Not enough skeletons in the closet: collections-based anatomical research in an age of conservation conscience.

The emergence of new technologies and improved computing power helped to introduce a renewed vitality in morphological research in recent decades. This is especially apparent in the new advances made in understanding the evolutionary morphology of the skeletal system in extinct and extant squamate reptiles. The new data generated as a result of the recent increase in attention are relevant not only for systematic analyses but also are valuable in their own right for contributing to holistic perspectives on organismal evolution, mosaic evolution in the rates of change in different anatomical systems, and broader patterns of macroevolution. A global community of morphological researchers now can share data through online digital collections, but opportunities for continued advance are hindered because we lack even basic data on patterns of variation of the skeletal system for virtually all squamate lineages. Most work on skeletal morphology of squamates is based on a sample size of n = 1; this is an especially noticeable phenomenon for studies relying on X-ray computed tomography technology. We need new collections of skeletal specimens, both material and digital, and new approaches to the study of skeletal morphology. Promising areas for continued research include the recent focus on skeletal elements not traditionally included in morphological studies (especially systematic analyses based upon morphological data) and efforts to elucidate patterns of variation and phylogenetically informative features of disarticulated skeletal elements.

Triassic marine reptiles gave birth to live young.

Sauropterygians form the largest and most diverse group of ancient marine reptiles that lived throughout nearly the entire Mesozoic era (from 250 to 65 million years ago). Although thousands of specimens of this group have been collected around the world since the description of the first plesiosaur in 1821 (ref. 3), no direct evidence has been found to determine whether any sauropterygians came on shore to lay eggs (oviparity) like sea turtles, or gave birth in the water to live young (viviparity) as ichthyosaurs and mosasauroids (marine lizards) did. Viviparity has been proposed for plesiosaur, pachypleurosaur and nothosaur sauropterygians, but until now no concrete evidence has been advanced. Here we report two gravid specimens of Keichousaurus hui Young from the Middle Triassic of China. These exquisitely preserved specimens not only provide the first unequivocal evidence of reproductive mode and sexual dimorphism in sauropterygians, but also indicate that viviparity could have been expedited by the evolution of a movable pelvis in pachypleurosaurs. By extension, this has implications for the reproductive pattern of other sauropterygians and Mesozoic marine reptiles that possessed a movable pelvis.

Relación entre desplazamiento de melanosomas y cambios de color en lagartijas machos: liolaemus tenuis tenuis: un estudio ultraestructural / Relationship between melanosomes displacement and color change in male lizards: liolaemus tenuis tenuis: an ultrastructural study

La mayor parte de los organismos multicelulares se caracterizan por un patrón de color distintivo y, a menudo, particular. Uno de los efectores relacionados con el proceso corresponde a células especiales, los cromatóforos. En este trabajo se demuestra mediante técnicas de microscopía electrónica, que en el dermis de reptiles sometidos a 35§C por 12 min, se produce una fuerte concentración de melanosomas en torno al núcleo de los melanóforos. Por el contrario, a 0§ los melanóforos presentan expansiones citoplasmáticas que contienen numerosos melanosomas. Asociados a los melanosomas en dispersión, se observan microtúbulos. Esta característica permite plantear la posible existencia de algún tipo de relación entre microtúbulos y movimiento de melanosomas en este reptil, cuando es sometido a bajas temperaturas, momento en que se oscurecen. Se destacan también, gruesos manojos tridimensionales de fibras colágenas asociadas a fibroblastos, estructuras, que para algunos autores, representarían un primordio de esclerificación dérmica, fenómeno que predecería a la fase fibrilar de la osificación dérmica o directa. Otro tipo de célula, los iridóforos, contienen placas reflectantes que reflejan la luz en direcciones determinadas

X-ray microanalysis of fossil dinosaur bone: age differences in the calcium and phosphorus content of Gallimimus bullatus bones.

Bones of dinosaurs, Gallimimus bullatus, belonging to selected age groups were studied using an X-ray microanalyser. Content of calcium and phosphorus, their distribution in the investigated areas and Ca/P ratio were determined. The obtained results revealed that the Ca/P ratio highest in the bones of young and middle-aged animals and decreased with age.

The system of cerebrospinal fluid-contacting neurons.

