Comparative anatomy of the bony labyrinth of extant and extinct porpoises (Cetacea: Phocoenidae)

The inner ear anatomy of cetaceans, now more readily accessible by means of nondestructive high‐resolution X‐ray computed tomographic (CT) scanning, provides a window into their acoustic abilities and ecological preferences. Inner ear labyrinths also may be a source for additional morphological characters for phylogenetic analyses. In this study, we explore digital endocasts of the inner ear labyrinths of representative species of extinct and extant porpoises (Mammalia: Cetacea: Phocoenidae), a clade of some of the smallest odontocete cetaceans, which produce some of the highest‐frequency clicks for biosonar and communication. Metrics used to infer hearing ranges based on cochlear morphology indicate that all taxa considered could hear high‐frequency sounds, thus the group had already acquired high‐frequency hearing capabilities by the Miocene (9–11 Mya) at the latest. Vestibular morphology indicates that extant species with pelagic preferences have similarly low semicircular canal deviations from 90°, values indicating more sensitivity to head rotations. Species with near‐shore preferences have higher canal deviation values, indicating less sensitivity to head rotations. Extending these analyses to the extinct species, we demonstrate a good match between those predicted to have coastal (such as Semirostrum cerutti) preferences and high canal deviation values. We establish new body length relationships based on correlations with inner ear labyrinth volume, which can be further explored among other aquatic mammals to infer body size of specimens consisting of fragmentary material.     

A Late Role for bmp2b in the Morphogenesis of Semicircular Canal Ducts in the Zebrafish Inner Ear

Background

The Bone Morphogenetic Protein (BMP) genes bmp2 and bmp4 are expressed in highly conserved patterns in the developing vertebrate inner ear. It has, however, proved difficult to elucidate the function of BMPs during ear development as mutations in these genes cause early embryonic lethality. Previous studies using conditional approaches in mouse and chicken have shown that Bmp4 has a role in semicircular canal and crista development, but there is currently no direct evidence for the role of Bmp2 in the developing inner ear.

Methodology/Principal Findings

We have used an RNA rescue strategy to test the role of bmp2b in the zebrafish inner ear directly. Injection of bmp2b or smad5 mRNA into homozygous mutant swirl (bmp2b^−/−) embryos rescues the early patterning defects in these mutants and the fish survive to adulthood. As injected RNA will only last, at most, for the first few days of embryogenesis, all later development occurs in the absence of bmp2b function. Although rescued swirl adult fish are viable, they have balance defects suggestive of vestibular dysfunction. Analysis of the inner ears of these fish reveals a total absence of semicircular canal ducts, structures involved in the detection of angular motion. All other regions of the ear, including the ampullae and cristae, are present and appear normal. Early stages of otic development in rescued swirl embryos are also normal.

Conclusions/Significance

Our findings demonstrate a critical late role for bmp2b in the morphogenesis of semicircular canals in the zebrafish inner ear. This is the first demonstration of a developmental role for any gene during post-embryonic stages of otic morphogenesis in the zebrafish. Despite differences in the early stages of semicircular canal formation between zebrafish and amniotes, the role of Bmp2 in semicircular canal duct outgrowth is likely to be conserved between different vertebrate species.     

The bony labyrinth of Platecarpus (Squamata: Mosasauria) and aquatic adaptations in squamate reptiles

Mosasaurs were among the last marine reptiles that lived before the Cretacesous–Paleogene extinction. Little is known about the sensory evolution of mosasaurs in relation to their aquatic lifestyle. In this study, the braincase of Platecarpus was CT-scanned and virtual models were constructed showing the bony labyrinth — or the inner ear — a sensory apparatus for balance and hearing. The virtual inner ear consists of the semicircular canals, vestibule, and cochlea. Compared with extant squamates, Platecarpus resembles sea snakes in having a small vestibule with a flat dorsal surface, but it differs from non-mosasaurian squamates in having rounded semicircular canals. Phylogenetic linear regression analysis supports a linear relationship, independent from phylogeny, between the length of the three semicircular canals and the length of the skull. The semicircular canals of Platecarpus are shorter than predicted, but the fossil data fell within the 95% prediction interval calculated from the extant data and the skull length of Platecarpus. Although size reduction of the bony labyrinth has been associated with aquatic adaptions in mammals, our results suggest that in squamates, semicircular canal size is related to skull size rather than habitat preference.     

