Hesham M. Sallam

Fossil and molecular evidence constrain scenarios for the early evolutionary and biogeographic history of hystricognathous rodents

The early evolutionary and paleobiogeographic history of the diverse rodent clade Hystricognathi, which contains Hystricidae (Old World porcupines), Caviomorpha (the endemic South American rodents), and African Phiomorpha (cane rats, dassie rats, and blesmols) is of great interest to students of mammalian evolution, but remains poorly understood because of a poor early fossil record. Here we describe the oldest well-dated hystricognathous rodents from an earliest late Eocene (≈37 Ma) fossil locality in the Fayum Depression of northern Egypt. These taxa exhibit a combination of primitive and derived features, the former shared with Asian “baluchimyine” rodents, and the latter shared with Oligocene phiomorphs and caviomorphs. Phylogenetic analysis incorporating morphological, temporal, geographic, and molecular information places the new taxa as successive sister groups of crown Hystricognathi, and supports an Asian origin for stem Hystricognathi and an Afro-Arabian origin for crown Hystricognathi, stem Hystricidae, and stem Caviomorpha. Molecular dating of early divergences within Hystricognathi, using a Bayesian “relaxed clock” approach and multiple fossil calibrations, suggests that the split between Hystricidae and the phiomorph-caviomorph clade occurred ≈39 Ma, and that phiomorphs and caviomorphs diverged ≈36 Ma. These results are remarkably congruent with our phylogenetic results and the fossil record of hystricognathous rodent evolution in Afro-Arabia and South America.

A fossil primate of uncertain affinities from the earliest late Eocene of Egypt

Paleontological work carried out over the last 3 decades has established that three major primate groups were present in the Eocene of Africa—anthropoids, adapiforms, and advanced strepsirrhines. Here we describe isolated teeth of a previously undocumented primate from the earliest late Eocene (≈37 Ma) of northern Egypt, Nosmips aenigmaticus, whose phylogenetic placement within Primates is unclear. Nosmips is smaller than the sympatric adapiform Afradapis but is considerably larger than other primate taxa known from the same paleocommunity. The species bears an odd mosaic of dental features, combining enlarged, elongate, and molariform premolars with simple upper molars that lack hypocones. Phylogenetic analysis across a series of different assumption sets variously places Nosmips as a stem anthropoid, a nonadapiform stem strepsirrhine, or even among adapiforms. This phylogenetic instability suggests to us that Nosmips likely represents a highly specialized member of a previously undocumented, and presumably quite ancient, endemic African primate lineage, the subordinal affinities of which have been obscured by its striking dental autapomorphies. Discriminant functions based on measurements of lower molar size and topography reliably classify extant prosimian primates into their correct dietary groups and identify Nosmips and Afradapis as omnivores and folivores, respectively. Although Nosmips currently defies classification, this strange and unexpected fossil primate nevertheless provides additional evidence for high primate diversity in northern Africa ≈37 million years ago and further underscores the fact that our understanding of early primate evolution on that continent remains highly incomplete.

A large-bodied anomaluroid rodent from the earliest late Eocene of Egypt: phylogenetic and biogeographic implications

ABSTRACT A new genus and species of anomaluroid rodent, Kabirmys qarunensis, is described based on isolated teeth, partial mandibles, and an edentulous partial maxilla from the earliest late Eocene Birket Qarun Locality 2 (BQ-2) in the Fayum Depression of northern Egypt. Kabirmys is the largest known Paleogene anomaluroid, with first lower molar area being about 2.5 times that of the roughly contemporaneous Nementchamys and Pondaungimys from Algeria and Myanmar, respectively. The genus exhibits distinctive features not seen in other Paleogene taxa, such as a complete mure, weak neo-endoloph, and open lingual sinus on the upper molars; Kabirmys lacks the complex enamel crenulations seen in Nementchamys and Pondaungimys. Phylogenetic analysis of dental features nests Kabirmys within crown Anomaluridae as a sister taxon of Nementchamys and Pondaungimys, but parsimony analysis following addition of a chronobiogeographic character places all of these taxa as basal stem members of Anomaluridae. This new evidence indicates that there was considerable diversity in body size and molar morphology among African anomaluroids near the middle-late Eocene boundary, and suggests that the group had an ancient origin on that landmass. Kabirmys shares some primitive features with the possible zegdoumyid ‘Glibia’ namibiensis from the Paleogene of Namibia, and suggests that anomaluroids might be derived from a zegdoumyid-like ancestor. The disappearance of anomaluroids in the upper (latest Eocene to early Oligocene) levels of the Fayum succession might be related to global cooling through the later Paleogene, which might have removed suitable habitats from northern Africa.

