Evolution of chameleon locomotion,or how to become arboreal as a reptile

High-speed, biplanar X-ray motion analysis, X-ray reconstruction of moving morphology (XROMM) and morphological studies have led to the identification of those traits which are considered to be crucial for the evolution of arboreal locomotion in chameleons. The loss of the extensive lateral undulation typical of reptiles needs to be compensated by high mobility in the shoulder girdle and a clear functional regionalization of the trunk. Large limb excursion angles provide a compliant gait and are made possible by a functional parasagittalization of fore- and hind limbs, at least temporarily. All these evolutionary novelties parallel very similar modifications in the evolution of the locomotor apparatus in therian mammals. We propose that the convergent “invention” of dynamic stability and a compliant gait seem to be responsible for the locomotor similarities between chameleons and mammals.     

Functional morphology of the middle ear in Chlorotalpa golden moles (Mammalia, Chrysochloridae): predictions from three models

The ossicular apparatus of golden moles in the genus Chlorotalpa has received comparatively little attention in the literature, although the malleus is known to be intermediate in size between the "unmodified" malleus of Amblysomus and the hypertrophied mallei found in some other golden moles. In the present study, the middle ear structures of three Chlorotalpa species (C. duthieae, C. sclateri, and C. arendsi) are described. Measurements of middle ear structures were applied into three existing models of middle ear function. The predictions from the models suggest that the airborne hearing of Chlorotalpa species is limited to relatively low frequencies, but the impedance transformation by the middle ear apparatus is expected to be reasonably efficient. The sensitivity of the middle ear apparatus to inertial bone conduction is intermediate between that predicted for Amblysomus and that predicted for species with hypertrophied mallei. Hearing in fossorial mammals may be limited by factors other than the middle ear apparatus: the predictions for Chlorotalpa must therefore be treated with caution. However, a consideration of the "intermediate" middle ear morphology of Chlorotalpa species sheds some light on the origin of ossicular hypertrophy in golden moles. The limited enlargement of the malleus seen in Chlorotalpa is expected to have improved seismic sensitivity by bone conduction significantly at low frequencies, while airborne hearing might not have been adversely affected.     

What did Morganucodon hear?

The structure of the middle and inner ear of Morganucodon , one of the oldest known mammals, is reviewed and compared to the structure of the ears of extant mammals, reptiles and birds with known auditory capabilities. Specifically, allometric relationships between ear dimensions (basilar-membrane length, tympanic-membrane area and stapes-footplate area) and specific features of the audiogram are defined in extant ears. These relationships are then used to make several predictions of auditory function in Morganucodon. The results point out that the ear structures of Morganucodon–Art similar in dimensions to ear structures in both extant small mammals–with predominantly high-frequency (10 kHz) auditory capabilities, and reptiles and birds- with better low and middle-frequency hearing (< 5 kHz). Although the allometric analysis cannot by itself determine whether Morganucodon heard more like present-day small mammals, or birds and reptiles, the apparent stiffness of the Morganucodon middle ear is both more consistent with the high-frequency mammalian middle ear and would act to decrease the sensitivity of a bird-reptile middle ear to low-frequency sound. Several likely hearing scenarios for Morganucodon are defined, including a scenario in which these animals had ears like those of modern small mammals that are selectively sensitive to high-frequency sounds, and a second scenario in which the Morganucodon ear was moderately sensitive to sounds of a narrow middle-frequency range (5–7 kHz) and relatively insensitive to sounds of higher or lower frequency. The evidence needed to substantiate either scenario includes some objective measure of the stiffness of the Morganucodon ossicular system, while a key datum needed to distinguish between the two hypotheses includes confirmation of the presence or absence of a cochlear lamina in the Morganucodon inner ear.     

Embryonic development of the fossorial gymnophthalmid lizards Nothobachia ablephara and Calyptommatus sinebrachiatus

The evolutionary history of the lizard family Gymnophthalmidae is characterized by several independent events of morphological modifications to a snake-like body plan, such as limb reduction, body elongation, loss of external ear openings, and modifications in skull bones, as adaptive responses to a burrowing and fossorial lifestyle. The origins of such morphological modifications from an ancestral lizard-like condition can be traced back to evolutionary changes in the developmental processes that coordinate the building of the organism. Thus, the characterization of the embryonic development of gymnophthalmid lizards is an essential step because it lays the foundation for future studies aiming to understand the exact nature of these changes and the developmental mechanisms that could have been responsible for the evolution of a serpentiform (snake-like) from a lacertiform (lizard-like) body form. Here we describe the post-ovipositional embryonic development of the fossorial species Nothobachia ablephara and Calyptommatus sinebrachiatus, presenting a detailed staging system for each one, with special focus on the development of the reduced limbs, and comparing their development to that of other lizard species. The data provided by the staging series are essential for future experimental studies addressing the genetic basis of the evolutionary and developmental variation of the Gymnophthalmidae.     

Hierarchical phylogenetics as a quantitative analytical framework for evolutionary developmental biology

Phylogenetics has inherent utility in evolutionary developmental biology (EDB) as it is an established methodology for estimating evolutionary relationships and for making comparisons between levels of biological organization. However, explicit phylogenetic methods generally have been limited to two levels of organization in EDB-the species and the gene. We demonstrate that phylogenetic methods can be applied broadly to other organizational levels, such as morphological structures or cell types, to identify evolutionary patterns. We present examples at and between different hierarchical levels of organization to address questions central to EDB. We argue that this application of "hierarchical phylogenetics" can be a unifying analytical approach to the field of EDB.     

Histology and structural integration of the major morphologies of the Cypriniform Weberian apparatus

The Weberian apparatus, a diagnostic feature of otophysan fishes, is a novel hearing adaptation integrating several developmental and morphological systems (ear-vertebral column-swim bladder). Otophysan fishes are one of the largest and most successful freshwater clades, with over 10,000 species across most continents. The largest otophysan order, Cypriniformes, dominates the freshwaters of Asia, Europe, North America, and Africa. Spanning such a wide variety of environments, the Weberian apparatus undergoes morphological modifications to maintain functionality. Within Cypriniformes, we propose three distinct morphological classes of the Weberian apparatus based on the level of skeletal expansion around the swim bladder: simple (typical of most Cyprinidae), anterior plate (found in families such as Gyrinocheilidae, Catostomidae, and Botiidae), and encapsulated (either single-capsule as found, e.g., in Gobionidae and Cobitidae, or double-capsule as found, e.g., in Nemacheilidae and Balitoridae). Little ontological or comparative data exists regarding the construction or integration of these different morphologies, and less is known about the tissue level integration and variation within these morphologies. We used paraffin histology to document the hard and soft tissue anatomy of the Weberian apparatus in six species representing all morphological classes. We found sites of similarity across the morphologies including size and structure of the saccule, aspects of ossicle ossification, and swim bladder tunica composition, indicating potential sites of developmental and functional constraint. In contrast, we found differences across both auditory and nonauditory features in otic chamber size, ossification within ossicles and other vertebral elements, and composition of ligaments, indicating likely sites of adaptability. Some of these changes are likely evolutionary (taxonomic), but may be influenced by the environmental niche occupied by the clade. These results show a clear need for increased ontological and comparative study of the complete cypriniform Weberian apparatus, particularly histologically, as well as increased auditory studies across morphological types.     

Evidence for evolutionary changes in ontogeny: Paleontological, comparative-morphological, and molecular aspects

It has been noted that the integration of modern data of paleontology, comparative morphology, developmental biology, and molecular genetics forms the basis for understanding the mechanisms of evolutionary transformations of ontogeny. Paleontological and morphological evidence of the evolutionary changes in ontogeny are considered based on the data of cell and molecular biology and developmental genetics. It is shown that reorganizations of gene regulatory cascades (mainly Hox genes) play a key role in the evolution of the axial organization of animals and modifications of the limb structure of metazoans, whereas the formation of new types of structures was apparently determined by the emergence of new populations of stem cells in embryogenesis (for example, neural crest cells in the evolution of vertebrates).     

