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.     

Morphology and phylogenetic interpretation of a new Cambrian edrioasteroid (Echinodermata) from Spain

Abstract: The edrioasteroid, Aragocystites belli gen. nov. sp. nov. from the middle Cambrian Murero Formation of Spain, is described based on a small number of very well‐preserved specimens. Important anatomical characteristics include star‐shaped and pseudoclavate theca, rare or absent epispires, well‐developed interradially positioned oral plates and several unorganized cover plates associated with each widely exposed flooring plate. A phylogenetic analysis including several Cambro–Ordovician species shows it is more derived than Stromatocystites and Totiglobus but is a sister group to a clade comprising Cambraster and Edriodiscus. Ontogenetic observations based on juveniles of 5 mm in diameter suggest that this species changed thecal shape markedly during growth. A. belli gen. nov. sp. nov. probably lived in quiet environments where it attached directly to the sea floor on stabilized substrates.     

Skull anatomy of the Oligocene toothed mysticete Aetioceus weltoni (Mammalia; Cetacea): implications for mysticete evolution and functional anatomy

Toothed mysticetes of the family Aetiocetidae from Oligocene rocks of the North Pacific play a key role in interpretations of cetacean evolution because they are transitional in grade between dorudontine archaeocetes and edentulous mysticetes. The holotype skull of Aetiocetus weltoni from the late Oligocene (28–24 Ma) of Oregon, USA, has been further prepared, revealing additional morphological features of the basicranium, rostrum and dentary that have important implications for mysticete evolution and functional anatomy. The palate of Aetiocetus weltoni preserves diminutive lateral palatal foramina and associated delicate sulci which appear to be homologous with the prominent palatal foramina and sulci that occur along the lateral portion of the palate in extant mysticetes. In modern baleen whales these foramina allow passage of branches of the superior alveolar artery, which supplies blood to the epithelia of the developing baleen racks. As homologous structures, the lateral palatal foramina of A. weltoni suggest that baleen was present in this Oligocene toothed mysticete. Cladistic analysis of 46 cranial and dental characters supports monophyly of the Aetiocetidae, with toothed mysticetes Janjucetus and Mammalodon positioned as successive sister taxa. Morawanacetus is the earliest diverging aetiocetid with Chonecetus as sister taxon to Aetiocetus species. © 2008 The Linnean Society of London, Zoological Journal of the Linnean Society, 2008, 154 , 308–352.     

Redescription of Macurdablastus and redefinition of Eublastoidea as a clade of Blastoidea (Echinodermata)

Eublastoids are a large clade of blastoids; stemmed blastozoan echinoderms diagnosed by their conservative body plan (three basals, four deltoid plates and five radial plates), lancet plate supporting the ambulacra, and hydrospire respiratory structures. Although Eublastoidea was a highly successful clade in the middle and late Palaeozoic it is absent from early echinoderm radiations seen in the Cambrian and Ordovician record. Here we provide a re‐evaluation of Macurdablastus uniplicatus Broadhead from the Ordovician, using detailed morphological assessment based on advanced synchrotron tomography and phylogenetic analysis. Macurdablastus uniplicatus falls outside Eublastoidea because of the morphological differences in lancet plate and respiratory structures. The oldest recorded eublastoid is thus middle Silurian in age. The re‐evaluation of the morphology of Macurdablastus provides a basis for revising blastoid phylogeny and classification.     

Reinterpretation of Dracochela deprehendor (Arachnida: Pseudoscorpiones) as a stem‐group pseudoscorpion

Abstract: The middle Devonian (Givetian–Eifelian) pseudoscorpion Dracochela deprehendor Schawaller, Shear and Bonamo is redescribed from the type material and an additional palpal fragment. Dracochela differs from extant pseudoscorpions in having numerous spinules on the leg tarsi, the femur at least as long as the patella on the posterior legs, the stem of the arolia thick, most blades of the serrulae only weakly fused and in lacking a spinneret on the chelicera. The blades of the cheliceral rallum are shown to have been arranged in two rows, as in most Heterosphyronida. The cheliceral serrulae are compared with analogous structures in other arachnids (Notostigmata, Opiliones, Palpigradi, Schizomida and Scorpiones), and it is concluded that the panctenal state (all lamellae attached to finger) is plesiomorphic relative to the hemictenal state (apical lamellae raised), which has evolved independently in Heterosphyronida and Neobisioidea. The trichobothriotaxy of the chela of Dracochela is shown to be similar to that of the extant family Pseudotyrannochthoniidae. The growth of the chelal fingers followed the same pattern as that seen in modern pseudoscorpions, with most of the increase in length occurring at the base of the fingers. The family Dracochelidae Schawaller, Shear and Bonamo is treated as a plesion and assigned to the stem‐group of Pseudoscorpiones. The ordinal name Chelonethi Thorell is restricted to crown‐group pseudoscorpions, and the superordinal name Pseudoscorpiones Latreille is adopted for the total‐group (i.e. stem‐group plus Chelonethi).     

A re‐interpretation of the ambulacral system of Eumorphocystis (Blastozoa,Echinodermata) and its bearing on the evolution of early crinoids

Recent debates over the evolutionary relationships of early echinoderms have relied heavily on morphological evidence from the feeding ambulacral system. Eumorphocystis, a Late Ordovician diploporitan, has been a focus in these debates because it bears ambulacral features that show strong morphological similarity to early crinoid arms. Undescribed and well‐preserved specimens of Eumorphocystis from the Bromide Formation (Oklahoma, USA) provide new data illustrating that composite arms supported by a radial plate that bear a triserial arrangement of axial and extraxial components encasing a coelomic extension can also be found in blastozoans. Previous reports have considered these arm structures to be restricted to crinoids; these combined features have not been previously observed in blastozoan echinoderms. Phylogenetic analyses suggest that Eumorphocystis and crinoids are sister taxa and that shared derived features of these taxa are homologous. The evidence from the arms of Eumorphocystis suggests that crinoid arms were derived from a specialized blastozoan ambulacral system that lost feeding brachioles and strongly suggests that crinoids are nested within blastozoans.     

Tracing the evolution of the holothurian body plan through stem‐group fossils

The fossil echinoderm Palaeocucumaria, from the early Devonian Hunsrück Slate of southwestern Germany, has been studied using both traditional techniques and X‐ray microtomography, and its anatomy clarified. Phylogenetic analysis shows that it is a stem‐group holothurian with a combination of characters that help understand how the modern (crown‐group) holothurian body plan developed. Echinoids and holothurians have evolved along different paths, by differential growth of the larval‐ and rudment‐derived body regions. Palaeocucumaria shows that late stem‐group holothurians had a water vascular organization with a single external madreporite and calcified stone canal leading to the aboral end of the peripharyngeal coelom, and five primary radial water vessels that gave rise to tentacle‐like tube‐feet. This fossil data, in combination with a molecular phylogeny based on 18 s‐like rRNA gene sequence data, is used to order evolutionary steps in the making of the crown‐group holothurian body plan. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 109 , 670–681.     

Paired fin skeletons and relationships of the fossil group Porolepiformes (Osteichthyes: Sardcopterygii)

The endoskeletal girdles, anocleithrum and paired fin supports of the porolepiform fish Glyptolepis (Osteichthyes: Sarcopterygii: Porolepiformes) are figured and described. The pectoral fin skeleton is known from the proximal part only and the pelvic fin skeleton is fragmentary, but the scapulocoracoid, anocleithrum and pelvic girdle can be reconstructed in their entirety. The anocleithrum is entirely subdermal. The pectoral fin skeleton in shown to be biserial, with a large number of axial mesomeres, whereas the pelvic fin contains fewer mesomeres and is strongly asymmetrical with very few postaxial radials. The scapulocoracoid is essentially similar to a reconstruction figured by Jarvik (1980), but has a more elongate glenoid; this has functional implications. The pelvic girdle consists of two separate halves as in Eusthenopteron, but differs from that genus in lacking dorsolateral rami. A brief survey of the evidence of paired fin structure in other porolepiform genera is carried out to establish whether the structures seen in Glyptolepis are likely to be representative for the Porolepiformes. A study of the morphology and muscle attachments of the paired fin skeletons indicates that the pattern of fin movement was significantly different from that in Neoceratodus. The fin supports and girdles of Glyptolepis are compared with those of other sarcopterygian groups as well as with actinopterygians, placoderms and sharks, in order to establish evolutionary polarities. Glyptolepis is shown to display a number of derived characters. The information gained from the comparison is used to construct a maximum parsimony cladogram, which places coelacanths as the sister group of porolepiforms + lungfishes, with the rhizodonts + tetrapods and osteolepiforms as successive sister groups of this clade. Characters of uncertain polarity are considered in the light of this cladogram. A comparison with recently published cladograms shows that none are completely compatible with the results from this study.     

