Hostname: page-component-848d4c4894-x5gtn Total loading time: 0 Render date: 2024-06-02T08:51:45.666Z Has data issue: false hasContentIssue false
  • English
  • Français

Species-level phylogenetic analysis of pterocephaliids (Trilobita, Cambrian) from the Great Basin, western USA

Published online by Cambridge University Press:  14 July 2015

Melanie J. Hopkins
Melanie J. Hopkins*
Affiliation:
Department of the Geophysical Sciences, University of Chicago, 5734 S. Ellis Ave, Chicago, IL 60637, USA; current address: Department of Geology, Field Museum of Natural History, 1400 S. Lake Shore Drive, Chicago, Illinois 60605, USA,
Get access Rights & Permissions [Opens in a new window]

Abstract

Considerable systematic work devoted to late Cambrian trilobites includes very little species-level phylogenetic analysis. This paper presents the phylogenetic analysis of 36 species representing eight genera assigned to the Family Pterocephaliidae that occur in the Great Basin of the western United States during the Steptoean stage (Furongian). Continuous characters are treated in four different ways: discretization using finite mixture coding, discretization using gap-weighting, “as such” using ranges of values as implemented in the phylogeny program TNT, and exclusion altogether. Results indicate that even the inclusion of only a few continuous characters dramatically increases the resolution of nodes. Despite the different treatments of continuous characters, major features of the trees are shared across all results. The subfamily Pterocephaliinae is restricted to genera which possess a concave anterior border. Relative stratigraphic placement was estimated using a composite section built in CONOP and used to scale the tree topologies and to assess stratigraphic consistency. Although previously hypothesized multispecies evolutionary series are not supported by the results, tree topology, stratigraphic distribution, and optimized character state transformation support the interpretation of several sister taxa as direct ancestor-descendent pairs.

Type
Research Article
Information
Journal of Paleontology , Volume 85 , Issue 6 , November 2011 , pp. 1128 - 1153
Copyright
Copyright © The Paleontological Society 

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Adrain, J. M., Peters, S. E., and Westrop, S. R. 2009. The Marjuman trilobite Cedarina Lochman: Thoracic morphology, systematics, and new species from western Utah and eastern Nevada, U.S.A. Zootaxa, 2218: 35–58.CrossRefGoogle Scholar
Adrain, J. M. and Westrop, S. R. 2001. Stratigraphy, phylogeny, and species sampling in time and space, p. 291–322. In Adrain, J. M., Edgecombe, G. D., and Lieberman, B. S. (eds.), Fossils, Phylogeny, and Form. Topics in Geobiology, 19. Kluwer Academic/Plenum Publishers, New York.Google Scholar
Adrain, J. M. and Westrop, S. R. 2005. Late Cambrian ptychaspidid trilobites from western Utah: Implications for trilobite systematics and biostratigraphy. Geological Magazine, 142: 377–398.Google Scholar
Adrain, J. M. and Westrop, S. R. 2006. Notchpeakia, a new genus of Upper Cambrian (Sunwaptan) “entomaspidid” trilobites. Journal of Paleontology, 80: 1152–1171.Google Scholar
Akaike, H. 1974. A new look at the statistical model identification. IEEE Transactions on Automatic Control, 19: 716–723.Google Scholar
