, closer to modern tapirs than previous authors.

*Be warned, though - older references tend to use the term 'tapiroid' as a grade concept for non-rhinocerotoid tapiromorphs, including a number of taxa that would be regarded as stem-Ceratomorpha in this post.


Hyrachyus, an Eocene rhinocerotoid. Hyrachyus was very similar to the tapiroid 'Helaletidae' of the same time period (which is pretty much what one would expect, really) and represents the general basal morphology for Ceratomorpha. Picture from here, though it has a definite Zdenek Burian look about it.

The Lophialetidae and Deperetellidae were two strictly Asian late Eocene families that suffer from a severe lack of study. Both have been mostly regarded as tapiroids for as long as they have been known, but Holbrook (2001) pointed out that the evidence for doing so is pretty slight. Members of both families (supported as forming a monophyletic clade by Holbrook, 1999) showed a reduction in the number of toes from four to three and a longer, more slender foot than other tapiroids, indicating that they were more cursorial (Radinsky, 1969). The Eocene also saw the appearance of the first Tapiridae, which (with the possible exception of Colodon, depending on its position) seem to have been the only tapiroids to survive into the Oligocene. The earliest tapirid genus, Protapirus, has been described from both North America and Eurasia, but its monophyly is uncertain (Colbert, 2005).


Assortment of Amynodontidae as drawn by Stanton Fink - front to back, they are Cadurcodon, Gigantamynodon and Metamynodon. This isn't the first time I've used one of Stanton's drawings - other ones are here and here. I must confess to having something of a love-hate reaction to Stanton's work - his style isn't entirely to my taste aesthetically, but one thing I do think is great is how often he reconstructs animals that other artists just ignore. Besides, I can't draw to save myself, so I have absolutely no right to criticise.

The other superfamily, Rhinocerotoidea, has had a much greater diversity described, both in terms of number of species and morphological range. Three major families have been recognised - the Amynodontidae, Hyracodontidae and Rhinocerotidae. The middle Eocene to Middle Oligocene Amynodontidae were the really unfortunate members of the superfamily appearance-wise - as the saying goes, they would have not only been hit with the ugly stick, they would have fallen out of the ugly tree hitting every ugly branch on the way down. Amynodontids have mostly been characterised as subaquatic, like modern hippos, but Wall (1998) points out that only a single derived subgroup, the Metamynodontini, shows adaptations for such a lifestyle. The remaining amynodontids would have been terrestrial. One group of amynodontids, the Cadurcodontini, appears to have convergently evolved a short trunk like that of the tapirids.


A rather disgruntled looking Hyracodon, reconstructed by Heinrich Harder.

The Eocene to Oligocene Hyracodontidae are the real taxonomic dog's breakfast of the Rhinocerotoidea. Radinsky's (1966) influential definition of which taxa should be included in Hyracodontidae essentially amounted to "anything which doesn't belong to Amynodontidae or Rhinocerotidae". Characters that have been suggested to support a monophyletic Hyracodontidae, such as an elongate foot and three toes, are also found in other perissodactyls (in fact, if you look upwards you'll notice that I mentioned the exact same characters in connection with Lophialetidae). In general, hyracodontids were more cursorial than other rhinocerotoids, and small genera such as Hyracodon would have been fairly pony-like. Also usually included in the 'Hyracodontidae' where the gigantic Indricotheriinae, of which the central Asian Oligocene genus Paraceratherium is famed as the largest known land mammal*. The phylogenetic analysis of Holbrook (2001) supported treating the smaller Hyracodontinae as a separate family from the larger Indricotheriinae, but failed to support the latter as monophyletic.

*Though sometimes in disguise. Paraceratherium has held a few different names over the years - 'Indricotherium' and 'Baluchitherium' are two of the most commonly used. It remains a rather fraught question as to whether all these represent the same animal, or a number of closely related animals.


A herd of Paraceratherium (would Paraceratherium have really travelled in herds?) passing by scavenging Hyaenodon. Painting by Mauricio Antón.

And finally, the Rhinocerotidae. But I think I've rabbited on and wasted enough of everyone's time for today, so I guess I'll have to leave the hippo-like Teleoceras, or the double-horned Menoceras (two horns side by side, that is), or the gigantic Elasmotherium (with what must have been one of the most terrifying pieces of headgear this side of Arsinoitherium) for another time.

