Early Cambrian origin of modern food webs: evidence from predator arrow worms

Although palaeontological evidence from exceptional biota demonstrates the existence of diverse marine communities in the Early Cambrian (approx. 540-520 Myr ago), little is known concerning the functioning of the marine ecosystem, especially its trophic structure and the full range of ecological niches colonized by the fauna. The presence of a diverse zooplankton in Early Cambrian oceans is still an open issue. Here we provide compelling evidence that chaetognaths, an important element of modern zooplankton, were present in the Early Cambrian Chengjiang biota with morphologies almost identical to Recent forms. New information obtained from the lowermost Cambrian of China added to previous studies provide convincing evidence that protoconodont-bearing animals also belonged to chaetognaths. Chaetognaths were probably widespread and diverse in the earliest Cambrian. The obvious raptorial function of their circumoral apparatuses (grasping spines) places them among the earliest active predator metazoans. Morphology, body ratios and distribution suggest that the ancestral chaetognaths were planktonic with possible ecological preferences for hyperbenthic niches close to the sea bottom. Our results point to the early introduction of prey-predator relationships into the pelagic realm, and to the increase of trophic complexity (three-level structure) during the Precambrian-Cambrian transition, thus laying the foundations of present-day marine food chains.     

Beyond the Burgess Shale: Cambrian microfossils track the rise and fall of hallucigeniid lobopodians

Burgess Shale-type deposits are renowned for their exquisite preservation of soft-bodied organisms, representing a range of animal body plans that evolved during the Cambrian ‘explosion’. However, the rarity of these fossil deposits makes it difficult to reconstruct the broader-scale distributions of their constituent organisms. By contrast, microscopic skeletal elements represent an extensive chronicle of early animal evolution—but are difficult to interpret in the absence of corresponding whole-body fossils. Here, we provide new observations on the dorsal spines of the Cambrian lobopodian (panarthropod) worm Hallucigenia sparsa from the Burgess Shale (Cambrian Series 3, Stage 5). These exhibit a distinctive scaly microstructure and layered (cone-in-cone) construction that together identify a hitherto enigmatic suite of carbonaceous and phosphatic Cambrian microfossils—including material attributed to Mongolitubulus, Rushtonites and Rhombocorniculum—as spines of Hallucigenia-type lobopodians. Hallucigeniids are thus revealed as an important and widespread component of disparate Cambrian communities from late in the Terreneuvian (Cambrian Stage 2) through the ‘middle’ Cambrian (Series 3); their apparent decline in the latest Cambrian may be partly taphonomic. The cone-in-cone construction of hallucigeniid sclerites is shared with the sclerotized cuticular structures (jaws and claws) in modern onychophorans. More generally, our results emphasize the reciprocal importance and complementary roles of Burgess Shale-type fossils and isolated microfossils in documenting early animal evolution.     

A new trace fossil from the Middle Cambrian of the Grand Canyon, Arizona, USA

An unusual trace fossil from the Middle Cambrian Bright Angel Shale Formation of the Grand Canyon, Arizona, consisting of two rows of biserially opposed circular or oval depressions, with alternating symmetry, is described as Bicavichnites martini ichnogen. et ichnosp. nov. While specimens of this trace may represent the surface expression of a complex treptichnid-like burrow system, it is more likely that they are the walking traces of a bilaterally symmetrical benthic animal. The large variation in external width within the trackways is inconsistent with an arthropod producer. The trackway morphology and presence of limb spur marks suggest that the trace maker may have been a lobopodian, a Cambrian relative of modern onychophorans.     

AN ORDOVICIAN LOBOPODIAN FROM THE SOOM SHALE LAGERSTÄTTE, SOUTH AFRICA

Abstract:  The first lobopodian known from the Ordovician is described from the Soom Shale Lagerstätte, South Africa. The organism shows features homologous to Palaeozoic marine lobopodians described from the Middle Cambrian Burgess Shale, the Lower Cambrian Chengjiang biota, the Lower Cambrian Sirius Passet Lagerstätte and the Lower Cambrian of the Baltic. The discovery provides a link between marine Cambrian lobopodians and younger forms from the Silurian and Carboniferous. The new fossil preserves an annulated trunk, lobopods with clear annulations, and curved claws. It represents a rare record of a benthic organism from the Soom Shale, and demonstrates intermittent water oxygenation during the deposition of the unit.     

