Comparative cranio-mandibular myology of three species of Batoidea from the Southern Gulf of California, Mexico.

The mandibular apparatus of batoids (skates, electric rays, guitarfishes, stingrays, and sawfishes) is composed of a few skeletal elements to which the muscular bundles, responsible for all movements involved in the feeding mechanism, are inserted. The description of the different mandibular morphologies can help to understand the different feeding guilds in this group. In this study, we examined the cranio-mandibular myology of adult Rostroraja velezi, Narcine entemedor, and Zapteryx exasperata, three species of rays that coexist in the Southern Gulf of California, Mexico. This study described the muscles on the ventral and the dorsal surfaces for each species, identified the origins and insertions of these muscles, as well as the general characteristics of muscle morphology. There were 17 and 18 muscle bundles attached to the feeding apparatus, including five on the dorsal surface. Only the levator rostri, which elevates the rostrum during feeding, showed considerable differences in shape and size among species. The muscles of the adductor complex showed the greatest differences in size among the three species. N. entemedor presented the exclusive muscle X in the lower mandibular area and the extreme reduction of the coracohyoideus in the pharyngeal area derived from the absence of the basihyal cartilage. The information generated in our study supports the morphological specialization of electric rays (N. entemedor) for an almost exclusive suction feeding strategy.

Musculoskeletal anatomical changes that accompany limb reduction in lizards.

Muscles, bones, and tendons in the adult tetrapod limb are intimately integrated, both spatially and functionally. However, muscle and bone evolution do not always occur hand in hand. We asked, how does the loss of limb bones affect limb muscle anatomy, and do these effects vary among different lineages? To answer these questions, we compared limb muscular and skeletal anatomy among gymnophthalmid lizards, which exhibit a remarkable variation in limb morphology and different grades of digit and limb reduction. We mapped the characters onto a phylogeny of the group to assess the likelihood that they were acquired independently. Our results reveal patterns of reduction of muscle and bone elements that did not always coincide and examples of both, convergent and lineage-specific non-pentadactyl musculoskeletal morphologies. Among lineages in which non-pentadactyly evolved independently, the degree of convergence seems to depend on the number of digits still present. Most tetradactyl and tridactyl limbs exhibited profound differences in pattern and degree of muscle loss/reduction, and recognizable morphological convergence occurred only in extremely reduced morphologies (e.g., spike-like appendix). We also found examples of muscles that persisted although the bones to which they plesiomorphically attach had been lost, and examples of muscles that had been lost although their normal bony attachments persisted. Our results demonstrate that muscle anatomy in reduced limbs cannot be predicted from bone anatomy alone, meaning that filling the gap between osteological and myological data is an important step toward understanding this recurrent phenomenon in the evolution of tetrapods.

Cranial muscle development in the model organism ambystoma mexicanum: implications for tetrapod and vertebrate comparative and evolutionary morphology and notes on ontogeny and phylogeny.

There is still confusion about the homology of several cranial muscles in salamanders with those of other vertebrates. This is true, in part, because of the fact that many muscles present in early ontogeny of amphibians disappear during development and specifically during metamorphosis. Resolving this confusion is important for the understanding of the comparative and evolutionary morphology of vertebrates and tetrapods because amphibians are the phylogenetically most plesiomorphic tetrapods, concerning for example their myology, and include two often used model organisms, Xenopus laevis (anuran) and Ambystoma mexicanum (urodele). Here we provide the first detailed report of the cranial muscle development in axolotl from early ontogenetic stages to the adult stage. We describe different and complementary types of general muscle morphogenetic gradients in the head: from anterior to posterior, from lateral to medial, and from origin to insertion. Furthermore, even during the development of neotenic salamanders such as axolotls, various larval muscles become indistinct, contradicting the commonly accepted view that during ontogeny the tendency is mostly toward the differentiation of muscles. We provide an updated comparison between these muscles and the muscles of other vertebrates, a discussion of the homologies and evolution, and show that the order in which the muscles appear during axolotl ontogeny is in general similar to their appearance in phylogeny (e.g. differentiation of adductor mandibulae muscles from one anlage to four muscles), with only a few remarkable exceptions, as for example the dilatator laryngis that appears evolutionary later but in the development before the intermandibularis.

Jaw adductor muscles across lepidosaurs: a reappraisal.

