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. There is little reason to assume it was similar in general form to the aardvark. 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 favored the lower estimates, because those were based on armadillos, which have femora similar to those of
Plesiorycteropus. On the other hand, the caviomorph model produced a better estimate of brain size in
Plesiorycteropus. Any of the estimates makes it considerably larger than the largest living tenrec,
Tenrec ecaudatus, at up to . 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 Madagascar and elsewhere to have been at higher
risk of extinction.
Skull There are four known skulls (three of
P. madagascariensis and one of
P. germainepetterae), 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 estimated maximum skull length in
P. madagascariensis at . The length of the
frontal bone averages in
P. madagascariensis and is in
P. germainepetterae. The robust
nasal bones, preserved in a single specimen, are widest at the front, a feature unusual among placentals that is also seen in armadillos, and are also unusually flat. The
ethmoid labyrinth, in the
nasal cavity, was large, suggesting that
Plesiorycteropus had a good sense of smell. A much larger part of the
nasal septum, which separates the left and right nasal cavities, is ossified than usual in other mammals; MacPhee could find a similar condition only in sloths, which have a very short nose. The
lacrimal bone is relatively large. At it is a single
lacrimal canal, which opens near the
suture between the frontal and lacrimal bones, like in lipotyphlans. There is a small tubercle (absent in aardvarks) near this opening. The
orbital cavity, which houses the eyes, is relatively short, similar to the situation in pangolins and armadillos. A distinct tubercle is present on the suture between the frontal and
parietal bones in
P. germainepetterae, but not
P. madagascariensis.
P. madagascariensis has a more expansive braincase and a less pronounced narrowing between the orbits. similar to many other tenrecoids. As in pangolins and xenarthrans, little of the
squamosal bone can be seen from above. The
temporal lines on the braincase, which anchor muscles, are located lower in
P. germainepetterae. 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. In their descriptions of
Plesiorycteropus, Lamberton and Patterson posited different interpretations of the location of the
mandibular fossa, where the
mandible (lower jaw) articulates with the cranium. MacPhee found problems with either interpretation and suggested that the true mandibular fossa was part of the area Lamberton identified as such, at the side of the braincase. The fossa is small and low, suggesting that the animal was not capable of powerful biting. At the back of this fossa is a
pseudoglenoid proces, which is more prominent in
P. germainepetterae. parts of the petrosal are more developed in
P. madagascariensis.
Postcranium 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 only slowly from front to back, suggests that the tail was long. There is no evidence for the additional
joints between the vertebrae that are characteristic of xenarthrans. 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. In the back thoracics and all lumbars, a longitudinal
transarcual canal is present in the
neural arch. A
scapula (shoulder blade), only tentatively assigned to
Plesiorycteropus, has the
acromion, a
process, present, but the structure is probably not as large as in aardvarks or armadillos. Six humeri have been found; the bone is robust and an
entepicondylar foramen is present in the distal (far) end. There are three examples of the
radius, a compact and massive bone in
Plesiorycteropus which resembles the pangolin radius. The three known
ulnae show that the
olecranon process at the proximal (near) end is well-developed, but the distal end is narrow; the morphology of the bone suggests that the animal was capable of producing much force with its arms. The innominate is known from seven examples, but most are quite incomplete. It includes a narrow
ilium and long
ischium. The
ischial tuberosity, a narrow rough piece of bone in most placentals, is broad and smooth in
Plesiorycteropus. With 17 specimens, the femur is the best represented long bone. It is distinctive in its long
neck, similar only to the gymnure
Echinosorex according to MacPhee. A projection known as the
third trochanter is larger in
P. madagascariensis. Unlike in armadillos, the tibia and fibula are not inclined relative to each other, but about parallel. The
astragalus, which is known from four examples, is wide and short and contains a uniquely large
posteromedial process. Among the few known
phalanges, the proximal phalange is shorter than the middle one and the distal phalanges are narrow and clawlike. ==Ecology, behavior, and extinction==