Evolution of the middle ear apparatus in Talpid moles

The middle ear structures of eight species of mole in the family Talpidae (Mammalia: Eulipotyphla) were studied under light and electron microscopy. Neurotrichus, Parascalops, and Condylura have a simple middle ear cavity with a loose ectotympanic bone, ossicles of a "microtype" morphology, and they retain a small tensor tympani muscle. These characteristics are ancestral for talpid moles. Talpa, Scalopus, Scapanus, and Parascaptor species, on the other hand, have a looser articulation between malleus and ectotympanic bone and a reduced or absent orbicular apophysis. These species lack a tensor tympani muscle, possess complete bullae, and extensions of the middle ear cavity pneumatize the surrounding basicranial bones. The two middle ear cavities communicate in Talpa, Scapanus, and Parascaptor species. Parascaptor has a hypertrophied malleus, a feature shared with Scaptochirus but not found in any other talpid genus. Differences in middle ear morphology within members of the Talpidae are correlated with lifestyle. The species with middle ears closer to the ancestral type spend more time above ground, where they will be exposed to high-frequency sound: their middle ears appear suited for transmission of high frequencies. The species with derived middle ear morphologies are more exclusively subterranean. Some of the derived features of their middle ears potentially improve low-frequency hearing, while others may reduce the transmission of bone-conducted noise. By contrast, the unusual middle ear apparatus of Parascaptor, which exhibits striking similarities to that of golden moles, probably augments seismic sensitivity by inertial bone conduction.     

Developmental regulatory genes and echinoderm evolution

Modified interactions among developmental regulatory genes and changes in their expression domains are likely to be an important part of the developmental basis for evolutionary changes in morphology. Although developmental regulatory genes are now being studied in an increasing number of taxa, there has been little attempt to analyze the resulting data within an explicit phylogenetic context. Here we present comparative analyses of expression data from regulatory genes in the phylum Echinodermata, considering the implications for understanding both echinoderm evolution as well as the evolution of regulatory genes in general. Reconstructing the independent evolutionary histories of regulatory genes, their expression domains, their developmental roles, and the structures in which they are expressed reveals a number of distinct evolutionary patterns. A few of these patterns correspond to interpretations common in the literature, whereas others have received little prior mention. Together, the analyses indicate that the evolution of echinoderms involved: (1) the appearance of many apomorphic developmental roles and expression domains, some of which have plesiomorphic bilateral symmetry and others of which have apomorphic radial symmetry or left-right asymmetry; (2) the loss of some developmental roles and expression domains thought to be plesiomorphic for Bilateria; and (3) the retention of some developmental roles thought to be plesiomorphic for Bilateria, although with modification in expression domains. Some of the modifications within the Echinodermata concern adult structures; others, transient larval structures. Some changes apparently appeared early in echinoderm evolution (> 450 Ma), whereas others probably happened more recently (< 50 Ma). Cases of likely convergence in expression domains suggest caution when using developmental regulatory genes to make inferences about homology among morphological structures of distantly related taxa.     

A Giant Chelonioid Turtle from the Late Cretaceous of Morocco with a Suction Feeding Apparatus Unique among Tetrapods

Background

Secondary adaptation to aquatic life occurred independently in several amniote lineages, including reptiles during the Mesozoic and mammals during the Cenozoic. These evolutionary shifts to aquatic environments imply major morphological modifications, especially of the feeding apparatus. Mesozoic (250–65 Myr) marine reptiles, such as ichthyosaurs, plesiosaurs, mosasaurid squamates, crocodiles, and turtles, exhibit a wide range of adaptations to aquatic feeding and a broad overlap of their tooth morphospaces with those of Cenozoic marine mammals. However, despite these multiple feeding behavior convergences, suction feeding, though being a common feeding strategy in aquatic vertebrates and in marine mammals in particular, has been extremely rarely reported for Mesozoic marine reptiles.