The exact homologies of tetrapod jaw muscles remain unresolved, and this provides a barrier for phylogenetic analysis and tracing character evolution. Here, lepidosaur jaw muscles are surveyed using direct examination of species from 23 families and published descriptions of species from 10 families. A revised nomenclature is applied according to proposed homologies with Latimeria. Among lepidosaurs, variation was found in many aspects of jaw muscle anatomy. The superficial layers mm. levator and retractor anguli oris (LAO and RAO) are present in Sphenodon but not all squamates. The external jaw adductor muscles universally present in lepidosaurs are homologous with the main adductor muscle, A2, of Latimeria and include four layers: superficialis (A2-SUP), medialis (A2-M), profundus (A2-PRO), and posterior (A2-PVM). The A2-SUP appears divided in Agamidae, Gekkota, Xantusiidae, and Varanidae. The A2-M is layered lateromedial in lizards but anteroposterior in snakes. The names pseudotemporalis (PS) and pterygomandibularis (PTM) are recommended for subdivisions of the internal adductors of reptiles and amphibians, because the homology of this muscle with the A3' and A3 ″ of Latimeria remains inconclusive. The intramandibularis of lepidosaurs and Latimeria (A-ω) are homologous. The distribution of six jaw muscle characters was found to plot more parsimoniously on phylogenies based on morphological rather than and molecular data. Character mapping indicates that Squamata presents reduction in the divisions of the A2-M, Scincoidea presents reduction or loss of LAO, and two apomorphic features are found for the Gekkota.

Comparative anatomy, homologies and evolution of the pectoral and forelimb musculature of tetrapods with special attention to extant limbed amphibians and reptiles.

The main aim of the present work is to synthesize the information obtained from our dissections of the pectoral and forelimb muscles of representative members of the major extant taxa of limbed amphibians and reptiles and from our review of the literature, in order to provide an account of the comparative anatomy, homologies and evolution of these muscles in the Tetrapoda. The pectoral and forelimb musculature of all these major taxa conform to a general pattern that seems to have been acquired very early in the evolutionary history of tetrapods. Although some muscles are missing in certain taxa, and a clear departure from this general pattern is obviously present in derived groups such as birds, the same overall configuration is easily distinguishable in these taxa. Among the most notable anatomical differences between the groups, one that seems to have relevant evolutionary and functional implications, concerns the distal insertion points of the forearm musculature. In tetrapods, the muscles of the radial and ulnar complexes of the forearm are pleisomorphically mainly inserted onto the radius/ulna or onto the more proximal carpal bones, but in mammals some of these muscles insert more distally onto bones such as the metacarpals. Interestingly, a similar trend towards a more distal insertion of these muscles is also found in some non-mammalian tetrapod taxa, such as some anurans (e.g. Phyllomedusa). This may be correlated with the acquisition of more subtle digital movement abilities in these latter taxa.

Origin, evolution and homologies of the Weberian apparatus: a new insight / Origen, evolución y homologías del aparato weberiano: un nuevo acercamiento

The Weberian apparatus is essentially a mechanical device improving audition, consisting of a double chain of ossicles joining the air bladder to the inner ear. Despite being one of the most notable complex systems of teleost fishes and the subject of several comparative, developmental and functional studies, there is still much controversy concerning the origin, evolution and homologies of the structures forming this apparatus. In this paper I provide a new insight on these topics, which takes into account the results of recent works on comparative anatomy, paleontology, and ontogeny as well as of a recent extensive phylogenetic analysis including not only numerous otophysan and non-otophysan extant otocephalans but also ostariophysan fossils such as Chanoides macropoma, Clupavus maroccanus, Santanichthys diasii, Lusitanichthys characiformis, Sorbininardus apuliensis and Tischlingerichthys viohli. According to the evidence now available, the Weberian apparatus of otophysans seems to be the outcome of a functional integration of features acquired in basal otocephalans and in basal ostariophysans, which were very likely not directly related with the functioning of this apparatus, and of features acquired in the nodes leading to the Otophysi and to the clade including the four extant otophysan orders, which could well have been the result of a selection directly related to the functioning of the apparatus.

