Mandibular Characters Research Articles

Morphometric characterization of Holocene mandibles expands the ecological baseline for understanding gibbon extinction dynamics

Human activities have driven biodiversity loss for millennia, and conservation of ‘refugee species’ that survive as remnant populations requires insights from historical baselines. However, reconstructing the past distribution and ecology of such species is challenging due to data limitations with specimen-based archives. Here, we assess the taxonomic identity of two gibbon mandibles from the Wumingshan Neolithic site in Guangxi, China. Although ancient DNA extraction was unsuccessful, a suite of linear and geometric morphometric analyses using dental and mandibular characters reveals that these mandibles fall within or close to variation shown by extant Chinese Nomascus gibbons and can be assigned to the cao vit gibbon N. nasutus. This is now one of the world’s rarest mammals, with a surviving population of 74 individuals in one site. Comparative assessment of bioclimatic, abiotic and anthropogenic parameters for Wumingshan and other sites where N. nasutus historically occurred reveals the species was formerly a landscape generalist but is now restricted to a high-elevation refugium with reduced human pressures. Our multidisciplinary analyses provide a new baseline on niche requirements and vulnerability for N. nasutus with implications for population management, demonstrating the importance of integrating environmental archives into conservation planning.

A new dentition-based phylogeny of Litopterna (Mammalia: Placentalia) and ‘archaic’ South American ungulates

Abstract Ever since the discovery of Macrauchenia patachonica by Charles Darwin in 1834, the affinities of litopterns—a group of extinct South American Native Ungulates (SANUs)—have been elusive. In particular, the interfamilial relationships and timing of the familial diversification within the order Litopterna have not been addressed with adequate taxon and character sampling, and modern phylogenetic methods. We address these issues using a new morphological matrix of 703 dental and mandibular characters, scored for the earliest litopterns alongside early SANUs of other orders (Astrapotheria, Notoungulata, Pyrotheria, and Xenungulata). We also included members of families that have been often included within Litopterna, such as Didolodontidae, Protolipternidae, Indaleciidae, and Notonychopidae, the last two sometimes grouped in the order Notopterna. We conducted maximum parsimony and undated and tip-dated Bayesian phylogenetic analyses. Our results indicate that (1) didolodontids, protolipternids, and kollpaniines should be considered early SANUs, but not particularly closely related to any order, (2) Indaleciidae and Notonychopidae usually form a monophyletic group (Notopterna), and (3) Litopterna is a monophyletic unit composed of four families [Adianthidae, Anisolambdidae (subfamilies Anisolambdinae and Sparnotheriodontinae), Macraucheniidae, Proterotheriidae], and tentatively the notoptern families Indaleciidae and Notonychopidae with a probable origin ~64.0 Mya in the Early Palaeocene.

Paleophylogeography of Notiosorex desert shrews with description of a new species

Abstract The genus Notiosorex is the only group of shrews in North America with adaptations to arid or semiarid zones. The genus was described with a single variable species, Notiosorex crawfordi, from which 5 new species have since been distinguished. To date, the phylogenetic relationships of Notiosorex species have only been partially analyzed and it is possible that there are still distinct species included within the catch-all of N. crawfordi. Here, we use geometric morphometrics on cranial and mandibular characters of the described extant species, 3 fossil species, and a distinctive population of N. crawfordi as a proxy for an integrated assessment of phylogenetic relationships of all Notiosorex species. Our results indicate that the population from the Altiplano Mexicano is more similar to, yet distinct from, N. villai than it is to N. crawfordi—we describe it as a new species. We also used the resulting tree to reconstruct phylogeographic history within the genus, which suggests that Notiosorex sp. nov., N. villai, N. evotis, and N. tataticuli all diverged allopatrically as populations from the ancestral area that is currently occupied by N. crawfordi (and in the deeper past by the fossil species N. harrisi), and pushed south into the Gulf Coast, the Altiplano, and Baja California within the last 5 million years following the end of the Miocene.

A large brachyopoid from the Middle Triassic of northern Arizona and the diversity of brachyopoid temnospondyls from the Moenkopi Formation

Brachyopoids represent a diverse and late surviving temnospondyl group, lasting until the Early Cretaceous. Here, we report on brachyopoid material previously assigned to Hadrokkosaurus bradyi that represents a distinct brachyopoid taxon, characterised by a smaller number of large, robust mandibular teeth, a feature rarely observed in other temnospondyls. We also revisit an angular previously referred to Hadrokkosaurus potentially belonging to other temnospondyl taxa present in the Middle Triassic of North America. In light of the abundance of material of possible taxa distinct from Hadrokkosaurus, we express the need to re-examine previously collected specimens as new information changes the landscape of palaeontology. Parsimony analyses using exclusively mandibular characters recover the new brachyopoid taxon from the locality in a polytomy with Hadrokkosaurus and Vanastega at the base of Brachyopoidea, adding to a diversity of mandibular morphology of temnospondyls in the Middle Triassic of North America.

A peirosaurid mandible from the Albian–Cenomanian (Lower Cretaceous) of Algeria and the taxonomic content of Hamadasuchus (Crocodylomorpha, Peirosauridae)

Abstract Peirosaurids form an extinct clade of terrestrial crocodylomorphs from the Cretaceous of Africa and South America. Here, we describe a new mandibular ramus attributable to Hamadasuchus cf. rebouli from the Albian–Cenomanian of La Gara Samani (Algeria). We propose an emended diagnosis for this taxon, originally described from a left dentary fragment from the Kem Kem Group of Morocco and discuss the assignment of the specimens currently referred to it. Using ontogenetic series of extant crocodylians, we show that several mandibular characters commonly used to differentiate between close taxa instead record intraspecific or ontogenetic variability. In contrast, reliable mandibular characters enable us to propose that the current taxonomic content of Hamadasuchus rebouli should be reduced to three specimens, pending future description of relatable cranial remains. Finally, we demonstrate the importance of mandibular characters in phylogenies, by recovering the new specimen from La Gara Samani as closely related to North African peirosaurids on the basis of a data matrix designed solely on mandibular characters.

Axonomic revision of the Australian native bee subgenus Australictus (Hymenoptera: Halictidae: Halictini: genus Lasioglossum) – “Wood-Splitting Axe Bees”

Walker, K.L. 2022. Taxonomic revision of the Australian native bee subgenus Australictus (Hymenoptera: Halictidae: Halictini: genus Lasioglossum) – “Wood-Splitting Axe Bees”. Memoirs of Museum Victoria 81: 135–162. The Australian Lasioglossum Curtis 1833 subgenus Australictus Michener 1965 is revised. Of the 11 available names listed by Michener (1965) for the subgenus Australictus, six are placed in synonymy. A species placed by Michener (1965) in the Lasioglossum subgenus Parasphecodes Smith 1853 is recombined to the subgenus Australictus, and four other species, placed in Parasphecodes by Michener (1965), are synonymised with this valid, recombined taxon, and the species name of the taxon is reverted to its original spelling. In addition, a species placed in Australictus by Michener (1965) is synonymised with a valid species in the Lasioglossum subgenus Chilalictus Michener 1965. These changes provide five valid names for the subgenus Australictus. New synonymies, recombined names and valid species proposed for Lasioglossum (Australictus) are as follows: New synonymies – Lasioglossum (Australictus) kurandense (Cockerell 1914) syn. nov., Lasioglossum (Australictus) nigroscopaceum (Friese 1917) syn. by Cockerell 1929 but listed by Michener (1965: 165) as valid = Lasioglossum (Australictus) davide (Cockerell 1910a); Lasioglossum (Australictus) insculptum (Cockerell 1918) syn. nov., Lasioglossum (Australictus) rufitarsum (Rayment 1929) syn. nov. and Lasioglossum (Australictus) fulvofasciae Michener 1965 syn. nov. = Lasioglossum (Australictus) tertium (Dalla Torre 1896); Lasioglossum (Australictus) franki (Friese 1924) syn. nov. = Lasioglossum (Chilalictus) orbatum (Smith 1853). New combination and new synonymies – Lasioglossum (Parasphecodes) lithuscum (Smith 1853) comb. nov. moved to Lasioglossum (Australictus) lithusca; Lasioglossum (Parasphecodes) adelaidae (Cockerell 1905) syn. nov., Lasioglossum (Parasphecodes) griseipenne (Cockerell 1929) syn. nov., Lasioglossum (Parasphecodes) stuchilum (Smith 1853) syn. nov., Lasioglossum (Parasphecodes) wellingstoni (Cockerell 1914) syn. nov. = Lasioglossum (Australictus) lithusca. Valid is Lasioglossum (Australictus) plorator (Cockerell 1910b). New female subgeneric mandibular characters are added to Michener’s (1965) diagnostics for Australictus – mandible with elongated and enlarged preapical tooth, reduction in width of basal tooth at apical end and in dorsal view, broadening of width at base of mandible. The mandibular modifications, widening of the head basally and enlarged gena are associated with Australictus behaviour to nest in wood rather than ground nesting in soil as is usual for Halictidae bees. The shape of the female mandible, especially in dorsal view, resembles a wood-splitting axe – hence the common name coined here, “Wood-Splitting Axe Bees”. Australictus is the first record of wood-nesting bees for Australian Halictidae. All valid species are redescribed; keys to both sexes, montage diagnostic images and distribution maps are provided to assist with species identification.

The ecological diversification and evolution of Teleosauroidea (Crocodylomorpha, Thalattosuchia), with insights into their mandibular biomechanics.

Throughout the Jurassic, a plethora of marine reptiles dominated ocean waters, including ichthyosaurs, plesiosaurs and thalattosuchian crocodylomorphs. These Jurassic ecosystems were characterized by high niche partitioning and spatial variation in dietary ecology. However, while the ecological diversity of many marine reptile lineages is well known, the overall ecological diversification of Teleosauroidea (one of the two major groups within thalattosuchian crocodylomorphs) has never been explored. Teleosauroids were previously deemed to have a morphologically conservative body plan; however, they were in actuality morphofunctionally more diverse than previously thought. Here we investigate the ecology and feeding specializations of teleosauroids, using morphological and functional cranio-dental characteristics. We assembled the most comprehensive dataset to date of teleosauroid taxa (approximately 20 species) and ran a series of principal component analyses (PC) to categorize them into various feeding ecomorphotypes based on 17 dental characteristics (38 specimens) and 16 functionally significant mandibular characters (18 specimens). The results were examined in conjunction with a comprehensive thalattosuchian phylogeny (153 taxa and 502 characters) to evaluate macroevolutionary patterns and significant ecological shifts. Machimosaurids display a well-developed ecological shift from: (1) slender, pointed tooth apices and an elongate gracile mandible; to (2) more robust, pointed teeth with a slightly deeper mandible; and finally, (3) rounded teeth and a deep-set, shortened mandible with enlarged musculature. Overall, there is limited mandibular functional variability in teleosaurids and machimosaurids, despite differing cranial morphologies and habitat preferences in certain taxa. This suggests a narrow feeding ecological divide between teleosaurids and machimosaurids. Resource partitioning was primarily related to snout and skull length as well as habitat; only twice did teleosauroids manage to make a major evolutionary leap to feed distinctly differently, with only the derived machimosaurines successfully radiating into new feeding ecologies.

A systematic compendium of turtle mandibular anatomy using digital dissections of soft tissue and osteology.

Turtles are a charismatic reptile group with a peculiar body plan, which most notably includes the shell. Anatomists have often focused descriptive efforts on the shell and other strongly derived body parts, such as the akinetic skull, or the cervical vertebrae. Other parts of turtle osteology, like the girdles, limbs, and mandibles, are documented with less rigor and detail. The mandible is the primary skeletal element involved in food acquisition and initial food processing of turtles, and its features are thus likely linked to feeding ecology. In addition, the mandible of turtles is composed of up to seven bones (sometimes fused to as little as three) and has thus anatomical complexity that may be insightful for systematic purposes and phylogenetic research. Despite apparent complexity and diversity to the mandible of turtles, this anatomical system has not been systematically studied, not even in search of characters that might improve phylogenetic resolution. Here, we describe the mandibular osteology for all major subclades of extant turtles with the help of digitally dissected 3D models derived from high-resolution computed tomography (μCT) scans of 70 extant species. We provide 31 fully segmented mandibles, as well as 3D models of the mandibular musculature, innervation, and arterial circulation of the cryptodire Dermatemys mawii. We synthesize observed variation into 51 morphological characters, which we optimize onto a molecular phylogeny. This analysis shows some mandibular characters to have high systematic value, whereas others are highly homoplastic and may underlie ecological influences or other factors invoking variation.

