The Grisons

Spend a bit of time following discussions of nature documentaries and other popular representations of biodiversity, and one topic you're likely to see come up is the biases that tend to exist in what gets represented. Images from eastern and southern Africa predominate while the west and north of that continent get overlooked. Europe and North America receive much more attention than the temperate regions of Asia. Another region whose diversity tends to go underrepresented is South America. The casual observer might think this continent is all monkeys and jaguars but South America is also home to notable radiations of dogs, deer, rodents, and other animals that many people would associate more with other parts of the world. Among these overlooked elements of the South American fauna are the local species of mustelid, including the grisons of the genus Galictis.

Greater grison Galictis vittata, copyright Tony Hisgett.

Grisons are somewhat ferret- or skunk-like animals found across almost the entirety of South America, and north into southern Mexico. They are greyish in colour dorsally (the name 'grison' itself means 'grey') with a black face and underparts. A pale stripe separates the upper and lower parts across the top of the face and continues diagonally back to the shoulders. They feed on small vertebrates and tend to be solitary hunters though they may sometimes form small family groups. They are primarily terrestrial and diurnal in habits. They have a reputation for ferocity; residents of Chile apparently have a history of using comparisons to grisons to describe unchecked rage (Yensen & Tarifa 2003b), in a similar manner to references to wolverines and honey badgers in other parts of the world. Contrasting colour patterns like those of the grisons are associated in other musteloids (such as skunks) with the production of offensive odours for defence, and grisons also produce strong-smelling secretions from their anal glands. Though some sources have claimed the odour produced by the lesser grison to be worse than a skunk's, it appears that these reports are exaggerated (Yensen & Tarifa 2003b).

Lesser grison Galictis cuja, copyright Ken Erickson.

Most authors have recognised two species of grison, the greater grison Galictis vittata and the lesser grison G. cuja*, as corroborated by a recent taxonomic study of the genus by Bornholdt et al. (2013). As their names indicate, the greater grison is generally larger and more robust than the lesser, being about 60 to 76 cm in total length versus 44 to 68 cm for the lesser grison (Yensen & Tarifa 2003b). The tail is also proportionately shorter in the greater grison (30% of the total length for the greater, 40% for the shorter). Fur is relatively longer and denser in the lesser grison, giving it more of a fluffy look. Whereas the dorsal fur is always a plain grey in the greater grison, it may often have a yellowish tinge in the lesser (not always, though). The two are generally distinct in range and habitat, as well. The greater grison is an animal of tropical forests and inhabits the northern part of the genus' range in Central America and northern and western South America. The lesser grison inhabits drier habitats, in arid or temperate regions, and so occupies the southern and eastern parts of the continent. The ranges of the species are known to overlap in Bolivian and Paraguay where their respective biomes approach each other.

*Some sources have listed a third species G. allamandi but this seems have been something of a 'ghost' taxon born from confusion whether the name 'G. vittata' applied to the greater or lesser species.

The genus Galictis arrived in South America as part of the Great American Biotic Interchange, about three million years ago. The general consensus is that it is derived from the genus Trigonictis of the North American Pliocene. Indeed, it has even been suggested that the two North American species of Trigonictis might represent independent ancestors of Galictis, with the larger T. macrodon giving rise to the greater grison and the smaller T. cookii birthing the lesser grison (Yensen & Tarifa 2003a). This certainly would seem overly complicated, though, and molecular data are more in line with a more recent separation of the species.

REFERENCES

Bornholdt, R., K. Helgen, K.-P. Koepfli, L. Oliveira, M. Lucherini & E. Eizirik. 2013. Taxonomic revision of the genus Galictis (Carnivora: Mustelidae): species delimitation, morphological diagnosis, and refined mapping of geographical distribution. Zoological Journal of the Linnean Society 167: 449–472.

Yensen, E., & T. Tarifa. 2003a. Galictis vittata. Mammalian Species 727: 1–8.

Yensen, E., & T. Tarifa. 2003b. Galictis cuja. Mammalian Species 728: 1–8.

Predators of the European Eocene

Among mammals in today's modern fauna, the role of terrestrial carnivore is dominated by members of one particular lineage, known (appropriately enough) as the Carnivora. But travel back in time to the Eocene period, roughly 56 to 34 million years ago, and you'll find a range of now extinct groups sharing that role. This post is looking at one of those groups, the proviverrines.

The Proviverrinae are a subgroup of the Hyaenodontidae, one of the two families of carnivores commonly associated as the creodonts. I've discussed creodonts before, and the overhanging question of whether they form a coherent evolutionary group. Currently, my impression is that most mammal palaeontologists seem inclined to think that hyaenodontids and oxyaenids probably do not share an immediate common ancestry. However, nor is there any clear idea of what else either group may relate to.

Skull of Cynohyaenodon cayluxi, photographed by Ghedoghedo.

Historically, proviverrines have been treated as the basal grade from which other groups of hyaenodontids were derived with representatives known from Europe and North America. However, a phylogenetic analysis of early hyaenodontids by Solé (2013) lead to a division of the 'proviverrines' between three monophyletic subfamilies: the Proviverrinae proper, the Sinopinae and the Arfiinae. Under this system, the Proviverrinae are a uniquely European group. As is standard in mammalian palaeontology, proviverrines (in the strict sense) are distinguished from other hyaenodontids by features of the teeth. Notable among these is the presence of a double root on the first lower premolar of most proviverrines; other hyaenodontids have a single root on this tooth.

The earliest proviverrines are known from the very beginning of the Eocene (Solé et al. 2014). Current thinking is that their ancestors probably immigrated into Europe around this time from Africa. The Late Paleocene Tinerhodon disputatum from northern Africa resembles a proviverrine in overall appearance but was probably more basally placed in respect to hyaenodontids as a whole. The name 'Proviverra' can be read as 'early civet' and while proviverrines were not related to modern civets (which are, of course, true carnivorans) this is probably not a bad indication of the overall appearance of their original appearance. These were very small animals, probably less than 100 g in body weight, and probably had a fairly generalised diet of small vertebrates and invertebrates. At first, proviverrines seem to have been restricted to southern Europe, what is now Spain and the very southernmost part of France. Northern Europe was inhabited by the Arfiinae and Sinopinae, as well as species of Oxyaenidae (the other 'creodont' family). Sinopinae were also found in southern Europe and may have excluded the proviverrines from evolving larger size. However, the other hyaenodontids and oxyaenids went extinct in Europe not to long after the beginning of the Eocene. A turnover in the mammalian fauna of North America around this time appears to be due to a cooling of the climate; though the evidence for climate cooling is less clear in Europe, it seems reasonable that it was going through similar changes. With their competitors out of the picture, the proviverrines rapidly diversified into the regions and niches that had been left unoccupied.

Lesmesodon edingeri, photographed by Ghedoghedo.

The largest proviverrines, members of the genera Prodissopsalis, Paenoxyaenoides and Matthodon, would eventually reach weights of close to twenty kilograms, about as large as a medium-sized dog. They would also diversify in their habits. Members of the genera Oxyaenoides and Paenoxyaenoides were cursorial hypercarnivores, their dentition specialised for a diet almost exclusively of meat*, like that of a modern cat. Matthodon and Quercytherium, in contrast, were genera whose dentition showed more adaptations for cracking hard materials such as bone. They may have had lifestyles more like those of hyaenas, with Matthodon (which combined adaptations for hypercarnivory and bone-cracking) perhaps being more of an active hunter than Quercytherium.

*These two genera also provide an excellent example of the role of convergent evolution in the evolution of mammalian carnivores. Their appearance to other hypercarnivorous hyaenodontids was such that it was only recently that they were recognised as proviverrines rather than members of other subfamilies no longer thought to have been found in Europe. And not only are they remarkably convergent on other subfamilies, the phylogenetic analysis of proviverrines by Solé et al. (2014) suggests that they're not even directly related to each other within that clade.

Proviverrines remained the dominant mammalian carnivores in Europe for about the next twenty million years but then went into a sharp decline. This reversal of fortunes may have been due to the increasingly cool, dry conditions developing at this time, and/or it may have been related to competition from the first true carnivorans arriving in Europe. The larger, more specialised proviverrines disappeared rapidly when their time came. The last surviving genus, Allopterodon, was a small form, little more than one kilogram in weight, and had a generalised dentition indicating a relatively unspecialised diet. This may have been a return to something like the lineage's original form but it would not save it: by the end of the Eocene, the proviverrines would be completely extinct.

REFERENCES

Solé, F. 2013. New proviverrine genus from the Early Eocene of Europe and the first phylogeny of Late Palaeocene–Middle Eocene hyaenodontidans (Mammalia). Journal of Systematic Palaeontology 11 (4): 375–398.

