摘要:

In order to facilitate the use of ichthyolith subtypes described in parts I and II of this catalog, colloquial names have been assigned. These names are briefly descriptive of each ichthyolith and can be used in a way similar to binomial names. They provide a means of referring to the ichthyoliths in a more standard way which may be found easier to use than multiple letters and numbers.

ISSN:0272-4634    

DOI:10.1080/02724634.1983.10011961

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

A review of the evidence suggests that ancestral placoderms were not armored, but that dermal bones were acquired, independently of Osteichthyes, probably in the Late Silurian. It is believed that these ancestors were covered with denticles or tesserae, some of which were retained in a few Devonian orders. Primitive forms lacked the placoderm dermal cranial bone pattern that is recognizable in most orders; they also lacked a trunk shield which was derived in more advanced orders from the ancestral shoulder girdle. The evolutionary significance of some dermal bones is discussed: in the skull, the centrals, postpineal, nuchal, “premedian,” postnasals, and paranuchals; in the trunk shield, the anterior ventro-laterals, intero-laterals, antero-ventrals, anterior medio-ventrals, spinals, and posterior ventro-laterals.

ISSN:0272-4634    

DOI:10.1080/02724634.1983.10011962

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

The flight performances ofPteranodon ingensandNyctosaurus gracilisfrom the Upper Cretaceous of Kansas were modeled using data from a Sailvane hang-glider which has an airfoil similar to that of a pterosaur. The aerodynamics of large pterosaurs were mainly dictated by three parameters: low wing loadings, wings with high aspect ratios, and the performance of the thin cambered airfoil. Given maximum muscular efforts,NyctosaurusandPteranodoncould have taken off at airspeeds of 1.5 and 4 m/sec, respectively. These airspeeds included windspeed, running speed, and a flapping component, so takeoff presented no problems. Landing speeds were also slow. The sustained power output ofPteranodonwas not enough for continuous level flapping flight. A maximum burst of power allowed level flapping or climbing flight. However, this required anaerobic muscle operation and was only maintained briefly. The power profile shows thatPteranodonwas a soarer. On the other hand, the sustained power output ofNyctosauruswas more than enough for continuous level flapping. However, the animal probably reduced the metabolic cost of transport by alternate gliding and flapping as in gulls. Inasmuch as the power required for soaring is much lower than that for flapping or alternate gliding and flapping,Nyctosaurusprobably soared whenever the weather was suitable. The gliding performance of the Kansas pterosaurs was characterized by slow horizontal and vertical speeds, excellent gliding angles, and narrow ranges of horizontal speeds. The pterosaurs flew far from shore in a warm, calm climate. Their aerodynamics were ideal for slope soaring along a low relief coastline and for convection-current soaring.Pteranodonand probably alsoNyctosaurusobtained seafood by skimming the waves and/or landing and seizing fish and crustaceans. Compared to soaring birds, large pterosaurs were specialized for low power requirements and a narrow range of slow horizontal flight speeds.

ISSN:0272-4634    

DOI:10.1080/02724634.1983.10011963

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

All known nasal horns of the Pleistocene Palearctic woolly rhinoceros,Coelodonta antiquitatis(Blumb.), are laterally flattened and transversely banded. A nasal horn discovered in the Museum of Paleontology, University of Helsinki, Finland, is described and figured. The old literature on woolly rhino horns is reviewed and the relevant plates from Brandt (1849) are reproduced. The differences between nasal and frontal horns are discussed and the shape of the nasal horn is interpreted as primary. The old contention that the woolly rhino used its nasal horn to shovel snow is supported, and the dynamics and significance of this behaviour are discussed. The transverse bands are interpreted as annuli and suggest a stronger sexual dimorphism in horn size inCoelodonta antiquitatisthan in living rhinos. Such dimorphism in a probably migratory rhinoceros of a strongly seasonal environment would be in accordance with the general relationships proposed by Geist (1974) and Jarman (1974).

ISSN:0272-4634    

DOI:10.1080/02724634.1983.10011964

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

ISSN:0272-4634    

DOI:10.1080/02724634.1983.10011965

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor