Read an Excerpt
Extinct Madagascar
Picturing the Island's Past
By Steven M. Goodman, William L. Jungers The University of Chicago Press
Copyright © 2014 The University of Chicago
All rights reserved.
ISBN: 978-0-226-15694-1
CHAPTER 1
Introduction
General
It is important to mention at the onset that this book is not intended to be a technical summary of what we know about ecological change and animal extinction on Madagascar in recent geological history. Instead, given our own fascination in trying to understand and perhaps partially answer the question as to what happened to an extraordinary assortment of endemic Malagasy animals that no longer roam the Earth, we decided to bring to a general audience an overview of these subjects. Our own particular research interests, which accent different aspects of these questions, are presented in the text. While enormous strides have been made in the past decades to understand different facets of "what happened," we still lack many of the critical details to properly weigh and put in balance factors induced by natural climate change versus those due to human modifications of the landscape. Critical for the latter "anthropogenic" aspect is the incomplete archaeological record of Madagascar, so that questions such as when humans originally arrived on the island remain controversial and uncertain. The complete story is like a puzzle, but several linking pieces are missing or insufficiently known to provide the complete window into what transpired. After the general opening sections in Part 1 to set the stage, Part 2 has twenty plates created by Velizar Simeonovski as centerpieces for reasonably well-known paleontological and archaeological localities. Discussing each individual plate, we unfold different pieces of the puzzle for a variety of sites and extinct species based on different sources of information. His plates, each of which acts as a separate "window into the past," bring our narratives to life.
As we learn more about the island of Madagascar, which covers nearly 600,000 square kilometers—the size of California with a good portion of Oregon—it becomes clear that a single, unequivocal response to the question of what happened is a fleeting possibility. No panacea exists for several reasons. Given the ecological, geological, topographical, meteorological, and cultural complexities and variation found across this massive landscape, multiple and different factors at the regional level have to be invoked to explain dramatic change during short periods of geological time, that is, on a scale of a few thousand years. As suggested by the late Robert Dewar some years back, if scientists working on Madagascar have come to understand one aspect, "it seems less and less appropriate to expect a single, uniform cause for the extinctions will be found" (83). Hence, in following this point, we suggest that an island-wide response as to what happened to the ecosystems and their constituent animals is inappropriate and implausible; there simply is no single "silver bullet." The different biological regions and cultural aspects in various cases need to be examined individually. Many debates remain to be resolved concerning what factors are responsible for these changes. Our intent with this book has been to summarize and provide a glimpse into decades of detailed scientific studies for a general audience in order to help them discover the extraordinary island of Madagascar and appreciate all of the recent changes that have taken place.
Aspects of Format
We have tried to write this book in a relatively nontechnical style. Words and expressions are occasionally used that might not be familiar to a general audience, but at first use and sometimes deeper into the text, we have tried to explain such terms. Further, while it is important to provide a certain number of bibliographic references for critical points and information presented in the text, particularly for documentary purposes and for those wanting additional details, we have done this in a light-handed fashion. Rather than congesting the text with such citations, we have used a number system, with complete reference information at the end of the book. Finally, we have included two indexes, one to the scientific names and another of Malagasy locality names used in the text.
We differentiate between two different types of illustrations used in this book. The term "plate" specifically refers to paintings by Velizar Simeonovski that are presented in Part 2; these twenty plates capture the different site-specific ecosystems and animals that occurred or still occur on the island. On the inside front cover is a map of the different localities for the twenty plates, providing the reader a key to their geographical position. In the text associated with these plates, different themes are discussed and considerable cross-references are made between them. In several cases, a small black-and- white figure and associated text are presented adjacent to a plate to provide a key to the identification of the animals depicted. The term "figure" refers to all of the other illustrations presented in this book. Associated with their often-complex names and considerable number of syllables, Malagasy locality names can be difficult for the non- initiated. In Figure 1, we present the placement for most localities mentioned in the text and distinguish between paleontological and archaeological sites.
