Notoungulate caudal cranium.

69 pages : illustrations ; 26 cmThe composition of the caudal cranium in Notoungulata, an extinct group of endemic South American "ungulates," has never been properly clarified. Some investigators have claimed that so-called "adventitious" elements, or elements not known to occur in other placentals, existed in the auditory regions of certain typotheres and toxodontians. Others have disputed this, arguing that sutures or other indicia that supposedly provide evidence of the developmentally independent origins of these alleged ossifications are either misinterpreted or inconstant. This study attempts to resolve the question of composition, as far as it is possible to do in the case of a wholly extinct clade, with detailed micro-CT investigations of several key taxa, including Oldfieldthomasia (Oldfieldthomasiidae), Paedotherium (Hegetotheriidae), and Cochilius (Interatheriidae). Results show that Santiago Roth was incorrect in asserting that certain notoungulates, such as pachyrukhine hegetotheres, possessed cranial elements (serrialis, posttympanicum, etc.) that are unrepresented in other placentals. George Gaylord Simpson also thought Roth was wrong, but erred in claiming to have discovered concrete evidence of two other ossifications, denoted by him as Xa and Xp, in the auditory region of Oldfieldthomasia. In adult notoungulates the interparietal complex is usually fused with the parietal, or supraoccipital, or both elements. As in certain other mammals, dorsal exposure of the supraoccipital is limited in notoungulates because it is often overplated by the interparietal complex, which thus provides a sort of "second" roof for the caudal cranium. However, there is no interparietal involvement in the middle ear cavity. Finally, for the first time plausible grounds can be offered for the existence of an entotympanic in a notoungulate (Cochilius). Evidence is increasing for the proposition that entotympanics are much more widespread than previously thought, and may in fact be present in most of the major groups of placentals. In summary, this study shows that in terms of participating elements there is nothing unique about the notoungulate caudal cranium, which was evidently as tightly constrained compositionally as it is in other placentals. Nevertheless, this portion of the skull, still notably underutilized in notoungulate studies, could be a crucial source of new characters for assessing higher-level relationships not only among notoungulates, but also among South American ungulates and their possible relatives

Heptaxodontid basicrania and relationships.

70 p. : ill. (some col.) ; 26 cm.What, if much of anything, are "Antillean heptaxodontids"? Over the course of nearly a century and a half, these caviomorph rodents, with their distinctive quasilamellar cheek teeth and generally large body size, have been diversely regarded as members of Chinchilloidea, or Cavioidea, or Octodontoidea; as distinct enough to warrant their own family or subfamily, or as no more than an offshoot within Dinomyidae or Capromyidae; and as having diverged from other caviomorph clades as early as the Oligocene, or as recently as the late Neogene. Similar uncertainties concern the taxonomic content of the group. It has been repeatedly suggested that the Antillean Heptaxodontidae as usually organized may be paraphyletic, but no adequate character-based arguments have appeared that might form a strong basis for reassessment. This paper attempts to arrive at some serviceable solutions to the heptaxodontid problem by utilizing the character-rich domain of the auditory region. Thus Amblyrhiza inundata (St. Martin/Anguilla) and Elasmodontomys obliquus (Puerto Rico), the chief subjects of this contribution, have traditionally been regarded as closely related on the basis of dental features. Yet certain basicranial characters, analyzed here for the first time, reveal that Amblyrhiza possesses derived features of bullar development and middle-ear vascularization that are found in this specific combination only in Chinchilloidea. These features are also seen in the Mio-Pliocene Patagonian taxon Eumegamys, reinforcing the position that it belongs in this grouping as well. The basicranial morphology of Elasmodontomys is rather primitive, and where it should be placed cladistically remains indeterminate, although its likeliest position is within Octodontoidea. Although it is taken for granted that no single set of morphological features will satisfactorily capture relationships throughout a large group like Caviomorpha, the absence of basicranial characters in most morphology-based systematic discussions of these rodents is glaring. The results reported here, while suggestive in their own right, should now be tested against much larger datasets

