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The oldest described eurypterid: a giant Middle Ordovician (Darriwilian) megalograptid from the Winneshiek Lagerstätte of Iowa.

Lamsdell JC, Briggs DE, Liu HP, Witzke BJ, McKay RM - BMC Evol. Biol. (2015)

Bottom Line: Phylogenetic analysis places Pentecopterus at the base of the Megalograptidae, united with the two genera previously assigned to this family by the shared possession of two or more pairs of spines per podomere on prosomal appendage IV, a reduction of all spines except the pair on the penultimate podomere of appendage V, and an ornamentation of guttalate scales, including angular scales along the posterior margin of the dorsal tergites and in longitudinal rows along the tergites.The relatively derived position of megalograptids within the eurypterids indicates that most eurypterid clades were present by the Middle Ordovician.The high degree of appendage specialization in eurypterids is only matched by arachnids within chelicerates, supporting a sister taxon relationship between them.

View Article: PubMed Central - PubMed

Affiliation: Department of Geology and Geophysics, Yale University, 210 Whitney Avenue, New Haven, CT, 06511, USA. james.lamsdell@yale.edu.

ABSTRACT

Background: Eurypterids are a diverse group of chelicerates known from ~250 species with a sparse Ordovician record currently comprising 11 species; the oldest fully documented example is from the Sandbian of Avalonia. The Middle Ordovician (Darriwilian) fauna of the Winneshiek Lagerstätte includes a new eurypterid species represented by more than 150 specimens, including some juveniles, preserved as carbonaceous cuticular remains. This taxon represents the oldest described eurypterid, extending the documented range of the group back some 9 million years.

Results: The new eurypterid species is described as Pentecopterus decorahensis gen. et sp. nov.. Phylogenetic analysis places Pentecopterus at the base of the Megalograptidae, united with the two genera previously assigned to this family by the shared possession of two or more pairs of spines per podomere on prosomal appendage IV, a reduction of all spines except the pair on the penultimate podomere of appendage V, and an ornamentation of guttalate scales, including angular scales along the posterior margin of the dorsal tergites and in longitudinal rows along the tergites. The morphology of Pentecopterus reveals that the Megalograptidae are representatives of the derived carcinosomatoid clade and not basal eurypterids as previously interpreted.

Conclusions: The relatively derived position of megalograptids within the eurypterids indicates that most eurypterid clades were present by the Middle Ordovician. Eurypterids either underwent an explosive radiation soon after their origination, or earlier representatives, perhaps Cambrian in age, remain to be discovered. The available instars of Pentecopterus decorahensis suggest that eurypterids underwent extreme appendage differentiation during development, a potentially unique condition among chelicerates. The high degree of appendage specialization in eurypterids is only matched by arachnids within chelicerates, supporting a sister taxon relationship between them.

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Limulus polyphemus and Pentecopterus decorahensis, cuticular features of tergites. aLimulus polyphemus, cracking of the cuticular surface. b–qPentecopterus decorahensis, mesosomal tergites. b SUI 140020, portion of tergite showing row of enlarged scales and cracking of the cuticle. c SUI 140044, sparse scale ornamentation and cracking of the surface. d SUI 140039, weathered portion of cuticle showing advanced stages of cracking. e SUI 140046, regular scale ornament. f SUI 139954, lateral portions of articulated tergites. g SUI 140038, anterior portion of tergite showing the articulating facet devoid of ornamentation. h SUI 140027, tergite showing row of enlarged scales and posterior doublure. i SUI 140042, smooth anterior articulating facet and central row of enlarged guttalate scales. j SUI 140043, scale ornament. k SUI 140057, lateral portion of tergite showing ancillary row of scales along margin. l SUI 140045, anterior articulating facet of tergite. m SUI 140026, widely spaced follicles. n SUI 140028, uniform scale ornament. o SUI 140021, showing faint cracking of the cuticle. p SUI 140022, merging of scales towards posterior of tergite and fragment of posterior doublure. q SUI 140025, broadening and merging of rounded scales towards rear of tergite. AF = articulating facet, CC = cuticular cracking, FO = follicles, PD = posterior doublure, SC = scales, SR = scale row. Scale bars = 10 mm
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Fig16: Limulus polyphemus and Pentecopterus decorahensis, cuticular features of tergites. aLimulus polyphemus, cracking of the cuticular surface. b–qPentecopterus decorahensis, mesosomal tergites. b SUI 140020, portion of tergite showing row of enlarged scales and cracking of the cuticle. c SUI 140044, sparse scale ornamentation and cracking of the surface. d SUI 140039, weathered portion of cuticle showing advanced stages of cracking. e SUI 140046, regular scale ornament. f SUI 139954, lateral portions of articulated tergites. g SUI 140038, anterior portion of tergite showing the articulating facet devoid of ornamentation. h SUI 140027, tergite showing row of enlarged scales and posterior doublure. i SUI 140042, smooth anterior articulating facet and central row of enlarged guttalate scales. j SUI 140043, scale ornament. k SUI 140057, lateral portion of tergite showing ancillary row of scales along margin. l SUI 140045, anterior articulating facet of tergite. m SUI 140026, widely spaced follicles. n SUI 140028, uniform scale ornament. o SUI 140021, showing faint cracking of the cuticle. p SUI 140022, merging of scales towards posterior of tergite and fragment of posterior doublure. q SUI 140025, broadening and merging of rounded scales towards rear of tergite. AF = articulating facet, CC = cuticular cracking, FO = follicles, PD = posterior doublure, SC = scales, SR = scale row. Scale bars = 10 mm

Mentions: Figures 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 23 and 24Fig. 1


The oldest described eurypterid: a giant Middle Ordovician (Darriwilian) megalograptid from the Winneshiek Lagerstätte of Iowa.

