Middle Jurassic evidence for the origin of Cupressaceae: A paleobotanical context for the roles of regulatory genetics and development in the evolution of conifer seed cones

Abstract

Scitistrobus duncaanensis extends the fossil record for anatomically preserved seed cones of the Cupressaceae backward from the Upper Jurassic to the Aalenian Stage of the Middle Jurassic. The cone displays a previously unknown combination of characters that we regard as diagnostic for seed cones of early-divergent Cupressaceae and helps to clarify the sequence of structural changes that occurred during the transition from ancestral voltzialean conifers to morphologically recognizable Cupressaceae. Hypotheses of homology underpinning such transformational series can be tested by ongoing reciprocal illumination between the morphology of fossil taxa and the morphogenesis and developmental genetics of their extant crown-group relatives.

A new species ofAthrotaxites(Athrotaxoideae, Cupressaceae) from the Upper Cretaceous Raritan Formation, New Jersey, USA

“…Likewise, Athrotaxites Unger (1849) has taxonomic priority over Athrotaxopsis Fontaine (1889). Numerous molecular clock studies have estimated the divergence age of crown Athrotaxis to have occurred in the Neogene (e.g., Leslie et al 2012;Mao et al 2012;Yang et al 2012), whereas its stem lineage has been dated as Mesozoic (e.g., Spencer et al 2015). More specifically, the stem age has been suggested as Late Jurassic or Early Cretaceous, which is also concordant with its fossil record (Dong et al 2014), since the first appearance of the athrotaxoids is in the Late Jurassic (Florin 1940).…”

Stockeystrobusgen. nov. (Cupressaceae), and the evolutionary diversification of sequoioid conifer seed cones

“…This has led some authors to suspect that some conifer seed cones may be equivalent to simple, rather than compound shoot systems, and therefore have an independent evolutionary origin from conifers that have compound seed cones (e.g., Tomlinson et al 1993). However, more recent studies that include transformational series of cone scale morphologies from Voltziaceae to Cupressaceae (Rothwell et al 2011), and that emphasize comparative developmental morphology (Schulz and Stützel 2007) and the regulatory genetics that underlies variations in mature cone scale structure (Rothwell et al 2011;Rudall et al 2011;Spencer et al 2015), reveal that all cupressaceous cones are variously modified compound shoot systems as originally hypothesized by Florin (1951Florin ( , 1954 and summarized by Rothwell et al (2011). These studies explain our inability to recognize morphologically distinct bracts and ovuliferous scales in the compound seed cones of sequoioid Cupressaceae, including Stockeystrobus.…”

“…A similar pollination mechanism appears to characterize Saxegothaea conspicua Lindley (Tison 1908;Chamberlain 1935), but it is unclear whether the post-pollination nucellus displays a highly convoluted apical region. Although the structure of the pollen chamber has been characterized for several species of both living and extinct Cupressaceae e.g., Arnoldi 1900; Takaso and Owens 1996;Owens et al 1998;Tomlinson 2012;Spencer et al 2015), Stockeystrobus digitata is the first species of the family in which this character has been found. This feature could be interpreted as either a strong indication that a specialized pollination mechanism like those of Araucariaceae and Saxegothaea (Tison 1908;Owens et al 1998) also was characteristic of some Cretaceous species of the subfamily Sequoioideae, or that it is plesiomorphic among the (Sciadopityaceae + Cupressaceae) + (Araucariaceae + Podocarpaceae) clade (Leslie et al 2012) as a whole.…”

“…Species of particularly informative systematic significance are represented by reproductive organs (e.g., Florin 1938Florin -1945La Pasha and Miller 1981;Clement-Westerhof and van Konijenberg-van Cittert 1991;Matsumato et al 1997;Hernandez-Castillo et al 2001;Hernandez-Castillo et al 2005;Escapa et al 2008;Rothwell et al 2011;Bosma et al 2012;Leslie et al 2012). These include the most ancient representatives of the family Cupressaceae (Escapa et al 2008) and specimens that display apparently pleisomorphic seed cone morphologies within the family (Spencer et al 2015). Ana-tomically preserved fossil seed cones serve as important intermediates for a transformational series from Voltziaceae to Cupressaceae (Rothwell et al 2011).…”

X-ray micro-computed tomography (micro-CT) of pyrite-permineralized fruits and seeds from the London Clay Formation (Ypresian) conserved in silicone oil: a critical evaluation

“…He continued to report his work in short articles on permineralized plants including a few micro-CT images, and at conferences in Japan and China (Nishida 2005(Nishida , 2007a(Nishida , 2007bNishida and Otodani 2007;Nishida et al 2008) and at the International Organisation of Palaeobotany Conferences (IOP) in Bonn (Nishida 2008) and Tokyo (Nishida and Kotake 2012). Micro-CT has now become quite frequently used in the study of plant fossils, including in recent literature on fruits and seed cones (e.g., Collinson et al 2012b;Feng et al 2014;Gee et al 2014;Herrera et al 2015;Rozefelds et al 2015;Spencer et al 2015;Su et al 2015;Crepet et al 2016) and was used by DeVore et al (2006) to study a fruit from the London Clay Formation. Spencer et al (2013) combined micro-CT imaging with study of subsequently produced wafered sections to obtain requisite cellular detail.…”