Gill‐filament ossifications: a possible morphological synapomorphy uniting the families Balitoridae and Cobitidae (Ostariophysi: Cypriniformes)

Ossifications associated with the gill filaments of members of the Balitoridae and Cobitidae are described for the first time. Although gill‐filament ossifications are common in teleosts, similar ossifications were not observed in other members of the order Cypriniformes. Their presence is interpreted as a shared and derived character uniting the families Balitoridae and Cobitidae as a monophyletic group.     

Homology of the palpebral and origin of supraorbital ossifications in ornithischian dinosaurs

Maidment, S.C.R. & Porro, L.B. 2010: Homology of the palpebral and origin of supraorbital ossifications in ornithischian dinosaurs. Lethaia , Vol. 43, pp. 95–111.
The palpebral is a small ossification that projects across the orbit in some ornithischian dinosaurs and its presence is considered a synapomorphy of the clade. By contrast, other ornithischians lack the palpebral but possess accessory ossifications, commonly termed supraorbitals, which form the dorsal margin of the orbit. The homology of the ornithischian palpebral to one or more of the supraorbitals is widely accepted in the literature, but this homology has never been explicitly tested and no hypotheses have been proposed regarding the function of the palpebral or why it was incorporated into the orbital margin. As homology is synonymous with synapomorphy, incorrect homology statements can lead to incorrect hypotheses of relationships being obtained during cladistic analysis. The primary and secondary homologies of the ornithischian palpebral and the anterior supraorbital of more derived members of the major ornithischian clades are tested and we demonstrate that these homology hypotheses can be accepted. Osteological correlates indicate that the palpebral supported a layer of connective tissue that roofed the orbit; ossification of this connective tissue resulted in the incorporation of the palpebral into the skull roof and gave rise to additional supraorbital elements, which are neomorphic ossifications. Large-scale structural changes in the ornithischian skull, including dermal ossifications associated with display or defence and the development of complex feeding mechanisms, may have led to the incorporation of the palpebral into the skull roof. □ Functional morphology , homology , Ornithischia , palpebral , supraorbital.     

Gnathostome vertebrae and the classification of the Amphibia

Four pairs of arcualia were primitively present in each segment of gnathostomes. The individual vertebral ossifications of early temnospondyls are most economically interpreted as the endochondral ossifications of these cartilaginous arcualia. Centra have formed independently on at least two occasions within the tetrapods and arcualia play little or no part in the formation of true centra in any living form. The so called pleuro- and intercentra of the temnospondyls can in no way be homologized with the centra of either lissamphibians or amniotes. The Nectridea are considered to be the sister group of the Lissamphibia and the Aistopoda the sister group of these two. The anthracosaurs, seymourians and microsaurs are regarded as amniotes. There is no evidence for resegmentation in the vertebral column.     

Skeletal development of the direct-developing caecilian <Emphasis Type="Italic">Gegeneophis ramaswamii</Emphasis> (Amphibia: Gymnophiona: Caeciliidae)

A few previous studies of skeletal and especially skull development in Gymnophiona often provided contradictory results. We studied the development of the skull and vertebral column of Gegeneophis ramaswamii, a direct-developing Indian caeciliid, based on 13 specimens. The chondrocranium forms at (Brauer in Zool Jahrb Anat 12:477-508,1899) stage 38. First dermal and perichondral ossifications occur at stage 40. The first dermal bones to form are the mentomeckelian, dentary, angular, vomer, and premaxillary. These are followed by the coronoid, palatine, pterygoid, maxillary, and the skull-roofing bones. The last occurring dermal ossifications are the parasphenoid and the squamosal. We present evidence for the occurrence of a lacrimal bone. No ectopterygoid, basioccipital, supraoccipital, pleurosphenoid, postorbital, or supratemporal elements were found. We assess the homology of the bones constituting the caecilian skull and discuss the above-mentioned terminologies. The phylogenetic implications of our findings are briefly discussed and we conclude that the evidence from developmental morphology is at present consistent with a monophyletic Lissamphibia of temnospondyl origin.     