Almeida, M. T. and Bisby, F. A. 1984. A simple method for establishing taxonomic characters from measurement data. Taxon, 33: 405–409.CrossRefGoogle Scholar
Archie, J. W. 1985. Methods for coding variable morphological features for numerical taxonomic analysis. Systematic Zoology, 34: 326–345.Google Scholar
Baum, B. R. 1988. A simple procedure for establishing discrete characters from measurement data, applicable to cladistics. Taxon, 37: 63–70.Google Scholar
Bremer, K. 1988. The limits of amino acid sequence data in angiosperm phylogenetic reconstruction. Evolution, 42: 795–803.CrossRefGoogle ScholarPubMed
Burnham, K. P. and Anderson, D. R. 2002. Model Selection and Multimodel Inference. (second edition) Springer-Verlag, Inc., New York, 488 p.Google Scholar
Chappill, J. A. 1989. Quantitative characters in phylogenetic analysis. Cladistics, 5: 219–234.Google Scholar
Chatterton, B. D. E., Edgecombe, G. D., Speyer, S. E., Hunt, A. S., and Fortey, R. A. 1994. Ontogeny and relationships of Trinucleodea (Trilobita). Journal of Paleontology, 68: 523–540.Google Scholar
Chatterton, B. D. E. and Ludvigsen, R. 1998. Upper Steptoean (Upper Cambrian) trilobites from the McKay Group of southeastern British Columbia, Canada. Paleontological Society Memoir, 49: 1–43.Google Scholar
Colless, D. H. 1980. Congruence between morphometric and allozyme data for Menidia species: A reappraisal. Systematic Zoology, 29: 288–299.Google Scholar
Farris, J. 1970. Methods for computing Wagner trees. Systematic Zoology, 19: 83–92.Google Scholar
Foote, M. 1996. On the probability of ancestors in the fossil record. Paleobiology, 22: 141–151.Google Scholar
Fortey, R. A. 1997. Classification, p. 289–302. In Kaesler, R. L. (ed.), Treatise of Invertebrate Paleontology. Pt. O. Trilobita (Revised). Geological Society of America and University of Kansas Press, Lawrence.Google Scholar
Fortey, R. A. and Chatterton, B. D. E. 1988. Classification of the trilobite suborder Asaphina. Palaeontology, 31: 165–222.Google Scholar
Garcia-Cruz, J. and Sosa, V. 2006. Coding quantitative character data for phylogenetic analysis: A comparison of five methods. Systematic Biology, 31: 302–309.Google Scholar
Gogin, I. Ya. 1990. Novye pozdnekembriyskie trilobity Sette-Dabana (New Late Cambrian trilobites of the Sette-Daban). Ezhegodnik Vsesoyuznogo paleontologicheskogo obshchestva, 33: 140–152. (In Russian).Google Scholar
Goldman, N. 1988. Methods for discrete coding of morphological characters for numerical analysis. Cladistics, 4: 59–71.Google Scholar
Goloboff, P. A., Farris, J. S., and Nixon, K. C. 2008. TNT, a free program for phylogenetic analysis. Cladistics, 24: 774–786.Google Scholar
Goloboff, P. A., Mattoni, C. I., and Quinteros, A. S. 2006. Continuous characters analyzed as such. Cladistics, 22: 589–601.Google Scholar
Grant, R. E. 1962. Trilobite distribution, upper Franconia Formation (Upper Cambrian), southeastern Minnesota. Journal of Paleontology, 36: 965–998.Google Scholar
Guerrero, J. A., de Luna, E., and Sanchez-Hernandez, C. 2003. Morphometrics in the quantification of character state identity for the assessment of primary homology: An analysis of character variation of the genus Artibeus (Chiroptera: Phyllostomidae). Biological Journal of the Linnean Society, 80: 45–55.Google Scholar
Hall, J. and Whitfield, R. P. 1877. Paleontology: Fossils of the Potsdam Group. U.S. Geological Exploration 40th Parallel, 4: 199–231.Google Scholar
Hardy, M. C. 1985. Testing for adaptive radiation: The ptychaspid (Trilobita) biomere of the Late Cambrian, p. 379–397. In Valentine, J. W. (ed.), Phanerozoic Diversity Patterns. Princeton University Press.Google Scholar
Hohensee, S. R. and Stitt, J. H. 1989. Redeposited Elvinia zone (Upper Cambrian) trilobites from the Collier Shale, Ouachita Mountains, west-central Arkansas. Journal of Paleontology, 63: 857–879.Google Scholar
Hopkins, M. J. 2010. Intraspecific variation, its geographic structure, and the relationship between variation and duration, with examples from Cambrian trilobites and Recent fiddler crabs. Unpublished , University of Chicago, 375 p.Google Scholar
Hopkins, M. J. In press. How species longevity, intraspecific morphological variation, and geographic range size are related: A comparison using late Cambrian trilobites. Evolution.Google Scholar
Hughes, N. C. and Rushton, A. W. A. 1990. Computer-aided restoration of a Late Cambrian ceratopygid trilobite from Wales, and its phylogenetic implications. Palaeontology, 33: 429–445.Google Scholar
Hupé, P. 1953. Classe des trilobites. Traite de Paleontologie, 3.44–246.Google Scholar
Hurvich, C. M. and Tsai, C.-L. 1989. Regression and time series model selection in small samples. Biometrika, 76: 297–307.Google Scholar
Jell, P. A. and Adrain, J. M. 2003. Available generic names for trilobites. Memoirs of the Queensland Museum, 48: 331–553.Google Scholar
Kitching, I. J., Forey, P. L., Humphries, C. J., and Williams, D. M. 1998. Cladistics: The Theory and Practice of Parsimony Analysis (second edition). Systematics Association Publication No 11, 228 p.Google Scholar
Kobayashi, T. 1935. The Cambro–Ordovician formations and faunas of South Chosen. Paleontology. Pt. 3: Cambrian faunas of South Chosen with a special study on the Cambrian trilobite genera and families. Journal of the Faculty of Science, Imperial University of Tokyo (Section II), 4: 49–344.Google Scholar
Kobayashi, T. 1936. On the Parabolinella fauna from Province Jujuy, Argentina, with a note on the Olenidae. Japanese Journal of Geology and Geography, 13: 85–102.Google Scholar
Kobayashi, T. 1938. Upper Cambrian fossils from British Columbia with a discussion of the isolated occurrences of the so-called “Olenus” beds of Mt. Jubilee. Japanese Journal of Geology and Geography, 15: 150–192.Google Scholar
Kurtz, V. E. 1975. Franconian (Upper Cambrian) trilobite faunas from the Elvins Group of southeast Missouri. Journal of Paleontology, 49: 1009–1043.Google Scholar
Lazarenko, N. P. and Nikiforov, N. I. 1968. Complexes of trilobites from the Upper Cambrian deposits of the Kulumbe River (northwestern Siberian Platform). Uchenye Zapiski, 23: 20–80. (In Russian).Google Scholar
Lochman, C. 1938. Upper Cambrian faunas of the Cap Mountain Formation of Texas. Journal of Paleontology, 12: 72–85.Google Scholar
Lochman, C. 1940. Fauna of the basal Bonneterre Dolomite (Upper Cambrian) of southeastern Missouri. Journal of Paleontology, 14: 1–53.Google Scholar
Lochman, C. 1950. Upper Cambrian faunas of the Little Rocky Mountains, Montana. Journal of Paleontology, 24: 322–349.Google Scholar
Lochman, C. 1964. Upper Cambrian faunas from the subsurface Deadwood Formation, Williston Basin, Montana. Journal of Paleontology, 38: 33–60.Google Scholar
Lochman, C. and Duncan, D. 1944. Early Upper Cambrian faunas of central Montana. Geological Society of America Special Papers, 54, 181 p.Google Scholar
