Plesiorycteropus, also known as the bibymalagasy or Malagasy aardvark, is a recently extinct genus of mammals from Madagascar. Upon its description in 1895, it was classified with the aardvark, but more recent molecular evidence instead suggests that it is most closely related to the tenrecs (a group extant on the island). Two species are currently recognized, the larger P. madagascariensis and the smaller P. germainepetterae. They probably overlapped in distribution, as subfossil remains of both species have been found in the same site.
Knowledge of the skeletal anatomy is limited, as only limb, partial pelvis, and skull bones have been recovered to date. Plesiorycteropus was probably a digging animal that fed on insects such as termites and ants. It also shows adaptations for climbing and sitting. Estimates of its mass range from . When and why it became extinct remains unknown. One bone has been radiocarbon dated to 200 BCE; forest destruction by humans may have contributed to its extinction.
Taxonomy
Identification and species French naturalist Henri Filhol first described Plesiorycteropus madagascariensis in 1895 on the basis of a partial skull found at the cave of Belo. His description was vague even by 19th-century standards, but he placed the animal close to the aardvark (Orycteropus).MacPhee, 1994, p. 11 The generic name combines Ancient Greek plesio- "near" with Orycteropus, the genus of the aardvark, and the specific name refers to Madagascar. Charles Lamberton, who had access to a larger sample for his 1946 review of the genus, noted substantial variation, but did not attempt to differentiate multiple species. In 1994, Ross MacPhee again reviewed Plesiorycteropus and was able to separate two species, the larger P. madagascariensis and a new, smaller species that he named Plesiorycteropus germainepetterae after scientist Germaine Petter. The two species differ in a number of morphological characters in addition to size.MacPhee, 1994, p. 32
Remains of Plesiorycteropus have been misidentified as rodents and primates. Charles Immanuel Forsyth Major described Myoryctes rapeto in 1908 as a "giant subfossil rat" on the basis of two innominate bones (pelvic bones).Forsyth Major, 1908, p. 97 The generic name was replaced by Majoria in 1915, because Myoryctes was preoccupied by the name of a nematode worm.Thomas, 1915, p. 58 However, according to MacPhee, innominates of Majoria are identical to those assigned to Plesiorycteropus. Guillaume Grandidier assigned a well-preserved femur (upper leg bone) to a gigantic relative of the living votsovotsa (Hypogeomys antimena), a large rodent, which he described as Hypogeomys boulei. Lamberton identified this femur as Plesiorycteropus and MacPhee concurred.MacPhee, 1994, p. 33 Remains of both Majoria rapeto and Hypogeomys boulei fall at the upper end of the size range of the genus, indicating that they are referable to P. madagascariensis. Another Plesiorycteropus innominate was mistakenly assigned to Daubentonia robusta, the extinct giant aye-aye,MacPhee, 1994, pp. 33–34 and other material has been misidentified as of a dwarf lemur (Cheirogaleus).Godfrey et al., 2001, p. 71
Relationships Filhol had classified Plesiorycteropus as close to the aardvark on the basis of morphological similarities. In his 1946 review, Charles Lamberton was unable to provide a definitive allocation, confused by the various similarities he saw with aardvarks, pangolins, armadillos, and anteaters. He believed it was most likely a primitive, isolated member of "Edentata", a group in which he included aardvarks, pangolins, and Xenarthra (sloths, armadillos, and anteaters). He rejected some alternatives, such as a close affinity to aardvarks or the possibility that the material assigned to Plesiorycteropus did not in fact represent a single animal.MacPhee, 1994, pp. 13–14 Bryan Patterson, who revised tubulidentates (the order of which the aardvark is the only living representative) in the 1970s, accepted Plesiorycteropus as a member of the group, dismissing many similarities with pangolins and other animals as convergent.Patterson, 1975, p. 215 However, he placed it as the only member of its own subfamily Plesiorycteropodinae in view of its differences from other tubulidentates (subfamily Orycteropodinae), and hypothesized that it arrived on Madagascar in the Eocene, at the same time as the lemurs.Patterson, 1975, p. 216 Johannes Thewissen, who critiqued some aspects of Patterson's classification in 1985, also accepted Plesiorycteropus as a tubulidentate without comment.MacPhee, 1994, p. 24
