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The global paleomonsoon concept predicts an antiphase response of monsoon rainfall in the Northern and Southern Hemispheres at timescales where there is asymmetric solar forcing and/or asymmetric hemispheric temperature changes. However, as different monsoon systems have different sensitivities to local, regional, and global forcing, rainfall response may vary regionally, particularly during large global climatic changes such as the last deglaciation where warming occurred in both hemispheres. Despite its role as a key Southern Hemisphere counterpart to the Arabian and Indian summer monsoons, the behavior of the summer monsoon in the Southern Hemisphere of the Indian Ocean during the last deglaciation is unknown. Therefore, we present a new high‐resolution, precisely dated, and replicated speleothem stable isotope record from Tsimanampesotse National Park in southwest Madagascar that covers the last deglaciation. We show that speleothem growth phases respond largely to movements of the Southern Hemisphere summer Hadley circulation (summer extent of the tropical rainbelt/mean Intertropical Convergence Zone location), with some contribution from sea surface temperature changes at key times, such as during the Bølling‐Allerød. In contrast, speleothem δ¹⁸Ο responds primarily to sea surface temperature, in particular the location of the deep atmospheric convection isotherm, while summer Hadley circulation changes take a secondary role. Separating the varying influences of temperature and atmospheric circulation in controlling southwest Madagascan rainfall is critical to understanding rainfall variability in both the past and the future.

 

Most researchers believe that Madagascar’s megafauna went extinct between 2000 and 1000 years ago. Across Madagascar, fossil specimens of the island’s endemic (and now extinct) pygmy hippopotamuses, elephant birds, giant lemurs, horned crocodiles, and other vertebrates larger in body size than 10 kg commonly date to the first millennium of the Common Era (CE) or earlier; few records date to the second millennium CE. Whereas megafaunal populations appear to have crashed almost simultaneously near the end of the first millennium CE, small populations can survive in remote pockets for centuries after precipitous species decline, perhaps longer. Examining the differences in the population dynamics of declining species and other factors can help to better identify the ultimate timing of extinction. Ever since Etienne de Flacourt traveled to Madagascar in the late 1600s, Malagasy stories of large-bodied wild animals have been recorded. Many include fantastic, clearly mythical creatures, but some provide anatomical or behavioral details which are consistent with legends or even direct observations of real, albeit potentially already extinct, species (including elephant birds, hippopotamuses, and some giant lemurs). In December 1989, at 06:00 hours, one of us (BZF) witnessed a large euplerid carnivoran locally known as fosabe (big fosa) or fosa jobijoby (blackish fosa) who had entered his field tent at Montagne d’Ambre. The animal was “twice the size and much darker than the common fossa” (Freed, 1996, p. 34). The individual was black and weighed approximately 20-25 kg. Freed wrote that the animal was well known to the local people and that “many local people also reported seeing it”. The animal fits paleontologists’ expectations for Cryptoprocta spelea, a large carnivoran known from the fossil record, believed to have been extinct for at least 1000 years. In June 2020, we recorded modern accounts of the big fosa. One of us (ESN) visited villages in four different sectors (Northwest, Northeast, East, and West) of Montagne d’Ambre National Park and the Forêt d’Ambre Special Reserve to examine potential regional differences and/or similarities in the stories of this animal, and whether such accounts include mythical elements, relevant anatomical information, and/or credible recent sightings. We also recorded stories of an Endangered extant animal, the aye-aye of the genus Daubentonia (also known locally as the kakahely). Ultimately, we believe this folklore provides clues that may help elucidate the geography of decline and possible late survival of an “extinct” megafaunal animal on Madagascar. 

The Mahafaly karst of southwestern Madagascar is rich with subfossil deposits. Vintany Cave (also known as Aven Cave), a submerged cave at Tsimanampesotse National Park, is the most subfossil-dense submerged cave known in the world. In particular, the cave has yielded abundant remains of birds, including some that are extinct. Among 1077 bird specimens recovered under water from the cave floor and from excavated sediments at this site, 35 different taxa were identified. Taxonomic attributions were made through comparative morphological analysis, using comparative osteological museum collections. The majority of these species still occur inside the park. Five extinct taxa were recovered from the cave, including one species of elephant bird (Aepyornithidae, Mullerornis modestus), two species of giant endemic ground couas (Cuculidae, Coua cf. berthae and C. cf. primaeva), a shelduck (Alopochen sirabensis, Anatidae), and a lapwing (Charadriidae, Vanellus madagascariensis). Two extant taxa, Haliaeetus vociferoides (Accipitridae) and Threskiornis bernieri (Threskiornithidae) are locally extirpated, but exist at other localities in Madagascar. Remains of Greater Vasa Parrots (Psittaculidae, Coracopsis vasa) are predominant. Some of the identified extinct and locally extirpated taxa from Vintany Cave have an aquatic dependence, most specifically freshwater, that suggests that there has been environmental modification such as reduction of the important water sources in the region of Tsimanampesotse, and wetter conditions in the area in the past. 

