Figure 3 - uploaded by Brian R. Pratt
Content may be subject to copyright.
Source publication
The ptychoparioid trilobite Blainia gregaria Walcott, 1916 is described for the first time from the late middle Cambrian (Series 3) of the Argentine Precordillera. It occurs commonly in the upper part of La Laja Formation, a carbonate platform succession that crops out in the Precordillera Oriental of San Juan where it reaches a thickness of some 6...
Contexts in source publication
Context 1
... values indicate a relatively wide intraspecific variation of some attributes but not others. Besides the variation in measured parameters, three endmember cranidial morphotypes are identified on the basis of intergrading differences in the preglabellar field (Figure 3). Type 1 exhibits a relatively long frontal area with broad, shallow anterior border furrow that widens medially towards the anterior glabellar furrow, forming a plectrum-like depression. ...
Context 2
... by other species attributed to Blainia and Glyphaspis including those not placed here in synonymy with B. gregaria. Cranidium type 1 with the median depression is exhibited by G. dearbornensis Deiss, 1939 (pl. 16, fig. 22). Cranidium type 2 with a relatively well impressed anterior border furrow occurs in: G. perconcava Poulsen, 1927 (pl. 17, fig. 3), G. cowanensis Resser, 1938 (pl. 8, fig. 39), G. tetonensis Resser, 1937 (Melzak andWestrop, 1994, pl. 3, fig. 2 fig. 10). Cranidium type 3 with a shallow anterior border furrow is seen in: Amecephalina curticei Resser, 1938 (pl. 8, fig. 59), A. coosensis Resser, 1938 (pl. 8, fig. 58), G. robusta Deiss, 1939 (pl. 16, fig. 12), G. ...
Context 3
... Glyphaspis including those not placed here in synonymy with B. gregaria. Cranidium type 1 with the median depression is exhibited by G. dearbornensis Deiss, 1939 (pl. 16, fig. 22). Cranidium type 2 with a relatively well impressed anterior border furrow occurs in: G. perconcava Poulsen, 1927 (pl. 17, fig. 3), G. cowanensis Resser, 1938 (pl. 8, fig. 39), G. tetonensis Resser, 1937 (Melzak andWestrop, 1994, pl. 3, fig. 2 fig. 10). Cranidium type 3 with a shallow anterior border furrow is seen in: Amecephalina curticei Resser, 1938 (pl. 8, fig. 59), A. coosensis Resser, 1938 (pl. 8, fig. 58), G. robusta Deiss, 1939 (pl. 16, fig. 12), G. storeyi Deiss, 1939 (pl. 16, fig. 35), G. ...
Context 4
... impressed anterior border furrow occurs in: G. perconcava Poulsen, 1927 (pl. 17, fig. 3), G. cowanensis Resser, 1938 (pl. 8, fig. 39), G. tetonensis Resser, 1937 (Melzak andWestrop, 1994, pl. 3, fig. 2 fig. 10). Cranidium type 3 with a shallow anterior border furrow is seen in: Amecephalina curticei Resser, 1938 (pl. 8, fig. 59), A. coosensis Resser, 1938 (pl. 8, fig. 58), G. robusta Deiss, 1939 (pl. 16, fig. 12), G. storeyi Deiss, 1939 (pl. 16, fig. 35), G. kwaguntensis Resser, 1945 (pl. 26, figs 2, 3), G. parkensis Rasetti, 1951 (pl. 34, figs 5, 6), G. cf. G. capella (Walcott, 1916(Schwimmer, 1989 fig. 3.13), and G. sp. 1 Melzak and Westrop, 1994 (pl. l4, fig. 12). On the other hand, specimens ...
Context 5
... fig. 3), G. cowanensis Resser, 1938 (pl. 8, fig. 39), G. tetonensis Resser, 1937 (Melzak andWestrop, 1994, pl. 3, fig. 2 fig. 10). Cranidium type 3 with a shallow anterior border furrow is seen in: Amecephalina curticei Resser, 1938 (pl. 8, fig. 59), A. coosensis Resser, 1938 (pl. 8, fig. 58), G. robusta Deiss, 1939 (pl. 16, fig. 12), G. storeyi Deiss, 1939 (pl. 16, fig. 35), G. kwaguntensis Resser, 1945 (pl. 26, figs 2, 3), G. parkensis Rasetti, 1951 (pl. 34, figs 5, 6), G. cf. G. capella (Walcott, 1916(Schwimmer, 1989 fig. 3.13), and G. sp. 1 Melzak and Westrop, 1994 (pl. l4, fig. 12). On the other hand, specimens attributed to G. tetonensis by Melzak and Westrop (1994) show less variation in the length ...
