Early larval ontogeny of the Permo-Carboniferous temnospondyl Sclerocephalus

The early larval development of the temnospondyl Sclerocephalus sp. is analyzed, based on 38 specimens from the Lower Rotliegend (Permo-Carboniferous boundary) of the Saar-Nahe Basin (south-west Germany). The study focuses on the smallest larval specimens, which exemplify changes in both proportions and ossification patterns. In comparison with dissorophoid larvae, the skull ossifies more fully and at a much faster rate; the smallest specimens already have completely formed circumorbital bones that are sutured throughout. Sculpturing undergoes two marked changes, first from uniformly pitted to pits of variable size and regional differentiation, and finally to the origin of ridges. The palate of small larvae differs from that of larger specimens in patterns of dentition, having more teeth including a denticle field on the cultriform process. The mandible of small larvae is described for the first time, being narrower than in adults and having three dentigerous coronoid elements. The smallest specimens have poorly ossified neural arches, lack vertebral centra, and have faintly ossified humeri, femora, and very poorly developed distal elements. The posterior ribs, metapodia, and phalanges appeared after the dermal elements of the pectoral girdle, whereas the scapulocoracoid and ischium are absent throughout the larval period. Early growth and differentiation of the limbs and the ilium illustrates the developmental patterning of the appendages, which proceeded from proximal to distal. Dermal squamation is uniform in small stages, consisting of round or oval osteoderms with pronounced growth rings; in large larvae, they start to differentiate in certain body regions.     

The evolution of the scalation pattern in temnospondyl amphibians

In most Palaeozoic temnospondyls, thin round-oval scales covering the flanks and the back of the trunk can be distinguished from ventral, elongate gastral scales arranged in a chevron pattern. The extensive growth series of the temnospondyl Sclerocephalus reveals that the morphology of the gastral scales in small larvae corresponds to the round-oval scales of the rest of the body. During subsequent ontogeny, the gastral scales differentiate and attain a spindle-shaped morphology. The tapering end of each gastral scale fits into a dorsal groove on the medial adjacent scale. This arrangement allowed telescoping of the scales and thus provided a high degree of flexibility. In the ontogenetically most advanced specimens of Sclerocephalus the gastral scales attain a rhomboid outline, and the articulation by well-defined facets has reduced the flexibility between them. In most temnospondyls, the gastral scales retain the 'juvenile' spindle-shape or the 'larval' round-oval shape, which can be interpreted as a paedomorphic trait. This suggests that the different types of gastral scales in temnospondyls, as well as the scales of the back and the flanks, can be traced back to the same Anlage of round-oval scales that differentiated early in ontogeny. In the Mesozoic, a complete reduction of dermal scalation occurred independently in distinct dissorophoid, capitosauroid, and trematosauroid temnospondyls. This reduction was probably the result of several factors unique to each group, such as cutaneous respiration, the demand for greater mobility, and the decreased importance of belly protection in fully aquatic temnospondyls.  © 2007 The Linnean Society of London, Zoological Journal of the Linnean Society , 2007, 150 , 815–834.     

An investigation into the cladistic relationships and monophyly of therocephalian therapsids (Amniota: Synapsida)

A comprehensive phylogenetic investigation was performed to elucidate the cladistic relationships and possible monophyly of therocephalian therapsids (Amniota: Synapsida). The phylogenetic positions of 30 therapsid taxa were examined under maximum parsimony, including 23 therocephalian genera. The analysis incorporated 110 cranial and postcranial characters in order to assess the interrelationships of basal therocephalians and eutherocephalians and their relationships to Cynodontia, representing the most complete review of therocephalian phylogeny to date. The analysis supports the hypothesis that Therocephalia represents the monophyletic sister taxon to Cynodontia, with as many as 15 morphological synapomorphies, in contrast with other recent analyses of lesser taxon sampling. The results also support the hypothesis that Scylacosauridae is more closely related to Eutherocephalia than to the basal therocephalian family Lycosuchidae, supporting a ‘Scylacosauria’ clade. The taxa suggested here to be neotenic forms (e.g. Ictidosuchoides and Ictidosuchops) are positioned near the base of a monophyletic Baurioidea. Neotenic development of the therocephalian feeding apparatus and evolutionary parallelism with cynodonts are suggested to have been important trends in the early evolution of baurioid therocephalians into the Late Permian and Early Triassic.     

