Abdounodus
| Abdounodus | ||||||||||||
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Lower jaw of Abdounodus |
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| Temporal occurrence | ||||||||||||
| Paleocene ( Zealand ) | ||||||||||||
| 61.6 to 59.2 million years | ||||||||||||
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Abdounodus | ||||||||||||
| Gheerbrant & Sudre , 2001 | ||||||||||||
Abdounodus is an extinct genus and a very early representative of Afrotheria , a group of higher mammals from Africa. Within the Afrotheria it is placed near the Paenungulata , whichcontainthe elephants , hyrax and manatees . Abdounodus lived in the Paleocene about 61 to 59 million years ago. Fossil remains of the animals come from phosphate -containing deposits in the Ouled-Abdoun Basin in Morocco, North Africa. The finds made so far are rather small and mainly include remains of pine. They allow only a few statements about the way of life, but due to the structure of the teeth it can be assumed that it was a herbivore. The structure of the molars also provides information about the development of the tooth shape in the pasenungulata. The first fossils were discovered in the late 1990s,and Abdounodus was described and namedin 2001. Initially, the shape was seen as a representative of primitive ungulates, later the relationship with the Afrotheria was recognized.
features
So far, individual skull fragments and parts of the mandible are available from Abdounodus . Due to the fragmented material, only a few features can be described. The infraorbital foramen lay above the third premolar , the anterior insertion of the zygomatic arch began at the level of the second molar and thus further anterior than in the Ocepeia, which was about the same age . The position of the infraorbital foramen suggests that the orbit was above the first molar, which would also correspond to the suture between the maxilla and the zygomatic bone . The suture of the upper jaw with the palatine bone extended to the first or second molar. The lower jaw reached a length of 5.8 cm and a height of 1.15 cm on the horizontal bone body. Overall, it was built relatively gracefully, on the outside the horizontal bone puffed up a little, but this did not reach the dimensions of Ocepeia . As a result, the lower jaw branch had a width of up to 0.87 cm. The lower edge was slightly convex. A small mental foramen existed below the third premolar, and a second, significantly larger one further forward in the area of the symphysis . The latter was rather short, ended before the third premolar and showed no adhesions. The corolla protruded so that it was comparatively higher than that of Ocepeia . The total height of the lower jaw on the ascending branch was 3.6 cm. The front edge of the crown process sloped upwards, the angle to the alveolar plane was about 120 °. The articular process was clearly separated from the crown process and was located significantly lower, approximately at the level of the occlusal plane, the mandibular joint widened laterally. The angular process, however, was poorly developed. Strong marks of the masticatory muscles appeared on the ascending branch. The mandibular foramen was large and located below the base of the articular branch and below the apex of the crown process.
The exact composition of the dentition is unknown, as the front teeth have not survived. Only the last two premolars and the three molars of the upper and lower row of teeth remained. The teeth were closed, but in front of the third premolar in the lower jaw there was a diastema 2.2 mm in length to the preceding tooth, in this case only alveolar. It is unclear whether this tooth represented another premolar or already the canine . The molars were all low-crowned ( brachyodont ) and definitely bunodont , that is, the chewing surface of the teeth had a humped pattern. Typically, there were two pairs of main bumps, which in turn gave the teeth a bilophodontic character. The cusps of the teeth were sometimes clearly inflated, but the enamel folds between the cusps were rather weak. However, there was a W-shaped ectoloph on the lip side of the molars, so that the molars had a selenodontic appearance (the shear edge appeared crescent-shaped). The premolars were submolariform in shape with one or two main cusps. In the lower jaw, the fourth premolar and the first molar reached the largest dimensions with dimensions of 5 by 3.5 and 4.8 by 3.3 mm, i.e. the two centrally located teeth. In the upper jaw, however, the second molar was largest with a length of 5.1 and a width of 6.4 mm. The length of the upper row of teeth from the third premolar to the third molar was 23.8 mm.
Fossil finds
The few finds of Abdounodus come from the Ouled Abdoun Basin in Morocco . This is about 70 km south of Casablanca . The basin is particularly important for its rich phosphate deposits , which formed in the transition from the Cretaceous to the early Paleogene . The phosphate-containing sediments are not continuous, but from N to S they reach a thickness of 30 to 300 m and cover a period of around 25 million years ( Maastrichtian to Ypresian 72 to 48 million years ago). This makes them one of the most extensive deposition sequences of this type in the area of the former Tethys Ocean . The deposits were created in a marine environment, with the sea being relatively shallow, warm and close to the mainland. They are rich in fossils and, in addition to numerous marine life, also terrestrial vertebrates occur. A total of around 330 species have been recorded so far, including the oldest remains of Cenozoic mammals in all of Africa. The Ouled Abdoun Basin became known, among other things, for the primeval trunk animals that appear here , of which Eritherium and Daouitherium belong to the earliest forms. Most of the fossils are found in phosphate mining. This takes place in several mines spread across the Ouled Abdoun Basin.