Context 6
... furrow is seen in: Amecephalina curticei Resser, 1938 (pl. 8, fig. 59), A. coosensis Resser, 1938 (pl. 8, fig. 58), G. robusta Deiss, 1939 (pl. 16, fig. 12), G. storeyi Deiss, 1939 (pl. 16, fig. 35), G. kwaguntensis Resser, 1945 (pl. 26, figs 2, 3), G. parkensis Rasetti, 1951 (pl. 34, figs 5, 6), G. cf. G. capella (Walcott, 1916(Schwimmer, 1989 fig. 3.13), and G. sp. 1 Melzak and Westrop, 1994 (pl. l4, fig. 12). On the other hand, specimens attributed to G. tetonensis by Melzak and Westrop (1994) show less variation in the length of the preglabellar ...
Context 7
... type 1 with no or just a minimal median indentation of the posterior border is exhibited by: G. perconcava Poulsen, 1927 (pl. 17 , fig. 4), G. cf. G. concava [sic] (Miller, 1936, pl. 8, fig. 17), G. sp. (Miller, 1936, pl. 8, fig. 39), G. cowanensis (Resser, 1938, pl. 8, fig. 39), G. levis Deiss, 1939, pl. 16, fig. 11 fig. 18), G. delicata Deiss, 1939 (pl. 16, fig. 23), G. similis Deiss, 1939 (pl. 16, fig. 26), G. cf. similis (Deiss, 1939, pl. 16, fig. 25), G. vulsa Resser, 1945 (pl. 22, fig. 12), G. tecta Resser, 1945 (pl. 22, fig. 15), G. kwaguntensis (Resser, ...
Context 8
... type 1 with no or just a minimal median indentation of the posterior border is exhibited by: G. perconcava Poulsen, 1927 (pl. 17 , fig. 4), G. cf. G. concava [sic] (Miller, 1936, pl. 8, fig. 17), G. sp. (Miller, 1936, pl. 8, fig. 39), G. cowanensis (Resser, 1938, pl. 8, fig. 39), G. levis Deiss, 1939, pl. 16, fig. 11 fig. 18), G. delicata Deiss, 1939 (pl. 16, fig. 23), G. similis Deiss, 1939 (pl. 16, fig. 26), G. cf. similis (Deiss, 1939, pl. 16, fig. 25), G. vulsa Resser, 1945 (pl. 22, fig. 12), G. tecta Resser, 1945 (pl. 22, fig. 15), G. kwaguntensis (Resser, 1945, pl. 25, fig. 13, pl. 26, figs 3, 4), G. ...
Context 9
... G. cowanensis (Resser, 1938, pl. 8, fig. 39), G. levis Deiss, 1939, pl. 16, fig. 11 fig. 18), G. delicata Deiss, 1939 (pl. 16, fig. 23), G. similis Deiss, 1939 (pl. 16, fig. 26), G. cf. similis (Deiss, 1939, pl. 16, fig. 25), G. vulsa Resser, 1945 (pl. 22, fig. 12), G. tecta Resser, 1945 (pl. 22, fig. 15), G. kwaguntensis (Resser, 1945, pl. 25, fig. 13, pl. 26, figs 3, 4), G. parkensis (Rasetti, 1951, pl. 34, figs 6, 7), B. buttsi (Rasetti, 1965, pl. 120, figs 6, 10), G. cf. parkensis (Hu, 1971, pl. 11, figs 26-28, 30), G. tetonensis (Melzak and Westrop, 1994, pl. 4, figs 6, 7, 10; as Americare tetonensisLochman and Hu, 1960, pl. 100, figs 48, 52, 53, 56), Asaphiscus gregarius ...
Context 10
... pl. 26, figs 3, 4), G. parkensis (Rasetti, 1951, pl. 34, figs 6, 7), B. buttsi (Rasetti, 1965, pl. ...
