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Purussaurus (giant Miocene caiman) bite force + diapsid tooth count



Ben Creisler
bcreisler@gmail.com

Two recent papers that may be of interest:

In PLoS ONE:

Tito Aureliano, Aline M. Ghilardi, Edson Guilherme, Jonas P.
Souza-Filho, Mauro Cavalcanti & Douglas Riff (2015)
Morphometry, Bite-Force, and Paleobiology of the Late Miocene Caiman
Purussaurus brasiliensis.
PLoS ONE 10(2): e0117944.
doi:10.1371/journal.pone.0117944
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0117944


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.

****

Caleb Marshall Brown, Collin S. VanBuren, Derek W. Larson, Kirstin S.
Brink, Nicolás E. Campione, Matthew J. Vavrek and David C. Evans
(2015)
Tooth counts through growth in diapsid reptiles: implications for
interpreting individual and size-related variation in the fossil
record.
Journal of Anatomy (advance online publication)
DOI: 10.1111/joa.12280
http://onlinelibrary.wiley.com/doi/10.1111/joa.12280/abstract

Tooth counts are commonly recorded in fossil diapsid reptiles and have
been used for taxonomic and phylogenetic purposes under the assumption
that differences in the number of teeth are largely explained by
interspecific variation. Although phylogeny is almost certainly one of
the greatest factors influencing tooth count, the relative role of
intraspecific variation is difficult, and often impossible, to test in
the fossil record given the sample sizes available to palaeontologists
and, as such, is best investigated using extant models. Intraspecific
variation (largely manifested as size-related or ontogenetic
variation) in tooth counts has been examined in extant squamates
(lizards and snakes) but is poorly understood in archosaurs
(crocodylians and dinosaurs). Here, we document tooth count variation
in two species of extant crocodylians (Alligator mississippiensis and
Crocodylus porosus) as well as a large varanid lizard (Varanus
komodoensis). We test the hypothesis that variation in tooth count is
driven primarily by growth and thus predict significant correlations
between tooth count and size, as well as differences in the frequency
of deviation from the modal tooth count in the premaxilla, maxilla,
and dentary. In addition to tooth counts, we also document tooth
allometry in each species and compare these results with tooth count
change through growth. Results reveal no correlation of tooth count
with size in any element of any species examined here, with the
exception of the premaxilla of C. porosus, which shows the loss of one
tooth position. Based on the taxa examined here, we reject the
hypothesis, as it is evident that variation in tooth count is not
always significantly correlated with growth. However, growth
trajectories of smaller reptilian taxa show increases in tooth counts
and, although current samples are small, suggest potential correlates
between tooth count trajectories and adult size. Nevertheless,
interspecific variation in growth patterns underscores the importance
of considering and understanding growth when constructing taxonomic
and phylogenetic characters, in particular for fossil taxa where
ontogenetic patterns are difficult to reconstruct.