Solé, F., J. Falconnet & L. Yves. 2014. New proviverrines (Hyaenodontida) from the early Eocene of Europe; phylogeny and ecological evolution of the Proviverrinae. Zoological Journal of the Linnean Society 171: 878–917.

Variations on a Tayra

Subspecies can be a funny thing in the world of animal taxonomy. Millions of litres of ink have been spilt over the years arguing over how one defines a species but a lot less has been invested in discussing the nature of subspecies. For some popular species concepts (such as the most popular iteration of the 'phylogenetic species concept'), one might question whether any concept of subspecies could be applied at all (I could suggest some hypothetical situations but just how applicable or practical they are is a further matter). Essentially, most subspecies concepts distill down to 'a population that is distinct enough to warrant recognition but somehow doesn't quite qualify as a species'. Historically, the rank has tended not to receive a lot of usage among animals outside groups subject to particularly high levels of taxonomic attention—most particularly, vertebrates and butterflies—and many currently recognised animal subspecies were first named in days when taxon descriptions tended to be much briefer and taxonomists were under less pressure to explain their reasoning. Because subspecies tend to be, by their nature, vague and difficult to define, and because evaluating them often requires detailed population analysis within a species, these historical subspecies have a tendency to linger, unchallenged, in taxonomic listings. And with that as background, tayras.

Tayra Eira barbara photographed in Peru, copyright eMammal. Photography location would indicate this individual to be either E. b. madeirensis or E. b. peruana.

The tayra Eira barbara is a large mustelid (a member of the family including weasels, otters and badgers) found in warmer regions of Central and South America, its distribution extending down to about the level of the southern edge of Brazil. They are long-bodied but robust animals, kind of looking like a 'roided-up stoat. They grow to a head-body length of two feet or more (up to about 71 centimetres) with a tail about two-thirds as long again. Adult males tend to be a third as large again as females and more muscular around the fore quarters. Comparisons have often been made between tayras and the martens Martes of the Northern Hemisphere and molecular studies confirm a relationship between these two genera, as well as the wolverines Gulo. Closer fossil relatives are known from North America and it seems likely that the tayra originated on that continent then spread southwards. Ruiz-García et al. (2013) suggested that the degree of genetic divergence between tayras found in South America might indicate the species may have arrived there about eight million years ago, before the formation of the Panamanian land bridge. Tayras are not the only species for which this possibility has been suggested; these early arrivals may have reached South America by island-hopping between earlier-emerging segments of the eventual connection.

Tayras are diurnal omnivores, their known diet ranging from fruits to small animals to honey. In captivity, it seems they will accept pretty much anything offered to them. Tayras are the only animals other than humans that have been recorded caching unripe fruit in order to eat it after it finishes ripening. It is still not certain to what degree tayras are solitary or social; though commonly regarded as solitary, they have been recorded hunting howler monkeys in groups (Shostell & Ruiz-Garcia 2013). Tayras are mostly found in forests; in some areas they may adjust to more open habitats but seemingly only under sufferance (Presley 2000). Though not regarded as 'arboreal' per se, tayras are adept climbers. Their well developed carpal vibrissae ('whiskers' on the wrists) presumably contribute to this ability. Their wide distribution and adaptability mean that tayras are not currently regarded as of conservation concern though habitat degradation has reduced their numbers in some areas.

Tayra from Belize, presumably the light-headed Eira barbara senex, from Wikimedia Commons.

The body and tail of tayras are generally dark brown or black with the head being distinctly lighter in coloration (light brown or grey to yellow). Leucistic and albino individuals are not that uncommon (yellow tayras are apparently particularly common in Guyana). A patch of pale coloration, varying from a spot to a broad triangle, is often (but not always) present on the chest and throat. Recent taxonomic listings (e.g. Presley 2000) have recognised seven subspecies of tayra distinguished by coloration. The Mexican Eira barbara senex has a greyish white head with the light coloration extending to dark yellow shoulders and a dark brown body. Eira barbara inserta, found in southern Honduras and Nicaragua, is a dark subspecies with a dark brown head, black body and no throat patch. The Colombian E. b. sinuensis is darker than E. b. senex with the nape a darker brown than the head; it may or may not possess a throat patch. Eira barbara barbara, found in southern Brazil, eastern Bolivia and Paraguay, is lighter than E. b. sinuensis but darker than E. b. senex and has a yellowish throat patch. The northern Brazilian E. b. madeirensis is a chocolate brown with the head slightly lighter than the body; again, a throat patch may or may not be present. The Peruvian and western Bolivian E. b. peruana is similar to the last subspecies but has darker legs and a black tail. Finally, E. b. poliocephala, which has a distribution centred on the Guianas, is similar to E. b. barbara but with a darker yellow throat patch and yellow shoulder patches that sometimes merge with the throat patch to form a complete collar.

