Browsing by Author "McDowell, Samuel Booker."
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Item The Greater Antillean insectivores. Bulletin of the AMNH ; v. 115, article 3(New York : [American Museum of Natural History], 1958) McDowell, Samuel Booker."The two genera of West Indian insectivores, Solenodon and Nesophontes, have been placed in separate superfamilies, Tenrecoidea and Soricoidea, respectively. This classification is based primarily on the sculpture of the lingual portion of the upper molars. Examination of the skull, however, reveals very close agreement between the two genera, and this agreement is seen further in the form of the buccal portion of the molars. So close is the apparent relationship between the two genera that they are here placed in the same family, Solenodontidae. The fossil (Oligocene) genus Apternodus is not even a member of the same order (Lipotyphla) as its supposed relative Solenodon. Apternodus is so peculiarly specialized that its relationships are obscure, but its basicranial structure suggests creodont, rather than insectivore, affinities. Palaeoryctes (Puerco), supposed to be an ancestral zalambdodont, is not related to any of the living zalambdodont groups, bearing only an equivocal dental resemblance to modern forms and showing a creodont-like rather than lipotyphlan-like basicranium. It is suggested that the families Deltatheridiidae and Palaeoryctidae be merged, under the latter name. A classification of the lipotyphlous insectivores is presented, based primarily on cranial structure: Order Lipotyphla. Suborder Erinaceomorpha. Family Erinaceidae, family Dimylidae, family Talpidae. Suborder Soricomorpha. Superfamily Tenrecoidea. Family Tenrecidae, family Chrysochloridae. Superfamily Soricoidea. Family Solenodontidae, family Soricidae. Solenodon and Nesophontes appear to represent a line that separated from a presoricid stem not later than the Upper Eocene, and there is no reason to believe that the divergence of the two genera did not take place in the West Indies"--P. 210.Item New taxa and cryptic species of neotropical snakes (Xenodontinae), with commentary on hemipenes as generic and specific characters. (Bulletin of the American Museum of Natural History, no. 385)(American Museum of Natural History., 2014-03-06) Myers, Charles W.; McDowell, Samuel Booker.Eutrachelophis, new genus is established to accommodate E. bassleri, new species, and E. steinbachi (Boulenger), new combination; a third species close to E. bassleri awaits naming. These taxa are placed in the Eutrachelophiini, new tribe, to express hypothesized relationship with the Xenodontini, which are defined by presence of hemipenial apical discs (a character lost in several species). The acalyculate spiny hemipenis of Eutrachelophis bassleri is unique among "xenodontines" in having a noncapitate, well-formed capitulum in the form of a nude dome; bifurcation is lacking even in the insertion of the major retractor muscle; the sulcus spermaticus is centrolineal in the retracted organ but becomes centrifugal during eversion. The hemipenis of Eutrachelophis steinbachi is strikingly different in being deeply divided, with long spiny lobes tipped with tufts of sender spines, but it resembles those of some other colubrids (e.g., South American Xenodon suspectus; African Mehelya poensis). Based on hemipenial comparisons, E. bassleri and E. steinbachi seem unlikely congeners. Nonetheless, global comparisons of viscera, head glands, head muscles, color pattern, skull, and dentition indicate that they are congeneric despite hemipenial differences. Neither E. bassleri nor E. steinbachi shows sufficient resemblance to any other "xenodontine" that would suggest an alternative phylogeny. Overall resemblance in so many details, especially of the skull, is not reasonably explained by convergence. Therefore, contrary to dogma, the hemipenes in this case provide no clues to generic affinity. An explanatory hypothesis has Eutrachelophis bassleri and E. steinbachi derived from common stock, but with hemipenial lobes in the bassleri lineage suppressed during embryonic development. It further suggests that the unusual broad, hemispherical nude apex in E. bassleri is homologous with the interlobular smooth, expandable terminal basin in E. steinbachi. The hemipenial differences in Eutrachelophis are not inconsistent with growing awareness that evolution of male genitalia may outpace changes in other characters without predictable limits to complexity. Fine-scale Hox gene expression might account for the novel hemipenis of E. bassleri. Although it is well established that snake hemipenes generally give at least a hint of relationship, a widely held belief that they are taxonomically stable and relatively free of selection pressures must be abandoned. Hemipenes (and probably female cloacae) are not "neutral" or "uncorrelated" characters but are subject to intense selection pressure requiring successful copulation, hence successful reproduction. The belief that one description or illustration suffices to typify a species (or genus) has no merit without proper sampling. Intraspecific variation is commonplace in geographically widespread species--sometimes, not always, signaling the presence of unnamed cryptic species. Examples are given of intraspecific variation in different kinds of hemipenial features. Also provided are examples of evolutionary plasticity and extreme divergence in snake hemipenes, with a few references to female cloacae, about which much less is known....Item The snakes of the Huon Peninsula, Papua New Guinea. American Museum novitates ; no. 2775(New York, N.Y. : American Museum of Natural History, 1984) McDowell, Samuel Booker.; Archbold Expedition to New Guinea 1964)The snakes known from the Huon Peninsula (from the longitude of Lae eastward) are listed and discussed, mainly on the basis of spcimens collected by the Seventh Archbold Expedition but using other