Ordovician graptolite evolutionary radiation: a review

Abstract

Based on the global graptolite genera and higher rank taxa, we propose three radiation stages through the Ordovician. The isograptid type of development is present within anisograptids predominating in the Tremadocian. Thus, the evolutionary radiation of the Anisograptid fauna from Tremadocian is proposed as the beginning of the Ordovician graptolite radiation. The second graptolite radiation event is the radiation of the Dichograptid fauna, which began from the T. fruticosus Biozone. The third radiation event, the radiation of Diplograptid fauna began immediately after that of the dichograptids. This radiation includes the peak in total diversity of all the Ordovician graptoloids in the Nemagraptus gracilis Biozone. The radiation extended through the Sandbian and Katian and then was interrupted by a major extinction during the early Hirnantian. Thus, the Ordovician graptolite radiation events coincide with those of the three graptolite faunas proposed by Bulman. The distribution and expansion of the Ordovician graptolites in South China may exemplify the graptolite origination pattern, which begins from the slope belt and expanded into both the shelf and oceanic zones.

The early evolution of feathers: fossil evidence from Cretaceous amber of France

“…The morphology of the new fossils described herein, with a rachis forming 'primitive' vanes without barbules, is entirely consistent with the shafted feathers displayed by these two theropods. According to this, and to the current evolutionary model of increasing complexity in feather morphologies ( Norell & Xu 2005;Xu 2006;Xu & Norell 2006;Zhang et al 2006), the French amber feathers may thus belong to a non-avian theropod dinosaur. It is noteworthy that isolated teeth of troodontids were recovered from the amber deposit considered here ( Vullo et al 2007).…”

“…Microraptor) with modern feathers of stage V (remiges), a character that was hitherto considered to be unique to birds (Prum & Brush 2002) and now is recognized to have a more ancient origin among non-avian dinosaurs (Sereno 2004). Jinfengopteryx, though formerly assigned to an avialan bird ( Ji et al 2005), is more likely a troodontid with pennaceous feathers of stage IV ( Xu & Norell 2006). Finally, Ji et al (2001) and Xu et al (2001) inferred the existence of a rachis in a pattern of branched barbs for the dromaeosaur Sinornithosaurus and a still unnamed Chinese theropod ('filaments jointed at their bases along a central filament' and 'filaments appearing to be around a central rachis', respectively).…”

The Global Diversity of Hemichordata

“…Fewer than 30 extant pterobranch species have been described [ 59 ]. Though graptolites display expansive evolutionary radiation [ 55 , 56 , 60 ], all extant pterobranch species belong to one of two genera: Rhabdopleura or Cephalodiscus . Note that the previously recognized genera ( Atubaria ) is not considered valid because the only description of its sole member, Atubaria heterolopha , [ 61 ] is regarded as a questionable species [ 62 ].…”