Bony-toothed birds (Pelagornithidae) were among the largest volant birds, but their representatives from the upper size range have so far been known only from very fragmentary fossils. Here we report an exceptionally well-preserved giant species from the late Miocene of the Bahía Inglesa Formation in northern Chile, in which most major limb bones are complete and uncrushed. The fossil has the longest wing skeleton of any bird, and its wingspan in life was at least 5.2 m. Mass estimates of 16–29 kg are, however, surprisingly low and within the range of large extant volant birds, or only moderately above. The fossil constitutes the most substantial record of the Pelagornithidae (bony-toothed birds), and is assigned to a new species, Pelagornis chilensis. It is one of the largest known pelagornithids and the three-dimensionally preserved bones allow recognition of many previously unknown osteological features, especially concerning the vertebrae, pectoral girdle, and limb elements. We revise the taxonomy of Neogene pelagornithids and propose classification of all Miocene and Pliocene species into a single genus, Pelagornis. Osteological features are highlighted in which giant Neogene Pelagornithidae differ from their smaller Palaeogene relatives.

The few records of Jurassic fishes from Antarctica comprise several actinopterygians. Here we describe the first fish material recovered from the Latady Group, upper Middle to lower Upper Jurassic southern Antarctic Peninsula—one indeterminate actinopterygian and two teleosts, including a Leptolepidae indet. The content of the family Leptolepidae is revised and the assignment of Leptolepidae indet. to family level is based on three uniquely derived characters proposed here (vertebrae with thin and smooth autocentra; autocentra and chordacentra not constricting the notochord; and lack of cavities for adipose tissue in the walls of the autocentra). The new finding changes previous interpretations that Leptolepidae s. str. is a Northern Hemisphere family. The presence of Middle Jurassic leptolepids in Antarctica as well as in the Lower Jurassic of Chile, South America, supports the hypothesis that during Jurassic times more than one center of diversification of teleost fishes were operating in far distant regions of the world. Amongst the new material are the oldest marine teleosts (middle—late Callovian to early Kimmeridgian) recovered from Antarctica. They represent the most southern distribution of teleosts during the Jurassic.

A new species of Enchodus (Aulopiformes: Enchodontidae) is described from a quarry exposure of the La Negra facies of the El Doctor Formation (Cretaceous: Albian to Cenomanian) in the state of Hidalgo, central México. It is an elongate fish with many generic and familial characters, including dermal ornamentation of tubercles atop rows of ridges; a palatine with a single, large tooth; and a triangular preopercle. It has a number of unique characters that include the presence of an orbitosphenoid, absence of dorsal scutes, and dorsal fin rays that share common pterygiophores. A phylogenetic analysis places the new species as the sister to Enchodus gladiolus. The new species of Enchodus is the most abundant fish species at the locality. Using mandible length as an indicator of overall size, the range in lengths suggests that this species lived at or near the locality. This is further supported by other species that have individuals of large and small sizes.

Much of Mesozoic diversity within the lungfishes (Osteichthyes: Dipnoi) has traditionally been relegated to the genus Ceratodus, primarily on the basis of the highly stereotypical dental plates characteristic of post-Devonian lungfishes. The new genus Potamoceratodus contains the single species P. guentheri (Marsh, 1878), comb. nov. Newly discovered material allows clarification of the features of this species, including description of a complete skull roof and partial palate. The new genus can be differentiated from the European Ceratodus on the basis of characters of the skull roof, palate, and dentition, including lack of tubercular ornamentation of the skull roof, modest convexity of the dorsal skull roof, absence of sensory sulci anteriorly in the EF bone, and an enlarged and elongate anterior odontode series on the pterygoid dental plate. The North American Ceratodus record is reexamined in light of more complete material from the Temple Canyon localities of the Morrison Formation of Colorado, USA. Ceratodus is found to be an assemblage of forms with disparate cranial morphology. The succession of North American lungfish communities in the late Paleozoic and Mesozoic is most characteristic of serial replacement rather than in situ evolution, and it is possible that the isolation of North America subsequent to the breakup of Laurentia contributed to the regional extinction of lungfishes in North America.

The Lower Permian amphibamid Doleserpeton annectens (Temnospondyli) is of great importance to our understanding of the origin of modern amphibians. Here, we describe this taxon in detail. The pedicellate bicuspid dentition of Doleserpeton is more similar to that of modern amphibians than any other Palaeozoic form, including Gerobatrachus. The dermal bones of the skull are almost completely smooth, unlike other dissorophoids. The braincase and parts of the postcranial skeleton are more highly ossified than in other amphibamids, and Doleserpeton is unlikely to represent a juvenile stage. The ribs are relatively short and posteriorly curved, as in many modern amphibians, but unlike most lepospondyls. The palate shares numerous features with modern amphibians, including the configuration of the interpterygoid vacuities and the structure of the vomers. We propose that the closest sister taxon to Amphibamidae is Dissorophidae (armored dissorophoids) and that the trematopids are more basally situated than has been suggested by some studies. Micropholis is probably not basal to the other amphibamids, and the clade support for a monophyletic Amphibamidae is surprisingly weak unless Dissorophidae and branchiosaurs are included in this taxon. Doleserpeton adds to the strong evidence for a temnospondyl origin of batrachians, particularly for anurans, and the hypothesis proposing a lepospondyl origin of modern amphibians is therefore questioned. Doleserpeton also shares numerous features with Eocaecilia, pointing to a monophyletic origin of lissamphibians from amphibamid temnospondyls.

The postcranial skeleton of Mesosaurus tenuidens, a reptile from the Lower Permian of eastern South America and southern Africa, is redescribed and illustrated in detail. The number of presacral vertebrae varies in M. tenuidens from 29 to a maximum of 33, which falls just short of the maximum (34–35 presacrals) known in its close relative Stereosternum tumidum. A cleithrum is reported for the first time in a mesosaur. The head of the interclavicle is triangular, rather than diamond-shaped as in other basal reptiles, including S. tumidum. The carpus of M. tenuidens is apomorphic in that the intermedium and the lateral centrale are coossified. The lateral centrale pedis is absent. Reappraisal of the aquatic adaptations of M. tenuidens suggests strongly that this reptile was fully dedicated to an aquatic lifestyle. Pervasive pachyostosis of the postcrania probably allowed animals to maintain neutral buoyancy in the uppermost 3–4 m of the water column. Additionally, such pachyostosis may have helped to control rolling at the surface, or perhaps served to maintain forward momentum during periods of gliding while moving underwater. Limited movement at the elbow and the ankle suggests that M. tenuidens could not walk on land, but individuals may have been able to push themselves across terrestrial substrates, perhaps in a manner analogous to that seen in female extant marine turtles on nesting beaches.

We describe Prosictodon dubei, gen. et sp. nov., from the Abrahamskraal Formation, Karoo Basin, Middle Permian of South Africa. Diagnostic characters of P. dubei include postorbitals that slope ventrolaterally and overlap the parietals nearly completely; median anterior palatal ridges that converge with the posterior median palatal ridge, forming a V-shaped structure; caniniform process with an anterior edge that is set off from the palatal rim forming a notch; ‘postcanine’ teeth present on the maxilla; a ventrally directed transverse flange of the pterygoid with an obtuse posterior margin; a short interpterygoid vacuity that does not reach the level of the palatine pads; a dentary table that forms an elongate grooved surface on the dorsal surface of the dentary, bounded laterally by a low ridge and medially by a tall, thin, dorsally convex blade; ‘postcanine’ teeth present on the dentary blade; and the absence of a posterior dentary sulcus. A phylogenetic analysis confirms that P. dubei is a member of Pylaecephalidae, although we cannot corroborate that it is the sister taxon of Diictodon feliceps. The holotype of P. dubei was collected low in the Tapinocephalus Assemblage Zone in the northwestern Karoo Basin, near the contact between the Ecca and Beaufort groups, within the stratigraphic range of Robertia but above the ranges of Eodicynodon and Colobodectes. On-going research suggests dicynodonts in the Tapinocephalus Assemblage Zone appeared in sequence (Colobodectes first; Lanthanostegus, Robertia, Prosictodon second; Diictodon and Pristerodon third), in contrast to earlier works that portrayed Diictodon, Robertia, and Pristerodon as occurring throughout the zone.

The fragmentary holotype and only known material of Platecarpus tympaniticus Cope, 1869, is redescribed and compared to other closely related plioplatecarpine mosasaurs. Re-characterization of the holotype reveals the following similarities to Platecarpus ictericus: exoccipital-basioccipital suture transversely oriented in condylar view; basal tubera not inflated and widely separated along ventral midline; cervical intervertebral joint surface strongly curved; seventh cervical vertebra lacking articulating intercentrum (i.e., hypapophyseal peduncle). In addition, the relatively complete right quadrate of the holotype of P. tympaniticus is virtually indistinguishable from those of P. ictericus. Quadrate characters, when combined with the four previously mentioned characters, uniquely diagnose both P. tympaniticus and P. ictericus among known mosasaur taxa. Because P. tympaniticus was established before P. ictericus, the former becomes the specific senior synonym of the latter, and is also the generic type of Platecarpus.

