Hopefully it is well known that we still have a lot to learn about the planet's extant macrofauna. And, by 'macrofauna', I'm not talking about nematodes, molluscs or insects but, yes, about such things as mammals. In fact, on mammals specifically, discovery rates indicate that we really should expect the discovery of new species for a long while yet. In a new article in Proceedings of the National Academy of Sciences, Ceballos & Ehrlich (2009) bring attention to the fact that 408 new mammal species (representing about 10% of the total mammal species inventory and belonging to 18 traditional 'orders') have been named since 1993. What, they ask, does this mean for our understanding of biodiversity, and for conservation and management?

Ceballos & Ehrlich (2009) are not, of course, the first to point out that new mammals are 'not so seldom' (Pine 1994): you might know this because, well, you already know it (Heuvelmans 1983, Patterson 2000, 2001, Shuker 2002, Collen et al. 2004), or you might know it because I've mentioned it at Tet Zoo many times. While 60% of the 408 new mammals are cryptic species (those formerly included within another species, and later elevated to species status following genetic analysis or a re-evaluation of how much variation is tolerable within a species), the other 40% are not. This 40% is where we find the really exciting, distinctive new animals: Ceballos & Ehrlich (2009) mention the Saola Pseudoryx nghetinhensis [shown above], Giant muntjac Megamuntiacus vuquangensis [shown below], Kipunji Rungwecebus kipunji, the pygmy sloth Bradypus pygmaeus, Maues marmoset Callithrix mauesi*, Solomons islands monkey-faced bat Pteralopex taki, the Brazilian phyllostomid bat Xeronycteris vieirai and the Peruvian chinchilla rat Cuscomys ashaninka as among the neatest of such.

* Ceballos & Ehrlich (2009) incorrectly refer to this as 'a white titi monkey' (p. 3841). Titi monkeys Callicebus are altogether different from marmosets and are not part of the same group.

How have such new species been discovered? The 'exploration of new regions has been the main factor for the discovery of as much as 40% of the new species' (p. 3843): this goes for Amazonian monkeys, rodents from the Philippines, hoofed mammals, rodents and rabbits from south-east Asia, and specific examples such as the Arunachal macaque Macaca munzala [shown below] from north-east India and the Grey-faced sengi Rhynchocyon udzungwensis from Tanzania. Despite the assumption that modern discoveries of new species might rely on cutting-edge technology, in virtually all of these cases, discovery was made in the old-fashioned way. The respective biologists went into a new area, looked around, recorded what they saw, and found new stuff. In some cases (I'm thinking here of the Kipunji and Leaf deer Muntiacus putaoensis) they spoke to local people and heard about animals that later turned out to be both real, and new. Only in the case of the Grey-faced sengi did new technology (camera traps) play a direct role in discovery. However, note that a few other possible new mammal species have been documented by camera-traps (e.g., the brocket reported by Trolle & Emmons (2004)).

What sorts of mammals are involved?

Ceballos & Ehrlich (2009) then looked at how the new mammal species are distributed phylogenetically: are some groups yielding more species than others and, if so, why? Unsurprisingly, the occurrence of new species is not random, but shows a strong correlation with total species richness. In other words, big groups yield more new species than do small groups. Even so, primates, bats, rodents and marsupials all score surprisingly highly, while lipotyphlans*, artiodactyls and carnivorans all score lower than expected.

* The author refer to members of this group as soricomorphs. I think this is because they needed to make it clear that they were not including tenrecs (which are afrotherians) along with shrews and moles. Tenrecs score highly in terms of numbers of post-1993 species, shrews and kin do not (despite 21 post-1993 shrew species and one mole!).

The poor score that artiodactyls get is slightly surprising given the number of new muntjacs named in recent years (all from south-east Asia). In fact 11 post-1993 artiodactyls are listed by Ceballos & Ehrlich (2009), but this is still not a significantly high figure compared to total species richness. You might think that this taxonomic bias relates directly to body size (that is, we find more rodents because rodents are mostly small and hence better at escaping attention than carnivorans or artiodactyls), but this is not clear and in fact there are some indications that it is not the most important factor. Body size might even be downright unimportant in fact, as many of the post-1993 mammals are relatively large-bodied members of their groups. Might the comparatively low numbers of new artiodactyls and carnivorans mean that these groups have been more intensively studied than have primates, rodents or marsupials? That's an interesting question that would require further research [Leaf deer shown below].

