Scott D. Sampson

LATE CRETACEOUS TERRESTRIAL VERTEBRATES FROM MADAGASCAR: IMPLICATIONS FOR LATIN AMERICAN BIOGEOGRAPHY1

Abstract The Mahajanga Basin Project, initiated in 1993 and centered in Upper Cretaceous strata of northwestern Madagascar, has resulted in the discovery of some of the most complete, well-preserved, and significant specimens of Late Cretaceous vertebrate animals from the Southern Hemisphere and indeed the world. Among the most important finds are various specimens of crocodyliforms, non-avian dinosaurs, and mammals; these finds have the potential to provide key insights into the biogeographic and paleogeographic history of Gondwana. Madagascar has been physically isolated from Africa for over 160 million years and from all other major landmasses for more than 85 million years. The closest known relatives of many of the Late Cretaceous Malagasy taxa are penecontemporaneous forms from South America (primarily Argentina) and India, thus documenting a previously unrecognized high level of cosmopolitanism among Gondwanan vertebrates near the end of the Cretaceous. The family-level taxa that are shared among Madagascar, South America, and the Indian subcontinent are not known from penecontemporaneous horizons in mainland Africa, but it cannot yet be confidently determined if this is due to differential extinction, poor sampling, true absence (i.e., the taxa were never present on Africa), or some combination thereof. Nonetheless, currently available geologic and paleontologic data are most consistent with the Africa-first model, suggesting that Africa was the first of the major Gondwanan landmasses to be fully isolated prior to the Albian/Cenomanian boundary, and that its terrestrial vertebrate faunas became progressively more provincial during the Cretaceous, while those on other Gondwanan landmasses remained relatively cosmopolitan until the later stages of the Late Cretaceous.

Titanosaurid (Sauropoda) osteoderms from the Late Cretaceous of Madagascar

ABSTRACT In 1896 Charles Deperet described a fauna of dinosaurs from the Upper Cretaceous (?Campanian) Maevarano Formation from the Mahajanga Basin of northwest Madagascar. Among the dinosaurs was a titanosaurid sauropod that he named Titanosaurus madagascariensis. He attributed to the titanosaurid a large, thick circular osteoderm. His referral of an osteoderm to a sauropod was widely doubted until 1980 when Bonaparte and Powell described Saltasaurus loricatus, an armored titanosaurid from Argentina. Since then titanosaurid osteoderms have been recognized from Spain, France and Malawi. In 1996, we collected three isolated and eight associated osteoderms from the Maevarano Formation, confirming Deperets prescient observation. They range in length from 3 cm to 17 cm, and in thickness up to 6.5 cm. At least one of the two titanosaurids we now recognize from Madagascar was covered with a sparse armor, and that the skin was in places nearly 7 cm thick.

Sex and destiny: The role of mating signals in speciation and macroevolution

A growing body of research posits a central role for mating signals in speciation and the reproductive isolation of species, yet there has been relatively little consideration of mating signal evolution within macroevolutionary theory. Factors that influence the divergence of fertilization systems generally, and mating signals specifically, may incidentally influence rates of speciation and patterns of species sorting. Potential key processes include: genetic drift, natural selection (differential survival), selection for mate recognition, and sexual selection. This paper explores the integration of mating signal evolution into macroevolution and hierarchy theory, arguing that speciational patterns may frequently result from “effect sorting”; in which microevolutionary processes operating at the organismal level have macroevolutionary effects at the clade level. Preliminary evidence indicates that sexual selection is a widespread and potent evolutionary force that, together with other mechanisms, may have...

Chapter IV - A Cretaceous End to a Lost World

This chapter provides illustrations of dinosaurs by different artists; the paintings and sculptures illustrated are only a fraction of the Lazendorf collection. The drawings, paintings, and sculptures in this chapter invite viewers to step back in time and experience the world and several of its most celebrated inhabitants as they once were. The artwork in this volume uses balance, composition, perspective, and color in concert with factual information to create riveting images of the past that capture the interest and imagination of a very wide audience. This art represents a new level of excellence and originality. Throughout this chapter, an effort has been made to provide a scientific context for the sculptures and drawings. The chapter highlights the artists and scientists, who worked together to generate glimpses of dinosaurs in life, with their brief biographical information.