The structurally complex ankles of Triassic archosaurs (Reptilia: Diapsida) have been repeatedly described, and tarsal characters have played an important role in analyses of archosaur phylogeny. Morphological variations in the ankle joint undoubtedly had a major impact on locomotion, but the functional implications of many ankle features remain poorly understood. This paper investigates the function of one such structure, the prominent and highly distinctive lateral to posterolateral calcaneal process that occurs throughout basal archosaurs and is homologous to the heel-like calcaneal tuber of pseudosuchians. A morphologically analogous lateral process occurs in extant varanid lizards, and X-ray rotoscopic analysis of the limb movements of savannah monitors (Varanus exanthematicus) indicates that the lateral process rotates into a vertical orientation as the limb retracts. As the varanid lateral process approaches the vertical, it becomes increasingly effective in adding to the propulsive moment arm of m. peroneus longus. A computer model of the ankle was compared to modified versions in which the lateral process and the associated proximal expansion of the fifth metatarsal were eliminated, and this virtual experiment demonstrated that the combination of the two structures increases the peak propulsive moment arm of the varanid m. peroneus longus by over 26%. The lateral calcaneal process of basal archosaurs probably acted similarly, enhancing the ability of the peroneus musculature to contribute to propulsion during walking. Like the calcaneal tuber of pseudosuchian archosaurs, the primitive lateral process was a lever that contributed to locomotion by allowing ankle plantarflexion to generate a greater propulsive moment.

The best-known South American Early Triassic archosauriform belongs to a putative proterosuchid briefly reported by José Bonaparte in 1981, collected from the Quebrada de los Fósiles Formation (Puesto Viejo Group, Argentina). This specimen consists of well-preserved natural external molds of a partial postcranium that preserve dorsal vertebrae, osteoderms, a dorsal rib, a possible gastralium, a chevron, a humerus, an ilium, two metapodials, and an ungual. We re-describe this specimen and identify autapomorphies that allow us to recognize Koilamasuchus gonzalezdiazi, gen. et sp. nov. The presence of an iliac blade with a slightly convex dorsal margin and with a maximum length more than 3 times its maximum height places Koilamasuchus within Archosauriformes. A cladistic analysis of basal Archosauriformes positions Koilamasuchus more crownwards than Proterosuchus, Sarmatosuchus, Fugusuchus, and Osmolskina, as the sister taxon of the clade that includes Erythrosuchidae and Archosauria. Proterosuchidae is found to be paraphyletic. The presence of an iliac preacetabular process, a pubic peduncle that forms an angle lower than 45° to the longitudinal axis of the ilium, and dorsal body osteoderms positions Koilamasuchus in Archosauriformes more crownwards than proterosuchids. Koilamasuchus is more basal than erythrosuchids within Archosauriformes because of the presence of dorsal ribs with a poorly developed proximal end. Koilamasuchus importantly increases the diversity of Archosauriformes during the biotic recovery following the Permo-Triassic mass extinction.

Metriorhynchids were a peculiar group of fully marine Mesozoic crocodylomorphs. The derived genera Dakosaurus and Geosaurus exhibit a macroevolutionary trend towards extreme hypercarnivory, underpinned by a diverse array of craniodental adaptations, including denticulate serrated (ziphodont) dentition. A comparative analysis of serrations in Metriorhynchidae shows that known Dakosaurus species had conspicuous denticles, in contrast to the microscopic denticles of Geosaurus. A new tooth from the Nusplingen Plattenkalk of Germany provides evidence for a previously unknown large species of Geosaurus. Metriorhynchid specimens from the upper Kimmeridgian—lower Tithonian of Southern Germany show that ziphodont species of Dakosaurus and Geosaurus co-occurred in the Nusplingen and Solnhofen Seas. Although these genera are similarly denticulate, they diverge in overall crown morphology. Therefore, resource/niche partitioning via craniodental differentiation is posited as maintaining two contemporaneous genera of highly predatory metriorhynchids. Additionally, the new generic name Torvoneustes is proposed for “Geosaurus” carpenteri, the only known metriorhynchid with false-ziphodont dentition. A cladistic analysis shows that ziphodont dentition may have evolved independently in Dakosaurus and Geosaurus, or been acquired earlier by their common ancestor and secondarily lost in Torvoneustes and related taxa.

