Why Octopus Arms Don’t Get Tangled Up


Unlike humans, octopuses are not constantly aware of the location of their arms.  So with eight limbs in motion, it’s a wonder how their arms don’t get tangled up together.

According to researcher Guy Levy at the Hebrew University of Jerusalem, “We thought about it and we said, ‘How is it possible that the arms don’t grab each other?'”

Levy and his colleague Nir Nesher conducted a series of experiments with octopus arms. They observed that the suckers on the octopus arm would grab objects within its reach, but it would not grab anything with octopus skin. Their studies suggested that octopus skin has a repellent chemical. The sucker on an octopus arm can “taste” this repellent, so it does not grab on to it.

According to Roger Hanlon, of the Marine Biological Laboratory in Woods Hole, Massachusetts, “In fact, many of the sensory neurons known to occur in cephalopod suckers have unknown functions. The authors have widened our view of octopus sensory perception and provided some stimulating research questions to pursue.”

For more on this study, including a podcast, visit the NPR website.

To learn more fun facts about octopuses, see Animal Fact Guide’s common octopus facts page.

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Tiny Tyrannosaur Fossil Discovered in Alaska

A fossil of a small tyrannosaur that lived 70 million years ago was recently discovered in northern Alaska. The pygmy dinosaur, called Nanuqsaurus hoglundi (which means “polar bear lizard”), is believed to be a close relative of Tyrannosaurus Rex.

N. hoglundi was much smaller than the T. Rex. Its skull measures 25 inches as compared to the T. Rex‘s 60-inch skull.  Researchers have postulated that the pygmy tyrannosaur’s smaller stature was an adaptation to the cooler Arctic climate. Although the Arctic would have been much warmer in the Cretaceous Period than it is today, bouts of cold temperatures would have caused variations in the food supply.

Below is an illustration of the relative size of N. hoglundi (A) as compared to its larger cousin T. Rex (B and C). Although N. hoglundi was only about half the size of the T. Rex, it still was an impressive 23 feet from head to tail.


Nanuqsaurus hoglundi (A) as compared to T. Rex (B and C) and other species. The scale bar equals 1 meter. Courtesy PLoS.

Learn more at Discover Magazine and Smithsonian.

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Polite Marmoset Monkey Conversations

Are you as polite as this marmoset monkey? Photo credit: BirdPhotos.com.

Are you as polite as this marmoset monkey? Photo credit: BirdPhotos.com.

Princeton University researchers discovered that marmosets (a kind of new world monkey) take turns speaking with one another, similar to people! During their vocal exchanges, which can last up to 30 minutes, the monkeys wait their turn to speak. They don’t interrupt each other.

According to one of the study’s authors, Asif Ghazanfar:

“We were surprised by how reliably the marmoset monkeys exchanged their vocalizations in a cooperative manner, particularly since in most cases they were doing so with individuals that they were not pair-bonded with.

“This makes what we found much more similar to human conversations and very different from the coordinated calling of animals such as birds, frogs, or crickets, which is linked to mating or territorial defense.”

This research on marmoset vocalizations could provide clues about the early development of conversation in humans.

For more information, see:

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Were Dinosaurs Cold-Blooded or Warm-Blooded?

There has been a debate among scientists about whether dinosaurs were cold-blooded and sluggish (like reptiles today) or warm-blooded and active (like mammals today).  Professor  Roger Seymour from the University of Adelaide in Australia believes that one indicator of dinosaurs’ activity level can be found in their bones.

His theory boils down to this: In the thigh bone of animals, there are tiny holes, known as nutrient foramen, that distribute blood to the bone cells.  In highly active animals like mammals, these holes are relatively large because their bones require more blood keep them healthy.  In less active animals like reptiles, the holes are relatively small.

Centrosaurus apertus

Measuring the nutrient foramen of a ceratopsian dinosaur, Centrosaurus apertus.
Photo by Dr Donald Henderson, Curator of Dinosaurs from the Royal Tyrrell Museum in Alberta, Canada.

Sarah Smith, a student of Professor Seymour, measured holes in the bones of a range of mammals, from mice to elephants, and reptiles from lizards to crocodiles using specimens from Australian museums.  With the data in tow and comparisons made to the size of the holes, the size of the body, and the animal’s metabolic rate, Seymour determined that the “sizes of the holes were related closely to the maximum metabolic rates during peak movement in mammals and reptiles. The holes found in mammals were about 10 times larger than those in reptiles.”

Museum curators from Canada and Germany then collected data on the holes found in dinosaur fossil bones in their collections.  The specimens were from a wide range of dinosaurs from bipedal and quadrupedal carnivores and herbivores, large and small.