The water vascular system and functional morphology of Paleozoic asteroids

Asteroids of all geologic ages share a single basic body form, surficial skeletal arrangement, and aspects of water vascular construction. In almost all described Paleozoic species, however, either podial pores to the interior of the arm were lacking, or they are directed laterally, above the adambulacrals. They are internal and above the ambulacrals in known post-Paleozoic species and the Pennsylvanian Calliasterella. Certain features of the ambulacral skeletal arrangement also differ. Calliasterella is the closest known Paleozoic relative of post-Paleozoic asteroids. Classifications of asteroids that stress only overall form and surticial skeletal arrangement erroneously include Paleozoic and Holocene species in common ordinal or even lower level groupings. Taxonomic revision is premature: however, most known Paleozoic asteroids represent primitive lineages. Transitional forms allow reconstruction of events leading to the modern arrangement. Ampullar and skeletal arrangements of post-Paleozoic asteroids appear to offer some functional advantages over those of their precursors, but as early as the Ordovician, diverse feeding habits had evolved and ecological roles paralleled those of Holocene species.     

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.     

Tikiguania and the antiquity of squamate reptiles (lizards and snakes)

Tikiguania estesi is widely accepted to be the earliest member of Squamata, the reptile group that includes lizards and snakes. It is based on a lower jaw from the Late Triassic of India, described as a primitive lizard related to agamids and chamaeleons. However, Tikiguania is almost indistinguishable from living agamids; a combined phylogenetic analysis of morphological and molecular data places it with draconines, a prominent component of the modern Asian herpetofauna. It is unlikely that living agamids have retained the Tikiguania morphotype unchanged for over 216 Myr; it is much more conceivable that Tikiguania is a Quaternary or Late Tertiary agamid that was preserved in sediments derived from the Triassic beds that have a broad superficial exposure. This removes the only fossil evidence for lizards in the Triassic. Studies that have employed Tikiguana for evolutionary, biogeographical and molecular dating inferences need to be reassessed.     

The evolution of insect sperm − an unusual character system in a megadiverse group

Spermatozoa provide an unusual character system, with a limited number of components organized in a single cell. Similar spermatozoa occur in groups widely separated in the phylogenetic tree of Metazoa. Nevertheless, the character system contains phylogenetic information. Hexapoda have acquired spermatophores along with the switch from aquatic to terrestrial habitats, and related to this, a multitude of different sperm types. The aim of this study is a formal evaluation of the phylogenetic information content of spermatozoa. For the first time, sperm characters are coded for formal phylogenetic analyses. Different approaches are used and compared. Mainly due to a high level of homoplasy, the evaluation of sperm characters alone is insufficient for a reconstruction of the phylogeny of the group. Yet, a reliable reconstruction of the evolution of insect sperm is possible when character transformations are assessed using a phylogeny based on extensive molecular data. Important changes took place in the early evolution of Hexapoda. Sperm characters support some major clades (e.g. Hexapoda, Dicondylia, Polyneoptera, Psocodea), but important steps in the evolution are not reflected by transformations of spermatozoa, notably the rise of Pterygota or Holometabola. Important innovations are the formation of mitochondrial derivatives and the acquisition of accessory microtubules. Some features are conservative, whereas others evolved rapidly (e.g. presence or absence of the acrosome vesicle). Some groups are conservative in their sperm features (e.g. Odonata, Heteroptera), whereas the evolution of spermatozoa was distinctly accelerated in others (e.g. Ephemeroptera). The rate of evolution can change drastically in closely related groups. Profound changes in the morphologically uniform Zoraptera underline that sperm evolution can follow a pattern very different from the general somatic morphology. The mode of character reconstruction preferred here will be useful for the evaluation of specialized morphological character systems and strengthen the concept of evolutionary morphology.     

