Ocepeia
| Ocepeia | ||||||||||||
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Upper jaw of Ocepeia |
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| Temporal occurrence | ||||||||||||
| Paleocene | ||||||||||||
| 61.6 to 56 million years | ||||||||||||
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| Systematics | ||||||||||||
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| Scientific name of the family | ||||||||||||
| Ocepeiidae | ||||||||||||
| Gheerbrant , 2014 | ||||||||||||
| Scientific name of the genus | ||||||||||||
| Ocepeia | ||||||||||||
| Gheerbrant & Sudre , 2001 | ||||||||||||
Ocepeia is an extinct genus that is one of the ancestral forms of today's Afrotheria . It lived 61 to 56 million years ago and comprised small representatives from 3.5 to 12 kg body weight. Ocepeia is onlyprovenfrom the Ouled Abdoun Basin in Morocco , which is very rich in fossils. The fossils are distributed over a longsequence ofdeposition of phosphate-containing sediments and are mostly discovered when these are broken down. Inaddition to some fragments of the lower jaw, thefinds from Ocepeia mainly include two partial skulls, which represent the most extensive and complete of a higher mammal from the beginning of the Cenozoic era in Africa. The characteristics of the skull and the teeth suggest a closer systematic relationship with the Paenungulata , so that Ocepeia is related to the proboscis and manatees . However, there are also some characteristics that put the genus in a relationship with the Afroinsectiphilia and thus with the Tenreks and the aardvark . Ocepeia was first described in 2001, as only dental finds were available at that time, the genus was considered to be related to the ungulate-like, now extinct, condylarthra . The skull finds discovered later led to a re-evaluation of the family ties in 2014.
features
Ocepeia was a small representative of the early higher mammals , which has so far only been passed down through a few remains of the skull and fragments of teeth. On the basis of this, an average weight of 3.5 kg is assumed for smaller relatives, while larger ones weigh around 12 kg. So far, the skull is only documented for the smaller form. This reconstructed reached a length of 9 cm and a width at the zygomatic arches of 6.5 cm. In general, the skull was low and very robust, especially on the parietal , occipital and temporal bones of the skull there were thickened bones with small, air-filled chambers. The rostrum , on the other hand, was very short and only made up about a third of the length of the skull. But it was very high at around 2.5 cm. This made the entire forehead line appear to be clearly straight. The short snout was caused by reducing the length of the frontal and nasal bones . The nasal bone widened backwards and stood high above the also very short middle jawbone . As a result, an equally short but high nasal interior was formed, which also appeared quite voluminous due to its large width. The zygomatic arches swung wide and had a strong structure. In contrast to the shortened snout, the skull was elongated, especially on the parietal bones. Between these paired bones, a 4 cm long, sturdy crest was attached, but it was not formed like a leaf. The eye window was comparatively far back in the skull, above the second to third molars .
The lower jaw has not survived in full, but it also showed a robust structure with a very high bone body, which reached a height of 1.7 cm below the second molar and was also slightly thickened in the middle area with a width of 0.9 cm. The symphysis was relatively short and partially fused. The articular processes clearly towered above the row of teeth. A large mental foramen was located between the canine and the anterior premolar , a smaller one between the posterior premolar and the anterior molar. The dentition was already reduced and was characterized by the loss of the anterior premolars. The tooth formula was accordingly :, a total of 36 teeth were formed. The incisors are only incompletely known, but the second in the upper jaw was markedly enlarged and protruded slightly obliquely forwards ( procumbent ), while the third in both the upper and lower jaw was very small or greatly reduced. The canine had a pointed and slightly conical shape and had a sharp edge on the front. It partly protruded clearly beyond the other teeth. A short diastema separated it from the anterior dentition, none was formed from the posterior one, which is due to the shortening of the muzzle, despite the reduced number of premolars. The molars were designed with a low crown ( brachyodont ) and were relatively large. The premolars showed partial molarizations and thus resembled the posterior molars. A bumpy enamel pattern ( bunodont ) was formed on the chewing surface , but the humps on the cheek-side chewing surface formed a unit that connected a W-shaped course of the tooth enamel, so that a bunoselenodont-like impression was created. The size of the molars increased slightly backwards. The length varied between 6.4 and 7 mm for the smaller representatives with a row length from the canine to the last molar of 4.1 cm.
