First fossil evidence of Palaeocarya (Engelhardioideae: Juglandaceae) from India and its biogeographical implications

Abstract

Even though presently indigenous to eastern Himalaya in India, no Engelhardioideae have been reported from the Cenozoic sediments of India till date. Here, we report the first Indian occurrence of a characteristic engelhardioid winged samaroid fruit having a tri-lobed wing (oblong-ovate median lobe and two lateral lobes) and a globose nut from the latest Neogene (Pliocene: Rajdanda Formation) sediments of Chotanagpur Plateau, eastern India. This is the first fossil evidence of relict family Juglandaceae from the Indian Cenozoic. We determine its taxonomic position on the basis of detailed macromorphological comparison with similar extant and fossil specimens and discuss its palaeoclimatic significance in terms of the present-day distribution of modern analogous species. We assign this Pliocene winged fruit specimen to the morphogenus Palaeocarya sect. Monocosta Manchester and describe it as a new species, namely Palaeocarya indica Hazra, Hazra M & Khan sp. nov. Palaeocarya sect. Monocosta has rich fossil records from the Cenozoic sediments of Europe, North America, and eastern Asia (China, Korea), but the modern analog, Engelhardia, is presently native only to India and neighboring Southeast Asia. We discuss the possible causes of disappearance of Engelhardia from the present-day vegetation of Chotanagpur Plateau. Its disappearance may be related to the gradual intensification of monsoonal rainfall seasonality since the Pliocene. Here, we also review in detail the biogeographic history of Palaeocarya sect. Monocosta and suggest its possible migration routes.

First reliable Miocene fossil winged fruits record of Engelhardia in Asia through anatomical investigation

“…Almost all winged fruit fossils similar to modern Engelhardia are assigned to the fossil genus Palaeocarya Saporta, and only a few of them have been observed with septal structures within the nutlets, including Palaeocarya macroptera (Brongniart) Jähnichen, Palaeocarya olsoni (Brown) Manchester, Palaeocarya hispida H. H. Meng et Z. K. Zhou, and Palaeocarya indica Hazra, Hazra M. et Khan. 3 , 27 , 39 , 43 , 57 P. macroptera has been found extensively in Eocene to Pliocene sediments in Europe. 3 , 57 The nutlets of P. macroptera possess narrow secondary septa, with 2 or basal 4 chambers and a hook-shaped bulging appendage in the middle of the compartment.…”

“…P. indica was found in the Pliocene of eastern India and its nutlet is hispid, subdivided by a septum into two compartments. 43 Hazra et al. 43 believed that P. indica is most similar to the extant E. spicata .…”

“…Subsequently, the majority of discovered engelhardioid winged fruit fossils have been assigned to the fossil genera Palaeocarya . 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 Despite this, some engelhardioid winged fruit fossils have still been assigned to Engelhardia , for example, Engelhardia macroptera (Brongniart) Unger discovered in the Cenozoic of Europe. 45 , 46 , 47 , 48 , 49 , 50 However, it is more appropriate to attribute these fossils to Palaeocarya rather than Engelhardia , because these fossils do not possess further characteristics beyond the revision by Manchester.…”

Plant diversity and ecology on the Qinghai–Tibet Plateau

“…The paleo‐altitude of this region was further inferred to be less than 2400 m at this stage. In addition, we also include one fossil report from the low‐altitude foot of the southern Himalaya (Hazra et al, 2021).…”

Two new species from Sulawesi and Borneo facilitate phylogeny and taxonomic revision of Engelhardia (Juglandaceae)

“…For instance, Engelhardia possesses a rich Cenozoic fossil record; in particular the fruits fossils can be well-preserved in the sediment. This has encouraged researchers to utilize both paleo-distribution data and distinctive morphological characters to untangle the evolution and radiation of the Juglandaceae ( Manchester, 1987 , 1994 ; Manos and Stone, 2001 ; Manos et al., 2007 ; Stone, 2010 ; Meng et al., 2015 , 2022 ; Song et al., 2020 ; Hazra et al., 2021 ; Zhang et al., 2022a ). In 2020, we integrated the morphology, molecular phylogeny, and a large-scale field investigation to provide insights into the species delimitation of Engelhardia .…”