Plant fossils from the Panama Canal provide direct evidence of the ancient history of many common Neotropical forest trees. During the early Miocene (19 Million years ago), Panama was still separated from South America by the Central American Seaway. At that time, the fauna of Panama had more in common with North America than with South America, but the flora was like that of South America. This means that while most animals had to wait for the formation of the isthmus (about 3 Million years ago) to migrate between the continents, the exchange of plants between the two continents began much earlier.
Studies of plant macrofossils (things like fruits and wood) provide details about the flora that compliment the data from pollen analysis because they often permit more precise identifications and they provide ecological information. So far, researchers working on early Miocene plant macrofossils from the Canal Zone have documented extinct relatives of palms, mangroves, Sacoglottis (Humiriaceae), Guazuma (Malvaceae), Oreomunnea (Juglandaceae), and Parinari (Chrysobalanaceae); and more are forthcoming.
This week, a study led by my former student Chris Nelson was published in the International Journal of Plant Sciences. The focus was a fossil plant closely related to mamey apple (Mammea americana L.), a fruit tree common in the neotropics today. This work contributed to a more complete picture of the early Miocene forests of Panama, but it also reveals a lot about the history of the mamey apple. Mammea is a genus in the Calophyllaceae with 70 species growing in tropical forests around the world; but only two, including the widely cultivated mamey apple, are native to the Americas. This occurrence provides a minimum age for the evolution of the genus Mammea, and a minimum age for its colonization of the neotropics. Furthermore, this minimum age information can be used in future studies that combine fossils and genetic sequence data to understand the evolution of the Mammea and its relatives.
References:
Berry, E.W. 1918. The fossil higher plants from the Canal Zone. Bulletin of the U.S. National Museum 103: 15–44.
Herrera, F., S.R. Manchester, C. Jaramillo, B. MacFadden, and S.A. da Silva-Caminha. 2010. Phytogeographic history and phylogeny of the Humiriaceae. International Journal of Plant Sciences 171: 392–408.
Herrera, F., S.R. Manchester, R. Koll, and C.A. Jaramillo. 2014. Fruits of Oreomunnea (Juglandaceae) in the early Miocene of Panama. In W.D. Stevens, O.M. Montiel, and P.H. Raven [eds.], Paleobotany and Biogeography: A Festschrift for Alan Graham in his 80th year, 124–133. Missouri Botanical Garden Press, St. Louis, Missouri, USA.
Jaramillo, C.A., E. Moreno, V.O. Ramírez, S.A.F. Silva-Caminha, A. de la Barrera, and A. de la Barrera. 2014. Palynological record of the last 20 million years in Panama. In Paleobotany and Biogeography: A Festschrift for Alan Graham in his 80th year, 134–251. Missouri Botanical Garden Press, St. Louis, Missouri, USA
Jud, N.A., C.W. Nelson*, and F.H. Herrera 2016. New Parinari fossils from the early Miocene of Panama and the fossil record of Chrysobalanaceae. American Journal of Botany 103(2): 277–289.
Nelson, C.W. and N.A. Jud 2017. Biogeographic implications of Mammea paramericana sp. nov. from the lower Miocene of Panama and the evolution of the Calophyllaceae. International Journal of Plant Sciences 178(3): 241–257.
Retallack, G. J., & Kirby, M.X. 2007. Middle Miocene global change and paleogeography of Panama. Palaios, 22(6), 667-679.
Rodríguez-Reyes, O., H. Falcon-Lang, P. Gasson, M. Collinson, and C. Jaramillo. 2014. Fossil woods (Malvaceae) from the lower Miocene (early to mid-Burdigalian) part of the Cucaracha Formation of Panama (Central America) and their biogeographic implications. Review of Palaeobotany and Palynology 209: 11–34.