Principal Findings

A relative of fossil protostegid and dermochelyoid sea turtles, Ocepechelon bouyai gen. et sp. nov. is a new giant chelonioid from the Late Maastrichtian (67 Myr) of Morocco exhibiting remarkable adaptations to marine life (among others, very dorsally and posteriorly located nostrils). The 70-cm-long skull of Ocepechelon not only makes it one of the largest marine turtles ever described, but also deviates significantly from typical turtle cranial morphology. It shares unique convergences with both syngnathid fishes (unique long tubular bony snout ending in a rounded and anteriorly directed mouth) and beaked whales (large size and elongated edentulous jaws). This striking anatomy suggests extreme adaptation for suction feeding unmatched among known turtles.

Conclusion/Significance

The feeding apparatus of Ocepechelon, a bony pipette-like snout, is unique among tetrapods. This new taxon exemplifies the successful systematic and ecological diversification of chelonioid turtles during the Late Cretaceous. This new evidence for a unique trophic specialization in turtles, along with the abundant marine vertebrate faunas associated to Ocepechelon in the Late Maastrichtian phosphatic beds of Morocco, further supports the hypothesis that marine life was, at least locally, very diversified just prior to the Cretaceous/Palaeogene (K/Pg) biotic crisis.     

Testing the directionality of evolution: the case of chydorid crustaceans

Although trends are of central interest to evolutionary biology, it is only recently that methodological advances have allowed rigorous statistical tests of putative trends in the evolution of discrete traits. Oligomerization is one such proposed trend that may have profoundly influenced evolutionary pathways in many types of animals, especially arthropods. It is a general hypothesis that repeated structures (such as appendage segments and spines) tend to evolve primarily through loss. Although largely untested, this principle of loss is commonly invoked in morphological studies of crustaceans for drawing conclusions about the systematic placements of taxa and about their phylogeny. We present a statistical evaluation of this hypothesis using a molecular phylogeny and character matrix for a family of crustaceans, the Chydoridae, analysed using maximum likelihood methods. We find that a unidirectional (loss-only) model of character evolution is a very poor fit to the data, but that there is evidence of a trend towards loss, with loss rates of structures being perhaps twice the rates of gain. Thus, our results caution against assuming loss a priori, in the absence of appropriate tests for the characters under consideration. However, oligomerization, considered as a tendency but not a rule, may indeed have had ramifications for the types of functional and ecological shifts that have been more common during evolutionary diversification.     

An elaboration of the evolutionary morphological basis for the systematics of the Plathelminthes

Compared with Hennig's phylogenetical systematics which has as its aim the retracing of genealogical relations between taxonomic groups, evolutionary morphological systematics is equally justified. Classifications of basic plans, morphological types, and morphofunctional systems of organisms serve as the foundation of evolutionary morphological systems. They are constructed on the basis of thorough understanding and further iteration of morphological transformation in phylogenetical branches based on the constructional pecularities of the morphofunctional systems. The evolutionary morphological approach in systematics is important especially for elaborating macrosystems dealing with vastly divergant groups where it is impossible to trace their real genealogy. The general principles of evolutionary morphological systematics are considered. A variant of the classification system of the Plathelminthes is suggested.     

Recognition of adaptiveness and reconstruction of the adaptation process

The problem of recognition of phyletic adaptations as an important area of evolutionary interpretation and synthesis of data on morphology and ecology is discussed. The disadvantages and limitations of the traditional approach, the so-called “adaptationist program,” and means of overcoming them are analyzed, as are additional possibilities provided by biomechanical analysis of parts of the musculoskeletal system; prospects of applying energy criterion of adaptiveness are also considered. To illustrate this point, a version of evolution of jaw apparatus and the middle ear of theromorphs is presented, which demonstrates that the degree of adaptiveness of any given trait should only be assessed in the context of the given evolutionary scenario. The conclusion has been drawn that it is necessary to study both sides of adaptation: the condition of being adapted and the process of adapting.     