Context 11
... pl. 26, figs 3, 4), G. parkensis (Rasetti, 1951, pl. 34, figs 6, 7), B. buttsi (Rasetti, 1965, pl. 120, figs 6, 10), G. cf. parkensis (Hu, 1971, pl. 11, figs 26-28, 30), G. tetonensis (Melzak and Westrop, 1994, pl. 4, figs 6, 7, 10; as Americare tetonensisLochman and Hu, 1960, pl. 100, figs 48, 52, 53, 56), Asaphiscus gregarius (Schwimmer, 1989, fig. 3.10), and G. capella and G. cf. G. capella (Schwimmer, 1989, figs 3.17-3.19). Pygidium type 2 with a shallow median indentation of the posterior border is exhibited by: a second specimen of G. cowanensis (Resser, 1938, pl. 8, fig. 40) and B. buttsi (Rasetti, 1965, pl. 120, fig. 9), A. curticei (Resser, 1938, pl. 8, fig. 60), G. indenta ...
Context 12
... and G. capella and G. cf. G. capella (Schwimmer, 1989, figs 3.17-3.19). Pygidium type 2 with a shallow median indentation of the posterior border is exhibited by: a second specimen of G. cowanensis (Resser, 1938, pl. 8, fig. ...
Context 13
... pl. 4, figs 6, 7, 10; as Americare tetonensisLochman and Hu, 1960, pl. 100, figs 48, 52, 53, 56), Asaphiscus gregarius (Schwimmer, 1989, fig. 3.10), and G. capella and G. cf. G. capella (Schwimmer, 1989, figs 3.17-3.19). Pygidium type 2 with a shallow median indentation of the posterior border is exhibited by: a second specimen of G. cowanensis (Resser, 1938, pl. 8, fig. 40) and B. buttsi (Rasetti, 1965, pl. 120, fig. 9), A. curticei (Resser, 1938, pl. 8, fig. 60), G. indenta (Deiss, 1939, pl. 16, fig. 7), and G.? cf. G.? curticei (Melzak and Westrop, 1994, pl. 5, figs 1, 2). Pygidium type 3 with a deep median indentation is seen in G. dearbornensis (Deiss, 1939, pl. 16, fig. ...
Context 14
... fig. 3.10), and G. capella and G. cf. G. capella (Schwimmer, 1989, figs 3.17-3.19). Pygidium type 2 with a shallow median indentation of the posterior border is exhibited by: a second specimen of G. cowanensis (Resser, 1938, pl. 8, fig. 40) and B. buttsi (Rasetti, 1965, pl. 120, fig. 9), A. curticei (Resser, 1938, pl. 8, fig. 60), G. indenta (Deiss, 1939, pl. 16, fig. 7), and G.? cf. G.? curticei (Melzak and Westrop, 1994, pl. 5, figs 1, 2). Pygidium type 3 with a deep median indentation is seen in G. dearbornensis (Deiss, 1939, pl. 16, fig. ...
Similar publications
The Furongian (Upper Cambrian; Jiangshanian and Sunwaptan) Tunnel City Group (Lone Rock Formation and Mazomanie Formation), exposed in Wisconsin and Minnesota, represents a shallow-marine clastic environment during a time of exceptionally high sea level. Lithofacies from shoreface to transitional-offshore settings document deposition in a wave- and...
New and archival collections from the Chelsey Drive Group of the Avalon terrane of Cape Breton Island, Nova Scotia, Canada, yield late Cambrian trilobites and agnostoid arthropods with full convexity that contrast with compacted, often deformed material from shale and slate typical of Avalonian Britain. Four species of the agnostoid Lotagnostus for...
A new late Mississippian trilobite species, Kaskia pitkinensis, new species, is described from the Pitkin Formation of Arkansas. Kaskia pitkinensis, recovered from early Serpukhovian strata, is the youngest species of the Kaskia clade known in the United States. Kaskia c.f. K. wilsoni (Walter, 1924) also is illustrated. Cyrtoproetus kerhini, new sp...
