Crocodiles In Seychelles

[Vernon]

Seychelles News Agency) - An ecologist working on the Seychelles most far-flung coral atoll stumbled upon a really old pair of crocs earlier this year, a discovery which could be the key to unlocking an evolutionary mystery.

What Dr Dennis Hansen chanced upon earlier this year is not the plastic footwear, which he says can sometimes sadly be found washed up on the shores of the atoll, but rather the fossils of two or more crocodiles.

According to Hansen, an ecologist from the Institute of Evolutionary Biology and Environmental Studies at the University of Zurich, initial estimates put the crocs' age back to some time around what is known as the Pleistocene era -- perhaps about 120,000 years ago. This is expected to be confirmed upon closer examination by experts at the University of Zurich.

In modern times, there have been no fearsome crocodiles roaming this giant atoll -- UNESCO World Heritage Site since 1982 -- located some 1,100 kilometres away from the Seychelles main island, Mah.

Frustratingly, though, the fossils were firmly embedded in the stone, and Hansen could not remove any of them without running the risk of destroying them, so he took some photographs and marked the spot with his GPS. But then, setting off to walk back to the hut, he crossed a slightly higher dry point of the pond, a small level patch covered in dried mud and loose soil.

Any nearby witnesses - probably a couple of tortoises trying to have their quiet evening wallow in the pond - would have seen plenty of jumping around and heard a lot of happy swearing, recalls Dr Hansen.

Going back to the pond next day with other members of the Zurich-Aldabra Research Platform (ZARP) expedition, the researchers sifted through other loose fossil remains, and found more crocodile bones, including a crocodile vertebra, and a second, smaller crocodile jaw fragment, indicating the remains of at least two crocodiles.

Dr Hansen is now trying to get university funding to ship the remains back to Zurich University where they can be cleaned and examined by palaeontologists. It is hoped the researchers can confirm the age of the fossils and the exact species of crocodile.

Although the inner granitic islands of the Seychelles were reportedly heaving with enormous saltwater crocodiles when they were first explored and settled in the 1700s, they were quickly hunted into the history books, and nothing remains of their existence apart from some skeletal remains at the natural history museum and a few geographical names around the inner islands.

The 2006 research by Christopher Brochu pointed to the crocodiles, which were called Aldabrachampsus, as being very small, or miniature, and horned. Brochu argued against them being endemic to the islands, saying it was more likely that they arrived from northern Madagascar, where a similar species, now also extinct, once lived.

As to the future, Dr Hansen who is now no stranger to the fact that Aldabra has endless surprises and treasures is certain that Aldabra still holds many more secrets left to be uncovered.

(Seychelles News Agency) - Seychelles - a group of 115 islands in the western Indian Ocean - is well known for its rich biodiversity and unique natural beauty, and the island nation places great importance on the protection of its endemic species.

Unfortunately, some have already become extinct, with some species surviving only a few years after the first settlers came to these shores. This week SNA presents five species once found in Seychelles that are now extinct (unless you find one and prove science wrong!)

This type of butterfly known scientifically as Euploea rogeri was discovered in 1820, and after these sightings, they were not seen again. This species was never caught. However, illustrations of the butterfly were published in Germany in 1837.

Last seen in the 1950s, this beetle is believed to have become extinct after trees which served as its habitat was destroyed. It is also believed that a disease might have caused its population to be wiped out.

Early travelers to Seychelles in 1609 reported that saltwater crocodiles were the most-sighted animal along the coastal regions of many islands in the archipelago. Many think that the extinction of these crocodiles came after colonization around 1819. It is only after their disappearance that it was discovered that the crocodiles were endemic to the islands and were neither the Nile crocodile nor Mugger crocodile. Only last year an ecologist working on the Seychelles atoll of Aldabra found crocodile fossils believed to be 100,000 years old.

This was a type of orchid which was endemic to Seychelles but is now extinct. This terrestrial orchid species was found on the island of Mah and was yellowish-white in colour. A specimen was collected in May 1902 from Cascade on the east coast of the island. Local researchers say that this was probably collected at the mountain known as Plateau. A sample of the orchid can be found at the Royal Botanic Gardens, in Kew in the United Kingdom.