Heterotopic ossifications in a mouse model of albright hereditary osteodystrophy

Albright hereditary osteodystrophy (AHO) is characterized by short stature, brachydactyly, and often heterotopic ossifications that are typically subcutaneous. Subcutaneous ossifications (SCO) cause considerable morbidity in AHO with no effective treatment. AHO is caused by heterozygous inactivating mutations in those GNAS exons encoding the α-subunit of the stimulatory G protein (Gα(s)). When inherited maternally, these mutations are associated with obesity, cognitive impairment, and resistance to certain hormones that mediate their actions through G protein-coupled receptors, a condition termed pseudohypoparathyroidism type 1a (PHP1a). When inherited paternally, GNAS mutations cause only AHO but not hormonal resistance, termed pseudopseudohypoparathyroidism (PPHP). Mice with targeted disruption of exon 1 of Gnas (Gnas(E1-/+)) replicate human PHP1a or PPHP phenotypically and hormonally. However, SCO have not yet been reported in Gnas(E1+/-) mice, at least not those that had been analyzed by us up to 3 months of age. Here we now show that Gnas(E1-/+) animals develop SCO over time. The ossified lesions increase in number and size and are uniformly detected in adult mice by one year of age. They are located in both the dermis, often in perifollicular areas, and the subcutis. These lesions are particularly prominent in skin prone to injury or pressure. The SCO comprise mature bone with evidence of mineral deposition and bone marrow elements. Superficial localization was confirmed by radiographic and computerized tomographic imaging. In situ hybridization of SCO lesions were positive for both osteonectin and osteopontin. Notably, the ossifications were much more extensive in males than females. Because Gnas(E1-/+) mice develop SCO features that are similar to those observed in AHO patients, these animals provide a model system suitable for investigating pathogenic mechanisms involved in SCO formation and for developing novel therapeutics for heterotopic bone formation. Moreover, these mice provide a model with which to investigate the regulatory mechanisms of bone formation.     

Structure of the skin of Agonus cataphractus (Teleostei)

The skin of the scuted teleost Agonus cataphractus has been investigated by histochemical methods, SEM and TEM. The anterior dorsal skin bears tubercles of epidermis overlying tiny ossifications (scutelets) superficial to the main scutes. The epidermis secretes a cuticular layer containing acidic non-sulphated glycoproteins, but there are no mucous goblet cells in the external skin. Non-mucous sacciform cells of two types are present in the epidermis, also numerous chloride cells. Scanning electron microscopy reveals variation in the microridge pattern of superficial epithelial cells, thought to relate to arrival at the surface and secretion of the cuticle. The major scutes overlap anteriorly, contrary to the normal arrangement of scales, indicating that they are secondary ossifications. The type of mineralization is similar to that of acellular bone. The scutes are set directly in the collagen of the dermis. They have a girdered structure with radial and cross bars, inserting on both faces of a thin plate. The interstices are occupied by unmineralized collagen, and extrinsic collagen bundles impinge on the bone. Non-mineralized parts of the dermis contain tracts of microfibrils in addition to collagen; these are best developed in the flexible gular skin and in the barbels and are interpreted as elastic tissue, although an amorphous component was not seen. The barbels have a core of connective tissue without a cartilaginous skeleton and bear taste buds and numerous chloride cells.     

The differential diagnosis of isolated ossicles in the region of the dens axis

2 osteological specimens of the atlanto-occipital region with accessory ossicles sitting on the dens axis are described. Considering the anatomical and radiological literature, the differential diagnosis of isolated accessory ossicles in the region of the dens axis is discussed (e.g. os odontoideum, ossiculum terminale BERGMANN persistens, ossifications of the ligamentous apparatus).     

Skeletal development in the African elephant and ossification timing in placental mammals

We provide here unique data on elephant skeletal ontogeny. We focus on the sequence of cranial and post-cranial ossification events during growth in the African elephant (Loxodonta africana). Previous analyses on ossification sequences in mammals have focused on monotremes, marsupials, boreoeutherian and xenarthran placentals. Here, we add data on ossification sequences in an afrotherian. We use two different methods to quantify sequence heterochrony: the sequence method and event-paring/Parsimov. Compared with other placentals, elephants show late ossifications of the basicranium, manual and pedal phalanges, and early ossifications of the ischium and metacarpals. Moreover, ossification in elephants starts very early and progresses rapidly. Specifically, the elephant exhibits the same percentage of bones showing an ossification centre at the end of the first third of its gestation period as the mouse and hamster have close to birth. Elephants show a number of features of their ossification patterns that differ from those of other placental mammals. The pattern of the initiation of the ossification evident in the African elephant underscores a possible correlation between the timing of ossification onset and gestation time throughout mammals.     

Postembryonic development of the cephalic region in Heterobranchus longifilis

At hatching, Heterobranchus longifilis does not display any primordia of the cephalic skeleton. The latter appears 12 h post–hatching and develops in three stages up to day 16. The first stage (12 h to 2 days) involves almost exclusively the development of the chondrocranium. During the second period (days 3–8), dermal elements of the splanchnocranium appear. The final stage is marked by resorption of the cartilages, progressively replaced by ossifications (days 10–16). At their appearance the elements of the splanchnocranium are fused together, as are the first neurocranial elements. Later, the splanchnocranium splits up. By the time the yolk sac is completely resorbed, the buccal and pharyngeal jaws are present, the suspensoria and hyoid bars are partially developed, and the parasphenoid partially closes the hypophyseal fenestra. These structures delimit a buccal cavity that is probably functional, i.e. capable of participating in the intake of exogenous food. Next to continue its development is principally the splanchnocranium, completing the walls of the buccal cavity. Cartilage resorption parallels the appearance of endochondral ossifications (except for the trabecular bars). Braincase closure begins to accelerate once the buccal system is complete.     

