Bony labyrinth morphology in early neopterygian fishes (Actinopterygii: Neopterygii)

Endocasts of the osseous labyrinth have the potential to yield information about both phylogenetic relationships and ecology. Although bony labyrinth morphology is well documented in many groups of fossil vertebrates, little is known for early Neopterygii, the major fish radiation containing living teleosts, gars and the bowfin. Here, we reconstruct endocasts of the bony labyrinth and associated structures for a sample of Mesozoic neopterygian fishes using high‐resolution computed tomography. Our sample includes taxa unambiguously assigned to either the teleost (Dorsetichthys, “Pholidophorus,” Elopoides) and holostean (“Aspidorynchus,” “Caturus,” Heterolepidotus) total‐groups, as well as examples of less certain phylogenetic position (an unnamed parasemionotid and Dapedium). Our models provide a test of anatomical interpretations for forms where bony labyrinths were reconstructed based on destructive tomography (“Caturus”) or inspection of the lateral wall of the cranial chamber (Dorsetichthys), and deliver the first detailed insights on inner ear morphology in the remaining taxa. With respect to relationships, traits apparent in the bony labyrinth and associated structures broadly support past phylogenetic hypotheses concerning taxa agreed to have reasonably secure systematic placements. Inner ear morphology supports placement of Dapedium with holosteans rather than teleosts, while preserved structure in the unnamed parasemionotid is generalized to the degree that it provides no evidence of close affinity with either of the crown neopterygian lineages. This study provides proof‐of‐concept for the systematic utility of the inner ear in neopterygians that, in combination with similar findings for earlier‐diverging actinopterygian lineages, points to the substantial potential of this anatomical system for addressing the longstanding questions in the relationships of fossil ray‐finned fishes to one another and living groups. J. Morphol. 279:426–440, 2018. © 2016 Wiley Periodicals, Inc.     

Validation of plaster endocast morphology through 3D CT image analysis

A crucial component of research on brain evolution has been the comparison of fossil endocranial surfaces with modern human and primate endocrania. The latter have generally been obtained by creating endocasts out of rubber latex shells filled with plaster. The extent to which the method of production introduces errors in endocast replicas is unknown. We demonstrate a powerful method of comparing complex shapes in 3-dimensions (3D) that is broadly applicable to a wide range of paleoanthropological questions. Pairs of virtual endocasts (VEs) created from high-resolution CT scans of corresponding latex/plaster endocasts and their associated crania were rigidly registered (aligned) in 3D space for two Homo sapiens and two Pan troglodytes specimens. Distances between each cranial VE and its corresponding latex/plaster VE were then mapped on a voxel-by-voxel basis. The results show that between 79.7% and 91.0% of the voxels in the four latex/plaster VEs are within 2 mm of their corresponding cranial VEs surfaces. The average error is relatively small, and variation in the pattern of error across the surfaces appears to be generally random overall. However, inferior areas around the cranial base and the temporal poles were somewhat overestimated in both human and chimpanzee specimens, and the area overlaying Broca's area in humans was somewhat underestimated. This study gives an idea of the size of possible error inherent in latex/plaster endocasts, indicating the level of confidence we can have with studies relying on comparisons between them and, e.g., hominid fossil endocasts.     

Endocranial morphology of Pygoscelis calderensis (Aves,Spheniscidae) from the Neogene of Chile and remarks on brain morphology in modern Pygoscelis

The endocranial anatomy of Pygoscelis calderensis, a fossil species from the Bahía Inglesa Formation (Middle Miocene–Pliocene) of Chile, South America, was described through CT scans. Reconstructions of the fossil P. calderensis and endocasts for the living Pygoscelis adeliae, and Pygoscelis papua are provided here for the first time. Comparisons with the extant congeneric species P. adeliae, Pygoscelisantarctica and P. papua indicate that the morphological pattern of the brain and inner ear of the extant pygoscelids has been present already in the Middle Miocene. The neurological morphology suggests that the paleobiology of the extinct form would have been similar to the extant species. It was probably true for diet, feeding behaviour and diving kinematics.     

Endoskeletal structure in Cheirolepis (Osteichthyes,Actinopterygii), An early ray‐finned fish

As the sister lineage of all other actinopterygians, the Middle to Late Devonian (Eifelian–Frasnian) Cheirolepis occupies a pivotal position in vertebrate phylogeny. Although the dermal skeleton of this taxon has been exhaustively described, very little of its endoskeleton is known, leaving questions of neurocranial and fin evolution in early ray‐finned fishes unresolved. The model for early actinopterygian anatomy has instead been based largely on the Late Devonian (Frasnian) Mimipiscis, preserved in stunning detail from the Gogo Formation of Australia. Here, we present re‐examinations of existing museum specimens through the use of high‐resolution laboratory‐ and synchrotron‐based computed tomography scanning, revealing new details of the neuro‐cranium, hyomandibula and pectoral fin endoskeleton for the Eifelian Cheirolepis trailli. These new data highlight traits considered uncharacteristic of early actinopterygians, including an uninvested dorsal aorta and imperforate propterygium, and corroborate the early divergence of Cheirolepis within actinopterygian phylogeny. These traits represent conspicuous differences between the endoskeletal structure of Cheirolepis and Mimipiscis. Additionally, we describe new aspects of the parasphenoid, vomer and scales, most notably that the scales display peg‐and‐socket articulation and a distinct neck. Collectively, these new data help clarify primitive conditions within ray‐finned fishes, which in turn have important implications for understanding features likely present in the last common ancestor of living osteichthyans.     

Integrating 2D and 3D shell morphology to disentangle the palaeobiology of ammonoids: a virtual approach

Based on data derived from computed tomography, we demonstrate that integrating 2D and 3D morphological data from ammonoid shells represents an important new approach for investigating the palaeobiology of ammonoids. Characterization of ammonite morphology has long been constrained to 2D data, with only a few studies collecting ontogenetic data in 180° steps. Here we combine this traditional approach with 3D data collected from high‐resolution nano‐computed tomography. Ontogenetic morphological data on the hollow shell of a juvenile ammonite Kosmoceras (Jurassic, Callovian) was collected. 2D data was collected in 10° steps and show significant changes in shell morphology. Preserved hollow spines show multiple mineralized membranes never reported before, representing temporal changes in the ammonoid mantle tissue. 3D data show that chamber volumes do not always increase exponentially, as was generally assumed, but may represent a proxy for life events, such as stress phases. Furthermore, chamber volume cannot be simply derived from septal spacing in forms comparable to Kosmoceras. Vogel numbers represent a 3D parameter for chamber shape, and those for Kosmoceras are similar to other ammonoids (Arnsbergites, Amauroceras) and modern cephalopods (Nautilus, Spirula). Two methods to virtually document the suture line ontogeny, used to document phylogenetic relationships of larger taxonomic entities, were applied for the first time and present a promising alternative to hand drawings. The curvature of the chamber surfaces increases during ontogeny due to increasing strength of ornamentation and septal complexity. As this may allow for faster handling of cameral liquid, it could compensate for decreasing SA/V ratios through ontogeny.     

Morphological evolution of the mammalian jaw adductor complex

The evolution of the mammalian jaw during the transition from non‐mammalian synapsids to crown mammals is a key event in vertebrate history and characterised by the gradual reduction of its individual bones into a single element and the concomitant transformation of the jaw joint and its incorporation into the middle ear complex. This osteological transformation is accompanied by a rearrangement and modification of the jaw adductor musculature, which is thought to have allowed the evolution of a more‐efficient masticatory system in comparison to the plesiomorphic synapsid condition. While osteological characters relating to this transition are well documented in the fossil record, the exact arrangement and modifications of the individual adductor muscles during the cynodont–mammaliaform transition have been debated for nearly a century. We review the existing knowledge about the musculoskeletal evolution of the mammalian jaw adductor complex and evaluate previous hypotheses in the light of recently documented fossils that represent new specimens of existing species, which are of central importance to the mammalian origins debate. By employing computed tomography (CT) and digital reconstruction techniques to create three‐dimensional models of the jaw adductor musculature in a number of representative non‐mammalian cynodonts and mammaliaforms, we provide an updated perspective on mammalian jaw muscle evolution. As an emerging consensus, current evidence suggests that the mammal‐like division of the jaw adductor musculature (into deep and superficial components of the m. masseter, the m. temporalis and the m. pterygoideus) was completed in Eucynodontia. The arrangement of the jaw adductor musculature in a mammalian fashion, with the m. pterygoideus group inserting on the dentary was completed in basal Mammaliaformes as suggested by the muscle reconstruction of Morganucodon oehleri. Consequently, transformation of the jaw adductor musculature from the ancestral (‘reptilian’) to the mammalian condition must have preceded the emergence of Mammalia and the full formation of the mammalian jaw joint. This suggests that the modification of the jaw adductor system played a pivotal role in the functional morphology and biomechanical stability of the jaw joint.     