A nearly complete skull of Eutretauranosuchus delfsi was uncovered at the upper Jurassic Dry Mesa Dinosaur Quarry in the Brushy Basin Member of the Morrison Formation in western Colorado. It permits an expanded description of the taxon. Like the holotype, from Canyon City, Colorado, the Dry Mesa specimen probably represents a subadult, based on faint parallel lincations in the frontal, incomplete ossification in the otic region, incomplete sculpturing of the dermal bone, and an incompletely fused occipital condyle. The Dry Mesa specimen is compared with the type specimen, crocodyliformes Amphicotylus, photographs of the type specimen, and other related crocodyliformes described in the literature. A phylogenetic analysis lends support to a close relationship between Eutretauranosuchus, Calsoyasuchus, and Sunosuchus.

Many current debates about biodiversity and large-scale evolution have identified the need for comprehensive species inventories. Such species lists may be incomplete because more collecting is needed, or because of errors by systematists. Empirical studies show that error rates are high, as much as 30–50% for many living and fossil groups. A clear requirement is skilled systematists, and more of them; but who does the best work? An empirical investigation of the 321 authors who named all 1400 species of dinosaurs since 1824 shows that prolific authors do worse than authors who name only a few dinosaurs, and the key difference is between the 147 authors who named only one species, and the 174 who named two or more. The most prolific author was Othniel Marsh, who named 98 species of dinosaurs (including 80 non-avian dinosaurs and 18 Mesozoic birds), but only 35 (36%) of his names are currently regarded as valid. The poor showing by prolific authors is not a result of their working at different times over the last two centuries, nor on dinosaurs of a particular age, body size, or quality class, nor that their work has been over-revised, but most likely because many prolific authors of dinosaur species names have been too interested in splitting species. Current tougher refereeing standards and international communication should continue to improve standards in naming new taxa.

Ceratopsians, or horned dinosaurs, display a spectrum of variation in the system of depressions or sinuses on the dorsum of the skull. Derived non-ceratopsoid neoceratopsians such as Protoceratops and Zuniceratops variably possess a frontoparietal depression rostral to the dorsotemporal fenestrae. In ceratopsids, such as Triceratops, the depression is roofed secondarily by bone to form a supracranial sinus. The sinuses vary in their lateral extent, with the most restricted condition found in Centrosaurus and Styracosaurus. The sinuses are suggested to be pneumatic structures, although it cannot be determined if they are paranasal, paratympanic, or pharyngeal in origin. The inferred pneumatic diverticula that supplied the sinus extended from the dorsotemporal fenestrae into the sinus via a pair of channels on the dorsum of the skull. Ontogenetically, the sinus began as a shallow depression on the roof of the skull that was enclosed by excavation into the cranial bone and overgrowth of bone. Sinus morphology in bovid mammals, frequently invoked analogues for ceratopsids, is not correlated with behaviors such as head butting, but differences in sinus placement and anatomy between the groups temper the use of bovid sinuses as an analogy for ceratopsid sinuses. The development of a closed sinus in ceratopsids from an open depression was probably associated with an increase in skull size and the accompanying relatively greater loads applied to the horns (in order to maintain the structural integrity of the skull), as well as an anatomical reorganization of the ceratopsian skull.

Two eobaatarid multituberculates, Heishanobaatar triangulus gen. et sp. nov. and Eobaataridae gen. et sp. indet, and an ?albionbaatarid multituberculate, Kielanobaatar badaohaoensis gen. et sp. nov., from the Lower Cretaceous (Aptian to Albian) Shahai and Fuxin formations in Liaoning Province, northeastern China, are described. Heishanobaatar triangulus is a moderate-sized multituberculate characterized by lower jaw dental formula 1.0.3.2, slender lower incisor, single-rooted p2, triangular p3 in lateral view, p4 with eight serrations, m1 with cusp formula 2:2, and m2 with cusp formula 1 (coalesced):2. Kielanobaatar badaohaoensis is characterized by upper anterior premolars with relatively flat occlusal surfaces, roughly pentangular P1 in occlusal view, P1 and P2 with three cusp rows (cusp formulae 1:3:2), and P3 with four cusps (cusp formula 2:2). Together with already described three species of eobaatarids from the same localities, they demonstrate that there were quite diverse multituberculates in Asia in the late Early Cretaceous, and suggest that the mammalian fauna known from the Shahai and Fuxin formations probably show a transitional state from the mammalian fauna of the Yixian Formation to Late Cretaceous Asian faunas.