Conservation, predictions, and the future

Finally, the authors looked at the distribution of the post-1993 species and examined what this might mean for conservation and anthropogenic threat. 81% of the new species have restricted ranges of less than 10,000 square km, hence making them theoretically prone to extinction. However, while 24% of the areas inhabited by the new species are affected by agriculture and human population, 61% of the areas inhabited by the post-1993 species 'have relatively little anthropogenic threat'. The take-home point is that a proportion of the new species are in small areas directly threatened by spreading agriculture and population, but that not all are.

The fact that so many new mammals have been found in recent years leads Ceballos & Ehrlich (2009) to conclude that other groups of animals, many of which are less well studied than mammals (and generally always more speciose), 'likely contain many more species than are currently described' (p. 3843). The authors also note that many species have likely gone extinct without our knowledge, and they speculate that extinction rates have therefore been grossly underestimated.

Given the implication inherent to this study (viz, that much yet remains to be found), what is going to come next? Perissodactyls were not included in the Ceballos & Ehrlich (2009) dataset, but future publications might mean that they should be (hint hint). Sirenians were not either, but if Marc van Roosmalen is right about the species-level status of his new manatee Trichechus bernhardi [shown here], they should be too. A large number of new primates are currently in the process of being named (mostly from Madagascar and Amazonia), so we can be confident that members of this group will continue to rank highly in the species discovery data for a while. Judging by recent finds (e.g., Pearsonomys annectans Patterson, 1992, Salinomys delicatus Braun & Mares, 1995, Chibchanomys orcesi Jenkins & Barnett, 1997, Pteralopex taki Parnaby, 2002, Laonastes aenigmamus Jenkins et al, 2005, Xeronycteris vieirai Gregorin & Ditchfield, 2005, Styloctenium mindorensis Esselstyn, 2007) weird bats and rodents will also continue to appear for a long while yet.

As stated earlier, it is not news to mammalogists, or to zoologists or biologists in general, that new, often large mammals are still regularly found, and that more remain to be found. Nevertheless it remains surprising and counter-intuitive to many: we should, I argue, bring attention to it as often as possible.

For previous articles on recently discovered mammal species see...

UPDATE: as pointed out below by Erich Fitzgerald, two other recent papers have also covered the issue of recently described mammal diversity and should be consulted by anyone interested: Reeder et al. (2007) and Schipper et al. (2008).

Refs - -

Ceballos, G. & Ehrlich, P. R. 2009. Discoveries of new mammal species and their implications for conservation and ecosystem services. Proceedings of the National Academy of Sciences 106, 3841-3846.

Collen, B., Purvis, A. & Gittleman, J. L. 2004. Biological correlates of description dates in carnivores and primates. Global Ecology and Biogeography 13, 459-467.

Heuvelmans, B. 1983. How many animal species remain to be discovered? Cryptozoology 2, 1-24.

Patterson, B. D. 2000. Patterns and trends in the discovery of new Neotropical mammals. Diversity and Distributions 6, 145-151.

- . 2001. Fathoming tropical biodiversity: the continuing discovery of Neotropical mammals. Diversity and Distributions 7, 191-196.

Pine, R. H. 1994. New mammals not so seldom. Nature 368, 593.

Reeder, D. M., Helgen, K. M. & Wilson, D. E. 2007. Global trends and biases in new mammal species discoveries. Occasional Papers, Museum of Texas Tech University 269, 1-35.

Schipper, J., Chanson, J. S., Chiozza, F., Cox, N. A., Hoffmann, M., Katariya, V., Lamoreux, J., Rodrigues, A. S. L., Stuart, S. N., Temple, H. J., Baillie, J., Boitani, L., Lacher, T. E., Jr., Mittermeier, R. A., Smith, A. T., Absolon, D., Aguiar, J. M., Amori, G., Bakkour, N., Baldi, R., Berridge, R. J., Bielby, J., Black, P. A., Blanc, J. J., Brooks, T. M., et al. 2008. The status of the world's land and marine mammals: diversity, threat, and knowledge. Science 322, 225-230.

Shuker, K. P. N. 2002. The New Zoo. House of Stratus, Thirsk, North Yorkshire.

Trolle, M. & Emmons, L. H. 2004. A record of a dwarf brocket from Madre de Dios, Peru. Deer Specialist Group Newsletter 19, 2-5.