Cranial endocast of Anagale gobiensis (Anagalidae) and its implications for early brain evolution in Euarchontoglires

Anagalids are an extinct group of primitive mammals from the Asian Palaeogene thought to be possible basal members of Glires. Anagalid material is rare, with only a handful of crania known. Here we describe the first virtual endocast of an anagalid, based on the holotype of Anagale gobiensis (AMNH 26079; late Eocene, China), which allows for comparison with published endocasts from fossil members of modern euarchontogliran lineages (i.e. primates, rodents, lagomorphs). The endocast displays traits often observed in fossorial mammals, such as relatively small petrosal lobules and a low neocortical ratio, which would be consistent with previous inferences about use of subterranean food sources based on heavy dental wear. In fact, Anagale gobiensis has the lowest neocortical ratio yet recorded for a euarchontogliran. This species was olfaction-driven, based on the relatively large olfactory bulbs and laterally expansive palaeocortex. The endocast supports previous inferences that relatively large olfactory bulbs, partial midbrain exposure and low encephalization quotient are ancestral for Euarchontoglires, although the likely fossorial adaptations of Anagale gobiensis may also partly explain these traits. While Anagale gobiensis is a primitive mammal in many aspects, some of its derived endocranial traits point towards a new, different trajectory of brain evolution within Euarchontoglires.     

Endocranial volumes of early African hominids, and the role of the brain in human mosaic evolution

Volumetric data are presented for 16 of the early hominids from both South and East Africa. Although the sample sizes are small, the statistical data support the conclusion that at least three taxa are represented; Australopithecus africanus, A. robustus, and Homo habilis. These data, plus certain morphological attributes, indicate that the brains of early hominids were reorganized to a human pattern, regardless of their small endocranial capacities. Some speculative suggestions are made regarding the possible relationship between brain and body weights, as well as Stephan's (1972) “progression indices”. If the speculations are correct, they provide additional support for the idea that brain reorganization occurred early in human evolution, and that concepts which regard the brain as having a more terminal role in human mosaic evolution are incorrect, as all of the fossil encephalization or “progression indices” are in the range of modern Homo sapiens.     

Decoding the drivers of deep-time wetland biodiversity: insights from an early Permian tropical lake ecosystem

Wetlands are important to continental evolution, providing both arenas and refugia for emerging and declining biotas. This significance and the high preservation potential make the resulting fossiliferous deposits essential for our understanding of past and future biodiversity. We reconstruct the trophic structure and age of the early Permian Manebach Lake ecosystem, Germany, a thriving wetland at a time when the tropical biosphere faced profound upheaval in the peaking Late Palaeozoic Icehouse. Nine excavations, high-resolution spatiotemporal documentation of fossils and strata, and U–Pb radioisotopic dating of tuffs allow us to distinguish autogenic and allogenic factors shaping the limnic biocoenosis. The Manebach Lake was an exorheic, oxygen-stratified, perennial water body on the 10¹–10² km² scale, integrated into the catchment draining much of the European Variscides. Lake formation paralleled an Asselian regional wet climatic interval and benefited from rising base level due to post-Variscan half-graben tectonics. Stromatolite-forming cyanobacteria, bivalves, several crustaceans, amblypterids and xenacanthid sharks formed a differentiated biocoenosis in the lake. Fossil stomach remains and teeth prove the rare presence of acanthodians, branchiosaurs and large amphibians. The results indicate woody-debris-bearing lake littorals devoid of semi-aquatic and aquatic plants as places suitable for stromatolites to grow, underpin the model of declining freshwater-shark diversity in most Permian Variscan basins, demonstrate fish/amphibian ratios in limnic assemblages to measure lake perenniality and reveal taphonomic biases in lake taphocoenoses. Our outcomes call for more knowledge about the diversity, ecology and fossilization pathways of past limnic biotas, particularly microorganisms and actinopterygian fishes, to reconstruct deep-time continental ecosystems.     

Anatomy of the Cranial Endocast of the Bottlenose Dolphin, Tursiops truncatus, Based on HRXCT

Endocranial surfaces, volumes, and interconnectivities of extant and fossil odontocetes potentially offer information on the general architecture of the brain and on the structure of the specialized cetacean circulatory system. Although conventional methods for acquiring such data have generally involved invasive preparation of the specimen, particularly in the case of fossils, new tomographic technologies afford nondestructive access to these internal morphologies. In this study we used high-resolution X-ray computed tomography (HRXCT) to scan a skull of the extant Tursiops truncatus (Cetacea: Odontoceti). We processed the data to reveal the cranial endocast and details of internal skeletal architecture (data at www.digimorph.org). Major features that can be discerned include aspects of the specimen's hypertrophied retia mirabilia, the major canals and openings of the cranial cavity, and the relationship of the brain and endocranial circulatory structures to the surrounding skeleton. CT data also provide information on the shape of the brain that may be lost in conventional anatomical preparations, and readily provide volumetric and linear measurements of the endocast and its individual segments. These results demonstrate the utility of HRXCT for interpreting the internal cranial anatomy of both extant and fossil cetaceans.     

A mineralogical method to determine cyclicity in the taphonomic and diagenetic history of fossilized bones

The study of authigenic minerals within the voids of a fossilized bone can reveal its diagenetic history. When the order of precipitation of minerals is plotted on an Eh/pH diagram any cyclicity in the diagenetic history is revealed. If one cycle is displayed then it can be assumed that the bone has been found in its original bed of deposition; if two cycles or more are revealed then reworking or environmental change may have taken place. This is demonstrated in a case study of two bones from the Wealden Group (Lower Cretaceous) from the Isle of Wight, UK.     

Habits, functional morphology and the evolution of pycnogonids

Recent work on functional morphology has revealed not only how a wide range of animals work, but shows the significance of their shapes in great detail. Also, sound evidence of evolution is provided. A new approach towards the understanding of Pycnogonida comes from an appreciation of the significance of their general habits and shapes and from the structure and mode of action of their legs. Recent fossil evidence shows that the arachnids had at least two terrestrial landings, occurring millions of years apart in time. At least two, but probably more, separate arachnid lines lived in the sea. It is concluded that pycnogonids evolved from one such aquatic group which never became terrestrial.     

Reconsidering the status and affinities of the ornithischian dinosaur Tatisaurus oehleri Simmons, 1965

The early Mesozoic fossil fauna collected from the Lower Lufeng Formation of Yunnan Province, China, has attracted considerable interest and attention since its discovery in the late 1930s. Its importance reflected a combination of its comparatively remote geographical position and, more particularly, the similarities of its fauna compared with approximately contemporary discoveries from Europe, North and South America, and southern Africa. The fragmentary and poorly preserved Lufeng ornithischian dinosaur Tatisaurus oehleri was described in 1965 and proved taxonomically and systematically enigmatic from the start. Originally assigned, with some noted ambivalence, to the basal ('primitive') group of ornithischians known as hypsilophodontids, since 1965 Tatisaurus has been variously ignored, assigned to a more rigorously defined Hypsilophodontidae, referred to both of the armoured (thyreophoran) ornithischian dinosaur clades (Stegosauria and Ankylosauria), or referred to a more basal position within the thyreophoran lineage. In 1996 the holotype of Tatisaurus was renamed Scelidosaurus oehleri , and the genus Scelidosaurus was proposed as an index fossil of the ' Scelidosaurus biochron' with the potential to be used for the global stratigraphic correlation of Early Jurassic (early Sinemurian) rocks. Because of this chequered history Tatisaurus oehleri Simmons, 1965 has been re-examined and is redescribed so that its taxonomic status and systematic position could be reassessed. Tatisaurus is identified as a basal thyreophoran (armoured ornithischian dinosaur); there is no basis for amalgamating it in synonymy with the genus Scelidosaurus , and the proposed creation of a ' Scelidosaurus biochron' for the purposes of biostratigraphic correlation of Lower Jurassic outcrops has no utility whatever. © 2007 The Linnean Society of London, Zoological Journal of the Linnean Society , 2007, 150 , 865–874.     