El aparato weberiano es esencialmente un dispositivo mecánico que mejora la audición, consiste en una doble cadena de osículos que unen la cámara de aire al oído interno. A pesar de ser uno de los sistemas complejos más notables de peces teleósteos y objeto de varios estudios comparativos, de desarrollo y funcionales, todavía hay mucha controversia sobre el origen, evolución y homologías de las estructuras que forman este aparato. En este trabajo se proporciona una nueva visión sobre estos temas, que tiene en cuenta los resultados de los últimos trabajos sobre la anatomía comparada, paleontología y la ontogenia, así como de un reciente análisis filogenético amplio que incluyen no sólo numerosos otocéfalos Otofisios y no Otofisios existentes, sino también fósiles Ostariofisios como Chanoides macropoma, Clupavus maroccanus, Santanichthys diasii, Lusitanichthys characiformis, Sorbininardus apuliensis y Tischlingerichthys viohli. Según las pruebas disponibles, el aparato weberiano de Otofisios parece ser el resultado de una integración funcional de las características adquiridas en otocéfalos basales y en ostariofisios basales, los cuales muy probablemente no estén directamente relacionados en el funcionamiento de este aparato, y las características adquiridas en los nodos que condujeron a los Otofisios y al clade incluyendo las cuatro órdenes existentes otofisios, que bien podrían haber sido el resultado de una selección directamente relacionada con el funcionamiento del aparato.

Teleostean phylogeny based on osteological and myological characters / Filogenia de teleosteos basada en características osteológicas y miológicas

Despite the progresses done in the field of teleostean phylogeny in the last decades, recent studies continué to raise questions concerning the higher-level relationships of this remarkably diverse group of fishes. The main aim of the present work is to help to clarify teleostean higher-level relationships. For that purpose, we undertook a cladistic analysis including 70 terminal taxa of 20 different orders and 271 morphological characters, concerning mainly osteological and myological structures of the cephalic region , pectoral girdle and fins and anterior vertebrae. In the consensus cladogram obtained, the elopomorphs appear as the most basal extant teleosts. The osteoglossomorphs included in the analysis are grouped in a monophyletic clade, which is the sister-group of the remaining non-elopomorph teleosts. The Otocephala, the Clupeiformes, and the Ostariophysi appear as monophyletic clades, thus contradicting the results of some recent molecular cladistic analyses placing the Alepocephaloidea inside the Otocephala. In fact, the monophyly of the Argentiniformes (Alepocephaloidea + Argentinoidea) is well supported by the cladistic analysis of the present work. This cladistic analysis also provides support for the monophyly of the Alepocephaloidea, of the Argentinoidea, of the Galaxioidea + Osmeroidea, and of the Esociforines. However, it does notprovide strong evidence to resolve the relationships between the Argentiniformes, Salmoniformes, Esociformes, Osmeriformes and Neoteleostei, although it does indicate that the salmoniforms might be closely related to the Neoteleostei and that the Esociformes and the Osmeriformes might constitute a monophyletic unit. The monophyly of the Cypriniformes + Characiformes + Gymnotiformes + Siluriformes, of the Characiformes + Gymnotiformes + Siluriformes and of the Gymnotiformes + Siluriformes is well supported.

A pesar de los avances realizados en relacion a la filogenia de los teleosteos en las últimas décadas, los estudios recientes siguen planteando cuestiones relativas a los altos niveles de relacion de este notable grupo de diversos peces. El principal objetivo del presente trabajo es contribuir a aclarar los altos niveles de relacion de teleosteos. Con este propósito, se llevó a cabo un análisis cladístico entre 70 taxones terminales de 20 órdenes diferentes y 271 caracteres morfológicos, principalmente en relacion con estructuras osteológicas y miológicas de la region cefálica, cintura escapular y las aletas anteriores y vértebras. En el cladograma de consenso obtenido, los elopomorfos aparecen como los teleosteos más básicos existentes. Los osteoglosomorfos incluidos en el análisis se agrupan en un ciado monofilético, que es el grupo hermano de los restantes teleosteos no elopomorfos. Los Otocephala, los clupeiforines, y los ostariofisios aparecen como ciados monofiléticos, contradiciendo así los resultados de algunos análisis moleculares cladísticos recientes incluyendo los Alepocephalidae dentro Otocephala. De hecho, la monofilia de los Argentiniformes (Alepocephaloidea + Argentinoidea) está bien apoyada por el análisis cladístico del presente trabajo. Este análisis cladístico también proporciona apoyo para la monofilia de los Alepocephaloidea, de los Argentinoidea, de los Galaxioidea + Osmeroidea, y de los Esociformes. Sin embargo, no proporciona pruebas sólidas para resolver las relaciones entre los Argentiniformes, Salmoniformes, Esociformes, Osmeriformes y Neoteleostei, aunque indica que los salmoniformes podrían estar estrechamente relacionados con los Neoteleostei, y que los Esociformes y los Osmeriformes podrían constituir una unidad monofilética. La monofilia de los Cypriniformes + Characiformes + Gymnotiformes + Siluriformes, de los Characiformes + Gymnotiformes + Siluriformes y de los Gymnotiformes + Siluriformes está bien apoyada.

