Plesiorycteropus
| Plesiorycteropus | ||||||||||||
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Speculative drawing by Plesiorycteropus |
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| Plesiorycteropodidae | ||||||||||||
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| Plesiorycteropus | ||||||||||||
| Filhol , 1895 |
Plesiorycteropus is an extinct genus of mammals that lived in Madagascar and did not becomeextinctuntil the late Holocene . Fossil remains of the animals have been discovered at around a dozen sites in the central and western parts of the island. These are smaller animals that, according to their skeleton structure, followed a burrowing, possibly also a tree-climbing way of life and probablyate invertebrates . Originally, a closer relationship between Plesiorycteropus and aardvark was assumed, to which the sometimes used German common name Madagascan aardvark refers. Later investigations suggested a position in a separate family, Plesiorycteropodidae, and a separate order, Bibymalagasia, with rather unclear relationships. More recent genetic studies, on the other hand, have shown a closer relationship to the Tenre kitties . The genus was scientifically introduced in 1895. It includes two known species, P. madagascariensis and P. germainepetterae .
features
Skull features
Plesiorycteropus was significantly smaller than an aardvark and significantly larger than the tenreks, reaching a weight of 6 to 18 kg. The complete skeleton has not survived, and the front part of the snout and the teeth are missing from the skull. Existing skulls had lengths of 6.6 to 7.7 cm between the frontal bone and the occiput , the possible total length should have been around 10 cm. The width of the skull varied from 3.6 to 3.8 cm. When viewed from above, it narrowed to 2.5 to 2.8 cm in the area of the eyes, then widened again in the nasal region. Due to the existing rostral skull area, a conical , stocking-ended snout can be assumed. Signs of the blunt snout can be found in the nasal bones , which, atypically for higher mammals, widened forward. The ossified nasal septum is also striking . The zygomatic arch did not form a closed arch, it consisted of a robust front arch attachment and a more delicate rear arch. The posterior part of the skull was clearly rounded and had no special bone marks, temporal lines were weak and lay relatively low without meeting in the middle. It should also be emphasized that the parietal bone was longer than the frontal bone. The occiput was strongly angled and formed a flat, almost vertical end of the skull, the joints for the cervical spine had two clearly separated joint surfaces. At the base of the skull, the connection to the lower jaw consisted of a flat joint pit, which was located near the posterior zygomatic arch attachment at about the level of the palatine bone . Since neither the lower and the upper jaw have survived, it is unclear whether the animals had teeth.
Skeletal features
The number of vertebrae, especially in the area of the trunk, is unknown. According to certain assumptions, the spine consisted of seven cervical, five or six lumbar and seven sacral vertebrae. There are also five articulated vertebrae of the anterior caudal spine. Their only slight decrease in size indicates that the tail must have been relatively long. The caudal vertebrae had massive transverse processes that suggest a very powerful tail. The limbs were generally strong and had numerous muscle marks. The humerus was 7.1 to 7.6 cm long and had a slightly elongated joint head. On the shaft side there was a massive deltopectoral ridge, which protruded clearly to the side in the middle of the shaft. The lower joint end (elbow joint) widened noticeably, with a larger proportion falling on the two epicondyles. The ulna showed a strongly elongated and strong upper articular process ( olecranon ), which was around 3 cm in relation to the total length of the bone of 8.2 cm. In contrast, the ulna thinned noticeably towards the bottom. The spoke was relatively short with 5.4 to 5.7 cm, but built robustly with a simple, radial head and a laterally pressed shaft. The femur is best narrated by all long bones. It has a length of 11 to 12.4 cm. The almost hemispherical joint head sat on a long neck, which is a clear difference to the aardvark and some tenreks. The same applies to the strong angling of the neck from the longitudinal axis of the femur, as well as the high position of the great rolling hill, which clearly towered over the joint head. A bone rib ran down from the Great Rolling Hill, it ended up about halfway down the shaft into the Third Rolling Hill. The lower joint end had an asymmetrical construction with a larger inner and a smaller outer joint roller. The tibia and fibula were fused together at both ends and reached a length of 9.1 to 9.5 cm. In side view, both had a relatively straight course, in the aardvark and the tenreks the fibula is more twisted. The lack of an additional bone process on the outer joint socket of the upper joint end (processus falciformis), which is formed in aardvark. As in many, but not all, Afrotheria, the upper ankle is formed only by the tibia and ankle bone. The skeleton of the hands and feet, except for the talus, and individual metapodia and phalanges are hardly known. The metapodia were short and wide with wide anterior and narrow posterior joint ends and a slightly curved shaft. The first phalanges of fingers and toes may have been shorter than the middle ones, which is not the case with the aardvark. The short terminal phalanges had distinctive lateral narrowing, but it is unclear from which ray they originate.