Development of rules for vaccine engineering based on the variability of peptide fragments in closely related proteins

Based on the protein sequence data bank (PIR), the "variable fragment" bank, comprising pairs of closely related proteins, containing one or more strongly differing sites of primary structures was formed. The bank includes 465 "variable fragments" of 383 protein pairs. Amino acid residues composition of "variable fragments" was examined and indexes of potential amino acid residues variability was formed. An analysis of amino acid fragments replaceability was carried out by substituting the N-, C-terminal, or middle part of a chain), the fragments length differences and physico-chemical properties of residues, such as volume, hydrophobicity, polarity, isoelectric point, etc. Some general empirical rules of peptide insertions in carrier-proteins were created based on these analyses. The rules are directed for performing modifications maintaining the common structure and function of the carrier-protein molecule. The selection scheme for determining the regions suitable for modification and the criteria for defining the width of acceptable modifications in this regions were suggested. The use of potential variability profile for detecting regions suitable for peptide insertion was considered on the model of hepatitis B surface protein.     

Auditory systems of Heteromyidae: functional morphology and evolution of the middle ear.

Middle ears (515) from 26 species of the rodent family Heteromyidae - genera Dipodomys, Microdipodops, Perognathus, and Liomys - were studied both grossly and histologically, for qualitative and quantitative comparisons. Middle ear modifications characteristic of each genus are qualitatively described. Quantitative comparisons are made among the 26 species in the study. Some correlations between middle ear size and other measurements are discussed. The middle ear is an acoustical transformer that for best efficiency must match the impedance of the cochlea to the impedance of the air in the external auditory meatus. It accomplishes this by a pressure increase and a velocity decrease through the combined effects of the lever and areal ratios; however, because the important consideration is a matching of two impedances rather than an absolute pressure increase, the pressure transformer ratio is a less informative measure of the middle ear's efficiency than is the impedance transform ratio. The impedance transformer mechanism is explained (from a morphological point of view), and equations are presented. Dipodomys, Microdipodops, and Perognathus have a theoretical transmission (at the resonant frequency) of 94-100% of the incident acoustical energy; Liomys, 78-80%. The areal ratio of stapes footplate to 2/3 tympanic membrane is remarkably constant among the species, varying only from 0.04 to 0.07: in Dipodomys and Microdipodops this small ratio is due to the very large tympanic membrane; in Perognathus and Liomys it is due to the extremely small stapes footplate. The lever ratio of incus to malleus varies from 0.28 to 0.33 in Dipodpmys and Microdipodops, from 0.37 to 0.46 in Perognathus, and from 0.55 to 0.60 in Liomys. In addition, the middle ear volumes and the morphology of tympanic membrane, ossicles, ligaments, and muscles, all combine to minimize both mass and stiffness. All these data suggest middle ear mechanisms which are very efficient over a broad frequency range. The middle ear modifications found in heteromyids are adaptive in predator avoidance, especially in areas of little natural cover; nevertheless, contrary to expectations, there is no firm relationship between habitat and the extent of these modifications in the 26 species. However, environment did apparently plan an important role in the evolution of the family, and this is discussed.     

The middle ear of the skull of birds The Procellariiformes

Much emphasis has been placed on the middle ear region of reptiles and mammals as a taxonomic character. However, the anatomy of the middle ear region of birds has yet to be described adequately. The literature on the middle ear of birds is reviewed briefly and then the osteology and soft anatomy of the middle ear region of the skull are described for the families of the avian order Procellariiformes. Particular emphasis is paid to the foramina and paths of the nerves and blood vessels. Also discussed is the morphology of the basicranium and the quadrate. Comparative analyses of the characters are used to assess taxonomic conclusions.     

