In conjunction with the EXPO in Milan, the important exhibition “ Spinosaurus: lost giant of the Cretaceous” was set up in the historic Palazzo Dugnani, formerly home to the Museum of Natural Sciences.
Spinosaurus, larger than even Spielberg's T. rex, is considered the largest carnivorous dinosaur ever. Its diet consisted exclusively of fish, which it caught thanks to the controlled buoyancy of its dense, cavity-free bones and the conical teeth, adapted to grasping and holding slimy, slippery bodies, which armed its narrow, elongated snout. Its "fishing" territory was the warm, shallow freshwaters of North Africa, which it patrolled by paddling with its broad feet equipped with flattened claws. The numerous pressure sensors housed in its snout constituted a passive sonar system that allowed it to detect the position of its prey: among these was the Mawsonia, an extinct species related to the modern coelacanth, a "small fish" that could reach 4 meters in length and weigh between 500 and 900 kg, faithfully reconstructed and displayed in the exhibition.
www.youtube.com/watch?v=P28uzFe5SYk
Mawsonia lavocati , one of the largest fish ever to exist, a large freshwater coelacanth that lived between 390 and 100 million years ago, was a popular prey for Spinosaurus and the large crocodiles that shared its habitat. Its jaw, thanks to a special joint in its skull, could rotate upward, greatly increasing the opening of its mouth. The slow, synchronized movement of its fleshy fins was similar to walking on the riverbed rather than true swimming. Coelacanths, or crossopterygians , are a class of fish with pectoral and anal fins mounted on fleshy protuberances, supported by bones similar to the humerus and femur of tetrapods, and a caudal fin divided into three lobes, the central one including an extension of the notochord. They have the vestiges of non-functional lungs and are considered among the oldest vertebrates with jaws but above all the precursors of amphibians (tetrapods) which in turn gave rise to reptiles, birds and mammals and therefore our very distant ancestors, with all due respect to creationists.
They lived at the same time as plants began to colonize land and coral reefs were expanding in the sea. These fish were thought to have become extinct 65 million years ago, at the end of the Cretaceous, along with all the dinosaurs. After the end of this period, all traces of coelacanths disappear from the fossil record found so far. The hypothesized reason for this disappearance is that coelacanths likely became completely extinct only in shallow, coastal, or freshwater environments, while surviving in the deep sea. Fossils of animals deposited in deep waters are very difficult to bring to the surface, where paleontologists can discover them. It's a thrilling surprise to see, on the television screen next to the perfect reproduction of Mawsonia, the wonderful images of the living coelacanth taken by Laurent Ballesta during the "Gombessa" expedition carried out in 2013 in the Jesser Canyon opposite Sodwana Beach in South Africa, 70 km from the border with Mozambique: a truly extraordinary video. www.youtube.com/watch?v=q_yURFPJH3I It is estimated that at least thirty specimens survive in that area, "visible" at a depth of approximately 100-130 meters.
Coelacanths possess a distinctive type of cosmoid scales, a characteristic exclusive to some extinct fish groups, as well as an electroreceptive apparatus, called the rostral organ, located in the anterior part of the skull, which probably helps the animal locate prey. The coelacanth's eyes are extremely sensitive to light, thanks to the presence of the tapetum lucidum , a reflective membrane located behind the retina, which reflects captured light back onto it, increasing vision in low-light conditions. The first evidence of the existence of coelacanths came on December 22, 1938, when Captain Harry Goosen, commander of the fishing vessel Nerita, telephoned his friend Marjorie Courtenay-Latimer, a young and enterprising curator at the museum in East London, South Africa, informing her that they had caught a strange blue fish near the mouth of the Chalumna River. After bringing the fish to the museum, Dr. Latimer realized she was unable to classify it or preserve it because it was too large to be placed in a refrigerator. She decided to turn to her colleague Professor James Leonard Brierley Smith for identification and, in the meantime, had it stuffed by a taxidermist. Smith finally reached the museum and recognized the fish as a coelacanth, a genus known at the time only from fossil specimens. He later recounted that he " was no less amazed than seeing a dinosaur walking down the street ." The species was named Latimeria chalumnae , in honor of its discoverer and the waters where it was caught. It was called the most important naturalistic discovery of the 20th century. A worldwide search for new specimens was undertaken, with a prize of £100, a considerable sum for African fishermen of the time. Fourteen years later, a specimen was found in the Comoros, and it was discovered that the fish had always been known to the local indigenous people: fishermen on the island of Anjouan couldn't understand why such an inedible fish, called by them gombessa or mame , was so highly prized, even though it occasionally ended up in their nets by mistake. Its scales were so hard they could be used like sandpaper, and it secreted a laxative mucus and could only be eaten after drying. Today, however, they are well aware of the importance of the discovery and of the fact that it is an endangered species, and whenever a coelacanth is caught, it is immediately thrown back into the sea. Video: https://www.youtube.com/watch?v=u_F98seuWXU
A specimen, caught in 1952 by fisherman Ahmed Hussain, was initially classified as an entirely different species, Malania anjounae (named after Daniel François Malan, then prime minister of South Africa, and the island of Anjouan), but the missing dorsal fin was later discovered to be merely an accident. Ironically, Malan was a creationist, and after discovering that the supposed ancestor of all higher life on Earth had been named after him, he was very upset. In 1997, Arnaz and Mark Erdmann, while browsing the market on Manado Tua, a small island in the Bunaken Marine Park in Sulawesi, Indonesia, on their honeymoon, noticed what looked like a gombessa , but was brown instead of blue, on the stalls.
