Alisa J. Winkler

Lothagam: a record of faunal change in the late Miocene of East Africa

ABSTRACT Lothagam is a richly fossiliferous late Miocene site near the western shore of Lake Turkana, northern Kenya. This site has yielded a diverse fauna documenting a chronological interval poorly known from elsewhere in Africa. Lothagam was first collected by an American research group in the late 1960s and early 1970s. Field studies by the National Museums of Kenya between 1989–1993 have recovered many additional vertebrate fossils, including species previously unknown from Lothagam. This contribution presents a revised, formal stratigraphic framework, initial results of a vertebrate systematic revision, and new interpretations of the paleoenvironmental setting. Analysis of the sedimentary facies and their fossil content indicates the presence of a large, slow moving, well-oxygenated perennial river with abundant backswamps and ponds. Comparisons with faunas from earlier middle to late Miocene Kenyan localities suggest that a major environmental change occurred at the end of the Miocene.

Oligocene mammals from Ethiopia and faunal exchange between Afro-Arabia and Eurasia

Afro-Arabian mammalian communities underwent a marked transition near the Oligocene/Miocene boundary at approximately 24 million years (Myr) ago. Although it is well documented that the endemic paenungulate taxa were replaced by migrants from the Northern Hemisphere, the timing and evolutionary dynamics of this transition have long been a mystery because faunas from about 32 to 24 Myr ago are largely unknown. Here we report a late Oligocene fossil assemblage from Ethiopia, which constrains the migration to postdate 27 Myr ago, and yields new insight into the indigenous faunal dynamics that preceded this event. The fauna is composed of large paenungulate herbivores and reveals not only which earlier taxa persisted into the late Oligocene epoch but also demonstrates that one group, the Proboscidea, underwent a marked diversification. When Eurasian immigrants entered Afro-Arabia, a pattern of winners and losers among the endemics emerged: less diverse taxa such as arsinoitheres became extinct, moderately species-rich groups such as hyracoids continued into the Miocene with reduced diversity, whereas the proboscideans successfully carried their adaptive radiation out of Afro-Arabia and across the world.

Faunal interchange and Miocene terrestrial vertebrates of southern Asia

Problems of stratigraphic completeness and poor temporal resolution make analysis of faunal change in terrestrial sequences difficult. The fluvial Neogene Siwalik formations of India and Pakistan are an exception. They contain a long vertebrate record and have good chronostrati- graphic control, making it possible to assess the influence of biotic interchange on Siwalik fossil communities. In Pakistan, the interval between 18 and 7 Ma has been most intensively studied and changes in diversity and relative abundance of ruminant artiodactyls and muroid rodents are documented with temporal resolution of 200,000 years. Within this interval, diversity varies con- siderably, including an abrupt rise in species number between 15 and 13 Ma, followed by a decline in ruminant diversity after 12 Ma and a decline in muroid diversity in two steps at 13 and 10 Ma. Significant changes in relative abundance of taxa include an increase in bovids between 16.5 and 15 Ma, a decrease in tragulids after 9 Ma, and a very abrupt increase in murids at 12 Ma. Megacri- cetodontine rodents also decrease significantly at 12 Ma, and smaller declines -re recorded among myocricetodontine and copemyine rodents after 16 Ma. An increase of dendromurine rodents at 15.5 Ma is also observed. There is also a trend of progressive size increase among giraffoids and bovids throughout the sequence. We have also investigated relationships between biotic interchange and diversity, body size, and relative abundance, concluding that (1) the rapid increase in ruminant and muroid diversity was largely due to immigration, whereas in situ speciation had only a secondary role; (2) during intervals of increasing diversity, resident lineages did not have higher than average rates of in situ speciation; (3) during intervals with rising diversity, greater extinction did not accompany increased immi- gration; (4) during intervals with falling diversity, there may have been greater extinction in recently invading lineages; and (5) change in diversity was independent of changes in relative abundance and body size.

Systematics and biogeography of middle Miocene rodents from the Muruyur Beds, Baringo District, Kenya

ABSTRACT Preliminary excavations in western Kenya from the middle Miocene Muruyur Beds, in particular from the Kipsaramon site complex (15.5 Ma), are yielding a diverse rodent fauna from a poorly documented period of African prehistory. Seven families (?sciurids, pedetids, anomalurids, thryonomyids, diamantomyids, myophiomyids, and cricetodontids) are represented. Thryonomyoids are dominant; cricetids and murids of modern aspect are currently unknown. The fauna includes a mixture of primitive early Miocene taxa (e.g., Diamantomys and Notocricetodon) and also more derived taxa (i.e., Thryonomyidae genus and species large). A new small anomalurid, Anomalurus parvus, sp. nov., is reported. Faunal composition and the distribution of rodent taxa from the Muruyur Beds show similarities with early and middle Miocene sites in East Africa, Namibia, and Saudi Arabia. Comparison of early and middle Miocene African rodent faunas suggests a period of relative faunal stability among rodent taxa during this time.

Bone strain following application of a rigid bone plate: An in vitro study in human mandibles

This study evaluated the effect of a bone plate on mandibular bone strain patterns during static loading. A stainless steel bone plate was unilaterally attached to five human mandibles, which were then subjected to static loads of 60 kiloponds. Four strain gauges attached to the cortical bone were used to measure the strain patterns within the mandible both before and after the bone plate was attached. The results showed that statistically significant alterations in the strain patterns occurred following plating of the mandible. The mandible with the plate attached became more stiff, presumably due to the difference in modulus of elasticity between the plate and the bone. However, this increase in stiffness was relatively small when compared with both total strain under load and strain produced by tightening of the bone screws.

Dispersalist implications of Paraulacodus indicus: A South Asian rodent of African affinity

The rodent family Thryonomyidae, especially the middle Miocene Paraulacodus indicus from Pakistan, presents the minimum biogeographic and biostratigraphic conditions required to document intercontinental dispersal. Thryonomyids have a long evolutionary history in Africa, where the closest relatives (congeneric) to P. indicus occur. The Siwalik fossil record of the Indian Subcontinent is sufficient to precisely date the range of P. indicus and demonstrates the lack of a close relative in that region. A scenario of long distance dispersal from Africa to southern Asia in the middle Miocene best explains the Siwalik occurrence of P. indicus. Paraulacodus indicus is more closely related to P. johanesi and other African middle Miocene species than to the smaller Kochalia from older and coeval Siwalik stratigraphic horizons. We reconstruct two dispersal events of Thryonomyidae from Africa to the Indian Subcontinent, the first prior to 16.3 Ma, and the second about 13 Ma.

Systematics, Paleobiogeography, and Paleoenvironmental Significance of Rodents from the Ibole Member, Manonga Valley, Tanzania

The late Miocene and Pliocene fossil record documents important changes in rodent faunal composition heralding the advent of the modern East African fauna. Most significant among these changes is the beginning of the radiation of the Murinae, the true rats and mice, whose earliest African record is 12–10 Ma, and which currently dominate rodent assemblages in sub-Saharan Africa. The rodent record for the late Miocene and Pliocene is better than that for the middle Miocene, but still woefully inadequate. Hence the significance of late Neogene rodent remains from the Manonga Valley, in north-central Tanzania.

The middle Pleistocene rodent Atopomys (Cricetidae: Arvicolinae) from the eastern and south-central United States

ABSTRACT New records of Atopomys salvelinus from West Virginia and Florida, and additional remains of A. texensis from Texas are reported. A partial mandible of A. salvelinus with M1–2 from Alachua County, Florida, is the first record of the genus from that state, and the most complete specimen of Atopomys known. Although M3s of A. texensis have not been recovered, three M3s of A. salvelinus are now known from Hamilton Cave, West Virginia. These teeth, as well as the others, are similar to those of the Blancan arvicoline genus Nebraskomys. These similarities support Hibbards (1970) suggestion that Nebraskomys was ancestral to Atopomys.

Chapter 23: Tedford's Gerbils from Afghanistan

Abstract Thirty-five years ago Dick Tedford and Len Radinsky collected the remains of three individuals of a new gerbil in the hill country of Afghanistan. Tedfords gerbil is a new, large species of a widespread late Neogene genus, Abudhabia. The material is extraordinarily complete, including three crania and many of the postcrania. The extinct taxon is clearly a gerbil based on dental and cranial features, while it has a relatively underived basicranium. The long hind limb proportions appear strongly derived. The bulla is enlarged and the mastoid is little inflated, not as inflated as in many gerbils. The fossil form is a primitive taterilline and suggests homoplasy in ear structure and dentition among modern taxa.

The Lower Third Premolar of Serengetilagus praecapensis (Mammalia: Lagomorpha: Leporidae) from Laetoli, Tanzania

The present study suggests evolutionary changes in the morphology and size of the lower third premolar of the leporid Serengetilagus praecapensis from the Upper Ndolanya and Upper Laetolil Beds, Laetoli, Tanzania (ca. 3.85–2.66 Ma). Mandibular depth at p3 was compared also as a proxy indicator of size. The occlusal morphology of p3s from Laetoli is variable, but most commonly the tooth is crescentic with a posteroexternal reentrant (PER) extending about half way across the width of the tooth, plus distinct anteroexternal (AER) and anterior (AR) reentrants. An anterointernal reentrant (AIR) is weak to distinct. A proportionally higher percentage of p3s from the Upper Ndolanya Beds (50%) and the uppermost Upper Laetolil Beds (ULB, between Tuff 7 and the Yellow Marker Tuff, 49%) had a weak AIR compared to only 29% of specimens from between Tuffs 5–7, ULB. The higher frequency of a weak AIR in the geologically younger population is interpreted as the character state being newly reversed to the plesiomorphic condition (AIR weak to absent). There are only two poorly preserved p3s from the Lower Laetolil Beds: on both specimens the AIR and AR are weak to absent (plesiomorphic condition). AR is almost always present on p3s from the Upper Ndolanya and Upper Laetolil Beds. On average, p3s from the Upper Ndolanya Beds are slightly shorter and narrower, and the mandibles slightly less deep at the level of p3 than those from the Upper Laetolil Beds. However, the range of variation of measurements is quite similar between samples from the Upper Ndolanya and Upper Laetolil Beds. A specimen from the Upper Ndolanya Beds (EP 1223/03.1) has a p3 proportionally wider than mean values for other specimens from both the Upper Ndolanya and Upper Laetolil Beds. In conjunction with p3 occlusal morphology, this specimen may represent a new, as yet unnamed, species. Although interesting, the differences observed between samples from the Upper Ndolanya Beds and subunits of the Upper Laetolil Beds are not considered adequate for separation into a distinct species or subspecies.