Reassessment of the phylogenetic position of conulariids (?Ediacaran‐Triassic) within the subphylum medusozoa (phylum cnidaria)

Abstract

SYNOPSIS Fossil taxa of uncertain phylogenetic affinities can play a crucial role in the analysis of character evolution within major extant groups. Marques & Collins (2004) concluded that conulariids (?Ediacaran-Triassic) are an extinct group of medusozoan cnidarians most closely related to Stauromedusae. However, only six of the 87 characters used by these authors can be observed in conulariid fossils. Rescoring the character states of conulariids in a conservative manner yields a new hypothesis for the phylogenetic position of conulariids, namely that they are the sister group of the scyphozoan order Coronatae rather than Stauromedusae, which is revealed as the earliest diverging lineage of Medusozoa. This new hypothesis also implies several different sequences of character evolution within Cnidaria. Specifically, the presence of a periderm completely covering the polyp in conulariids and coronates appears to be derived within Scyphozoa. Strobilation appears to be a synapomorphy uniting conulariids, Coronatae, Rhizostomeae and Semaeostomeae. This result supports the controversial interpretation of one exceptionally preserved conulariid that potentially shows that these animals produced ephyrae by strobilation. Finally, the pelagic adult medusa stage and the giant fibre nerve net appear to be features that are derived within Medusozoa.

Phylogenetics of Hydroidolina (Hydrozoa: Cnidaria)

“…Although our analyses and previous molecular phylogenetic analyses (Marques & Collins, 2000;Marques, 2001a;Collins, 2002;Collins et al, 2006;Van Iten et al, 2006) do not support the monophyly of Anthoathecata, the dissolution or re-definition of Anthoathecata is premature and should await clarification of relationships between major hydroidolinan clades. Capitata in the traditional sense comprises two clades, the Aplanulata, recognized by the lack of a free-swimming planula (Petersen, 1990) and Capitata sensu stricto.…”

Embryos, polyps and medusae of the Early Cambrian scyphozoan Olivooides

“…Their shared similarities include an annulated conical test, fine longitudinal sculpture and a bluntly tapering apex with radial folds. Conulariids, in turn, share characteristics with coronate scyphozoans including, in particular, a conical, two-layered, peridermal sheath ornamented with transverse annulations and fine longitudinal striations, that completely encloses the polyp, as well as evidence of strobilation; certain conulariids and coronates also exhibit tetramerally arranged internal peridermal projections, seriated in coronates and some but not all conulariids, and located in conulariids at positions interpreted as homologous to the perradii and interradii of coronates and other scyphozoans [23,[24][25][26][27]. Evidence for a cnidarian affinity for conulariids may be compelling because of their similarities to coronate scyphozoans [26,28,29].…”

Conuláridos misisípicos de Nochixtlán, Oaxaca, México: consideraciones sistemáticas, estratigráficas y paleobiogeográficas

“…Para América del Norte se han referido en Estados Unidos de América (Driscoll, 1963;Babcock & Feldmann, 1986a;Fraunfelter & Jennings, 1988;van Iten & Cox, 1992;van Iten et al, 1996;Hughes et al, 2000;Weldon & Shi, 2003;van Iten et al, 2005;van Iten et al, 2006). También existen reportes para Europa (Steul, 1984;Jerre, 1994;Brood, 1995;McKinney et al, 1995;van Iten et al, 2005), África (Babcock et al, 1995;van Iten et al, 2008) y Asia (Ivanstov & Fedonkin, 2002;van Iten et al, 2013).…”

“…Oponentes de esta hipótesis ofrecen una idea alternativa basada en similitudes homólogas que sólo son compartidas por los conuláridos y organismos que están fuera del grupo de los cnidarios, constituyendo un phylum extinto, probablemente tripoblástico (Kozlowski, 1968;Steul, 1984;Babcock & Feldmann, 1986a;Babcock, 1991;Brood, 1995). Sin embargo, van Iten et al (2006) proponen una hipótesis en la cual los conuláridos son considerados el grupo hermano del orden Coronatae; esta hipótesis implica diferencias en la secuencia de la evolución de algunos caracteres dentro de los cnidarios, específi camente, el peridermo que cubre completamente a los pólipos en los conuláridos y en los coronados parece derivar de los Scyphozoa; por otra parte la estrobilación es una sinapomorfía que une a los conuláridos con los órdenes Coronatae, Rhizostomeae y Semaeostomeae; lo anterior apoya la interpretación controversial de un conulárido excepcionalmente conservado que muestra potencialmente que estos animales producían brazos por estrobilación (van Iten, 1989(van Iten, , 1991a.…”