Major advances have been made in the past few decades in our understanding of extinct and living animals of Madagascar. New insights are now available on their distribution, ecology, and classification (taxonomy). Given these diverse studies, various scientists maintain differing interpretations of certain types of data and, naturally, opinions vary. Hence, the systematics or classifications for different organisms presented in this book are in some cases in a state of flux. As a case in point, the giant extinct tortoises of Madagascar were classically placed in the genus Geochelone, with two recognized species: Geochelone abrupta and Geochelone grandidieri. Subsequently, it was proposed that these species should be placed in the genus Dipsochelys, and this in turn created more debate. Accordingly, a petition supported by numerous scientists working on reptiles has been sent to the International Commission on Zoological Nomenclature in an effort to stabilize the taxonomy of these animals; in this case, for certain living and extinct giant tortoises, the generic name would be Aldabrachelys. Herein, we use this genus for the two extinct species of Madagascar, Aldabrachelys abrupta and Aldabrachelys grandidieri, as well as the extant Aldabra tortoise, Aldabrachelys gigantea. We have used the abbreviation "sp." for species and "spp." in its plural form.
The Artist
Velizar Simeonovski is a native of Bulgaria. In 1987 he graduated from the Professional Art School of Applied Arts in Sofia, and in 1995 he received his MS in vertebrate zoology from the Sofia University (his thesis was on aspects of wild and feral cats). His current research interests are in the evolution of external mammal traits, such as spots, stripes, and different types of pelage patterns, including aspects of variation and development. Using his considerable knowledge of animal anatomy and careful observation of wild and captive animals, he has an extraordinary capacity to reconstruct and figure extinct animals. Starting with bony characters, he is able to layer on muscles and add skin and other ornamentation (Figure 2). His ability to bring his subjects to life distinguishes him from many other artists working in this domain.
In late 2002, Velizar was in contact with Tom Gnoske at the Field Museum in regard to Tom's recent discoveries on lion ecology. They formed an important bond over their common interests in Carnivora, and the following year Tom was able to organize Velizar's visit to Chicago so they could work on some joint projects. Subsequently, the word got around to scientific and exhibition members at the museum about Velizar's extraordinary talents, and he was engaged to illustrate a number of different scientific works, field guides, and general public exhibits. His work has now been incorporated into permanent museum exhibitions, as well as temporary shows around the world.
While his original training was in traditional art forms and techniques, which he used during the earlier portions of his career, he has also embraced rapidly changing digital technologies. In fact, all of the plates presented in this book are "computer art," that is, drafted and drawn on a computer. Given Velizar's profound curiosity of how the animal world functions, combined with his training in biology and unparalleled talents to create flesh from bone, his current work has helped to create a new genre of art.
Geological Time, Dates, and Radiocarbon Dating
In this book, we focus on a very recent period of geological time, specifically the Holocene Epoch, which commenced slightly less than 12,000 years BP (see Figure 3). Most of the bone and pollen deposits discussed in this book are from the Holocene, although some are slightly older and date from the Late Pleistocene, about 40,000 years BP. These two epochs, Holocene and Pleistocene, form the period known as the Quaternary. Given that the Earth is over 4.5 billion years old, the period we are discussing is less than 0.0009 percent of its history! For a little more perspective, members of the genus Homo, to which we belong, evolved near the beginning of the Pleistocene approximately 2.3 million years ago in Africa, another blink of the eye in terms of deep geological time.
Scientists use several different time scales to gauge the date or period of past events. As most of the dating we employ in this book is based on radiocarbon analysis (see below), we employ the time scale known as "years before present," which is abbreviated throughout the book as "years BP." (The term "years BP" is equivalent to calendar years before present, or cal yr BP.) As the testing of nuclear weapons in the 1950s greatly changed the proportion of carbon isotopes in the atmosphere, the date of 1 January 1950, at the start of these activities, is used as the cutoff year of this system. Hence, using our modern calendar, a date of 150 years BP in the year 2014 is 150 + 64 (i.e., 2014 - 1950) = 214 years ago.
The advent of radiocarbon techniques in the 1950s provided an important development for dating organic materials recovered from archaeological and recent paleontological sites. Carbon is found in nature in different isotope forms, with the dominant one being carbon-14 (14C). Physicists have been able to calculate with a high level of precision the rate that 14C degrades into its different isotopic forms. During the process of photosynthesis, when plants assimilate and fix carbon dioxide into their organic tissues, they incorporate 14C at levels largely equivalent to those found in the atmosphere. As the system of photosynthesis is fundamental to most food chains, whether it involves a herbivorous animal such as a beetle or a gazelle that eats plants, carnivorous birds that consume beetles, or leopards that feed on gazelles, all have measurable levels of 14C in their tissues. Thus, in turn, based on the degradation of this isotope starting with the death of the plant or animal in question, the period it was living can be estimated with considerable precision. This technique—whether for wood, charcoal, or bone found at an archaeological site or a recent paleontological site—works for a variety of organisms that were alive within the past 60,000 years. Because of the manner in which 14C degrades, other dating techniques need to be employed for older plant and animal material.
