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Infamous 'death roll' almost universal among crocodile species
Study: Infamous 'death roll' almost universal among crocodile species

by University of Tennessee at Knoxville

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Paleosuchus palpebrosus, also known as Cuvier's dwarf caiman. Credit: Kent Vliet/University of Florida.

The iconic "death roll" of alligators and crocodiles may be more common among species than previously believed, according to a new study published in Ethology, Ecology & Evolution and coauthored by a researcher at the University of Tennessee, Knoxville.
Contrary to popular belief, crocodiles can't chew, so they use a powerful bite coupled with a full-bodied twisting motion—a death roll—to disable, kill, and dismember prey into smaller pieces. The lethal movement is characteristic of both alligators and crocodiles and has been featured in numerous movies and nature documentaries.
Until now, the death roll had only been documented in a few of the 25 living crocodilian species, but how many actually do it?
"We conducted tests in all 25 species, and 24 of them exhibited the behavior," said lead author Stephanie Drumheller-Horton, a paleontologist and adjunct assistant professor in the Department of Earth and Planetary Sciences at UT.
For the research, Drumheller-Horton teamed up with Kent Vliet from the University of Florida and Jim Darlington, curator of reptiles at the St. Augustine Alligator Farm.
It was previously believed that slender-snouted species, like the Indian gharial, didn't roll because their diets consist of small prey like fish, eaten whole.
But it turns out that feeding isn't the only time the animals might roll.
"Aggression between individual crocodylians can become quite intense, often involving bites and death rolls in establishing dominance or competition for females," Vliet said.
Paleosuchus palpebrosus, commonly called Cuvier's dwarf caiman, is the only species that did not perform a death roll under experimental conditions. "Although, it's also possible that they were just being uncooperative," said Darlington.
And the fossil ancestors of modern crocodiles? If they share a similar body plan and lifestyle with their modern counterparts, it's likely that they could death roll, too.
"Crocodile relatives have played the role of semi-aquatic ambush predator since the Age of Dinosaurs," said Drumheller-Horton.
Whether in the Northern Territories of Australia, a lake in the Serengeti, or a watering hole in the late Cretaceous, chances are that a patient predator is waiting in the water to surprise its next meal with a burst of speed, a powerful bite, and a spinning finish.

Journal Reference:
Stephanie K. Drumheller et al, Surveying death roll behavior across Crocodylia, Ethology Ecology & Evolution (2019). DOI: 10.1080/03949370.2019.1592231

The “death roll” is an iconic crocodylian behaviour, and yet it is documented in only a small number of species, all of which exhibit a generalist feeding ecology and skull ecomorphology. This has led to the interpretation that only generalist crocodylians can death roll, a pattern which has been used to inform studies of functional morphology and behaviour in the fossil record, especially regarding slender-snouted crocodylians and other taxa sharing this semi-aquatic ambush predator body plan. In order to test this hypothesis, we surveyed death roll behaviour across animals representing all extant crocodylian species. Animals were prompted to death roll using two methods of stimulation: a feeding cue and an escape cue. The feeding cue involved presenting each animal with a bait item, to which resistance would be applied during a biting event. The second cue involved capturing each animal with a rope or catch pole, a standard technique for capturing crocodylians, but one that also often prompts an attempt to escape. All species tested, except Paleosuchus palpebrosus, exhibited the behaviour in response to at least one of the stimuli. This included the following slender-snouted species: Gavialis gangeticus, Tomistoma schlegelii, Mecistops cataphractus, Mecistops leptorhynchus, Crocodylus johnstoni, and Crocodylus intermedius. The patterns of death roll behavior observed in this survey suggest that this behaviour is not novel to any one crocodylian clade, morphotype, or dietary niche. Also, the prevalence of death rolling behaviour across Crocodylia in response to perceived threats indicates that it is not solely, or maybe even primarily, a feeding behaviour, but is also utilised during inter- and intra-specific conflict as a means to escape or injure an opponent. The results of this case study highlight the importance of using multiple modern analogues when attempting to correlate form and function across diverse clades, both living and extinct.
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