Ontogeny of cranial ossification in the small-mouthed salamander, Ambystoma texanum (Matthes)

The ontogenetic sequence of cranial bony structure from initial ossifications through metamorphosis in Ambystoma texanum is described on the basis of 128 cleared and stained specimens. For convenience of discussion nine stages are recognized on the basis of conspicuous events. Cranial bones ossify and are modified in a definite sequence, and comparisons of complete sequences among groups of salamanders may prove useful in classification and in better understanding of relationships.     

A mixed-age classed ‘pelycosaur’ aggregation from South Africa: earliest evidence of parental care in amniotes?

Living species of mammals, crocodiles and most species of birds exhibit parental care, but evidence of this behaviour is extremely rare in the fossil record. Here, we present a new specimen of varanopid 'pelycosaur' from the Middle Permian of South Africa. The specimen is an aggregation, consisting of five articulated individuals preserved in undisturbed, close, lifelike, dorsal-up, subparallel positions, indicating burial in 'life position'. Two size classes are represented. One is 50% larger than the others, is well ossified, has fused neurocentral sutures and is distinguished by a coat of dermal ossifications that covers the neck and shoulder regions. We regard this individual to be an adult. The remaining four skeletons are considered to be juveniles as they are approximately the same size, are poorly ossified, have open neurocentral sutures and lack dermal ossifications. Aggregates of juvenile amniotes are usually siblings. Extant analogues of adult and juvenile groupings suggest that the adult is one of the parents, leading us to regard the aggregation as a family group. The Late Middle Permian age of the varanopid family predates the previously known oldest fossil evidence of parental care in terrestrial vertebrates by 140 Myr.     

Comparative skeletogenesis of the Oriental Tree Frog Hyla orientalis (Anura: Hylidae)

The ontogeny of skeletal development of the Oriental Tree Frog, Hyla orientalis (Bedriaga, 1890), is followed from tadpole to froglet and compared with four other hylid species i.e., Hypsiboas lanciformis, Hypsiboas pulchellus, Phyllomedusa vaillanti and Pseudis platensis. Our analysis and comparison is based on cleared and double-stained specimens. The parasphenoid is the first skeletal element that ossified in Hyla orientalis is followed by the exoocipital, prootic, axial and appendicular skeletal elements, frontoparietal, nasal, upper jaw, squamosal, pterygoid, lower jaw, vomer and quadratojugal. Ossification initiated at early Stage 33 in Hyla orientalis whereas in other hylids it begins after Stage 37. Major transformations of the larval jaw were visible after Stage 42. Cranial ossifications were completed after appendicular and axial ossifications of Hyla orientalis. All skeletal elements ossified before the end of the metamorphosis, a unique feature of Hyla orientalis in comparison to the other hylids studied here.     

Evolution and homology of the astragalus in early amniotes: new fossils, new perspectives

The reorganization of the ankle in basal amniotes has long been considered a key innovation allowing the evolution of more terrestrial and cursorial behavior. Understanding how this key innovation arose is a complex problem that largely concerns the homologizing of the amniote astragalus with the various ossifications in the anamniote tarsus. Over the last century, several hypotheses have been advanced homologizing the amniote astragalus with the many ossifications in the ankle of amphibian-grade tetrapods. There is an emerging consensus that the amniote astragalus is a complex structure emerging via the co-ossification of several originally separate elements, but the identities of these elements remain unclear. Here we present new fossil evidence bearing on this contentious question. A poorly ossified, juvenile astragalus of the large captorhinid Moradisaurus grandis shows clear evidence of four ossification centers, rather than of three centers or one center as posited in previous models of astragalus homology. Comparative material of the captorhinid Captorhinikos chozaensis is also interpretable as demonstrating four ossification centers. A new, four-center model for the homology of the amniote astragalus is advanced, and is discussed in the context of the phylogeny of the Captorhinidae in an attempt to identify the developmental transitions responsible for the observed pattern of ossification within this clade. Lastly, the broader implications for amniote phylogeny are discussed, concluding that the neomorphic pattern of astragalus ossification seen in all extant reptiles (including turtles) arose within the clade Diapsida.     

