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Ocepeia (Middle Paleocene of Morocco): the oldest skull of an afrotherian mammal.

Gheerbrant E, Amaghzaz M, Bouya B, Goussard F, Letenneur C - PLoS ONE (2014)

Bottom Line: This results from conflict with undetected convergences of Paenungulata and Perissodactyla in our cladistic analysis, such as the shared bilophodonty.The selenodont pattern best supports the stem paenungulate position of Ocepeia; that, however, needs further support.In addition, the autapomorphic family Ocepeiidae supports the old--earliest Tertiary or Cretaceous--endemic evolution of placentals in Africa, in contrast to hypotheses rooting afrotherians in Paleogene Laurasian "condylarths".

View Article: PubMed Central - PubMed

Affiliation: Centre de Recherches sur la Paléobiodiversité et les Paléoenvironnements, CNRS-MNHN-UPMC, Muséum National d'Histoire Naturelle, Dpnt Histoire de la Terre, Paris, France.

ABSTRACT
While key early(iest) fossils were recently discovered for several crown afrotherian mammal orders, basal afrotherians, e.g., early Cenozoic species that comprise sister taxa to Paenungulata, Afroinsectiphilia or Afrotheria, are nearly unknown, especially in Africa. Possible stem condylarth-like relatives of the Paenungulata (hyraxes, sea-cows, elephants) include only Abdounodus hamdii and Ocepeia daouiensis from the Selandian of Ouled Abdoun Basin, Morocco, both previously only documented by lower teeth. Here, we describe new fossils of Ocepeia, including O.grandis n. sp., and a sub-complete skull of O. daouiensis, the first known before the Eocene for African placentals. O.daouiensis skull displays a remarkable mosaic of autapomophic, ungulate-like and generalized eutherian-like characters. Autapomorphies include striking anthropoid-like characters of the rostrum and dentition. Besides having a basically eutherian-like skull construction, Ocepeia daouiensis is characterized by ungulate-like, and especially paenungulate-like characters of skull and dentition (e.g., selenodonty). However, some plesiomorphies such as absence of hypocone exclude Ocepeia from crown Paenungulata. Such a combination of plesiomorphic and derived characters best fits with a stem position of Ocepeia relative to Paenungulata. In our cladistic analyses Ocepeia is included in Afrotheria, but its shared derived characters with paenungulates are not optimized as exclusive synapomorphies. Rather, within Afrotheria Ocepeia is reconstructed as more closely related to insectivore-like afroinsectiphilians (i.e., aardvarks, sengis, tenrecs, and golden moles) than to paenungulates. This results from conflict with undetected convergences of Paenungulata and Perissodactyla in our cladistic analysis, such as the shared bilophodonty. The selenodont pattern best supports the stem paenungulate position of Ocepeia; that, however, needs further support. The remarkable character mosaic of Ocepeia makes it the first known "transitional fossil" between insectivore-like and ungulate-like afrotherians. In addition, the autapomorphic family Ocepeiidae supports the old--earliest Tertiary or Cretaceous--endemic evolution of placentals in Africa, in contrast to hypotheses rooting afrotherians in Paleogene Laurasian "condylarths".

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Ocepeia daouiensis, Selandian, Phosphate level IIa of Sidi Chennane, Ouled Abdoun Basin, Morocco.MNHN.F PM45, 3 D CT scan modelling of the left periotic in ventral view showing middle ear anatomy (A), transparency showing inner ear anatomy (B) and dorsal (cerebellar) view (C). Abbreviations: cochl can: cochlear canal; fen cochl: fenestra cochleae (f. rotunda); fen vest: fenestra vestibuli (f. ovalis); med: medial; tegm tymp: tegmen tympani; post: posterior; subarcuata foss: subarcuata fossa. Scale bar: 5 mm.
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pone-0089739-g006: Ocepeia daouiensis, Selandian, Phosphate level IIa of Sidi Chennane, Ouled Abdoun Basin, Morocco.MNHN.F PM45, 3 D CT scan modelling of the left periotic in ventral view showing middle ear anatomy (A), transparency showing inner ear anatomy (B) and dorsal (cerebellar) view (C). Abbreviations: cochl can: cochlear canal; fen cochl: fenestra cochleae (f. rotunda); fen vest: fenestra vestibuli (f. ovalis); med: medial; tegm tymp: tegmen tympani; post: posterior; subarcuata foss: subarcuata fossa. Scale bar: 5 mm.