Lamsdell JC, Briggs DE, Liu HP, Witzke BJ, McKay RM - BMC Evol. Biol. (2015)

Limulus polyphemus and Pentecopterus decorahensis, cuticular features of tergites. aLimulus polyphemus, cracking of the cuticular surface. b–qPentecopterus decorahensis, mesosomal tergites. b SUI 140020, portion of tergite showing row of enlarged scales and cracking of the cuticle. c SUI 140044, sparse scale ornamentation and cracking of the surface. d SUI 140039, weathered portion of cuticle showing advanced stages of cracking. e SUI 140046, regular scale ornament. f SUI 139954, lateral portions of articulated tergites. g SUI 140038, anterior portion of tergite showing the articulating facet devoid of ornamentation. h SUI 140027, tergite showing row of enlarged scales and posterior doublure. i SUI 140042, smooth anterior articulating facet and central row of enlarged guttalate scales. j SUI 140043, scale ornament. k SUI 140057, lateral portion of tergite showing ancillary row of scales along margin. l SUI 140045, anterior articulating facet of tergite. m SUI 140026, widely spaced follicles. n SUI 140028, uniform scale ornament. o SUI 140021, showing faint cracking of the cuticle. p SUI 140022, merging of scales towards posterior of tergite and fragment of posterior doublure. q SUI 140025, broadening and merging of rounded scales towards rear of tergite. AF = articulating facet, CC = cuticular cracking, FO = follicles, PD = posterior doublure, SC = scales, SR = scale row. Scale bars = 10 mm
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4556007&req=5

Fig16: Limulus polyphemus and Pentecopterus decorahensis, cuticular features of tergites. aLimulus polyphemus, cracking of the cuticular surface. b–qPentecopterus decorahensis, mesosomal tergites. b SUI 140020, portion of tergite showing row of enlarged scales and cracking of the cuticle. c SUI 140044, sparse scale ornamentation and cracking of the surface. d SUI 140039, weathered portion of cuticle showing advanced stages of cracking. e SUI 140046, regular scale ornament. f SUI 139954, lateral portions of articulated tergites. g SUI 140038, anterior portion of tergite showing the articulating facet devoid of ornamentation. h SUI 140027, tergite showing row of enlarged scales and posterior doublure. i SUI 140042, smooth anterior articulating facet and central row of enlarged guttalate scales. j SUI 140043, scale ornament. k SUI 140057, lateral portion of tergite showing ancillary row of scales along margin. l SUI 140045, anterior articulating facet of tergite. m SUI 140026, widely spaced follicles. n SUI 140028, uniform scale ornament. o SUI 140021, showing faint cracking of the cuticle. p SUI 140022, merging of scales towards posterior of tergite and fragment of posterior doublure. q SUI 140025, broadening and merging of rounded scales towards rear of tergite. AF = articulating facet, CC = cuticular cracking, FO = follicles, PD = posterior doublure, SC = scales, SR = scale row. Scale bars = 10 mm
Mentions: Figures 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 23 and 24Fig. 1

Bottom Line: Phylogenetic analysis places Pentecopterus at the base of the Megalograptidae, united with the two genera previously assigned to this family by the shared possession of two or more pairs of spines per podomere on prosomal appendage IV, a reduction of all spines except the pair on the penultimate podomere of appendage V, and an ornamentation of guttalate scales, including angular scales along the posterior margin of the dorsal tergites and in longitudinal rows along the tergites.The relatively derived position of megalograptids within the eurypterids indicates that most eurypterid clades were present by the Middle Ordovician.The high degree of appendage specialization in eurypterids is only matched by arachnids within chelicerates, supporting a sister taxon relationship between them.

View Article: PubMed Central - PubMed

Affiliation: Department of Geology and Geophysics, Yale University, 210 Whitney Avenue, New Haven, CT, 06511, USA. james.lamsdell@yale.edu.

ABSTRACT

Background: Eurypterids are a diverse group of chelicerates known from ~250 species with a sparse Ordovician record currently comprising 11 species; the oldest fully documented example is from the Sandbian of Avalonia. The Middle Ordovician (Darriwilian) fauna of the Winneshiek Lagerstätte includes a new eurypterid species represented by more than 150 specimens, including some juveniles, preserved as carbonaceous cuticular remains. This taxon represents the oldest described eurypterid, extending the documented range of the group back some 9 million years.

Results: The new eurypterid species is described as Pentecopterus decorahensis gen. et sp. nov.. Phylogenetic analysis places Pentecopterus at the base of the Megalograptidae, united with the two genera previously assigned to this family by the shared possession of two or more pairs of spines per podomere on prosomal appendage IV, a reduction of all spines except the pair on the penultimate podomere of appendage V, and an ornamentation of guttalate scales, including angular scales along the posterior margin of the dorsal tergites and in longitudinal rows along the tergites. The morphology of Pentecopterus reveals that the Megalograptidae are representatives of the derived carcinosomatoid clade and not basal eurypterids as previously interpreted.

Conclusions: The relatively derived position of megalograptids within the eurypterids indicates that most eurypterid clades were present by the Middle Ordovician. Eurypterids either underwent an explosive radiation soon after their origination, or earlier representatives, perhaps Cambrian in age, remain to be discovered. The available instars of Pentecopterus decorahensis suggest that eurypterids underwent extreme appendage differentiation during development, a potentially unique condition among chelicerates. The high degree of appendage specialization in eurypterids is only matched by arachnids within chelicerates, supporting a sister taxon relationship between them.

Show MeSH
Related in: MedlinePlus