Miocene hominoids

Explaining in simple terms the so-called aquatic ape theory.
Human ancestors during the Ice Ages (Pleistocene Homo after +-2 mill.yrs ago) did not disperse intercontinentally running over open plains as popularly assumed, but followed African & Eurasian coasts & rivers, where their diet included shallow-aquatic & waterside foods, which are rich in brain-specific nutrients, e.g. DHA, iodine, taurine, oligo-elements.

Biological reconstruction of ape and human (hominoid) evolution, mostly based on comparative, fossil, paleo-environmental and DNA evidence.

Schematically:

(I) arboreal to aquarboreal:
The evolution from monkey to ape body-plan is best explained by a transition from tree-dwelling to living in flooded forests (Mio-Pliocene).

(II) aquarboreal to littoral:
The evolution from ape/australopith to Homo body-plan can mostly be explained by a transition to a coastal and waterside lifestyle during the Ice Ages (early-Pleistocene dispersal along African and Eurasian coasts).

The Late Miocene sequence at Haritalyangar, Himachal Pradesh, India, has produced abundant remains of the hominid Sivapithecus and the sivaladapids Sivaladapis and Indraloris. Also recovered from these sediments is an isolated and worn upper molar that was made the holotype of Krishnapithecus krishnaii and assigned to the Pliopithecoidea. However, the heavy wear and absence of definitive pliopithecoid features on the tooth rendered the assignment to this superfamily unconvincing. Here, we describe two lower molars from Haritalyangar that bear unmistakable pliopithecoid features and that are plausibly assignable to the same species as the type specimen of K. krishnaii. They convincingly demonstrate for the first time the presence of the Pliopithecoidea in South Asia. The new molars also reveal that K. krishnaii was perhaps the largest known pliopithecoid and that it possessed highly derived postcanine dental morphology. Because of its highly derived nature, it is difficult to determine its relationships within Pliopithecoidea, but a sister taxon relationship with either the Dionysopithecidae or Pliopithe-cinae is equally plausible; it is only distantly related to the Crouzeliinae. It is sufficiently distinct, however , from all other pliopithecoids to warrant placement in a separate family.