Mentions: Periotic (Figs. 5–6). Both the right and left petrosals are present in MNHN.F PM45, although the structural details in ventral view are poorly preserved. The petrosal of Ocepeia is large and especially long: 1) the pars cochlearis is small and very anterior with a strong rostral tympanic process extending to the level of the anterior margin of the postglenoid process; 2) the pars mastoidea is very long and widely exposed ventrally between posttympanic (squamosal) and paroccipital processes (both separated from about 10 mm). The enlarged pars mastoidea is a remarkable feature of Ocepeia that is shared with proboscideans. The pars cochlearis and promontorium are ovoid, long, and slightly oblique with respect to the longitudinal axis. The promontorium extends posteriorly to the postglenoid process level, and it is more ventral than the basioccipital. It is inflated and located anteriorly. Its almond shape resembles that of Hyopsodus (p). The promontorium has a smooth surface and it bears a stout ridge that is oblique postero-laterally. This ridge is bounded antero-laterally by a sulcus probably for the internal carotid artery (d). The promontorium sulcus for stapedial artery is absent. The rostral tympanic process of the petrosal is salient anteriorly to the promontorium. The epitympanic wing of the periotic medial to the promontorium is absent (p). The fenestra vestibuli (oval window) is very small (area  = 0.312 mm2), and much smaller than the fenestra cochleae. The size of the fenestra vestibuli of Ocepeia daouiensis, and correlatively of its stapes, is well below the regression line for fenestra vestibuli area versus body mass in modern mammals [48]. In fact, the small size of the fenestra vestibuli of Ocepeia daouiensis is in close proportion to Numidotherium koholense[49]. This is a possible derived feature shared with paenungulates, although sirenians show an early divergent trend to hypertrophy of the ear ossicles. It should be noted that the small size of the f. vestibuli correlates with that of the promontorium and inner ear (see below). The fenestra vestibuli is elliptical with a high stapedial ratio (2.05) which is generalized in placentals [42], [50].


Ocepeia (Middle Paleocene of Morocco): the oldest skull of an afrotherian mammal.

Gheerbrant E, Amaghzaz M, Bouya B, Goussard F, Letenneur C - PLoS ONE (2014)

Ocepeia daouiensis, Selandian, Phosphate level IIa of Sidi Chennane, Ouled Abdoun Basin, Morocco.MNHN.F PM45, 3 D CT scan modelling of the left periotic in ventral view showing middle ear anatomy (A), transparency showing inner ear anatomy (B) and dorsal (cerebellar) view (C). Abbreviations: cochl can: cochlear canal; fen cochl: fenestra cochleae (f. rotunda); fen vest: fenestra vestibuli (f. ovalis); med: medial; tegm tymp: tegmen tympani; post: posterior; subarcuata foss: subarcuata fossa. Scale bar: 5 mm.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3935939&req=5