Tayra photographed in a zoo in Panama, copyright Dirk van der Made. Being a zoo individual, its origins are a bit more open than the other individuals shown on this page, but Panama is home to Eira barbara inserta and E. b. sinuensis.

Such is the received wisdom as recorded by Presley (2000) but does it accurately reflect population distributions? Ruiz-García et al. (2013) conducted an analysis of mitochondrial genes from tayras representing the five South American subspecies (i.e. excluding E. b. senex and E. b. inserta). They found that of these five subspecies, only E. b. poliocephala (as represented by specimens from French Guiana) could potentially be differentiated genetically. Samples from the ranges of the other four 'subspecies' were intermingled in analyses, leading Ruiz-García et al. to suggest that they should be merged into a single subspecies E. b. barbara (it may also be worth me mentioning that, when I was looking for images to illustrate this post, I had difficulty finding ones in which the supposed differences between subspecies were recognisable). Of course, that leaves the status of the two Central American subspecies undetermined. It may be of note that they seem to be more distinct in appearance than some of the hitherto-recognised South American subspecies but it remains to be seen just how significant this is.

REFERENCES

Presley, S. J. 2000. Eira barbara. Mammalian Species 636: 1–6.

Ruiz-García, M., N. Lichilín-Ortiz & M. F. Jaramillo. 2013. Molecular phylogenetics of two Neotropical carnivores, Potos flavus (Procyonidae) and Eira barbata (Mustelidae): no clear existence of putative morphological subspecies. In: Ruiz-Garcia, M., & J. M. Shostell (eds) Molecular Population Genetics, Evolutionary Biology and Biological Conservation of Neotropical Carnivores pp. 37–84. Nova Publishers: New York.

Shostell, J. M., & M. Ruiz-Garcia. 2013. An introduction to Neotropical carnivores. In: Ruiz-Garcia, M., & J. M. Shostell (eds) Molecular Population Genetics, Evolutionary Biology and Biological Conservation of Neotropical Carnivores pp. 1–34. Nova Publishers: New York.

Walruses, Sea Lions and Fur Seals

Adaptation to a primarily aquatic lifestyle has happened numerous times within mammals, but some groups have radiated more in this environment than others. One particularly well-known group of marine mammals is the pinnipeds, the seals and sea lions.

Australian sea lions Neophoca cinerea on a beach on Kangaroo Island, copyright Diver Dave.

Pinnipeds are highly modified for life in the water, with streamlined bodies and all four limbs modified into flippers. When I was young, many of the animal books that I read referred to pinnipeds as their own distinct order within the mammals. However, it has long been recognised that pinnipeds are derived from within the Carnivora and these days they are almost universally treated as a subgroup of the latter. Modern pinnipeds are divided between three families: the Phocidae ('true' seals), Otariidae (fur seals and sea lions) and Odobenidae (which has only one living species, the walrus Odobenus rosmarus). While some morphological analyses have argued for a relationship between the walrus and the Phocidae, the majority view treats the walrus and the Otariidae as together forming a clade Otarioidea, commonly referred to as the eared seals. There has historically also been some argument about whether the pinnipeds represent a single clade; some have argued for two separate origins, Otarioidea being related to bears whereas Phocidae were supposed to be closer to otters and weasels. However, the current majority supports a single origin for the group.

Northern fur seals Callorhinus ursinus, photographed by M. Boylan.

Eared seals differ from true seals in the possession of small external ears, and the ability to turn the hind flippers back under the body so that they can still function (if somewhat awkwardly) as feet when moving on land. I have seen Australian sea lions on coastal islands near Perth (there are boat tours that will take you to see them) and I can confirm that they can run along the beach at a surprising speed when they wish to. True seals have the hind flippers permanently directed behind them and so are forced to awkwardly belly-flop along when not swimming (doubtless as a result of this, true seals also differ from eared seals in that males lack an external scrotum). In the water, the hind flippers provide the main source of propulsion in true seals whereas eared seals get more of their thrust from the fore flippers (sea lions have been said to swim like penguins). As an aside, eared seals are also apparently unusual among mammals in that their milk completely lacks lactose. The lactose intolerant among you need not be denied dairy, you need only milk a walrus.

Mounted skeleton of Allodesmus sp., copyright Momotarou2012.

