Rostral Bone Research Articles

A new juvenile Yamaceratops (Dinosauria, Ceratopsia) from the Javkhlant Formation (Upper Cretaceous) of Mongolia.

Here we report a new articulated skeleton of Yamaceratops dorngobiensis (MPC-D 100/553) from the Khugenetjavkhlant locality at the Shine Us Khudag (Javkhlant Formation, ?Santonian-Campanian) of the eastern Gobi Desert, Mongolia, which represents the first substantially complete skeleton and the first juvenile individual of this taxon. The specimen includes a nearly complete cranium and large portions of the vertebral column and appendicular skeleton. Its skull is about 2/3 the size of the holotype specimen, based on mandibular length. Its juvenile ontogenetic stage is confirmed by multiple indicators of skeletal and morphological immaturity known in ceratopsians, such as the long-grained surface texture on the long bones, the smooth external surface on the postorbital, open neurocentral sutures of all caudal vertebrae, a large orbit relative to the postorbital and jugal, the low angle of the lacrimal ventral ramus relative to the maxillary teeth row, narrow frontal, and straight ventral edge of the dentary. Osteohistological analysis of MPC-D 100/553 recovered three lines of arrested growth, implying around 3 years of age when it died, and verified this specimen’s immature ontogenetic stage. The specimen adds a new autapomorphy of Yamaceratops, the anteroventral margin of the fungiform dorsal end of the lacrimal being excluded from the antorbital fossa. Furthermore, it shows a unique combination of diagnostic features of some other basal neoceratopsians: the ventrally hooked rostral bone as in Aquilops americanus and very tall middle caudal neural spines about or more than four times as high as the centrum as in Koreaceratops hwaseongensis, Montanoceratops cerorhynchus, and Protoceratops andrewsi. The jugal with the subtemporal ramus deeper than the suborbital ramus as in the holotype specimen is also shared with A. americanus, Liaoceratops yanzigouensis, and juvenile P. andrewsi. Adding 38 new scorings into the recent comprehensive data matrix of basal Neoceratopsia and taking into account the ontogenetically variable characters recovered Y. dorngobiensis as the sister taxon to Euceratopsia (Leptoceratopsidae plus Coronosauria). A second phylogenetic analysis with another matrix for Ceratopsia also supported this position. The new phylogenetic position of Y. dorngobiensis is important in ceratopsian evolution, as this taxon represents one of the basalmost neoceratopsians with a broad, thin frill and hyper-elongated middle caudal neural spines while still being bipedal.

350 Cross Over Septal Flap Technique for Choanal Atresia Surgery: Two Centre Series with Outcomes

Abstract Introduction Choanal atresia (CA) is a congenital obstruction of the posterior nasal aperture due to nasal cavity canalisation failure. Endoscopic endonasal surgery has led to successful CA repair and fewer complications compared to open surgery. We describe our surgical technique that uses septal mucosal flaps without need for stenting or subsequent intubation. Method A multicentre retrospective review of patients who underwent surgery using the cross over septal technique. Patient demographics and outcomes were recorded. Flap design: bilateral vertical septal mucosa incisions are performed on either side of the posterior third of the septum to form two mucoperiosteal flaps. The posterior vomer and atretic plates are removed. One flap is pedicled superiorly and rotated over the bare sphenoid rostral bone. The contralateral flap is pedicled inferiorly and rotated to cover exposed bone of nasal cavity floor. Lateral nasal wall mucosal integrity is maintained. This technique is used both for unilateral and bilateral atresia. Results Twelve patients from 2013 to 2020 were included. Age range was 0.07-50 years, male to female ratio of 1:5. Ten patients had unilateral CA, two had bilateral. Nine had bony CA, the remainder mixed. 5 patients (mean age 2.8 years) underwent second-look endoscopy under sedation an average 36 days following primary surgery. Conclusions The cross over technique for CA has low morbidity and 100% success in our multicentre series. Use of mucoperiosteal flaps to cover the exposed bone, removal of vomer and minimal instrumentation to the lateral nasal wall are the best ways to avoid postoperative stenosis.

On the structure and development of the parasphenoid and the ventral rostral bones in Acipenser baerii and Polyodon spathula (Actinopterygii, Acipenseriformes).

