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Bibymalagasy or Malagasy aardvarks (Plesiorycteropus)

The bibymalagasy or Malagasy aardvarks (Plesiorycteropus) compries a recently extinct eutherian genus from Madagascar. It was described in 1895 and was classified with the aardvark, but there is little evidence to link it to aardvarks or any other order of mammals. It is now placed in its own order, Bibymalagasia, which may be part of the Afrotheria. Molecular evidence suggests it is related to tenrecs.

Only limb and partial pelvis and skull bones have been recovered. Plesiorycteropus was probably a digging animal that ate termites, ants and other insects. It hows adaptations for climbing and sitting. Estimates of its mass range from 6-18 kg (13-40 lb). One bone has been radiocarbon dated to 2,200 years ago; forest destruction by humans may have contributed to its extinction.

French naturalist Henri Filhol described P. madagascariensis in 1895 from a partial skull found at the cave of Belo. He placed the animal near aardvark (Orycteropus); 'plesio' is greek for 'near' (1). Charles Lamberton had access to a larger sample for his 1946 review of the genus and noted substantial variation, but did not try to differentiate multiple species (1) In 1994, Ross MacPhee separated two species, the larger P. madagascariensis and smaller P. germainepetterae. The two species also differ in some morphological characters (1)

Remains of Plesiorycteropus have been misidentified as rodents and primates. Charles Immanuel Forsyth Major described Myoryctes rapeto in 1908 as a "giant subfossil rat", based on two pelvic bones) (2) The generic name was replaced by Majoria in 1915, as Myoryctes was preoccupied by a nematode worm.(3). MacPhee said innominates of Majoria are identical to those assigned to Plesiorycteropus. Guillaume Grandidier assigned a femur to a gigantic relative of the living votsovotsa, a large rodent, which he named Hypogeomys boulei. Lamberton identified this femur as Plesiorycteropus and MacPhee concurred (1). Remains of both Majoria rapeto and H. boulei fall at the upper end of the size range of the genus, so they refer to P. madagascariensis (1). Another Plesiorycteropus innominate was mistakenly assigned to Daubentonia robusta, the extinct giant aye-aye (1) and other material has been misidentified as of a dwarf lemur (Cheirogaleus) (4).

Filhol classified Plesiorycteropus as close to the aardvark due to morphological similarities. In his 1946 review, Charles Lamberton could not provide a definitive allocation, confused by the various similarities he saw with aardvarks, pangolins, armadillos and anteaters. He thought it was probably a primitive, isolated member of "Edentata", a group where 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 represent one animal (1). Bryan Patterson revised tubulidentates in the 1970s and accepted Plesiorycteropus as a member of the group, dismissing many similarities with pangolins and other animals as convergent (5). He placed it as the only member of the subfamily Plesiorycteropodinae due to differences from other tubulidentates (subfamily Orycteropodinae) and hypothesized that it arrived on Madagascar in the Eocene, at the same time as the lemurs (5). Johannes Thewissen critiqued some aspects of Patterson's classification in 1985, but accepted Plesiorycteropus as a tubulidentate (1).

Ross MacPhee reviewed Patterson's and Thewissen's contributions in 1994 and found little support to classify Plesiorycteropus as a tubulidentate (1). 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 lipotyphlans (shrews, moles, hedgehogs and allies)—there was no compelling evidence linking it to any other eutherian group (1). He erected a separate order, Bibymalagasia, for Plesiorycteropus (1), arguing that it was unacceptable to leave a Recent eutherian unassigned to any order and that further material or analysis was unlikely to show close affinities of Plesiorycteropus other orders (1). He considered it possible but unlikely that a few fossil taxa, such as Palaeorycteropus and Leptomanis from Paleogene France, would be found to be bibymalagasians.[1] Analyses published by Robert Asher and colleagues in 2003, 2005, and 2007 (6), based on morphology, sometimes combined with DNA sequence data, gave different estimates of the relationships of Plesiorycteropus. Some placed it within Afrotheria near to aardvarks or Afrosoricida, but others supported a relationship with hedgehogs (6). A 2004 morphological study by Inés Horovitz, focusing on extinct South American ungulates, placed Plesiorycteropus among tubulidentates and nearer the extinct aardvark relative Myorycteropus than to Orycteropus (7). A 2013 study by Michael Buckley examined preserved collagen sequences in Plesiorycteropus bones. Buckley found the animal was closely related to tenrecs and suggested it should be placed in the order Tenrecoidea with the tenrecs and golden moles (8).