Citations
... There is an extremely rich history of both traditional and geometric morphometric approaches aimed at furthering our understanding of varied aspects of trilobite evolution, across taxonomic scales. In fact, the wealth of these studies as applied to specific trilobite species or groups are too numerous to fully cover outside of a dedicated review (e.g., Abe and Lieberman, 2012;Bordonaro et al., 2013;Crônier et al., 2005Crônier et al., , 2004Crônier et al., , 1998Crônier and Fortey, 2006; Delabroye and Cronier, . CC-BY-NC-ND 4.0 International license made available under a (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. ...
Trilobite cephalic morphology impacted the autecology of individuals, and is critical for high- and low-level taxonomic assignments. Disparity in trilobite cephalon shape varied through time and was integral to the occupation of a diversity of ecological niches. To fully appreciate trilobite cephalic evolution, we must understand how this disparity varies, and what factors control cephalon morphometry. We explore the disparity of trilobite cephala through the Palaeozoic, and analyse the associations between cephalic morphometry and taxonomic assignment and geological Period, using a dataset of 983 2D trilobite cephalon outlines. Elliptical Fourier transformation visualised as a Principal Components Analysis suggests significant differences in morphospace occupation for order and Period groups, and comparisons of disparity measures also suggest significantly different disparities between the groups. Trilobite cephalic disparity peaks in the Ordovician and Devonian. The Cambrian–Ordovician expansion of morphospace occupation appears a result of radiation to new niches, and thus all trilobite orders were established by the late Ordovician. In comparison, the morphospace expansion from the Silurian to Devonian seems solely a result of within-niche diversification rather than novel niche occupation. However, analyses interrogating the regions of morphospace occupied, including centroid distances, average pairwise shape comparisons and Linear Discriminant Analysis demonstrate that, except for the order Harpida and the Cambrian and Ordovician Periods, order and geological Period could not be robustly predicted for an unknown trilobite. Further, Kmeans clustering analyses suggest the total dataset naturally subdivides into only seven groups that do not correspond with taxonomic orders, though Kmeans clusters do decrease in number through the Palaeozoic, aligning with findings of decreasing disparity.
... Howell, 1935Peronopsidae Westergård, 1936 Peronopsis bonnerensis Resser, 1939Peronopsis Hawle & Corda, 1847Ptychagnostidae Kobayashi, 1939 Ptychagnostus intermedius (Tullberg, 1880) Ptychagnostus Jaekel, 1909Trilobita Walch, 1771Eodiscida Kobayashi, 1939 Eodiscidae Raymond, 1913 Pagetia walcotti Rasetti, 1966Pagetia Walcott, 1916Redlichiida Richter, 1932Olenellidae Walcott, 1890Fremontella Harrington, 1956Olenellus Hall, 1861Corynexochida Kobayashi, 1935Dolichometopidae Walcott, 1916 Athabaskia anax (Walcott 1916) Bathyuriscus mendozanus (Rusconi, 1945) Glossopleura Poulsen 1927Dorypygidae Kobayashi, 1935Kootenia Walcott, 1889Oryctocephalidae Beecher, 1897 Oryctocephalites Resser, 1939Tonkinella Mansuy, 1916Zacanthoididae Swinnerton, 1915 Zacanthoides Walcott, 1888Illaenidae Hawle & Corda, 1847Leiostegiidae Bradley, 1925Phacopida Salter, 1864 Encrinuridae Angelin, 1854 Aulacopleurida Adrain, 2011Alokistocaridae Resser, 1939Ehmaniella Resser, 1937Elrathia Walcott, 1924 Elrathiella domensa Sundberg, 1994Elrathiella Poulsen, 1927Proehmaniella Sundberg 1994Marjumiidae Kobayashi, 1935Marjumia Walcott, 1916Telephinidae Marek, 1952Asaphida Salter, 1864emend. Fortey & Chatterton, 198 Raphiophoridae Angelin, 1854 Mendolaspis salagastensis Rusconi 1951 Trinucleidae Hawle & Corda, 1847Olenida Adrain, 2011Asaphiscidae Raymond 1924Blountia Walcott 1916 Cedariidae Raymond, 1937Cedaria Walcott 1924 Amecephalus arrojosensis (Lochman in Cooper et al., 1952) Eokochaspis nodosa Sundberg & McCollum, 2000Hadrocephalites Sundberg & McCollum, 2002 Kochaspis coosensis Resser 1938 Kochiella maxeyi Rasetti, 1951Kochiella Poulsen, 1927 Mexicella mexicana Lochman, 1948 Ptychobaba buttsi (Resser, 1938) Blainia gregaria (Walcott, 1916) Figure 5. A, Blainia gregaria (Walcott, 1916), pygidium (modified from Bordonaro et al., 2013). Scale bar = 5 mm. ...