In the jaws of a titan: 3D comparative anatomy of the mandibles of the Canary giant lizards (Gallotiinae: Gallotia)

ABSTRACT An iconic, insular, endemic genus of lizards (Gallotia) is present on the Canary Islands (Spain), comprising gigantic to smaller-sized species. Despite numerous studies on various biological aspects of this genus, the osteological knowledge available is scarce. This makes it difficult to identify to species level the bone remains recovered from both living and extinct taxa, which is essential to understanding the evolution of this genus through time, its distribution and its migratory patterns. Herein, a detailed description, comparison and discussion of each mandibular bone of all the living giant species and the fossil taxon G. goliath is presented. First detailed descriptions of G. intermedia and G. bravoana are presented, and interspecific and ontogenetic characters to be considered for Gallotia and related taxa in future works are proposed. Disentangling the intra- and interspecific variability of the mandible, as well as its ontogenetic changes through time, is of special interest for a variety of reasons. These include: a) to evaluate paleobiodiversity; b) to evaluate intraspecific variation and ontogenetic changes; c) to establish mandibular characters for specific identification; d) as previous step in performing computational biomechanics studies based on 3D models to shed in-depth light on feeding ecology.

Phylogenetic positions of Paronychomys Jacobs and Basirepomys Korth and De Blieux relative to the tribe Neotomini (Rodentia, Cricetidae)

Abstract A recent study on the fossil history of North American woodrats and their relatives suggested that the Neotomini includes two subtribes: the Neotomina (woodrats; Tsaphanomys, Neotoma, Hodomys, Xenomys) and Galushamyina (reprats: Protorepomys, Galushamys, Miotomodon, Repomys, Nelsonia). The extinct Miocene Lindsaymys was proposed as a possible early neotominan, but not formally included in the Neotomini. In other studies, two extinct genera, Basirepomys and Paronychomys, occasionally have been treated as related to neotominans, but their ancestry had not been formally explored in detail. We performed a phylogenetic analysis on representatives of all genera with 40 dental and mandibular characters likely to be preserved in fossil material. The analysis resulted in a single most parsimonious tree supporting a neotominan-galushamyinan tribal classification of the Neotomini, and securely placed Lindsaymys within the Neotomina. None of the Basirepomys and Paronychomys species or Protorepomys bartlettensis nested within the Neotomini. The three Basirepomys species, possibly a paraphyletic group, are not closely related to Repomys, and Paronychomys (minus P. shotwelli = Tsaphanomys shotwelli) is not closely related to Onychomys, but is a possible sister group to the Neotomini. With the understanding that further study may remove it from Protorepomys, P. bartlettensis is tentatively retained within the genus, representing a relatively underived species possibly ancestral to both neotominan clades. Neotoma species of the extinct subgenus Paraneotoma and extant Neotoma may be paraphyletic at the generic level, but that determination will require further study.

Cranial Morphology of the Flat-Headed Bat Myotis planiceps (Chiroptera: Vespertilionidae) in the Context of American Myotis

Myotis planiceps is an insectivorous species with a distinctive flat-headed morphology among Myotis species. Its distribution is restricted to the northeastern Mexico highlands, and uses trees of Yucca carnerosana to roost. The particular ecological and morphological characteristics of this species make it a likely resource-use specialist. We evaluated the morphological specialization of M. planiceps as compared with thirteen American congeners belonging to different dietary categories, using a geometric morphometric protocol and multivariate statistical analyses. We estimated morphological differences across dietary categories, including M. planiceps as a separate group, and evaluated the effect of cranial size and diet on variations in cranial morphology. We found a significant differentiation of this species in all the cranial shape characters, with soft insectivores as the dietary group closest to M. planiceps. Additionally, diet explained similar percentages of shape variance in cranial and mandibular characters, and the highest interaction between diet and cranial size was recorded in the braincase. In general, the smallest sizes and thinner skulls were observed in soft insectivores. Our findings do not support a significant relationship between skull shape characters, described by the first principal component, and hardness of food items, but we found a significant association with the mandible shape. No phylogenetic structure was observed in the residual variance of these models. We found trends of change in cranial morphology associated with specialized habitats, the mandibular characters being more contrasting in the fishing bat M. vivesi, and the braincase morphology being more contrasting in M. planiceps, a species that lives in restricted habitats and probably feeds on soft insects.