Acipenseriformes (sturgeons and paddlefishes) are currently recognized as sister-group of Neopterygii (bowfin, gars and teleosts) and along with Polypteriformes (bihirs) constitute the two most basal taxa among living ray-finned fishes. Acipenseriforms uniquely possess a large preoral snout which distinguishes them from other actinopterygians. It is covered ventrally by a longitudinal series of exoskeletal elements which extends along the middle part of the snout from the parasphenoid to the very anterior tip of the head. These cranial elements, highly variable in size, number and proportions, are generally referred to as ventral rostral bones. The homologies of these bones remain unresolved. The issue is getting even more complicated because of vague nature of the parasphenoid of acipenseriforms, with which the ventral rostral series is in a contact. Paradoxically, the homology of this bone of acipenseriforms has never been subjected to thorough survey based on the early development and morphology of this bone. Here, the development of the parasphenoid and the ventraI rostral bones in Siberian sturgeon Acipenser baerii and American paddlefish Polyodon spathula is investigated based on a large sample of specimens of both species ranging from larvae just posthatching to juveniles of 50days posthatching. Data obtained in this study allowed to establish primary homologies of the parasphenoid and the ventral rostral bones of Acipenseriformes and to address the evolutionary history of the snout in these fishes.

The sandwich structure of keratinous layers controls the form and growth orientation of chicken rhinotheca.

The upper beak bone of birds is known to be overlain by the rhinotheca, which is composed of the horny sheath of keratinous layers. However, the details of the structure and growth pattern of the rhinotheca are yet to be understood. In this study, the microstructure of the rhinotheca from chicken specimens of different growth stages (ranging from 1 to ~80days old) was analyzed using a combination of thin section and scanning electron microscopy observations, and small-angle X-ray scattering analysis. We found that the rhinotheca comprises three different layers - outer, intermediate, and inner layers - throughout its growth. The outer layer arises from the proximal portion of the beak bone and covers the dorsal surface of the rhinotheca, whereas the intermediate and inner layers originate in the distal portion of the beak bone and underlie the outer layer. This tri-layered structure of the rhinotheca was also observed in wild bird specimens (grey wagtail, king quail, and brown dipper). On the median plane, micro-layers making up the outer and inner layers are bedded nearly parallel to the rostral bone at the base. However, more distally positioned micro-layers of the outer layer are more anteverted distally. The micro-layers of the intermediate layer are bedded nearly perpendicular to those of the outer and inner layers on the median plane. The growth of micro-layers in the intermediate layer adds thickness to the rhinotheca, which causes the difference in profile between the beak bone and the rhinotheca in the distal portion of the beak. Moreover, the entire intermediate layer grows distally as new proximal micro-layers form. The outer layer is dragged distally by the intermediate layer as a result of its distal growth, for the three layers are closely packed to each other at their boundaries. Furthermore, the occurrence of the intermediate and inner layers in the distal portion of the rostral bone may be because the distal end of the beak is frequently used and worn, and the rhinotheca therefore needs to be replaced more frequently at the distal end. The rhinotheca structure described here will be an important and useful factor in the reconstruction of the beaks of birds in extinct taxa.

New data and diagnosis for the Arctic ceratopsid dinosaur Pachyrhinosaurus perotorum

The pachyrostran centrosaurine dinosaur Pachyrhinosaurus perotorum is the geologically youngest (Maastrichtian, 70–68.5 Ma) centrosaurine, and latitudinally highest distributed ceratopsid yet known. Continued preparation of material collected from the type locality, the Kikak-Tegoseak Quarry, has produced more examples of cranial material from multiple individuals, including partial skulls and incomplete parietals. The original reconstruction of the type parietal was incorrect, and the element is similar to that of other Pachyrhinosaurus species in bearing medially directed epiparietal 2 processes along its posterior margin. Pachyrhinosaurus perotorum is diagnosed by an upturned tip of the rostrum; a dorsally shifted rostral bone lacking a sharply downturned, parrot-like beak; an enlarged median ridge at the posterior end of the nasal boss; and, tentatively, a posterior sulcus on epiparietal 2 and a canal passing dorsoventrally through the base of epiparietal 2. A cladistic phylogenetic analysis incorporating new data from this and other recent studies of centrosaurine relationships recovers a monophyletic Pachyrhinosaurus clade. Pachyrhinosaurus perotorum and P. canadensis are found to be sister taxa, united by the presence of an extra ossification on the lateral surface of the rostrum between the narial fossa and nasal boss, and by enlarged supraorbital bosses that contact or nearly contact the posterior end of the nasal boss. Parietal and squamosal frill ornamentations alone do not adequately address the variables in craniofacial morphology needed to distinguish between species of Pachyrhinosaurus.

