1,122 research outputs found
EVOLUTIONARY TRENDS IN TRIASSIC DICYNODONTIA
Triassic Dicynodontia differ from most of their Permian ancestors in a number of
specialisations that reach extremes in the Upper Triassic. These are ( 1) increase in total body size,
(2) increase in the relative length of the snout and secondary palate by backward growth of the
premaxilla, (3) reduction in the length of the fenestra medio-palatinalis combined with
posterior migration out of the choanal depression, (4) shortening and dorsal expansion of the
intertemporal region, (5 ) fusion of elements in the front part of the brain-case, (6) posterior
migration of the reflected lamina of the mandible, (7) disappearance of the quadrate foramen
and the development of a process of the quadrate that extends along the quadrate ramus of the
pterygoid. It is thought that the occurrence of the last feature in Dinodontosaurus platygnathw Cox
and Jacheleria colorata Bonaparte warrants the transfer of the species platygnathus to the genus
Jacheleria and the erection of a new subfamily, Jachelerinae nov.
It is concluded that the specialisations of the Triassic forms can be attributed to adaptation to
a Dicroidium-dominated flora
A NEW TRIASSIC VERTEBRATE FAUNA FROM SOUTH WEST AFRICA
A new fauna of mammal-like reptiles is described from a continental sequence of
sediments in South West Africa hitherto known as the Etjo Beds. These include
representatives of the Anomodontia (two new forms and one known from the Karroo
basin), Bauriamorpha, (one specimen comparable with a known form), Cynodontia (one
new form and two known from the Karroo basin) and one small eriopoid amphibian. On
the basis of this faunal assemblage it can be shown that there is a disconformity between
the upper Plateau Sandstone Formation containing traces of Dinosaurs of possible
Carnian-Norian age and a lower Omingonde Mudstone Formation with this new fauna,
of essentially Upper Beaufort (Scythian/Anisian) age. The two formations are
distinguished on lithological grounds. The Triassic sequence in the neighbouring Doros
area is thought to be equivalent to the Plateau Sandstone Formation
A RE-EVALUATION OF THE GENUS TROPIDOSTOMA SEELEY
The type specimens of Cteniosaurus platyceps Broom, Dicynodon acutirostris
Broom, and Dicynodon validus Broom were re-examined and were found to be very
similar in a number of features rarely encountered in other Anomodontia. The skull of
the type of Cteniosaurus platyceps is described in some detail. It is concluded that the
above species must be considered to be junior synonyms of Tropidostoma microtrema
(Seeley)
A RE-EVALUATION OF THE SYSTEMATICS AND MORPHOLOGY OF CERTAIN ANOMODONT THERAPSIDA
The cranial morphology of a number of
specimens assigned to the genera Oudenodon,
Rhachiocephalus, Aulacephalodon and Pelanomodon
was investigated (Keyser, 1969). It was
found that the internal morphology and the
general structure of the skulls show great agreement.
Many of the differences between the genera
can be associated with the size of the skull. The
main differences between the genera lie in the
specialisation of the biting mechanism and in the
relative size and shape of the nasal and prefrontal
bosses. It is suggested that the genera Oudenodon
and Rhachio cephalus bit off their food with the
sides of the horn-covered jaws while the broadnosed
genera Aulacephalodon and Pelanomodon
bit with the transverse anterior tips of the jaws.
This difference in the morphology of the jaws is
probably indicative of a fundamental dichotomy
between the two groups of genera. A similar
dichotomy has been suggested for Triassic dicynodonts
by Cox (1965)
Improved VAS regression soundings of mesoscale temperature structure observed during the 1982 atmospheric variability experiment
An Atmospheric Variability Experiment (AVE) was conducted over the central U.S. in the spring of 1982, collecting radiosonde date to verify mesoscale soundings from the VISSR Atmospheric Sounder (VAS) on the GOES satellite. Previously published VAS/AVE comparisons for the 6 March 1982 case found that the satellite retrievals scarcely detected a low level temperature inversion or a mid-tropospheric cold pool over a special mesoscale radiosonde verification network in north central Texas. The previously published regression and physical retrieval algorithms did not fully utilize VAS' sensitivity to important subsynoptic thermal features. Therefore, the 6 March 1982 case was reprocessed adding two enhancements to the VAS regression retrieval algorithm: (1) the regression matrix was determined using AVE profile data obtained in the region at asynoptic times, and (2) more optimistic signal-to-noise statistical conditioning factors were applied to the VAS temperature sounding channels. The new VAS soundings resolve more of the low level temperature inversion and mid-level cold pool. Most of the improvements stems from the utilization of asynoptic radiosonde observations at NWS sites. This case suggests that VAS regression soundings may require a ground-based asynoptic profiler network to bridge the gap between the synoptic radiosonde network and the high resolution geosynchronous satellite observations during the day
A new bauriamorph from the Omingonde Formation (Middle Triassic) of South West Africa
Abstract of paper presented at Karoo SymposiumA new genus and species of bauriamorph therapsid from the Anisian Omingonde Formation
(Middle Triassic) of South West Africa is described as Herpetogale marsupialis gen. et sp. nov.
This new form is chronologically the latest known member of the therocephalian lineage. It is in
many ways more advanced than Bauria, but it also displays a number of more primitive features .
It is advanced in its reduced postcanine series, slightly larger secondary palate, smaller suborbital
fossae, and more pronounced coronoid processes of the dentaries, displaying laterally very
distinct fossae maJsetericae. A very distinct crista IacialiJ is developed in front of the orbit. Primitive
features are the presence of a pineal foramen and complete postorbital bars. Conspicuous and
no doubt specialised are the pronounced "cheek cavities" well demarcated above by maxillary
overhangs and below by shelf-like expansions on the dentaries. This arrangement suggests "cheek
pouches" for food storage reminiscent of a habit in modem primates and certain rodents. The skull is complete, very little distorted or damaged, with lower jaw in occlusion. Besides an account
of the cranial morphology, attention is also given to jaw musculature and the taxonomic
position of the Bauriamorpha.Non
Critical shoe contact area ratio for sliding on a tennis hard court
Dimples have been used in the design of some modern tennis shoe outsoles to enhance sliding ability on hard courts. Experiments were performed with bespoke rubber samples possessing various numbers of holes, which served to simulate dimples in tennis shoe treads. The aim of the research was to assess the effect of contact area on sliding friction. As the ratio of holes to solid rubber increased, a critical ratio was reached whereby the static friction coefficient decreased by more than 11% for tread-to-court pressures comparable to real tennis play. Although this study analyzed bespoke rubber samples and not actual tennis shoe treads, shoe manufacturers should be interested in the existence of a critical dimple ratio that could aid them in the creation of tennis shoes suited for sliding on hard courts
Evaluation of the synoptic and mesoscale predictive capabilities of a mesoscale atmospheric simulation system
The overall performance characteristics of a limited area, hydrostatic, fine (52 km) mesh, primitive equation, numerical weather prediction model are determined in anticipation of satellite data assimilations with the model. The synoptic and mesoscale predictive capabilities of version 2.0 of this model, the Mesoscale Atmospheric Simulation System (MASS 2.0), were evaluated. The two part study is based on a sample of approximately thirty 12h and 24h forecasts of atmospheric flow patterns during spring and early summer. The synoptic scale evaluation results benchmark the performance of MASS 2.0 against that of an operational, synoptic scale weather prediction model, the Limited area Fine Mesh (LFM). The large sample allows for the calculation of statistically significant measures of forecast accuracy and the determination of systematic model errors. The synoptic scale benchmark is required before unsmoothed mesoscale forecast fields can be seriously considered
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