As the largest-bodied member of the family Lemuridae and the presumed primary disperser of large seeds, Pachylemur, now extinct, was a critical member of Madagascar’s primate communities. Material of this genus has been found at almost all subfossil sites across Madagascar, but extensive samples of this taxon are known from very few. It has been one of the more historically neglected of the “giant” extinct lemurs, as it is not very different in morphology from its nearest extant relative, Varecia, except in body size. The flooded cave called Vintany at the Tsimanampesotse National Park in southwestern Madagascar has yielded numerous specimens of P. insignis, including whole skulls and mandibles, many isolated postcranial elements, and, importantly, partial associated skeletons of immature individuals. This material allows us to address previously unanswered questions regarding its paleobiology, including questions concerning its growth and development. This article focuses specifically on its life history profile (especially developmental sequences and life history-related traits such as Retzius line periodicity of the teeth and endocranial volume in adults). We ask to what extent, despite its larger size, did Pachylemur “grow” like its smaller-bodied relatives? Did its dental eruption sequence and index of Relative Retardation of the Replacement teeth resemble those of its closest relatives? Did it, like other lemurs, have a Retzius line periodicity that is lower than “expected” for a primate of its body size, and if so, what is the likely significance of this? Was its brain smaller than expected for a primate of its body size? For these and other questions, we evaluate how large-bodied lemurs differ from anthropoids of comparable body size. 

The relative importance of climate and humans in the disappearance of the Malagasy megafauna remains under debate. Data from southwestern Madagascar imply aridification contributed substantially to the late Holocene decline of the megafauna (the Aridification Hypothesis). Evidence for aridification includes carbon isotopes from tree rings, lacustrine charcoal concentrations and pollen assemblages, and changes in fossil vertebrate assemblages indicative of a local loss of pluvial conditions. In contrast, speleothem records from northwestern Madagascar suggest that megafaunal decline and habitat change resulted primarily from human activity including agropastoralism (the Subsistence Shift Hypothesis). Could there have been contrasting mechanisms of decline in different parts of Madagascar? Or are we lacking the precisely dated, high resolution records needed to fully understand the complex processes behind megafaunal decline? Reconciling these contrasting hypotheses requires additional climate records from southwestern Madagascar. We recovered a stalagmite (AF2) from Asafora Cave in the spiny thicket ecoregion, ~10 km from the southwest coast and just southeast of the Velondriake Marine Reserve. U-series and 14C dating of samples taken from the core of this stalagmite provide a highly precise chronology of the changes in hydroclimate and vegetation in this region over the past 3000 years. Speleothem stable oxygen and carbon isotope analyses provide insight into past rainfall variability and vegetation changes respectively. We compare these records with those for a stalagmite (AB2) from Anjohibe Cave in northwestern Madagascar. Lastly, odds ratio analyses of radiocarbon dates for extinct and extant subfossils allow us to describe and compare the temporal trajectories of megafaunal decline in the southwest and the northwest. Combined, these analyses allow us to test the Aridification Hypothesis for megafaunal extinction. 

Taolambiby, a key subfossil site in southwestern Madagascar, has yielded many bones of extinct large lemurs and associated fauna in excavations spanning more than a century. In 2004 our group collected a 4.4 m sediment profile from deposits near prior excavations. Our aim was to use sedimentological and palynological inferences to examine the interaction between climate change and human activities, in order to better understand how each may have contributed to local extirpations. The basal age of this profile was ca. 3500 cal yr BP. Lithology of the excavated and cored material showed many changes in sediment regime, reflecting the variable natureof the basin’s hydrology. After ca. 1500 cal yr BP, the record shows successive drying of the site and subsequent erosion and redeposition. After this time, pollen and spores were not preserved but charcoal particles continued to provide a record of local and regional fires up to the present. Between 340 and 250 cm below surface, pollen was well-preserved, showing evidence for a mixture of mesic and xeric vegetation, including many trees, shrubs, forbs, and ferns, most still found in the adjacent Bezà Mahafaly Special Reserve. This pollen record, spanning the period from ca. 3000 - 1500 cal yr BP, shows evidence for increased wetness at the beginning of the period and subsequent aridification. Coprophilous fungus spores (Sporormiella) are high during this same interval, suggesting the local presence of abundant megafauna, but decline with increasing aridification. 

Madagascar is famous today not only for its unique biodiversity, but also for the high levels of endemism of plants and animals. Less appreciated is the fact that, in the recent past, the island had even greater biodiversity with many other endemic animals such as giant lemurs, elephant birds, pygmy hippopotami, tortoises, and crocodiles that have gone extinct within the past 2000 years. The extinction of many of these groups is thought to be the result of both human activities and environmental change. Most research has focused on the lemurs, hippopotami, and elephant birds. Other recently extinct animals, including the Malagasy horned crocodile (Voay robustus), are relatively poorly known. Madagascar’s subfossil crocodylians include two taxa: the extinct V. robustus (the Malagasy horned crocodile) and the extant Crocodylus niloticus. The latter arrived on Madagascar relatively recently and we know little about the habitat preferences, distributions and ecological interactions (if any) of either species during the Holocene. In order to better understand the recent history of crocodylian extinction in Madagascar, we must first identify which species were present and where they were found. We present here a description of subfossil crocodylian material collected from the newly discovered subfossil site of Tsaramody (Sambaina Basin), a high-elevation wetlandenvironment. At 1655 m, it represents the highest elevation subfossil site on the island. Here we describe both cranial (e.g., premaxillary, jugal, and squamosal “horns”) and postcranial elements (e.g., osteoderms). Our research indicates that crocodile material from Tsaramody appears morphologically to belong to V. robustus, the extinct species. However, oval tuberosities on the frontal bone and a triangular extension of the squamosal bone suggest previously unrecognized variation.