Osteology and relationships ofPseudotrichonotus altivelis (Teleostei: Aulopiformes: Pseudotrichonotidae)

The osteology of the rate Japanese fishPseudotrichonotus altivelis is described based on several specimens collected off the Izu Peninsula. Relationships ofPseudotrichonotus are discussed based on osteological comparisons with other neoteleosts. The placement ofPseudotrichonotus among iniomous fishes has been questioned because of its lower numbers of caudal-fin, pelvic-fin, and branchiostegal rays. Our investigation supports an iniomous affinity forPseudotrichonotus, specifically as a member of the Aulopiformes. Within that group,Pseudotrichonotus belongs in a new suborder diagnosed herein, the Synodontoidei, which also includes the Aulopidae (Aulopus), Synodontidae (Synodus andTrachinocephalus), and Harpadontidae (Harpadon andSaurida). A synodontoid affinity forAulopus has never been suggested, but numerous osteological features support the monophyly of this clade. Synodontoids have a peculiar proximal segmentation of most principal caudal-fin rays, expanded neural and haemal spines on posterior vertebrae, cartilage extending along the ventral margin of the anterior ceratohyal, ventral displacement of the first one to three epineurals, supraneurals with large laminar expansions and six or more branchiostegals on the posterior ceratohyal. They lack median caudal cartilages. Among synodontoids,Pseudotrichonotus is the sister group of the Synodontidae plus Harpadontidae, with which it shares paired peritoneal pigment spots, an abrupt transition between the epipleurals in and beneath the horizontal septum, and absence of the fourth pharyngobranchial toothplate. Our study does not support a previously proposed relationship betweenBathysaurus and synodontids. deceased     

Life cycles,plasticity and palaeoecology in temnospondyl amphibians

In the largest early tetrapod clade, the temnospondyls, ontogenies were diverse and quite distinct from the life cycles of extant amphibians. Three well‐studied clades exemplify the diversity of these long‐extinct ontogenies, here analysed with respect to their bearing on developmental plasticity, reaction norms and evolution. Sclerocephalus readily adjusted by means of developmental evolution to different lake environments. In addition, plasticity (reaction norm) played a significant role, apparent both morphologically and by altered developmental traits. Size increase and extension of the ontogenetic trajectory gave larger predators, a phenomenon also found in the dissorophoid Micromelerpeton. Whereas Sclerocephalus was throughout preying on the same fishes, Micromelerpeton was able to fit into different trophic levels. In the branchiosaurid Apateon, a biphasic life cycle was established, with metamorphosis producing a terrestrial morph in some species; truncation of the ontogenetic trajectory gave a sexually mature larva as an alternative morph (neoteny). Plasticity was high in the larval morphs, permitting neotenes to live as filter feeders or small carnivores. Fine‐tuning of development permitted Apateon populations to adjust to specific lake properties and readily change from a filter‐feeding to carnivorous mode of life. In the nonmetamorphosing Triassic Gerrothorax, morphology was extremely conserved, but histology reveals much plasticity at the microscopical level, correlating with fluctuating salinity and water energy. In responding to environmental fluctuations by enhanced plasticity, the studied temnospondyls managed to populate lakes inhabitable to other tetrapods and fishes.     

The systematic relationships of the snake genus Anomochilus

Phylogenetic analysis of 38 skeletal characters, 12 muscular characters and 15 visceral characters in 17 major snake clades plus Anomochilus suggests that Anomochilus is the sister taxon of all other living alethinophidian snakes. However, skeletal, muscular and visceral character sets analysed separately or in pairs give four groups of nonconcordant tree topologies. Based on the cladogram derived from the total evidence, two families are erected to prevent the existing family Uropeltidae from becoming paraphyletic: Anomochilidae, for the Malaysian and Indonesian genus Anomochilus , and Cylindrophiidae, for the Sri Lankan, Southeast Asian and Indonesian genus Cylindrophis and the Upper Eocene fossil Eoanilius.     

