High Blood Flow Into the Femur Indicates Elevated Aerobic Capacity in Synapsids Since the Synapsida-Sauropsida Split

Varanids are the only non-avian sauropsids that are known to approach the warm-blooded mammals in stamina. Furthermore, a much higher maximum metabolic rate (MMR) gives endotherms (including birds) higher stamina than crocodiles, turtles, and non-varanid lepidosaurs. This has led researchers to hypothesize that mammalian endothermy evolved as a second step after the acquisition of elevated MMR in non-mammalian therapsids from a plesiomorphic state of low metabolic rates. In recent amniotes, MMR correlates with the index of blood flow into the femur (Qi), which is calculated from femoral length and the cross-sectional area of the nutrient foramen. Thus, Qi may serve as an indicator of MMR range in extinct animals. Using the Qi proxy and phylogenetic eigenvector maps, here we show that elevated MMRs evolved near the base of Synapsida. Non-mammalian synapsids, including caseids, edaphosaurids, sphenacodontids, dicynodonts, gorgonopsids, and non-mammalian cynodonts, show Qi values in the range of recent endotherms and varanids, suggesting that raised MMRs either evolved in synapsids shortly after the Synapsida-Sauropsida split in the Mississippian or that the low MMR of lepidosaurs and turtles is apomorphic, as has been postulated for crocodiles.

The Evolution of Dragline Initiation in Spiders: Multiple Transitions from Multi- to Single-Gland Usage

Despite the recognition of spider silk as a biological super-material and its dominant role in various aspects of a spider’s life, knowledge on silk use and silk properties is incomplete. This is a major impediment for the general understanding of spider ecology, spider silk evolution and biomaterial prospecting. In particular, the biological role of different types of silk glands is largely unexplored. Here, I report the results from a comparative study of spinneret usage during silk anchor and dragline spinning. I found that the use of both anterior lateral spinnerets (ALS) and posterior median spinnerets (PMS) is the plesiomorphic state of silk anchor and dragline spinning in the Araneomorphae, with transitions to ALS-only use in the Araneoidea and some smaller lineages scattered across the spider tree of life. Opposing the reduction to using a single spinneret pair, few taxa have switched to using all ALS, PMS and the posterior lateral spinnerets (PLS) for silk anchor and dragline formation. Silk fibres from the used spinnerets (major ampullate, minor ampullate and aciniform silk) were generally bundled in draglines after the completion of silk anchor spinning. Araneoid spiders were highly distinct from most other spiders in their draglines, being composed of major ampullate silk only. This indicates that major ampullate silk properties reported from comparative measurements of draglines should be handled with care. These observations call for a closer investigation of the function of different silk glands in spiders.

Reduced antennal segmentation in a new species from Iran of the genus Aeolothrips (Thysanoptera: Aeolothripidae)

The number of antennal segments in adults of the different families and genera in the insect order Thysanoptera varies between five and nine. The plesiotypic number is considered to be nine (Zhang et al. 2019), and fossil thrips reported to have 10 to 15 segments (Tong et al. 2019) are generally considered to be aberrations in which the terminal segment bears transverse striae. The 9-segmented condition occurs particularly amongst species that exhibit several other characters in a plesiomorphic state, including all Melanthripidae, two genera of Merothripidae, also most species of Fauriellidae, Stenurothripidae, Heterothripidae, and Aeolothripidae (Mound et al. 1980). Curiously, members of a few genera of Thripidae (Palmer & Mound 1985; Minaei 2012) also have nine antennal segments, but this is considered a reversion from the 8-segmented condition that is assumed to be plesiomorphic for that family (Zhang et al. 2019). Variation between eight and nine segments occurs in the genus Anaphothrips, and within that genus a few species exhibit intraspecific variation in antennal segmentation (Mound & Masumoto 2009). Intraspecific variation in various characters, including body size, color and wing length, is well documented for the order Thysanoptera (Mound 2005 a, b). However, amongst the 207 listed species of Aeolothripidae there has never been any report of a species bearing antennae with other than nine segments, although these vary in length and shape amongst the different genera. We here describe from Iran a curious species of the genus Aeolothrips that is unusual in having only seven antennal segments, with the number reduced to six or even five in a few individuals in which the terminal segments are fused. These females with 7-segmented antennae were initially considered to be aberrant individuals of some other species. However, 25 females with such antennae have been collected over two years, all from a group of Tamarix trees. Despite extensive studies on the genus Aeolothrips in Iran (Alavi & Minaei 2018, 2019), with 30 species now being recorded from this country, no other species has been found with the same colour pattern of the body and fore wings. We therefore conclude that the available specimens represent a valid species in which the antennal segmentation is reduced, and with the terminal segments unstable.

Morphological diversity of stylets in Kolhymorbis (Mollusca: Pulmonata: Segmentinidae)

The taxonomy of freshwater pulmonates (Hygrophila) relies heavily on morphology of their reproductive system, most notably on the characters of the copulatory apparatus. For this reason, taxonomically important components of the copulatory apparatus such as penial stylets have always received much attention in the morphological studies on Hygrophila. The present study describes the stylets of Kolhymorbis bogatovi Zatrawkin et Moskvicheva in Zatrawkin, 1985 and K. shadini Starobogatov et Streletzkaja, 1967 and compares them with the previously described stylet of K. angarensis (Dybowski et Grochmalicki, 1925). The lengths of the stylets vary within the genus from 20 to 30 μm. In K. bogatovi, the stylet is a trough-shaped plate with a distal portion twisted 110° counterclockwise with respect to the proximal portion. The stylet of K. shadini is also a trough-shaped plate, but its walls are curved in such a way that the stylet forms a hollow cone with a beveled tip. The slit between the opposite lateral flanks of the stylet is wide proximally, but narrows down distally. The stylets of all three Kolhymorbis species differ markedly in their shape. The trough-shaped stylet of K. angarensis most likely represents the plesiomorphic state; the stylet of K. bogatovi may have originated from this type of stylet by increasing the curvature of the walls and counterclockwise twisting of the distal portion of the stylet. The cone-shaped stylet of K. shadini may have evolved from the plesiomorphic type by widening of the proximal portion and by even more pronounced curving of the walls throughout the length of the stylet without distal twisting. The penial stylets of Kolhymorbis species are compared with those of Palaearctic genera of the family Segmentinidae Baker, 1945 and the taxonomic utility of the stylet characters is evaluated.

Evolution of dinosaur epidermal structures

Spectacularly preserved non-avian dinosaurs with integumentary filaments/feathers have revolutionized dinosaur studies and fostered the suggestion that the dinosaur common ancestor possessed complex integumentary structures homologous to feathers. This hypothesis has major implications for interpreting dinosaur biology, but has not been tested rigorously. Using a comprehensive database of dinosaur skin traces, we apply maximum-likelihood methods to reconstruct the phylogenetic distribution of epidermal structures and interpret their evolutionary history. Most of these analyses find no compelling evidence for the appearance of protofeathers in the dinosaur common ancestor and scales are usually recovered as the plesiomorphic state, but results are sensitive to the outgroup condition in pterosaurs. Rare occurrences of ornithischian filamentous integument might represent independent acquisitions of novel epidermal structures that are not homologous with theropod feathers.

Phylogenetic patterns of character evolution in the hyobranchial apparatus of early tetrapods

ABSTRACTThe morphologies of the hyobranchial apparatus in early tetrapods are reviewed, based primarily on first-hand examination and supplemented by published descriptions. The basic arrangement of the “aquatic” hyobranchium, with four pairs of branchial arches and internal gills, was conserved to a remarkable degree across the fish–to–tetrapod transition and was retained in further evolution in adults of several tetrapod lineages. Thus, a fish-like hyobranchium in basal tetrapods does not necessarily represent a larval or paedomorphic character, respectively, as was often suggested in analogy to extant salamanders. Rather, it represents the plesiomorphic state of the adult hyobranchium in tetrapods. The changes in the hyobranchium during the fish–to–tetrapod transition include the reduction of the number of skeletal elements and their morphological simplification. In all three presently discussed scenarios of lissamphibian origin, the temnospondyl, lepospondyl and diphyly hypotheses, the internal gills were reduced independently within temnospondyls and on the amniote stem below seymouriamorphs. Evidence of remodelling into a true “terrestrial” hyobranchium, with reduction of the posterior branchial arches and modification to support terrestrial tongue feeding, is scarce in early tetrapods. It evolved within temnospondyls in zatracheids, amphibamids and lissamphibians, as well as once or several times in early amniotes or in their immediate stem-forms.

