A shark as long as a tennis court

Dr Anjani Ganase, coral reef ecologist, brings the latest scientific research on an extinct giant shark, how tonka bean trees make space in the Panamanian forests and how our ears are like fish gills.

Lightning strikes a tonka bean tree

Researchers have discovered that mature tonka bean trees in the forests of Panama benefit from being struck by lightning. Typically, lightning strikes in the region can result in the death of 40-50 per cent of tall canopy trees in the Panamanian forests of Barro Colorado Nature Monument Forest.

Tonka bean trees and their large crowns are 50-70 per cent more likely to be struck by lightning than other species of tall trees. It seems that most tonka bean trees have a high likelihood of surviving a lightning strike and being relatively unscathed compared to other species. Not only is the tree undamaged but the parasitic vines and neighbouring trees are often worse off experiencing most of the burns.

Using over 40 years of collected data, scientists confirm that a lightning strike of a tonka bean tree results in about 2.4 tons of biomass loss in surrounding trees, while attached vines suffer up to 80 per cent die back. It is thought that the trunk of the tonka bean tree is more conductive, allowing the electricity to flow through the tree rather than building up heat and causing burning. Loss of surrounding trees and vines extends the life span of the tonka bean tree (14 fold), thereby providing more opportunities for reproduction.

The average mature tonka bean tree in the Panamanian forest can grow to 40 m in height with a trunk diameter bigger than 60 cms. These trees live to several hundred years, and it is estimated that over the lifespan of a mature tonka bean tree, it can be struck by lightning five times on average. This means that there is recurring control of competitive plants and parasitic vines.

Our evolutionary origins are fishy

The outer ear of a mammal is oddly shaped and weird-looking. The ear folds seem unnecessary in contrast to the smooth conical disc devices, like the satellite dish, that we’ve invented to collect sound signals. The path of evolution is meandering and mysterious. All land animals evolved from the ocean, a place that really has no use for an ear. However, on land, the growth of ears provided clear benefits for mammals.

Researchers from the School of Medicine, University of Southern California, found that the outer ear of mammals can be linked evolutionarily to the gills of ancient fish. Both organs share a unique tissue called elastic collagen that make the outer ear (and gills) flexible but durable. In present day, the tissue is predominantly found in mammals and it seems the outer ear is likely to have evolved from ancient fish gills.

As elastic collagen is not fossilised, scientists had to use DNA where the genes for the tissue in mammals are matched with those of modern-day zebrafish, and also with horseshoe crabs which are evolutionarily much older than mammals and our fishy ancestors. The genes were also present in the gills of horseshoe crabs.

In previous studies, scientists had used the same method for finding the evolutionary path of the middle ear structure and found that it was linked to the fused jaw bone of ancient fish. Based on this, scientists moved on to investigate the origins of the outer ear. The next step is to find the genes in other organisms of intermediate evolution between ancient fish and mammals, such as lizards and amphibians. It is speculated that similar genetics may be found in the ear canals of these animals.

The new and improved megalodon

Otodus megalodon, also known as the megalodon or The Meg for short, has been popularised as a supersized version of the great white sharks in pop culture. This stemmed from research where fossil remains were assumed to be similar to that of present day great white sharks but not compared to any other species of shark. No fossil record of the whole animal exists: only specific body parts are able to fossilise, such as the spine or vertebrae, the teeth, and the scales. Fortunately, there was one complete meg spine found in Belgium measuring 11 m long to be used as a reference.

For the first time, scientists from DePaul University reassessed the body proportions and shape of the megalodon using body size references from 148 modern species and 20 extinct species of sharks. Using these references, researchers were able to model the body length of the shark based on the size of the largest vertebra as well as the length of the spine. Modelled estimates for body length based on the length of the spine indicated that the head of the shark added another 1.8 metres, while the tail would be an additional 3.6 metres resulting in a body length of 16.4 metres or about 54 feet (bigger than the width of a football field). Using the diameter of the largest vertebra (15cm or six inches size based on the Belgium record), estimates model a body length of 24.8 m or 80 feet (length of a tennis court).

Once the body length range can be estimated, this permits new insights into the biology of the shark, such as its shape, swimming speeds, diet and even reproduction. It is thought that given the giant body length, a body shape resembling a great white shark is simply feasible for efficient swimming. Judging by the modern-day ocean giants – the whale sharks, basking sharks, and even whales – researchers think that it is likely that the megalodon would have a body similar to that of the lemon shark which has a much sleeker profile. Given this hydro-dynamic shape, the shark is more likely to cruise at a slower speed compared to the great white shark.

Just imagine a shark that is some 24 metres in length, being capable of birthing live pups three to four metres in length, which is the average size of a full grown, modern day great white shark. Megalodons probably had a similar diet to great white sharks, feeding on whales and seals. In fact, the rise of great white sharks in oceans is thought to have led to the demise of megalodons because of feeding competition.