Lochman, C. and Hu, C.-H. 1960. Upper Cambrian faunas from the northwest Wind River Mountains, Wyoming, Pt. I. Journal of Paleontology, 34: 793–834.Google Scholar
Lochman, C. and Hu, C.-H. 1961. Upper Cambrian faunas from the northwest Wind River Mountains, Wyoming, Pt. II. Journal of Paleontology, 35: 125–146.Google Scholar
Lochman, C. and Hu, C.-H. 1962a. An Aphelaspis zone faunule from Logan, Montana. Journal of Paleontology, 36: 431–441.Google Scholar
Lochman, C. and Hu, C.-H. 1962b. Upper Cambrian faunas from the northwest Wind River Mountains, Wyoming, Pt. III. Journal of Paleontology, 36: 1–28.Google Scholar
Lochman-Balk, C. 1970. Upper Cambrian faunal patterns on the craton. Geological Society of America Bulletin, 81: 3197–3224.Google Scholar
Lochman-Balk, C. 1974. Late Dresbachian (Late Cambrian) biostratigraphy of North America. Geological Society of America Bulletin, 85: 135–140.Google Scholar
Lu, Y.-H. and Qian, Y.-Y. 1983. New zonation and correlation of the Upper Cambrian Changshanian Stage in North China. Acta Paleontologica Sinica, 22: 235–257.Google Scholar
Ludvigsen, R. 1991. The median suture of Asaphida: A monophyletic character? The Trilobite Papers, 3: 11–13.Google Scholar
Luo, H. 1983. New finds of trilobites from Late Cambrian in western Yunnan, p. 1–30. In Contributions to the Geology of the Qinghai-Xizang (Tibet) Plateau.Google Scholar
Michevich, M. F. and Johnson, M. S. 1976. Congruence between morphological and allozyme data in evolutionary inference and character evolution. Systematic Zoology, 25: 260–270.Google Scholar
Osleger, D. and Read, J. F. 1993. Comparative analysis of methods used to define eustatic variations in outcrop: Late Cambrian interbasinal sequence development. American Journal of Science, 293: 157–216.Google Scholar
Palmer, A. R. 1954. The faunas of the Riley Formation in central Texas. Journal of Paleontology, 28: 709–786.Google Scholar
Palmer, A. R. 1955. Upper Cambrian Agnostidae of the Eureka District, Nevada. Journal of Paleontology, 29: 86–101.Google Scholar
Palmer, A. R. 1956. The type species of Litocephalus Resser, 1937 (Trilobita). Journal of Paleontology, 30: 608–610.Google Scholar
Palmer, A. R. 1960. Trilobites of the Upper Cambrian Dunderberg Shale, Eureka District, Nevada. U.S. Geological Survey Professional Paper, 334-C: 53–109.Google Scholar
Palmer, A. R. 1962. Glyptagnostus and associated trilobites in the United States. U.S. Geological Survey Professional Paper, 374-F, 45 p.Google Scholar
Palmer, A. R. 1965a. Biomere: A new kind of biostratigraphic unit. Journal of Paleontology, 39: 149–153.Google Scholar
Palmer, A. R. 1965b. Trilobites of the Late Cambrian Pterocephaliid biomere in the Great Basin, United States. U.S. Geological Survey Professional Paper, 493, 105 p.Google Scholar
Palmer, A. R. 1968. Cambrian trilobites of east-central Alaska. U.S. Geological Survey Professional Paper, 559-B, 115 p.Google Scholar
Palmer, A. R. 1979. Biomere boundaries re-examined. Alcheringa, 3: 33–41.Google Scholar
Palmer, A. R. 1981. Subdivision of the Sauk sequence, p. 160–162. In Taylor, M. E. (ed.), Short Papers for the Second International Symposium on the Cambrian System. U.S. Geological Survey Open-File Report 81–743.Google Scholar