Subfossil Finds and Extinctions
Around a dozen sites with remains of Plesiorycteropus are known to date . These are concentrated in central, western and southern Madagascar . The vast majority of the finds come from Sirave and Ampoza in the southwest and from Ampasambazimba in the central area of the island. The latter site was discovered in 1902. It is very rich in fossils and goes back to a former lake. Radiocarbon dates on an extinct lemur showed an age of around 1035 years BP . At around 2154 BP, a measured value for Masinandraina near Antsirabe in central-eastern Madagascar is significantly older . Much more recent data was provided by studies on the bat site of the Anjohikely Cave near Anjohibe in northwest Madagascar. Here an age of 510 years BP was determined on a bones of a bat . Plesiorycteropus also appeared here with lemurs and hippos . It could be, however, that individual finds were relocated to a greater extent. All known sites are in nowadays rather drier areas of the island. Possibly Plesiorycteropus was adapted to narrow forest areas in the vicinity of wetlands such as swamps and rivers.
The reasons for the extinction are not fully understood. The island of Madagascar was only settled by humans around 2300 years ago. This was followed by a mass extinction of larger animals, which affected the Malagasy hippos, several groups of primate (such as the Megaladapidae and the Palaeopropithecinae ) and the giant elephant birds . Mostly hunting, slash and burn or the introduction of neozoa are cited as the main cause of the extinction of these animals. It is also possible that climatic changes, such as the gradual drying up of the western part of the island and the associated decline in forests there, accelerated the decline of large animals. The exact causes remain speculative. However, through the discovery of other, smaller mammals such as Microgale macpheei , it could be shown that not only did the large animal fauna disappear, but that the lines of smaller vertebrates were also affected by extinction.
Way of life
Locomotion
Plesiorycteropus shows a diverse combination of characteristics. Clear signs of a digging way of life stand out above all through modifications to the front legs. On the humerus there is a distinct deltopectoral ridge as a muscle attachment point; its expression on the lateral humerus shaft reinforces the forward movement of the arm through the deltoid muscle attached here . Furthermore, the lower joint ( elbow joint ) is widened, just like the olecranon of the ulna shows a strong extension. Both speak for an extremely strong forearm and finger muscles. The rather small joint facet on the head of the spoke, which connects the bone with the ulna, allows only a small amount of leeway in the rotational movement of the forearm, which should have been around 20 °. The hand bones are built short and broad overall. At the distal ends of the metacarpal bones there are deep joint spaces. These prevented the phalanxes attached there from shearing sideways when exposed to heavy use. In addition, the back legs are longer than the front legs. They could also have been used when digging, for example to support or shovel away the spill. Also striking are the broad transverse processes of the first caudal vertebrae, which allow a broad, muscular tail to be reconstructed. On the other hand, some skeletal features speak in favor of a climbing way of life, although it must be said, with restrictions, that both fossorial and arboreal locomotion require similar physical conditions. The high position of the humeral head made it possible for Plesiorycteropus to raise its arms to shoulder height or above, which is typical for climbing animals. Likewise, the thin end of the ulna that tapers downwards could speak for such a capability. On the other hand, jumping locomotion, as was postulated in part due to the high rolling mound on the thigh bone, seems rather unlikely, as the general proportions of the hind limbs do not support this. The very long femoral neck, which is not found in other burrowing animals including the aardvark, is also unusual. Another special feature is found on ischial , especially in the expression of the ischial tuberosity as a triangular platform similar to some great apes and the armadillos in the latter they served to hang the bony carapace. In Plesiorycteropus there were probably pronounced skin pads, which enabled the animals to take a sitting position despite the thick tail.
Diet
Since the front part of the skull is missing in the fossil material so far, little can be said about the structure of the teeth and, as a result, about the diet. In general, the facial muscles were poorly developed, which indicates the scarcely existing bone markings of the skull and the low position of the temporal ridges. The joint of the skull and the lower jaw is also relatively low, roughly at the level of the palatine bone. The weakness of the glenoid pit indicates a rather low bite force. All these traits are characteristic of animals with an insectivorous diet, possibly with a specialization in ants . Such a way of feeding goes hand in hand with digging and / or climbing locomotion, so that the animals have looked for their food, for example, underground in the ground or in trees. Food intake may have occurred opportunistically, which can be concluded from the general size of Plesiorycteropus , among other things . However, the sense of smell does not seem to have been as highly developed as in animals with a comparable diet, such as the aardvark , which is concluded from the comparatively smaller olfactory cortex and the also smaller olfactory bulb . It is unclear whether there was a comparatively long snout as in other specialized insectivores due to the missing front part of the skull.
Systematics
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Inner systematics of Afrotheria according to Buckley 2013
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Plesiorycteropus is an extinct genus of the higher mammals , the exact systematic position of which is disputed. Molecular genetic studies from the 2013 reference the genre in a close relationship with the Tenrekartigen (Afrosoricida) and within the tenrecs (Tenrecidae). The Tenrekartigen turn belong together with other original African animals such as the proboscis animals (Proboscidea), the hyraxes (Hyracoidea), the manatees (Sirenia), the aardvark (Tubulidentata) or the elephant-shrews (Macroscelidea) to a community group known as Afrotheria is called. The family relationships were determined genetically and are not based on anatomical similarities. Within the Afrotheria, the tenre kites are closest to the elephants.
Two species of Plesiorycteropus are currently recognized:
P. madagascariensis was first scientifically described by Henri Filhol in 1895 together with the genus Plesiorycteropus . Filhol had studied fossil remains from Belo sur Mer around 60 km south of Morondava on the west coast. These had previously been collected by M. Grevé along with numerous other bone finds and sent to Paris. For his first description, Filhol only presented a partial skull find in a short text note. The skull itself shows not overgrown bone seams and therefore probably represents a young animal. The generic name Plesiorycteropus is made up of the Greek word πληςιος ( plēsios ) for "almost" or "almost" and the scientific name Orycteropus for the aardvark. The second species, P. germainepetterae , was first described by Ross DE MacPhee in 1994 . The type material, also a partial skull without a snout, belongs to a full-grown animal and comes from central Madagascar, probably from Ampasambazimba. MacPhee named the species after Germaine Petter from the Muséum national d'histoire naturelle in Paris. Compared to P. madagascariensis , P. germainepetterae is the smaller representative, its cerebral skull is also smaller and more spherical and the indentation behind the eyes is clearer, as well as the bone crest on the occiput shows a clear indentation.
There are two synonyms for Plesiorycteropus and P. madagascariensis . In 1908, Charles Immanuel Forsyth Major established the species Myoryctes rapeta using a pelvic bone from Antsirabe in central Madagascar . He was convinced of it. to have the rest of a giant rat in front of you. Seven years later, Oldfield Thomas noticed that the name Myoryctes was already preoccupied and gave it the name Majoria . In 1912, Guillaume Grandidier named Hypogeomys boulei based on a thigh bone from Ampasambazimba and referred his new species to the Votsotsa line . MacPhee then recognized in 1994 that the bone material of both species belonged to Plesiorycteropus and united them with one another; in the case of Hypogeomys boulei , Charles Lamberton had already suspected this almost fifty years earlier.
Research history - "Malagasy aardvarks" or "giant ducklings"?