CHD7 mutational analysis and clinical considerations for auditory rehabilitation in deaf patients with CHARGE syndrome

Background

Otologic manifestations are one of the most consistent findings of CHARGE syndrome found in more than 90%. Since genetic analysis of the CHD7 gene has rarely been performed in previous reports dealing with ear abnormalities, the genotypic spectrum of CHD7 mutations was analyzed in deaf patients with CHARGE syndrome, and the clinical considerations concerning auditory rehabilitation were investigated.

Methods

Nine Korean patients with CHARGE syndrome showing profound hearing loss and semicircular canal aplasia were included. All 38 exons of CHD7 were analyzed by direct sequencing. For splice site variations, in silico and exon-trapping analyses were performed to verify the pathogenicity of nucleotide variations. Clinical features and the outcome of auditory rehabilitation were also analyzed.

Results

Eight of 9 patients revealed alterations of the CHD7 gene including 3 frameshift, 2 nonsense, 2 splice site, and 1 missense mutations. Five of 9 patients were clinically diagnosed as atypical CHARGE syndrome but demonstrated various mutations of the CHD7 gene. One familial case showed intra-familial variability. Radiologic findings suggesting cochleovestibular nerve deficiency were identified in most of the patients. Of the 8 patients who underwent cochlear implantation, 5 patients demonstrated favorable outcome. Larger diameter of the cochleovestibular nerve on imaging and absence of severe mental retardation were factors related to better outcome after cochlear implantation rather than the type of CHD7 mutations. Auditory brainstem implantation was performed in two patients who did not benefit from cochlear implantation.

Conclusions

Genetic analysis of the CHD7 gene should be performed in cases with semicircular canal aplasia even when other typical features of CHARGE syndrome are absent. For auditory rehabilitation in CHARGE syndrome, cochlear implantation should be strongly recommended in selected cases with favorable prognostic factors. Auditory brainstem implantation may be a viable option in patients with CHARGE syndrome who have failed to benefit from cochlear implantation.     

The Video Head Impulse Test (vHIT) Detects Vertical Semicircular Canal Dysfunction

Background

The video head impulse test (vHIT) is a useful clinical tool to detect semicircular canal dysfunction. However vHIT has hitherto been limited to measurement of horizontal canals, while scleral search coils have been the only accepted method to measure head impulses in vertical canals. The goal of this study was to determine whether vHIT can detect vertical semicircular canal dysfunction as identified by scleral search coil recordings.

Methods

Small unpredictable head rotations were delivered by hand diagonally in the plane of the vertical semicircular canals while gaze was directed along the same plane. The planes were oriented along the left-anterior-right-posterior (LARP) canals and right-anterior-left-posterior (RALP) canals. Eye movements were recorded simultaneously in 2D with vHIT (250 Hz) and in 3D with search coils (1000 Hz). Twelve patients with unilateral, bilateral and individual semicircular canal dysfunction were tested and compared to seven normal subjects.

Results

Simultaneous video and search coil recordings were closely comparable. Mean VOR gain difference measured with vHIT and search coils was 0.05 (SD = 0.14) for the LARP plane and −0.04 (SD = 0.14) for the RALP plane. The coefficient of determination R² was 0.98 for the LARP plane and 0.98 for the RALP plane and the results of the two methods were not significantly different. vHIT and search coil measures displayed comparable patterns of covert and overt catch-up saccades.

Conclusions

vHIT detects dysfunction of individual vertical semicircular canals in vestibular patients as accurately as scleral search coils. Unlike search coils, vHIT is non-invasive, easy to use and hence practical in clinics.     

Comparative Analysis of Vestibular System Development in Various Groups of Mammals Living under Different Environmental Conditions

We have conducted for the first time a comparative study of the prenatal development of the vestibular system in representatives of pinnipeds (Phocidae, Otariidae, Odobenidae) and cetaceans (Odontoceti, Mysticeti) in comparison with terrestrial mammals. This allowed us to perform a detailed study of the structural organization of the inner ear in species with different ecological specialization, to find out adaptive aspects and stages of the formation of cochlear and vestibular structures in each of the studied species, and to correlate it with the properties of the environment. Studies on early embryogenesis of the labyrinth in cetaceans and pinnipeds, which represent a special direction in the evolution of placentates, give a significant contribution to the solution of the problem of the evolutionary origin of the labyrinth in the mammals studied. Sensory systems clearly demonstrate the scope of evolutionary and adaptive transformations, which appear in mammals during the transition from the terrestrial to the aquatic mode of life. At the same time, these results may provide help in understanding the general trends of the development of structure and function of the inner ear in mammals as a whole.     

Digital Reconstruction of the Otic Region and Inner Ear of the Non-Mammalian Cynodont Brasilitherium riograndensis (Late Triassic, Brazil) and Its Relevance to the Evolution of the Mammalian Ear

The external anatomy of the petrosal, the bony labyrinth of the inner ear, and the stapes of Brasilitherium riograndensis (specimen UFRGS-PV-1043-T) were investigated by digital 3D reconstructions based on μCT scan images. Brasilitherium is the most basal taxon bearing a distinct promontorium, although less inflated than that of Morganucodon and still lacking a flat medial facet. A bony wall formed by the petrosal separates the cochlear canal and the vestibule from the brain cavity, with an internal acoustic meatus bearing distinct foramina for the facial nerve (VII) and vestibulocochlear nerve (VIII). The semicircular canals are irregular in shape, the anterior canal being the largest and the lateral one the smallest. Brasilitherium has an elongated but straight cochlear canal. The stapes resembles the morphology of derived non-mammaliaform cynodonts, such as Probainognathus and Pachygenelus, and differs from Thrinaxodon. By the allometric relationship of the cochlear canal and the estimated body mass, Brasilitherium can be grouped with Yunnanodon and Morganucodon in a regression line, which is below the line of mammals and above the line of non-avian reptiles. Brasilitherium fits in a sequence of gradual elongation of the cochlear canal associated with the enhancement in the capacity to hear higher frequencies. Among the constraints that might have triggered these transformations in small, insectivorous, and possibly nocturnal Mesozoic cynodont taxa is the improvement of detecting acoustically active insects.     

Phylogenetic analysis of conservation priorities for aquatic mammals and their terrestrial relatives, with a comparison of methods

Background

Habitat loss and overexploitation are among the primary factors threatening populations of many mammal species. Recently, aquatic mammals have been highlighted as particularly vulnerable. Here we test (1) if aquatic mammals emerge as more phylogenetically urgent conservation priorities than their terrestrial relatives, and (2) if high priority species are receiving sufficient conservation effort. We also compare results among some phylogenetic conservation methods.

Methodology/Principal Findings

A phylogenetic analysis of conservation priorities for all 620 species of Cetartiodactyla and Carnivora, including most aquatic mammals. Conservation priority ranking of aquatic versus terrestrial species is approximately proportional to their diversity. However, nearly all obligated freshwater cetartiodactylans are among the top conservation priority species. Further, ∼74% and 40% of fully aquatic cetartiodactylans and carnivores, respectively, are either threatened or data deficient, more so than their terrestrial relatives. Strikingly, only 3% of all ‘high priority’ species are thought to be stable. An overwhelming 97% of these species thus either show decreasing population trends (87%) or are insufficiently known (10%). Furthermore, a disproportional number of highly evolutionarily distinct species are experiencing population decline, thus, such species should be closely monitored even if not currently threatened. Comparison among methods reveals that exact species ranking differs considerably among methods, nevertheless, most top priority species consistently rank high under any method. While we here favor one approach, we also suggest that a consensus approach may be useful when methods disagree.

Conclusions/Significance

These results reinforce prior findings, suggesting there is an urgent need to gather basic conservation data for aquatic mammals, and special conservation focus is needed on those confined to freshwater. That evolutionarily distinct—and thus ‘biodiverse’—species are faring relatively poorly is alarming and requires further study. Our results offer a detailed guide to phylogeny-based conservation prioritization for these two orders.     

Morphological variation among the inner ears of extinct and extant baleen whales (Cetacea: Mysticeti)

