Giant subfossil lemur graveyard discovered, submerged, in Madagascar

Teasing Apart Impacts of Human Activity and Regional Drought on Madagascar’s Large Vertebrate Fauna: Insights From New Excavations at Tsimanampesotse and Antsirafaly

Madagascar experienced a major faunal turnover near the end of the first millenium CE that particularly affected terrestrial, large-bodied vertebrate species. Teasing apart the relative impacts of people and climate on this event requires a focus on regional records with good chronological control. These records may document coeval changes in rainfall, faunal composition, and human activities. Here we present new paleontological and paleoclimatological data from southwestern Madagascar, the driest part of the island today. We collected over 1500 subfossil bones from deposits at a coastal site called Antsirafaly and from both flooded and dry cave deposits at Tsimanampesotse National Park. We built a chronology of Late Holocene changes in faunal assemblages based on 65 radiocarbon-dated specimens and subfossil associations. We collected stalagmites primarily within Tsimanampesotse but also at two additional locations in southern Madagascar. These provided information regarding hydroclimate variability over the past 120,000 years. Prior research has supported a primary role for drought (rather than humans) in triggering faunal turnover at Tsimanampesotse. This is based on evidence of: (1) a large freshwater ecosystem west of what is now the hypersaline Lake Tsimanampesotse, which supported freshwater mollusks and waterfowl (including animals that could not survive on resources offered by the hypersaline lake today); (2) abundant now-extinct terrestrial vertebrates; (3) regional decline or disappearance of certain tree species; and (4) scant local human presence. Our new data allow us to document the hydroclimate of the subarid southwest during the Holocene, as well as shifts in faunal composition (including local extirpations, large-vertebrate population collapse, and the appearance of introduced species). These records affirm that climate alone cannot have produced the observed vertebrate turnover in the southwest. Human activity, including the introduction of cattle, as well as associated changes in habitat exploitation, also played an important role.

A juvenile subfossil crocodylian from Anjohibe Cave, Northwestern Madagascar

Madagascar’s subfossil record preserves a diverse community of animals including elephant birds, pygmy hippopotamus, giant lemurs, turtles, crocodiles, bats, rodents, and carnivorans. These fossil accumulations give us a window into the island’s past from 80,000 years ago to a mere few hundred years ago, recording the extinction of some groups and the persistence of others. The crocodylian subfossil record is limited to two taxa, Voay robustus and Crocodylus niloticus, found at sites distributed throughout the island. V. robustus is extinct while C. niloticus is still found on the island today, but whether these two species overlapped temporally, or if Voay was driven to extinction by competing with Crocodylus remains unknown. While their size and presumed behavior was similar to each other, nearly nothing is known about the growth and development of Voay, as the overwhelming majority of fossil specimens represent mature adult individuals. Here we describe a nearly complete juvenile crocodylian specimen from Anjohibe Cave, northwestern Madagascar. The specimen is referred to Crocodylus based on the presence of caviconchal recesses on the medial wall of the maxillae, and to C. niloticus based on the presence of an oval shaped internal choana, lack of rostral ornamentation and a long narrow snout. However, as there are currently no described juvenile specimens of Voay robustus, it is important to recognize that some of the defining characteristics of that genus may have changed through ontogeny. Elements include a nearly complete skull and many postcranial elements (cervical, thoracic, sacral, and caudal vertebrae, pectoral elements, pelvic elements, forelimb and hindlimb elements, osteoderms). Crocodylus niloticus currently inhabits Madagascar but is locally extinct from this particular region; radiometric dating indicates an age of ∼460–310 years before present (BP). This specimen clearly represents a juvenile based on the extremely small size and open sutures/detached neural arches; total body length is estimated to be ∼1.1 m (modern adults of this species range from ∼4–6 m). This fossil represents the only juvenile subfossil crocodylian specimen reported from Madagascar.