In his first description, Filhol compared the skull of Plesiorycteropus with that of the aardvark ( Orycteropus ) and referred his new genus to the so-called Edentata, a family group of mammals assumed at the time that was characterized by the lack of teeth or the formation of homodontic dentition and the today anteaters , sloths and armadillos (all subordinate articulated animals ), the pangolins (superior Laurasiatheria ) and the aardvark (superior Afrotheria ) included. The idea was picked up by Charles Lamberton almost sixty years later . He himself examined several subfossil sites in Madagascar in the 1930s and 1940s and discovered remains of Plesiorycteropus . This enabled him to submit a comprehensive osteological work on the previously known skeleton in 1946 . Lamberton found that the skeleton of Plesiorycteropus reflected features of the aardvark, pangolin and anteater, so that the genus looked like a chimera . For him, however, there were the greatest similarities with the aardvark.
In the period that followed, the closer relationship between Plesiorycteropus and the aardvark was discussed more frequently. However, in 1958, DG MacInnes saw few matches with Plesiorycteropus when describing Myorycteropus , a fossil aardvark from the Miocene of eastern Africa . Accordingly, in his opinion, the latter was not related to the aardvark and its extinct ancestors. In contrast, Bryan Patterson classified Plesiorycteropus in a revision of the recent aardvark and its fossil precursors from 1975 as a close relative of the aardvark and relegated it to the same order, the tubular teeth (Tubulidentata). The correspondences identified by Lamberton with the pangolins and the anteaters were recognized by Patterson as convergent characteristics that expressed no closer relationship. In order to underline the close relationship with the aardvark, he established the subfamily Plesiorycteropodinae within the tubular teeth. This contained only Plesiorycteropus , while the Orycteropodinae, the second subfamily of the order, included today's aardvark and the African and Eurasian fossil forms. In 1985, studies of the cranium and brain initially confirmed the close relationship between Plesiorycteropus and the aardvark.
In 1994, Ross DE MacPhee carried out the most extensive investigations of the skeletal finds that had been preserved until then. He came to the conclusion that Plesiorycteropus was only apparently similar to the aardvark due to its burrowing way of life. As was the case with pangolins and anteaters before, such features can also be found in numerous other mammals with underground locomotion, so they also represent a convergent development. In contrast, the wider skeleton shows numerous differences to the aardvark. This includes the formation of small canals on the vertebrae in Plesiorycteropus . Therefore MacPhee put the genus in a new mammal order, which he called Bibymalagasia (which literally means "animals of Madagascar"). However, MacPhee emphasized that the complete skeleton of Plesiorycteropus is not yet known, the reconstruction of the exact relationships remains difficult. After examining the inner ear with the cochlea and the semicircular canals, Plesiorycteropus deviates from other Afrotheria, which would support the position within its own order.
All previous investigations were based on an anatomical comparison of the skeleton of Plesiorycteropus with other, similar mammals. The molecular genetic studies published in 2013 on the known finds of Plesiorycteropus revealed a closer relationship with the Tenre-kitties. Plesiorycteropus was therefore incorporated into this order and the order of Bibymalagasia dissolved. With regard to the size of the animals, the representatives of Plesiorycteropus are now considered to be giant relatives of the Tenreks ( giant tenrecs ). Since the Tenreks have adapted to the most diverse habitats in Madagascar with ground-dwelling, burrowing, tree-climbing and semi-aquatic forms, it seems plausible to attribute the diverse skeletal-anatomical mixture of digging and climbing properties of the much larger Plesiorycteropus to this relationship.
