The first Miocene fossils from coastal woodlands in the southern East African Rift

Abstract

The Miocene was a key time in the evolution of African ecosystems witnessing the origin of the African apes and the isolation of eastern coastal forests through an expanding arid corridor. Until recently, however, Miocene sites from the southeastern regions of the continent were unknown. Here, we report the first Miocene fossil teeth from the shoulders of the Urema Rift in Gorongosa National Park, Mozambique. We provide the first 1) radiometric ages of the Mazamba Formation, 2) reconstructions of paleovegetation in the region based on pedogenic carbonates and fossil wood, and 3) descriptions of fossil teeth. Gorongosa is unique in the East African Rift in combining marine invertebrates, marine vertebrates, reptiles, terrestrial mammals, and fossil woods in coastal paleoenvironments. The Gorongosa fossil sites offer the first evidence of woodlands and forests on the coastal margins of southeastern Africa during the Miocene, and an exceptional assemblage of fossils including new species.

Keywords: Evolutionary biology; Forestry; Geochemistry.

Graphical abstract

Figure 1

The East African Rift System (A) The East African Rift System (EARS) with the Eastern Branch, the Western Branch, and some of the major basins and rifts, including the Urema Graben at its southern end. The development of the EARS since the Miocene has played a major role in shaping the physical environments and modifying the conditions under which plants and animals have been evolving in eastern Africa. Shaded area depicts hypothetical extent of arid corridor during the Miocene. Base map from Nasa Shuttle Radar Topography Mission (https://www2.jpl.nasa.gov/srtm/). (B) Number of Miocene paleontological localities along the EARS by latitude. There are many Miocene localities in the rift near the equator, but the record away from the equator, especially to the south, is very sparse. Gorongosa is the only Miocene paleontological locality in the southern ∼1500 km of the EARS. Locality data from the Paleobiology Database https://paleobiodb.org/classic.

Figure 2

Map of Gorongosa National Park along the East African Rift Valley The park hosts a wide range of environments. The new paleontological sites on the Cheringoma Plateau are ∼95 km from the coast.

Figure 3

Gorongosa Paleontological Localities and geological formations (A) Geological map of Gorongosa National Park and surrounding areas. (B) Vertical geological cross section of the Urema Rift stretching from Mount Gorongosa to Inhaminga village. (C) Map section showing the locations of the fossiliferous sites (GPL = Gorongosa Paleontological Locality). Figure modified from Habermann et al. and references therein, with new paleontological localities added.

Figure 4

Stratigraphic sections Modified and updated from Habermann et al.

Figure 5

Stable carbon and oxygen isotopes δ¹³C and δ¹⁸O related to the stratigraphic column of GPL-1NE.

Figure 6

Silicified tree trunk with bark preserved at Menguere Hill

Figure 7

Photomicrographs of thin sections of fossil wood specimen PPP-G-36 from Menguere Hill, Entandrophragmoxylon sp. (Meliaceae, African Mahogany) (A) Transverse section showing large mostly solitary vessels, vasicentric to aliform parenchyma, and wide rays with dark contents. (B) Radial longitudinal section with a vertical column of axial parenchyma cells, and horizontal radial parenchyma cells that are procumbent. (C) Tangential longitudinal section with vertical columns of axial parenchyma cells and lens-shaped outline of rays with circular parenchyma cells. Letters: V = vessel; R = ray; P = axial parenchyma. Scale bars: A = 1cm; B, C = 500 μm.

Figure 8

Gorongosa fossil sharks, all in the genus Galeocerdo, tiger sharks (A) PPG2019-P-129. (B) PPG2019-P-127. (C) PPG2018-P-224. (D) PPG2019-P-176. (E) PPG2017-P-121. (F) PPG2019-P-126.

Figure 9

Fossil shark principal component analysis (A) PCA of 600 Miocene shark teeth from the genera Carcharhinus, Galeocerdo, Hemipristis, and Physogaleus, and including the two Gorongosa complete crowns. (B) PCA of 547 Miocene shark teeth of the species Galeocerdo sp., and Physogaleus sp., and the Gorongosa specimens. (C) PCA of shark teeth including the species G. aduncus, G. capellini, G. clarkensis, G. cuvier, G. eaglesomei, and G. mayumbensis, with the Gorongosa specimens.

Figure 10

Some fossil reptiles from Gorongosa (A, E, and F) Testudines. (B–D and G–K) Crocodylia.

Figure 11

Fossil hyracoids (A) Hyracoid left mandible PPG2018-P-1. (B) Hyracoid right mandibular fragment, PPG2018-P-2. (C) PPG2018-P-2 in occlusal view.

Figure 12

Shape analysis of hyracoid p3-m3 (A) Thyrohyrax specimen (DPC 2763) showing the landmarks (orange spheres) and semi-landmarks (light blue spheres) used in this study. This specimen was selected to display the 3D coordinates as it corresponds to the specimen closest to the multivariate mean in this analysis. (B) Principal component analysis (PCA) of the dental shape variables (only the two first PCs are shown).

Figure 13

Shape analysis of hyracoid m3 (A) Afrohyrax specimen (ZP349) showing the landmarks (orange spheres) and semi-landmarks (light blue spheres) used in this study. This specimen was selected to display the 3D coordinates as it corresponds to the specimen closest to the multivariate mean in this analysis. (B) Principal component analysis (PCA) of the m3 shape variables (only the two first PCs are shown).

Figure 14

Hyracoid phylogeny Maximum credibility (MCC) tree summarizing 75,000 hyracoid phylogenies obtained from a Bayesian phylogenetic analysis. The length of the bars on the MCC tree corresponds to the temporal 95% highest posterior density interval (HPD), while the color represents posterior support. Numbers on the phylogeny correspond to node numbers in Table S9.