THE COLDEST CASE

By Pam Eastlick

Welcome to The Deep science and technology column where we cover topics from the deep sea to deep space and beyond.

Greetings everyone! I thought I’d dip into the animal files this week and see what’s new with the other critters that share our planet with us. And it turns out that the first story isn’t about what’s new but about what’s old. Researchers based in Pisa, Italy have used the latest forensic techniques to discover how a dolphin died. Admirable, you say, but hardly news. Well it is, if the corpse is over 4 million years old!

The team has done careful forensic analysis of the bite marks on the fossilized skeleton of a 9-foot long dolphin discovered in northern Italy and reconstructed the events that led to the dolphin’s death. They’ve also determined the probable identity of the killer: a 12-foot long shark that goes by the improbable name of Cosmopolitodus hastalis.

The edges of the bite marks are smooth which ruled out several species of sharks that have serrated teeth. The researchers looked at the mouths of fossilized shark specimens and compared the size and shape of the teeth with the marks on the dolphin’s ribs. This allowed them to narrow the list of suspects to Cosmopolitodus hastalis. It also helped that old Cosmo and his buddies were common in the waters where the dolphin swam.

Detailed analysis of the bite pattern allowed the researchers to go even further. The deepest and clearest incisions are on the dolphin’s ribs. This indicates that the shark attacked from below and probably took out a big part of the unfortunate Flipper’s abdomen by shaking its head violently. After the dolphin died, it rolled over on its back where the shark bit again, close to the fleshy dorsal fin.

The researchers say the study is significant because it demonstrates ‘fossilized behavior’ and gives us a glimpse of the ecological interactions between organisms in prehistoric seas. Fossil remains of prey species with shark bite marks provide direct evidence of what prehistoric sharks ate and how they behaved.

I must confess that it sounds to me like shark behavior hasn’t changed much in four million years!

Skeleton of the dolphin, preserved for 4 million years with the bite marks across its ribs from the shark attack the killed it. (Credit: Giovanni Bianucci)

And for a story a little closer to home in both time and space, have you ever wondered why so many spider webs have those ‘X’s’ on them? A study by researchers at the University of Melbourne has discovered that the white silk crosses are used by orb-weaving spiders to protect their webs from damage.

The team collected a group of orb-weaving spiders and left them to build their webs in the laboratory. Some of the completed webs were severely damaged, others lightly damaged and the remainder left alone. The response of the spiders was then observed.

The team found that orb-weaving spiders respond to severe damage to their webs by building bigger silk crosses, but if the damage is mild they don’t bother adding extra decoration.

The researchers think the dense crosses help make webs more visible to larger animals that might accidentally walk or fly into them and they are not unlike the tape we humans put on a glass door. The spider’s normal prey is small insects who apparently don’t notice the crosses until it’s far too late!

Decorative white silk crosses are an ingenious tactic used by orb-weaving spiders to protect their webs from damage. (Credit: Image courtesy of University of Melbourne)