Fossil finds
Finds of ocepeia were previously only in Ouled Abdoun-basin in Morocco found that about 70 kilometers south of Casablanca is located. The Ouled Abdoun Basin is rich in phosphate- containing deposits that were formed in the transition from the Cretaceous to the early Paleogene . The phosphate- containing sediments , which are not continuously formed, reach a thickness of 30 to 300 m from N to S 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 . These are marine deposits that were created under the influence of a warm, near-continental and mostly shallow sea. They are rich in fossils, especially marine life, but also land vertebrates. So far, around 330 species have been identified, including the oldest remains of Cenozoic mammals in all of Africa. The Ouled Abdoun Basin is best known for the primeval trunk animals that appear here, of which Eritherium and Daouitherium are among the oldest forms. Most of the fossils are found during phosphate mining, which takes place in several mines spread across the Ouled Abdoun Basin.
The first find came in 1997 in the Grand Daoui area in the east of the basin during a research expedition of the Muséum national d'histoire naturelle in Paris , during the same period pieces were bought on French fossil markets. These are right and left fragments of the lower jaw that were used to establish the genus Ocepeia and represent the smaller form O. daouiensis . Further finds of the same kind later came to light from Sidi Chennane in the southeast of the Ouled-Abdoun-Basin, such as an almost complete lower jaw with the complete posterior dentition (P3 to M3) and some anterior lower jaw fragments with the alveoli of the anterior teeth. With the development of new sites in the area of Sidi Chennane at the beginning of the 21st century, the most important finds so far could be recovered, two partial skulls that can probably be assigned to a young adult male and female animal. The finds of O. daouiensis come mainly from an older find layer, the Lower Bone Bed , near the base of the so-called Bed IIa . The entire sequence of Bed IIa is generally dated to the late Paleocene , the Thanetium . Due to local stratigraphic conditions, however, the older Seelandium , which belongs to the late Middle Paleocene, cannot be separated from the Thanetium. However, characteristic additional finds, such as the Plattenkiemer fauna, and isotope investigations with the help of carbon support dating the lower area of Bed IIa in the Seelandium, which means that the finds are between 61 and 58 million years old. Remains of a larger species, called O. grandis , came to light from the Upper Bone Bed at the upper end of Bed IIa . This representative is represented by several lower jaw parts and isolated teeth. Since most of these are finds made by local workers, the exact origin within the Ouled Abdoun basin cannot always be precisely defined. The Upper Bone Bed can be clearly assigned to the Thanetium and should therefore be between 58 and 56 million years old.
Paleobiology
body weight
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For the reconstruction of the body weight, the lengths of the molars and the skull were mainly used, a method that has proven itself especially in ungulates. Originally, the weight of was O. daouiensis with 5.2 kg to 6.1 adopted and would thus be similar to heavy as the condylarths belonging Ectocion . Later measurements on the first molar gave figures of 7.9 to 9.3 kg for the smaller O. daouiensis and 19.5 kg for the larger O. grandis . However, since today's ungulates ( cloven- toed ungulates and odd- toed ungulates ) show more pronounced differences in size with regard to the smaller anterior and larger posterior molars than is the case with Ocepeia with its only slightly varying posterior molars, these values must be regarded as too high. The results for simultaneous measurements on the rearmost molar are 2.7 to 3.5 kg for O. daouiensis and 10.4 to 12.3 kg for O. grandis , which should be more realistic in terms of tooth size compared to today's ungulates . When the body weight was determined with the help of the skull dimensions, a mass of 3.4 to 4 kg could be calculated for O. daouiensis ( no remains of the skull of O. grandis are known), which is roughly in the range of the results for the third molar. O. daouiensis therefore had a body weight comparable to that of today's Schliefern .
Way of life
The design of the molars with their selenobunodont chewing surface pattern suggests a general herbivorous way of life. The rounded tooth enamel cusps speak for a rather soft food, such as leaves that could be easily crushed with them, which could also be determined with the help of signs of wear on some teeth. However, since O. grandis has significantly more pointed bumps, which are better suited for grinding or shredding food, a consumption of harder materials can be assumed here. Above all, the short snout, which is not known from ungulates and is more reminiscent of primates, is unusual . Possibly this was related to a special adaptation to the habitat, whereby due to the missing body skeleton it can only be speculated whether Ocepeia possibly followed a primate-like, tree-dwelling ( arboricole ) way of life.
