AMMONITES AND NAUTILOIDS OF WADl HAJAR 



63 



a compressed body-chamber. The latter, however, is crushed later- 

 ally, and it may originally have had a whorl thickness like that off! 

 jarryi. 



The age assessments of Gill et al (1985: 744) in Israel and Enay 

 et al (1987: 36, 44) in Jebel Tuwaiq were based on the whole fauna 

 of ammonites and they concluded that the main occurrence of 

 Pachyerymnoceras is in the Middle Callovian, Coronatum Zone. 

 There is no evidence for the presence of Upper Callovian in Jebel 

 Tuwaiq, but it is possible that Pachyerymnoceras extends into the 

 Upper Callovian, Athleta Zone, in Israel. Several specimens of 

 Pachyeiymnoceras from Ethiopia were described and figured by 

 Zeiss ( 1 974), and in the absence of accompanying ammonites of age 

 significance, he concluded that their age was Upper Callovian from 

 the range of the genus elsewhere, mainly in Europe. The evidence 

 suggests that the most likely age of the Yemeni occurrence is 

 Coronatum Zone, Middle Callovian, but Upper Callovian is a possi- 

 bility. 



Occurrence. Middle and upper parts of the Shuqra Formation, 

 Jebel Billum and Al Ma'abir; Middle Callovian. Coronatum Zone 

 (?or Upper Callovian). 



Family ASPIDOCERATIDAE Zittel, 1895 

 Subfamily ASPIDOCERATINAE Zittel, 1895 



Remarks. Aspidoceratids make up only a small proportion of the 

 Yemen ammonite fauna in numbers of specimens, but they are 

 present at five horizons from the top of the Oxfordian to the top of the 

 Tithonian. The view sometimes expressed (eg. Callomon & Cope, 

 1971: 159; Callomon, /ViVerma&Westermann, 1984: 64) that high 

 variation in whorl shape and ornament will be found in single-bed 

 assemblages of Aspidoceratids does not seem to be borne out in the 

 single horizon collections from Yemen. Thus the collections of 

 Orthaspidoceras gortanii, O. avellanum and Simaspidoceras 

 argobbae described below are as closely defined as many other 

 species of ammonites from single horizons. Much progress in 

 sorting out the synonymy of the multiplicity of specific names was 

 made by Checa (1985) in his monograph on the family, and his work 

 is largely followed here. However, comment on parts of the generic 

 nomenclature seems to be necessary. Aspidoceras itself is 

 bituberculate, at least at some growth stage, and its whorls are 

 typically involute, globular and depressed, though more evolute 

 species do occur, eg. A. apeimuucum. Orthaspidoceras embraces 

 species with only one row of tubercles or spines, which may occur 

 anywhere between mid-lateral and the edge of the umbilicus. In the 

 latter position they sometimes point inwards over the umbilicus, but 

 some specimens have been figured (Checa, 1985: pi. 29, fig. 1; pi. 

 32, fig. 3; pi. 33, fig. 1 ) that have tubercles pointing inwards over the 

 umbilicus on the inner whorls, changing to tubercles directed nor- 

 mal to the surface on larger whorls. Such specimens seem to cast 

 doubt on the usefulness of the genus Physodoceras Hyatt, 1900, 

 which has been used for specimens that have inwardly pointing 

 tubercles on inner whorls. According to Checa (1985: 132) 

 Physodoceras only occurs as high as the Divisum Zone, or possibly 

 the Acanthicum Zone, in the Kimmeridgian. There are higher spe- 

 cies, mainly from the Beckeri Zone onwards, that tend towards more 

 involute whorls and loss of ornament, and Checa (1985: 184) 

 divided these off as his new genus Schaireria (type species, 

 Aspidoceras avellanum Zittel, 1870). These appear to be a continu- 

 ation of trends already seen in Orthaspidoceras. and it does not seem 

 necessary to split them off as a new genus. In any case, most of the 

 poorly dated ammonites from Ethiopia described by Scott ( 1 943) are 

 almost certainly of Beckeri/Hybonotum Zone age, rather than older. 



and one of them is Glahrophysodoceras Scott (1943: 82), which is 

 involute and nearly smooth, and has priority ower Schaireria if a new 

 generic name is thought to be necessary for such forms. The 

 youngest recorded Aspidoceratids are Aspidoceras rogoznicense 

 (Zejszner), A. taverai Checa and Orthaspidoceras [?Schaireria] 

 longaeva (Leanza) in the lower two zones of the Berriasian in SE 

 Spain (Checa e? fl/, 1986). 



Genus ASPIDOCERAS Zittel, 1868 



Type species. Ammonites rogoznicensis Zejszner, 1846. by 

 monotypy. 



Synonym. Acanthosphaerites Rollier, 1922 (type species. Am- 

 monites accmthicus Oppel, 1863). 



Aspidoceras rogoznicense (Zejszner, 1846) PI. 10, fig. 1 



1846 Ammonites rogoznicensis Zejszner: pi. 4, fig. 4. 



1868 Ammonites (Aspidoceras) rogoznicense Zejszner; Zittel: 



116, pi. 24, figs 4, 5. 

 1870 Aspidoceras zeuschneri Zittel: 87, pi. 7, fig. 4. 

 71897 Aspidoceras euomphalum Steuer: 69, pi. 5 (19), figs 1^. 



1928 Aspidoceras haupti Krantz: 12, pi. 4, fig. 2. 

 71943 Aspidoceras iphiceroides Waagen; Scott: 79, pi. 16, figs 1, 



3. 

 1973 Aspidoceras cf. andinum Steuer; Verma & Westermann: 



191,pl. 36, fig. 1. 

 1973 Ai/j/cforfra.? /i(7«/>r; Krantz; Verma & Westermann: 193, pi. 



36, fig. 2; pi. 37, fig. 1. 

 1973 Aspidoceras cf haupti Krantz; Verma & Westermann: 194, 



pi. 35, fig. 3. 

 1980 Aspidoceras euomphalum Steuer; Leanza: 41, pi. 8, fig. 1. 

 1985 Aspidoceras rogoznicense (Zejszner); Checa: 98, pi. 16, 



figs 1-4. 



Material. Two specimens, CA579-80, from bed 36, Mintaq 

 Member, Mintaq Salt Dome. 



U 



Description. The larger specimen consists of a third of a whorl of 

 massive body-chamber, which is uncrushed near the aperture at 205 

 mm diameter, but is progressively crushed on one side towards the 

 smaller broken end; poorly preserved parts of the inner whorls are 

 also seen; there are no septa on the body-chamber, which may be 

 complete at the aperture and is possibly adult. The final whorl is very 

 massive and has an evenly rounded, depressed whorl section, a deep 

 umbilicus and vertical umbilical walls. Traces of two rows of bold 

 tubercles can be seen on the inner whorls, and reduced tubercles 

 remain on the outer whorl, which appears to show modified adult 

 ornament. Part of the latter is low relief ribbing or striation present 

 near the aperture, where it is projected forwards in crossing the 

 venter, and includes one deeper groove that might be a constriction. 

 The smaller specimen is seen mainly as a series of whorl cross- 

 sections of up to 100 mm diameter preserved in very hard limestone 

 matrix; as in the larger specimen, the whorl thickness is considerably 

 more than the whorl height. 



Remarks. According to the work of Checa (1985: 111 &c) a 

 bituberculate Aspidoceras with massive depressed whorls in the 

 Berriasian has to belong to Aspidoceras rogoznicense (Zejszner). In 



Measurements 







D 



Wh 



Wb 



CA579 205 



86 (0.42) 



120(0.59) 



CA580 102 



42(0.41) 



56 (0.55) 