A new lower actinopterygian fish from the Upper Mississippian Bluefield Formation of West Virginia, USA.

The Upper Mississippian Bluefield Formation of the Mauch Chunk Group in southeastern West Virginia is known for its preservation of a variety of invertebrate taxa and early tetrapod trackways, but no lower actinopterygian remains have been formally described from these Carboniferous rocks. Here, the first lower actinopterygian fish is described from the Bluefield Formation of West Virginia. This fish is represented by a nearly complete articulated specimen with a three-dimensional snout and an unobstructed view of the gular and branchiostegal region. This new taxon is defined by a unique set of characters, which include features of the snout, circumorbital series, cheek, and operculo-gular region. These features make this fish different and distinct from previously described Carboniferous fishes. Some of the morphological features of note include the presence of a distinct lacrimal, premaxillary, ventral rostral and dorsal rostral bones, a narrow infraorbital ventral to the orbit, and a large crescent shaped infraorbital that contacts a single dermosphenotic. There is an anteriorly inclined hatchet-shaped preoperculum and six small suborbital bones anterior to the expanded region of this bone that filling the space between the preoperculum, dermosphenotic, and infraorbital. Posterior to the preoperculum, there is a single wedge-shaped dermohyal and a series of three rectangular anteopercular bones. The anteopercular bones extend halfway down the anterior border of the rectangular operculum. A median gular, two pairs of lateral gulars, and at least eight branchiostegal rays are present. The heterocercal caudal fin is deeply cleft and inequilobate. The scales have pectinated posterior margins and bear diagonal ridges of ganoine. The description of this new taxon represents the first actinopterygian and the first vertebrate body fossil described from the Bluefield Formation and the second actinopterygian taxon described from the Mauch Chunk Group in West Virginia.

Increasing the fish diversity of the Triassic faunas of Gondwana: a new redfieldiiform (Actinopterygii) from the Middle Triassic of Argentina and its palaeobiogeographical implications

AbstractA new actinopterygian, Calaichthys tehul gen. et sp. nov. is described on the basis of a few, well‐preserved specimens from the Anisian Cerro de Las Cabras Formation, Cuyo Basin in Mendoza Province. The new genus shows a combination of primitive characters (e.g. deep posterior region of the maxilla contacting the preopercle, a suspensorium backwardly oriented) and more advanced characters (e.g. distally segmented fin rays, hemiheterocercal caudal fin) and is thus considered to be a ‘subholostean’ fish. The new taxon is assigned to Redfieldiiformes on the basis of its single branchiostegal plate‐like ray, a median gular plate, pectoral fins with stout, stiff, mainly non‐segmented and distally branched fin rays, long and robust fringing fulcra in all fins, basal fulcra bordering both lobes of the caudal fin, and opposite dorsal and anal fins. Calaichthys is characterized by a combination of characters some of which are unique among redfieldiiforms (i.e. strongly ornamented but thin scales with a serrated posterior margin, smooth skull roof bones, extrascapulars with a bifid posterior margin, three suborbital bones, a hatchet‐shaped preopercle, rectangular and slender opercle, deep mouth gape, entopterygoid and ectopterygoid with small pointed teeth disposed in several series, unornamented rostral bone, massive pectoral fins and delicate dorsal, pelvic and anal fins). Calaichthys provides novel information about the anatomy of redfieldiiforms, in particular in relation with the fins and associated scaly elements, as well as the scale morphology and their disposition over the body. Our work confirms for the first time that redfieldiiforms occur in South America. Redfieldiiforms seem to have originated in Gondwana and shown two diversity peaks: in the Anisian and the Carnian. Calaichthys is coeval with those redfieldiiforms of the Middle Triassic (Anisian) of Africa and Australia dwelling in ephemeral lakes.