Living mysticetes (baleen whales) and odontocetes (toothed whales) differ significantly in auditory function in that toothed whales are sensitive to high‐frequency and ultrasonic sound vibrations and mysticetes to low‐frequency and infrasonic noises. Our knowledge of the evolution and phylogeny of cetaceans, and mysticetes in particular, is at a point at which we can explore morphological and physiological changes within the baleen whale inner ear. Traditional comparative anatomy and landmark‐based 3D‐geometric morphometric analyses were performed to investigate the anatomical diversity of the inner ears of extinct and extant mysticetes in comparison with other cetaceans. Principal component analyses (PCAs) show that the cochlear morphospace of odontocetes is tangential to that of mysticetes, but odontocetes are completely separated from mysticetes when semicircular canal landmarks are combined with the cochlear data. The cochlea of the archaeocete Zygorhiza kochii and early diverging extinct mysticetes plot within the morphospace of crown mysticetes, suggesting that mysticetes possess ancestral cochlear morphology and physiology. The PCA results indicate variation among mysticete species, although no major patterns are recovered to suggest separate hearing or locomotor regimes. Phylogenetic signal was detected for several clades, including crown Cetacea and crown Mysticeti, with the most clades expressing phylogenetic signal in the semicircular canal dataset. Brownian motion could not be excluded as an explanation for the signal, except for analyses combining cochlea and semicircular canal datasets for Balaenopteridae. J. Morphol. 277:1599–1615, 2016. © 2016 Wiley Periodicals, Inc.     

Increased rate of hair keratin gene loss in the cetacean lineage

Background

Hair represents an evolutionary innovation that appeared early on mammalian evolutionary history, and presumably contributed significantly to the rapid radiation of the group. An interesting event in hair evolution has been its secondary loss in some mammalian groups, such as cetaceans, whose hairless phenotype appears to be an adaptive response to better meet the environmental conditions. To determine whether different repertoire of keratin genes among mammals can potentially explain the phenotypic hair features of different lineages, we characterized the type I and II clusters of alpha keratins from eight mammalian species, including the hairless dolphin and minke whale representing the order Cetacea.

Results

We combined the available genomic information with phylogenetic analysis to conduct a comprehensive analysis of the evolutionary patterns of keratin gene clusters. We found that both type I and II gene clusters are fairly conserved among the terrestrial mammals included in this study, with lineage specific gene duplication and gene loss. Nevertheless, there is also evidence for an increased rate of pseudogenization in the cetacean lineage when compared to their terrestrial relatives, especially among the hair type keratins.

Conclusions

Here we present a comprehensive characterization of alpha-keratin genes among mammals and elucidate the mechanisms involved in the evolution of this gene family. We identified lineage-specific gene duplications and gene loss among the Laurasiatherian and Euarchontoglires species included in the study. Interestingly, cetaceans present an increased loss of hair-type keratin genes when compared to other terrestrial mammals. As suggested by the ‘less-is-more’ hypothesis, we do not rule out the possibility that the gene loss of hair-type keratin genes in these species might be associated to the hairless phenotype and could have been adaptive in response to new selective pressures imposed by the colonization of a new habitat. Our study provides support for the idea that pseudogenes are not simply ‘genomic fossils’ but instead have adaptive roles during the evolutionary process.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-869) contains supplementary material, which is available to authorized users.     

Functional morphological adaptations of the bony labyrinth in marsupials (Mammalia,Theria)

Diprotodontia represents the largest and ecologically most distinct order of marsupials occurring in Australasian being highly divers in size, locomotion, habitat preferences, feeding, and activity pattern. The spatial orientation in the habitat and therefore the three‐dimensional space is detected by the vestibular system of the inner ear, more precisely by the three semicircular canals. In this study, we investigated the bony labyrinth of diprotodontian and selected non‐diprotodontian marsupial mammals of almost all genera with noninvasive micro‐CT scanning and 3D‐reconstructions. In principal component analyses, the subterranean taxon can be separated from gliding and saltatorial taxa, whereas arboreal species can be separated from saltatorial specimens. The highest PCA loadings of this functional distinction are clearly found in the diameter of the semicircular canals, whereas the overall shape (height, width, length) of the semicircular canals is less important. Additionally, the investigated arboreal and fossorial species of South America are nested in the morphospace of the Australasian taxa. Even if a phylogenetic signal in the anatomy of the bony labyrinth cannot be excluded entirely, the main functional morphological signal of the vestibular system is found in the diameter of the semicircular canals. With the large dataset of extant marsupial mammals analysed here, the locomotion mode of extinct taxa can be inferred in future studies independent of any evidence of postcranial material.     

Electrical Vestibular Stimulation after Vestibular Deafferentation and in Vestibular Schwannoma

Background

Vestibular reflexes, evoked by human electrical (galvanic) vestibular stimulation (EVS), are utilized to assess vestibular function and investigate its pathways. Our study aimed to investigate the electrically-evoked vestibulo-ocular reflex (eVOR) output after bilateral and unilateral vestibular deafferentations to determine the characteristics for interpreting unilateral lesions such as vestibular schwannomas.

Methods

EVOR was recorded with dual-search coils as binocular three-dimensional eye movements evoked by bipolar 100 ms-step at EVS intensities of [0.9, 2.5, 5.0, 7.5, 10.0]mA and unipolar 100 ms-step at 5 mA EVS intensity. Five bilateral vestibular deafferented (BVD), 12 unilateral vestibular deafferented (UVD), four unilateral vestibular schwannoma (UVS) patients and 17 healthy subjects were tested with bipolar EVS, and five UVDs with unipolar EVS.

Results

After BVD, bipolar EVS elicited no eVOR. After UVD, bipolar EVS of one functioning ear elicited bidirectional, excitatory eVOR to cathodal EVS with 9 ms latency and inhibitory eVOR to anodal EVS, opposite in direction, at half the amplitude with 12 ms latency, exhibiting an excitatory-inhibitory asymmetry. The eVOR patterns from UVS were consistent with responses from UVD confirming the vestibular loss on the lesion side. Unexpectedly, unipolar EVS of the UVD ear, instead of absent response, evoked one-third the bipolar eVOR while unipolar EVS of the functioning ear evoked half the bipolar response.

Conclusions

The bidirectional eVOR evoked by bipolar EVS from UVD with an excitatory-inhibitory asymmetry and the 3 ms latency difference between normal and lesion side may be useful for detecting vestibular lesions such as UVS. We suggest that current spread could account for the small eVOR to 5 mA unipolar EVS of the UVD ear.     

Intraspecific variation in the domestic cat bony labyrinth revealed by different measurement techniques

The knowledge of intraspecific variation is important to make assumptions on an interspecific level. To study intraspecific variation in the bony labyrinth morphology of the domestic cat, eleven specimens of Felis silvestris catus and two additional subspecies (F. s. lybica, F. s. ornata) were investigated. The sample comprises skulls of adult males and females, as well as juvenile cats. Each bony labyrinth endocast was virtually reconstructed based on µCT scans. To estimate the radius of curvature of each inner ear semicircular canal, three different approaches were tested. The comparison of the different methods resulted in different absolute values for the measured radii. The assumed best structure to precisely characterize the size of a semicircular canal is the inner perimeter. Within the tested sample, the anterior semicircular canal is always the largest, while the posterior semicircular canal is the second largest and the lateral semicircular canal the smallest in most cases. The coefficient of variation lies below 10% for all bony labyrinth measurements within the sample. The inner perimeter values of each semicircular canal are similar within all investigated specimens, even though the skull length of adult cats is twice as long as that of juvenile cats. Thus, inner ear biometry of the domestic cat seems stable throughout growth series and can therefore be used for systematic and ecological studies and the inclusion of juvenile individuals is reasonable. It is noteworthy that the inner perimeter values of the semicircular canals do not vary as much as the values of the angles spanned between the three canals within the sample. The inner ear within the cat skull is oriented about 25° to 31° to the palate (angle between the plane anchored to the lateral semicircular canals (SC) and the plane anchored to the palate). The cochlea coils between 3.00 and 3.25 turns in the investigated sample.     

Comparative analysis of vestibular system development in various groups of mammals living under different environmental conditions

We have conducted for the first time a comparative study of the prenatal development of the vestibular system in representatives of pinnipeds (Phocidae, Otariidae, Odobenidae) and cetaceans (Odontoceti, Mysticeti) in comparison with terrestrial mammals. This allowed us to perform a detailed study of the structural organization of the inner ear in species with different ecological specialization, to find out adaptive aspects and stages of the formation of cochlear and vestibular structures in each of the studied species, and to correlate it with the properties of the environment. Studies on early embryogenesis of the labyrinth in cetaceans and pinnipeds, which represent a special direction in the evolution of placentates, give a significant contribution to the solution of problem about the evolutionary origin of the labyrinth in mammals studied. Sensory systems clearly demonstrate the scope of evolutionary and adaptive transformations, which appear in mammals during the transition from the terrestrial to the aquatic mode of life. At the same time, these results may provide help in understanding the general trends of the development of structure and function of the inner ear in mammals as a whole.     