Palmer, A. R. 1982. Biomere boundaries: a possible test for extraterrestrial perturbation of the biosphere, p. 469–476. In Silver, L. T. and Schultz, P. H. (eds.), Geological Implications of Impacts of Large Asteroids and Comets on the Earth. Geological Society of America Special Paper 190.Google Scholar
Park, T.-Y. and Choi, D. K. 2009. Post-embryonic development of the Furongian (Late Cambrian) trilobites Tsinania canens: implications for life mode and phylogeny. Evolution and Development, 11: 441–455.Google Scholar
Peng, S. 1992. Upper Cambrian biostratigraphy and trilobite faunas of the Cili-Taoyuan area, northwestern Hunan, China. Memoirs of the Association of Australasian Palaeontologists, 13, 119 p.Google Scholar
Peng, S., Babcock, J. A., and Lin, H. 2004. Polymerid Trilobites from the Cambrian of Northwestern Hunan, China. Vol. 2: Ptychopariida, Eodiscida, and undetermined forms. Science Press, Beijing, 355 p.Google Scholar
Pratt, B. R. 1992. Trilobites of the Marjuman and Steptoean stages (Upper Cambrian), Rabbitkettle Formation, southern Mackenzie Mountains, northwest Canada. Paleontographica Canadiana, No. 9, 179 p.Google Scholar
Qian, Y.-Y. 1994. Trilobites from Middle Upper Cambrian (Changshan Stage) of north and northeast China. Palaeontologia Sinica, Vol. 183, 190 p.Google Scholar
Qiu, H.-A., Lu, Y.-H., Zhu, Z.-L., Bi, D.-C., Lin, T.-R., Zhou, Z.-Y., Zhang, Q.-Z., Qian, Y.-Y., Ju, T.-Y., Han, N.-R., and Wei, X.-Z. 1983. Trilobita, p. 28–254, 574–609, pl. 211–288. In Paleontological Atlas of East China, 1, Early Paleozoic Vol. Geological Publishing House, Beijing. (In Chinese).Google Scholar
Rae, T. C. 1998. The logical basis for the use of continuous characters in phylogenetic systematics. Cladistics, 14: 221–228.CrossRefGoogle ScholarPubMed
Resser, C. E. 1935. Nomenclature of some Cambrian trilobites. Smithsonian Miscellaneous Collections, 93, 46 p.Google Scholar
Resser, C. E. 1937. Third contribution to nomenclature of Cambrian trilobites. Smithsonian Miscellaneous Collections, 95, 29 p.Google Scholar
Resser, C. E. 1938. Fourth contribution to nomenclature of Cambrian fossils. Smithsonian Miscellaneous Collections, 97, 43 p.Google Scholar
Resser, C. E. 1942. New Upper Cambrian trilobites. Smithsonian Miscellaneous Collections, 103, 136 p.Google Scholar
Roemer, F. 1849. Texas, mit besondered Rücksicht auf deutsche Auswanderung und die physischen Verhältnisse des Landes nach eigener Beobachtung geschildert, Bonn, 464 p.Google Scholar
Rozova, A. V. 1963. Biostratigraphic scheme of the upper and upper-middle Cambrian and new upper Cambrian trilobites. Geologiya i Geofizika, 9: 3–20.Google Scholar
Sadler, P. M., Kemple, W. G., and Kooser, M. A. 2003. Contents of the compact disc: CONOP9 Programs for solving the stratigraphic correlation and seriation problems as constrained optimization, p. 461–465. In Harries, P. J. (ed.), Approaches in High-Resolution Stratigraphic Paleontology, Topics in Geobiology, 21. Kluwer Academic Publishers, Dordrecht.Google Scholar
Shaw, A. B. 1957. Quantitative trilobite studies II. Measurement of the dorsal shell of non-agnostidean trilobites. Journal of Paleontology, 31: 193–207.Google Scholar
Sheets, H. D. 2003. FMCBox. Canisius College, Buffalo, New York.Google Scholar
Sokal, R. R. and Rohlf, F. J. 1995. Biometry (third edition). W. H. Freeman and Co., New York, 887 p.Google Scholar
Stevens, P. F. 1991. Character states, morphological variation, and phylogenetic analysis: A review. Systematic Botany, 16: 553–583.Google Scholar
Stitt, J. H. 1971a. Cambrian–Ordovician trilobites, western Arbuckle Mountains. Oklahoma Geological Survey Bulletin, 110, 83 p.Google Scholar
Stitt, J. H. 1971b. Repeating evolutionary patterns in Late Cambrian trilobite biomeres. Journal of Paleontology, 45: 178–181.Google Scholar
Stitt, J. H. 1975. Adaptive radiation, trilobite paleoecology, and extinction, Ptychaspid Biomere, Late Cambrian of Oklahoma. Fossils and Strata, 4: 381–390.Google Scholar
Stitt, J. H. 1977. Late Cambrian and earliest Ordovician trilobites, Wichita Mountains area, Oklahoma. Oklahoma Geological Survey Bulletin, 124, 79 p.Google Scholar
Stitt, J. H. 1998. Trilobites from the Cedarina dakotaensis zone, lowermost part of the Deadwood Formation (Marjuman State, Upper Cambrian), Black Hills, South Dakota. Journal of Paleontology, 72: 1030–1046.Google Scholar
Stitt, J. H. and Perfetta, P. J. 2000. Trilobites, biostratigraphy, and lithostratigraphy of the Crepicephalus and Aphelaspis zones, lower Deadwood Formation (Marjuman and Steptoean stages, Upper Cambrian), Black Hills, South Dakota. Journal of Paleontology, 74: 199–223.Google Scholar
Stitt, J. H., Rucker, J. D., Boyer, N. D., and Hart, W. D. 1994. New Elvinia zone (Upper Cambrian) trilobites from new localities in the Collier Shale, Ouachita Mountains, Arkansas. Journal of Paleontology, 68: 518–523.Google Scholar
Strait, D. S., Moniz, M. A., and Strait, P. T. 1996. Finite mixture coding: A new approach to coding continuous characters. Systematic Biology, 45: 67–78.Google Scholar
Sun, Y.-C. 1935. The Upper Cambrian trilobites faunas of North China. Palaeontologia Sinica series B, Vol. 7, 93 p.Google Scholar
Swiderski, D. L., Zelditch, M. L., and Fink, W. L. 1998. Why morphometrics is not special: Coding quantitative data for phylogenetic analysis. Systematic Biology, 47: 508–519.Google Scholar
Swofford, D. L. 1998. PAUP*: Phylogenetic analysis using parsimony* 4.0. Sinauer, Sunderland, MS.Google Scholar
Thiele, K. 1993. The holy grail of the perfect character: The cladistic treatment of morphometric data. Cladistics, 9: 275–304.Google Scholar
Thorpe, R. S. 1984. Coding morphometric characters for constructing distance Wagner networks. Evolution, 38: 244–255.Google Scholar
Ulrich, E. O. 1924. Notes on new names in table of formations and on physical evidence of breaks between Paleozoic systems in Wisconsin. Transactions of the Wisconsin Academy of Science, Arts, and Letters, 21: 71–107.Google Scholar
Wagner, P. J. and Erwin, D. H. 1995. Phylogenetic patterns as tests of speciation models, p. 87–122. In Erwin, D. H. and Anstey, R. L. (eds.), New Approaches to studying speciation in the fossil record. Columbia University Press, New York.Google Scholar
Walcott, C. D. 1884. Paleontology of the Eureka District. U.S. Geological Survey Monographs, 8, 298 p.Google Scholar
Walcott, C. D. 1890. Description of new forms of Upper Cambrian fossils. U.S. National Museum Proceedings, 13: 267–279.Google Scholar
Walcott, C. D. 1912. New York Potsdam-Hoyt fauna. Smithsonian Miscellaneous Collections, 57: 251–304.Google Scholar
Walcott, C. D. 1916. Cambrian Geology and Paleontology III. No. 5, Cambrian Trilobites. Smithsonian Miscellaneous Collections, 64: 303–456.Google Scholar
Walcott, C. D. 1924. Cambrian Geology and Paleontology V. No. 2, Cambrian and Ozarkian trilobites. Smithsonian Miscellaneous Collections, 75: 53–60.Google Scholar