Cerebrospinal fluid (CSF)-contacting neurons are located periventricularly or inside the brain ventricles; they contact the CSF via their dendrites, perikarya or axons. Most of the CSF-contacting nerve cells send dendritic processes into the ventricular cavity where they form ciliated terminals. These ciliated dendritic endings resemble those of known sensory cells, yet their role is still unknown. There are two types of CSF-contacting dendritic terminals. One bears solitary 9 X 2 + 0 cilia; it is present in different hypothalamic regions such as the paraventricular organ and the vascular sac. The magnocellular neurosecretory nuclei also contain CSF-contacting neurons, which probably furnish information about the parameters of the CSF for the regulatory function of the hypothalamo-hypophyseal system. CSF-contacting nerve cells of the parvocellular hypothalamic nuclei are suspected to participate in hypothalamo-adenohypophyseal regulation. A second type of CSF-contacting dendritic terminal bears many stereocilia and is found in the central canal of the spinal cord. This type of terminal is also supplied with a 9 X 2 + 2 kinocilium that may contact Reissner's fiber, the secretory material of the subcommissural organ. Resembling mainly mechanoreceptors, these spinal CSF-contacting neurons appear to form axon terminals of the neurosecretory type at the external circumference of the spinal cord. Developing and/or regressing photoreceptor cells of the retina and pineal complex may display a similar dendritic structure characteristic of hypothalamic CSF-contacting neurons. Axons penetrating into the ventricles innervate the apical surface of the ependyma and/or the CSF-contacting dendritic terminals. Some bipolar neurons of the retina form so-called Landolt's clubs; these may be considered as the retinal component of the CSF-contacting neuronal system. Since in the lancelet nearly all nerve cells contact the CSF, the CSF-contacting neurons represent a specialized, but phylogenetically old cell type, a "protoneuron" in the vertebrate brain. They may be derived phylogenetically by inversion of the ciliated neurons found in the plate-like nervous system of more primitive deuterostomians.

Organization of ascending spinal projections in Caiman crocodilus.

Ascending spinal projections in the caiman (Caiman crocodilus) were demonstrated with Nauta and Fink-Heimer methods following hemisections of the third spinal segment in a series of twelve animals. These results were compared with earlier data in the literature obtained from a turtle, a snake, and a lizard using the same experimental and histological procedures. The results show remarkable similarities considering that each species represents a different reptilian order with different evolutionary history and habitat. However, the caiman displays several important peculiarities. Although the dorsal funiculus of the caiman contains the largest number of ascending spinal projections of the four species examined, this funiculus has not differentiated into cuneate and gracile fasciculi as is the case in the tegu lizard. The ventro-lateral ascending spinal projections follow a fundamentally similar general morphologic pattern in the four species with only minor variations. The anatomical arrangement in the caiman and tegu lizard appears most similar in the high cervical and the medullary regions; however, this is not the case in midbrain and thalamic regions where considerably more extensive projections are seen in the caiman. In the caiman an extensive spinal connection to the ventro-lateral nucleus of the dorsal thalamus is present; this connection is reminiscent of the mammalian spinal projection to the ventro-basal complex. The caiman has in common with the other three reptilian species a small projection to another dorsal thalamic region that is apparently homologous to the mammalian intralaminar nuclei, which are the destination of the mammalian paleospinothalamic tract.

Cells of origin of pathways descending to the spinal cord in some quadrupedal reptiles.

The cells of origin of pathways descending to the spinal cord have been determined in several quadrupedal reptiles, viz., the turtle Pseudemys scripta elegans and Testudo hermanni and the lizards Tupinambis nigropunctatus and Varanus exanthematicus, following a technique introduced by Kuypers and Maisky ('75). This technique was very effective in producing retrograde transport of HRP to a great many neurons in the hypothalamus and in the brain stem. Projections from the hypothalamus (the nucleus paraventricularis and the nucleus periventricularis hypothalami), the interstitial nucleus of the film, the nucleus ruber, the nucleus of Edinger-Westphal, the locus coeruleus, the subcoeruleus area, a conspicuous cell group comparable to Kuypers and Maisky's (75, '77) lateral pontine area, the magnocellular reticular formation, the ventrolateral, ventromedial, and descending vestibular nuclei, the dorsal motor nucleus of the vagus, and the nucleus of the solitary tract, reach at least as far as the lumbar intumescence. Projections from two somatosensory nuclei, i.e., the nucleus descendens nervi trigemini and the nucleus funiculi dorsalis, as well as the laminar nucleus of the torus semicircularis, have been demonstrated to at least the ninth spinal segment. The two deep cerebellar nuclei, particularly the medial cerebellar nucleus, were found to project contralaterally to the spinal cord, in the lizard Varanus exanthematicus at least as far as the seventh segment; in the turtles studied so far, only projections as far caudal as the fourth spinal segment could be demonstrated. Data on the funicular trajectory of various descending pathways could also be obtained. It seems likely that in the reptiles studied, in addition to rubrospinal and reticulospinal pathways, projections from the hypothalamus, the nucleus of Edinger-Westphal, the cell group comparable to the mammalian lateral pontine area, the locus coeruleus, and subcoeruleus area, and the nucleus of the solitary tract pass via the lateral funiculus. The pathways descending from the hypothalamus and brain stem to the spinal cord in the quadrupedal reptiles studied appear to show remarkable similarities to pathway in mammals as regards their cells of origin as well as their funicular trajectory. It seems likely that some of the projections demonstrated, viz., from the locus coeruleus, at least part of the cell group comparable to the lateral pontine area, as well as the cells in and around the dorsal motor nucleus of the vagus, are noradrenergic pathways.