Different Level of Intraspecific Variation of the Bony Labyrinth Morphology in Slow- Versus Fast-Moving Primates

The vestibular system of the inner ear detects the motions of the head and is involved in maintaining balance. For this reason, this organ has been deeply studied and several scientists have tried to link its morphology with the locomotor behavior of an animal. Via high-resolution computed microtomography and geometric morphometric methods, we analyzed the intraspecific variation of the 3D morphology of the bony labyrinth (inner ear) in four species of primates differing in their locomotor adaptations: two being slow-moving taxa (Nycticebus and Perodicticus), and two being fast-moving taxa (Callithrix and Microcebus). Basically, there are very few analyses of the inter-individual variation of this organ in mammals in general, and this approach has never been attempted in primates thus far. Our results show that variation of the bony labyrinth morphology is expressed by the same ways in the different species (e.g., differences in the size, shape, and orientation of the semicircular canals, and in the width and height of the cochlea), but that slow-moving taxa exhibit a higher amount of intraspecific variation than do fast-moving taxa. Our results strengthen support for a previously published hypothesis, according to which a relaxation of the selective pressure applied to the morphology of the bony labyrinth is the likely reason for this higher amount of intraspecific variation in slow-moving taxa, and that it may be related to a reduced functional demand for rapid postural adjustments.     

A Giant Chelonioid Turtle from the Late Cretaceous of Morocco with a Suction Feeding Apparatus Unique among Tetrapods

Background

Secondary adaptation to aquatic life occurred independently in several amniote lineages, including reptiles during the Mesozoic and mammals during the Cenozoic. These evolutionary shifts to aquatic environments imply major morphological modifications, especially of the feeding apparatus. Mesozoic (250–65 Myr) marine reptiles, such as ichthyosaurs, plesiosaurs, mosasaurid squamates, crocodiles, and turtles, exhibit a wide range of adaptations to aquatic feeding and a broad overlap of their tooth morphospaces with those of Cenozoic marine mammals. However, despite these multiple feeding behavior convergences, suction feeding, though being a common feeding strategy in aquatic vertebrates and in marine mammals in particular, has been extremely rarely reported for Mesozoic marine reptiles.

Principal Findings

A relative of fossil protostegid and dermochelyoid sea turtles, Ocepechelon bouyai gen. et sp. nov. is a new giant chelonioid from the Late Maastrichtian (67 Myr) of Morocco exhibiting remarkable adaptations to marine life (among others, very dorsally and posteriorly located nostrils). The 70-cm-long skull of Ocepechelon not only makes it one of the largest marine turtles ever described, but also deviates significantly from typical turtle cranial morphology. It shares unique convergences with both syngnathid fishes (unique long tubular bony snout ending in a rounded and anteriorly directed mouth) and beaked whales (large size and elongated edentulous jaws). This striking anatomy suggests extreme adaptation for suction feeding unmatched among known turtles.

Conclusion/Significance

The feeding apparatus of Ocepechelon, a bony pipette-like snout, is unique among tetrapods. This new taxon exemplifies the successful systematic and ecological diversification of chelonioid turtles during the Late Cretaceous. This new evidence for a unique trophic specialization in turtles, along with the abundant marine vertebrate faunas associated to Ocepechelon in the Late Maastrichtian phosphatic beds of Morocco, further supports the hypothesis that marine life was, at least locally, very diversified just prior to the Cretaceous/Palaeogene (K/Pg) biotic crisis.     

The petrosal and inner ear of the Late Jurassic cladotherian mammal Dryolestes leiriensis and implications for ear evolution in therian mammals

Dryolestes leiriensis is a Late Jurassic fossil mammal of the dryolestoid superfamily in the cladotherian clade that includes the extant marsupials and placentals. We used high resolution micro‐computed tomography (µCT) scanning and digital reconstruction of the virtual endocast of the inner ear to show that its cochlear canal is coiled through 270°, and has a cribriform plate with the spiral cochlear nerve foramina between the internal acoustic meatus and the cochlear bony labyrinth. The cochlear canal has the primary bony lamina for the basilar membrane with a partially formed (or partially preserved) canal for the cochlear spiral ganglion. These structures, in their fully developed condition, form the modiolus (the bony spiral structure) of the fully coiled cochlea in extant marsupial and placental mammals. The CT data show that the secondary bony lamina is present, although less developed than in another dryolestoid Henkelotherium and in the prototribosphenidan Vincelestes. The presence of the primary bony lamina with spiral ganglion canal suggests a dense and finely distributed cochlear nerve innervation of the hair cells for improved resolution of sound frequencies. The primary, and very probably also the secondary, bony laminae are correlated with a more rigid support for the basilar membrane and a narrower width of this membrane, both of which are key soft‐tissue characteristics for more sensitive hearing for higher frequency sound. All these cochlear features originated prior to the full coiling of the therian mammal cochlea beyond one full turn, suggesting that the adaptation to hearing a wider range of sound frequencies, especially higher frequencies with refined resolution, has an ancient evolutionary origin no later than the Late Jurassic in therian evolution. The petrosal of Dryolestes has added several features that are not preserved in the petrosal of Henkelotherium. The petrosal characters of dryolestoid mammals are essentially the same as those of Vincelestes, helping to corroborate the synapomorphies of the cladotherian clade in neural, vascular, and other petrosal characteristics. The petrosal characteristics of Dryolestes and Henkelotherium together represent the ancestral morphotype of the cladotherian clade (Dryolestoidea + Vincelestes + extant Theria) from which the extant therian mammals evolved their ear region characteristics. © 2012 The Linnean Society of London, Zoological Journal of the Linnean Society, 2012, 166 , 433–463.     

