A juvenile subfossil crocodylian from Anjohibe Cave, Northwestern Madagascar

Abstract

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.

A new late Pleistocene subfossil site (Tsaramody, Sambaina basin, central Madagascar) with implications for the chronology of habitat and megafaunal community change on Madagascar's Central Highlands

“…A single date for Voay from the coastal site of Ankilibehandry in western Madagascar proves that this species, like Madagascar's other megafauna, survived into the late Holocene (1920 ± 30 14 C a bp , or 1813 ± 78 cal a bp , CAMS 167399; previously unpublished). A single radiocarbon date for subfossil Crocodylus niloticus from Anjohibe in the north‐west is more recent (360 ± 25 14 C a bp , or 385 ± 75 cal a bp , CAMS 150524; Crowley & Samonds, ; Mathews & Samonds, ). These two dates are consistent with the recent arrival of C. niloticus to Madagascar but fail to resolve the question of possible prolonged temporal overlap between V. robustus and C. niloticus , or specifically whether Crocodylus may have outcompeted Voay , or if Voay disappeared before Crocodylus arrived (Brochu, ; Burney et al ., ).…”

A giant phytosaur (Diapsida, Archosauria) from the Upper Triassic of India with new insights on phytosaur migration, endemism and extinction

“…The total body length estimated for these groups of phytosaur individuals is as follows: Skeletally immature or juvenile individuals, characterized by unfused cranial and neurocentral sutures, large orbits relative to the skull, poorly developed muscle scars, and cranial and mandibular ornamentation (Buffrénil 1982; Brochu 1996; Fara & Hungerbühler 2000; Holliday & Nesbitt 2013; Witzmann et al . 2014; Mathews & Samonds 2016; Griffin et al 2021) had a total body length of <5 m. Skeletally mature or adult individuals that had well‐developed muscle scars, and ornamentation on the skull and mandible, and fused cranial and neurocentral sutures (Fara & Hungerbühler 2000; Holliday & Nesbitt 2013; Witzmann et al . 2014; Mathews & Samonds 2016; Griffin et al .…”

“…2014; Mathews & Samonds 2016; Griffin et al 2021) had a total body length of <5 m. Skeletally mature or adult individuals that had well‐developed muscle scars, and ornamentation on the skull and mandible, and fused cranial and neurocentral sutures (Fara & Hungerbühler 2000; Holliday & Nesbitt 2013; Witzmann et al . 2014; Mathews & Samonds 2016; Griffin et al . 2021) attained full body size >7 m. Transitional or sub‐adult individuals had a total body length of 5–7 m. These were characterized by features intermediate to the skeletally immature and mature individuals, such as partially fused sutures between bones, moderately developed muscle scars, and cranial and mandibular ornamentations.…”