The earliest eared seals are known from the Miocene when they appear to have originated in the northern Pacific. Two extinct families from this place and period, the Enaliarctidae and Desmatophocidae, are commonly included in the Otarioidea, though it remains possible that either of these families should be placed outside the pinniped crown group, or closer to the true seals. The early Miocene Enaliarctidae differ from other otarioids in retaining differentiated premolars and molars (later forms have the cheek teeth uniform in appearance) and may well represent the ancestral form of the group. The mid- to late Miocene Desmatophocidae combined a rather Phocidae-like skull with a more Otarioidea-like post-cranium; the best-known genus Allodesmus had larger eyes than other otarioids and may have hunted in deep waters. One species of desmatophocid, Allodesmus sinanoensis, may have reached a length approaching five metres, making it larger than a modern walrus and rivalling the elephant seals in size. I highly recommend a series of posts on Allodesmus written a few years back by Robert Boessenecker (1, 2, 3, 4) that cover just about everything you might want to know about this animal.

Skull of Gomphotaria pugnax, from Robert Boessenecker.

Though only one walrus species is generally recognised in the modern fauna, the family was much more diverse in the past. However, most fossil Odobenidae lacked the tusks of a modern walrus and would have been more similar at a glance to sea lions. These early odobenids would have probably been generalist fish-feeders (Boessenecker & Churchill 2013). The modern walrus, in contrast, feeds primarily on bivalves. They don't crush the clam's shell but grab it with their lips and then suck powerfully enough that the meat is ripped out. Other than the tusks, the teeth of a modern walrus are small and weak; one close fossil relative, the Pliocene Valenictus chulavistensis, went so far as to lose the non-tusk teeth entirely. The tusks themselves are usually thought to function in display and the like rather than having any prominent role in feeding. However, it is an intriguing detail that the fossil whale Odobenocetops that converged in its feeding biology with walruses also possessed a large tusk. The non-tusk teeth were still used in feeding in the fossil clam-feeding walrus genera Dusignathus and Gomphotaria, which had a pair of large forward-directed tusks in both the upper and lower jaws.

Suckling South African fur seals Arctocephalus pusillus, copyright Robur.q.

The majority of living eared seals belong to the Otariidae, which have been divided in the past between the fur seals and sea lions. Fur seals tend to be smaller than sea lions and possess a dense layer of underfur. However, more recent phylogenetic studies (particularly molecular ones) have thrown this distinction out the window (e.g. Higdon et al. 2007). Instead, the northern fur seal Callorhinus ursinus of the north Pacific is probably the sister species to all other living otariids. Even the southern fur seals, generally placed in a single genus Arctocephalus, may not be monophyletic relative to the New Zealand sea lion Phocarctos hookeri (as a result, some authors have suggested resurrecting the genus Arctophoca for all southern fur seals other than the South African fur seal Arctocephalus pusillus). The South American fur seal Otaria flavescens may also be associated with this latter group. The two north Pacific sea lions, Steller's sea lion Eumetopias jubatus and the Californian sea lion Zalophus californianus, form a clade outside the southern otariids. The remaining species is the Australian sea lion Neophoca cinerea whose position has been harder to pin down: some analyses place it close to the New Zealand sea lion but others position it well away from all other southern otariids, possibly even outside all other otariids except the northern fur seal.

Walruses Odobenus rosmarus crowded on shore, from here.

Fur seals and sea lions were heavily hunted in the past for pelts and oil and some species remain endangered. Climate change poses a particular threat to cold-water species; for instance, recent years have seen significant contractions in walrus ranges, leading to dramatic crowding in the locations remaining. Conversely, the Antarctic fur seal Arctocephalus gazella, once feared extinct, has apparently exhibited a population explosion in recent decades, perhaps because lowered whale populations have led to more food being available for seals.

REFERENCES

Boessenecker, R. W., & M. Churchill. 2013. A reevaluation of the morphology, paleoecology, and phylogenetic relationships of the enigmatic walrus Pelagiarctos. PLoS One 8 (1): e54311.

Higdon, J. W., O. R. P. Bininda-Emonds, R. M. D. Beck & S. H. Ferguson. 2007. Phylogeny and divergence of the pinnipeds (Carnivora: Mammalia) assessed using a multigene dataset. BMC Evolutionary Biology 7: 216.

Repenning, C. A., & R. H. Tedford. 1977. Otarioid seals of the Neogene. Geological Society Professional Paper 992: i–vi, 1–93, 24 pls.