Primary homologies of the circumorbital bones of snakes

Some snakes have two circumorbital ossifications that in the current literature are usually referred to as the postorbital and supraorbital. We review the arguments that have been proposed to justify this interpretation and provide counter‐arguments that reject those conjectures of primary homology based on the observation of 32 species of lizards and 81 species of snakes (both extant and fossil). We present similarity arguments, both topological and structural, for reinterpretation of the primary homologies of the dorsal and posterior orbital ossifications of snakes. Applying the test of similarity, we conclude that the posterior orbital ossification of snakes is topologically consistent as the homolog of the lacertilian jugal, and that the dorsal orbital ossification present in some snakes (e.g., pythons, Loxocemus, and Calabaria) is the homolog of the lacertilian postfrontal. We therefore propose that the terms postorbital and supraorbital should be abandoned as reference language for the circumorbital bones of snakes, and be replaced with the terms jugal and postfrontal, respectively. The primary homology claim for the snake “postorbital” fails the test of similarity, while the term “supraorbital” is an unnecessary and inaccurate application of the concept of a neomorphic ossification, for an element that passes the test of similarity as a postfrontal. This reinterpretation of the circumorbital bones of snakes is bound to have important repercussions for future phylogenetic analyses and consequently for our understanding of the origin and evolution of snakes. J. Morphol. 274:973–986, 2013. © 2013 Wiley Periodicals, Inc.     

Appendicular skeleton in Bachia bicolor (Squamata: Gymnophthalmidae): osteology,limb reduction and postnatal skeletal ontogeny

The osteology of the appendicular skeleton and its postnatal development are described in Bachia bicolor, a serpentiform lizard with reduced limbs. The pectoral girdle is well developed and the forelimb consists of a humerus, ulna, radius, five carpal elements (ulnare, radiale, distal carpals 4–3, centrale), four metacarpals (II, III, IV, V) and phalanges (phalangeal formula X‐2‐2‐2‐2). In the hindlimb, the femur is small and slender, and articulates distally with a series of ossified amorphous and extremely reduced elements that correspond to a fibula, tibia and proximal and distal tarsals 4 and 3. The pelvic girdle consists of ischium, pubis and ilium, but its two halves are widely separated; the ilium is the least reduced element. We describe the ossification and development during postnatal skeletal ontogeny, especially of epiphyseal secondary centres, ossifications of carpal elements, apophyseal ossifications and sesamoids. Compared to other squamates, B. bicolor shows an overall reduction in limb size, an absence of skeletal elements, a fusion of carpal elements, an early differentiation of apophyseal centres, and a low number of sesamoids and apophyseal centres. These observations suggest that the reductions are produced by heterochronic changes during postnatal development and probably during embryonic development; therefore the appendicular skeleton exhibits a pattern of paedomorphic features.     

Cranial Morphology of the Brachystelechid ‘Microsaur’ Quasicaecilia texana Carroll Provides New Insights into the Diversity and Evolution of Braincase Morphology in Recumbirostran ‘Microsaurs’

Recumbirostran ‘microsaurs,’ a group of early tetrapods from the Late Carboniferous and Early Permian, are the earliest known example of adaptation to head-first burrowing in the tetrapod fossil record. However, understanding of the diversity of fossorial adaptation within the Recumbirostra has been hindered by poor anatomical knowledge of the more divergent forms within the group. Here we report the results of μCT study of Quasicaecilia texana, a poorly-known recumbirostran with a unique, broad, shovel-like snout. The organization of the skull roof and braincase of Quasicaecilia is found to be more in line with that of other recumbirostrans than previously described, despite differences in overall shape. The braincase is found to be broadly comparable to Carrolla craddocki, with a large presphenoid that encompasses much of the interorbital septum and the columella ethmoidalis, and a single compound ossification encompassing the sphenoid, otic, and occipital regions. The recumbirostran braincase conserves general structure and topology of braincase regions and cranial nerve foramina, but it is highly variable in the number of ossifications and their extent, likely associated with the reliance on braincase ossifications to resist compression during sediment compaction and mechanical manipulation by epaxial and hypaxial musculature. Expansion of the deep ventral neck musculature in Quasicaecilia, autapomorphic among recumbirostrans, may reflect unique biomechanical function, and underscores the importance of future attention to the role of the cervical musculature in contextualizing the origin and evolution of fossoriality in recumbirostrans.     

New Evidence for a Discrete Supratemporal Bone in the Jurassic Ichthyosaur Temnodontosaurus

The temporal region in Temnodontosaurus trigonodon and Temnodontosaurus platyodon consists of three discrete ossifications. These bones are identified as the supratemporal, bordering much of the temporal opening, and in mid-cheek, the squamosal, which is in contact with the quadratojugal along its ventral margin. Interpretation of the bone in mid-cheek position as a neomorphic "supernumerary" ossification is rejected. The supratemporal bone of ichthyosaurs is functionally convergent with the squamosal of diapsids. The size and configuration of the supratemporal casts doubt on the supposition that ichthyosaurs were diapsids.