Relationships of Cetacea (Artiodactyla) Among Mammals: Increased Taxon Sampling Alters Interpretations of Key Fossils and Character Evolution

Background

Integration of diverse data (molecules, fossils) provides the most robust test of the phylogeny of cetaceans. Positioning key fossils is critical for reconstructing the character change from life on land to life in the water.

Methodology/Principal Findings

We reexamine relationships of critical extinct taxa that impact our understanding of the origin of Cetacea. We do this in the context of the largest total evidence analysis of morphological and molecular information for Artiodactyla (661 phenotypic characters and 46,587 molecular characters, coded for 33 extant and 48 extinct taxa). We score morphological data for Carnivoramorpha, †Creodonta, Lipotyphla, and the †raoellid artiodactylan †Indohyus and concentrate on determining which fossils are positioned along stem lineages to major artiodactylan crown clades. Shortest trees place Cetacea within Artiodactyla and close to †Indohyus, with †Mesonychia outside of Artiodactyla. The relationships of †Mesonychia and †Indohyus are highly unstable, however - in trees only two steps longer than minimum length, †Mesonychia falls inside Artiodactyla and displaces †Indohyus from a position close to Cetacea. Trees based only on data that fossilize continue to show the classic arrangement of relationships within Artiodactyla with Cetacea grouping outside the clade, a signal incongruent with the molecular data that dominate the total evidence result.

Conclusions/Significance

Integration of new fossil material of †Indohyus impacts placement of another extinct clade †Mesonychia, pushing it much farther down the tree. The phylogenetic position of †Indohyus suggests that the cetacean stem lineage included herbivorous and carnivorous aquatic species. We also conclude that extinct members of Cetancodonta (whales + hippopotamids) shared a derived ability to hear underwater sounds, even though several cetancodontans lack a pachyostotic auditory bulla. We revise the taxonomy of living and extinct artiodactylans and propose explicit node and stem-based definitions for the ingroup.     

The earliest evidence of holometabolan insect pupation in conifer wood

Background

The pre-Jurassic record of terrestrial wood borings is poorly resolved, despite body fossil evidence of insect diversification among xylophilic clades starting in the late Paleozoic. Detailed analysis of borings in petrified wood provides direct evidence of wood utilization by invertebrate animals, which typically comprises feeding behaviors.

Methodology/Principal Findings

We describe a U-shaped boring in petrified wood from the Late Triassic Chinle Formation of southern Utah that demonstrates a strong linkage between insect ontogeny and conifer wood resources. Xylokrypta durossi new ichnogenus and ichnospecies is a large excavation in wood that is backfilled with partially digested xylem, creating a secluded chamber. The tracemaker exited the chamber by way of a small vertical shaft. This sequence of behaviors is most consistent with the entrance of a larva followed by pupal quiescence and adult emergence — hallmarks of holometabolous insect ontogeny. Among the known body fossil record of Triassic insects, cupedid beetles (Coleoptera: Archostemata) are deemed the most plausible tracemakers of Xylokrypta, based on their body size and modern xylobiotic lifestyle.

Conclusions/Significance

This oldest record of pupation in fossil wood provides an alternative interpretation to borings once regarded as evidence for Triassic bees. Instead Xylokrypta suggests that early archostematan beetles were leaders in exploiting wood substrates well before modern clades of xylophages arose in the late Mesozoic.