Embryos of therizinosauroid theropods from the Upper Cretaceous of China: diagnosis and analysis of ossification patterns

Exceptionally complete, in ovo dinosaur embryos from the Upper Cretaceous of China are analysed. Ossification patterns of these embryos suggest that they died during the final third of their development. The therizinosauroid identity of the embryos follows from: (1) an edentulous premaxilla with a sharp downturned edge; (2) dentary with a lateral shelf; (3) teeth with fan-shaped crowns, with a few marginal cusps; (4) humerus with a massive deltopectoral crest extending proximally, with a pointed proximomedial tuberosity; (5) ilium with an expanded and hooked preacetabular process; (6) strongly curved hypertrophied manual unguals tapering to sharp points. These embryos are closest to two Chinese therizinosauroids, Neimongosaurus yangi Zhang et al . 2001 and Erliansaurus bellamanus Xu et al . 2002 . An elongated narial opening, reduced basipterygoid process, low cervical neural spines, a transversely narrow pubic apron, and a pubic foot expanded anteriorly are found in these embryos and are synapomorphies uniting the Therizinosauroidea and the Oviraptorosauria. Fusion of cervical and caudal neural arches and centra, complete ossification of thoracic ribs and ilium, possible co-ossification of tibia and fibula, fused pubes, complete meta- and acropodial elements, together with small portions of unossified epiphyses of long bones suggest an advanced precociality of these embryos.     

Skeletal development and abnormalities of the vertebral column and of the fins in hatchery-reared turbot Scophthalmus maximus

To describe the skeletal development and abnormalities in turbot Scophthalmus maximus, samples were collected every day from hatching to 60 days after hatching (DAH). A whole-mount cartilage and bone-staining technique was used. Vertebral ontogeny started with the formation of anterior haemal arches at 5·1 mm standard length (L(S) ) c. 11 DAH, and was completed by the full attainment of parapophyses at 16·9 mm L(S) c. 31 DAH. Vertebral centra started to develop at 6·3 mm L(S) c. 16 DAH and ossification in all centra was visible at 11·0 mm L(S) c. 25 DAH. The caudal fin appeared at 5·1 mm L(S) c. 11 DAH and ossification was visible at 20·6 mm L(S) c. 37 DAH. The onset of dorsal and anal fin elements appeared at 5·8 mm L(S) c. 15 DAH and 6·3 mm L(S) c. 16 DAH, respectively. Ossifications of both dorsal fin and anal fin were visible at 20·6 mm L(S) c. 37 DAH. The pectorals were the only fins present before first feeding, their ossifications were completed at 23·5 mm L(S) c. 48 DAH. Pelvic fins began forming at 7·2 mm L(S) c. 19 DAH and calcification of the whole structure was visible at 19·8 mm L(S) c. 36 DAH. In the present study, 24 types of skeletal abnormalities were observed. About 51% of individuals presented skeletal abnormalities, and the highest occurrence was found in the haemal region of the vertebral column. As for each developmental stage, the most common abnormalities were in the dorsal fin during early metamorphic period (stage 2), vertebral fusion during climax metamorphosis (stage 3) and caudal fin abnormality during both late-metamorphic period (stage 4) and post-metamorphic period (stage 5). Such research will be useful for early detection of skeletal malformations during different growth periods of reared S. maximus.     

Phylogenetic relationships within the Archiloa genus complex (Proseriata,Monocelididae)

Of the seven genera which we have recognised within the Archiloa genus complex sensu Karling (1966) the cosmopolitan genus Archilina is the most primitive and is characterised only by plesiomorphic characters, and has to be considered paraphyletic. All other species of the Archiloa genus complex are hypothesized to be derived from Archilina-like ancestors through different evolutionary lineages. One lineage led to the genera Archiloa, Inaloa, Archilopsis and Monocelopsis, taxa found in the Atlantic and the Mediterranean. These genera are monophyletic and their relationships are analyzed. The genera Mesoda (Brazil) and Tajikina (Northern Pacific) can be considered as two other separate lineages. Similarly, within what we now consider as the genus Archilina different lineages can be recognized in different regions.     