Seymour explained their findings:

“On a relative comparison to eliminate the differences in body size, all of the dinosaurs had holes in their thigh bones larger than those of mammals. The dinosaurs appeared to be even more active than the mammals.  We certainly didn’t expect to see that.  These results provide additional weight to theories that dinosaurs were warm-blooded and highly active creatures, rather than cold-blooded and sluggish.”

To learn more, see Seymour’s article, “Blood flow to long bones  indicates activity metabolism in mammals, reptiles and dinosaurs”.

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Underwater Spiders

Diving bell spider

Photo of a diving bell spider by Dr Stefan Hetz.

Professor Roger Seymour (School of Earth & Environmental Sciences, University of Adelaide) and Dr Stefan Hetz (Institute for Biology, Humboldt University) have provided new insights into the lives of diving bell spiders (Argyroneta aquatica), which are air-breathing spiders that spend the majority of their lives underwater.  The researchers’ study revealed that the spiders trap air in dome-shaped webs they build between aquatic plants.  These bubbles act as gills, extracting oxygen from the water and providing enough air for the spiders to breathe for more than 24 hours.  The spiders come up to the surface about once a day to supplement their air supply.

Up until now, scientists did not know how long the spiders stayed under water or how they used the diving bells to breathe.

According to Seymour:

Previous research had suggested the spiders had to come to the surface as often as every 20–40 minutes throughout the day.  Instead, we found that the spiders could sit still for long periods of time, continuing to use their diving bells to extract oxygen even from the most stagnant water on a hot day. Being able to stay still for so long – without having to go to the surface to renew the air bubble – protects the spiders from predators and also keeps them hidden from potential prey that come near.

Each spider constructs a net of silk in vegetation beneath the surface and fills it with air carried down on its abdomen and rear legs.  The spiders spend their entire lives submerged and even lay their eggs in their diving bells.  They are fascinating creatures but unfortunately they are becoming increasingly rare in Europe.

Seymour and Hetz’s findings will be published in The Journal of Experimental Biology.

Diving bell spider

Photo of a diving bell spider by Dr Stefan Hetz.

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2010 Interesting Animal Discoveries

As 2010 comes to a close, we thought it would be fun to take a look back at some of the amazing animal discoveries that came to light in the past year.

Israel’s “Lifting Door” Spider
With a leg span of 14 cm (5.5 in.), a new spider found in the dune of the Sands of Samar in Israel is the largest of its type in the Middle East. In addition, scientists have concluded that Cerbalus aravensis is a nocturnal spider that lives in an underground den with a “lifting door” made of glued sand particles so the den remains camouflaged.

Cerbalus aravensis spider

Photo by Yael Olek

Ecuador’s Scaly-Eyed Gecko

Recent exploration by U.S. and Ecuadorian researchers have found more than 30 new species of animals in Ecuador, including the scaly-eyed gecko. A full-grown scaly-eyed gecko is small enough to sit atop the eraser of a pencil. These geckos crawl along the forest floor, making them difficult to spot.
Scaly-eyed gecko

Dinosaurs’ True Colors

Two groups of researchers using electron microscope technology have determined the true colors of two species of dinosaurs.  Sinosauropteryx, a turkey-sized carnivorous dinosaur, had reddish-orange feathers and striped tail.  Anchiornis huxleyi, a chicken-sized dinosaur, had black and white wings and red crown – similar to some woodpeckers.

Sinosauropteryx, a feathered dinosaur

Sinosauropteryx, a feathered dinosaur

All-Black King Penguin

An extremely rare all-black penguin was photographed near Antartica by Andrew Evans of National Geographic.  The king penguin doesn’t look like his tuxedoed counterparts because of what one scientist described as a “one in a zillion kind of mutation.”
All-black king penguin

World’s Largest (and Toughest) Spider Web

A newly discovered spider in Madagascar builds the longest and largest orb webs in the world. The spider, called Darwin’s bark spider, builds webs over rivers that can measure up to 2.8 square meters (about 30 square feet)!  The webs are made of the toughest biomaterial yet discovered and can catch 30 or more insects at any given time.
largest spider web

Reclusive Loris Photographed

One of the most reclusive primates in the world, the Horton Plains slender loris, has only been spotted four times since 1937. So rare were sightings that researchers thought this loris had gone extinct sometime between sightings in 1939 and 2002.  As deforestation has led to a decline in all populations of slender loris, researchers made the effort this year to study the nocturnal primates in their native habitat in Sri Lanka and southern India.  This photo was taken as part of the study.
Horton Plains slender loris

Giant Penguin Fossils

Scientists in Peru uncovered the fossils of a Water King, a giant 5-foot penguin that weighed twice as much as an emperor penguin (the world’s largest living penguin) and lived 36 million years ago.  The fossils, which included well-preserved feathers and scales, led scientists to determine that the Water King had brown and gray feathers, unlike the black and white feathers we associate with modern penguins, and it was a very strong swimmer and diver.
Giant Prehistoric Penguin

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