The first discovery of Abdounodus , a fragment of the lower jaw, was probably picked up by local fossil collectors in 1997, so its exact location is unknown. The find later came to the Muséum national d'histoire naturelle in Paris. In the period that followed, further fossil remains came to light. These could be associated with the Lower Bone Bed des Bed IIa in the local stratigraphy of the Ouled-Abdoun Basin, the Bed IIa generally dated to the late Paleocene , more precisely the Thanetian 59 to 56 million years ago. Overall, the Lower Bone Bed is very fossil-proof and contains mainly fish and birds , as well as some fossil finds of mammals. In addition to Abdounodus , these include the remains of Ocepeia , another very primitive representative of Afrotheria, and of Eritherium . The fish fauna of Bed IIa , above all the characteristic Plattenkiemer fauna, allowed the find layer to be found in the Seelandium before 61 to 59 million; however, for local stratigraphic reasons, this level of the Paleocene cannot be separated from the Thanetium within the Ouled Abdoun Basin. Isotope studies with the help of carbon were later able to clearly assign Bed IIa to the Seelandium.
Paleobiology
The bunodonte chewing surface pattern speaks for a herbivore. Significant signs of wear on the outer sides of the lower and inner sides of the upper molars, which are also flat, indicate clear horizontal chewing movements. The tubercles cut the food rather than grind it. In addition, there were strong vertical biting forces, so that Abdounadus probably specialized primarily in harder parts of plants.
Systematics
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Systematic position of the Embrithopoda according to Gheerbrant et al. 2018
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Abdounodus is an extinct species within the superiority of the Afrotheria , one of the four main lines of higher mammals (Eutheria). An assignment to a specific Afrotheria family has not yet taken place. However, Abdounodus is more closely related to the genus Ocepeia , which was also found in the Ouled Abdoun Basin as a form of about the same age. Both Abdounodus and for ocepeia is a closer relationship to the paenungulata and thus the trunk animals (Proboscidea), the closing distance (Hyracoidea) and sea cows accepted (Sirenia). This presumed relationship is expressed in the common, superior taxon of the Paenungulatomorpha .
The closer relationship between Abdounodus , Ocepeia and Paenungulata is particularly evident in the tooth features. The decisive factor is the bilophodontic chewing surface pattern of the molars, which can also be found in the earliest proboscis such as the Eritherium or the snakes. The four main cusps ( quadritubercular ), which give the teeth their bilophodontic character, are the paraconus and the hypoconus as well as the metaconus and the protoconus, related to the maxillary molars. There are structurally similar teeth in pair (Artiodactyla) and Unpaired ungulates (Perissodactyla), which is why they were originally combined with the Paenungulata to form the ungulata (ungulates).
It is noteworthy in both Abdounodus and Ocepeia that the bilophodontic teeth are not yet fully developed, but that the originally tritubercular tooth pattern of the higher mammals consisting of three main tubercles (without hypoconus) is more or less clearly recognizable. In both forms, the hypoconus is strikingly close to the protoconus. It can therefore be assumed that the originally not formed hypoconus arose from the metaconulus. The metaconulus represents a small side hump which is connected to the protoconus in more primitive higher mammals. During the formation process, the metaconulus slowly migrated away from the protoconus on the tongue side and then later formed the hypoconus. The process is more advanced in Abdounodus than in Ocepeia , so that the former appears to be phased younger than the latter. The shaping of a Hypoconus from the Metaconulus in paenungulata stands in striking contrast to the molars of odd-toed ungulates and some extinct ancestral group representatives Euungulata where the Hypoconus grew out of a cingulate (a Zahnschmelzwulst) (in cloven-hoofed animals, the Hypoconus also developed from the Metaconulus). For this reason, the bilophodontic teeth of the Paenungulata and the odd-toed ungulate or various members of the Euungulata trunk group should be understood as a convergent development and not as an expression of a closer relationship. The hypoconus of the Paenungulata is sometimes referred to as the pseudohypoconus because of its different origin.
Research history
The first scientific description of Abdounodus was carried out by Emmanuel Gheerbrant and Jean Sudre in 2001. They cited the lower jaw fragment that had been picked up in 1997 by fossil collectors in the Ouled Abdoun Basin. It thus represents the holotype (copy number MNHN PM21), it comprises a left branch of the lower jaw with the remaining teeth from the third premolar to the second molar. The generic name Abdounodus is made up of the place where it was found, the Ouled Abdoun basin, and the Greek word ὀδούς ( odoús ) for “tooth”. Gheerbrant and Sudre created with Abdounodus hamdii a kind and honored with the epithet the then general manager responsible for the phosphate mining area Mohamed Hamdi, who supported the paleontological research strongly. In their first description, the two first authors referred the genus to the family Mioclaenidae , a member of the form-rich but not self-contained group of " Condylarthra " ("parent hoofed animals"). The view has also been partially adopted by other scientists. The Mioclaenidae were then considered to be relatively widespread across North and South America as well as Europe and Africa, but later analyzes reduced them to the North American forms. Due to further new finds of Abdounodus in the form of mandibular remains, Gheerbrant worked out numerous differences to the Mioclaenidae in 2010, but kept the genus within the "Condylarthra". It was only the discovery of individual parts of the upper jaw that prompted him, in collaboration with other research colleagues, to place Abdounodus near the paenungulata.
literature
- Emmanuel Gheerbrant, Andrea Filippo and Arnaud Schmitt: Convergence of Afrotherian and Laurasiatherian Ungulate-Like Mammals: First Morphological Evidence from the Paleocene of Morocco. PLoS ONE 11 (7), 2016, p. E0157556 doi: 10.1371 / journal.pone.0157556
Individual evidence
- ↑ a b c d e f g h Emmanuel Gheerbrant, Andrea Filippo and Arnaud Schmitt: Convergence of Afrotherian and Laurasiatherian Ungulate-Like Mammals: First Morphological Evidence from the Paleocene of Morocco. PLoS ONE 11 (7), 2016, p. E0157556
- ↑ a b c d Emmanuel Gheerbrant, Jean Sudre, Mohamed Iarochene and Abdelkader Moumni: First ascertained African “Condylarth” mammals (primitive ungulates: cf. Bulbulodentata and cf. Phenacodonta) from the earliest Ypresian of the Ouled Abdoun Basin, Morocco. Journal of Vertebrate Paleontology 21 (1), 2001, pp. 107-118
- ↑ a b c Emmanuel Gheerbrant: Primitive Ungulates (“Condylarthra” and Stem Paenungulata). In: Lars Werdelin and William Joseph Sanders (eds.): Cenozoic Mammals of Africa. University of California Press, Berkeley, Los Angeles, London, 2010, pp. 563-571
- ↑ a b c Lászlό Kocsis, Emmanuel Gheerbrant, Mustapha Mouflih, Henri Cappetta, Johan Yans and Mbarek Amaghzaz: Comprehensive stable isotope investigation of marine biogenic apatite from the late Cretaceous – early Eocene phosphate series of Morocco. Palaeogeography, Palaeoclimatology, Palaeoecology 394, 2014, pp. 74-88
- ↑ Emmanuel Gheerbrant, Jean Sudre, Henri Cappetta, Mohamed Iarochene, Mbarek Amaghzaz and Baâdi Bouya: A mew large mammal from the Ypresian of Morocco: Evidence of surprising diversity of early proboscideans. Acta Palaeontologica Polonica 47 (3), 2002, pp. 493-506
- ↑ Emmanuel Gheerbrant: Paleocene emergence of elephant relatives and the rapid radiation of African ungulates. PNAS. 106 (6), 2009, pp. 10717-10721
- ^ Cyrille Delmer: Reassessment of the generic attribution of Numidotherium savagei and the homologies of lower incisors in proboscideans. Acta Palaeontologica Polonica 54 (4), 2009, pp. 561-580
- ↑ a b Emmanuel Gheerbrant, Jean Sudre, Henri Cappetta, Cécile Mourer-Chauviré, Estelle Bourdon, Mohamed Iarochene, Mbarek Amaghzaz and Baâdi Bouya: Les localités à mammifères des carrières de Grand Daoui, bassin des Ouled Abdounét, Maroc, Yprésatien: premier ↑ of the lieux. Bulletin de la Societe Geologique de France 174 (3), 2003, pp. 279-293
- ↑ Johan Yans, M'Barek Amaghzaz, Baadi Bouya, Henri Cappetta, Paola Iacumin, László Kocsis, Mustapha Mouflih, Omar Selloum, Sevket Sen, Jean-Yves Storme and Emmanuel Gheerbrant: First carbon isotope chemostratigraphy of the Ouled Abdoun phosphate basin, Morocco ; implications for dating and evolution of earliest African placental mammals. Gondwana Research 25, 2014, pp. 257-269
- ↑ Emmanuel Gheerbrant, Arnaud Schmitt and László Kocsis: Early African Fossils Elucidate the Origin of Embrithopod Mammals. Current Biology 28 (13), 2018, pp. 2167–2173, doi: 10.1016 / j.cub.2018.05.032
- ^ John P. Hunter and Jukka Jernvall: The hypocone as a key innovation in mammalian evolution. PNAS 92, 1995, pp. 10718-10722
- ↑ Kenneth D. Rose: The beginning of the age of mammals. Johns Hopkins University Press, Baltimore, 2006, pp. 1-431 (pp. 223-225)
- ↑ Thomas E. Williamson and Thomas D. Carr: Bomburia and Ellipsodon (Mammalia: Mioclaenidae) from the Early Palaeocene of New Mexico. Journal of Paleontology 81 (5), 2007, pp. 966-985
