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Endocarps of Pyrenacantha (Icacinaceae) from the Early Oligocene of Egypt

Premise of research. The fossil record of Pyrenacantha (Phytocreneae tribe, Icacinaceae) includes well-documented species from the Paleogene of North and South America, but to date, no fossils have been described from its present geographic range, the Old World tropics. We document endocarp remains from the early Oligocene Jebel Qatrani Formation, Fayum Province, Egypt, representing the first fossil evidence of this genus from Africa. We discuss the systematic affinities of these fossils as well as their biogeographic and paleoecological implications.

Methodology. The fossil endocarps were studied by a combination of computed tomography scanning and reflected light microscopy and were extensively compared with modern fruits from multiple herbaria (representing all extant genera of Phytocreneae and numerous species of Pyrenacantha) to assess their systematic affinities. We also compared the Jebel Qatrani material with previously described Phytocreneae fossils.

Pivotal results. The Jebel Qatrani fossils conform to Pyrenacantha in their overall size, surface ornamentation (pitted), and tubercle morphology and size (tubercles are peg shaped to spiny, like the tubercles of numerous extant species of Pyrenacantha, and the tubercle length-to-diameter ratio is well above 1.0, a feature that further distinguishes Pyrenacantha from other Phytocreneae genera). However, the combination of characters shown by the Jebel Qatrani fossils is unique among modern and fossil species of Pyrenacantha, and therefore we describe them herein as a new species: P. simonsii Stull, Tiffney, Wing & Manchester, sp. nov.

Conclusions. The fossils described here indicate that Pyrenacantha has been present in Africa since at least the earliest Oligocene. Although Pyrenacantha is known from the Eocene of midlatitude North America and probably Europe, suggesting a Holarctic origin with subsequent restriction to the tropics in response to climatic cooling, the absence of older Paleogene fossils in Africa could instead reflect inadequate sampling. Given that all modern species of Pyrenacantha (and Phytocreneae in general) are climbers, we can infer that P. simonsii likely also had a climbing growth form, which is consistent with ecological interpretations of the Jebel Qatrani flora as representing at least a gallery forest if not a more widespread forest with appreciable rainfall.