摘要:

The modern Sirenia have been little studied because of their present rarity and the difficulty of observing fully aquatic animals even though so large. These mammals are the only large aquatic herbivores. One of the three modern forms, Steller's seacow, is recently extinct; the dugong of the tropical Indo‐Pacific region is now rare almost everywhere apart from some of the northern waters of Australia, while the manatee of the two sides of the tropical Atlantic is both marine and riverine but has become very scarce.The two authors have, over 12 years, endeavoured by means of personal visits to the Guianas, Australia, Torres Strait, Ceylon and elsewhere, and by copious correspondence, to gather material so as to summarize the present distribution and status of the Sirenia. This information is presented in a setting of conservation and eventual rational use as meat animals and in other ways. There is also reference to the history and manner of exploitation which has brought the Sirenia to their present lowly state. The main residual stock is that in northernmost Australian waters, and there numbers may now indeed begin again to increas

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1973.tb00708.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

From a study of the perforations in the heterostracan carapace and the impressions on the inner surface of the bony plates it is suggested that the Heterostraci in most features belonged to a structural stage from which it was possible to derive both the gnathostomes and the cyclostomes (including the cephalaspids and anaspids).However, the structure of the gills and the presence of a spiracle in the Heterostraci indicate that they were more closely related to the gnathostome stock.

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1973.tb00709.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1973.tb00710.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY