New observations on morphological variation of genus Vetulicola with quadrate carapace from the Cambrian Chengjiang and Guanshan biotas, South China
Authors:
Li et al
Abstract:
Vetulicolians are enigmatic fossils with a debated phylogenetic position; they first appeared during the Cambrian evolutionary explosion. The early Cambrian Chengjiang and Guanshan biotas from South China exhibit the highest taxonomic diversity of vetulicolians, with ten species described to date. Here we conduct a comparative study on the most common members of Genus Vetulicola that bear a quadrate carapace from these two biotas. Two morphotypes are recognized both within Vetulicola rectangulata from the Chengjiang Biota and within a new undetermined species, Vetulicola sp. from the Guanshan Biota. In both localities morphotypes differ from each other in the presence/absence of a posteroventral projection in the anterior body, and this is interpreted to possibly represent sexual dimorphism. These two Vetulicola species from the Chengjiang and Guanshan biotas also exhibit other morphological differences. Most notable is the position of the junction between the anterior and posterior parts of the body which is further towards the anterior in the specimens from the Guanshan Biota than those from the Chengjiang Biota. In addition, the expansion of the distal portion of the posterior body occurs from the third segment in the Chengjiang specimens but from the fourth segment in the Guanshan specimens. The most likely interpretation of these differences is that they reflect evolutionary adaption of the swimming ability of Vetulicola with a quadrate carapace from the Chengjiang to the Guanshan Biota.
A rare 520 million year old fossil shaped like a 'squashed bird's nest' that will help to shed new light on life within Earth's ancient seas has been discovered in China by an international research team - and will honour the memory of a University of Leicester scientist who passed away earlier this year.
The research team behind the discovery was led by Professor Xianguang Hou from the Yunnan Key Laboratory for Palaeobiology at Yunnan University in China with collaboration from the Universities of Leicester and Oxford.
The fossil, from Chengjiang in southern China, is of a probable 'chancelloriid', a group of bizarre, balloon-shaped animals with an outer skeleton of defensive spines. The animal was flattened during the fossilisation process so that it looks like a squashed bird's nest.
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In southern China, rocks 520 million years old in Chengjiang County, Yunnan Province yield a diverse array of fossils preserved with traces of their soft anatomy, including their legs, eyes, guts and even brains.
Amongst the fossils are many animals that can be related to modern forms, including distant relatives of arthropods such as crabs and lobsters, and a wide variety of worms.
There are also several enigmatic fossils that don't seem to fit in with anything living today, and amongst these are the chancelloriids.
New articulated protospongiid sponges from the early Cambrian Chengjiang biota
Authors:
Chen et al
Abstract:
Sponges are among the earliest diverging crown-group animals and widely regarded as the earliest biomineralizing animals. Indeed, unambiguous hexactine sponge spicules first occur in the lowermost Cambrian strata of the Fortunian Stage. Articulated sponge skeletons interpreted as hexactinellids and demosponges have been reported from Cambrian Stage 2–3 strata at multiple localities. Articulated sponge skeletons in the Chengjiang biota (Cambrian Stage 3), however, are dominated by forms interpreted as demosponges, despite the exceptional preservation in this biota. Here, we report new articulated sponge skeletons from the Chengjiang biota, including Paradiagoniella magna n. gen. n. sp. and P. xiaolantianensis n. gen. n. sp. The skeleton of both species consists of ranked stauractines and rare oxeas (straight or curved diactines), as well as hexactines in the former species. Their stauractines form irregular, nested, local sub-quadrules oriented obliquely to the sponge body axis. Sub-quadrules of different ranks are not in parallel arrangement. The two species are tentatively placed in the family Protospongiidae, which as currently defined may be a paraphyletic group including members of the total-group hexactinellids and perhaps stem-group siliceans. The phylogenetic placement of P. magna and P. xiaolantianensis is uncertain but, like many other protospongiids, they could be members of the total-group hexactinellids or stem-group siliceans. The diactines in the two species could be secondarily reduced hexactine-based spicules; alternatively, these two species may represent an evolutionary grade of stem-group siliceans with both diactines and hexactine-based spicules, the latter of which was lost in demosponges. A comprehensive cladistics analysis is needed to resolve the exact phylogenetic placement of the two species described here.
New data on the palaeobiology of the enigmatic yunnanozoans from the Chengjiang Biota, Lower Cambrian, China
Authors:
Cong et al
Abstract:
Interpretation of the enigmatic soft-bodied yunnanozoans from the Lower Cambrian (Stage 3, Series 2) Chengjiang Biota has remained controversial for decades because of their strange body plan and their variable taphonomic alteration. Proposed affinities have ranged from stem bilaterian to stem vertebrate. A study of over seven hundred slabs, many newly collected, from five sections at two localities demonstrates that yunnanozoans have sclerotized dorsal and axial segments, a body cavity, a unique feeding region and a coiled alimentary canal. Although two genera have been previously discriminated, all specimens have the same number of filamentous arches (seven pairs) and of ventral circular structures (four pairs); this indicates that Haikouella Chen, Huang and Li, 1999 is a junior synonym of Yunnanozoon Hou, Ramsköld and Bergström, 1991. Our analysis reveals new details of the putative pharyngeal pores of Yunnanozoon lividum, and although there are similarities with the gill slits of deuterostomes, the question of their homology remains moot. The filamentous arches and their supporting rods were probably sclerotized and represent a specialized feeding structure. Yunnanozoans exhibit characters that are open to a number of alternative interpretations of putative homology, encompassing comparisons with deuterostomes and protostomes (including members of the Platyzoa). Given their unique features, and the current lack of secure homologies, the affinities of yunnanozoans should continue to be considered in a wider bilaterian context.
Diversity and species abundance patterns of the early Cambrian (Series 2, Stage 3) Chengjiang Biota from China
Authors:
Zhao et al
Abstract:
Lagerstätten from the Precambrian–Cambrian transition have traditionally been a relatively untapped resource for understanding the paleoecology of the “Cambrian explosion.” This quantitative paleoecological study is based on 10,238 fossil specimens belonging to 100 animal species, 11 phyla, and 15 ecological categories from the lower Cambrian (Series 2, Stage 3) Chengjiang biota (Mafang locality near Haikou, Yunnan Province, China). Fossils were systematically collected within a 2.5-meter-thick sequence divided into ten stratigraphic intervals. Each interval represents an induced time-averaged assemblage of various event (obrution) beds of unknown duration. Overall, the different fossil assemblages are taxonomically and ecologically similar, suggesting the presence of a single community type recurring throughout the Mafang section. The Mafang community is dominated by epibenthic vagile hunters or scavengers, sessile suspension feeders, and infaunal vagile hunters or scavengers represented primarily by arthropods, brachiopods, and priapulids, respectively. Most species have low abundance and low occurrence frequencies, whereas a few species are numerically abundant and occur frequently. Overall, in structure and ecology the Mafang community is comparable to the middle Cambrian (Series 3, Stage 5) Burgess Shale biota (Walcott Quarry, Yoho National Park, British Columbia, Canada). This suggests that, despite variations in species identity within taxonomic and ecological groups, the structure and ecology of Cambrian Burgess Shale-type communities remained relatively stable until at least the middle Cambrian (Series 3, Stage 5) in subtidal to relatively deep-water offshore settings in siliciclastic soft-substrate environments.
The burrow dwelling behavior and locomotion of palaeoscolecidian worms: New fossil evidence from the Cambrian Chengjiang fauna
Authors:
Diying Huang, Junyuan Chen, Maoyan Zhu and Fangchen Zhao
Abstract:
Palaeoscolecidian worms are abundant components in Paleozoic shallow marine communities; however, their life habits remain poorly known. Here we present evidence of burrow dwelling behavior of palaeoscolecidian worms based on well-preserved specimens of Cricocosmia jinningensis and Mafangscolex sinensis from the lower Cambrian Maotianshan Shale. C. jinningensis was found living within elongate burrows, either of cylindrical or more rarely of swollen sac-like shape, while M. sinensis lived in elongate and slender tube-like burrows. The wall of the burrow has a sharp boundary from the surrounding sediment, which may have been consolidated by the worm itself and it resembles the Recent priapulid worm Maccabeus. It is demonstrated that M. sinensis makes a snake-twisting movement in its burrow that differs from crawling behavior of C. jinningensis by the use of two rows of lateral plates. The lined burrows of Maotianshania cylindrica previously reported are in fact made by C. jinningensis and M. sinensis.