New phiomorph rodents from the latest Eocene of Egypt, and the impact of Bayesian “clock”-based phylogenetic methods on estimates of basal hystricognath relationships and biochronology

The Fayum Depression of Egypt has yielded fossils of hystricognathous rodents from multiple Eocene and Oligocene horizons that range in age from ∼37 to ∼30 Ma and document several phases in the early evolution of crown Hystricognathi and one of its major subclades, Phiomorpha. Here we describe two new genera and species of basal phiomorphs, Birkamys korai and Mubhammys vadumensis, based on rostra and maxillary and mandibular remains from the terminal Eocene (∼34 Ma) Fayum Locality 41 (L-41). Birkamys is the smallest known Paleogene hystricognath, has very simple molars, and, like derived Oligocene-to-Recent phiomorphs (but unlike contemporaneous and older taxa) apparently retained dP4∕4 late into life, with no evidence for P4∕4 eruption or formation. Mubhammys is very similar in dental morphology to Birkamys, and also shows no evidence for P4∕4 formation or eruption, but is considerably larger. Though parsimony analysis with all characters equally weighted places Birkamys and Mubhammys as sister taxa of extant Thryonomys to the exclusion of much younger relatives of that genus, all other methods (standard Bayesian inference, Bayesian “tip-dating,” and parsimony analysis with scaled transitions between “fixed” and polymorphic states) place these species in more basal positions within Hystricognathi, as sister taxa of Oligocene-to-Recent phiomorphs. We also employ tip-dating as a means for estimating the ages of early hystricognath-bearing localities, many of which are not well-constrained by geological, geochronological, or biostratigraphic evidence. By simultaneously taking into account phylogeny, evolutionary rates, and uniform priors that appropriately encompass the range of possible ages for fossil localities, dating of tips in this Bayesian framework allows paleontologists to move beyond vague and assumption-laden “stage of evolution” arguments in biochronology to provide relatively rigorous age assessments of poorly-constrained faunas. This approach should become increasingly robust as estimates are combined from multiple independent analyses of distantly related clades, and is broadly applicable across the tree of life; as such it is deserving of paleontologists’ close attention. Notably, in the example provided here, hystricognathous rodents from Libya and Namibia that are controversially considered to be of middle Eocene age are instead estimated to be of late Eocene and late Oligocene age, respectively. Finally, we reconstruct the evolution of first lower molar size among Paleogene African hystricognaths using a Bayesian approach; the results of this analysis reconstruct a rapid latest Eocene dwarfing event along the lineage leading to Birkamys.

A Revision of the Upper Cretaceous Lepidosirenid Lungfishes from the Quseir Formation, Western Desert, Central Egypt

ABSTRACT We evaluate new lungfish remains from the Upper Cretaceous Quseir Formation in the Western Dessert of southern Egypt. Taxa include Lavocatodus protopteroides, L. humei, L. giganteus, and Protopterus nigeriensis. We treat Lavocatodus as members of Lepidosirenidae based on the presence of a well-defined medial articular surface, in the absence of a symphyseal surface of corresponding prearticular bones. Material of L. protopteroides represents the first example of an adult specimen, supporting the retention of the species as valid, and not a junior synonym of L. humei. Specimens of L. humei are the most abundant in the assemblage, and all exhibit the medial articular surface, a feature that is absent from specimens of Ceratodus; therefore, we reassign additional specimens of ‘C.’ humei to Lavocatodus. New specimens of L. giganteus extend the temporal and spatial ranges of the species (the type material of L. giganteus is from Paleocene deposits of In Farghas, Mali). Finally, a new specimen of Protopterus represents the oldest record of the genus in Egypt. The prearticular is confidently assigned to Protopterus based on the presence of only three ridges on the tooth plate, a medial symphyseal suture, a coronoid process, and a shallow tooth crown plus prearticular depth. We further assign it to P. nigeriensis based the length and merger of tooth ridges. Furthermore, the oldest Cenomanian specimens reported from the Sudan Wadi Milk Formation are assigned to P. nigeriensis, which would extend the temporal range of P. nigeriensis by roughly 14 Ma.