... Additional information: The specimens are referred in published bibliography (Beresi et al., 2017;Bordonaro, 2014a & b;Bordonaro & Banchig, 2007;Bordonaro & Fojo, 2011;Bordonaro et al., 2008Bordonaro et al., , 2013Pratt & Bordonaro, 2014). ...
... In turn, Plesioparabolina mendozana Rusconi, 1945, from the outer 10 platform, was reassigned to the species Bathyuriscus mendozanus (Bordonaro & Fojo, 2011). Likewise, Glyphaspis Poulsen, 1927was synonymized with Blainia Walcott, 1916, and their 30 species with Blainia gregaria (Bordonaro et al., 2013). ...
... Acrocephalops gibber, the type species of Acrocephalops, was described by C. Poulsen (1927) Poulsen (1964), established that Acrocephalops occurred together with Glyphaspis perconcava Poulsen, 1927 and Glyphaspis parkensis Rasetti, 1951 in strata assigned to the Bathyuriscus-Elrathina Biozone of the Cape Wood Formation, but he neither illustrated nor described the new material. Bordonaro et al. (2013) regarded Glyphaspis Poulsen, 1927 as a junior subjective synonym of Blainia Walcott, 1916, which was followed with reservation by Peel (2020a;2021) (1976). Resser (1935Resser ( , 1938 assigned several Miaolingian species from the Appalachians to Acrocephalops but Schwimmer (1989) referred most of them to Alokistocare americanum (Walcott, 1916), which Sundberg (1999) transferred to Altiocculus Sundberg, 1994. ...
The ptychoparioid trilobites Eldoradia and Acrocephalops (Family Bolaspididae) are described from the middle Cambrian (Miaolingian Series) of northern Greenland (Laurentia). Eldoradia, originally described from the Secret Canyon Shale of Nevada, is recorded from south-western Wulff Land, North Greenland, where it occurs together with Modocia and Olenoides. Eldoradia caerulioris n. sp. is established. The occurrence of Eldoradia in the lower part of the Blue Cliffs Formation indicates a minimum late middle Cambrian age (Miaolingian Series, Guzhangian Stage) for the base of the formation. Type material of Acrocephalops, a relative of Eldoradia originally proposed on the basis of material from the Miaolingian Series (Wuliuan Stage) of Inglefield Land, North-West Greenland, is redescribed.
... Cambrian trilobites occur sporadically in the autochthonous platform succession (Bordonaro et al., 2008(Bordonaro et al., , 2013, but more commonly in large limestone olistostroliths in Ordovician shales (e.g., Bordonaro and Fojo, 2011;Tortello, 2011) which represent blocks of fossiliferous upper slope facies (Bordonaro, 2003). While the Laurentian aspect of the trilobite faunas is evident, relatively few species have been documented in sufficient detail to make firm biostratigraphic and biogeographic comparisons. ...
... All five of the taxa identified to the specific level from the lower Soldano Member have been described previously from Laurentian deposits, mostly from the Great Basin but also from western Canada and one from the southern Appalachians. The Laurentian affinity of the Precordillera persisted through the Cambrian (Benedetto et al. 1999;Bordonaro et al., 2008Bordonaro et al., , 2013 into the Middle Ordovician when Gondwanan taxa began to make their presence felt (Benedetto et al., 1999). ...
A tectonically undeformed portion of the lower part of La Laja Formation is exposed at Cerro El Molle near San Juan, Precordillera of western Argentina. It consists of shallow-water, variably argillaceous lime mudstone and sporadically interbedded bioclastic grainstone deposited in an inner shelf setting. The El Estero Member and the basal 0.2 m of the Soldano Member contain a trilobite fauna of olenelloids and 'simple' ptychoparioids indicative of the early Cambrian (series 2, stage 4; Dyeran stage of Laurentia). The succeeding 50 m of the lower Soldano Member yield trilobites characteristic of the early middle Cambrian (series 3, stage 5; Delamaran stage of Laurentia). In ascending order of occurrence, Amecephalus arrojosensis, Kochiella maxeyi and Eokochaspis nodosa, along with several other taxa, including Ptychobaba n. gen. (type species Ptychoparella buttsi), belong to the traditional lower Plagiura-Poliella Biozone. However, while this fauna is similar to that of the Great Basin, the nominative species of the Eokochaspsis nodosa and overlying Amecephalus arrojosensis biozones recognized in southern Nevada occur in reverse order in the Soldano Member. This suggests that the ranges of these species overlap, thereby reducing the temporal resolution in the Precordillera into a combined Amecephalus arrojosensis-Eokochaspis nodosa Biozone. Argillaceous lime mudstones at the top yield Mexicella mexicana, indicative of the Mexicella mexicana Biozone recognized in the Great Basin, which is equivalent to the traditional Albertella Biozone of Laurentia. Because corynexochids are almost absent, the low-diversity 'kochaspid'-dominated biofacies appears to typify the platform interior. The fauna is entirely Laurentian in composition, reinforcing notions of a close proximity of Cuyania to Laurentia during the Cambrian that enabled faunal migration and interchange. The absence of a late early Cambrian to early middle Cambrian hiatus correlative with the Hawke Bay Event, however, suggests no close affinity to the Iapetus-facing margin of eastern Laurentia.
... Cambrian trilobites occur sporadically in the autochthonous platform succession (Bordonaro et al., 2008(Bordonaro et al., , 2013, but more commonly in large limestone olistostroliths in Ordovician shales (e.g., Bordonaro and Fojo, 2011;Tortello, 2011) which represent blocks of fossiliferous upper slope facies (Bordonaro, 2003). While the Laurentian aspect of the trilobite faunas is evident, relatively few species have been documented in sufficient detail to make firm biostratigraphic and biogeographic comparisons. ...
... All five of the taxa identified to the specific level from the lower Soldano Member have been described previously from Laurentian deposits, mostly from the Great Basin but also from western Canada and one from the southern Appalachians. The Laurentian affinity of the Precordillera persisted through the Cambrian (Benedetto et al. 1999;Bordonaro et al., 2008Bordonaro et al., , 2013 into the Middle Ordovician when Gondwanan taxa began to make their presence felt (Benedetto et al., 1999). ...
A tectonically undeformed portion of the lower part of La Laja Formation is exposed at Cerro El Molle near San Juan, Precordillera of western Argentina. It consists of shallow-water, variably argillaceous lime mudstone and sporadically interbedded bioclastic grainstone deposited in an inner shelf setting. The El Estero Member and the basal 0.2 m of the Soldano Member contain a trilobite fauna of olenelloids and ‘simple’ ptychoparioids indicative of the early Cambrian (series 2, stage 4; Dyeran stage of Laurentia). The succeeding 50 m of the lower Soldano Member yield trilobites characteristic of the early middle Cambrian (series 3, stage 5; Delamaran stage of Laurentia). In ascending order of occurrence, Amecephalus arrojosensis , Kochiella maxeyi and Eokochaspis nodosa , along with several other taxa, including Ptychobaba n. gen. (type species Ptychoparella buttsi ), belong to the traditional lower Plagiura–Poliella Biozone. However, while this fauna is similar to that of the Great Basin, the nominative species of the Eokochaspsis nodosa and overlying Amecephalus arrojosensis biozones recognized in southern Nevada occur in reverse order in the Soldano Member. This suggests that the ranges of these species overlap, thereby reducing the temporal resolution in the Precordillera into a combined Amecephalus arrojosensis–Eokochaspis nodosa Biozone. Argillaceous lime mudstones at the top yield Mexicella mexicana , indicative of the Mexicella mexicana Biozone recognized in the Great Basin, which is equivalent to the traditional Albertella Biozone of Laurentia. Because corynexochids are almost absent, the low-diversity ‘kochaspid’-dominated biofacies appears to typify the platform interior. The fauna is entirely Laurentian in composition, reinforcing notions of a close proximity of Cuyania to Laurentia during the Cambrian that enabled faunal migration and interchange. The absence of a late early Cambrian to early middle Cambrian hiatus correlative with the Hawke Bay Event, however, suggests no close affinity to the Iapetus-facing margin of eastern Laurentia.