The extensive outpouring of the Oligocene Trap basalts over eastern Africa and western Arabia was interrupted by a period of quiescence marked by the deposition of terrestrial sediments. These so-called intertrappean beds are often lignitiferous and yield recurrent floras and faunas, sometimes represented by endemic mammals. We intended to highlight the peculiar features of these sedimentary intercalations using a large-scale approach including eastern Africa and the western Arabian peninsula. Starting from a new mapping in the Eritrean highland, the intertrappean beds resulted a continuous level that was a few tens of meters thick and traceable for some tens of kilometers. They consist of fluvial red, green and gray mudstones and siltstones with subordinate channelized pebbly sandstones, and lignite seams. Two new 40Ar–39Ar datings constraint the age of the intertrappean beds between 29.0 Ma and 23.6 Ma. The outcrops near Mendefera have yielded the remains of two proboscidean families, the Deinotheriidae and the Gomphoteriidae. The morphological grade of the two Mendefera proboscideans would suggest a more derived stage than that of representatives of the same families from other Oligocene African sites (e.g., Chilga, Ethiopia). An Oligocene age could be inferred for them. The occurrence of the genus Prodeinotherium at Mai Gobro possibly represents the first occurrence of this taxon, while the Gomphotheirum sp. might represent the oldest occurrence of this taxon in Africa before its dispersal towards Asia and Europe. Proboscideans have also been found in the lowland intertrappean beds of Dogali near Massawa. These sediments were contiguous with the Eritrean highland intertrappean beds during the Oligocene, but are now tectonically displaced from them by two thousand meters of vertical topographical distance. Dogali is also known for the occurrence of possible Deinotheriidae remains and the primitive elephantoid Eritreum. Entering the Ethiopian highland, an inspection of the Agere Selam (Mekele) intertrappean beds revealed the occurrence of lacustrine limestones and diatomites, which were contrastingly quite subordinate with respect to the fine clastic sediments found in the nearby Amba Alaji area. Further south, the intertrappean section in the Jema valley (100 km north of Addis Ababa and close to the Blue Nile gorge) is 120 m thick with predominant clastic sediments and a few diatomite's at the top. Literature information from 35 additional sites, including northern Kenya, Yemen, Sudan and Saudi Arabia sections, confirms the fluvial and lacustrine depositional environment of the intertrappean beds, underlines the interest in their mammal fauna (Chilga, Losodok), and reports exploitable coal seams for some of them. As for the vegetal landscape in which the intertrappean beds were deposited, pollen and plant analysis results indicative of a tropical wet forest, similar to that of present-day western Africa. Another common feature of the intertrappean beds is their relatively limited thickness, averaging a few tens of meters, but reaching a few hundred meters in graben-related basins, such as Delbi Moye in southern Ethiopia. In most cases only thin, lens-shaped successions were deposited above the hummocky topography of their volcanic substratum, commonly unaffected by significant faulting. An average duration of the intertrappean beds is from one to three million years. This time interval is commonly matched by a few tens (or more rarely, hundreds) of meters of sediments left over after erosive episodes or depositional starvation. As to the lateral continuity of the intertrappean beds, the present-day outcrops show large differences: from some tens of kilometers in the Mendefera area, to a few tens of kilometres in the Jema valley, and to a few hundreds meters in the Agere Selam (Mekele) area. Even if it is difficult to quantify the original size of the sedimentation areas, it nevertheless proves that the intertrappean basins exceed thousands of square kilometers in only a single case (Mendefera), but were quite restricted in most cases. Their most likely endorheic and local character, together with a regional ill-defined fluvial network, was the effect of a water-course rerouting caused by the progressive rising of the eastern African and Arabian plateaux. Chronological constraints for the intertrappean beds can be inferred from the age of the hosting Trap succession and by the stratigraphical position that they occupy. Intervolcanic sedimentary episodes are typically found in the basaltic and subordinately rhyolitic successions that followed the 31–29 Ma old basaltic widespread paroxysm. With due caveats deriving from the discontinuous availability of datings specifically dedicated to this issue, we regard the age of the intertrappean beds as mostly encompassed in the interval from 29 to 27 Ma at the transition between the Early and Late Oligocene in the Ethiopia/Yemen Trap core. In marginal areas, such as SW Arabia, Eritrea and Kenya, the volcanic activity above the intertrappean beds resumed later, and its quiescence allowed a more prolonged period of sedimentation. The intertrappean beds fall in the second cooling event of the Oligocene climatic deterioration. During the contemporaneous apparent drop in the global sea-level and closure of the Tethyan Ocean between Arabia and southwestern Asia, connections were established between the African and the Eurasian continents. At that time, southwestern Asia was experiencing severe aridity with faunal exchanges toward the luxuriously vegetated eastern Africa.

Oreopithecus bambolii is a Late Miocene ape from Italy, first described in the late 19th century. Its interpretation is still highly controversial, especially in reference to its hand proportions and thumb morphology. In this study, the authors provide detailed descriptions of the available Oreopithecus pollical distal phalanx (PDP) specimens, as well as bivariate and multivariate morphometric analyses in comparison with humans, extant apes, selected anthropoid monkeys, and available Miocene PDP specimens. The multivariate results reveal two opposite poles on the hominoid PDP shape spectrum: on one side, a mediolaterally broad and dorsopalmarly short human PDP, and on the other side, the narrow and “conical” PDP of chimpanzees and orangutans. The authors contend that Oreopithecus exhibits intermediate PDP proportions that are largely primitive for hominoids because it shares morphological similarities with Proconsul. Furthermore, Oreopithecus displays a mediolaterally wide tuft for a hominoid, as well as a palmarly elevated attachment for a long tendon of a flexor muscle that is associated at its proximal edge with a proximal fossa and at its distal edge with an ungual fossa. These nonmetrical traits have been associated in humans with their capability to oppose and contact the proximal pads of the thumb and fingers, that is, pad-to-pad precision grasping. These traits reinforce previous studies that indicate a human-like thumb-to-hand length ratio compatible with pad-to-pad precision grasping in Oreopithecus. Although specific hand use is still unresolved in Oreopithecus, the results suggest enhanced manipulative skills (unrelated to stone tool-making) in this taxon relative to other (extant or fossil) hominoids

The morphology of the anterior dentition has received scant attention for purposes of taxonomic discrimination. Recently, however, lingual incisor morphology was used in differentiating several Miocene ape species and genera. This paper assesses the utility of this morphology for taxonomic discrimination by examining the nature and patterns of variation in lingual incisor morphology in extensive samples of modern chimpanzees, gorillas, orangutans, and gibbons. This paper documents discrete morphological traits on the lingual side of incisors. Trait frequencies are used in univariate and multivariate analyses to examine the apportionment of variation in species, subspecies, and populations. A correlation between lingual incisor traits, tooth dimensions, and sex attempts to determine if such factors affect the manifestation of traits. Finally, the findings are applied to understanding patterns of variation in the Miocene hominids. The study demonstrates that: 1) lingual incisor morphology differs substantially between the hylobatids and great apes; 2) variation in incisor traits is high within species, and most of it is found within local populations; and 3) incisor traits do not correlate significantly with incisor dimensions or sex. Species and to some extent subspecies of extant hominoids can be differentiated statistically using lingual incisor traits, but the frequency of traits such as continuous or discontinuous cingulum, or the presence or absence of pillars, differentiates them. Given this pattern of variation, I argue that it is necessary to assume and document similar patterns of variation in Miocene apes before incisor morphology is used for differentiating taxa. Am J Phys Anthropol, 2006. © 2005 Wiley-Liss, Inc.

The partial skeleton of Pierolapithecus, which provides the oldest unequivocal evidence of orthogrady, together with the recently described phalanges from Paşalar most likely attributable to Griphopithecus, provide a unique opportunity for understanding the changes in hand anatomy during the pronogrady/orthogrady transition in hominoid evolution. In this paper, we describe the Pierolapithecus hand phalanges and compare their morphology and proportions with those of other Miocene apes in order to make paleobiological inferences about locomotor evolution. In particular, we investigate the orthograde/pronograde evolutionary transition in order to test whether the acquisition of vertical climbing and suspension were decoupled during evolution. Our results indicate that the manual phalanges of Miocene apes are much more similar to one another than to living apes. In particular, Miocene apes retain primitive features related to powerful-grasping palmigrady on the basal portion, the shaft, and the trochlea of the proximal phalanges. These features suggest that above-branch quadrupedalism, inherited from stem hominoids, constituted a significant component of the locomotor repertories of different hominoid lineages at least until the late Miocene. Nonetheless, despite their striking morphological similarities, several Miocene apes do significantly differ in phalangeal curvature and/or elongation. Hispanopithecus most clearly departs by displaying markedly-curved and elongated phalanges, similar to those in the most suspensory of the extant apes (hylobatids and orangutans). This feature agrees with several others that indicate orang-like suspensory capabilities. The remaining Miocene apes, on the contrary, display low to moderate phalangeal curvature, and short to moderately-elongated phalanges, which are indicative of the lack of suspensory adaptations. As such, the transition from a pronograde towards an orthograde body plan, as far as this particular anatomical region is concerned, is reflected only in somewhat more elongated phalanges, which may be functionally related to enhanced vertical-climbing capabilities. Our results therefore agree with the view that hominoid locomotor evolution largely took place in a mosaic fashion: just as taillessness antedated the acquisition of an orthograde body plan, the emergence of the latter—being apparently related only to vertical climbing—also preceded the acquisition of suspensory adaptations, as well as the loss of primitively-retained, palmigrady-related features.

The Australopithecus afarensis partial skeleton A.L. 288-1, popularly known as “Lucy” is associated with nine vertebrae. The vertebrae were given provisional level assignments to locations within the vertebral column by their discoverers and later workers. The continuity of the thoracic series differs in these assessments,
which has implications for functional interpretations and comparative studies with other fossil hominins. Johanson and colleagues described one vertebral element (A.L. 288-1am) as uniquely worn amongst the A.L. 288-1 fossil assemblage, a condition unobservable on casts of the fossils. Here, we reassess the species attribution and serial position of this vertebral fragment and other vertebrae in the A.L. 288-1 series. When compared to the other vertebrae, A.L. 288-1am falls well below the expected size within a given spinal column. Furthermore, we demonstrate this vertebra exhibits non-metric characters absent in hominoids but common in large-bodied papionins. Quantitative analyses situate this vertebra within the genus Theropithecus, which today is solely represented by the gelada baboon but was the most abundant cercopithecoid in the KH-1s deposit at Hadar where Lucy was discovered. Our additional analyses confirm that the remainder of the A.L. 288-1 vertebral material belongs to A. afarensis, and we provide new level assignments for some of the other vertebrae, resulting in a continuous articular series of thoracic vertebrae, from T6 to T11. This work does not refute previous work on Lucy or its importance for human evolution, but rather highlights the importance of studying original fossils, as well as the efficacy of the scientific method.