Phylogenetic relationships among species of the genus Issatchenkia Kudriavzev

The phylogenetic relatedness of Issatchenkia spp. was estimated from partial rRNA sequences in two regions of the large subunit and one region of the small subunit. I. terricola was the most divergent species of the genus, differing from other members by 18% nucleotide differences in the highly variable 25S-635 region. These data indicate Issatchenkia to be the most divergent ascomycetous yeast genus presently known.     

Phylogenetic relationships in the genus Cheracebus (Callicebinae,Pitheciidae)

Cheracebus is a new genus of New World primate of the family Pitheciidae, subfamily Callicebinae. Until recently, Cheracebus was classified as the torquatus species group of the genus Callicebus. The genus Cheracebus has six species: C. lucifer, C. lugens, C. regulus, C. medemi, C. torquatus, and C. purinus, which are all endemic to the Amazon biome. Before the present study, there had been no conclusive interpretation of the phylogenetic relationships among most of the Cheracebus species. The present study tests the monophyly of the genus and investigates the relationships among the different Cheracebus species, based on DNA sequencing of 16 mitochondrial and nuclear markers. The phylogenetic analyses were based on Maximum Likelihood, Bayesian Inference, and multispecies coalescent approaches. The divergence times and genetic distances between the Cheracebus taxa were also estimated. The analyses confirmed the monophyly of the genus and a well-supported topology, with the following arrangement: ((C. torquatus, C. lugens), (C. lucifer (C. purinus, C. regulus))). A well-differentiated clade was also identified within part of the geographic range of C. lugens, which warrants further investigation to confirm its taxonomic status.     

Limb ossification patterns of the ichthyosaur Stenopterygius, and a discussion of the proximal tarsal row of ichthyosaurs and other neodiapsid reptiles

Limb ossification patterns for the Lower Jurassic (Toarcian) ichthyosaur, Stenopterygius , are described. It is found that limb ossification follows a continuous proximal to distal sequence from the propodial elements through to the terminal elements of 1st to 4th digit in the manus and the 1st to 3rd digit in the pes. The 5th manal and 4th pedal digit begin ossification later than more preaxial digits and also show evidence of proximal addition of elements near the distal mesopodial row in a manner consistent with delayed ossification of the 5th distal mesopodial in other diapsids. Ossification of manal elements in the Supernumerary 3–4 (S3-4) digit and the 5th digit appear interdependent; if one or the other is highly ossified, ossification of the other is retarded. The 1st pedal digit is considered to be lost in Stenopterygius and the 4th pedal digit is identified as the 5th digit. Delayed ossification of the mesopodium is not observed. The most preaxial proximal tarsal is identified as the centralc; the remaining proximal tarsals are the astragalus and calcaneum, and it is inferred that the astragalus and calcaneum ossified from within a single proximal cartilage.     

Osteology and relationships of the genus Spaniodon (Teleostei, Salmoniformes) from the Santonian (Upper Cretaceous) of Lebanon

The genus Spaniodon is decribed in detail. Contrary to previous authors, we have only recognized two species, S. elongatus and S. latus . Spaniodon shows the synapomorphies of clupeocephalans, protacanthopterygians and salmoniforms. Its relationships among salmoniforms are still undecided, although it could be closely related to the Osmeroidei. The main character that supports this grouping is the dermal part of the mesethmoid formed by the partial fusion of a pair of lateral dermethmoids, whereas the rostral is absent. These conclusions are also supported by a global phylogenetic study of the teleosts.     

The ontogeny of cinctans (stem‐group Echinodermata) as revealed by a new genus,GraciaCystis, from the middle Cambrian of Spain

Abstract:  A new cinctan echinoderm, Graciacystis ambigua gen. et sp. nov. from Cambrian Series 3 rocks of Spain, is described based on more than 100 articulated specimens that range from 6 to 14.5 mm in thecal length. This material shows that Graciacystis ambigua, while plastic in thecal shape, is highly conservative in its thecal construction, with a fixed number of marginal plates and very limited addition of plates in the stele and ventral membrane through ontogeny. Ventral swellings on marginal elements are absent from the smallest specimens and become gradually more marked during growth. A cladistic analysis shows Graciacystis to be a basal cinctan, more derived than Sotocinctus and the Trochocystitidae and as sister group to a large clade formed by Sucocystidae + Gyrocystidae. The determinate growth pattern seen in Graciacystis seems to be the general pattern for all cinctans.     