MacPhee considers the name "Madagascar aardvark" inappropriate as the animal may not be related to aardvarks. He proposed "bibymalagasy," Malagasy for "Malagasy animal", as a common name (1).

Plesiorycteropus is known from subfossil bones, such as skulls, all of which lack facial bones, and complete long bones such as the femur and humerus. There are no remains of most of the skeleton of the hand and foot (1). There is little reason to assume it was similar to the aardvark (9) No teeth or jaws referable to Plesiorycteropus have been found and it is assumed it was toothless (1).

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 6 kg (13 lb) for the smallest femur (P. germainepetterae) and the highest, based on comparative data from caviomorph rodents, was 18 kg (40 lb) for the largest femur (P. madagascariensis) (1). MacPhee favoured the lower estimates, as armadillos have femora similar to those of Plesiorycteropus (1). The caviomorph model produced a better estimate of brain size in Plesiorycteropus (1)

All of the three skulls of P. madagascariensis and the single one of P. germainepetterae miss the front (rostral) part and three are broken at about the same place (the paranasal cavities at the front of the braincase), suggesting that the front of the skull was thinner and more fragile than the back, which consists of thick bones (1). MacPhee estimated maximum skull length in P. madagascariensis at 101 mm (4 in). The length of the frontal bone averages 35.4 mm (1.39 in) in P. madagascariensis and 29.4 mm (1.16 in) in P. germainepetterae (1).

The robust nasal bones are widest at the front, a feature unusual among placentals, but also seen in armadillos, and are very flat (1). The large ethmoid labyrinth, in the nasal cavity, suggests that Plesiorycteropus had a good sense of smell (1). A much larger part of the nasal septum separates the left and right nasal cavities and is more ossified than in other mammals; MacPhee found a similar condition only in sloths, which have a very short nose (1). The lacrimal bone is relatively large. The single lacrimal canal opens near the suture between the frontal and lacrimal bones, as in lipotyphlans. There is a small tubercle (absent in aardvarks) near this opening (1). The orbital cavity, housing the eyes, is relatively short, similar to the situation in pangolins and armadillos (1). There is a tubercle on the suture between the frontal and parietal bones in P. germainepetterae, but not P. madagascariensis (1). P. madagascariensis has a more expansive braincase and a less pronounced narrowing between the orbits (1). There is a foramen rotundum (an opening in the bone of the orbit). The optic canal, housing the nerves leading to the eyes, is narrow, suggesting that the eyes were small (1) as in many tenrecoids (8). As in pangolins and xenarthrans, little of the squamosal bone can be seen from above (1). The temporal lines on the braincase, which anchor muscles, are located lower in P. germainepetterae (1). As in aardvarks, the parietals are relatively large. There is an interparietal bone. Unlike anteaters and pangolins, the occiput (back of the skull) is flat and vertical. Plesiorycteropus lacks notches above the foramen magnum (the opening that connects the brain to the spinal cord), which occur in aardvarks (1). The nuchal crest, a projection on the occiput, is straight in P. madagascariensis, but in P. germainepetterae it is interrupted in the middle, similar to the situation in armadillos and hyraxes (1).

