Petrosal and bony labyrinth morphology of the stem paenungulate mammal (Paenungulatomorpha) Ocepeia daouiensis from the Paleocene of Morocco.

Based on high-resolution computed tomography, we describe in detail the petrosal and inner ear anatomy of one of the few known African stem paenungulates (Paenungulatomorpha), Ocepeia daouiensis from the Selandian of the Ouled Abdoun phosphate basin (Morocco). The petrosal of Ocepeia displays some remarkable, probably derived features (among eutherians) such as relatively small pars cochlearis, pars canalicularis labyrinth (including small semicircular canals), a large wing-like pars mastoidea, a large and inflated tegmen tympani, and the dorsoventral orientation of the large canal for the ramus superior. The presence of small semicircular canals in Ocepeia is an interesting shared trait with tenrecoidean afrotherians. Otherwise, and consistent with a general primitive skull morphology, the middle ear and labyrinth of Ocepeia daouiensis is characterised by many plesiomorphic traits close to the eutherian generalised plan. This adds to the rather generalised morphology of the earliest crown paenungulates such as Eritherium, Phosphatherium and Seggeurius to support an ancestral paenungulatomorph morphotype poorly derived from the eutherian pattern. As a result, Ocepeia provides key morphological and fossil data to test phylogenetic relationships of the Afrotheria (including Paenungulatomorpha) at the placental root mostly inferred from molecular studies.

Early African Fossils Elucidate the Origin of Embrithopod Mammals.

Modern mammals rapidly evolved in the early Cenozoic in all continental provinces, including in Africa, with one of the first placental branches, the Afrotheria [1, 2]. Afrotherian evolution is at the origin of the major radiation of African ungulate-like mammals, including extant hyrax, elephant, and sea cow orders, which all belong to the Paenungulata. The paenungulate radiation also includes the extinct order Embrithopoda of uncertain interordinal relationships, which is best known for the giant and strangely specialized Oligocene genus Arsinoitherium. The Ouled Abdoun basin, Morocco, yielded exceptional Paleocene-Eocene fossils documenting the early paenungulate evolution [3-8]. Here we report two new small Ypresian species, Stylolophus minor n.g., n.sp. and cf. Stylolophus sp., which are the earliest and most primitive embrithopods. The cladistic analysis relates the Embrithopoda to crown paenungulates as the stem-group of the Tethytheria, which makes crown tethytherians restricted to extant elephant and sea cow orders. The Embrithopoda is therefore an early tethytherian offshoot predating the elephant and sea cow divergence. The resulting phylogeny supports a strictly African early radiation of the paenungulates excluding the Phenacolophidae and Anthracobunia. It sustains an at least early Paleocene African origin of the Embrithopoda. The unique tooth pattern of the embrithopods (hyperdilambdodont and pseudolophodont molars) is resolved as evolving early and directly from the dilambdodont (W-shaped labial molar crests) ancestral paenungulate morphotype. The specialized upper molar morphology with two transverse crests is convergent and non-homologous in embrithopods and crown Tethytheria. These convergences for specialized folivorous diet were driven by free herbivorous African niches in the early Paleogene.

A unique Cretaceous-Paleogene lineage of piranha-jawed pycnodont fishes.

The extinct group of the Pycnodontiformes is one of the most characteristic components of the Mesozoic and early Cenozoic fish faunas. These ray-finned fishes, which underwent an explosive morphological diversification during the Late Cretaceous, are generally regarded as typical shell-crushers. Here we report unusual cutting-type dentitions from the Paleogene of Morocco which are assigned to a new genus of highly specialized pycnodont fish. This peculiar taxon represents the last member of a new, previously undetected 40-million-year lineage (Serrasalmimidae fam. nov., including two other new genera and Polygyrodus White, 1927) ranging back to the early Late Cretaceous and leading to exclusively carnivorous predatory forms, unique and unexpected among pycnodonts. Our discovery indicates that latest Cretaceous-earliest Paleogene pycnodonts occupied more diverse trophic niches than previously thought, taking advantage of the apparition of new prey types in the changing marine ecosystems of this time interval. The evolutionary sequence of trophic specialization characterizing this new group of pycnodontiforms is strikingly similar to that observed within serrasalmid characiforms, from seed- and fruit-eating pacus to flesh-eating piranhas.

Convergence of Afrotherian and Laurasiatherian Ungulate-Like Mammals: First Morphological Evidence from the Paleocene of Morocco.