literature
- Ross DE MacPhee : Morphology, adaptations, and relationships of Plesiorycteropus, and a diagnosis of a new order of Eutherian mammals. In: Bulletin of the American Museum of Natural History. 220, 1994, ISSN 0003-0090 , pp. 1-214
- Ronald M. Nowak: Walker's Mammals of the World. 6th edition. Johns Hopkins University Press, Baltimore MD et al. 1999, ISBN 0-8018-5789-9
- Lars Werdelin: Bibymalagasia (Mammalia Incertae sedis). In: Lars Werdelin and William Joseph Sanders (eds.): Cenozoic Mammals of Africa. University of California Press, Berkeley, London, New York, 2010, pp. 113-114
Individual evidence
- ^ A b c d Charles Lamberton: Contribution à la connaissance de la faune subfossile de Madagascar. Note XV: Le Plesiorycteropus madagascariensis Filhol. Bulletin de'l Académie Malgache 25, 1946, pp. 25-53
- ↑ a b c d e f g h i j k Ross DE MacPhee: Morphology, adaptations, and relationships of Plesiorycteropus, and a diagnosis of a new order of eutherian mammals. Bulletin of the American Museum of Natural History 220, 1994, pp. 1-214
- ^ Ian Tattersall: A Note on the Age of the Subfossil Site of Ampasambazimba, Miarinarivo Province, Malagasy Republic. American Museum Novitates 252, 1973, pp. 1-6
- ↑ Brooke E. Crowley: A refined chronology of prehistoric Madagascar and the demise of the megafauna. Quaternary Science Reviews 29, 2010, pp. 2591-2603
- ↑ David Burney, Helen F. James, Frederick V. Grady, Jean-Gervais Rafamantanantsoa, Ramisilonina, Henry T. Wright and James B. Cowart: Environmental change, extinction and human activity: evidence from caves in NW Madagascar. Journal of Biogeography 24, 1997, pp. 755-767
- ^ Steven M. Goodman, Natalie Vasey and David A. Burney: Description of a new species of subfossil shrew tenrec (Afrosoricida: Tenrecidae: Microgale) from cave deposits in southeastern Madagascar. Proceedings of the Biological Society of Washington 120 (4), 2007, pp. 367-376
- ↑ Steven M. Goodman and William L. Jungers: Extinct Madagascar. Picturing the island's past. University of Chicago Press, 2014, pp. 1-206.
- ↑ a b B. Patterson: The fossil aardvarks (Mammalia: Tubulidentata). Bulletin of the Museum of Comparative Zoology 147, 1975, pp. 185-237
- ^ A b J. GM Thewissen: Cephalic evidence for the affinities of Tubulidentata. Mammalia 49, 1985, pp. 257-284
- ↑ a b c Michael Buckley: A Molecular Phylogeny of Plesiorycteropus Reassigns the Extinct Mammalian Order 'Bibymalagasia'. PlosOne 8 (3), 2013, p. E59614 doi : 10.1371 / journal.pone.0059614
- ^ A b Henri Filhol: Observations concernant les mammifères contemporains des Aepyornis à Madagascar. Bulletin du Museum d'histoire naturelle, Paris 1, 1895, pp. 12-14
- ^ A b Lars Werdelin: Bibymalagasia (Mammalia Incertae sedis). In: Lars Werdelin and William Joseph Sanders (eds.): Cenozoic Mammals of Africa. University of California Press, Berkeley, London, New York, 2010, pp. 113-114
- ^ Charles Immanuel Forsyth Major: A giant sub-fossil rat from Madagascar, Myoryctes rapeto. Geological Magazine 5 (5), 1908; Pp. 97–98 ( [1] )
- ↑ Oldfield Thomas: Notes on the Asiatic bamboo-rats (Rhizomys, etc). Annals and Magazine of Natural History 8 (16), 1915, pp. 56–61 ( [2] )
- ↑ Guillaume Grandidier: Un nouvelle espece subfossile d'Hypogeomys, l'H. Boulei GG Bulletin du Muséum national d'histoire naturelle 18, 1912, pp. 10–11 ( [3] )
- ↑ DG Maclnnes: Fossil Tubulidentata from East Africa. Fossil Mammals of Africa 10, 1956, pp. 1-38
- ↑ Julien Benoit, Thomas Lehmann, Martin Vatter, Renaud Lebrun, Samuel Merigeaud, Loic Costeur and Rodolphe Tabuce: Comparative anatomy and three-dimensional geometric-morphometric study of the bony labyrinth of Bibymalagasia (Mammalia, Afrotheria). Journal of Vertebrate Paleontology 35 (3), 2015, p. E930043 doi: 10.1080 / 02724634.2014.930043