The structure and development of the jaw adductor musculature in the turtle Chelydra serpentina

The investigation of the development of the trigeminal jaw adductor musculature in the turtle Chelydra serpentina documents the early aggregation of muscle rudiments around the innervating nerve branches, probably a consequence of inductive interaction. This may explain the early continuity of the intramandibularis with the intermandibularis muscle. Several aspects of muscle development differ in the turtle as compared to lizards. These differences highlight the fact that conjectures of homology, based on a static topographical correspondence of adult structures, cannot capture the dynamics of the developmental process. The intramandibularis muscle of turtles, comparable to that of crocodiles, represents a plesiomorphous structure which is not homologous to the intramandibularis muscle of lacertoid lizards, a derived feature of the Lacertoidea. A derived feature of the chelonian jaw adductor musculature is the posterodorsal expansion of the external adductor along a supraoccipital crest, developing according to a pattern of Haeckelian recapitulation. Muscle development serves to corroborate the concept of a monophyletic Eureptilia, including diapsids and synapsids, as opposed to the (paraphyletic) Anapsida. The impact of the differentiation of the external adductor into a pulley system on cranial kinesis is analysed in biomechanical terms.     

Phylogenetic relationships of the pygmy rice rats of the genus Oligoryzomys Bangs, 1900 (Rodentia: Sigmodontinae)

Sequences from two mitochondrial genes (cytochrome b and NADH1) were used to produce a molecular phylogeny for 12 named and two undescribed species of the genus Oligoryzomys. All analyses placed Oligoryzomys microtis as the most basal taxon, a finding consistent with previous studies that suggested the west‐central Amazon as a centre of origin for the tribe Oryzomyini to which Oligoryzomys belongs. Biogeographically, this suggests that Oligoryzomys had a South American origin, and later advanced northwards, entering Central America and Mexico more recently. Different analyses have provided consistent support for several additional clades that did not necessarily agree with the species groups hypothesized by previous studies. A molecular clock derived for these data suggests an origin for the genus of 6.67 Mya, with most speciation within the genus occurring between 3.7 and 1.5 Mya. © 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 160 , 551–566.     

The developmental floral morphology of Montrichardia arborescens (Araceae) revisited

The spadix of Montrichardia arborescens contains unisexual flowers without a perianth. The pistillate flowers are located in the basal portion of the inflorescence, and the staminate flowers are located in the apical portion. There is a narrow :zone between male flowers and female flowers consisting of atypical flowers. The portion of the atypical flowers facing the staminate zone exhibits staminate characters (stamens), and the portion facing the pistillate zone has an aborted gynoecium. The floral development of Montrichurdia is compared with that of Philodendron and a new interpretation of the morphology of atypical flowers of Montrichardia is proposed. Ontogenetic evidence supports relationships with Philodendron rather than Cercestis. 2001 The Linnean Society of London     

Osteology and myology of the cephalic region and pectoral girdle of the Chinese catfish Cranoglanis bouderius,with a discussion on the autapomorphies and phylogenetic relationships of the Cranoglanididae (Teleostei: Siluriformes)

The cephalic and pectoral girdle structures of the Chinese catfish Cranoglanis bouderius are described and compared with those of other catfishes as the foundation for an analysis on the Cranoglanididae autapomorphies and also for a discussion on the phylogenetic relationships between the cranoglanidids and the other catfishes. Our observations and comparisons indicate that cranoglanidids are defined, at least, by four autapomorphies, namely: 1) the cartilages associated with the mandibular barbels are broad, somewhat circular; 2) epioccipital with a well-developed posterodorsal process, which presents a large, deep, circular posterior concavity; 3) a well-defined, deep, anteroposteriorly elongated concavity formed by both the frontal and the lateral ethmoid to receive the anteromedial surface of the metapterygoid; 4) the adductor mandibulae A3" is dorsally divided into two bundles and partially inserted on the posterior portion of the primordial ligament. With respect to the phylogenetic relationships of the Cranoglanididae, this study strongly suggests that these fishes are probably closely related to the Ariidae and the Claroteidae.