Ancient phylogenetic divergence of the enigmatic African rodent Zenkerella and the origin of anomalurid gliding

The “scaly-tailed squirrels” of the rodent family Anomaluridae have a long evolutionary history in Africa, and are now represented by two gliding genera (Anomalurus and Idiurus) and a rare and obscure genus (Zenkerella) that has never been observed alive by mammalogists. Zenkerella shows no anatomical adaptations for gliding, but has traditionally been grouped with the glider Idiurus on the basis of craniodental similarities, implying that either the Zenkerella lineage lost its gliding adaptations, or that Anomalurus and Idiurus evolved theirs independently. Here we present the first nuclear and mitochondrial DNA sequences of Zenkerella, based on recently recovered whole-body specimens from Bioko Island (Equatorial Guinea), which show unambiguously that Zenkerella is the sister taxon of Anomalurus and Idiurus. These data indicate that gliding likely evolved only once within Anomaluridae, and that there were no subsequent evolutionary reversals. We combine this new molecular evidence with morphological data from living and extinct anomaluromorph rodents and estimate that the lineage leading to Zenkerella has been evolving independently in Africa since the early Eocene, approximately 49 million years ago. Recently discovered fossils further attest to the antiquity of the lineage leading to Zenkerella, which can now be recognized as a classic example of a “living fossil,” about which we know remarkably little. The osteological markers of gliding are estimated to have evolved along the stem lineage of the Anomalurus–Idiurus clade by the early Oligocene, potentially indicating that this adaptation evolved in response to climatic perturbations at the Eocene–Oligocene boundary (∼34 million years ago).

New adapiform primate fossils from the late Eocene of Egypt

Abstract Caenopithecine adapiform primates are currently represented by two genera from the late Eocene of Egypt (Afradapis and Aframonius) and one from the middle Eocene of Switzerland (Caenopithecus). All are somewhat anthropoid-like in several aspects of their dental and gnathic morphology, and are inferred to have been highly folivorous. Here we describe a new caenopithecine genus and species, Masradapis tahai, from the ~37 million-year-old Locality BQ-2 in Egypt, that is represented by mandibular and maxillary fragments and isolated teeth. Masradapis is approximately the same size as Aframonius but differs in having a more dramatic distal increase in molar size, more complex upper molar shearing crests, and an exceptionally deep mandibular corpus. We also describe additional mandibles and part of the orbit and rostrum of Aframonius which suggest that it was probably diurnal. Phylogenetic analyses place Masradapis either as the sister taxon of Aframonius (parsimony), or as the sister taxon of Afradapis and Caenopithecus (Bayesian methods). Bayesian tip-dating analysis, when combined with Bayesian biogeographic analysis, suggests that a common ancestor of known caenopithecines dispersed to Afro-Arabia from Europe between 49.4 and 47.4 Ma, and that a trans-Tethyan back-dispersal explains Caenopithecus’ later presence in Europe. For Masradapis: https://www.zoobank.org/urn:lsid:zoobank.org:act:41BC8459-7CCE-487F-BC59-1C34257D5C4E For Masradapis tahai: https://www.zoobank.org/urn:lsid:zoobank.org:act:C0A620AD-6FCA-4649-A980-FCA237AFE39D

Dental Eruption and Growth in Hyracoidea (Mammalia, Afrotheria)

ABSTRACT We investigated dental homologies, development, and growth in living and fossil hyracoids and tested if hyracoids and other mammals show correlations between eruption patterns, gestation time, and age at maturity. Unlike living species, fossil hyracoids simultaneously possess replaced P1 and canine teeth. Fossil species also have shorter crowns, an I3/i3, I2, and a hypoconulid on m3. Prenatal specimens of the living Procavia capensis and Heterohyrax brucei show up to three tooth buds posterior to dI1 and anterior to the seven upper cheek teeth that consistently erupt; erupted teeth include an anterior premolar but not a canine. Most lower cheek teeth finish eruption during growth in hyracoids, not after growth as in most other afrotherians. All hyracoids show the m1 at (lower) or near (upper) the beginning of eruption of permanent teeth; M3/m3 is the last permanent tooth to erupt. The living P. capensis erupts most lower antemolar loci before m2. In contrast, fossil hyraxes erupt lower antemolars after m2. Although the early eruption of antemolars correlates with increased gestation time and age at maturity in primates and Tupaia (i.e., ‘Schultzs rule’), and although modern hyraxes resemble some anthropoid primates in exhibiting long gestation and eruption of antemolars at or before molars, eruption patterns do not significantly covary with either life history parameter among afrotherians sampled so far. However, we do observe a shift in eruption timing and crown height in Procavia relative to fossil hyracoids, mirroring observations recently made for other ungulate-grade mammals.