New Triassic teleosts (Actinopterygii, Teleosteomorpha) from northern Italy and their phylogenetic relationships among the most basal teleosts

ABSTRACT This study provides new evidence of the diversity of Middle–Late Triassic teleosts with the description of new pholidophorids from Italy. The results of the phylogenetic analysis confirm the sister-group relationship [†Aspidorhynchiformes + †Pachycormiformes] as members of Teleosteomorpha and †Prohalecites as the oldest teleosteomorph. The apomorphy-based Teleostei includes a new interpretation of †Pholidophoriformes as a monophyletic group supported by numerous synapomorphies and comprising two families, †Pholidophoridae and †Eurycormidae, fam. nov. The latter is only known from the Upper Jurassic of Europe. The monophyletic family †Pholidophoridae is known by about a dozen European taxa and a Middle Triassic genus (†Malingichthys) from southern Asia, which is the oldest member of the family. The addition of new pholidophorids provides a new interpretation of the possible relationships and taxonomic arrangements within the family †Pholidophoridae. The genera †Pholidorhynchodon and †Eopholidophorus stand as pholidophorids with a unique morphology of the upper oral margin, including a median rostral bone bearing a few large conical teeth, laterodermethmoids armed with large teeth, and the premaxillae displaced from the middle region of the oral margin. This study confirms previous hypotheses of character evolution among basal members of Teleostei, with implications for holostean character evolution. The synapomorphies shared by crown-group Teleostei appeared stepwise more than 140 million years ago over many speciation events and did not arise in a single ancestral species. The analyses of character distribution reflect the gradual accumulation of features that diagnose the crown group. http://zoobank.org/urn:lsid:zoobank.org:pub:0CBDA307-1DD5-4D18-A539-F066E7BF13DC SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP Citation for this article: Arratia, G. 2017. New Triassic teleosts (Actinopterygii, Teleosteomorpha) from northern Italy and their phylogenetic relationships among the most basal teleosts. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2017.1312690.

The lower actinopterygian fauna from the Lower Carboniferous Albert shale formation of New Brunswick, Canada – a review of previously described taxa and a description of a new genus and species

Abstract. The Lower Carboniferous Albert shale formation of New Brunswick, Canada, is well-known for the preservation of countless articulated lower actinopterygian palaeoniscoid fishes. This site is at the boundary between the Devonian and the Lower Carboniferous, making the lower actinopterygians preserved at this site important. The taxonomic history of previously described Albert shale formation actinopterygians is reviewed here. Many of the earliest described actinopterygian taxa from the Albert Formation are represented by poorly preserved type specimens and have the distinction of being moved from one paraphyletic genus to another paraphyletic genus. While these taxa are in need of major redescriptions, such work is premature until the large paraphyletic or polyphyletic genera they have been placed in, Palaeonicus[m], †Rhadinichthys, and †Elonichthys, are redescribed. But there is new diversity within the Albert shale formation. Here, a new lower actinopterygian species, †Lambeia pectinatus, is described from one well-preserved specimen. This new species is characterized by dorsal ridge scales with pectinated posterior margins, body scales inserted between adjacent dorsal ridge scales, body scales with pectinated posterior and ventral margins, the presence of a ventral rostro-premaxilla and a median rostral bone, a separate and distinct antorbital bone, and a single supraorbital bone. This newly described species is distinct from previously described fishes from the Albert Formation, and the morphology of this newly described species is more similar to later Carboniferous fishes rather than Devonian fishes. This suggests that morphological features commonly seen in Carboniferous fishes and rarely seen in Devonian fishes were present early in the Carboniferous.

New beaked whales from the late Miocene of Peru and evidence for convergent evolution in stem and crown Ziphiidae (Cetacea, Odontoceti).

The Ziphiidae (beaked whales) represent a large group of open-ocean odontocetes (toothed cetaceans), whose elusive and deep diving behavior prevents direct observation in their natural habitat. Despite their generally large body size, broad geographical distribution, and high species number, ziphiids thus remain poorly known. Furthermore, the evolutionary processes that have led to their extreme adaptations and impressive extant diversity are still poorly understood. Here we report new fossil beaked whales from the late Miocene of the Pisco Formation (southern Peru). The best preserved remains here described are referred to two new genera and species, the Messinian Chavinziphius maxillocristatus and the Tortonian Chimuziphius coloradensis, based on skull remains from two marine vertebrate-rich localities: Cerro Los Quesos and Cerro Colorado, respectively. C. maxillocristatus is medium sized retains a complete set of functional lower teeth, and bears robust rostral maxillary crests similar to those of the extant Berardius. By contrast, C. coloradensis is small and characterized by large triangular nasals and moderately thickened premaxillae that dorsally close the mesorostral groove. Both species confirm the high past diversity of Ziphiidae, the richest cetacean family in terms of the number of genera and species. Our new phylogenetic and biogeographical analyses depart markedly from earlier studies in dividing beaked whales into two major clades: the Messapicetus clade, which, along with other stem ziphiids, once dominated the southeastern Pacific and North Atlantic; and crown Ziphiidae, the majority of which are found in deep-water regions of the Southern Ocean, with possible subsequent dispersal both globally (Mesoplodon and Ziphius) and to the cooler waters of the northern oceans (Berardius and Hyperoodon). Despite this relatively clear separation, both lineages seem to follow similar evolutionary trends, including (1) a progressive reduction of dentition; (2) an increase in the compactness and thickness of the rostral bones; (3) similar changes in facial morphology (e.g., elevation of the vertex); and (4) an increase of body size. We suggest that these trends may be linked to a convergent ecological shift to deep diving and suction feeding.