Lamberton and Patterson gave different interpretations of the location of the mandibular fossa, where the mandible articulates with the cranium in Plesiorycteropus. MacPhee suggested that the true mandibular fossa was part of the area Lamberton had identified as being at the side of the braincase. The fossa is small and low, suggesting that the animal was not capable of powerful biting (1). At the back of this fossa, the pseudoglenoid process is more prominent in P. germainepetterae (1).] In P. germainepetterae but not P. madagascariensis, a small opening, perhaps the vascular foramen, is next to the foramen ovale (1). The petrosal bone forms a relatively large part of the roof of the tympanic cavity, housing the middle ear (1); parts of the petrosal are more developed in P. madagascariensis (1). Endocasts indicate that the neopallium part of the brain was relatively small (1).

There are 34 known vertebrae of Plesiorycteropus. The animal had at least seven sacral and five or six lumbar vertebrae. A find of associated caudal vertebrae from the base of the tail, which diminish in size slowly from front to back, suggests that the tail was long. There is no evidence for the additional joints between the vertebrae of xenarthrans (1). In the seven known thoracic (chest) vertebrae, the articulations with the intervertebral disks are bean-shaped and much wider from side to side than from top to bottom (1). In the back thoracics and all lumbars, there is a longitudinal transarcual canal in the neural arch (1).

A scapula, tentatively assigned to Plesiorycteropus, has an acromion process that is probably smaller than in aardvarks or armadillos. The robust humerus has an entepicondylar foramen in the distal end (1). The compact, massive radius resembles a pangolin radius (1). The ulna has a well-developed olecranon process at the proximal end, but the distal end is narrow; the morphology of the bone suggests that the animal could produce great force with its arms (1).

The pelvis has a narrow ilium and long ischium (1). The ischial tuberosity is a narrow rough piece of bone in most placentals, but is broad and smooth in Plesiorycteropus (1). MacPhee (1) said the femur has a long neck, as in the gymnure (Echinosorex). A projection, the third trochanter, is larger in P. madagascariensis (1). The tibia and fibula are extensively fused into a tibiofibula, resembling that of armadillos in the extensive fusion in the compressed shaft of the tibia, the narrow articulation surface at the distal end and the broad space between the bones (1). Unlike armadillos, the tibia and fibula are not inclined relative to each other, but are about parallel (1). The wide, short astragalus contains a uniquely large posteromedial process (1). The metapodials (middle hand or foot bones) vary in size. They are short and are broad proximally and narrow distally (1). The proximal phalange is shorter than the middle one and the distal phalanges are narrow and clawlike (1). The forelimbs show specializations for scratch-digging, where the forefeet are placed against the substrate, the claws enter into the substrate and the forefeet are drawn back against the body (1)). Other specialised body parts include the large hindlimbs and broad tail (1). Some aspects of the vertebral column and the pelvis suggest that the animal often assumed an erect or sitting, posture (1). It may been able to climb like gymnures and shrew tenrecs (1). It probably ate insects such as ants and termites, but may also have eaten other soft food. Due to its small size, it probably did not forage in termite mounds, as an aardvark does (1).

MacPhee had material of Plesiorycteropus from 12 sites in central, western, and southern Madagascar. It may have lived in and near wetlands (1). P. madagascariensis is known from sites throughout this range, but P. germainepetterae has only been definitely recorded from the centre; small bones from southern sites may also belong to it. The two species apparently had widely overlapping ranges, as subfossil remains of both species occur in the same site (1).

MacPhee assumed that Pleiorycteropus may have become extinct around 1000 years ago, when the extinction of the rest of the subfossil fauna of Madagascar is thought to have concluded. Nothing like it was reported by 17th-century European explorers of the island (1) and one bone has been radiocarbon dated to around 2150 years ago (10). Some other recently extinct Madagascan animals were larger and not exclusively insectivorous, while some species with more specialized diets survived (1). Early human colonists of Madagascar may have caused the extinction of Plesiorycteropus by destroying forests and causing other disturbances (9).

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