昆明海口早寒武世澄江生物群中叶状红藻化石

主要报道了采自云南省昆明市海口马房村鞍山早寒武世筇竹寺组玉案山段澄江生物群中的叶状红藻-似红叶藻(新属、新种)(Paradelesseria sanguinea Xu,gen.et sp.Nov.).通过比较形态学研究,探讨了该宏观化石藻类的分类归属与亲缘关系,进一步丰富了澄江生物群生物物种多样性的认识,并为研究早寒武世生物演化及其古环境提供了新的化石证据.同时,通过对现生红藻的比较研究,进一步证明了澄江生物群在云南海口地区发生于一个水深在30 m以上的亚潮带和下潮间带的海水环境.     

The bivalved arthropods Isoxys and Tuzoia with soft‐part preservation from the Lower Cambrian Emu Bay Shale Lagerstätte (Kangaroo Island,Australia)

Abstract: Abundant material from a new quarry excavated in the lower Cambrian Emu Bay Shale (Kangaroo Island, South Australia) and, particularly, the preservation of soft‐bodied features previously unknown from this Burgess Shale‐type locality, permit the revision of two bivalved arthropod taxa described in the late 1970s, Isoxys communis and Tuzoia australis. The collections have also produced fossils belonging to two new species: Isoxys glaessneri and Tuzoia sp. Among the soft parts preserved in these taxa are stalked eyes, digestive structures and cephalic and trunk appendages, rivalling in quality and quantity those described from better‐known Lagerstätten, notably the lower Cambrian Chengjiang fauna of China and the middle Cambrian Burgess Shale of Canada.     

Community palaeoecology of the early Cambrian Maotianshan Shale biota: Ecological dominance of priapulid worms

The early Cambrian soft-bodied Maotianshan Shale (Chengjiang) biota of Yunnan Province, China provides a critical glimpse of animal life during the heart of the Cambrian radiation. The Shankou biota is the focus of this current work, and 9963 specimens from it have been examined and tallied. This collection of fossils represents a time-averaged assemblage of unknown duration from a 10-meter thick sequence. The predominantly benthic community recovered from this section is presumably autochthonous. This community was buried through several hundred millimeter to centimeter thick burial events. Only specimens interpreted as buried alive, based on either soft-part preservation or fully articulated skeletons, were counted. Algae were too fragmented to be counted. To avoid including synonymous species, diversity was evaluated at the genus level. A total of 57 genera from 9 phyla, encompassing 14 ecological groups, were found in this assemblage. The results reveal that the three most abundant genera comprise 43.2% of all specimens: the tubiform priapulid worm Paraselkirkia (16.0%), the diminutive priapulid worm Sicyophorus (14.3%), and the brachiopod Heliomedusa (12.9%). No other genera total more than 9% of specimens. At the phylum level, there is an interesting dichotomy between taxonomic diversity and ecological dominance. The arthropods are the most diverse phylum (37% of genera) and rank second in relative abundance of specimens (26.3%). The priapulids, however, with only 17.5% of genera is the most abundant group in the assemblage (43.2%). All other phyla, excluding brachiopods (19.6%), represent only 10.9% of the assemblage. Because of their sheer numerical abundance, this study indicates that priapulid worms may have exerted more influence on energy flow and community structure than other phyla in this particular trophic web. This result contrasts strongly with both traditional views of Maotianshan Shale biota palaeoecology, which often claimed arthropod dominance based solely on taxonomic diversity, and the palaeoecology of modern priapulids, which are relegated to marginal marine settings. This result also demonstrates the importance of collecting quantitative relative abundance data when performing palaeoecological investigations.     

Benthic primary producers in exceptionally preserved Cambrian biotas of North China

Strata situated within the South China Craton host several key Cambrian macroalgal assemblages, including those of the Chengjiang, Kaili, and Tsinghsutung Lagerstätte. In this report, Cambrian macroalgae are described for the first time from the North China Craton, an area that, during the early Paleozoic, was not contiguous with the South China Craton. The material collected from the Mantou Formation and overlying Zhangxia Formation (Miaolingian Series) in Shandong Province is preserved as carbonaceous compressions and includes abundant simple tubular forms. These fall into two groupings on the basis of size and have characteristics broadly comparable to Fuxianospira gyrata and Sinocylindra yunnanensis, both of which are well-known from the Chengjiang biota and may represent simple siphonous green algae. Additional material includes irregular circular to oval films referable to Morania fragmenta and a tuft-like form superficially similar to Marpolia spissa, taxa with possible cyanophyte affinities described initially on the basis of material from the Burgess Shale but also known from the Cambrian of South China. The material is typical of the “Cambrian Flora” and provides further support for the cosmopolitan distribution of this noncalcified macroalgal flora at low latitude settings during the Cambrian.     

贵州麻江地区寒武纪杷榔动物群的群落组成和生态空间分析*

寒武纪特异埋藏化石库保存了海洋生物群落最原始的生态结构, 为群落生态研究提供了宝贵材料。贵州寒武纪斜坡相区的杷榔动物群(第4期)具有较高的生物多样性, 但定量生态学研究相对薄弱。本研究对贵州麻江地区杷榔动物群的新产地平定剖面进行化石采集和分类统计, 并运用多元数理统计方法开展定量化分析。鉴定出腕足动物、海绵动物、刺胞动物、节肢动物、软舌螺动物、古虫动物、开腔骨动物和曳鳃动物8个化石门类, 计31属33种, 划分出12种生态类型。其中, 腕足动物具有最高的个体丰度(占比61.5%), 节肢动物物种分异度最高(占比60%), 群落以底栖固着生态类型为主, 游泳捕食为辅。对比分析结果显示, 寒武纪海洋群落具有空间异质性, 且节肢动物在影响群落组成和生态空间利用上起决定性作用。随水体深度增加, 海洋生态群落中的表栖类群出现明显扩张, 也体现了环境对群落面貌的塑造作用。     

Quantitative paleoecology of Cambrian (Series 2–Miaolingian) communities from central Sonora,Mexico

This work presents a paleoecological approach to study benthic communities preserved in Cambrian strata exposed at the Sahuaral locality in central Sonora, northwestern Mexico. Based on species richness and abundance, this work analyzed 627 individuals corresponding to 33 species from five distinctive Cambrian formations: the lowermost Proveedora Formation characterized by bioturbation horizons that record the occurrence of a benthic-infaunal biota from coastal shallow seas, followed by the Buelna Formation which contains reef deposits dominated by autotrophic epibenthic communities. The Cerro Prieto Formation was deposited in a high-energy shallow marine environment, dominated by primary consumers-epifaunal and suspensions feeders. The uppermost unit, the El Gavilán Formation, is an intercalation of shale and fossiliferous limestone characterized by the fossil remains of suspension feeders, detritus feeders and nektobenthic organisms of low energy deep water environments. The paleobiota consist of ichnofossils, microbial oncolites, chancellorids, brachiopods, hyolithids, and trilobites in a sequence of increasing diversity and complexity. Paleoecological indices (Simpson Dominance, Shannon-Weaver Index, Evenness Index, and Total Richness) were determined and compared in the study area. In addition, the effective number of species and the true diversities were obtained, which are similar between each station distributed in each formation. However, it is possible that the high degree of dominance is a factor to indicate an inequality between the true diversity and the species richness identified. These results provide new analytical and paleoecological criteria for better understanding depositional environments and fossil associations where the spatial distribution of benthic organisms, richness and abundance provide a valued window to Cambrian biotas. The structure of the marine community of the El Sahuaral area has a great affinity with other Cambrian communities, such as those from the Stephen Formation (Burgess Shale, British Columbia) and the Chengjiang biota of the Yangtze Shelf deposits in South China.     

The lobopodian Paucipodia inermis from the Lower Cambrian Chengjiang fauna, Yunnan, China

New specimens of Paucipodia inermis Chen, Zhou & Ramsköld, 1995, are described from the Lower Cambrian Chengjiang Lagerstätte in Haikou, Kunming. Details not previously seen in the Chengjiang material appear to be caused by early diagenetic processes. Some features not previously observed in Palaeozoic lobopodians include details of the dermomuscular sac, body cavities, contents of the gut, possible paired ventral nerve ganglia, and a rasping or biting apparatus with teeth. The latter implies a fundamental difference from onychophorans and rules out an ancestral position for Palaeozoic lobopodians. The supposed tail is shown to be the head, and it is shown that this animal possessed nine pairs of lobopods rather than six, as originally stated. The family Paucipodiidae n. fam. is introduced.     

寒武纪早期四方塔型壳属的胚胎发育及其系统学意义

寒武纪大爆发是生命演化史上重要的创新事件.我国澄江动物群(距今约5.18亿年)代表了寒武纪大爆发的高潮,而产自寒武系最底部,时代上早于澄江动物群的宽川铺生物群(距今约5.35亿年)则为研究寒武纪大爆发的第一幕提供了重要的埋藏窗口.宽川铺生物群产自陕南宁强、西乡等地寒武系底部宽川铺组钙质磷块岩和磷质碎屑灰岩中,以保存了大...     

Recent Priapulidae and their Early Cambrian ancestors: comparisons and evolutionary significance

Although priapulid worms form a relatively small phylum in present-day marine environments, they were important animals in Cambrian endobenthic communities. Two Early Cambrian priapulids, namely Xiaoheiqingella peculiaris and Yunnanpriapulus halteroformis nov. gen., nov. sp. from the Maotianshan Shale Lagerstätte of SW China are revised and described. Several key-features of the body plan of Recent Priapulidae are recognized in these two forms: 1) the four-fold body division (introvert, neck, trunk, and caudal appendage); 2) the well-developed introvert armed with ca. 25 longitudinal rows of scalids; 3) the caudal appendage; 4) the pharyngeal teeth arranged in a pentagonal disposition (Xiaoheiqingella); 5) the ventral nerve cord present in Yunnanpriapulus. This morphology indicates close evolutionary relationships with modern priapulids. Xiaoheiqingella and Yunnanpriapulus nov. gen. are tentatively placed within the recent family Priapulidae. The Priapulidae lineage may therefore have a remote origin (Early Cambrian) much older than was previously assumed (Priapulites; Late Carboniferous). The functional morphology of Xiaoheiqingella and Yunnanpriapulus nov. gen. suggests that these two worms were chiefly carnivorous with possible occasional mud-eating habits.     

Extraordinary fossils reveal the nature of Cambrian life: a commentary on Whittington (1975) ‘The enigmatic animal Opabinia regalis,Middle Cambrian,Burgess Shale,British Columbia’

Harry Whittington''s 1975 monograph on Opabinia was the first to highlight how some of the Burgess Shale animals differ markedly from those that populate today''s oceans. Categorized by Stephen J. Gould as a ‘weird wonder’ (Wonderful life, 1989) Opabinia, together with other unusual Burgess Shale fossils, stimulated ongoing debates about the early evolution of the major animal groups and the nature of the Cambrian explosion. The subsequent discovery of a number of other exceptionally preserved fossil faunas of Cambrian and early Ordovician age has significantly augmented the information available on this critical interval in the history of life. Although Opabinia initially defied assignment to any group of modern animals, it is now interpreted as lying below anomalocaridids on the stem leading to the living arthropods. This commentary was written to celebrate the 350th anniversary of the journal Philosophical Transactions of the Royal Society.     

Gut Contents as Direct Indicators for Trophic Relationships in the Cambrian Marine Ecosystem

Present-day ecosystems host a huge variety of organisms that interact and transfer mass and energy via a cascade of trophic levels. When and how this complex machinery was established remains largely unknown. Although exceptionally preserved biotas clearly show that Early Cambrian animals had already acquired functionalities that enabled them to exploit a wide range of food resources, there is scant direct evidence concerning their diet and exact trophic relationships. Here I describe the gut contents of Ottoia prolifica, an abundant priapulid worm from the middle Cambrian (Stage 5) Burgess Shale biota. I identify the undigested exoskeletal remains of a wide range of small invertebrates that lived at or near the water sediment interface such as hyolithids, brachiopods, different types of arthropods, polychaetes and wiwaxiids. This set of direct fossil evidence allows the first detailed reconstruction of the diet of a 505-million-year-old animal. Ottoia was a dietary generalist and had no strict feeding regime. It fed on both living individuals and decaying organic matter present in its habitat. The feeding behavior of Ottoia was remarkably simple, reduced to the transit of food through an eversible pharynx and a tubular gut with limited physical breakdown and no storage. The recognition of generalist feeding strategies, exemplified by Ottoia, reveals key-aspects of modern-style trophic complexity in the immediate aftermath of the Cambrian explosion. It also shows that the middle Cambrian ecosystem was already too complex to be understood in terms of simple linear dynamics and unique pathways.     

The Cambrian "explosion" of metazoans and molecular biology: would Darwin be satisfied?

The origins of metazoan bodyplans and the extent to which they are coincident with the Cambrian "explosion" are both areas of continuing debate. The fossil record has a unique advantage in terms of historical perspective, but remains highly contentious on account of the often controversial interpretations of particular groups (e.g. halkieriids, vetulicolians) and the heavy reliance on "windows" of exceptional preservation (e.g. Chengjiang, Burgess Shale). Molecular and developmental biology offer other unique insights, but may be problematic in terms of conflicting phylogenetic signals and questions revolving around gene co-option, evolution of developmental systems and even convergence. Such topics, far from frustrating the enterprise, actually widen our understanding of the nature of the evolutionary process with the exciting promise of the discovery of more general principles.     

贵州下寒武统牛蹄塘生物群中的双孔钱包海绵Crumillospongia biporosa

下寒武统澄江生物群、中寒武统布尔吉斯页岩生物群及下寒武统牛蹄塘生物群均产有Crumillospongiabi-porosa,由于产C.biporosa的牛蹄塘生物群下部层位低于澄江生物群,贵州遵义松林可能是C.biporosa的最低层位及发源地。本文描述了贵州遵义下寒武统牛蹄塘生物群的C.biporosa,为C.biporosa的发生、演化及古地理分布提供了重要的信息和证据。     

昆明海口早寒武世澄江生物群中叶状红藻化石

主要报道了釆自云南省昆明市海口马房村鞍山早寒武世筇竹寺组玉案山段澄江生物群中的叶状红藻-似红叶藻(新属、新种)(Paradelesseria sanguinea Xu,gen.et sp.Nov.)。通过比较形态学研究,探讨了该宏观化石藻类的分类归属与亲缘关系,进一步丰富了澄江生物群生物物种多样性的认识,并为研究早寒武世生物演化及其古环境提供了新的化石证据。同时,通过对现生红藻的比较研究,进一步证明了澄江生物群在云南海口地区发生于一个水深在30m以上的亚潮带和下潮间带的海水环境。     

寒武纪早期澄江生物群中受创伤的中间型始莱德利基三叶虫(Eoredlichia intermedia)

三叶虫是寒武纪海洋中的常见动物,其受伤愈合现象的化石记录可以反映生态系统内物种之间竞争关系。中国华南寒武纪早期澄江化石生物群因保存软躯体构造化石而成为研究寒武纪大爆发时期古海洋生态群落的绝佳窗口,然而,澄江生物群中三叶虫受伤愈合现象的化石至今未见报道。中间型始莱德利基虫(Eoredlichia intermedia Lu,1940)是澄江生物群的常见物种,也是我国寒武系第二个三叶虫化石带的标准带化石。在2 000余枚中间型始莱德利基虫标本中,发现两枚成体标本的头甲侧边缘、颊刺和胸甲肋节保存了不同程度的残缺。据此推测,Eoredlichia intermedia在生命活动过程中曾受到碎壳型捕食动物的攻击或其他伤害而形成伤口。伤口部位边缘加厚且光滑,显示了明显的愈合痕迹。这些特征表明始莱德利基虫在受到非致死的伤害后,具备自身修复损伤的能力。这是迄今所知最为古老的,也是在澄江生物群中首次发现的三叶虫受伤并且愈合的标本,反映了寒武纪第二世第三期底栖生态系统中碎壳型捕食者和三叶虫猎物之间的军备竞赛生态关系。