摘要:

Sutural complexity (the degree of interdigitation) of 13 cranial sutures was compared between male and female wild sheep (Ovis orientalis) to investigate a morphological feature that is potentially important with respect to stress transmission in the skulls of males during fighting. Most facial sutures (four of six) were not sexually dimorphic, but two sutures, the maxillojugal and jugolacrimal, had greater complexity in males than in females, suggesting that significant forces may be transmitted through the facial region of rams, most likely during horn clashing. Most of the braincase sutures (five of seven) were more complex in males than in females, and different factors appear to underlie this sexual dimorphism. In females, increased complexity of sutures during ontogeny was predicted best by variables measuring growth of the skull, brain or face, while in males, changes in complexity were predicted best by variables representing mechanical loading and frontal bone growth.

ISSN:0024-4082    

DOI:10.1111/j.1096-3642.1989.tb02312.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Two new species of sea pens referable to the genusCavernulariaValenciennes are described from Natal and Transkei, east coast of southern Africa, at depths of 24 and 190 to over 300 m. The two new species are distinguished from other members of the genus by unique combinations of features regarding the axis, colonial growth form, autozooid size, as well as the size, shape, and distribution of sclerites. A comparative review of the genus is included. The 13 presently recognized worldwide species are differentiated and a key for their separation, together with a table of comparative characters, is provided. Of these, ten (77%) are Indo‐Pacific in distribution whilst the remainder (23%) are presumably restricted to the eastern Atlantic. Four species are presently recorded from southern Africa. The deepest known bathymetric stations for the genus are here recorded from northern Namibia at 274 m, and from northern Natal at 310/320 m. Relationships to members of the related genusCavernulinaKükenthal&Broch are discuss

ISSN:0024-4082    

DOI:10.1111/j.1096-3642.1989.tb02313.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Maxillary and mandibular molars of the American opossum,Didelphis virginianaL., were viewed in the scanning electron microscope (SEM) after acid‐etching or after cutting and acid‐etching. Observations were made on enamel prism patterns as they relate to functional properties of the tooth at a particular site. Molars at different stages of wear were also observed under a dissecting microscope; worn surfaces were correlated with function and enamel ultrastructure. Pounding surfaces of molar cusps wear more rapidly than near‐vertical shearing surfaces or crushing basins (i.e. the trigon and talonid basin). Pounding surfaces are subjected to abrasion by food and arc not normally involved in tooth‐tooth contact. Near‐vertical shearing surfaces and basins used for crushing do experience tooth‐tooth contact, but are surprisingly more resistant to wear. Prisms at pounding sites approach the occlusal surface at a near 90° angle and are surrounded with very thick interprismatic (IP) enamel parallel to the occlusal surface of the tooth. The pounding pattern is present at tips of cusps and at occlusal surfaces of ridges of the tooth. At near‐vertical shearing surfaces, the prisms approach the outer surface obliquely and are surrounded with IP crystals which are perpendicular to the vertical surface. The angle between prismatic and IP enamel in these patterns is 60–90° in a cervical to occlusal direction. In basins of the tooth used principally for crushing and some shearing, IP enamel is perpendicular to the changing slope of the basin and the prisms are usually at a 55–65° angle to the IP enamel. When the pounding and shearing‐crushing patterns meet at a ridge, a distinct seam is observed. Pounding forces occur parallel to the long axis of the prisms and perpendicular to the thick IP enamel (i.e. perpendicular to the long axis of the IP crystals) lying on either side of the prisms. Shearing and crushing forces occur at an oblique angle to the prism, and interprismatic enamel is more evenly distributed about the prism. A spiral pattern is found at the bottoms of the trigon and talonid basins, but not at the bottom of the trigonid which is a non‐occluding basin. It is concluded that the differential rates of wear of the enamel surfaces are necessary in maintaining the sharp cutting edges and effective crushing basins of the tribosphenic molar, and the ultrastructural arrangements of the enamel prisms are of

ISSN:0024-4082    

DOI:10.1111/j.1096-3642.1989.tb02314.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

The generic nameUrothecaBibron, 1843 is revived for a group of Neotropical colubrid snakes diagnosed by a long, thickened but fragile tail and the presence of a specialized naked pocket on the asulcate surface of the hemipenial capitulum.Urothecaincludes those species previously placed in thelateristrigagroup of the genusRhadinaeaand the coral snake mimics usually referred to the genusPliocercus.The many names based upon the coral snake mimics are shown to represent two species at most:Urotheca elapoides,a bicolour (red and black) or tricolour (red, yellow and black) banded or ringed form found in Mexico and northern Central America andU. euryzona,which is usually bicolour (red, yellow or white and black) and ranges from Nicaragua to western Ecuador. Coloration inU. elapoidesresembles closely that of sympatric species of venomous coral snakes. Local variation in coloration and a geographic trend in the colour of the light rings (usually red in the north, white to the south) inU. euryzonaparallels similar colour variation in the sympatric venomous coral snakeMicrurus mipartitus.These patterns of variation add strong support to the idea that the two species are mimics of the highly venomous coral snakes.Urotheca,including the non‐mimetic speciesU. decipiens, U. fulmceps, U. guentheri, U. lateristriga, U. multilineataandU. pachyura,shares the characteristic of a very long and disproportionately thickened and fragile tail with the coral snake mimics of the distantly related genusScapkiodontophis.Members of both genera have a very high proportion (about 50%) of the tails broken indicating a probable predator escape device. Breakage is intercentral, with a calcified cap developing over the tip of the distal surface of the new terminal vertebra unlike the situation in many lizards where there is an intracentral fracture septum and the tail is regenerate

ISSN:0024-4082    

DOI:10.1111/j.1096-3642.1989.tb02315.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Evolutionary relationships among seven species from two genera (PantinonemertesandGeonemertes) of terrestrial nemerteans (phylum Nemertea) were estimated by a Wagner analysis of 27 morphological, ecological and life history characters.Pantinonemerteswas found to be a paraphyletic taxon, and it is suggested that this genus should be combined withGeonemertesto form a monophyletic group. A previous hypothesis for how terrestrial nemerteans evolved is discussed and compared to the results of the cladistic analysis. This suggests that terrestrial and semi‐terrestrial species evolved from a marine ancestor; the upper littoral and marine environments have been recolonized by descendants from a terrestrial ancesto

ISSN:0024-4082    

DOI:10.1111/j.1096-3642.1989.tb02316.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

ISSN:0024-4082    

DOI:10.1111/j.1096-3642.1989.tb02317.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY