Gorongosa by the sea: First Miocene fossil sites from the Urema Rift, central Mozambique, and their coastal paleoenvironmental and paleoecological contexts

Abstract

The East African Rift System (EARS) has played a central role in our understanding of human origins and vertebrate evolution in the late Cenozoic of Africa. However, the distribution of fossil sites along 3 the rift is highly biased toward its northern extent, and the types of paleoenvironments are primarily restricted to fluvial and lacustrine settings. Here we report the discovery of the first fossil sites from the Urema Rift at Gorongosa National Park (central Mozambique) at the southern end of the EARS, and reconstruct environmental contexts of the fossils. In situ and surface fossils from the lower member of the Mazamba Formation, estimated to be of Miocene age, comprise mammals, reptiles, fishes, invertebrates, palms, and dicot trees. Fossil and geological evidence indicates a coastal-plain paleoenvironmental mosaic of riverine forest/woodland and estuarine habitats that represent the first coastal biomes identified in the Neogene EARS context. Receiving continental sediment from source terranes west of today's Urema Graben, estuarine sequences accumulated prior to rifting as compound incised-valley fills on a low-gradient coastal plain following transgression. Modern environmental analogues are extremely productive habitats for marine and terrestrial fauna, including primates. Thus, our discoveries raise the possibility that the Miocene coastal landscapes of Gorongosa were ecologically-favorable habitats for primates, providing relatively stable maritime climate and ecosystem conditions, year-round freshwater availability, and food both from terrestrial and marine sources. The emerging fossil record from Gorongosa is beginning to fill an important gap in the paleobiogeography of Africa as no fossil sites of Neogene age have previously been reported from the southernmost part of the EARS. Furthermore, this unique window into past continentalmargin ecosystems of central Mozambique may allow us to test key paleobiogeographic hypotheses during critical periods of primate evolution.

Primate adaptations and evolution in the Southern African Rift Valley

“…At the workshop, Carvalho discussed how this project integrates studies of modern primate behavior, genetics, and morphology, with new archeological excavations in Gorongosa's extensive karstic system, as well as new Miocene fossil sites on the eastern shoulder of the rift (Figure 1). 9 Carvalho and colleagues saw the potential to focus on baboon behavior to learn more broadly about the processes by which primates adapt to complex and dynamic conditions, and about behavioral innovations that might emerge under particular ecological pressures. For example, one of the effects of the civil war was a severe decline of the park's carnivore communities, but lions are making a significant recovery in population size, leopards are returning, and wild dogs have been successfully reintroduced (Figures 5 and 6).…”

“…He discussed his hypothesis of hominin origins in the eastern coastal forests, 29 an idea that is receiving renewed attention 30 . In this light, the new fossil sites from Gorongosa acquire special importance, as they sample Miocene woodlands/forests in a coastal paleoenvironment, 9 and will allow for the testing of hypothesis about mammalian evolution in wooded coastal regions.…”

Study of the Karst Process Dynamics in Khózuè: Calcareous Massif of Cheringoma Plateau (Mozambique)

“…The geology of the region in which Mozambique is located is quite complex (Afonso, 1977;Iliffe et al, 1991;Afonso et al, 1998;DNG, 2006;Schlüter, 2006;Mueller et al, 2016;Mueller and Jokat, 2017;Habermann et al, 2019). Two geological structures mark the study area, Urema Graben -Rift Valley, which develops to the west of the Cheringoma/Inhaminga Plateau and slightly sloping towards the northeast-southwest and the vast Quaternary delta plain and consolidated dune coastlines which are generally orientated parallel to the coast-line (Schlüter, 2006;Steinbruch, 2010;Ministério da Administração Estatal, 2014).…”

Unsupervised learning of satellite images enhances discovery of late Miocene fossil sites in the Urema Rift, Gorongosa, Mozambique

“…Therefore, innovative risk-aversion methods that can maximize information and Figure 1 The great gaps of the African late Miocene: (A) Time gap: during this key period the African fossil record of primates is very incomplete (evaluated through species richness); but notice the split estimates from genomics; (B) spatial gap: virtually no fossils of this age are known in southeastern Africa, notice the strategic location of Gorongosa. Data extracted from paleobiodb.org, map adapted from Bobe et al (2018); (C) study area for k-means within the geological context of Gorongosa, adapted from Habermann et al (2019).…”

“…(A) GPL-1 outcrops, notice how the surrounding vegetation is far more dense and extensive than in typical fossil sites from the EARS; (B) GPL-1 in high-resolution satellite image, extracted from bing.com, shows a reduction of vegetation, but outcrops are barely noticeable; (C) GPL-1, in a black rectangle, appears brighter than surrounding areas, when being mapped by lower resolution Landsat 8 false colour (infrared) image, and the same happens with other fossil sites, suggesting that infrared bands might be a useful indicator of fossiliferous deposits. new fossil assemblages with hominins have also been guided by military, geological and topographic maps, aerial photography and satellite images (Asfaw et al, 1990;Malakhov, Dyke & King, 2009;Hlusko, 2018;Habermann et al, 2019). With recent advances in artificial intelligence, cheaply available computer power, and free access to satellite imagery of reasonable resolution, paleoanthropologists and GIS technicians have been implementing machine learning techniques to automate the demanding visual analysis of remote fossil site detection (e.g., Anemone, Emerson & Conroy, 2011;Conroy et al, 2012Conroy et al, , 2018Conroy, 2014;Emerson et al, 2015;Block et al, 2016;Wills, Choiniere & Barrett, 2018).…”