Morphometry, bite-force, and paleobiology of the late miocene caiman Purussaurus brasiliensis

Abstract

Purussaurus brasiliensis thrived in the northwestern portion of South America during the Late Miocene. Although substantial material has been recovered since its early discovery, this fossil crocodilian can still be considered as very poorly understood. In the present work, we used regression equations based on modern crocodilians to present novel details about the morphometry, bite-force and paleobiology of this species. According to our results, an adult Purussaurus brasiliensis was estimated to reach around 12.5 m in length, weighing around 8.4 metric tons, with a mean daily food intake of 40.6 kg. It was capable of generating sustained bite forces of 69,000 N (around 7 metric tons-force). The extreme size and strength reached by this animal seems to have allowed it to include a wide range of prey in its diet, making it a top predator in its ecosystem. As an adult, it would have preyed upon large to very large vertebrates, and, being unmatched by any other carnivore, it avoided competition. The evolution of a large body size granted P. brasiliensis many advantages, but it may also have led to its vulnerability. The constantly changing environment on a large geological scale may have reduced its long-term survival, favoring smaller species more resilient to ecological shifts.

Fig 1. Late Miocene fossil sites in Southwest Amazonia.

P. brasiliensis specimens recovered from sites 1–8. More specimens encountered at the Peruvian and Bolivian sites were assigned to Purussaurus sp. with no further taxonomic details. On the top right, the paleogeographical map showing the location of South America and the area of the Solimões Formation (white cross) during the Late Miocene (about 8 million years ago). Mollweide projection, latitude and longitude lines at 30° intervals. This map was created based on the work of Ron Blakey, available at http://cpgeosystems.com/paleomaps.html.

Fig 2. Purussaurus brasiliensis skull anatomy.

(A) P. brasiliensis UFAC 1403 skull in dorsal view. (B) P. brasiliensis UFAC 1403 skull in ventral view. (C) P. brasiliensis reconstruction skull UFAC 1403 and associated mandible UFAC 1118 with teeth in lateral view. Scale bar: 50 cm. Abbreviations: bo, basioccipital; ec, ectopterygoid; f, frontal; j, jugal; l, lacrimal; m, maxilla; n, nasal; oc, occipital condyle; p, parietal; pl, palatine; pm, premaxilla; po, postorbital; prf, prefrontal; pt, pterygoid; q, quadrate; qj, quadratojugal; sq, squamosal.

Fig 3. Measures and their abbreviations.

DCL, skull length, SVL, snout-vent length, TTL, total length (A) Purussaurus brasiliensis (B) Caiman latirostris. Scale bar: 100 cm.

Fig 4. Regression lines with 95% confidence bands obtained by the bootstrap procedure of A, DCL versus SVL (data from [22]); B, SVL versus TTL (data from [22]); C, TTL versus BM (data from [20]); and D, BM versus BF (data from [20]).

Fig 5. Purussaurus brasiliensis tooth collected at the “Cachoeira do Bandeira” site.

Scale bar: 3 cm.