Parental care in Cryptops hortensis (Donovan) (Chilopoda: Scolopendromorpha) from Serbia, the Balkan peninsula

Parental care in the geographically widespread cryptopid scolopendromorph Cryptops hortensis (Donovan) is described for the first time. It was observed that the adult female rolls her body around the mass of hatchlings with the ventral side against the brood. This finding supports the hypothesis that within the brooding centipedes, the female position with the terga outwards is a plesiomorphic state and probably a general feature of all Scolopendromorpha. In addition, the major external morphological characters of the fetus instar and adolescens I are described.

A new species of Nemuroglanis (Siluriformes: Heptapteridae) from the rio Guariba, rio Madeira basin, Brazil

Nemuroglanis furcatus is described from streams of the rio Guariba, a clear water tributary of the rio Aripuanã, rio Madeira basin in Brazil. Nemuroglanis furcatus can be distinguished from its congeners by the possession of a long lateral line, reaching the middle portion of the adipose-fin base; a narrow posterior cranial fontanel (16 to 27% of its length); and the anterior border of pectoral bridge with a pointed contour. The plesiomorphic state of some of the synapomorphies for Nemuroglanis in N. furcatus suggests that this species might be the sister-group to the remaining species of the genus. A key for all four valid species of Nemuroglanis species is provided.

Batfishes from the Eocene of Monte Bolca

Batfishes of the family Ogcocephalidae are derived lophiiform fishes characterized by having a dorsoventrally depressed body and a distinctive series of morphological features. A new genus and species of batfish, Tarkus squirei gen. et sp. nov., is described from the Eocene (Ypresian) limestone of the celebrated locality of Monte Bolca, Italy. It is based on five well-preserved specimens that display a unique combination of characters (body moderately depressed; disk rounded in outline; caudal peduncle thick and stout; frontals with median groove for the illicium; teeth present on jaws and palate; illicial bone pitted and trilobate; body covered with thick slightly overlapping tubercles) that support its recognition as a new genus of the family Ogcocephalidae. Tarkus gen. nov. is also characterized by having distally branched pectoral-fin rays, a condition unique within the family, and by a peculiar structure of the axial skeleton, which possibly represents the plesiomorphic state for the ogcocephalids. Tarkus gen. nov. shows a certain degree of phenetic affinity with the extant shallow-water batfish genera Halieutaea and (more particularly) Halieutichthys. The specimens of this taxon are the first articulated skeletal remains of the Ogcocephalidae ever recorded as fossils, also representing the oldest members of the family known to date. The general structure of the skeleton of Tarkus gen. nov. provides unambiguous evidence that the existence of the modern ogcocephalid body plan was already established in the early Eocene, and probably originated well before that period. Palaeoenvironmental considerations suggest that Tarkus gen. nov. was a tropical batfish that inhabited the inner-shelf palaeobiotopes of the central-western Tethys.

Pentastomid parasites from the Lower Palaeozoic of Sweden

ABSTRACTSmall phosphatised fossils from late Cambrian limestones of Västergötland, Sweden, share major external features with larval extant Pentastomida, such as a prominent head with two pairs of stumpy limbs adapted for attachment, and a slender trunk of four portions. Even such details, as paired forehead structures, pores on the inner edges of the head limbs and paired papillae at the rear of the trunk correspond with structures of extant pentastomid larvae. Neither the fossils nor the Recent pentastomids add any additional body segments during growth (segment constancy). Since characters of this kind and in this combination do not occur elsewhere, the fossils are recognised as true Pentastomida. Major differences, such as distinctly divided head limbs, partial occurrence of vestigial trunk limbs, and a different mode of trunk development during growth can be explained as representing merely the plesiomorphic state of characters of Pentastomida, indicating that the fossils are representatives of its stem-group prior to branching into the two Recent lineages. The fossils clearly document the marine origin of the Pentastomida, and that their specific morphology and parasitic life style were already established in the late Cambrian at a high degree of diversification, long before the terrestrialisation of their present final hosts, the tetrapods. General arthropod affinities are recognisable not least in the nature of the limbs, but the morphology of stem- and crown-group pentastomids gives no clues for closer relationship with any of the major (eu)arthropod taxa.