From Problem Taxa to Problem Solver: A New Miocene Family, Tranatocetidae, Brings Perspective on Baleen Whale Evolution

Miocene baleen whales were highly diverse and included tens of genera. However, their taxonomy and phylogeny, as well as relationships with living whales, are still a subject of controversy. Here, “Mesocetus” argillarius, a poorly known specimen from Denmark, is redescribed with a focus on the cranial anatomy. It was found to represent not only a new genus, Tranatocetus gen. nov., but also a new family; Tranatocetidae. The whales of this family have the rostral bones either overriding or dividing the frontals; the rostral bones are contacting the parietals and nasals dividing the maxillae on the vertex; the occipital shield is dorsoventrally bent. The tympanic bulla is particularly characteristic of this family featuring a short, narrow anterior portion with a rounded or squared anterior end and a wider and higher posterior portion that is swollen in the posteroventral area. A phylogenetic analysis including 51 taxa supports a monophyletic group comprising most Neogene and modern whales, with Tranatocetidae being possibly closer related to Balaenopteridae (rorquals) than to Cetotheriidae. Tranatocetidae exhibit a charahteristic bulla shape. In fact, all Neogene and modern mysticete families examined have a unique shape of the tympanic bulla that is diagnostic at family-level. Inclusion of problematic taxa like Tranatocetus argillarius in phylogenies brings new understanding of the distribution and diagnostic value of character traits. This underlines the need for re-examination of earlier described specimens in the light of the wealth of new information published in later years.

The skull of the Chinese sturgeon, Acipenser sinensis (Acipenseridae)

AbstractThe Chinese sturgeon, Acipenser sinensis, is a large member of Acipenseridae now found only in the Yangtze River and the Yellow and East China seas. The goal of this paper was to describe the skull of A. sinensis in the context of recent anatomical and systematic studies of sturgeons. Five specimens (354–670 mm standard length) were prepared as skeletons. The left and right parietals and frontals are broadly separated by a median fontanelle. The lateral‐most lateral extrascapular variably supports the confluence of the supratemporal, occipital and trunk lateral lines. There is no distinct ventral supraorbital process as found in other sturgeons. The anterodorsal portion of the snout is unique among Acipenseridae by having a single large anamestic dorsal rostral bone instead of a series of separate dorsal rostral bones. There are 0–2 lateral rostral bones on each side positioned anterior to but not in contact with the horizontal arm of the jugal. The dorsal surface of the neurocranium lacks a pineal opening, and its anterior tip is sharply pointed in the smaller specimens examined and gently curved in larger specimens. The anteromedial arm of the palatopterygoid is broad relative to other acipenserids. These new morphological data are discussed and compared among Acipenseridae.

A Ceratopsian Dinosaur from the Lower Cretaceous of Western North America, and the Biogeography of Neoceratopsia.

The fossil record for neoceratopsian (horned) dinosaurs in the Lower Cretaceous of North America primarily comprises isolated teeth and postcrania of limited taxonomic resolution, hampering previous efforts to reconstruct the early evolution of this group in North America. An associated cranium and lower jaw from the Cloverly Formation (?middle–late Albian, between 104 and 109 million years old) of southern Montana is designated as the holotype for Aquilops americanus gen. et sp. nov. Aquilops americanus is distinguished by several autapomorphies, including a strongly hooked rostral bone with a midline boss and an elongate and sharply pointed antorbital fossa. The skull in the only known specimen is comparatively small, measuring 84 mm between the tips of the rostral and jugal. The taxon is interpreted as a basal neoceratopsian closely related to Early Cretaceous Asian taxa, such as Liaoceratops and Auroraceratops. Biogeographically, A. americanus probably originated via a dispersal from Asia into North America; the exact route of this dispersal is ambiguous, although a Beringian rather than European route seems more likely in light of the absence of ceratopsians in the Early Cretaceous of Europe. Other amniote clades show similar biogeographic patterns, supporting an intercontinental migratory event between Asia and North America during the late Early Cretaceous. The temporal and geographic distribution of Upper Cretaceous neoceratopsians (leptoceratopsids and ceratopsoids) suggests at least intermittent connections between North America and Asia through the early Late Cretaceous, likely followed by an interval of isolation and finally reconnection during the latest Cretaceous.

An unusual modification of the jaws in cf. Alanqa, a mid-Cretaceous azhdarchid pterosaur from the Kem Kem beds of Morocco

A jaw bone attributed to the mid-Cretaceous azhdarchid pterosaur Alanqa saharica Ibrahim et al., 2010 is described. The new specimen from the Kem Kem beds of south eastern Morocco is unusual for the presence of expanded rostral bones that protrude above the occlusal surface of the jaws. The function of this unusual osteological modification is uncertain, but it is considered likely that it served a role in food processing, or perhaps jaw stability.

Foraging behavior of Chleuastochoerus (Suidae, Artiodactyla): A case study of skull and mandible morpho-functional analysis

The skull and mandible of a Late Miocene fossil pig, Chleuastochoerus, are compared morphologically with those of extant pigs and peccaries, and subjected to a functional analysis. The presence of a rostral bone in the skull and relatively strong rostral muscles indicates that Chleuastochoerus possessed considerable digging ability, though the relatively narrow occipital surface and the shortness of the skull would have restricted the range of motion through which the skull could be swung. The distinctive pre-zygomatic plate and over-canine arch-niche may have played a role in protecting the skull and canines during digging. The massive masticatory muscles, reconstructed based on well-developed parietal and zygomatic crests, would have enabled the mouth to close quickly and contributed to moving the mandible both longitudinally and laterally. The configuration of the cranio-mandibular joint and its relatively high position show clearly that Chleuastochoerus was capable of both crushing and grinding movements during mastication. The comparatively simple structure of the crown surfaces of the cheek teeth suggests that the food of Chleuastochoerus may have been softer than that of extant suids. The diet of Chleuastochoerus is postulated to fall between those of true forest pigs and open habitat pigs, and the habitat of Chleuastochoerus to be relatively humid forest edge or nearby areas of open steppe.

Rostral densification in beaked whales: Diverse processes for a similar pattern

As compared to other odontocetes (toothed whales), the rostrum of beaked whales (family Ziphiidae) often displays extensive changes in the shape, thickness, and density of its constituent bones. Previous morphological observations suggested that these modifications appeared in parallel in different ziphiid lineages. However, very few data were available on the compactness and histology of these rostral bones, which precluded the study of the processes at work for the development of such structures, as well as the interpretation of their functional implications. In this work we review the bibliographic data on the anatomy of the ziphiid rostrum and we add new observations on adults of several extinct and extant taxa. These observations are based on CT scans and transverse histological sections. Our results confirm that different bones (vomer, mesethmoid, premaxilla, maxilla) are involved in the various morphologies displayed by ziphiid rostra. Strong density contrasts are detected between bones and/or inside the bones themselves; for example, parts of the rostrum reach densities in the range of Neoceti ear bones, which are among the densest bones known hitherto. Furthermore, the histology of the pachyostotic and osteosclerotic bones proves to change from one taxon to the other; the degree of Haversian remodeling varies strongly between species: it can be absent (e.g. Aporotus recurvirostris), partial (e.g. aff. Ziphirostrum), or complete (e.g., Mesoplodon densirostris). The atypical secondary osteons known to be responsible for bone hypermineralization in the rostrum of M. densirostris occurred also in Choneziphius sp. Confronted with a phylogenetic framework, these anatomical and histological observations indicate that the acquisition of compact (osteosclerotic) and/or swollen (pachyostotic) bone is the result of a broad convergence between taxa, in response to common selective pressures. The functional dimension of this question is discussed with respect to what is known about extant ziphiid ecology.