The last twenty years have seen important findings in the area of paleoanthropology. The topic of man evolution fascinated scientist since Linnaeus (1758). The findings of several new genera and new species enabled the reconstruction of evolutionary trends. These trends lead to the identification of the unique living species Homo sapiens Linnaeus, 1758 (Hominidae: Homininae), starting from the splitting between Homininae and Paninae. The history of hominins' evolution was a very long one. During time the entire group took several evolutionary directions, showing an high adaptive capacity to the changes of the paleoenvironmental conditions.
Coppens (2013) provided an interesting sub-division of geological time using fossil of hominins. From geological and paleoecological settings, this author distinguished four temporal phases to re-arrange the chronostratigraphic distribution of species of Hominidae by correlating homologous part of fossils and by analyzing paleontological associations. Each phase is characterized by taxonomic and ecological homogeneity, bio-events and evolutionary degree of taxa belonging to a well defined phyletic lines (Palombo & Valli, 2003-04). Those groups may be considered a sort of continental biozones. The aim of this project is to demonstrate the validity of these phases as biozones marked by hominins.

Coppens Y. (2013) - Hominid evolution and the emergence of the genus Homo. In "Neurosciences and the Human Person: New Persperctives of Human Activities", Pontifical Academy of Science. Scripta varia, 121: 1-15.

Linnaeus C. (1758). Systema naturae per regna tria naturae, secundum classis, ordines, genera, species cum characteribus, differentiis, synonymis, locis. 10th ed. Vol. 1. Laurentii Salvii, Stockholm, Sweden.

Palombo M.R., Valli A.M.F. (2003-04) - Remarks on the biochronology of mammalian faunal complexes from the Pliocene to the middle Pleistocene in France. Geol. Romana, 37: 145-163.

For over a century, a Neogene fossil mammal fauna has been known in the Irrawaddy Formation in central Myanmar. Unfortunately, the lack of accurately located fossiliferous sites and the absence of hominoid fossils have impeded paleontological studies. Here we describe the first hominoid found in Myanmar together with a Hipparion (sl) associated mammal fauna from Irrawaddy Formation deposits dated between 10.4 and 8.8 Ma by biochronology and magnetostratigraphy. This hominoid documents a new species of ...

Most human-like features in australopiths (thick tooth enamel, smaller canine teeth, not-elongated arms-hands-fingers, not-elongated iliac blades, flat & short-toed feet, long & strong big-toes etc.) are not human-derived, but are hominid-primitive ("hominid" sensu African hominoids, versus "pongid" sensu Asian great apes), or even hominoid-primitive (Verhaegen 1993, 1995). This means that there are no scientific arguments to exclude the australopiths from being closer relatives of Gorilla or Pan than of Homo. This explains the remarkable paradox that most paleo-anthropologists believe that the African apes have few or no fossils, whereas they generally agree that the Asian great apes do have a lot of fossils (e.g. Siva-, Lufeng-, Khorat-, Giganto-pithecus).

New early Miocene forelimb fossils have been recovered from the Songhor and Lower Kapurtay localities in southwestern Kenya. We describe four specimens that are similar in size and functional capabilities. Their specific allocation is problematic but these forelimb specimens must belong to either Rangwapithecus gordoni or Proconsul africanus. If these new postcranial specimens should belong to R. gordoni, on the basis of size and common dental specimens found at Songhor, they represent a new elbow complex. The morphology of these fossils is anatomically and functionally similar to that of Proconsul. The proconsuloid elbow complex allows extensive forelimb rotations and is capable of performing arboreal quadrupedalism and climbing activities. No suspensory adaptations are apparent. The proconsuloid elbow complex remains a good ancestral condition for hominoid primates.