Morphology of the middle ear of golden moles (Chrysochloridae)

The middle ear structures of nine species of golden moles (family Chrysochloridae) were examined under the light microscope. Auditory structures of several of these species are described here for the first time in detail, the emphasis being on the ossicular apparatus. Confirming previous observations, some golden moles (e.g. Amblysomus species) have ossicles of a morphology typical of mammals, whereas others ( Chrysospalax , Chrysochloris , Cryptochloris and Eremitalpa species) have enormously hypertrophied mallei. Golden moles differ in the nature and extent of the interbullar connection, the shape of the tympanic membrane and that of the manubrium. The stapes has an unusual orientation, projecting dorsomedially from the incus. It has been proposed that hypertrophied ossicles in golden moles are adapted towards the detection of seismic vibrations. The functional morphology of the middle ear apparatus is reconsidered in this light, and it is proposed that adaptations towards low-frequency airborne hearing might have predisposed golden moles towards the evolution of seismic sensitivity through inertial bone conduction. The morphology of the middle ear apparatus sheds little light on the disputed ordinal position of the Chrysochloridae.     

Peculiarities of rostellum morphology and armature in the genera Kowalewskiella and Himantaurus (Cyclophyllidea: Dilepididae)

Scoleces of two dilepidid genera, Kowalewskiella Baczynska, 1914 and Himantaurus Spasskaja et Spassky, 1971, were investigated. The rostellar hooks of both are of davaineoid type, which is quite uncommon for the family. The morphology of their rostellar apparatus, especially the form of proboscis, differs much. But when the rostellum is retracted, the crown of hooks is folded in the same manner: hooks tips assume anterior direction. The muscular system of rostellar apparatus and the transformation of scolex in the act of rostellum's retraction of Kowalewskiella finds close analogy in Aploparaksis (family Hymenolepididae s.l.), and of Himantaurus--in Paradilepis (family Dilepididae). But such morphological and functional resemblance between scoleces of Kowalewskiella and Aploparaksis from one side and of Himantaurus and Paradilepis from another is undoubtedly a result of convergence. The morphological types of rostellar hooks in these pairs of genera are very different.     

The intermediate sperm type and genitalia of <Emphasis Type="Italic">Zorotypus shannoni</Emphasis> Gurney: evidence supporting infraordinal lineages in Zoraptera (Insecta)

The sperm ultrastructure and the male and female genital apparatus of Zorotypus shannoni were examined and documented in detail, mainly using transmission electron microscopy micrographs. The findings suggest an evolutionary trend shared with Z. hubbardi and Z. impolitus. The three species are characterized by enlarged mitochondrial derivatives and related modifications. Giant sperm are probably a synapomorphy of Z. hubbardi and Z. impolitus, whereas an intermediate condition of this feature is found in Z. shannoni. The monophyletic origin of Z. caudelli, Z. magnicaudelli, Z. huxleyi and Z. weidneri is suggested by characteristically modified axonemes. The presence of extra-acrosomal material is also an unusual feature for Zoraptera, but this condition also occurs in the majority of polyneopteran groups. The long and convoluted female spermathecal duct with secretory and duct-forming cells is a constant feature in Zoraptera. The enlarged seminal receptacle suggests an evolutionary link between the male genital structures and the sperm size on one hand, and the size of the female spermatheca on the other. The small and otherwise uniform group Zoraptera exhibits a remarkable variation of sperm types and genital structures, suggesting the impact of different types of selection. It is likely that cryptic female choice plays a major role in shaping the genital apparatus.     

东北小鲵中枢神经系统形态学与组织学初步研究（图版Ⅵ，上）

本文应用脊椎动物神经标本制作法和HE染色法,对东北小鲵中枢神经系统的外部形态和组织学结构进行了初步研究,描述了东北小鲵神经系统形态和组织学结构的特点,并与无尾两栖类和爬行类相对比,探讨了有尾两栖类的进化地位。结果表明：与无尾两栖类（如蛙）相比,东北小鲵中枢神经系统中,大脑半球较小,结构较为原始,小脑结构简单,是两栖类中较为原始的类群。此外,东北小鲵开始具有了臂神经丛和骶神经丛,但没有爬行类的发达,可作为两柄类向爬行类进化的证据之一。