File:"Solenopora" jurassica (fossil red algae) in limestone (Fieldbrash Deposit, Middle Jurassic; Cirencester, Gloucestershire, England) 2 (46792195132).jpg

“Solenopora” jurassica Nicholson in Brown, 1894 - fossil red algae in limestone from the Jurassic of Britain. (~7.8 centimeters tall)

Rhodophytes are red algae - they are the most common and widespread of marine macroalgae, but they often go unnoticed because of their frequently-dull coloration and nondescript growth forms. Over 7000 species of red algae are known in the Holocene - most of them are marine, plus some freshwater forms. Rhodophytes are also known in the fossil record. Very old fossil red algae have been reported from the upper Mesoproterozoic (~1.2 Ga) of northern Canada.

Red algae vary in color - not all are reddish. Rhodophytes can be red, pink, pale pink, lavender, purple, brownish-red, whitish, and yellowish. Fleshy red algae are usually weed-like to mossy to fuzzy in appearance. Calcareous red algae have skeletons with calcium carbonate (CaCO3 - calcite or aragonite). Calcareous red algae are important reef organisms - they include branching forms and crusts. Upon death, the hard part skeletal components of calcareous red algae become biogenic sediments in reef and peri-reef environments.

The remarkable fossil shown above is a "Solenopora" jurassica red alga with its pinkish coloration still preserved. It’s encased in a matrix of Middle Jurassic fossiliferous-oolitic limestone from Britain. Samples of this material have been nicknamed "beetroot stones". Biomarkers consistent with a rhodophyte affinity have been extracted from British beetroot stones (see Barden et al., 2015).

Previous studies have suggested that Jurassic fossils identified as Solenopora are not congeneric with the type species from the Ordovician of Estonia, Solenopora spongioides Dybowski, 1878. British Jurassic specimens are therefore assigned as "Solenopora" jurassica.

Classification: Rhodophyta, Rhodophyceae, “Solenoporaceae”

Stratigraphy: "Fieldbrash Deposit", Middle Jurassic (probably from the White Limestone Formation, Great Oolite Series, Bathonian Stage, upper Middle Jurassic, ~165-168 Ma)

Locality: unrecorded/undisclosed site at or near the town of Cirencester, southern Gloucestershire County, western England (southern Britain)

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