The oldest ionoscopiform from China sheds new light on the early evolution of halecomorph fishes

The Halecomorphi are a major subdivision of the ray-finned fishes. Although living halecomorphs are represented solely by the freshwater bowfin, Amia calva, this clade has a rich fossil history, and the resolution of interrelationships among extinct members is central to the problem of understanding the origin of the Teleostei, the largest clade of extant vertebrates. The Ionoscopiformes are extinct marine halecomorphs that were inferred to have originated in the Late Jurassic of Europe, and subsequently dispersed to the Early Cretaceous of the New World. Here, we report the discovery of a new ionoscopiform, Robustichthys luopingensis gen. et sp. nov., based on eight well-preserved specimens from the Anisian (242–247 Ma), Middle Triassic marine deposits of Luoping, eastern Yunnan Province, China. The new species documents the oldest known ionoscopiform, extending the stratigraphic range of this group by approximately 90 Ma, and the geographical distribution of this group into the Middle Triassic of South China, a part of eastern Palaeotethys Ocean. These new data provide a minimum estimate for the split of Ionoscopiformes from its sister clade Amiiformes and shed new light on the origin of ionoscopiform fishes.     

Mechanisms of light organ occlusion in flashlight fishes, family Anomalopidae (Teleostei:Beryciformes), and the evolution of the group

The circumtropical, nocturnal, shore-fish family Anomalopidae is characterized by a subocular luminous organ containing symbiotic luminous bacteria. The five known species are placed in four genera, one of which is new. Phthanophaneron is restricted to the eastern Pacific, Kryptophanaron to the western Atlantic, Photoblepharon is Indo-West Pacific in distribution and Anomalops is west Pacific. The symbiotic bacteria emit light continuously, and two superficially different mechanisms of occluding the glowing face of the organ are found. In Photoblepharon a black shutter of elastic skin is drawn up over the face of the organ, whereas in Anomalops the organ is rotated downward, so that only the heavily pigmented back of the organ is exposed. In Phthanophaneron and Kryptophanaron, both rotational and shutter mechanisms are present. Elucidation of the structures and linkages involved in light-organ occlusion reveals that the superficially different mechanisms are based on a common functional complex. In all four genera, the light organ is supported by a cartilaginous cup that articulates anteriorly with a cartilaginous stalk. Motive power for both the shutter and rotational mechanisms is supplied by the adductor mandibulae through a complex biomechanical linkage involving the ethmomaxillary ligament and a ligament unique to anomalopids, the Ligament of Diogenes. The structures involved in shutter erection and organ rotation are illustrated and described in detail for Photoblepharon and Anomalops and are compared with those in the other two forms; a functional hypothesis is advanced. Extrafamilial relationships of the Anomalopidae are discussed, and a hypothesis of the phylogenetic relationships of the four genera is derived from a cladistic analysis involving 19 non-light-organ characters and corroborated by some light-organ characters. Most characters associated with the light-organ complex cannot be polarized by conventional outgroup comparison, and the evolution of the light organ occlusion mechanisms is interpreted in light of the hypothesized phylogeny and a hypothesized ancestral mechanism. We propose that the common ancestor of anomalopids possessed a forced rotational mechanism like that of Phthanophaneron and Kryptophanaron. This was refined to a more efficient flipping rotational mechanism in Anomalops, the sister group of the lineage comprising the other three genera, within which the shutter mechanism was progressively refined. The ostensibly unnecessary complexity of the shutter mechanism is apparently a result of functional-morphological constraints imposed on the system by the pre-existence of a rotational mechanism. A brief zoogeographic scenario is proposed.     

Macrostructure and evolution of the digestive system in Echinoida (Echinodermata)

The structure of the digestive system in Echinoida has long been puzzling since comparative studies have suggested that a derived structure, the siphon, has apparently evolved twice independently. New observations on the digestive system in five species of Cidaroida, four species of the Diadematoida and three species of Echinothurioida are presented. The results show that the four diadematoid species have a siphon and the three species of Echinothurioida have a siphonal groove, contrary to previous assertions. These observations make the macrostructure of the echinoid digestive system fully consistent with more recent phylogenetic hypotheses based on molecular and general morphological data, and support the idea that a siphon has evolved only once, in the stem lineage of the Acroechinoidea.     