This contribution presents a morphofunctional analysis of the previously unknown appendicular skeleton of the paucituberculatans Palaeothentes minutus and Palaeothentes lemoinei from the Santa Cruz Formation (late early Miocene, Santa Cruz province, Argentina), performed in order to infer their locomotor behavior. In addition, a cladistic analysis was conducted to explore the phylogenetic information of postcranial features of Palaeothentes in the context of Marsupialia. The results indicate that Palaeothentes would have been an agile cursorial dweller, with leaping ability, similar to the extant paucituberculatan Caenolestes fuliginosus and the didelphid Metachirus nudicaudatus. This mode of locomotion is evidenced mainly by the following features: proximal location of the deltopectoral crest and bicipital tuberosity, reflecting rapid flexion at the gleno-humeral and elbow joints, respectively; shape of the humero-ulnar and humero-radial joints (deep and high humeral trochlea, deep olecranon fossa, deep trochlear notch, mediolaterally broad proximal trochlear crest), denoting a marked stability for flexion and extension; restrictive acetabulum, showing emphasized congruence at the hip joint; lengthened ischium and prominent femoral tubercle and ischial tuberosity, indicating an increased mechanical advantage of the rectus femoris and hamstring muscles; proximally projected greater trochanter, demonstrating a relatively great mechanical advantage of the gluteal muscles; and configuration of the upper ankle, lower ankle, and transverse tarsal joints, indicative of restrictive rotational movements (right angle between the medial and lateral astragalotibial facets, distal and proximal calcaneo-cuboid facet halves forming a right angle). A cladistic analysis positions Palaeothentes as the sister taxon to the extant Caenolestes, demonstrating that postcranial features support the monophyly of Paucituberculata.

We describe Galadi speciosus, gen. et sp nov., the second peramelemorphian (Yarala burchfieldi being the first) to be described from Oligo-Miocene deposits of Riversleigh World Heritage Property, northwestern Queensland. G. speciosus is represented by relatively complete craniodental material, including an exceptionally well-preserved skull. This taxon exhibits several apomorphies that clearly place it in the order Peramelemorphia, but it appears to be more plesiomorphic than any modern bandicoot. We present the first morphological phylogenetic analyses of Peramelemorphia, using 51 craniodental characters. Our analyses recover Yarala and Galadi speciosus outside crown group Peramelemorphia, with G. speciosus weakly supported as the sister taxon of the crown group. The craniodental morphology of G. speciosus, particularly its robust skull and proportionately short and broad snout, suggests that it filled a different ecological niche to extant bandicoots. We hypothesize that G. speciosus occupied a predominantly faunivorous, dasyurid-like niche in the Oligo-Miocene rainforests of Riversleigh, at a time when dasyurids appear to have been relatively rare.

The subfamily Mylodontinae, typified by Mylodon, is known from the Colloncuran (late Miocene of Patagonia, Argentina) to the late Pleistocene of South America and North America. Mylodontinae have been recorded during the Pleistocene of Argentina, including the genera Glossotherium, Paraglossotherium, Lestodon, and Mylodon, with Paraglossotherium and Mylodon not as well known as the other genera. In Argentina there have been traditionally four species of Mylodon, M. darwini, M. zeballozi, M. listai, and M. insigne, although the validity of some has been considered doubtful. A nearly complete skull with an associated mandible of Mylodon darwini from the late Pleistocene of Mesopotamia, Argentina, is described. The specimen represents the first record of the species in the Mesopotamian region. The morphometric analysis indicates that M. darwini had greater individual variability than previously thought. Although based on the results of the morphologic and morphometric analysis, the idea of sexual dimorphism for M. darwini is, for the time being, unwarranted. This new record also supports the idea that Mylodon had great ecological tolerance and was capable of inhabiting climates ranging from cold and arid to warm and humid, and even montane environments.

