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''Numidotherium'' ("Numidia beast") is an extinct genus of early proboscideans, discovered in 1984, that lived during the middle
Eocene The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''ēṓs'', ...
of North Africa some 46 million years ago. It was about 90-100 cm tall at the shoulder and weighed about 250-300 kg. The type species, ''N. koholense'', is known from an almost complete skeleton from the site of El Kohol, southern
Algeria ) , image_map = Algeria (centered orthographic projection).svg , map_caption = , image_map2 = , capital = Algiers , coordinates = , largest_city = capital , relig ...
, dating from the early/middle Eocene period. The animal had the size and the appearance of a modern
tapir Tapirs ( ) are large, herbivorous mammals belonging to the family Tapiridae. They are similar in shape to a pig, with a short, prehensile nose trunk. Tapirs inhabit jungle and forest regions of South and Central America, with one species inh ...
. In appearance, it was more slender and more plantigrade than an
elephant Elephants are the largest existing land animals. Three living species are currently recognised: the African bush elephant, the African forest elephant, and the Asian elephant. They are the only surviving members of the family Elephantida ...
, its closest modern relative.Libya Libya (; ar, ليبيا, Lībiyā), officially the State of Libya ( ar, دولة ليبيا, Dawlat Lībiyā), is a country in the Maghreb region in North Africa. It is bordered by the Mediterranean Sea to the north, Egypt to the east, Suda ...
, has been reassigned to its own genus, '' Arcanotherium''.

Description

''Numidotherium'' is one of the earliest representatives of the Proboscidea, and is known from several tooth and skull finds, and also from several postcranial fossils. It reached a shoulder height of 90 to 100 cm and was thus significantly larger than its predecessors ''
Phosphatherium ''Phosphatherium escuillei'' is a basal proboscidean that lived from the Late Paleocene to the early stages of the Ypresian age until the early Thanetian some 56 million years ago in North Africa. Research has suggested that ''Phosphatherium'' ...
'' and ''
Eritherium ''Eritherium'' is an extinct genus of early Proboscidea found in the Ouled Abdoun basin (early Thanetian age), Morocco. It lived about 60 million years ago. It was first named by Emmanuel Gheerbrant in 2009 and the type species is ''Eritherium a ...
''. Furthermore, it was characterized by a short trunk and quite long legs. The skull had a length of 37 cm and a raised cranial roof and had widely spreading zygomatic arches. As one of the earliest proboscideans, ''Numidotherium'' had air-filled bones in the roof of the skull, which, due to the increase in size and weight of the animal, offered a larger attachment point for the neck muscles. The rostrum was short and sloped steeply down from the forehead to the nose. The nasal bone was characterized by an elongated outer area of the nasal space (nares), while the intermaxillary bone was rather short and high. The shape of the rostrum created a high, but rather narrow, nasal interior. On the side of the upper jaw, a deep furrow ran from the intermaxillary bone to the anterior approach of the zygomatic arch. In some individuals the temporal ridges on the parietal bone formed a distinctive crest, in others they remained clearly separated. The occiput was also quite short in shape, with a robust occipital bulge. The joint surfaces here for articulating with the cervical spine were comparatively high. The lower jaw, up to 39 cm in length, was low but broad. The symphysis extended to the second premolar. The mental foramen lay below the third premolar tooth. The ascending branch loomed up and delimited a prominent masseteric fossa. The crown process was oriented slightly inwards. The number of teeth in the set of teeth was slightly reduced compared to older proboscideans. The second incisor in the upper jaw (I2) was significantly enlarged with a length of 4.5 cm and was conical in shape. Furthermore, it possessed only a thin layer of enamel. In the lower jaw, the first incisor, protruding obliquely forward (procumbent), was enlarged by 3.5 cm - the first examinations here looked at the second incisor as the enlarged one. These enlargements represent the preliminary stages of tusk formation in later proboscideans. There was a large diastema to each of the rear teeth, which could be up to 9.5 cm long. The premolars were characterized by a simple construction with a single raised enamel cusp. The molars, on the other hand, had two transversely positioned enamel ridges (bilophodont) and were reminiscent of those of tapirs. The entire posterior dentition can be described as a low crown (brachydont). The previously known
postcranial Postcrania (postcranium, adjective: postcranial) in zoology and vertebrate paleontology is all or part of the skeleton apart from the skull. Frequently, fossil remains, e.g. of dinosaurs or other extinct tetrapods, consist of partial or isolated s ...
skeleton comprises individual vertebrae, especially the first and second cervical vertebrae (
atlas An atlas is a collection of maps; it is typically a bundle of maps of Earth or of a region of Earth. Atlases have traditionally been bound into book form, but today many atlases are in multimedia formats. In addition to presenting geogra ...
and axis), which differ only slightly from those of other proboscideans. The
humerus The humerus (; ) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius and ulna, and consists of three sections. The humeral upper extremity consists of a r ...
reached a length of 30 cm and was robustly designed. The bones of the forearm,
ulna The ulna (''pl''. ulnae or ulnas) is a long bone found in the forearm that stretches from the elbow to the smallest finger, and when in anatomical position, is found on the medial side of the forearm. That is, the ulna is on the same side of t ...
and radius reached about the same length and were fused at the lower end. The upper joint end of the ulna ( olecranon) was relatively short and oriented backwards. The
thigh bone The femur (; ), or thigh bone, is the proximal bone of the hindlimb in tetrapod vertebrates. The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates with ...
measured 40.5 cm. The latter was clearly narrowed anteriorly and posteriorly, but had a very broad upper joint end and a third trochanter. The shin was significantly shorter at 26 cm. The forefoot and hindfoot had the "taxeopodous" arrangement of the root bones typical of proboscideans. That is, the individual bones of the palm and tarsal lay in rows one behind the other and not reciprocally to one another. As a result, there was no contact between the
lunate bone The lunate bone (semilunar bone) is a carpal bone in the human hand. It is distinguished by its deep concavity and crescentic outline. It is situated in the center of the proximal row carpal bones, which lie between the ulna and radius and the h ...
and the hamate on the forefoot. The special arrangement of the carpal bones suggests that an os centrale was formed between the lunate, the hamate and the trapezoid bone, which should be understood as a novel feature of the Proboscidea.

Discovery

''Numidotherium'' finds come exclusively from North Africa. The first specimens were discovered in El Kohol on the southern edge of the Atlas Mountains in Algeria. They come from the third layer of the El-Kohol Formation and date to the Middle Eocene. The rather extensive finds include a skull, a lower jaw and remains of the musculoskeletal system. A much older find from the Lower Eocene is known with a lower jaw fragment from a phosphate mine near Tamaguèlelt in northern Mali. However, this belongs to a much smaller representative and may have to be assigned to a different taxon. Further dental finds were found in connection with a rich fish fauna from Ad-Dakhla in Western Sahara and can be assigned to the transition from the Middle to the Upper Eocene.


Paleobiology

The construction of the
nasal bone The nasal bones are two small oblong bones, varying in size and form in different individuals; they are placed side by side at the middle and upper part of the face and by their junction, form the bridge of the upper one third of the nose. Ea ...
with the elongated outer nasal cavities suggests the presence of a short
proboscis A proboscis () is an elongated appendage from the head of an animal, either a vertebrate or an invertebrate. In invertebrates, the term usually refers to tubular mouthparts used for feeding and sucking. In vertebrates, a proboscis is an elong ...
in ''Numidotherium''. Barytherium'' and in '' Moeritherium''. The fused bones of the forearm support this view, but the
plantigrade 151px, Portion of a human skeleton, showing plantigrade habit In terrestrial animals, plantigrade locomotion means walking with the toes and metatarsals flat on the ground. It is one of three forms of locomotion adopted by terrestrial mammals. ...
structure of the forefoot shows adaptations to terrestrial locomotion, just as the low position of the eyes speaks against a water-dwelling way of life. The low-crowned molars with their typical, clearly formed lophodontic chewing surfaces indicate specialization in relatively soft vegetation, which should have predominantly included
leaves A leaf ( : leaves) is any of the principal appendages of a vascular plant stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, st ...
,
fruits In botany, a fruit is the seed-bearing structure in flowering plants that is formed from the ovary after flowering. Fruits are the means by which flowering plants (also known as angiosperms) disseminate their seeds. Edible fruits in partic ...
and
twig A twig is a thin, often short, branch of a tree or bush. The buds on the twig are an important diagnostic characteristic, as are the abscission scars where the leaves have fallen away. The color, texture, and patterning of the twig bark ar ...
s. The fibrous food was probably looked for on bushes at head height or just above it, characteristic grinding marks on the anterior premolars suggest that the animals wedged them in the mouth and tore them off with lateral movements of the head.
Isotope analysis Isotope analysis is the identification of isotopic signature, abundance of certain stable isotopes of chemical elements within organic and inorganic compounds. Isotopic analysis can be used to understand the flow of energy through a food w ...
of the teeth confirm this assumed terrestrial way of life. In the case of '' Numidotherium '' compared to ''Barytherium'' or ''Moeritherium'', these resulted in more fluctuating ratios of the oxygen isotope O18, which in the latter two are significantly more balanced due to their semi-aquatic way of life. It is possible that an adaptation to life in a semiaquatic environment occurred several times within the Proboscidea, whereby the question remains unanswered as to whether the proboscis, including today's
elephants Elephants are the largest existing land animals. Three living species are currently recognised: the African bush elephant, the African forest elephant, and the Asian elephant. They are the only surviving members of the family Elephantidae ...
, actually descended from some water-dwelling ancestors. The cochlea of ''Numidotherium'', which is built somewhat differently than that of today's elephants, turned out to be a further specialty. In ''Numidotherium'', for example, this has one and a half turns, whereas in elephants it has two. In the basal area of the winding, there are deviations in detail, for example in the clear formation of the lamina spiralis secundaria, which is responsible, among other things, for the perception of certain frequencies. Researchers therefore suspect that ''Numidotherium'' was more likely to perceive sounds in the higher frequency range, in contrast to today's elephants, which can also communicate in infrasound. The lower number of coils of the cochlea in ''Numidotherium'' also suggests a more limited auditory perception.Court, N; 1992 "Cochlea anatomy of Numidotherium koholense: Auditory acuity in the oldest known proboscidean." ''Lethaia 25'' (2): 211-215."


References

{{Taxonbar, from=Q149442 Eocene proboscideans Prehistoric placental genera Eocene mammals of Africa Fossil taxa described in 1986