Molecular-based analyses showed that extant "ungulate" mammals are polyphyletic and belong to the two main clades Afrotheria (Paenungulata) and Laurasiatheria (Euungulata: Cetartiodactyla-Perissodactyla). However, paleontological and neontological studies hitherto failed to demonstrate the morphological convergence of African and Laurasian "ungulate" orders. They support an "Altungulata" group including the Laurasian order Perissodactyla and the African superorder Paenungulata and characterized especially by quadritubercular and bilophodont molars adapted for a folivorous diet. We report new critical fossils of one of the few known African condylarth-like mammal, the enigmatic Abdounodus from the middle Paleocene of Morocco. They show that Abdounodus and Ocepeia display key intermediate morphologies refuting the homology of the fourth main cusp of upper molars in Paenungulata and Perissodactyla: Paenungulates unexpectedly have a metaconule-derived pseudohypocone, instead of a cingular hypocone. Comparative and functional dental anatomy of Abdounodus demonstrates indeed the convergence of the quadritubercular and bilophodont pattern in "ungulates". Consistently with our reconstruction of the structural evolution of paenungulate bilophodonty, the phylogenetic analysis relates Abdounodus and Ocepeia to Paenungulata as stem taxa of the more inclusive new clade Paenungulatomorpha which is distinct from the Perissodactyla and Anthracobunidae. Abdounodus and Ocepeia help to identify the first convincing synapomorphy within the Afrotheria-i.e., the pseudohypocone-that demonstrates the morphological convergence of African and Laurasian ungulate-like placentals, in agreement with molecular phylogeny. Abdounodus and Ocepeia are the only known representatives of the early African ungulate radiation predating the divergence of extant paenungulate orders. Paenungulatomorpha evolved in Africa since the early Tertiary independently from laurasiatherian euungulates and "condylarths" such as apheliscids. The rapid early Tertiary radiation of the Afrotheria and Paenungulatomorpha, as illustrated by the Paleocene Moroccan mammals, is concurrent with that of the Laurasiatheria in a general, explosive mammal evolution in both the South and North Tethyan continents following the K/Pg event.

Testing for Depéret's Rule (Body Size Increase) in Mammals using Combined Extinct and Extant Data.

Whether or not evolutionary lineages in general show a tendency to increase in body size has often been discussed. This tendency has been dubbed "Cope's rule" but because Cope never hypothesized it, we suggest renaming it after Depéret, who formulated it clearly in 1907. Depéret's rule has traditionally been studied using fossil data, but more recently a number of studies have used present-day species. While several paleontological studies of Cenozoic placental mammals have found support for increasing body size, most studies of extant placentals have failed to detect such a trend. Here, we present a method to combine information from present-day species with fossil data in a Bayesian phylogenetic framework. We apply the method to body mass estimates of a large number of extant and extinct mammal species, and find strong support for Depéret's rule. The tendency for size increase appears to be driven not by evolution toward larger size in established species, but by processes related to the emergence of new species. Our analysis shows that complementary data from extant and extinct species can greatly improve inference of macroevolutionary processes.

The ear region of earliest known elephant relatives: new light on the ancestral morphotype of proboscideans and afrotherians.

One of the last major clades of placental mammals recognized was the Afrotheria, which comprises all main endemic African mammals. This group includes the ungulate-like paenungulates, and among them the elephant order Proboscidea. Among afrotherians, the petrosal anatomy remains especially poorly known in Proboscidea. We provide here the first comparative CT scan study of the ear region of the two earliest known proboscideans (and paenungulates), Eritherium and Phosphatherium, from the mid Palaeocene and early Eocene of Morocco. It is helpful to characterize the ancestral morphotype of Proboscidea to understand petrosal evolution within proboscideans and afrotherians. The petrosal structure of these two taxa shows several differences. Eritherium is more primitive than Phosphatherium and closer to the basal paenungulate Ocepeia in several traits (inflated tegmen tympani, very deep fossa subarcuata and ossified canal for ramus superior of stapedial artery). Phosphatherium, however, retains plesiomorphies such as a true crus commune secundaria. A cladistic analysis of petrosal traits of Eritherium and Phosphatherium among Proboscidea results in a single tree with a low level of homoplasy in which Eritherium, Phosphatherium and Numidotherium are basal. This contrasts with previous phylogenetic studies showing homoplasy in petrosal evolution among Tethytheria. It suggests that evolutionary modalities of petrosal characters differ with the taxonomic level among Afrotheria: noticeable convergences occurred among the paenungulate orders, whereas little homoplasy seems to have occurred at intra-ordinal level in orders such as Proboscidea. Most petrosal features of both Eritherium and Phosphatherium are primitive. The ancestral petrosal morphotype of Proboscidea was not specialized but was close to the generalized condition of paenungulates, afrotherians, and even eutherians. This is consistent with cranial and dental characters of Eritherium, suggesting that the ancestral morphotypes of the different paenungulate orders were close to each other. Specializations occurred rapidly after the ordinal radiation of Paenungulata.