An expert noticed the photo of the fish they had posted online; DNA tests were conducted, demonstrating that the species, locally known as Rajah laut (king of the sea), was not the same as the African coelacanth: it was named Latimeria menadoensis . On October 28, 2000, in the protected waters of St. Lucia, South Africa, three divers—Pieter Venter, Peter Timm, and Etienne le Roux—found a coelacanth at a depth of 104 meters. On November 27, 2000, four of them (Pieter Venter, Gilbert Gunn, Christo Serfontein, and Dennis Harding) found three coelacanths, one of which was between 1,5 and 1,8 meters long, while the others measured approximately 1 to 1,2 meters. Divers managed to photograph and film these extraordinary fish in their natural habitat for the first time, but upon resurfacing, Dennis Harding died of a cerebral embolism he suffered while trying to help Christo Serfontein, who had lost consciousness. Between March and April 2002, the Jago bathyscaphe and the Fricke Dive Team, along with French documentary filmmaker Nicolas Hulot, managed to find a group of 15 coelacanths in the same area, including a female pregnant with several pups, establishing that they were an ovoviviparous species like sharks.
Unlike the latter, which have two hemipenes (modified pelvic fins), no male reproductive organs have yet been discovered. But the media hype surrounding the "living fossil" is being brought to the attention of Montpellier-based French biologist and photographer Laurent Ballesta, a child prodigy of underwater exploration (the youngest winner of the Palme d'Or at the Festival de l'Image Soumarine in Marseille and the only one to have won three), and the man who, in 2013, under the aegis of the Natural History Museum in Paris, captured the extraordinary photographs that brought the coelacanth to global attention. During the same expedition, DNA samples were collected, and a device was attached to the fish's back to record its migrations.
Genetic analysis confirmed the suspicion that L. chalumnae 's genes are evolving much more slowly than other terrestrial organisms, likely because this species lives in an environment—the deep waters off the coast of South Africa—that has changed very little over the last geological eras. Comparison of the coelacanth's genome with that of about twenty other vertebrate species also identified the genetic sequences affected by significant changes in the transition from aquatic to terrestrial life. In particular, researchers discovered numerous alterations in the genes that control the sense of smell, likely to efficiently detect volatile substances in the air rather than in water. Numerous changes also affected the genes that control the immune system, resulting in a response to new pathogens encountered on land. The third major change observed concerns the urea cycle: while fish eliminate the byproducts of protein breakdown in the form of ammonia, land animals rapidly convert this highly toxic substance into urea.
The reconstruction of the phylogenetic tree based on comparison with the RNA of another lobe-finned fish indicates that the closest relative of all tetrapods (and of Homo sapiens ) is Protopterus annectens, belonging to the Dipnoi pulmonata, and not its "cousin" coelacanth. But while the coelacanth's genome is comparable in size to that of humans, between two and three billion bases, that of Protopterus annectens , with its 139 billion bases, still presents almost insurmountable difficulties in being completely deciphered. Research continues.
DIVING WITH THE COELACANTH? WHERE AND HOW
There are two known species of coelacanth: the one from Sulawesi in Indonesia, where it lives at depths between 300 and 400 metres, making it completely unreachable by divers, and the African one, which can be observed in the stretch of sea from Kenya to South Africa, passing through the Comoros, Mozambique and Madagascar, at depths between 100 and 130 metres. This species can potentially be approached with the necessary trimix qualifications and equipped with computer-controlled closed-circuit rebretathers such as the Cis Lunar Poseidon MK VI.
Once you reach the dive site with the aid of a GPS, you must dive quickly and reach a depth of 100 meters in about two minutes to avoid missing the target due to strong currents. You explore the various caves, descending to 135 meters but not exceeding the maximum bottom time of 25-30 minutes: an extra six minutes results in an additional hour of decompression, which on average lasts four to five hours. The first deco stop is at 40 meters. The starting point for these daring dives is the TRITON DIVE LODGE www.tritondiving.co.za in SODWANA BEACH, SOUTH AFRICA, located 1 km across from Jesser Canyon, where there is a good chance of encountering the living fossil.
It is estimated that only about thirty divers have ever seen the coelacanth in the wild. When water temperatures exceed 20°C, the fish descend deeper. Co-owner of Triton Dive Lodge, a great trimix expert and pioneer of these deep-sea dives, Peter Timm was the first to see coelacanths in their natural habitat in 2000. He is said to have completed 300 dives beyond 100 meters and had 50 close encounters with the dinosaur fish. He made his organization and all his knowledge available to the success of Laurent Ballesta's "Operation Gombessa" in April–May 2013. He unfortunately died on June 18, 2014, while attempting to bring his dive partner to the surface from a depth of 60 meters, after she had fallen ill. They were attempting to retrieve a camera that had fallen into the sea from a boat the day before in Unkomass.
https://www.youtube.com/watch?v=8AJm9513Jh0
Videos made following the 2013 Gombessa expedition:
www.youtube.com/watch?v=6u8PG-Zmlr0 from SUPERQUARK (in Italian)
https://www.youtube.com/watch?v=q_yURFPJH3I
National Geographic video for FOCUS (in Italian)
Spinosaurus and Mawsonia photos: Nanni Fontana and Anna Giamborino for Geo-Model
