Blue whales are widely regarded as the largest mammals to have ever lived on Earth. With a maximum length of about 30 meters and a weight of nearly 200 tons, they are the animal kingdom's uncontested heavyweight champs.
Digging on a beach in Somerset, UK, a team of British paleontologists discovered the remnants of an ichthyosaur, a marine reptile that could compete with whales. "It is quite remarkable to think that gigantic, blue-whale-sized ichthyosaurs were swimming in the oceans around what was then the UK during the Triassic Period," said Dean Lomax, a paleontologist at the University of Manchester who led the study.
Giant jawbones.
Ichthyosaurs lived in the waters during much of the Mesozoic epoch, first appearing 250 million years ago. They had four paddle-like arms, vertical tail fins that extended downward in most species, and overall resembled enormous, reptilian dolphins with elongated, narrow jaws lined with fangs. And some of them were really large. The largest ichthyosaur skeleton ever discovered was uncovered in British Columbia, Canada, and it belonged to a particularly gigantic ichthyosaur known as Shonisaurus sikaniensis. However, they appear to be capable of becoming considerably larger.Lomax's team discovered a surangular, a long, curved bone found at the top of the lower jaw, behind the teeth, which is present in all reptiles. The bone measured 2.3 meters, which was 25% larger than the surangular found in the Shonisaurus sikanniensis skeleton. Using basic scaling and assuming the same body proportions, Lomax's team calculated the size of this newly discovered ichthyosaur to be between 22 and 26 meters, making it the largest marine reptile known. However, there was one more thing.
The investigators examined the surangular and found no evidence of the external fundamental system (EFS), which is a band of tissue located in the bone's outermost cortex. Its creation signals a slowing of bone growth, suggesting skeletal maturity. In other words, the enormous ichthyosaur most likely died while still young and growing.
Correcting the past
Five enormous bones were discovered in 1846 at the Aust Cliff near Bristol, in southwest England. They were excavated from the upper Triassic rock formation and named "dinosaurian limb bone shafts" before being displayed at the Bristol Museum, where one was damaged by bombing during WWII.However, in 2005, Peter M. Galton, a British paleontologist studying at the University of Bridgeport, observed something unusual in one of the remaining Aust Cliff bones. He called it a "unusual foramen" and suspected it was a nutrient channel. Later studies generally attributed the bones to dinosaurs, but noted features like an odd microstructure that was difficult to understand.
According to Lomax, all of the uncertainty stemmed from the fact that the Aust Cliff bones did not belong to dinosaurs and were not pieces of limbs. He pointed out that the nutrition foramen's form, shape, and microstructure were consistent with the ichthyosaur bone discovered in Somerset. The Aust Cliff bones differed in that they bore the EFS, a mature bone mark. If Lomax is true and these were indeed pieces of an ichthyosaur's surangular, they belonged to an adult creature.
Using the same scaling technique as the Somerset surangular, Lomax concluded that this adult individual was more over 30 meters long, slightly larger than the largest confirmed blue whale.
Looming extinction
"Late Triassic ichthyosaurs most certainly exceeded the known biological limits of vertebrates in terms of size. So much about these giants remains unknown, but one fossil at a time, we will be able to uncover their secrets," said Marcello Perillo, a member of the Lomax team in charge of investigating the bones' interior structure.This mysterious beast, however, did not endure very long. The surangular bone discovered in Somerset was buried just beneath a layer of seismite and tsunamite rocks, indicating the start of the end-Triassic mass extinction event, one of five mass extinctions in Earth's history. The Ichthyotian severnensis, as Lomax and his team named the species, most likely grew to enormous proportions before being extinct.
However, the end-Triassic mass extinction did not wipe out all ichthyosaurs. They lived, but never grew to similar sizes again. They competed with more agile and faster-swimming plesiosaurs and sharks, and they most likely competed for the same habitats and food sources. The last known ichthyosaurs were extinct around 90 million years ago.
0 Comments