The vast majority of dates reported in this book are from bone samples. In such cases, these dates are derived mostly from carbon isolated from the collagen portion of the bone, which includes both organic and inorganic portions. A critical step in this process is the separation of contaminated carbon, which is currently done in most labs with a special pre-treatment processing of the bone. Further, other artifacts can modify the accuracy of radiocarbon dates from chemical change or contamination, either natural or artificial. In any case, there are non-trivial technical hurdles in producing reliable dates, and not all published ones are necessarily accurate. Hence, this highlights the importance of having multiple dates from a given strata or horizon of a site that fall within the same immediate range. In cases when these are not available, other corroborative information needs to be marshaled. Further, the techniques used for radiocarbon dating pose other complications, such as how certain organisms stock or assimilate older 14C. Different calculations have been proposed to get around these problems, and they provide corrected estimates centered on calibrated maximum and minimum values for a given radiocarbon date. Herein we also use the mean of these values, often cited in the text as "mean calibrated date," which follows in parentheses the radiocarbon date in years BP. For example, the maximum and minimum 14C calibration dates for a lemur bone from a site yielded the dates of 2,360–3,450, with the mean of these values being 2,905, giving us the mean calibrated date. In virtually all cases, these different calibrated values are derived from the work of David Burney and colleagues or Brooke Crowley (54, 69).
Among plants, different systems exist when they convert light energy from the sun into chemical energy (photosynthesis) that is used to meet the plant's nutritional needs. Photosynthesis is at the origin of all organic carbon within the tissues of a plant, invertebrates that eat plants, vertebrates that consume the invertebrates, and carnivores that feed on the vertebrates. In this regard, different aspects of the diet of an organism can be followed based on the types of carbon within them. There are three types of photosynthesis, and these three processes give rise to different carbon cycling. Without going into too much detail, plants that trap carbon dioxide based on a three-carbon compound are C3 plants, and those that use a four-carbon compound are C,4or CAM plants; the C4 or CAM types of photosynthesis are differentiated during the period (night or day) in which they fix carbon dioxide. Now an extraordinary aspect is that based on carbon isotope values from radiocarbon-dated organic material, inferences can be made as to the type of photosynthetic cycle that a given plant underwent, or for animal-eating organisms the types of plants entering into the food chain that formed the basis of their diet. In Part 2 of this book, on several occasions we discuss this type of information to provide insight into different life-history traits of extinct animals.
What Is a Subfossil?
When most people think of a fossil, they envision some form of rock that holds traces of a formerly living organism, such as shell, bone, wood, coprolites, tracks, and so on. A number of different processes led to the creation of fossils, but one of the more common is the deposition of an organism or portions of it underwater and out of direct contact with the air; this anaerobic situation notably reduces the speed of tissue decomposition. Under certain conditions, remains can be rapidly buried in sediments, forming a mold. In such cases, the process of mineralization can commence, in which water heavily charged with precipitates, such as silica or calcite, come out of solution, fill the mold cavity, and form a rock replicate of the organism that made up the cast.
Now subfossils, as we refer to them herein, are the physical remains of animals (bone) or plants (wood, seeds, and pollen) but without any significant degree of mineralization. In some cases, subfossil remains look like they just came out of the stew pot, in largely perfect shape and only slightly discolored, while in other cases they are fragmented and notably decomposed. The remains of animals recovered in caves can be covered and/or infiltrated with calcite from active formations, although minerals have not replaced the bone itself (Figure 4). One of the very useful assets of subfossils is that they are essentially unmodified remains of the former living organism and can yield DNA for molecular genetic studies, carbon for radiocarbon dating, or different types of stable isotopes to examine dietary preferences of the organism; the latter two aspects are discussed above. Regrettably, in some cases, the manner in which the material was deposited, or perhaps something chemical in the surrounding soils, can degrade the valuable organic molecules.
(Continues...)
Excerpted from Extinct Madagascar by Steven M. Goodman, William L. Jungers. Copyright © 2014 The University of Chicago. Excerpted by permission of The University of Chicago Press.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site.