Características morfológicas y morfométricas de cinco especies de Criptotis (Mammalia:Soricomorpha)

Se examinaron ejemplares de cuatro especies monotípicas, Cryptotis mexicana (n = 48), C. obscura (n = 47),C. alticola (n = 8) y C. magna (n = 3); además, de una politípica, C. parva berlandieri (n = 1), C. p. pueblensis (n= 16) y C. p. soricina (n = 84). La gran mayoría del material proviene de localidades del centro de México, exceptolos de Cryptotis magna, C. obscura y C. p. berlandieri. Los ejemplares de C. mexicana, C. obscura y C. magnafueron recolectados en bosque mesófilo de montaña, los de C. alticola en bosque de Pinus sp. y Abies sp. y losde C. parva en bosque tropical y subtropical, mesófilo de montaña, bosque de Quercus sp. y bosques mixto depino-encino. Las medidas morfométricas de 25 variables externas, craneales y mandibulares se obtuvieron decada ejemplar. Las especies C. alticola, C. magna y C. parva se reconocieron con facilidad; sin embargo, en C.mexicana y en C. obscura se traslapan sus medidas pero se pudieron distinguir con el empleo de un AnálisisDiscriminante. Las medidas de C. magna fueron mayores que las de las otras cuatro especies, así como las deC. alticola en general lo fueron de C. mexicana, C. obscura y C. parva. La comparación de las medidas de C. p.pueblensis y C. p. soricina mostraron que las de la primera son mayores que las de la segunda. Variación sexualsecundaria se encontró solamente en C. p. soricina, en donde las hembras resultaron de mayores dimensionesque los machos. Se mencionan dos registros de simpatría entre C. obscura y C. parva y uno entre C. mexicanay C. parva.

Cranial Anatomy of the Desert Dormouse, Selevinia betpakdalaensis (Rodentia, Gliridae), revealed by Micro-Computed Tomography

The dormice (Gliridae) represent a relatively small family of rodents, but exhibit considerable variation in their cranial anatomy. The skull morphology of almost all genera of dormice was described from osteological specimens in an earlier publication. However, the rare desert dormouse, Selevinia betpakdalaensis, was only assessed using previous descriptions and photographic images, resulting in difficulties with assigning all cranial features within this particular genus. In this study, the crania and mandibles of two adult individuals of this genus were scanned using micro-computed tomography and virtually reconstructed. From these reconstructions, we describe in detail the highly unusual cranial and mandibular morphology of the desert dormouse and determine the states of the cranial and mandibular characters described previously. These morphological characters were used to compare this species with previously described dormouse genera, showing a clear resemblance between Selevinia and the small mouse-tailed dormouse genus Myomimus. Derived morphological features unique to Selevinia indicate clear adaptations to a desert-like environment, as well as hinting towards an insectivorous diet and burrowing lifestyle.

Variation in the Jaws and Teeth of the Amphisbaenian Zygaspis from Southern Africa

Amphisbaenians are an understudied family of worm‐like reptiles consisting of over 150 extant species in 23 genera. Relatively little is known about the cranial anatomy of the group because most members of the clade are small and poorly represented in collections. With skulls of some species only a few millimeters long, traditional anatomical methods are difficult to use. Collection curators are also hesitant to allow destructive analysis of specimens, because few specimens are generally available. Most modern studies of cranial anatomy of amphisbaenians are based upon high‐resolution X‐ray CT scans. CT scanning is nondestructive and allows for detailed examination of even small elements. Most of those studies remain focused on a single specimen and therefore do not account for variation beyond potential asymmetry in a single specimen. We focus on a collection of specimens from a single genus, Zygaspis, and examine their upper and lower jaws and teeth to better estimate morphological variation within a tightly circumscribed clade of Amphisbaenans. The cranial anatomy of Z. quadrifrons is well described, although the description is based on a single specimen. That baseline description now allows for both inter‐ and intraspecific variation to be estimated by expanding the previous work to include other specimens of Z. quadrifrons and other species in the genus. Here, we examined Z. quadrifrons, Z. vandami, Z. niger, Z. ferox, Z. violacea, Z. dolichomenta, and Z. kafuensis, whose collective distribution spans most of southern Africa from the southern reaches of the Democratic Republic of the Congo and the Tanzania/Mozambique border to southern South Africa. One adult specimen from each species was CT scanned and analyzed with Amira software. We examined over 20 dental and mandibular characters, including tooth count, size, and orientation, the presence or absence of specific teeth and processes, and the morphology of the coronoid articulation with other elements of the mandible. We found significant variation in several features, including apparent variation in replacement teeth. Our preliminary results suggest that inter‐ and intraspecific variation does exist and should be accounted for in functional and phylogenetic studies. Further analysis of the genus, with an increased sample size and broadening to incorporate other cranial variables, would allow enhanced exploration of the morphological variation that occurs within Zygaspis.Support or Funding InformationSam Houston State University