A giant rhinocerotoid (Mammalia, Perissodactyla) from the Late Oligocene of north-central Anatolia (Turkey)

A giant rhinocerotoid is described for the first time south of the Black Sea, in Turkey. The single specimen, a fragmentary radius referred to Paraceratherium sp., originates from conglomerates nearby at Gözükizilli, in the Çankiri–Çorum Tertiary basin. These layers correspond to the Lower member of the Kizilirmak Formation. The same locality (Gözükizilli-2) yields also the small rhinocerotid Protaceratherium sp., cf. P. albigense (Roman, 1912). Three other mammal localities (Gözükizilli-1, in the Lower Member of the formation, with several rodent species; Tepe 641 and Kizilirmak, in the Upper Member, with a diversified micro- and macro-mammal fauna) allow us to refer the Kizilirmak Formation as a whole to the Late Oligocene. All the observed taxa have strong Asian and/or European affinities, which precludes any geographical insulation for this part of Anatolia during the Late Oligocene.  © 2008 The Linnean Society of London, Zoological Journal of the Linnean Society, 2008, 152 , 581–592.     

Cranial anatomy and phylogenetic position of Suminia getmanovi, a basal anomodont (Amniota: Therapsida) from the Late Permian of Eastern Europe

Suminia getmanovi , a recently discovered basal anomodont from the Late Permian of Russia, is characterized by robust, 'leaf-shaped' teeth, and a masticatory architecture that is similar to that of the highly diverse and cosmopolitan group of Permo-Triassic herbivores, Dicynodontia (Anomodontia). Based on new material, the skull is reconstructed in three dimensions and described in detail. A cladistic analysis of the basal anomodonts, Patranomodon, Galeops, Otsheria, Ulemica , and Suminia , using 37 cranial characters, resulted in a single most parsimonious tree, in which Suminia is united with the Russian taxa, Ulemica and Otsheria. This clade, diagnosed by four unambiguous characters, is designated as Venyukovioidea. The South African anomodont, Galeops , appears as the sister taxon to Dicynodontia. Patranomodon is the most basal anomodont. The cladistic analysis suggests that a 'dicynodont-type' masticatory architecture, with an expanded adductor musculature and sliding jaw articulation, may have originated prior to the advent of the (Venyukovioidea + ( Galeops + Dicynodontia)) clade.     

Mandibular morphology and diet in the genusCebus

The influence of hard-object feeding on the size and shape of the mandibular corpus was investigated through a comparative biomechanical analysis of the jaws of adult femaleCebus apella andCebus capucinus. Computed tomography (CT) was used to discern the amount and distribution of cortical bone at M₂ and symphyseal cross sections. From these data, the biomechanical properties of the mandibular corpus were determined to assess the structural rigidity of the jaw with respect to the bending, torsional, and shear stresses that occur during mastication and incision. The mandibles ofC. apella are demonstrably more robust than those ofC. capucinus in terms of biomechanical rigidity; differences in corporeal size rather than shape largely account for the enhanced robusticity in the sample ofC. apella. The differences that separate the two taxa probably represent a structural response to the mechanical demands of durophagy inC. apella. These observations suggest that specialization on a diet of hard objects may be expected to result in an overall hypertrophy of bony contours throughout the mandibular corpus.