Westrop, S. R. 1986. Trilobites of the Upper Cambrian Sunwaptan Stage, southern Canadian Rocky Mountains, Alberta. Paleontographica Canadiana, No. 3, 179 p.Google Scholar
Westrop, S. R. 1988. Trilobite diversity patterns in an Upper Cambrian stage. Paleobiology, 14: 401–409.Google Scholar
Westrop, S. R. 1989. Macroevolutionary implications of mass extinction-evidence from an Upper Cambrian stage boundary. Paleobiology, 15: 46–52.Google Scholar
Westrop, S. R. 1996. Temporal persistence and stability of Cambrian biofacies: Sunwaptan (Upper Cambrian) trilobite faunas of North America. Palaeogeography, Palaeoclimatology, Palaeoecology, 127: 33–46.Google Scholar
Westrop, S. R. and Adrain, J. M. 2007. Bartonaspis new genus, a trilobite species complex from the base of the Upper Cambrian Sunwaptan Stage in North America. Canadian Journal of Earth Sciences, 44: 987–1003.Google Scholar
Westrop, S. R. and Adrain, J. M. 2009. The late Cambrian (Furongian; Steptoean) trilobite genus Xenocheilos Wilson, 1949: Systematics and biostratigraphic significance. Memoirs of the Association of Australasian Palaeontologists, 37: 351–368.Google Scholar
Westrop, S. R., Eoff, J. D., Ng, T.-W., Dengler, A. A., and Adrain, J. M. 2008. Classification of the Late Cambrian (Steptoean) trilobite genera Cheilocephalus Berkey, 1898 and Oligometopus Resser, 1936 from Laurentia. Canadian Journal of Earth Sciences, 45: 725–744.Google Scholar
Westrop, S. R. and Ludvigsen, R. 1987. Biogeographic control of trilobite mass extinction at an Upper Cambrian “biomere” boundary. Paleobiology, 13: 84–99.Google Scholar
Westrop, S. R. and Ludvigsen, R. 2000. The Late Cambrian (Marjuman) trilobites genus Hysteropleura Raymond from the Cow Head Group, western Newfoundland. Journal of Paleontology, 74: 1020–1030.Google Scholar
Westrop, S. R., Poole, R. A. W., and Adrain, J. M. 2010. Systematics of Dokimocephalus and related trilobites from the Late Cambrian (Steptoean; Millardan and Furongian series) of Laurentian North America. Journal of Systematic Palaeontology, 8: 545–606.Google Scholar
Whittington, H. B. 2003. The Upper Cambrian trilobites Plethopeltis and Leiocoryphe: Morphology, paedomorphism, classification. Journal of Paleontology, 77: 698–705.Google Scholar
Whittington, H. B. and Kelly, S. R. A. 1997. Morphological terms applied to Trilobita, p. 313–329. In Kaesler, R. L. (ed.), Treatise on Invertebrate Paleontology. Pt. O. Arthropoda 1, Trilobita, Revised. Geological Society of America and University of Kansas Press, Lawrence.Google Scholar
Wiens, J. J. 2001. Character analysis in morphological phylogenetics: Problems and solutions. Systematic Biology, 50: 689–699.Google Scholar
Wills, M. A. 1999. Congruence between phylogeny and stratigraphy: Randomization tests and the gap excess ratio. Systematic Biology, 48: 559–580.Google Scholar
Yuan, J.-L. and Yin, G.-Z. 1998. New polymerid trilobites from the Chefu Formation in early Late Cambrian of eastern Guizhou. Acta Palaeontologica Sinica, 37: 138–172.Google Scholar
Zhu, X.-J., Hughes, N. C., and Peng, S.-C. 2007. On a new species of Shergoldia Zhang & Jell, 1987 (Trilobita), the family Tsinaniidae and the order Asaphida, p. 243–353. In Laurie, J. R. and Paterson, J. R. (eds.), Papers in Honour of John H. Shergold 1938–2006. Memoirs of the Association of Australasian Palaeontologists, 34.Google Scholar