Body Size in Amblyrhiza inundata (Rodentia, Caviomorpha), an Extinct Megafaunal Rodent From the Anguilla Bank, West Indies: Estimates and Implications

Rodent species typically evolve larger mean body sizes when isolated on islands, but the extinct caviomorph Amblyrhiza inundata, known only from Quaternary cave deposits on the islands of Anguilla and St. Martin (northern Lesser Antilles), provides an unusually dramatic example of insular gigantism. Here we report on a series of body mass estimates for Amblyrhiza using predictive equations based on anteroposterior diameters and cortical cross-sectional areas of humeral and femoral diaphyses. Analyses of 14 isolated specimens (5 femoral, 9 humeral), all representing adult or near adult animals, yield body mass estimates ranging from slightly less than 50 kg to more than 200 kg. Body size estimates derived from humeral measurements are lower than those derived from femoral measurements, but the significance of this will remain unclear until matched limb bones (i.e., specimens from the same animal) are recovered. Incisor measurements are also highly variable, but in this case the distribution is demonstrably bimodal. Presence of multiple coeval species, temporal variation, limb heterogeneity, and sexual dimorphism all qualify as possible explanations of the variation encountered in Amblyrhiza data sets, but available samples are not adequate for making a robust choice among them. Body size affects many life history variables, including demography. Population estimates derived from empirical data and predictive equations suggest that only a few thousand individuals of Amblyrhiza could have occupied the islands of the Anguilla Bank at any one time during the Late Quaternary. At certain times-for example, during the last interglacial (Sangamonian) highstand-population numbers might have sunk to only a few hundred. Absolutely small population sizes of Amblyrhiza and severe fluctuations in island area during the late Quaternary surely affected its susceptibility to extinction, whether or not humans were ultimately responsible for the event (for which there is as yet no direct evidence)

New Tertiary fossils from Cuba and Puerto Rico.

30 p. : ill. (some col.) ; 26 cm.Includes bibliographical references (p. 25-30

Caribbean paleogeography

95 p. : ill., maps (some col.) ; 26 cm.Includes bibliographical references (p. 59-72)."This paper presents a series of detailed paleogeographical analyses of the Caribbean region, beginning with the opening of the Caribbean basin in the Middle Jurassic and running to the end of the Middle Miocene. Three intervals within the Cenozoic are given special treatment: Eocene-Oligocene transition (35-33 Ma), Late Oligocene (27-25 Ma), and early Middle Miocene (16-14 Ma). While land mammals and other terrestrial vertebrates may have occupied landmasses in the Caribbean basin at any time, according to the interpretation presented here the existing Greater Antillean islands, as islands, are no older than Middle Eocene. Earlier islands must have existed, but it is not likely that they remained as such (i.e., as subaerial entities) due to repeated transgressions, subsidence, and (not incidentally) the K/T bolide impact and associated mega-tsunamis. Accordingly, we infer that the on-island lineages forming the existing (i.e., Quaternary) Antillean fauna must all be younger than Middle Eocene. The fossil record, although still very poor, is consistent with the observation that most land mammals lineages entered the Greater Antilles around the Eocene-Oligocene transition. Western Laurasia (North America) and western Gondwana (South America) were physically connected as continental areas until the mid-Jurassic, ca. 170 Ma. Terrestrial connections between these continental areas since then can only have occurred via landbridges. In the Cretaceous, three major uplift events, recorded as regional unconformities, may have produced intercontinental landbridges involving the Cretaceous Antillean island arc. The Late Campanian/Early Maastrichtian uplift event is the one most likely to have resulted in a landbridge, as it would have been coeval with uplift of the dying Cretaceous arc. However, evidence is too limited for any certainty on this point. The existing landbridge (Panamanian Isthmus) was completed in the Pliocene; evidence for a precursor bridge late in the Middle Miocene is ambiguous. We marshal extensive geological evidence to show that, during the Eocene-Oligocene transition, the developing northern Greater Antilles and northwestern South America were briefly connected by a "landspan" (i.e., a subaerial connection between a continent and one or more offshelf islands) centered on the emergent Aves Ridge. This structure (Greater Antilles + Aves Ridge) is dubbed GAARlandia. The massive uplift event that apparently permitted these connections was spent by 32 Ma; a general subsidence followed, ending the GAARlandia landspan phase. Thereafter, Caribbean neotectonism resulted in the subdivision of existing land areas. The GAARlandia hypothesis has great significance for understanding the history of the Antillean biota. Typically, the historical biogeography of the Greater Antilles is discussed in terms of whether the fauna was largely shaped by strict dispersal or strict continent-island vicariance. The GAARlandia hypothesis involves elements of both. Continent-island vicariance sensu Rosen appears to be excludable for any time period since the mid-Jurassic. Even if vicariance occurred at that time, its relevance for understanding the origin of the modern Antillean biota is minimal. Hedges and co-workers have strongly espoused over-water dispersal as the major and perhaps only method of vertebrate faunal formation in the Caribbean region. However, surface-current dispersal of propagules is inadequate as an explanation of observed distribution patterns of terrestrial faunas in the Greater Antilles. Even though there is a general tendency for Caribbean surface currents to flow northward with respect to the South American coastline, experimental evidence indicates that the final depositional sites of passively floating objects is highly unpredictable. Crucially, prior to the Pliocene, regional paleoceanography was such that current-flow patterns from major rivers would have delivered South American waifs to the Central American coast, not to the Greater or Lesser Antilles. Since at least three (capromyid rodents, pitheciine primates, and megalonychid sloths) and possibly four (nesophontid insectivores) lineages of Antillean mammals were already on one or more of the Greater Antilles by the Early Miocene, Hedges' inference as to the primacy of over-water dispersal appears to be at odds with the facts. By contrast, the landspan model is consistent with most aspects of Antillean land-mammal biogeography as currently known; whether it is consistent with the biogeography of other groups remains to be seen"--P. 3

Optimization of double pulse pumping for Ni-like Sm x-ray lasers

We report a systematic study of double pulse pumping of the Ni-like Sm x-ray laser at 73 Angstrom, currently the shortest wavelength saturated x-ray laser. It is found that the Sm x-ray laser output can change by orders of magnitude when the intensity ratio of the pumping pulses and their relative delay are varied. Optimum pumping conditions are found and interpreted in terms of a simple model. (C) 1999 American Institute of Physics. [S0021-8979(99)07102-9]

Supersonic strain front driven by a dense electron-hole plasma

We study coherent strain in (001) Ge generated by an ultrafast laser-initiated high density electron-hole plasma. The resultant coherent pulse is probed by time-resolved x-ray diffraction through changes in the anomalous transmission. The acoustic pulse front is driven by ambipolar diffusion of the electron-hole plasma and propagates into the crystal at supersonic speeds. Simulations of the strain including electron-phonon coupling, modified by carrier diffusion and Auger recombination, are in good agreement with the observed dynamics.Comment: 4 pages, 6 figure

Single-shot divergence measurements of a laser-generated relativistic electron beam

Copyright 2010 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Physics of Plasmas, 17(11), 113106_1-113106_7, 2010 and may be found at http://dx.doi.org/10.1063/1.351459

Dwarf deer of Crete.

26 pages : illustrations (some color), map ; 26 cm.Age-graded fossils of Pleistocene endemic Cretan deer (Candiacervus spp.) reveal unexpectedly high juvenile mortality similar to that reported for extant mainland ruminants, despite the fact that these deer lived in a predator-free environment and became extinct before any plausible date for human arrival. Age profiles show that deer surviving past the fawn stage were relatively long-lived for ruminants, indicating that high juvenile mortality was not an expression of their living a "fast" life. Although the effects on survivorship of such variables as fatal accidents, starvation, and disease are difficult to gauge in extinct taxa, the presence of extreme morphological variability within nominal species/ecomorphs of Candiacervus is consistent with the view that high juvenile mortality can function as a key innovation permitting rapid adaptation in insular contexts