A New Mormoopid Bat from the Oligocene (Whitneyan and Early Arikareean) of Florida, and Phylogenetic Relationships of the Major Clades of Mormoopidae (Mammalia: Chiroptera)

A new genus and species of fossil bat, Koopmanycteris palaeomormoops, representing an ancient member of the endemic Neotropical family Mormoopidae, is described from the Oligocene of Florida. This new species is known from two paleokarst deposits in northern peninsular Florida, the early Oligocene (Whitneyan, 30–32 Ma) I-75 Local Fauna in Alachua County and the late Oligocene (early Arikareean, 26–28 Ma) Brooksville 2 Local Fauna in Hernando County. The discovery of Koopmanycteris extends the fossil record of the Mormoopidae back in time almost 30 million years. Compared to most other described taxa of North American Tertiary bats, the fossil sample of Koopmanycteris palaeomormoops is substantial, consisting of 50 specimens including: P4, all lower teeth from p3 through m3, dentary, petrosal, humerus, proximal radius, and femur. Koopmanycteris is morphologically intermediate between the two living genera of mormoopids, Mormoops and Pteronotus, but is most similar to the former taxon. Characters shared by Koopmanycteris and Mormoops include: large anterolabial basin on P4; large, double-rooted p3; secondary process ventral to angular process on dentary; absence of groove separating capitulum into medial and lateral portions on distal humerus; presence of prominent ridge on posterolateral edge of distal humeral shaft; rounded extremity on proximal radius; and presence of a prominent ridge or tubercle on posterodistal shaft of femur. All of these features appear to be relatively derived, with the exception of the large, double-rooted p3. In several mandibular characters, Koopmanycteris more closely resembles Pteronotus, including: pronounced posteroventral process on the symphysis; lack of curvature of ventral edge of horizontal ramus between posterior edge of symphysis and p4; and less pronounced dorsal upturning of ascending ramus compared to Mormoops. Koopmanycteris retains the primitive dental morphology of Mormoops, with a large double-rooted p3, and the primitive posterior mandibular morphology of Pteronotus, with the lesser degree of dorsal flexion of the ascending ramus. A phylogenetic analysis including all known extant mormoopid lineages as well as representative outgroups from other noctilionoid clades confirms that Koopmanycteris and Mormoops are sister taxa. These findings indicate that the lineages leading to Pteronotus and Mormoops were distinct by ∼30 Ma. The fossil record tentatively indicates that the Mormoopidae originated in North America in the early Oligocene or earlier, and may not have reached South America until the Pliocene following the onset of the Great American Biotic Interchange. Several lines of evidence support this hypothesis: (1) the earliest fossil record of the Mormoopidae is in the early Oligocene of Florida; (2) the greatest diversity and endemism of modern mormoopid species is in the West Indies; and (3) the absence of a pre–late Pleistocene record, lack of endemism, and marginal recent distribution of mormoopids in South America. Most species of living mormoopids are obligate cave dwellers, suggesting that the occurrence of caves and paleokarst deposits has affected both their modern distribution and fossil record.

New fossils of early and middle Miocene Choerolophodon from northern China reveal a Holarctic distribution of Choerolophodontidae

ABSTRACTAs one of the three major groups of gomphotheres, the Miocene Choerolophodontidae were long considered to have been distributed in Europe, Africa, and South Asia, with a few localities in East Asia, whereas choerolophodontids never extended into North America during the Miocene. In this paper, we report new Choerolophodon fossil materials from the early and middle Miocene of China, which suggest morphological similarities to the enigmatic North American Gnathabelodon thorpei. The new fossils were recovered from the lower Miocene of Linxia (C. guangheensis) and the middle Miocene of Junggar (Choerolophodon sp.) basins, suggesting the persistence of this genus in East Asia during the early–middle Miocene. The cheek tooth morphology of the new specimens resembles that of early–middle Miocene Choerolophodon from elsewhere (i.e., C. palaeindicus, C. kisumuensis, and C. chioticus), in addition to striking affinities with Gnathabelodon thorpei. The upper tusk and mandibular characters of G. thorpei, which include upwardly bent maxillary tusks without enamel bands, and elongated and trough-like mandibular symphysis without mandibular tusks, also support its relationship with the choerolophodontids. The occurrence of a possible member of Choerolophodontidae in the late Miocene of North America (i.e., G. thorpei) reveals intercontinental dispersals of choerolophodontids from East Asia across Beringia possibly between 16.0 and 11.0 Ma, at roughly the same time as other proboscideans, e.g., Mammutidae, Amebelodontidae, and Gomphotheriidae. Together, these new materials significantly revise previously established models of the geographic distribution, taxonomic diversity, and ecological adaptations of Choerolophodontidae within China and elsewhere across the Holarctic.