Comparison of the pineal complex, retina and cerebrospinal fluid contacting neurons by immunocytochemical antirhodopsin reaction.

The presence of rhodopsin was investigated by an indirect immunocytochemical method in the pineal complex of various vertebrates (Carassius auratus, Cyprinus carpio, Hypophthalamichthys molitrix, Lucioperca lucioperca, Triturus vulgaris, Bombina bombina, Rana esculenta, Pseudemys scripta elegans, Lacerta agilis et viridis, white leghorn chickens, rat), in the retina of Lebistes reticulatus, Lucioperca lucioperca, Rana esculenta, Lacerta agilis, Pseudemys scripta elegans, the chicken and the rat, and the cerebrospinal (CSF) contacting neurons of Triturus vulgaris. The outer segments of the photoreceptor terminals of the pineal organ, frontal organ, parapineal organ of lower vertebrates and of the retina of the species investigated, were intensely stained with the antirhodopsin reaction. There was no significant positivity in the pineal organ of the reptiles, the chicken and the rat, and the parietal eye of the lizards. We failed to demonstrate any immunoreactive staining in the CSF contacting neurons of various hypothalamic areas and of the spinal cord. The light microscopic immunocytochemical results seem to contradict a photoreceptive role of the CSF contacting neurons and strengthen the view that the receptory cells of the pineal complex of lower vertebrates are involved in light perception by means of the visual pigment rhodopsin.

The cell masses in the diencephalon of Amphisbaena darwini heterozonata Burmeister (Amphisbaenia, Squamata, Reptilia).

The cell masses of the diencephalon of Amphisbaena darwini heterozonata are studied and confronted with those of other reptiles, specially with the burrowing ophidian Typhlopidae. The main differences are in the thalamus dorsalis. The amphisbaenids share with the Typhlopidae the absence of the lateral and pretectal geniculate bodies, and share with the squamate reptiles, differing from the typhlopids, the remaining structures of the dorsal thalamus, characterized by the well-developed nucleus rotundus. These features support the idea that the amphisbaenids could be situated within the Squamata at the same level as in Ophidia and Lacertilia. The adaptive processes toward a burrowing behavior have not been the same in amphisbaenids and in the typhlopids. The causes of the dissimilarities of the dorsal thalamus could be related to other sense and non-sense systems apart from the optic. The morphology of the elements of the cell masses has been studied by the Golgi method.

Ciliated neurons and different types of synapses in anterior hypothalamic nuclei of reptiles.

The magnocellular paraventricular and supraoptic nuclei and the parvocellular preoptic and periventricular nuclei have been studied by light and electron microscopy in Emys orbicularis, Lacerta agilis and Elaphe longissima. The ultrastructure of cerebrospinal fluid (CSF)-contacting neurons was described in the preoptic and periventricular nuclei of Emys and Lacerta species. Single 9 X 2 + 0 cilia similar to those of the CSF-contacting dendritic terminals were found on perikarya of non CSF-contacting nerve cells, in all four investigated nuclei. The cilia project from funnel-like invaginations of the perikarya into the intercellular space. In the neurons of the nuclei studied, granular vesicles were found, their size being mainly 1,600 A in the paraventricular nucleus, about 1,800 A in the supraoptic nucleus, 1,100 A in the periventricular nucleus and 800 A, or up to 1,250 A in the preoptic nucleus. In general, the neurons possess synapses of the axo-somatic, axo-somatic spine, axo-dendritic and axo-dendritic spine types. In the supraoptic nucleus, multiple interdigitated synapses were observed. Presynaptically, eif different sizes (600 to 800 A, about 1,100 A, 1250 A, and up to 2,000 A) were found. It is discussed whether the above described 9 X 2 + 0 cilia may represent some kind of hypothalamic sensory structure that earlier physiological studies postulated to exist. The ciliated hypothalamic perikarya are considered by the authors to be a more differentiated form of the CSF-contacting neurons. The different types of synapses indicate multilateral connections of the nerve cells of the nuclei studied.