scholarly journals A Stem Group Brachiopod From The Lower Cambrian: Support For A Micrina (Halkieriid) Ancestry

Palaeontology ◽  
2002 ◽  
Vol 45 (5) ◽  
pp. 875-882 ◽  
Author(s):  
Lars E. Holmer ◽  
Christian B. Skovsted ◽  
Alwyn Williams
Keyword(s):  
Lower Cambrian ◽  
Stem Group

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.

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 Setatella significans, a new name for mickwitziid stem group brachiopods from the lower Cambrian of Greenland and Labrador

GFF ◽  
2010 ◽  
Vol 132 (2) ◽  
pp. 117-122 ◽  
Author(s):  
C.B. Skovsted ◽  
M. Streng ◽  
I. Knight ◽  
L.E. Holmer
Keyword(s):  
Lower Cambrian ◽  
New Name ◽  
Stem Group

scholarly journals Paterimitra pyramidalisfrom South Australia: scleritome, shell structure and evolution of a lower Cambrian stem group brachiopod

Palaeontology ◽  
2013 ◽  
Vol 57 (2) ◽  
pp. 417-446 ◽  
Author(s):  
Cecilia M. Larsson ◽  
Christian B. Skovsted ◽  
Glenn A. Brock ◽  
Uwe Balthasar ◽  
Timothy P. Topper ◽  
...  
Keyword(s):  
Shell Structure ◽  
Lower Cambrian ◽  
South Australia ◽  
Stem Group

Leanchoilia guts and the interpretation of three-dimensional structures in Burgess Shale-type fossils

Paleobiology ◽  
2002 ◽  
Vol 28 (1) ◽  
pp. 155-171 ◽  
Author(s):  
Nicholas J. Butterfield
Keyword(s):  
Lower Cambrian ◽  
Chemical Reactivity ◽  
Three Dimensional ◽  
Gut Contents ◽  
Phylogenetic Position ◽  
Internal Source ◽  
Last Common Ancestor ◽  
Burgess Shale ◽  
Stem Group ◽  
Deposit Feeding

The Burgess Shale arthropod Leanchoilia superlata Walcott 1912, commonly preserves a three-dimensional axial structure generally interpreted as gut contents. Thin-section examination shows this instead to be phosphatized biserially repeated midgut glands, including exceptional preservation of subcellular features. The preferential mineralization of these structures is related to their unusually high chemical reactivity and probably to an internal source of phosphate. Sub-millimetric lineations previously interpreted as annular musculature are in fact planar, sometimes radially arranged, subdivisions of these glands. Ventral rows of isolated phosphate patches appear to represent the same tissue.In extant arthropods, extensively developed midgut glands are related to a rich but infrequent diet with a primary function in storage. Their conspicuous occurrence in unambiguous fossil predators such as Sidneyia and Laggania (Anomalocaris) suggests they served a similar role in the Cambrian; by extension, their conspicuous occurrence in Leanchoilia suggests it was a predator or scavenger.Phosphatized midguts with a structure essentially indistinguishable from that of Leanchoilia are also found in Burgess Shale Odaraia, Canadaspis, Perspicaris, Sidneyia, Anomalocaris, and Opabinia. All are characterized by a distinctive sub-millimetric arrangement of planar elements that is not found in extant arthropods or trilobites, suggesting they diverged before the last common ancestor of extant forms; i.e., they represent stem-group arthropods.Three-dimensionally preserved guts are widely preserved in the Lower Cambrian Chengjiang biota but, unlike those in the Burgess Shale, appear to be filled with sediment. Although generally interpreted as evidence of deposit feeding, the form of these structures points to early permineralization of (sediment-free) midgut glands that were subsequently altered to clay minerals. There is no evidence of deposit feeding in the Chengjiang; indeed, there is a case to be made for deposit feeding not being generally exploited generally until after the Cambrian.Fossils with three-dimensionally preserved axes from the Lower Cambrian Sirius Passet biota have been interpreted as lobopodians; however, most of the putative lobopodian features find alternative interpretations as aspects of Leanchoilia-type midgut glands. Although Kerygmachela is reliably identified as a stem-group arthropod, its phylogenetic position remains unresolved owing to the non-preservation of critical external features and to the plesiomorphic nature of its Leanchoilia-type midgut.

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.

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.

The morphology and phylogenetic significance ofKerygmachela kierkegaardiBudd (Buen Formation, Lower Cambrian, N Greenland)

1998 ◽  
Vol 89 (4) ◽  
pp. 249-290 ◽  
Author(s):  
Graham E. Budd
Keyword(s):  
Fossil Record ◽  
Lower Cambrian ◽  
Cephalic Region ◽  
The Other ◽  
Burgess Shale ◽  
Phylogenetic Significance ◽  
Long Tail ◽  
Caudal Region ◽  
Stem Group ◽  
Paraphyletic Group

AbstractSpecimens ofKerygmachela kierkegaardiBudd are described, from the Lower Cambrian Sirius Passet fauna of N Greenland. The cephalic region is characterised by a pair of stout unsegmented appendages each bearing long spinose processes, and an anterior mouth. The trunk shows alternating rows of tubercles and transverse annulations along the axis, to which are attached 11 pairs of gill-bearing lateral lobes and lobopodous limbs. The caudal region is small, and bears two long tail spines. There is some evidence for circular musculature arranged around the trunk and a dorsal, longitudinal sinus, and several details of the muscular pharynx have been preserved.The combination of characters found inKerygmachelaallows it to be allied with the lobopods, represented in the extant fauna by the onychophorans, tardigrades, and possibly the pentastomids, and in the Cambrian fossil record by a morphologically diverse set of taxa, some of which are not assignable to the extant groupings. It also shares important characters with the previously problematic Burgess Shale formsOpabinia regalisWalcott andAnomalocarisWhiteaves, and the Sirius Passet form Pambdelurion Budd. These taxa together form a paraphyletic group at the base of the clade of biramous arthropods. The position of the so-called ‘Uniramia’ remains unclear. It can be demonstrated from the reconstruction of the arthropod stem-group that full arthropod segmentation has a different derivation from that of the annelids. In line with other recent analyses, this suggests that the ‘Articulata’ of Cuvier should be dismantled, and the arthropods considered to be a group of protostomes which are phylogenetically distinct from the classic spiralians. Arthropod affinities may rather lie with the other moulting animals, in the so-called ‘Ecdysozoa’.

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