Phylogeny of Early Cretaceous spatangoids (Echinodermata: Echinoidea) and taxonomic implications

Abstract

ABSTRACT. A phylogenetic analysis of 36 species provides a test for the taxonomy and the history of Early Cretaceous spatangoids. Most taxonomic units from genera to suborders are consistent with the proposed phylogenetic framework. We retain Hemiasterina, Micrasterina, Hemiasteridae, Schizasteridae, Hemiaster, Heteraster, Mecaster, and Periaster as original monophyletic groups. However, all of these clades originate without the classical apomorphies normally ascribed to them. We suggest a revision of their diagnoses and of the generic attributions of basal species. Some illdefined, 'primitive', and paraphyletic taxa are recognised: Toxaster, Epiaster, Palhemiaster, and Toxasteridae. Even if they do not have phylogenetic meaning, they are retained here, pending a more complete revision.KEY WORDS: Spatangoida, Echinoidea, phylogeny, systematics, Cretaceous.T H E phylogeny of higher-level taxa of echinoids (order and above) is now considered to be robust (Smith 1981(Smith , 1984. In this framework, the order Spatangoida appears as a well-supported monophyletic group, with its first occurrence in the lowermost Cretaceous (Berriasian). While the monophyly of Spatangoida is largely consensual, the precise origin of the order is still unclear and has been the subject of several hypotheses in the last 50 years. Eble (2000) noted the lack of phylogenetic information for early Spatangoida and Holasteroida. Roots of these two orders are generally sought in disasteroid-like ancestors. Beurlen (1934) and Mortensen (1950) proposed Metaporinus as the ancestor of the Spatangoida. However, this hypothesis implied a reversion to a compact structure of the apical system because the first Disasteroida had already evolved by extension and disjunction of the apical system. Durham and Melville (1957) rooted the Spatangoida within the Galeropygidae. Their alternative hypothesis excluded the reversion but implied a stratigraphical gap of more than 50 myr. Later, Durham (1966) suggested that the Holasteroida, Spatangoida and Cassiduloida arose from a common ancestor at the beginning of the Jurassic. Afterwards, most authors retained the hypothesis of Devriès (1960a) that holasteroids and spatangoids both arose from disasteroids (Fischer 1966;Mintz 1966; Smith 1981 Smith , 1984. According to Devriès (1960a) the first spatangoid is Toxaster laffittei from the Berriasian. This species displays transitional features between Disasteroida and Spatangoida, such as a compact apical system and protamphisternous plastron. Other transitional forms to the more derived Spatangoida are found in nominal species such as Toxaster holasteroides and T. africanus, that show a progressive compaction of the apical system to an ethmophract pattern. However, consensus is still lacking. For example, Clavel (in Jablonski and Bottjer 1990) rejected Toxaster laffittei as a Spatangoida and moved it to Holasteroida as Holaster cordatus. In this latter hypothesis, Proholaster auberti is a good candidate for ancestor of the Spatangoida. Smith (1984) proposed an e...

The phylogeny and classification of post-Palaeozoic echinoids

“…There have been two detailed phylogenetic analyses of spatangoids recently (Villier et al 2004;Stockley et al 2005). Our analysis identifies basically the same pattern, with toxasterids as the most primitive member and hemiasterids, aeropsids and micrasterids as relatively deep branches that just survive to the present.…”

“…While there have been relatively few analyses that cover the entire group, there have been a relatively large number of cladistic analyses that have focussed on individual groups within the Echinoidea aimed at understanding detailed relationships: cidaroids (Smith & Wright 1989;Matsuoka & Inamori 1999), echinothurioids (Smith & Wright 1990;Mooi et al 2004), diadematoids (Smith & Wright 1990;Lessios 2001), stirodonts (Smith & Wright 1990), camarodonts (Smith 1988;McCartney et al 2000;Jeffery et al 2003;Lee 2003;Lee et al 2004), primitive irregulars (Smith & Anzalone 2000;Solovjev & Markov 2004;Barras 2006Barras , 2007Saucède et al 2007), cassiduloids (Suter 1994;Smith 2001;Saucède & Néraudeau 2006), clypeasteroids (Marshall 1992;Mooi 1987;Wang 1994;Mooi & Peterson 2000;Mooi et al 2000), holasteroids (David 1988;Mooi & David 1996;Smith 2004) and spatangoids (Markov & Solovjev 2001;Villier et al 2004;Stockley et al 2005;Kroh 2007). All provide detailed snapshots of parts of the phylogenetic tree of echinoids.…”

Phylogenetic relationships of spatangoid sea urchins (Echinoidea): taxon sampling density and congruence between morphological and molecular estimates

“…It is therefore imperative that classifications and phylogenetic hypotheses of spatangoids are constructed from all available data. The recent paper by Mortensen (1950) and Fischer (1966 Villier et al . (2004) has started this process by compiling a large database of morphological characters for the early Cretaceous genera of Spatangoida and subjecting it to a rigorous cladistic analysis.…”

“…As outgroup for the morphological analyses we used Toxaster retusus , one of the stratigraphically earliest fossils and one that has traditionally been considered as one of the most primitive (Mortensen 1950(Mortensen , 1951Fischer 1966;Villier et al . 2004).…”

Mecaster texanus (Echinoidea) from Turonian-Coniacian strata in the Sergipe-Alagoas Basin, Brazil

“…Their tests exhibit evidence to suggest that they lived epifaunally in an anoxic-dysoxic environment (NEUMANN, 1996;MANSO & SOUZA-LIMA, 2003a;VILLIER et al, 2004;KAMYABI SHADAN et al, 2014). Micraster (Epiaster) dartoni (COOKE, 1955), now Epiaster dartoni, was recorded from the lower Albian.…”