Reviewing Patterson's and Thewissen's contributions in 1994, Ross MacPhee found little support for the classification of Plesiorycteropus as a tubulidentate in their data.MacPhee, 1994, pp. 23–24 MacPhee used a cladistic analysis of eutherians to ascertain the relationships of the genus, but found that while different analytic variants supported different affinities—with aardvarks, hyraxes, ungulates (hooved mammals), and even lipotyphlans (shrews, moles, hedgehogs, and allies)—there was no compelling evidence linking it to any other eutherian group.MacPhee, 1994, pp. 198–199 Therefore, he erected a separate order for Plesiorycteropus, named Bibymalagasia,MacPhee, 1994, p. 201 arguing that it would be unacceptable to leave a Recent eutherian unassigned to any order and that discovery of more material, or further analysis, was unlikely to demonstrate close affinities of Plesiorycteropus with any other order.MacPhee, 1994, pp. 202–203 He considered it possible but unlikely that a few fossil taxa, such as Palaeorycteropus and Leptomanis from the Paleogene of France, would eventually be found to be bibymalagasians.MacPhee, 1994, p. 201; Tabuce et al., 2008, p. 6, for age of the fossils Various analyses published by Robert Asher and colleagues in 2003, 2005, and 2007, based on morphology combined with DNA sequence data in some analyses, produced different estimates of the relationships of Plesiorycteropus, some placing it within Afrotheria close to aardvarks or Afrosoricida, but others supporting a relationship with the hedgehog Erinaceus.Asher et al., 2003, p. 148; 2005, p. 919; Asher, 2007, figs. 1–2 A 2004 morphological study by Inés Horovitz, focusing on extinct South American ungulates (such as Notoungulata and Litopterna), placed Plesiorycteropus among tubulidentates and closer to the extinct aardvark relative Myorycteropus than to Orycteropus.Horovitz, 2004, fig. 1
A 2013 study by Michael Buckley examined preserved collagen sequences in Plesiorycteropus bones. He found the animal was most closely related to the tenrecs, a family of insectivorous afrotherian mammals endemic to Madagascar.Buckley, 2013, p. 1 Tenrecs are believed to have diversified from a common ancestor that lived 29–37 million years (Ma) agoDouady et al., 2002Poux et al., 2008, p. 7Everson et al., 2016, p. 898 after dispersing from Africa via a single rafting event.Ali and Huber, 2010 Buckley's analysis showed that Plesiorycteropus and the two members of subfamily Tenrecinae tested formed a monophyletic group, within a larger clade in which golden moles are the sister group;Buckley, 2013, p. 6, Fig. S3, Text S1-S2 he suggested that Plesiorycteropus should be placed in the order Tenrecoidea along with tenrecs as well as African otter shrews and golden moles (the latter two diverged from tenrecs about 47–53 Ma ago and 59–69 Ma ago, respectively). He did not test members of the other two Tenrecidae subfamilies or otter shrews, leaving open the possibility that Plesiorycteropus nests within Tenrecidae.
Common names "Madagascar aardvark" has been used as a common name for Plesiorycteropus, but MacPhee considered it inappropriate because the animal may not be related to aardvarks. Instead, he proposed "bibymalagasy" as a common name, a manufactured Malagasy word meaning "Malagasy animal".MacPhee, 1994, p. 30
Description Plesiorycteropus is known from a number of subfossil bones, comparable to coverage of some of the poorly known subfossil lemurs, such as Daubentonia robusta. The material includes several skulls, all of which are missing the facial bones, complete long bones such as the femur and humerus (upper arm bone), and other bones, but some elements are still unknown, including most of the skeleton of the hand and foot.MacPhee, 1994, pp. 29–30 There is little reason to assume it was similar in general form to the aardvark. No teeth or jaws referable to Plesiorycteropus have been found, and it is generally assumed that the animal was toothless.MacPhee, 1994, p. 13; Nowak, 1999, p. 1050
Based on the area of a femur cross-section, MacPhee calculated estimates of body mass. The lowest estimate, based on comparative data from armadillos and pangolins, was for the smallest femur he had (referable to P. germainepetterae) and the highest estimate, based on comparative data from caviomorph rodents, was for the largest available femur (P. madagascariensis); estimates from primates fell between those extremes.MacPhee, 1994, table 14 MacPhee favored the lower estimates, because those were based on armadillos, which have femora similar to those of Plesiorycteropus.MacPhee, 1994, p. 147 On the other hand, the caviomorph model produced a better estimate of brain size in Plesiorycteropus.MacPhee, 1994, p. 148 Any of the estimates makes it considerably larger than the largest living tenrec, Tenrec ecaudatus, at up to .Stephenson et al., 2016 The higher estimates would make it larger than any extant native Malagasy mammal. This is consistent with the trend for larger members of the late Pleistocene and Holocene faunas of MadagascarBurney et al., 2003Burney et al., 2004 and elsewhereBurney and Flannery, 2005 to have been at higher risk of extinction.
Skull There are four known skulls (three of P. madagascariensis and one of P. germainepetterae),MacPhee, 1994, table 6 each of which is damaged. All are missing the front (rostral) part, and three are broken at about the same place (at the paranasal cavities, at the front of the braincase), suggesting that the front part of the skull was thinner and more fragile than the back part, which consists of thick bones.MacPhee, 1994, p. 35 MacPhee estimated maximum skull length in P. madagascariensis at . The length of the frontal bone averages in P. madagascariensis and is in P. germainepetterae.MacPhee, 1994, table 7