The two previously known skulls show differences in robustness. One skull has a generally stronger structure with enlarged canines and a stronger and higher sagittal crest, while the other is more delicate. This is associated with a sexual dimorphism , according to which males were built stronger than females. The pneumatized bones on the skull, which represent a parallel development to the proboscis, are remarkable on both skulls. Their function is unknown, but they may represent a specialized structure that contributed to the transmission of sounds.
The structure of the inner ear allows individual further conclusions to be drawn about the way of life of Ocepeia . In general, the inner ear is relatively small compared to the skull. Ocepeia shares the property with some of today's Afroinsectiphilia such as the Tenreks and the Goldmullen . The cochlea has a comparatively high share of around 66%. Their absolute volume is around 11.7 mm³ compared to the entire labyrinth with 17.5 mm³. It has 2.13 turns, resulting in about 765 °, significantly more than in early proboscis animals as numidotherium or early hyraxes as Seggeurius . A lamina spiralis secundaria (secondary lamina) is formed at the base turn, which is also found in early proboscis. Both the number of turns and the secondary lamina are indicators of auditory perception . In today's elephants , the cochlea shows more turns and a secondary lamina is missing, which means that the basilar membrane is widely expanded in them. This is considered an adaptation to hearing in the infrasound range , which is well pronounced in elephants. According to calculations, the perceived frequency range with Ocepeia was between 0.12 and 29.5 kHz . Thus, the animals were only partially sensitive to low tones, but sometimes more strongly than in other early higher mammals , which is also supported by the narrow width of the secondary lamina in Ocepeia . The upper value touches the ultrasound range , but here, too, Ocepeia does not show itself to be an outspoken specialist, since the secondary lamina only takes up the basic spiral of the cochlea. The semicircular canals, on the other hand, are well formed, but small and thin. The largest is the front, typical of numerous higher mammals, the smallest the outer. The posterior semicircular canal is at an angle of 25 ° to the base of the skull. This means that when the posterior semicircular canal was positioned horizontally, the head assumed a position with the nose pointing downwards, which is also the case with armadillos . Such an anatomical arrangement is sometimes associated with a greater intake of food close to the ground. Sometimes the circumference of the semicircular canals is also used to reconstruct the agility and visual acuity of an animal, both of which increase with the size of the semicircular canals. In the case of Ocepeia , the small semicircular canals suggest poor agility and reduced visual acuity, the latter being coincident with a reconstructed eye size of around 15 mm. However, the expressiveness of the semicircular canals is also viewed critically.
Systematics
External and internal systematics
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Systematic position of the Embrithopoda according to Gheerbrant et al. 2018
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Ocepeia is a genus of the Ocepeiidae family and is the only member thereof. This in turn belongs to the Afrotheria , one of the four great main lines of the higher mammals . Within the Afrotheria, Ocepeia is one of the ancestral forms. An exact assignment to a specific order has not yet been made, but there is a likelihood that the genus is related to the Paenungulata and thus to the proboscis , snipers and manatees .