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

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".

A radiation of arboreal basal eutherian mammals beginning in the Late Cretaceous of India.

India's Late Cretaceous fossil mammals include the only undisputed pre-Tertiary Gondwanan eutherians, such as Deccanolestes. Recent studies have suggested a relationship between Deccanolestes and African and European Paleocene adapisoriculids, which have been variably identified as stem euarchontans, stem primates, lipotyphlan insectivores, or afrosoricids. Support for a close relationship between Deccanolestes and any of these placental mammal clades would be unique in representing a confirmed Mesozoic record of a placental mammal. However, some paleogeographic reconstructions place India at its peak isolation from all other continents during the latest Cretaceous, complicating reconstructions of the biogeographic history of the placental radiation. Recent fieldwork in India has recovered dozens of better-preserved specimens of Cretaceous eutherians, including several new species. Here, we incorporate these new specimens into an extensive phylogenetic analysis that includes every clade with a previously hypothesized relationship to Deccanolestes. Our results support a robust relationship between Deccanolestes and Paleocene adapisoriculids, but do not support a close affinity between these taxa and any placental clade, demonstrating that Deccanolestes is not a Cretaceous placental mammal and reinforcing the sizeable gap between molecular and fossil divergence time estimates for the placental mammal radiation. Instead, our expanded data push Adapisoriculidae, including Deccanolestes, into a much more basal position than in earlier analyses, strengthening hypotheses that scansoriality and arboreality were prevalent early in eutherian evolution. This comprehensive phylogeny indicates that faunal exchange occurred between India, Africa, and Europe in the Late Cretaceous-Early Paleocene, and suggests a previously unrecognized ∼30 to 45 Myr "ghost lineage" for these Gondwanan eutherians.

The oldest modern therian mammal from Europe and its bearing on stem marsupial paleobiogeography.

We report the discovery of mammalian tribosphenic teeth from the basal Cenomanian of southwestern France that we refer to a new primitive marsupial-like form identified as a basal taxon of Marsupialiformes, a new clade recognized here to include the crown group Marsupialia and primitive stem lineages more closely related to Marsupialia than to Deltatheroida. Arcantiodelphys marchandi gen et sp nov. shares several significant marsupial-like features (s.l.) with marsupialiform taxa known from the North American Mid-Cretaceous. Among marsupialiforms, it shows a closer resemblance to Dakotadens. This resemblance, which is plesiomorphic within "tribotherians," makes Arcantiodelphys one of the most archaic known Marsupialiformes. Moreover, Arcantiodelphys is characterized by an original and precocious crushing specialization. Both the plesiomorphic and autapomorphic characteristics of Arcantiodelphys among Marsupialiformes might be explained by an Eastern origin from Asian stem metatherians, with some in situ European evolution. In addition, the presence of a mammal with North American affinities in western Europe during the early Late Cretaceous provides further evidence of a large Euramerican biogeographical province at this age or slightly before. Concerning the paleobiogeographical history of the first stem marsupialiforms during the Albian-Cenomanian interval, 2 possible dispersal routes from an Asian metatherian ancestry can be proposed: Asia to Europe via North America and Asia to North America via Europe. The main significance of the Archingeay-Les Nouillers mammal discovery is that it indicates that the beginning of the stem marsupialiforms history involved not only North America but also Europe, and that this early history in Europe remains virtually unknown.

Paleocene emergence of elephant relatives and the rapid radiation of African ungulates.

Elephants are the only living representatives of the Proboscidea, a formerly diverse mammalian order whose history began with the 55-million years (mys) old Phosphatherium. Reported here is the discovery from the early late Paleocene of Morocco, ca. 60 mys, of the oldest and most primitive elephant relative, Eritherium azzouzorum n.g., n.sp., which is one of the earliest known representatives of modern placental orders. This well supported stem proboscidean is extraordinarily primitive and condylarth-like. It provides the first dental evidence of a resemblance between the proboscideans and African ungulates (paenungulates) on the one hand and the louisinines and early macroscelideans on the other. Eritherium illustrates the origin of the elephant order at a previously unknown primitive stage among paenungulates and "ungulates." The primitive morphology of Eritherium suggests a recent and rapid paenungulate radiation after the Cretaceous-Tertiary boundary, probably favoured by early endemic African paleoecosystems. At a broader scale, Eritherium provides a new old calibration point of the placental tree and supports an explosive placental radiation. The Ouled Abdoun basin, which yields the oldest known African placentals, is a key locality for elucidating phylogeny and early evolution of paenungulates and other related endemic African lineages.