collections as well. The taxonomy of the genus Dendralaphis in the Australian region is discussed and the following species are recognized: D. punctulatus (including D. lineolatus); d. calligastra, D. salomonis, D. lorentzi, D. papuensis (these four have usually been regarded as conspecific); and D. gastrostictus (including D. meeki); hemipenial morphology, dentition, and braincase form are used for discriminating the species. A misidentification of Typhlops inornatus as Ramphotyphlops flaviventer is corrected. The snake fauna, like the frog and lizard faunas previously discussed by Zweifel, is most easily explained as the result of dispersal to a Pliocene island that became joined (probably in the Pleistocene) to the New Guinea mainland, with a lowland fauna occupying this zone of juncture. Little, if any, endemicity is indicated for the Huon snake fauna and there is no special resemblance to the snake fauna of nearby New Britain and Umboi"--P. [1].Item The systematic position of Lanthanotus and the affinities of the anguinomorphan lizards. Bulletin of the AMNH ; v. 105, article 1(New York : [American Museum of Natural History], 1954) McDowell, Samuel Booker.; Bogert, Charles M. (Charles Mitchill), 1908-1992."The external features of the Bornean lizard, Lanthanotus borneensis Steindachner, are described, together with the skull, the hyoid, the tongue, and the roentgenogram of the postcranial osteology. The various theories concerning the relationships of Lanthanotus are evaluated. The belief that Lanthanotus is related to the Chinese lizard Shinisaurus crocodilurus Ahl is shown to be unsupported by either the internal or external morphology. Nor is there evidence of close relationship between Lanthanotus and Heloderma, although these two genera are most frequently placed together in the family Helodermatidae. On the other hand, structural resemblances between Lanthanotus and Varanus are found to be both numerous and important. However, it is here shown that there is still greater affinity between Lanthanotus and three Cretaceous families believed to be closely related to Varanus, the Aigialosauridae, Mosasauridae, and Dolichosauridae. Lanthanotus represents a monotypic family closely related to aigialosaurs and dolichosaurs. Lanthanotus shows many of the features to be expected in an ancestor of the snakes, and the close similarities between Lanthanotus and the boid-like, colubrid-like, and particularly the leptotyphlopid snakes, materially strengthen the argument that the snakes are derived from platynotan (Varanus-like) lizards. In contrast to other limbless reptiles commonly referred to the Serpentes, the Typhlopidae show no particular resemblance in cranial structure to either the platynotan lizards or the snakes (including Leptotyphlops). Reasons are advanced for believing that the Typhlopidae are wrongly placed in the Serpentes (or Ophidia) and represent a line of anguinid-like lizards that has become convergent to the Serpentes. Incidental to the work upon which we base the conclusions summarized above, several additional observations have been made on the anatomy and relationships of the saurian infraorder Anguinomorpha. The most important conclusions reached are as follows: 1. The family Pygopodidae is not related to the Anguinomorpha but represents an aberrant line of geckos, modified by a reduction of the limbs but retaining many features of the gekkonids. 2. The family Cordylidae (long known as Zonuridae) is not related to the Anguinomorpha but instead is closely related to the Gerrhosauridae, a family that differs in relatively minor ways from the Lacertidae. 3.The fossil family Euposauridae, frequently placed in or near the Anguinomorpha, shows no clear evidence of affinity to the Anguinomorpha and is not even definitely referable to the Squamata. 4. After the removal of these three families, the Anguinomorpha become a natural group, the members of which are characterized by their peculiar tongue structure, their method of tooth replacement, and a unique combination of osteological characters. The group, here considered an infraorder, contains the families Anguinidae (Anguidae auct.), Xenosauridae, Anniellidae, Helodermatidae, Varanidae, Aigialosauridae, Mosasauridae, Dolichosauridae, and Lanthanotidae. 5. This group, the Anguinomorpha, appears to have undergone an early separation into two main lines of evolution, here considered taxonomically as two superfamilies: Diploglossa (or Anguinoidea) and Platynota (or Varanoidea). 6. The line here called Diploglossa (Anguinidae, Xenosauridae, and Anniellidae) includes the more primitive families, primarily adapted to a crushing action of the jaws, with rigid mandibles. None of the known forms can be considered directly ancestral to the platynotan line. 7. The remainder of the Anguinomorpha represent a line (Platynota or Varanoidea) the jaws of which are primarily adapted for a grasping action, with a progressive development through the families of a hinge in the middle of the ramus of the lower jaw. This line includes forms distinctly more predatory in habits than is usual in the members of the first line. 8. The beaded lizards (Heloderma) have most recently been classified among the members of the first (diploglossan) line. But careful study of the morphology of Heloderma shows it to be close to Varanus, and a member of the second (platynotan) series, as was believed by most of the earlier workers. Although specialized in many respects, in other features of its structure Heloderma appears to be near the ancestral form that gave rise to the Platynota. 9. Upon examination of the skull, the Chinese genus Shinisaurus of previously unknown affinities proves to be a close relative of the Mexican genus Xenosaurus. The fossil genera Exostinus, Melanosaurus, and Necrosaurus (also known as Palaeovaranus) also appear to be members of the Xenosauridae. A revised classification of the Anguinomorpha is presented"--P. 134-135.