This is Mazon Monday post #266. What's your favorite Mazon Creek fossil? Tell us at email:[email protected].
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After Lesquereux (1879)
Rhacophyllum cornutum was described by Leo Lesquereux in 1879. Lesquereux was a Swiss-born bryologist and a pioneer of American paleobotany. Lesquereux is credited with naming the Mazon Creek fossil deposit in his 1870 report "Report on the Fossil Plants of Illinois".
Lesquereux in 1864 (Wikipedia)
R. cornutum is relatively rare plant species in the Mazon Creek fossil biota, although it is known from various other Pennsylvanian Period fossil locations in North America and Europe. It is characterized by it's "Y" shaped stalks and rounded, blunt lobes at the tips. There has been some debate regarding its exact classification. Associations with the tree fern Crenuloperis acadia (Mazon Monday #115) have been found along with common features with Kankakeea gundyi (Mazon Monday #262). This has led some to propose it as a different stages of the tree fern growth process.
is a problematic
Rhacophyllum cornutum Lesquereux, 1879
1879-80. Rhacophyllum cornutum Lesquereux: p. 317, pl. 57, fig. 3
1958. Rhacophyllum cornutum Lesquereux; Langford: p. 290, figs. 537-547
1969. Aphlebia; Darrah: pl. 21, fig. 2; pl. 24, fig. 1;DESCRIPTION: The main rachis appears thick and composed of a tight bundle of fibers. All surfaces have a rough appearance. The leaves are thick and highly variable. When small, they are spikes or half-round lobes (see Fig. 2); when large, they look like small Aphlebia leaves (see Fig. 3), but with veins generally visible.
REMARKS: Rhacophyllum cornutum is uncommon, but the most common Rhacophyllum/Aphlebia species in the Mazon Creek flora. Darrah lumped the genera Aphlebia and Rhacophyllum together, calling both names meaningless. This does not seem to be the case with R. cornutum. Some fossils show R. cornutum growing from the bases of tree fern fronds. Several specimens show this attachment (see Figs. 5, 6). R. cornutum and the vegetative bud Kankakeea grundyi share several features. Both have dense, fibrous stems that are covered with small pits. It has been shown that K. grundyi is the vegetative shoot of the tree fern that produces Crenulopteris acadica. It it could be reasonably concluded that R. cornutum is borne from this same plant, but in different stages of the plant's growth process.
Specimens
Multiple specimens can be found on the website of the Field Museum's paleobotany collections.
Field Museum specimen PP 58035
Field Museum specimen PP 32985
Field Museum specimen PP 32987
ESCONI member Ralph Jewell (Fossil Friday #262)