Osteology and Myology of the Cephalic Region and Pectoral Girdle of Heptapterus mustelinus, Comparison With Other Heptapterins, and Discussion on the Synapomorphies and Phylogenetic Relationships of the Heptapterinae and the Pimelodidae (Teleostei: Siluriformes) / Osteología y Miología de la Región Cefálica y de la Cintura Pectoral del Heptapterus mustelinus, Comparación con Otros Heptapterinos, y Discusión de las Sinapomorfías y Relaciones Filogenéticas de los Heptapterinae y Pimelodidae (Telostei: Siluriformes)

The cephalic and pectoral girdle structures of the heptapterin Hepapterus mustelinus (Nemuroglanis clade') are described and compared to those of two representatives of the other, more plesiomorphic, main heptapterin group, namely Goeldiella eques and Rhamdia guatemalensis ('basal clade'), as well as of several other catfishes, as the foundation for a discussion on the synapomorphies and phylogenetic relationships of the Heptapterinae. In addition to the five synapomorphies commonly referred in the literature, there is another potential Heptapterinae synapomorphy: the well-developed maxilla forming a completely closed, deep tube to enclose the base of the maxillary barbel. The subfamilies Pimelodinae, Heptapterinae and Pseudopimeodinae seem to form a monophyletic assemblage, thus contradicting the commonly accepted idea that the family Pimelodidae is not a natural group.

Las estructuras de la región cefálica y de la cintura pectoral de Heptapterus mustelinus ('Nemuroglanis clade') son descritas y comparadas con las de dos representantes de un grupo más plesiomórfico, Goeldiella eques y Rhamdia guatemalensis ('basal clade'), así como las de otros peces gato, como fundamento para la discusión de las relaciones filogenéticas y de las sinapomorfías de los Heptapterinae. Además, de las cinco sinapomorfías referidas comúnmente en la literatura, este estudio advierte una otra sinapomorfía de Heptapterinae: la bien desarrollada maxila formando un tubo completamente cerrado para la base del bigote maxilar. Las subfamilias Pimelodinae, Heptapterinae y Pseudopimelodinae parecen formar un grupo natural.

Homoplasies, Consistency Index and the Complexity of Morphological Evolution: Catfishes as a Case Study for General Discussions on Phylogeny and Macroevolution / Homoplasias, índice de Consistencia y la Complejidad de la Evolución Morfológica: Peces Gato como un Estudio de Caso para Discusiones Generales en Filogenia y Macroevolución

Catfishes constitute a highly diversified, cosmopolitan group that represents about one third of all freshwater fishes and is one of the most diverse Vertebrate taxa. The detailed study of the Siluriformes can, thus, provide useful data, and illustrative examples, for broader discussions on general phylogeny and macroevolution. In this short note I briefly expose how the study of this remarkably diverse group of fishes reveals an example of highly homoplasic, complex 'mosaic' morphological evolution.

Los peces gato constituyen un grupo cosmopolita ampliamente diversificado, el cual representa cerca de un tercio de todos los peces de agua dulce, y es uno de los taxones más diversos de vertebrados. El detallado estudio de los Siluriformes puede, de esta forma, proveer datos útiles y ejemplos ilustrativos para amplias discusiones de filogenia general y macroevolución. En esta comunicación expondré brevemente cómo el estudio de este grupo notoriamente diverso revela un ejemplo de amplia homoplasia y un complejo «mosaico¼ de evolución morfológica.