The First Cetacean Record from the Osaka Group (Middle Pleistocene, Quaternary) in Osaka, Japan

Abstract. A new partial skeleton consisting of a left mandible and five caudal vertebrae, OMNH-QV 282 from the Osaka Group (Middle Pleistocene, about 0.3 million years ago) of Osaka City is reported as the first cetacean record from the group. The skeleton is identified as Balaenopteridae gen. et sp. indet. based on the combination of mandibular characters, such as having a small mandibular foramen, reflected neck in dorsal view and lack of a satellite process of the mandible. OMNH-QV 282 expands diversity for the local fauna, and also adds evidence for the existence of large-sized balaenopterids from a poorly known epoch, the Middle Pleistocene.

Probing the origin of matching functional jaws: roles of Dlx5/6 in cranial neural crest cells

Gnathostome jaws derive from the first pharyngeal arch (PA1), a complex structure constituted by Neural Crest Cells (NCCs), mesodermal, ectodermal and endodermal cells. Here, to determine the regionalized morphogenetic impact of Dlx5/6 expression, we specifically target their inactivation or overexpression to NCCs. NCC-specific Dlx5/6 inactivation (NCC∆Dlx5/6) generates severely hypomorphic lower jaws that present typical maxillary traits. Therefore, differently from Dlx5/6 null-embryos, the upper and the lower jaws of NCC∆Dlx5/6 mice present a different size. Reciprocally, forced Dlx5 expression in maxillary NCCs provokes the appearance of distinct mandibular characters in the upper jaw. We conclude that: (1) Dlx5/6 activation in NCCs invariably determines lower jaw identity; (2) the morphogenetic processes that generate functional matching jaws depend on the harmonization of Dlx5/6 expression in NCCs and in distinct ectodermal territories. The co-evolution of synergistic opposing jaws requires the coordination of distinct regulatory pathways involving the same transcription factors in distant embryonic territories.

Geomys tyrioni, a new species of early Pleistocene dwarf pocket gopher from the Meade Basin of southwestern Kansas

A new early Pleistocene dwarf pocket gopher species is described from the Short Haul, Aries A, and Nash 72 assemblages in the Borchers Badlands of Meade County, Kansas. Geomys tyrioni is defined by its diminutive size and modern dental and mandibular masseter muscle configuration. G. tyrioni , currently known from the interval of about 2.0–1.70 millions of years ago (Ma), replaced the larger G. floralindae and G. quinni of the slightly earlier (2.11 Ma) Borchers assemblage. Mandibular and dental characters place G. tyrioni in the group of Geomys including the extant Great Plains G. bursarius . Within about 24,000 years after the Nash 72 assemblage, G. tyrioni was replaced by modern-sized Geomys cf. G. bursarius in the Rick Forester assemblage, the earliest record of the extant plains pocket gopher in the Meade Basin and North America. G. tobinensis Hibbard is synonymized with G. bursarius . An evolutionary scenario is provided for the Meade Basin geomyines based on current information, and it is suggested that ashfalls may have played a significant role in geomyine cladogenesis and turnover.

An external mandibular fenestra and other archosauriform characters in basal pterosaurs re-examined

It was claimed that pterosaurs had external mandibular fenestrae, antorbital fossae and muscle scars homologous with the femoral fourth trochanter of archosauriforms, and that those characters suggested that the Pterosauria were within the clade Erythrosuchus + Archosauria. Pertinent parts of available specimens are described to confirm that one pterosaur had external mandibular fenestrae and one had antorbital fossae. However, arguments are presented that possession of external mandibular fenestrae does not support inclusion of the Pterosauria within the clade Erythrosuchus + Archosauria and that the antorbital fossae in the one pterosaur are not homologous with those of the clade Erythrosuchus + Archosauria. Arguments are also presented that the possession of a m. caudofemoralis scar by some pterosaurs does not support inclusion of the Pterosauria within the clade Erythrosuchus + Archosauria, whereas the lack of homologous antorbital fossae and a mound-like or aliform fourth trochanter supports exclusion of the Pterosauria from that clade.