The Chiropteran Premaxilla: A Reanalysis of Morphological Variation and Its Phylogenetic Interpretation

The mammalian premaxilla, which bears the incisor teeth, is composed of a body and two processes (nasal and palatine) that articulate with other rostral bones via four cranial sutures. In bats, the premaxilla is modified in many ways, and this variation has been extensively used in bat systematics. The premaxilla has provided characters to diagnose a number of important taxonomic groupings—most notably, the division of Microchiroptera into the infraorders Yinochiroptera and Yangochiroptera. Recent molecular studies have challenged the monophyly of Microchiroptera, and several families have been transferred to clades other than those in which they were placed traditionally. Because premaxillary characters have figured prominently among those used to establish the traditional classification of bats, we compared the anatomy of the bone across suprageneric bat groups and provide revised descriptions of its variation. On the basis of extensive material examined, we generated 16 new characters, of which at least 12 are partially applicable to all Chiroptera, and several of which are informative within specific bat groups. Three new characters code variation in the basic structure of the chiropteran premaxilla in a new way. As a result, the traditional character defining Yinochiroptera (a “movable premaxilla”) was found to lack an anatomical basis; by contrast, Yangochiroptera was still supported. Still, a tree search using just the new premaxillary characters recovered Yinochiroptera as monophyletic. Even with a low character-to-taxon ratio, premaxillary characters recover a number of clades recognized in recent phylogenetic studies of bats. Mapping of characters onto the latest molecular and morphological chiropteran trees required many more extra steps in the former than in the latter. Our interpretation of premaxillary variation in bats suggests two opposing trends in different lineages: one toward weakening and eventual loss of the bone, and the other toward a strengthening via suture fusion. We conclude that, despite some homoplasy, the chiropteran premaxilla is richer in potentially phylogenetically informative characters than previously thought and that it should be explored further in systematic studies of bats at a variety of systematic levels.

NEW ONYCHODONTIFORM (OSTEICHTHYES; SARCOPTERYGII) FROM THE LOWER DEVONIAN OF VICTORIA, AUSTRALIA

Abstract The Onychodontiformes is a poorly known sarcopterygian fish group, with four genera currently described, predominantly from the Middle-Late Devonian. A new onychodont, Bukkanodus jesseni n. gen. and sp., from the Fairy Formation, Victoria, Australia, is of Early Devonian (mid-late Pragian) age, representing one of the oldest known occurrences of this group. Other Pragian onychodonts are represented by a single lower jaw from China, while older occurrences (Lochkovian) include a lower jaw also from China and isolated teeth from Nevada. The Australian material, though disarticulated, includes skull, jaw, and palatal and dental specimens. These specimens share characteristics with younger onychodont taxa, including a laterally compressed tooth whorl with main and accessory rows containing an equal number of teeth, an anteriorly arched shape of the premaxilla, a lateral rostral bone participating in the orbital margin, parietals separated in the midline by small bones, the insertion of the basispheno...

Observations on the skulls of sturgeons (Acipenseridae): shared similarities of Pseudoscaphirhynchus kaufmanni and juvenile specimens of Acipenser stellatus

A novel hypothesis uniting Acipenser stellatus and Pseudoscaphirhynchus as sister groups has recently been proposed based on analysis of DNA sequences. In this paper I compare specimens of A. stellatus and P. kaufmanni, and show that they share several putatively derived similarities in the structure of their skulls, including: the presence of large spines on the dermal bones of skull; lateral extrascapular bones that enclose the confluence of the posttemporal, supratemporal, and otic sensory canals; elongate dorsal rostral bones; border rostral bones distinct in shape from dorsal rostral bones; greatly enlarged jugal that lacks a median flange; rostral canal bones that loop posteriorly at the anterior commissure of the rostral sensory canals; and the presence of an elongate, flat, and broad posterior ventral rostral bone. These similarities support a close relationship between A. stellatus and Pseudoscaphirhynchus, but still remain to be critically tested.

A New Protoceratopsid (Dinosauria: Neoceratopsia) from the Late Cretaceous of Inner Mongolia, China

Abstract An almost complete skull, which was collected from the Upper Cretaceous of the Bayan Mandahu area in Inner Mongolia, China by the Sino‐Canadian Dinosaur Project, is described and assigned to a new genus of protoceratopsid dinosaur, Magnirostris dodsoni gen. et sp. nov. This new taxon is distinguished from other protoceratopsids by the robust rostral bone and the existence of incipient orbital horn cores. The existence of an additional antorbital fenestra indicates a close relationship between Magnirostris and Bagaceratops.