Osteology and Myology of the Cephalic Region and Pectoral Girdle of Pangasius macronema, With a Discussion on the Synapomorphies and Phylogenetic Relationships of the Pangasiidae (Teleostei: Siluriformes) / Osteología y Miología de la Región Cefálica y de la Cintura Pectoral del Pangasius macronema, con una Discusión de las Sinapomorfías y Relaciones Filogenéticas de los Pangasiidae (Telostei; Siluriformes)

The cephalic and pectoral girdle structures of Pangasius macronema are described and compared with those of another representative of the same genus, Pangasius larnaudii, and of representatives of the other pangasiid genus, Helicophagus leptorhynchus and Helicophagus typus, as well as of several other catfishes, as the foundation for a discussion of the synapomorphies and phylogenetic relationships of the Pangasiidae. The following two features could constitute Pangasiidae autapomorphies: 1) presence of prominent crest on the dorso-lateral surfaces of both the hyomandibulo-metapterygoid and the ento-ectopterygoid; 2) presence of a large, circular foramen between the anterodorsomedial surface of the extrascapular, the dorsomesial surface of the pterotic and the dorsolateral surface of the parieto-supraoccipital. With respect to the phylogenetic relationships of the Pangasiidae, this family is seemingly closely related to the Schilbidae.

Se describen las estructuras cefálicas y la cintura pectoral del Pangasius macronema y son comparadas con las de otros representantes del mismo género, Pangasius larnaudü, y las de otros Pangásidos, Helicophagus leptorhynchus y Helicophagus typus, así como de varios otros peces gato, como base para la discusión de las sinapomorfías y relaciones filogenéticas de los Pangásidos. Las siguientes dos características constituyen autapomorfías de los Pangásidos: 1) Presencia de una cresta prominente sobre la cara dorsolateral del hueso hyomandíbulo-metapterigoídeo y el hueso entopterigoídeo. 2) Presencia de un amplio foramen circular entre la superficie anterodorsomedial del hueso extracapsular, la cara dorsomedial del hueso pterótico y la cara dorsolateral del hueso parieto-supraoccipital. Con respecto a las relaciones filogenéticas de los Pangásidos, esta familia está aparentemente relacionada a la familia Schilbidae.

Cordelia's Dilemma, Historical Bias, and General Evolutionary Trends: Catfishes as a Case Study for General Discussions on Phylogeny and Macroevolution / Dilema de Cordelia, Sesgos Históricos y Tendencias Evolutivas Generales: Los Bagres Como un Estudio de Caso Para Discusiones Generales en Filogénesis y Macroevolución

As noted Gould in his recent and last book «The structure of evolutionary theory¼, discourses on the high importance and frequency of evolutionary trends have consumed a great part of the research on the history of clades. Although aware that natural selection theoretically yields adaptation to immediate environments, many authors defend such trends as generalised improvements somehow conferring advantages across most or all experienced environments. The high importance given to evolutionary trends is questioned by Gould, who considers that such a high importance given to such evolutionary trends bears no necessary relationship to the relative frequency or casual weight of these events in evolution, but mainly to a major bias: trends tell histories, and evolution is a narrative history. In the present paper I briefly discuss this subject arguing that the case study provided by catfishes, a remarkably diverse group of Vertebrates reputed by its «general evolutionary trends¼, supports Gould's view according to which careful phylogenetic analysis of a clade often contradicts the supposed importance of general evolutionary trends in that clade's evolution.

Como señala Gould en su reciente y último libro «La estructura de la teoría evolutiva¼, las discusiones sobre la gran importancia y frecuencia de tendencias evolutivas han consumido una gran parte de la investigación sobre la historia de clados. Aún conociendo que la selección natural, teóricamente, se adapta a un ambiente específico, muchos autores defienden tales tendencias como mejoras generalizadas, las cuales de alguna manera confieren ventajas a través de la mayoría o de todas las experiencias medioambientales. La gran importancia dadas a las tendencias evolutivas es cuestionada por Gould, quien considera que esta gran importancia es debida a un sesgo histórico: tendencias cuentan historias y, la evolución es una historia narrativa. En el presente trabajo comento brevemente este tema argumentando que el estudio realizado en bagres, un grupo de Vertebrados notablemente diverso, contradice la supuesta gran importancia de las tendencias evolutivas generales en la evolución de clados.