Hyolithellus in life position from the Lower Cambrian of North Greenland

2011 ◽  
Vol 85 (1) ◽  
pp. 37-47 ◽  
Author(s):  
Christian B. Skovsted ◽  
John S. Peel
Keyword(s):  
Lower Cambrian ◽  
Tube Wall ◽  
Center Of Mass ◽  
Sediment Surface ◽  
Vertical Orientation ◽  
Stem Group ◽  
First Occurrence ◽  
Tubular Specimens ◽  
North Greenland

Tubular specimens belonging to Hyolithellus from silty dolostones of the basal Aftenstjernesø Formation of North Greenland may represent the first occurrence of this widespread Cambrian fossil in life position. A high proportion of preserved specimens are oriented normal to bedding with the tapering end of the tube down. Occasional undulations in the growth of the tubes indicate that the animal actively adjusted its growth to achieve a vertical orientation in relation to the sediment surface. Increasing thickness of the tube wall towards the tapering end shifted the center of mass downwards and resulted in greater stability in the sediment. The tube remained open at both ends throughout ontogeny; it was most likely secreted by an annelid-grade animal which pumped water into the sediment through the tube. Hyolithellus and similar tubular fossils from the Lower Cambrian probably represent stem group annelids.

Kleptothule rasmusseni gen. et sp. nov.: an ?olenellinid-like trilobite from the Sirius Passet fauna (Buen Formation, Lower Cambrian, North Greenland)

1995 ◽  
Vol 86 (1) ◽  
pp. 1-12 ◽  
Author(s):  
Graham E. Budd
Keyword(s):  
Lower Cambrian ◽  
Complete Analysis ◽  
Stem Group ◽  
Number Of Segments ◽  
North Greenland

AbstractThe Lower Cambrian Sirius Passet fauna from Peary Land, North Greenland, is a rich repository of soft-bodied and poorly-sclerotised fossils. A new arthropod from the fauna, Kleptothule rasmusseni, is described. The animal is broadly trilobite-like, possessing a trilobed exoskeleton which is divided into distinct cephalic, thoracic and caudal regions. However, it is unusual in that it possesses a large number of segments, and demonstrates pronounced cephalic segmentation, and a very narrow cephalon and thorax. There is some evidence that the exoskeleton was lightly mineralised.Kleptothule is compared to some of the olenellimd trilobites, especially those taxa that possess a many-segmented ‘opisthothorax’. Its morphology raises some issues discussed by Lauterbach (1983) in his assignment of some olenellids to the stem-group of the chelicerates. However, it is not considered herein that such a model can be supported. A complete analysis of basal trilobites and the stem-group leading to them must await a fuller description of key taxa from China and Greenland.

Occurrence of the Enigmatic Bivalved FossilApistoconchain the Lower Cambrian of Southeast Shaanxi, North China Platform

2014 ◽  
Vol 88 (2) ◽  
pp. 359-366 ◽  
Author(s):  
Guoxiang Li ◽  
Zhifei Zhang ◽  
Hong Hua ◽  
Huining Yang
Keyword(s):  
Carbonate Rocks ◽  
Lower Cambrian ◽  
Morphological Analysis ◽  
North China ◽  
Bilateral Symmetry ◽  
Shaanxi Province ◽  
Single Type ◽  
Posterior Teeth ◽  
North China Platform ◽  
Stem Group

The early Cambrian calcareous skeletal fossilApistoconchaConway Morris is characterized by its two valves having posterior teeth and internal umbonal cavities. It has been reported from lower Cambrian Botomian-equivalent carbonate rocks in Australia, Mongolia, and Greenland. Here we report a new occurrence ofApistoconchain the lower Cambrian Xinji Formation of Luonan, southeast Shaanxi Province, North China Platform. Based on material (five ventral and four dorsal valves) from the Xinji Formation,Apistoconchacf.aphelesis systematically described and the taxonomic affinity ofApistoconchais discussed. The shell ofApistoconchapossesses an ‘antero-posterior’ plane of bilateral symmetry, and its two valves apparently articulated in life, although the tooth-like structures and pits show little resemblance to the teeth and sockets, respectively, of bivalved shells of rhynchonelliform brachiopods or pelecypods.Apistoconchacannot be assigned to the crown groups of either brachiopods or mollusks, even though functional morphological analysis indicates thatApistoconchamay be a ‘stem-group brachiopod’. UnlikeApistoconcha, the morphologically similarTianzhushanellaLiu is known only from a single type of valve lacking posterior teeth and pits.Tianzhushanellamay represent either a univalved animal or a bivalved animal, the other valve of which has not yet been identified. Even though bothApistoconchaandTianzhushanellamay represent stem-group brachiopods, they probably correspond to different stages of brachiopod evolution. Thus assignment ofApistoconchaandTianzhushanellato the same family (Tianzhushanellidae) may obscure their phylogenic implications.

Articulated halkieriids from the Lower Cambrian of North Greenland and their role in early protostome evolution

1995 ◽  
Vol 347 (1321) ◽  
pp. 305-358 ◽  
Keyword(s):  
Body Size ◽  
Molecular Biology ◽  
Lower Cambrian ◽  
Burgess Shale ◽  
Internal Anatomy ◽  
Middle Cambrian ◽  
Functional Consequence ◽  
Primitive State ◽  
North Greenland

Articulated halkieriids of Halkieria evangelista sp. nov. are described from the Sirius Passet fauna in the Lower Cambrian Buen Formation of Peary Land, North Greenland. Three zones of sclerites are recognizable: obliquely inclined rows of dorsal palmates, quincuncially inserted lateral cultrates and imbricated bundles of ventro-lateral siculates. In addition there is a prominent shell at both ends, each with radial ornamentation. Both sclerites and shells were probably calcareous, but increase in body size led to insertion of additional sclerites but marginal accretion of the shells. The ventral sole was soft and, in life, presumably muscular. Recognizable features of internal anatomy include a gut trace and possible musculature, inferred from imprints on the interior of the anterior shell. Halkieriids are closely related to the Middle Cambrian Wixaxia , best known from the Burgess Shale: this clade appears to have played an important role in early protostome evolution. From an animal fairly closely related to Wixaxia arose the polychaete annelids; the bundles of siculate sclerites prefigure the neurochaetae whereas the dorsal notochaetae derive from the palmates. Wixaxia appears to have a relic shell and a similar structure in the sternaspid polychaetes may be an evolutionary remnant. The primitive state in extant polychaetes is best expressed in groups such as chrysopetalids, aphroditaceans and amphinomids. The homology between polychaete chaetae and the mantle setae of brachiopods is one line of evidence to suggest that the latter phylum arose from a juvenile halkieriid in which the posterior shell was first in juxtaposition to the anterior and rotated beneath it to provide the bivalved condition of an ancestral brachiopod. H. evangelista sp. nov. has shells which resemble those of a brachiopod; in particular the posterior one. From predecessors of the halkieriids known as siphogonuchitids it is possible that both chitons (polyplacophorans) and conchiferan molluscs arose. The hypothesis of halkieriids and their relatives having a key role in annelid—brachiopod—mollusc evolution is in accord with some earlier proposals and recent evidence from molecular biology. It casts doubt, however, on a number of favoured concepts including the primitive annelid being oligochaetoid and a burrower, the brachiopods being deuterostomes and the coelom being an archaic feature of metazoans. Rather, the annelid coelom arose as a functional consequence of the transition from a creeping halkieriid to a polychaete with stepping parapodial locomotion.

scholarly journals Lower Cambrian trace fossils from northern Greenland

1988 ◽  
Vol 137 ◽  
pp. 43-53
Author(s):  
J Bergström ◽  
J.S Peel
Keyword(s):  
Lower Cambrian ◽  
Trace Fossils ◽  
Trace Fossil ◽  
East Greenland ◽  
North West ◽  
North Greenland

Rusophyciform and cruzianaeform trace fossils are described from Lower Cambrian siliciciastic shelf deposits in North-West and North Greenland. Cruziana cf. C. dispar Linnarsson, 1869 is reported from the Dallas Bugt Formation of Inglefield Land while a new ichnospecies, Rusophycus marginatus, occurs in the Buen Formation of Peary Land and in the equivalent Humboldt Formation of Daugaard-Jensen Land. These species show no similarity to the Cruziana sp. previously described from East Greenland. The occurrence of C. cf. C. dispar could indicate some similarity in Cambrian trace fossil 'ichnofaunas' between Greenland and Europe but available material is insufficient to ciarify this relationship.

scholarly journals The new stem-group brachiopod Oymurania from the lower Cambrian of Siberia

2014 ◽  
Author(s):  
Artem Kouchinsky ◽  
Lars Holmer ◽  
Galina Ushatinskaya ◽  
Michael Steiner
Keyword(s):  
Lower Cambrian ◽  
Stem Group

scholarly journals Trachyplax arctica, a New Multiplated Problematic Fossil from the Lower Cambrian of North Greenland

2009 ◽  
Vol 54 (3) ◽  
pp. 513-523 ◽  
Author(s):  
Cecilia M. Larsson ◽  
John S. Peel ◽  
Anette E.S. Högström
Keyword(s):  
Lower Cambrian ◽  
North Greenland

scholarly journals Experimental neoichnology of post-autotomy arm movements of sea lilies and possible evidence of thrashing behaviour in Triassic holocrinids

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Przemysław Gorzelak ◽  
Mariusz A. Salamon ◽  
Krzysztof Brom ◽  
Tatsuo Oji ◽  
Kazumasa Oguri ◽  
...  
Keyword(s):  
Arm Movements ◽  
Sediment Surface ◽  
Early Triassic ◽  
Stem Group ◽  
Wide Range ◽  
Mesozoic Marine Revolution ◽  
Water Species

Abstract Echinoderms exhibit remarkable powers of autotomy. For instance, crinoids can shed arm and stalk portions when attacked by predators. In some species, it has been reported that the autotomized arms display vigorous movements, which are thought to divert the attention of predators. This phenomenon, however, has not been well explored. Here we present results of experiments using the shallowest water species of living stalked crinoid (Metacrinus rotundus) collected at 140 m depth. A wide range of movements of detached arms, from sluggish writhing to violent flicks, was observed. Interestingly, autotomized arms produce distinct traces on the sediment surface. They are composed of straight or arched grooves usually arranged in radiating groups and shallow furrows. Similar traces were found associated with detached arms of the oldest (Early Triassic) stem-group isocrinid (Holocrinus). This finding may suggest that the origins of autotomy-related thrashing behaviour in crinoids could be traced back to at least the Early Triassic, underscoring the magnitude of anti-predatory traits that occurred during the Mesozoic Marine Revolution. A new ethological category, autotomichnia, is proposed for the traces produced by thrashing movements of shed appendages.

scholarly journals Swimming Turned on Its Head: Stability and Maneuverability of the Shrimpfish (Aeoliscus punctulatus)

2019 ◽  
Vol 1 (1) ◽  
Author(s):  
F E Fish ◽  
R Holzman
Keyword(s):  
Cross Sections ◽  
Swimming Performance ◽  
Center Of Mass ◽  
Leading Edge ◽  
Longitudinal Axis ◽  
The Body ◽  
Maximum Speed ◽  
Vertical Orientation ◽  
Neutrally Buoyant ◽  
Orientation Modification

Synopsis The typical orientation of a neutrally buoyant fish is with the venter down and the head pointed anteriorly with a horizontally oriented body. However, various advanced teleosts will reorient the body vertically for feeding, concealment, or prehension. The shrimpfish (Aeoliscus punctulatus) maintains a vertical orientation with the head pointed downward. This posture is maintained by use of the beating fins as the position of the center of buoyancy nearly corresponds to the center of mass. The shrimpfish swims with dorsum of the body moving anteriorly. The cross-sections of the body have a fusiform design with a rounded leading edge at the dorsum and tapering trailing edge at the venter. The median fins (dorsal, caudal, anal) are positioned along the venter of the body and are beat or used as a passive rudder to effect movement of the body in concert with active movements of pectoral fins. Burst swimming and turning maneuvers by yawing were recorded at 500 frames/s. The maximum burst speed was 2.3 body lengths/s, but when measured with respect to the body orientation, the maximum speed was 14.1 body depths/s. The maximum turning rate by yawing about the longitudinal axis was 957.5 degrees/s. Such swimming performance is in line with fishes with a typical orientation. Modification of the design of the body and position of the fins allows the shrimpfish to effectively swim in the head-down orientation.

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