... The genus Totoralia Tortello and Sabattini, 2011 is previously described only from Mendoza, Argentina. This extension of distribution is in accord with the recognition that crustal fragments accreted to the Andean margin within the Precordillera terrane were derived from Laurentia and yield typical Laurentian Cambrian faunal assemblages (Thomas and Astini, 1996;Benedetto et al., 2009;Tortello and Sabattini, 2011;Bordonaro et al., 2013). ...
Burgess Shale-type faunas provide unique insights into the Cambrian "explosion". Their degree of representativeness of Cambrian marine life in general is, however, less easy to establish. One line of evidence is to consider only the skeletal component of a Burgess Shale-type fauna and compare that with a typical Cambrian assemblage. This paper describes a new species of helcionelloid mollusk (Totoralia reticulata n. sp.) from the middle Cambrian Burgess Shale of British Columbia. Whilst much rarer than the co-occurring smooth shelled helcionelloid Scenella amii, the strongly costate morphology of Totoralia reinforces comparisons with Cambrian shelly faunas. The extension of the range of Totoralia from Argentina to Canada adds support to the proposed derivation of the Precordillera terrane of Mendoza from Laurentia.
Trilobites were recovered from four cores of the middle Cambrian Earlie Formation in southwestern Saskatchewan. Fossils occur in silty mudstone with interbedded siltstone and limestone, deposited in the inner detrital belt of the craton interior, under low-energy, subtidal conditions. Taxa identified include Kootenia dawsoni (Walcott 1889), Asaphiscus wheeleri Meek 1873, Blainia gregaria Walcott 1916b, Parehmania princeps Deiss 1939b, Ehmania weedi Resser 1935, Bolaspis labrosa (Walcott 1916a), and corynexochid gen. and sp. indet., indicating an age ranging from the lower to upper Altiocculus subzone of the Ehmaniella Zone, upper Wuliuan Stage. The upper Eldon and lower Pika formations located farther west in subsurface Alberta and the Rocky Mountains are considered to be age equivalent. Biostratigraphy confirms that strata overlying the Basal Sandstone Unit are diachronous and become progressively younger eastward. The trilobite fauna is lower in diversity relative to those in temporally equivalent units in the Rocky Mountains as well as the Great Basin, indicating that it may have experienced some environmental stressors, and that seafloor colonization was sporadic and opportunistic.
The biogeographic distribution of 14 laurentian ptychoparioid trilobite of the La Laja Formation, Middle Cambrian (Series 3) from the San Juan Precordillera, western Argentina is analyzed. The trilobites were endemic Laurentian species with restricted access to open oceans that inhabited the inner parts of the carbonate platform that rimmed the North American craton. Its presence in the restricted carbonatic platform of the Argentine Precordillera and its absence in the carbonatic facies of East Gondwana, particularly in Antarctica – Australia, are incompatible with dispersal by oceanic equatorial currents across an Iapetus open ocean in a Cuyania para- autochthonous gondwanan model. Instead, it is compatible with peri-laurentian dispersion in an allochthonous laurentian model, but only if Cuyania was environmentally connected to southern Laurentia. A modified allochthonous Laurentian model where the northern Cuyania is physically and environmentally connected to the southern Appalachians is proposed to explain the dispersion of endemic faunas without having to cross an open ocean.
Specimens from the Wheeler and Marjum Formations of Utah comprising an elongate stipe with freely projecting conical thecae are described as dithecoid graptolites, the first reported from these units. The Wheeler Shale specimens, assigned to Archaeolafoea monegettae (Chapman, 1919), provide the first record of Archaeolafoea Chapman, 1919 from the Cambrian of Laurentia and show clear fusellar structure in backscattered electron images, confirming a graptolite affinity for this taxon. Mastigograptus sp., described on the basis of a single well-preserved specimen from the Marjum Formation, shows for the first time in a Cambrian mastigograptid an arrangement of thecae similar to that known for Ordovician representatives of the genus.