Two types are distinguished within the genus Ocepeia :
- O. daouiensis Gheerbrant & Sudre , 2001; smaller and older species
- O. grandis Gheerbrant , 2014; larger and younger species
Relationship of Ocepeia to the large groups of Afrotheria
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Overall, the skull of Ocepeia is relatively primitive and shows some general characteristics of the higher mammals. Among other things, the lack of contact between the upper jaw and frontal bone is very original. Special features of the skull can be found, among other things, in the greatly shortened snout and the elongated brain skull, also in the short mandibular symphysis, the pressed design of the canine and the reduction of the anterior molars. In this respect, Ocepeia has some similarities to the primates , but these are likely to represent convergent developments. This also applies to the straight forehead line, which is reminiscent of the Pantolesta , extinct, semi-aquatic animals with a closer relationship to the insectivores . Preliminary cladistic analyzes saw Ocepeia close to the base of the Afrotheria and initially grouped it together with the extinct Ptolemaia, the aardvark ( Orycteropus ) still alive today and the great otter shrew ( Potamogale ), which belongs to the Tenre-like family . All three groups form the Afroinsectiphilia , whereby the affiliation of Ocepeia to the Afroinsectiphilia was based only on a few skull features, for example in the area of the eyes (reduced postorbital process ). The molars, however, indicate a possible closer position to the paenungulata . This is supported by the selenobunodontic chewing surface pattern of the posterior molars, which is a feature of many ungulate lines. The skull also has some features in common with the paenungulata, such as the wide interior of the nose and the structure of the zygomatic arch. The clearly enlarged and procumbent second upper incisors correspond roughly to those of the early proboscis , which belong to the crown group of the Paenungulata and from which the tusks later developed. The small third incisor in the lower jaw is also reminiscent of the early proboscis, although the reduction in Ocepeia is not as advanced as compared to Eritherium or even Phosphatherium . The already reduced first two premolars indicate, however, that Ocepeia is not directly in the ancestral line of today's representatives of the Paenungulata. Rather, the genus is an early branch of the original Afrotheria with a more generalized skull structure, which went through an independent development. Due to the mixture of characteristics of the Afroinsectiphilia and the Paenungulata, Ocepeia was temporarily regarded as a "transitional fossil" between these two groups of Afrotheria. In further cladistic analyzes in 2016, including further Paleocene African fossil finds, the close relationship with the Paenungulata was confirmed. The relationship can be shown, among other things, on the four-humped ( quadritubercular ) anterior molars, such as on the hypoconus, one of the main cusps of the maxillary molars, which in the paenungulata arose from a small side hump, the metaconule (which differs from the odd-toed ungulate , for example which the hypoconus developed from a cingulum, a bulge of tooth enamel). Since the hump in Ocepeia is not yet fully developed, the genus was placed on the basis of a new overarching taxon , the Paenungulatomorpha .
Research history
The first scientific description of Ocepeia was in 2001 by Emmanuel Gheerbrant and Jean Sudre using two mandibular fragments from the Grand Daoui region of the Ouled Abdoun Basin in Morocco . The holotype (copy number : CPSGM-MA1 ) includes the right branch of the lower jaw with the preserved posterior premolar and the first molar. The generic name Ocepeia is derived from the initials of Office Chérifien des Phosphates (OCP), the national, Moroccan company for the mining of phosphate. Since only four teeth were known at that time, based on their design, they were assigned to the Phenacodonta , a group of primeval ungulates that were mainly found in North America during the Paleocene and Eocene . However, there were also similarities to the Arctocyonidae , which belong to the trunk group of the Condylarthra or to the own group of the Procreodi . Loxolophus and Lambertocyon in particular had similarly designed low-crowned teeth and generally robust teeth. In a study of further finds carried out a few years later, Ocepeia was assigned to the Paenungulata with unexplained family membership , for which individual features of the molars were responsible. The new skull material from Sidi Chennane led to a new interpretation, so that Ocepeia can now be regarded as the basal representative of Afrotheria, which is possibly close to the Paenungulata due to the selenobunodont molars. In addition, in this latest study , Ocepeia was incorporated into the Ocepeiidae family named after him.
Individual evidence
- ↑ a b c d e f g h i j Emmanuel Gheerbrant, Mbarek Amaghzaz, Baadi Bouya, Florent Goussard and Charlène Letenneur: Ocepeia (Middle Paleocene of Morocco): The Oldest Skull of an Afrotherian Mammal. PLoS ONE 9 (1), 2014, p. E89739, doi: 10.1371 / journal.pone.0089739
- ↑ a b c d e f 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 d e 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 Emmanuel Gheerbrant: Paleocene emergence of elephant relatives and the rapid radiation of African ungulates. PNAS. 106 (6), 2009, pp. 10717-10721
- ↑ 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, 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 Abdoun, Maroc, Yprésien des lieuxatétat ét . Bulletin de la Societe Geologique de France 174 (3), 2003, pp. 279-293
- ↑ 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
- ↑ 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
- ↑ a b Emmanuel Gheerbrant, Arnaud Schmitt and Guillaume Billet: Petrosal and bony labyrinth morphology of the stem paenungulate mammal (Paenungulatomorpha) Ocepeia daouiensis from the Paleocene of Morocco. Journal of Anatomy, 2020, doi: 10.1111 / joa.13255
- ↑ 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
- ^ 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
- ↑ 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
- ↑ Kenneth D. Rose: The beginning of the age of mammals. Johns Hopkins University Press, Baltimore, 2006, pp. 1-431 (pp. 223-225)