Development and morphology of ciliary urns in the sea cucumber Synaptula hydriformis (Echinodermata: Holothuroidea)

Sea cucumbers (holothuroids) lack the only known echinoderm immune organ, the axial organ. Holothuroids of the families Synaptidae and Chiridotidae have coelomic organs, known as ciliary urns, that gather and excrete waste and, therefore, might function in immunity. Although ciliary urns are widely reported and illustrated in the literature, the process and histology of urn development remain unknown. Development and structure of ciliary urns were examined in Synaptula hydriformis using scanning electron, brightfield, and scanning laser confocal microscopy. Mature urns occurred on all three mesenteries in 10‐tentacled young and later growth stages, and developing urns were found in post‐pentactulae, 10‐tentacled young, and released juveniles. Developing urns were circular clusters of ciliated collar cells protruding from the mesentery. The cells increased in number to form the sessile cushion stage with a shallow lumen. The subsequent spoon‐shaped stage had a stalk and a deepened lumen with an extensive ciliary field where coelomocytes began to accumulate. Mature urns had a thin stalk and cornucopia‐shaped body with an abluminal epithelium of squamous cells and an adluminal epithelium of densely packed ciliated collar cells. Cell boundaries of the rim of mature urns and of the stalk and body of developing urns were outlined on one or both sides by microvilli and an elevated cell membrane. Ciliary urns resembling the cushion‐stage urns of S. hydriformis have been described in the sea star Archaster typicus. If urns in these groups are homologous, it is likely that cushion urns are plesiomorphic and that they are present and have been overlooked in other echinoderms.     

New occurrence of the family Hipponicharionidae (Bradoriida, Arthropoda), in the lower and middle Cambrian of the Cadenas Ibéricas, Spain

The bradoriids Hipponicharion aff. hispanicum and Wimanicharion aff. matthewi are reported from the lower and middle Cambrian strata of the Cadenas Ibéricas, Spain. The genus Hipponicharion seems to be restricted to the Acadobaltic Province. Wimanicharion has been recorded from Sweden and Canada (Nova Scotia). The new discovery of Wimanicharion in Spain indicates its similar palaeobiogeographical distribution to Hipponicharion.     

Phylogenetics,character evolution,and distribution patterns of the greenbriers,Smilacaceae (Liliales), a near‐cosmopolitan family of monocots

Smilacaceae, composed of Smilax and Heterosmilax, are a cosmopolitan family of > 200 species of mostly climbing monocots with alternate leaves characterized by reticulate venation, a pair of petiolar tendrils and usually prickly stems. Although there has been a long history of studying Smilax since Linnaeus named the genus in 1753, the phylogenetic history of this dioecious family remains unclear. Here we present results based on nuclear ribosomal internal transcribed spacer (nrITS) and plastid matK and rpl16 intron DNA sequence data from 125 taxa of Smilacaceae. Our taxon sampling covers all sections of Smilax and Heterosmilax and major distribution zones of the family; species from Ripogonaceae and Philesiaceae are used as outgroups. Our molecular analysis indicates that phylogenetic relationships largely contradict the traditional morphological classification of the family, instead showing a conspicuous geographical pattern among the species clades. The previously recognized genus Heterosmilax was found to be embedded in Smilax. Species in the family are separated into primarily New World and Old World clades, except for a single species lineage, Smilax aspera, that is sister to the remaining species of the family, but with poor statistical support. Ancestral character state reconstructions and examination of distribution patterns among the clades provide important information for future taxonomic revisions and historical biogeography of the group. © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2013, 173 , 535–548.     

Molecular phylogeny of the order Euryalida (Echinodermata: Ophiuroidea), based on mitochondrial and nuclear ribosomal genes

The existing taxonomy of Euryalida, one of the two orders of the Ophiuroidea (Echinodermata), is uncertain and characterized by controversial delimitation of taxonomic ranks from genus to family-level. Their phylogeny was not studied in detail until now. We investigated a dataset of sequence from a mitochondrial gene (16S rRNA) and two nucleic genes (18S rRNA and 28S rRNA) for 49 euryalid ophiuroids and four outgroup species from the order Ophiurida.The monophyly of the order Euryalida was supported as was the monophyly of Asteronychidae, Gorgonocephalidae and an Asteroschematidae + Euryalidae clade. However, the group currently known as the Asteroschematidae was paraphyletic with respect to the Euryalidae. The Asteroschematidae + Euryalidae clade, which we recognise as an enlarged Euryalidae, contains three natural groups: the Asteroschematinae (Asteroschema and Ophiocreas), a new subfamily Astrocharinae (Astrocharis) and the Euryalinae with remaining genera. These subfamilies can be distinguished by internal ossicle morphology.