At the start of their research, paleobiologists Christine Janis and Borja Figueirido simply wanted to determine the hunting style of an extinct marsupial called Thylacine (also known as the "marsupial wolf" or the "Tasmanian tiger").
In the end, the Australian relic, which has a very dog-like head but with both cat- and dog-like features in the skeleton, proved to be uniquely unspecialized, but what emerged from the effort is a new classification system that can capably predict the hunting behaviors of mammals from measurements of just a few forelimb bones.
Brown University researchers have devised a dataset of forelimb bone measurements that can be used to classify the hunting style of mammalian predators. The now-extinct thylacine (front), shown juxtaposed with its still extant Australian rival the dingo, had forelimb anatomy that was curiously unspecialized for any particular hunting style.
Credit: Image courtesy of Carl Buell
"We realized what we are also doing was providing a dataset or a framework whereby people could look at extinct animals because it provides a good categorization of extant forms," said Janis, professor of ecology and evolutionary biology at Brown University, and co-author of a paper describing the framework in the Journal of Morphology.
For example, the scapulas (shoulder blades) of leopards (ambush predators who grapple with rather than chase their prey) and those of cheetahs (pursuit predators who chase their prey over a longer distance) measure very differently. So do their radius (forearm) bones. The shapes of the bones, including areas where muscles attach, place the cheetahs with other animals that evolved for chasing (mainly dogs), and the leopards with others that evolved for grappling (mostly other big cats).
"The main differences in the forelimbs really reflect adaptations for strength versus adaptations for speed," Janis said.
In plots of the data in the paper, cheetahs and African hunting dogs appear to be brethren by their scapular proportions even though one is a cat and one is a dog. But the similar scapulas don't lie: both species are acknowledged by zoologists to be pursuit predators.
In all, Janis and Figueirido of the Universidad de Malaga in Spain made 44 measurements on five forelimb bones in 62 specimens of 37 species of ranging from the Arctic fox to the thylacine. In various analyses the data proved helpful in sorting out the behaviors of their bones' owners.
Given measurements from all of the forelimb bones of an animal, for example, they could accurately separate ambush predators from pursuit predators 100 percent of the time and ambush predators from pouncing predators 95 percent of the time. Results were similar for analyses based on the humerus (upper arm bone). They were always able to make correct classifications between the three predator styles more than 70 percent of the time, even with just one kind of bone.
The elusive thylacine
The thylacine has not been known from mainland Australia in recorded human history, and by official accounts it disappeared from the Australian island of Tasmania by 1936 (although some locals still believe they may be around). In a similar vein, the beasts evaded Janis and Figueirido's attempts at a neat classification of their mode of carnivory. By some bones they were ambushers. By others they were pursuers. In the end, they weren't anything but thylacines.
Janis notes that they could do just fine as generalists, given their relative lack of competition. Historically Australia has hosted less predator diversity than the Serengeti, for example.
"If you are one the few predators in the ecosystem, there's not a lot of pressure to be specialized," she said.
In the thylacine's case the evidence from forelimb bone measurements supports their somewhat unusual status by the standards of the rest of predatory mammals as generalists. For other extinct predators, the framework will support other conclusions based on these same standards.
"One thing you tend to see is that people want to make extinct animals like living ones, so if something has a wolf-like head with a long snout as does the thylacine, although its skull is more delicate than that of a wolf, then people want to make it into a wolf-like runner," she said. "But very few extinct animals actually are as specialized as modern day pursuit predators. People reconstruct things in the image of the familiar, which may not reflect reality."
But Janis said she hopes the framework will provide fellow paleobiologists with an empirical basis for guiding those determinations.
The Bushnell Foundation supported the study with a research and teaching grant. The Museum of Comparative Zoology at Harvard University, the American Museum of Natural History in New York, and Australia's Museum Victoria and Queensland Museum provided access to specimens for measurement.
David Orenstein | Eurek Alert!
Why some neurons “outsource” their cell body
21.04.2015 | Nationales Bernstein Netzwerk Computational Neuroscience
Bubbles dilemma solved after more than twenty years
21.04.2015 | University of Twente
Max Planck researcher Buhalqem Mamtimin determines how much nitrogen oxide is released into the atmosphere from agriculturally used oases.
In order to make statements about current and future air pollution, scientists use models which simulate the Earth’s atmosphere. A lot of information such as...
Scientists at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) and the University of Konstanz are working on storing and processing information on the level of single molecules to create the smallest possible components that will combine autonomously to form a circuit. As recently reported in the academic journal Advanced Science, the researchers can switch on the current flow through a single molecule for the first time with the help of light.
Dr. Artur Erbe, physicist at the HZDR, is convinced that in the future molecular electronics will open the door for novel and increasingly smaller – while also...
Cells of the vascular system of vertebrates can fuse with themselves. This process, which occurs when a blood vessel is no longer necessary and pruned, has now been described on the cellular level by Prof. Markus Affolter from the Biozentrum of the University of Basel. The findings of this study have been published in the journal “PLoS Biology”.
The vascular system is the supply network of the human organism and delivers oxygen and nutrients to the last corners of the body. So far, research on the...
Astronomers from Chalmers University of Technology have used the giant telescope Alma to reveal an extremely powerful magnetic field very close to a supermassive black hole in a distant galaxy
Astronomers from Chalmers University of Technology have used the giant telescope Alma to reveal an extremely powerful magnetic field very close to a...
A team of physicists from MPQ, Caltech, and ICFO proposes the combination of nano-photonics with ultracold atoms for simulating quantum many-body systems and creating new states of matter.
Ultracold atoms in the so-called optical lattices, that are generated by crosswise superposition of laser beams, have been proven to be one of the most...
13.04.2015 | Event News
25.03.2015 | Event News
19.03.2015 | Event News
21.04.2015 | Materials Sciences
21.04.2015 | Earth Sciences
21.04.2015 | Studies and Analyses