New Egyptian sauropod reveals Late Cretaceous dinosaur dispersal between Europe and Africa

Prominent hypotheses advanced over the past two decades have sought to characterize the Late Cretaceous continental vertebrate palaeobiogeography of Gondwanan landmasses, but have proved difficult to test because terrestrial vertebrates from the final ~30 million years of the Mesozoic are extremely rare and fragmentary on continental Africa (including the then-conjoined Arabian Peninsula but excluding the island of Madagascar). Here we describe a new titanosaurian sauropod dinosaur, Mansourasaurus shahinae gen. et sp. nov., from the Upper Cretaceous (Campanian) Quseir Formation of the Dakhla Oasis of the Egyptian Western Desert. Represented by an associated partial skeleton that includes cranial elements, Mansourasaurus is the most completely preserved land-living vertebrate from the post-Cenomanian Cretaceous (~94–66 million years ago) of the African continent. Phylogenetic analyses demonstrate that Mansourasaurus is nested within a clade of penecontemporaneous titanosaurians from southern Europe and eastern Asia, thereby providing the first unambiguous evidence for a post-Cenomanian Cretaceous continental vertebrate clade that inhabited both Africa and Europe. The close relationship of Mansourasaurus to coeval Eurasian titanosaurians indicates that terrestrial vertebrate dispersal occurred between Eurasia and northern Africa after the tectonic separation of the latter from South America ~100 million years ago. These findings counter hypotheses that dinosaur faunas of the African mainland were completely isolated during the post-Cenomanian Cretaceous.A new titanosaurian sauropod, Mansourasaurus, is the most complete terrestrial vertebrate from the post-Cenomanian Cretaceous of the African mainland. Phylogenetic analyses reveal the existence of a titanosaurian clade inhabiting both Africa and Europe at this time and a faunal connection between the two continents.

A New Genus and Species of Marine Catfishes (Siluriformes; Ariidae) From the Upper Eocene Birket Qarun Formation, Wadi El-Hitan, Egypt

Wadi El-Hitan, the UNESCO World Heritage Site, of the Fayum Depression in the northeast part of the Western Desert of Egypt, has produced a remarkable collection of Eocene vertebrates, in particular the fossil whales from which it derives its name. Here we describe a new genus and species of marine catfishes (Siluriformes; Ariidae), Qarmoutus hitanensis, from the base of the upper Eocene Birket Qarun Formation, based on a partial neurocranium including the complete left side, partial right dentary, left suspensorium, two opercles, left pectoral girdle and spine, nuchal plates, first and second dorsal spines, Weberian apparatus and a disassociated series of abdominal vertebrae. All of the elements belong to the same individual and some of them were found articulated. Qarmoutus gen. nov. is the oldest and the most complete of the Paleogene marine catfishes unearthed from the Birket Qarun Formation. The new genus exhibits distinctive features not seen in other African Paleogene taxa, such as different sculpturing on the opercle and pectoral girdle with respect to that on the neurocranium and nuchal plates, denticulate ornamentation on the skull bones arranged in longitudinal rows and forming a radiating pattern on the sphenotic, pterotic, extrascapular and the parieto-supraoccipital, indentations or pitted ornamentation on the nuchal plates as well as the parieto-supraoccipital process, strut-like radiating pattern of ornamentation on the opercle from the proximal articulation to margins, longitudinal, curved, reticulate ridges and tubercular ornamentations on the cleithrum, sinuous articulation between the parieto-supraoccipital process and the anterior nuchal plate, long, narrow, and arrowhead shaped nuchal shield, very small otic capsules restricted to the prootic. Multiple parsimony and Bayesian morphological phylogenetic analyses of Ariidae, run with and without “molecular scaffolds”, yield contradictory results for the placement of Qarmoutus; the genus is either a phylogenetically basal ariid, or it is deeply nested within the ariid clade containing New World species of Sciades.