pone-0089739-g006: Ocepeia daouiensis, Selandian, Phosphate level IIa of Sidi Chennane, Ouled Abdoun Basin, Morocco.MNHN.F PM45, 3 D CT scan modelling of the left periotic in ventral view showing middle ear anatomy (A), transparency showing inner ear anatomy (B) and dorsal (cerebellar) view (C). Abbreviations: cochl can: cochlear canal; fen cochl: fenestra cochleae (f. rotunda); fen vest: fenestra vestibuli (f. ovalis); med: medial; tegm tymp: tegmen tympani; post: posterior; subarcuata foss: subarcuata fossa. Scale bar: 5 mm.
Mentions: Periotic (Figs. 5–6). Both the right and left petrosals are present in MNHN.F PM45, although the structural details in ventral view are poorly preserved. The petrosal of Ocepeia is large and especially long: 1) the pars cochlearis is small and very anterior with a strong rostral tympanic process extending to the level of the anterior margin of the postglenoid process; 2) the pars mastoidea is very long and widely exposed ventrally between posttympanic (squamosal) and paroccipital processes (both separated from about 10 mm). The enlarged pars mastoidea is a remarkable feature of Ocepeia that is shared with proboscideans. The pars cochlearis and promontorium are ovoid, long, and slightly oblique with respect to the longitudinal axis. The promontorium extends posteriorly to the postglenoid process level, and it is more ventral than the basioccipital. It is inflated and located anteriorly. Its almond shape resembles that of Hyopsodus (p). The promontorium has a smooth surface and it bears a stout ridge that is oblique postero-laterally. This ridge is bounded antero-laterally by a sulcus probably for the internal carotid artery (d). The promontorium sulcus for stapedial artery is absent. The rostral tympanic process of the petrosal is salient anteriorly to the promontorium. The epitympanic wing of the periotic medial to the promontorium is absent (p). The fenestra vestibuli (oval window) is very small (area  = 0.312 mm2), and much smaller than the fenestra cochleae. The size of the fenestra vestibuli of Ocepeia daouiensis, and correlatively of its stapes, is well below the regression line for fenestra vestibuli area versus body mass in modern mammals [48]. In fact, the small size of the fenestra vestibuli of Ocepeia daouiensis is in close proportion to Numidotherium koholense[49]. This is a possible derived feature shared with paenungulates, although sirenians show an early divergent trend to hypertrophy of the ear ossicles. It should be noted that the small size of the f. vestibuli correlates with that of the promontorium and inner ear (see below). The fenestra vestibuli is elliptical with a high stapedial ratio (2.05) which is generalized in placentals [42], [50].

Bottom Line: This results from conflict with undetected convergences of Paenungulata and Perissodactyla in our cladistic analysis, such as the shared bilophodonty.The selenodont pattern best supports the stem paenungulate position of Ocepeia; that, however, needs further support.In addition, the autapomorphic family Ocepeiidae supports the old--earliest Tertiary or Cretaceous--endemic evolution of placentals in Africa, in contrast to hypotheses rooting afrotherians in Paleogene Laurasian "condylarths".

View Article: PubMed Central - PubMed

Affiliation: Centre de Recherches sur la Paléobiodiversité et les Paléoenvironnements, CNRS-MNHN-UPMC, Muséum National d'Histoire Naturelle, Dpnt Histoire de la Terre, Paris, France.

ABSTRACT
While key early(iest) fossils were recently discovered for several crown afrotherian mammal orders, basal afrotherians, e.g., early Cenozoic species that comprise sister taxa to Paenungulata, Afroinsectiphilia or Afrotheria, are nearly unknown, especially in Africa. Possible stem condylarth-like relatives of the Paenungulata (hyraxes, sea-cows, elephants) include only Abdounodus hamdii and Ocepeia daouiensis from the Selandian of Ouled Abdoun Basin, Morocco, both previously only documented by lower teeth. Here, we describe new fossils of Ocepeia, including O.grandis n. sp., and a sub-complete skull of O. daouiensis, the first known before the Eocene for African placentals. O.daouiensis skull displays a remarkable mosaic of autapomophic, ungulate-like and generalized eutherian-like characters. Autapomorphies include striking anthropoid-like characters of the rostrum and dentition. Besides having a basically eutherian-like skull construction, Ocepeia daouiensis is characterized by ungulate-like, and especially paenungulate-like characters of skull and dentition (e.g., selenodonty). However, some plesiomorphies such as absence of hypocone exclude Ocepeia from crown Paenungulata. Such a combination of plesiomorphic and derived characters best fits with a stem position of Ocepeia relative to Paenungulata. In our cladistic analyses Ocepeia is included in Afrotheria, but its shared derived characters with paenungulates are not optimized as exclusive synapomorphies. Rather, within Afrotheria Ocepeia is reconstructed as more closely related to insectivore-like afroinsectiphilians (i.e., aardvarks, sengis, tenrecs, and golden moles) than to paenungulates. This results from conflict with undetected convergences of Paenungulata and Perissodactyla in our cladistic analysis, such as the shared bilophodonty. The selenodont pattern best supports the stem paenungulate position of Ocepeia; that, however, needs further support. The remarkable character mosaic of Ocepeia makes it the first known "transitional fossil" between insectivore-like and ungulate-like afrotherians. In addition, the autapomorphic family Ocepeiidae supports the old--earliest Tertiary or Cretaceous--endemic evolution of placentals in Africa, in contrast to hypotheses rooting afrotherians in Paleogene Laurasian "condylarths".

Show MeSH
Related in: MedlinePlus