Embryonic Ammonoid Shell Features: Intraspecific Variation Revisited

Two samples of ammonoids belonging to the Oppeliidae, Sublunuloceras virguloidesHecticoceras (Brightii) canaliculatum, are analyzed to estimate the intraspecific variability of embryonic shell features. The study of embryonic shell characters reveals two main shapes of protoconch, flattened and round. Prosiphons may be straight or slightly curved. New parameters for area are added to the linear parameters commonly found in the literature. Prosiphon length and caecum area vary greatly whereas protoconch and ammonitella diameter vary only slightly, and the ammonitella angle is almost constant. The protoconch-to-ammonitella size ratio behaves differently in each species, suggesting different patterns of embryonic growth. We compare our results with published data and discuss their significance for species determination and ontogenetic interpretation. The main finding is that intraspecific embryonic variation is greater than was previously believed.     

安徽巢湖地区早三叠世菊石序列

由于地处低纬度下扬子碳酸盐缓坡台地较深水区 ,安徽巢湖地区的下三叠统由一系列泥、灰岩旋回层组成 ,并含有丰富的菊石化石。通过对巢北平顶山和马家山一带上二叠统顶部和下三叠统多条剖面的系统研究 ,建立了在华南乃至低纬度特提斯地区具有代表性的、以属级分类单位为基础的下三叠统菊石生物地层序列 (从下而上 ) :Ophiceras Lytophiceras带、Gyronites Prionolobus带、Flemingites Euflemingites带、Anasibirites带、Columbites Tirolites带和Subcolumbites带。在提议的全球印度阶 奥伦尼克阶界线层型候选剖面———巢湖平顶山西坡剖面上 ,Flemingites Euflemingites带之底与牙形石Neospathoduswaageni首现点比较接近 ,可以作为本界线主要辅助标志之一。记述采自该区上二叠统顶部及下三叠统 ,尤其是印度阶 奥伦尼克阶界线附近的一些具有年代地层意义的菊石化石资料 。     

东昆仑山北坡早三叠世Spathian期菊石群的发现

东昆仑山北坡早三叠世Spathian期的菊石群由Procarnites kokeni(Arthaber),P. kunlunensis sp. nov. 和Proptychitoides trigonalis(Arthaber)组成。它们的出现表明早三叠世的海水已到达东昆仑山,所谓的三叠纪古昆仑山,至少其东部尚不存在,其古海岸线至少应划在阿尔金山与昆仑山之间。Procarnites-Proptychitoides菊石群的出现被看作是陆架深水或斜坡相的标志。由此推测,当前Procarnites-Proptychitoides群落的产地以北,应有陆架浅水相的沉积。同时,以阿尔金山为北缘、昆仑山为南缘的柴达木盆地的下面很可能隐伏有海相三叠系。从邻区布尔汗布达山(作为东昆仑山的东延部分)发育良好的旱、中三叠世海相沉积,笔者推测东昆仑山的海侵起自早三叠世,并延续至中三叠世。     

Ammonoid palaeobiology

This, the second in the series of virtual issues of Palaeontology, charts the development of concepts in ammonoid palaeobiology, with reference to nine selected papers published in this journal from 1965 onwards. These cover a broad range of topics: goniatite bed palaeoecology, systematics and evolution in Scaphites, flow dynamics of cephalopod shells, shell growth and differential geometry, septal function, ammonoid assemblage analysis, evolutionary trends, stratocladistics, and soft part preservation. Despite the growth and success of palaeobiological interpretations of ammonoid evolution, life, morphology and environments over the last 50 years, ammonoid research retains a great potential for the future.     

华南二叠纪茅口期的边缘海域及菊石群

华南陆表海沉积与生物的发育深受其东南边缘茅口期以来隆起来成陆的影响。边缘海域的相带自南东向北西,由陆地向浅海呈规律性排列;随着海退的继续,相带相应地向北西推移。海域内的菊石群专属性地发育于泥质沉积,强烈的土著性质显示其生活环境的局限性,不同于陆缘海斜坡同期的“南丹型”菊石和沉积。     

Dinosaur egg‐laying and nesting: The case of an Upper Maastrichtian site at Rennes‐le‐Chateau (Aude,France)

Variation in longevity of taxa in the fossil record has been recognized, but few studies have tested for correlation between position in morphospace and differential survivorship. A sample of 322 Triassic ammonoid species, each one representing a genus, was studied to test whether longer-lived genera were significantly further from the centre of morphospace than shorter-lived genera. Two empirical morphospaces were constructed from morphological data, and the deviation of each genus from the “average form” (centroid) was calculated. Spearman Rank Correlation and Kruskal-Wallis tests were used to test for any significant relationships between distance from the centre of morphospace and longevity. Some longer-lived taxa tended to plot further from the centre of morphospace, but the amounts of variance in longevity accounted for were small and largely statistically non-significant. Ammonoid clade-level morphological stasis appears to be the product of repeated reoccupation of the centre of morphospaces after taxonomic turnover events.     

西藏晚白垩世晚Campanian期至早Maastrichtian期菊石群——中国最年轻的菊石群

记述产自西藏南部仲巴县的一个中国目前所知最年轻的菊石群 ,含 2科 4属 6种 ,其中 4新种。据菊石群面貌和它们所产出的层位可以划分出上、下两个组合带 :上部Pachydiscuscf.hidakaensis Libycoceraszhongbaense组合带 ;下部Manambolitescujiangdingensis M .pivaeteaui组合带。产菊石的曲贝亚组的下段和上段的中、下部(82F5 0及其以下层位 )为晚Campanian期 ,上段上部 (即 82F5 2及其以上层位 )为早Maastrichtian期。     

Power scaling of ammonitic suture patterns from Cretaceous Ancyloceratina: constraints on septal/sutural complexity

The spatial scaling of 77 hemisutures from 65 species of Cretaceous heteromorphic ammonites was quantified with the fractal box‐counting method. Fractal dimensions within Baculites compressus did not significantly differ between adult hemisutures; however, the juvenile suture of this species did exhibit a significantly lower fractal dimension. This suggests that variation in sutural complexity between explicitly adult ontogenetic stages may not contribute to significant noise in comparisons between other species/morphotypes. High‐spired, three‐dimensionally coiled heteromorphs with a larger degree of septal asymmetry exhibit higher fractal dimensions in outer whorl hemisutures than inner whorl hemisutures due to their elongation and improved space occupation over a larger whorl surface. Three‐dimensionally coiled ammonites also have higher fractal dimensions on average (mean D_b = 1.45) with respect to their 2‐D coiled counterparts (mean D_b = 1.38). All ammonites in this study exhibit a positive trend between sutural complexity and shell size (proxied by whorl height). These relationships suggest that septal frilling is constrained by shell morphology and whorl section geometry during septal morphogenesis. This, in turn, influences the scaling, space‐filling properties and scaling limits of ammonitic suture patterns. Sutural/septal complexity is also found to positively influence the amount of liquid retained in marginal septal recesses. However, as these septa approach larger scales, less cameral liquid is retained per septal mass. This may further explain the positive relationship between sutural complexity and shell size.     

泰国早二叠世与Perrinites菊石动物群共生的verbeekinacean(筳)类

泰国中南部Saraburi地区Saraburi群的灰岩中,Kungurian期的verbeekinacean类与Perrinites菊石群在该地区的碎屑灰岩中共生。两种生态完全不同的生物群的共同存在,对只含单一类型化石的地层之间的区域地层对比有"搭桥"性的意义。