REFERENCES

Colbert, M. W. 2005. The facial skeleton of the Early Oligocene Colodon (Perissodactyla, Tapiroidea). Palaeontologia Electronica 8 (1): 8.1.12A.

Froehlich, D. J. 1999. Phylogenetic systematics of basal perissodactyls. Journal of Vertebrate Paleontology 19 (1): 140-159.

Holbrook, L. T. 1999. The phylogeny and classification of tapiromorph perissodactyls (Mammalia). Cladistics 15 (3): 331-350.

Holbrook, L. T. 2001. Comparative osteology of early Tertiary tapiromorphs (Mammalia, Perissodactyla). Zoological Journal of the Linnean Society 132 (1): 1-54.

Hooker, J. J., & D. Dashzeveg. 2004. The origin of chalicotheres (Perissodactyla, Mammalia). Palaeontology 47 (6): 1363-1386.

Radinsky, L. B. 1966. The families of the Rhinocerotoidea (Mammalia, Perissodactyla). Journal of Mammalogy 47 (4): 631-639.

Radinsky, L. B. 1969. The early evolution of the Perissodactyla. Evolution 23 (2): 308-328.

Wall, W. P. 1998. Amynodontidae. In Evolution of Tertiary Mammals of North America: Terrestrial Carnivores, Ungulates, and Ungulatelike Mammals (L. L. Jacobs & K. M. Scott, eds.) pp. 583-588. Cambridge University Press.

Dog's Life

Fossil skeleton of Hesperocyon gregarius, one of the earliest species of Canidae. Photo from Wikipedia.

Wild dogs, it has to be said, are often something of the poor relation among large carnivorans. While people ooh and aah over lions and tigers, are fascinated by bears, and giggle madly at otters, dogs tend to be given the cold shoulder. This has almost nothing to do with the subject of this post, other than that I am writing about dogs here, but it was a point I wanted to bring up.

The Canidae are one of the more basally-diverging groups of living carnivorans. Within the crown Carnivora, the first divergence is between the Feliformia on one hand, containing cats, mongooses and hyaenas, and the Caniformia on the other, containing dogs, bears, seals and weasels. Then within the Caniformia, the first divergence is between dogs and everything else. Fossils assigned to the Canidae date back to the late Eocene, nearly forty million years ago. However, these fossils all belong to extinct subfamilies, and the earliest members of the Canidae crown group don't appear until the later part of the Miocene, about ten million years ago (Wang et al., 2004). All modern canids belong to the subfamily Caninae. The African hunting dog (Lycaon pictus), Asian dhole (Cuon alpinus) and South American bush dog (Speothos venaticus) have been suggested to form a separate subfamily Simocyoninae on the basis of dental characteristics (they have only one cusp on the heel of the carnassial teeth instead of two as in other Caninae - Macdonald, 1984), but these species are not closely related (Bardeleben et al., 2005) and their shared dental features are probably independent adaptations to a more hypercarnivorous diet (I suspect it may also be related to their hypercarnivory that these three species seem to be the most obligately social of the canids). Just to further nail the coffin for the "Simocyoninae", the type genus Simocyon is itself unrelated to the modern species. It's not even a canid, but a fossil relative of Ailurus fulgens, the modern red panda (Salesa et al., 2006).


Reconstruction of two Epicyon species (Borophaginae) from Wang et al., 2004.

The two extinct subfamilies of Canidae, Hesperocyoninae* and Borophaginae, both diversified soon after the origin of the Canidae in the early Oligocene. The Hesperocyoninae were mostly relatively small (the largest, and the latest, of the hesperocyonines was Osbornodon fricki, which reached the size of a small wolf). Most hesperocyonines were hypercarnivorous, and the subfamily was never hugely diverse. They became extinct during the Oligocene, shortly before the diversification of the Caninae. The Borophaginae were a much more disparate bunch. The subfamily is best-known for the giant, hyaena-like, bone-cracking forms in the genera Epicyon and Borophagus (the latest species of Epicyon, E. haydeni, was the size of a large bear and the largest canid ever), but the borophagines actually covered the entire range of canid ecological diversity from large to small, from extreme hypercarnivore to extreme hypocarnivore. One borophagine genus, Cynarctoides, appears to have been completely herbivorous. Borophaginae became extinct about two million years ago at the end of the Pliocene.

*Hesperocyoninae as a whole may be paraphyletic with regard to the other subfamilies. But if I read Wang et al. (2004) correctly, it looks as though the majority of hesperocyonine genera (except, annoyingly enough, Hesperocyon itself) may still form a clade.


African hunting dog, Lycaon pictus. With their stick-thin legs and oversized ears, I've always felt hunting dogs look a bit like a young child's drawing of a dog brought to life. This photo is by Philip Gabrielsen, but an absolutely incredible (and more than a little creepy) photo of a pair of hunting dogs and a hyaena can be found here.

The Caninae did appear at about the same time as the other two subfamilies, but in contrast to the immediate radiations of the Hesperocyoninae and Borophaginae, the Caninae barely trickled along for the next thirty million years in the form of a series of small, conservative species all assigned to a single genus, Leptocyon. The Leptocyon lineage didn't diversify until the extinction of the smaller borophagines. As discussed in an earlier post, the basic division between crown canids is between Vulpes (most foxes) on one hand and a clade containing the wolf-like and South American canids on the other, with the positions of the grey foxes (Urocyon), bat-eared fox (Otocyon megalotis) and tanuki (Nyctereutes procyonoides) relative to this split more uncertain. While not quite as diverse as the borophagines, modern canids are still an ecologically varied bunch. Anyone who has ever owned a dog can probably vouch for their tendency to try and eat anything that is physically capable of getting down their throat (and a few things that aren't), and many dog species are omnivorous to some degree. Perhaps the most extreme example is the maned wolf (Chrysocyon brachyurus), which feeds on fruit about as much as it does on meat (Dietz, 1984).

There's a lot more I could write about here - the taxonomy of dingoes and singing dogs, and of the wolf complex in general, the origins of the red wolf (and how the ICZN fumbles on hybrids), and the natures of Dusicyon australis and Dusicyon hagenbecki, just for starters. But I've used up a morning already, so maybe I'll get back to them in a future post (I said maybe).

REFERENCES

Bardeleben, C., R. L. Moore & R. K. Wayne. 2005. A molecular phylogeny of the Canidae based on six nuclear loci. Molecular Phylogenetics and Evolution 37 (3): 815-831.

Dietz, J. M. 1984. Maned wolf. In All the World’s Animals: Carnivores (D. Macdonald, ed.) pp. 74-75. Torstar Books Inc.: New York.

Macdonald, D. W. 1984. The dog family. In All the World’s Animals: Carnivores (D. Macdonald, ed.) pp. 48-49. Torstar Books Inc.: New York.

Salesa, M. J., M. Antón, S. Peigné & J. Morales. 2006. Evidence of a false thumb in a fossil carnivore clarifies the evolution of pandas. Proceedings of the National Academy of Sciences of the USA 103 (2): 379-382.

Wang, X., R. H. Tedford, B. Van Valkenburgh & R. K. Wayne. 2004. Ancestry: Evolutionary history, molecular systematics, and evolutionary ecology of Canidae. In The Biology and Conservation of Wild Canids (D. W. Macdonald & C. Sillero-Zubiri, eds.) pp. 39-54. Oxford University Press.

Fantastic Mr Fox

The Tibetan fox (Vulpes ferrilata), a distinctive fox species restricted to the Tibetan Plateau. Photo from the BBC via Lioncrusher's Domain.

Foxes are a widespread assemblage of canid predators, found through most of the Holarctic and drier Africa and also here in Australia, where the red fox Vulpes vulpes was introduced quite successfully. Too successfully, in fact - foxes are one of the most significant invasive species in Australia, and a dire threat to many native species. Of the slightly more than ten species in the fox genus Vulpes, the red fox is undoubtedly the most familiar, being both the most widespread species overall as well as the most abundant in developed countries. However, the familiarity of the red fox is a little misleading, as Vulpes vulpes is actually one of the more distinctive species in the genus, being considerably larger and arguably more dog-like than other foxes.

The morphological analysis of the Canidae by Tedford et al. (1995) supported a division of the living members of the family between two lineages, the Vulpini containing Vulpes, and the Canini including Canis (the genus including the domestic dog) and the South American canids. This early division is consistent with the early appearance of fossil species assigned to Vulpes, with V. stenognathus coming from the Late Miocene (Lyras & van der Geer, 2003). The majority of Vulpini were included in Vulpes except for the bat-eared fox (Otocyon megalotis) and the two species of grey foxes (Urocyon). Two species in the Vulpes clade, the fennec fox (Vulpes zerda or Fennecus zerda) and the Arctic fox (Alopex lagopus) have been regarded as separate genera, but it seems pretty well-established that doing so renders Vulpes paraphyletic (Zrzavý & Řičánková, 2004). More recent analyses using both molecular and morphological data have continued to support the Vulpes-Canini division (Zrzavý & Řičánková, 2004; Bardeleben et al., 2005), but results differ about the relationships of Vulpes to Urocyon and/or Otocyon, which may fall in a Vulpini clade or may be basal to the Vulpes + Canini split. Still, all recent authors seem to agree that, contrary to many older sources, the grey foxes should not be included in Vulpes.


The Indian fox (Vulpes bengalensis), the species nominated by Macdonald (1984) as the most representative of the genus. A nice atmospheric shot by Jon Hall.

Relationships within the Vulpes clade are fairly uncertain. Zrzavý & Řičánková (2004) tentatively suggested a division between two major groups that both may or may not be monophyletic, an 'Afro-Asiatic' clade and an 'Holarctic' clade. The 'Afro-Asiatic' group includes the fennec and pale fox (V. pallida) of northern Africa, the Cape fox (V. chama) of southern Africa, Blanford's fox (V. cana) of central Asia and probably the Indian fox (V. bengalensis), with the fennec and Blanford's foxes forming a clade. Within the 'Holarctic' group, Rüppell's fox (V. ruppelli) inhabits northern Africa, the red fox can be found across the entire Holarctic, and the corsac (V. corsac) and Tibetan foxes (V. ferrilata) are found in central Asia. The circumpolar Arctic fox forms a clade in the Holarctic group with the V. velox/V. macrotis complex, the swift and kit foxes, of North America. All fox species seem to inhabit temperate or dry climates - note particularly the wide geographical division between the Cape fox and all other species of the genus.

While foxes are generally characterised as solitary animals, and certainly do not form packs in the manner of Canis and closely related genera, individuals of at least some species may form small groups, usually a male and a number of vixens. Members of a group will still forage for food separately (Macdonald, 1984). All foxes use a characteristic high pounce in capturing prey, springing upwards and landing on their quarry from directly above it.



Of course, foxes are also famed for being one of the few animals able to transform their appearance at will. They share this ability with the tanuki (Nyctereutes procyonoides), a canid whose phylogenetic position relative to the Vulpes-Canini split remains uncertain. Nevertheless, the foxes would doubtless like to point out that they are not as prone to buffoonery as tanuki. Because of the uncertain position of the tanuki and a shocking shortage of studies of shape-changing abilities in fox species other than V. vulpes, we cannot presently comment whether the shape-changing ability is a plesiomorphy of crown canids that has been lost in the Canini, or has been acquired independently in foxes and tanuki.

REFERENCES

Bardeleben, C., R. L. Moore & R. K. Wayne. 2005. A molecular phylogeny of the Canidae based on six nuclear loci. Molecular Phylogenetics and Evolution 37 (3): 815-831.

Lyras, G. E., & A. A. E. van der Geer. 2003. External brain anatomy in relation to the phylogeny of Caninae (Carnivora: Canidae). Zoological Journal of the Linnean Society 138 (4): 505-522.

Macdonald, D. W. 1984. Foxes. In All the World’s Animals: Carnivores (D. Macdonald, ed.) pp. 60-67. Torstar Books Inc.: New York.

Tedford, R. H., B. E. Taylor & X. Wang. 1995. Phylogeny of the Caninae (Carnivora: Canidae): the living taxa. American Museum Novitates 3146: 1-37.

Zrzavý, J., & V. Řičánková. 2004. Phylogeny of Recent Canidae (Mammalia, Carnivora): relative reliability and utility of morphological and molecular datasets. Zoologica Scripta 33 (4): 311-333.