Daubentonia is a plesiadapid, a sister to Plesiadapis, which is also not a primate. They nest with Carpolestes in the clade Glires (rabbits and rodents, etc.). And that makes the aye-aye the only living plesiadapid! And yes, it has a divergent big toe, but so does the basalmost placental, Monodelphis.
Figure 1. Daubentonia was considered a primate for over 150 years. Here it nests with Plesiadapis, rodents and rabbits. It’s the only living plesiadapid.
the AMNH website on Sir Richard Owen and the Aye-Aye, “For the first 100 years after the first aye-aye was brought to Europe in the 1780s, debate swirled over whether it was a rodent, a primate, or most closely related to a kangaroo.
“The root of this confusion lay in the aye-aye’s odd collection of behavioral and morphological traits that make it appear to be composed of spare parts of other animals: continuously growing front teeth, batlike ears, a foxlike tail, abdominal mammary glands, claws on most digits, and spindly, dexterous middle fingers.
“It uses its middle finger to tap along a branch and moves its ears forward and back to help locate hollow channels within the wood created by wood-boring insect larvae. Once it detects a channel, the aye-aye uses its specialized front teeth to pry open the wood and then inserts one of its fingers to extract the larvae.”
has been wrong before. And that’s okay. This is Science. We can fix mistakes. Tradition should never trump testing. If you’re not sure where a taxon should nest, if it is constantly described as weird or autapomorphic, you simply need to test your ‘ugly duckling‘ taxon against a larger gamut of candidates. You’ll probably find your taxon is not so weird after all, when compared to its true sisters. Daubentonia has ‘rodent-like’ teeth because it is more closely related to rodents. It’s as simple as that. And convergence happens.
Figure 2. Skeleton of Daubentonia (aye-aye). Like other plesiadapids, it convergences with the lemuroid primates.
According to the AMNH, Owen’s 1863 description
put arguments about the aye-aye’s taxonomy to rest as it focused “attention away from the striking unusual characteristics, like the continuously growing teeth, and toward primate-like characteristics such as forward-facing eyes and an opposable thumb, providing firm evidence for why the aye-aye should be classified as a primate.”
In the large reptile tree
(LRT), we don’t focus attention toward or away from anything. We score all the traits evenly and let PAUP figure out which taxa any new taxa nests most closely to. In this test, Daubentonia (Gmelin 1788. Geoffroy Saint-Hillaire 1795; 40 cm snout-vent length; extant) nested most closely with Plesiadapis within the clade Glires. The ever-growing teeth are traits inherited from a basal member of Glires. Only the hallux has a nail. The rest of the toes bear claws. The rest of the primate-like traits are convergent, probably due to its arboreal niche.
Discovered in 1780
by French zoologist, LJM Daubenton, it was originally identified as a squirrel (Gmelin 1788) and named Sciurus madagascariensis. Geoffrey Saint-Hilaire (1795) provided a new generic name. Daubentonia was first considered a primate by Schreber 1800 who renamed it Lemur psilodactylus, a name now considered an invalid junior synonym. More taxonomic misadventures can be found here.
Figure 3. Two clades within the Mammalia from the LRT. Here Daubentonia nests with Plesiadapis, both far from primates.
This is the yet another
‘rodent-like’ mammal that actually nests with rodents. Other similar originally mis-nested Glires we’ve already covered include:
- the Multituberculata – former allotheres
- Plesiadapids – a former basal primate
- Tupaia – one sort of tree shrew, the other is closer to bats, colugos, primates
- Macroscelides – one sort of elephant shrew, the other is closer to tenrecs.
- Chrysochloris – a golden mole
- Scutisorex – a shrew
- Potamogale and Echinops – two former tenrecs
- Apatemys – an apatemyid.
- Trogosus – a former tillodont
- Solenodon –
- Nambaroo – a former kangaroo
- Henkelotherium – a former pantothere
- Erinaceus – a hedgehog
- Shenhou – a former allothere
- Carpolestes – a former basal primate
- Maotherium – a former symmetrodont
- Zalambdalestes – a former non-placental eutherian
They all have big incisors.
A few, like Daubentonia and Tupaia, have a complete postorbital ring. The wide jugals of Plesiadapis and Taeniolabis, provide forward-oriented eyes, just like their sister, Daubentonia.
More taxonomic issues
according to Yoder et al. 1996. “Morphological studies of Daubentonia have been less consistent in their conclusions, finding the aye-aye to be either a highly derived member of the Malagasy primate family Indridae (Schwartz 1986), the basal-most branch of the strepsirrhines (Groves 1990), or unclassifiable in relation to other living primates (Oxnard 1981).”
according to Picone and Sineo 2012. “Both MP and BI topologies show Daubentonia as an independent monophyletic lineage, sister group of all other Strepsirhini.” (= Prosiminiii or lemurs). You should know, BTW, they tested only lemurs with Tupaia as the outgroup and Daubentonia nested between them, just like the LRT without all the taxon exclusion. A priori taxon exclusion is… once again… the main problem here.
Gmelin JF 1788. Caroli a Linné systema naturae per regna tria naturae, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima tertia, aucta, reformata. – pp. [1-12], 1-500. Lipsiae. (Beer).
Owen R 1863. Monograph on the Aye-Aye ((Chiromys madagascariensis, Cuvier)
Picone B and Sineo L 2012. The phylogenetic position of Daubentonia madagascariensis (Gmelin, 1788; primates, Strepsirhini) as revealed by chromosomal analysis. Caryologia: International Journal of Cytology, Cytosystematics and Cytogenetics 65(3):223-228. online here.
Geoffroy Saint-Hilaire E 1795. La décade philosophique, litteraire, et politique. Memoires d’Histoire Naturelle 4(28):193– 206.
Sterling E. 1994. Taxonomy and distribution of Daubentonia: a historical perspective.Folia Primatologica 62:8-13.
Yoder AD, Vilgalys R and Ruvolo M 1996. Molecular Evolutionary Dynamics of Cytochrome b in Strepsirrhine Primates: The Phylogenetic Significance of Third-Position Transversions. Mol. Biol. Evol. 13(10):1339-1350.