Among the archaic ‘ungulates,’ pleuraspidotheriids are well documented by skulls and postcranial elements of Pleuraspidotherium from Berru and Cernay-lès-Reims (late Paleocene, Paris Basin, France). Nevertheless, the relationships of pleuraspidotheriids (i.e., Pleuraspidotherium, Orthaspidotherium, and Hilalia) to other ‘condylarths’ have not been conclusively settled. They have been related to the typically North American Meniscotheriidae, Phenacodontidae, and Mioclaenidae, and even to the modern ungulates Perissodactyla and Artiodactyla. We here provide additional data, especially from the first complete skull of Orthaspidotherium, and highlight a mosaic of plesiomorphic and derived characters that distinguish Pleuraspidotheriidae from all other ‘ungulates.’ Their basicranial morphology approximates the ancestral morphotype of artiodactyls, but this results from symplesiomorphies. Pleuraspidotheriids exhibit the following synapomorphies: strong processes on the petrosal and enclosure of the facial nerve by the tympanic process and tympanohyal. Although their dentition resembles that of perissodactyls, meniscotheriids, and phenacodontids, the development of a pseudohypocone from the metaconule unambiguously shows that these similarities arose by convergence. Other evolutionary tendencies are the strong reduction of the hypoconulid, molarization of last premolars, development of lingual cingulum on M2, lengthening of the snout, and presence of diastemata. The pleuraspidotheriid tarsal morphology is primitive and not uncommon among ‘condylarths’ but presents some synapomorphies such as a calcaneum with a transverse cuboid facet and an astragalus with a squatting facet, cotylar fossa, and sustentacular hinge. Our study does not indicate a close relationship of Pleuraspidotheriidae with any of the archaic or modern ‘ungulates’ mentioned above. Instead, primitive arctocyonids could represent a possible ancestral morphotype for pleuraspidotheriids.

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.

A new species of Gliridae (Rodentia, Mammalia), Microdyromys remmerti, sp. nov., from the Aragonian type area in the Calatayud-Montalbán basin (Miocene, Spain) is described. This species is characterized by combining a relatively large size and a moderately complicated to very complicated and irregular dental morphology. It has a wide and continuous range of morphological variation with intermediate forms filling all the range. In the studied localities, M. remmerti, sp. nov., displays a general increase in the complexity of the dental pattern through time, showing a unique pattern of addition of extra ridges in the lower molars. Comparisons with morphologically similar species are discussed; a taxonomical and nomenclatorial issue regarding two named species of the genus is clarified. The combination of the morphometrical features that characterize M. remmerti, sp. nov., have never been found in any other glirid material outside the Calatayud-Montalbán basin, thus reinforcing the idea of the endemic character of the Gliridae faunas from the Iberian Miocene. Microdyromys koenigswaldi is proposed as most probable ancestor of M. remmerti, sp. nov. The divergent evolution of the latter species is discussed in its paleoecological context. The functional consequences of this morphological divergence could be related also with the opening of new ecological niches during the middle Aragonian (Middle Miocene).

Nonomys gutzleri, sp. nov., is described on the basis of isolated teeth from the late Duchesnean or early Chadronian upper member of the Pomerado Conglomerate, San Diego County, California, U.S.A. It differs from Nonomys simplicidens (early to middle Chadronian of Wyoming and Texas) in several characters, including molars 10–13% larger, more conical metaconids and protoconids on ml and m2, and small entoconid on m3. Nonomys gutzleri further differs from N. simplicidens in the apparently derived characters of one or more distinct cuspulids on the labial cingulid of m1 and m2, weaker ectolophids on m1–3, and lack of preprotocristid and metalophulid on m1–3. These characters foreshadow the conditions in Diplolophus. An isolated m1 (SDSNH 72232) from the Pomerado Conglomerate represents an unnamed new taxon of nonomyine morphologically intermediate between Nonomys and Diplolophus. It differs from Nonomys in having m1 19–28% larger than N. gutzleri, a much larger metastylid, and, similar to the conditions in Diplolophus insolens, in lacking a distinct anteroconid and a complete ectolophid, but in possessing an arch-like ridge structure on the posterior flank of the protoconid. However, SDSNH 72232 is 59–68% smaller than the m1 in D. insolens, is anteroposteriorly more elongated and much lower-crowned than the m1 of D. insolens, and has a separate metaconid and metastylid. The derived similarities between Nonomys, SDSNH 72232, and Diplolophus support their inclusion in a redefined subfamily Nonomyinae, but this subfamily is not confidently assignable to either Muroidea or Dipodoidea, and is allocated only to Myodonta, incertae sedis.