Aldabrachampsus is only known from fragmentary cranial and mandibular remains including the premaxilla, frontal bone, parietal, dentaries and squamosals among others. Some postcranial bones are also known including several vertebrae and a femur. Like most other crocodilians Aldabrachampsus possessed five teeth situated in the premaxilla, however the second to fifth are all aligned in a straight line rather than following a convex path. Following the premaxillary teeth the rostrum of the crocodile constricted, creating a notch for one of the dentary teeth. There is a toothless region (diastema) present between the second and third alveoli of the dentary. The orbital margins of both the frontal and prefrontal bone are raised. The main body of the frontal is shaped like a pentagon with a distinctly V-shaped suture with the parietals, excluding the frontal from contributing to the supratemporal fenestrae. The anterior process of the frontal bone is slender and notably protrudes from the body following a sudden sharp constriction. Of the parietal only the posterior section is known, which shows a flat surface and a deep notch in its rear margin exposing the occipital region. The squamosal bone widens towards its suture with the postorbital and the bone bears a horn-like projection that faces outwards. Similar structures are known in the Madagascar crocodile Voay, Crocodylus anthropophagus from Tanzania and even alligatoroids like Acresuchus and Ceratosuchus. In modern species both Siamese crocodiles and Cuban crocodiles share similar squamosal horns. However Aldabrachampsus differs from these taxa in two ways. The horns are notably less pointed, showing a more rounded morphology, and their apex is located towards the halfway point of the bone, rather than the squamosal horns of other crocodilians which reach their apex towards the posterior.[1]

The fragmentary nature of Aldabrachampsus has left its exact placement within Crocodilia somewhat ambiguous. Phylogenetic analysis suggests it is part of the family Crocodylidae, composed of the subfamilies Crocodylinae and Osteolaeminae. Although this relationship is recovered by the strict consensus tree, which results in a large polytomy rendering Aldabrachampsus's exact position unknown, other trees suggest potentially different relationships. In some trees, Aldabrachampsus is recovered as a sister taxon to Voay, while others find it to be a sister to Crocodylus palaeindicus. However, both these positions are weakly supported, based on a single morphological character (the exposed supraoccipital), which is expressed differently between the different crocodiles in question. Brochu, however, argues that despite being based on the same character, a relationship to Voay (then Crocodylus robustus) within Osteolaeminae was more likely due to the anatomy of the nares, palate and the squamosal horns, although they differ in shape.[2][1]

The first remains of Aldabrachampsus were found in Quaternary deposits of Point Hodoul at the eastern end of the Aldabra Atoll. The limestone cavities that yielded these remains also preserved the fossils of lizards, tortoises, birds and land snails and date to approximately 118,000 years ago. Just before the appearance of Aldabrachampsus the atoll was entirely submerged by water, which suggests that rather than being an endemic species affected by island dwarfism, this crocodile was already of small stature by the time it arrived on the island. The fragmentary nature and poorly resolved phylogenetic relationships however make it difficult to determine where Aldabrachampsus originated. It is possible that the genus arrived in the Aldabra Atoll from the east, assuming close relationship with Crocodylus palaeindicus, however Brochu again suggests that a relationship to Voay and thus an African or Malagasy origin is more likely. A Malagasy origin would be consistent with the proximity between the atoll and Madagascar, which has led to faunal exchanges between the islands, especially prominent in regards to tortoises. Given the small stature of Osteolaemus, it is possible that minute bodysize is ancestral to this grouping and was simply reversed by Voay on Madagascar. Another hypothesis meanwhile suggests that smaller bodysize is a trait evolved by Osteolaemus and Aldabrachampsus independently of one another.[1]

Fossil discoveries made at a dried up pond on Grande Terre Island corresponding to the Late Pleistocene Aldabra Limestone show evidence of a predator-prey relationship between crocodilians and the native giant tortoise Aldabrachelys gigantea. Several tortoise shell fragments from the site are known to bear distinct feeding marks in the form of unhealed puncture wounds inflicted to the nuchal armor, plastron and the pubis of the tortoise. It is possible that a crocodile attacked and killed a tortoise head on as it was drinking at a watering hole, puncturing the nuchal plate at the front of the shell rather than attacking the high, better defended sides of the turtle. Another possibility is that the tortoise was not killed by crocodiles and instead only scavenged on. Again the punctures on the nuchal shield are caused by the fact that this particular area allows for better access at the meat beneath the shell. However, as the crocodile remains found alongside the turtle bones are notably larger than any previously recorded Aldabrachampsus specimens and very fragmentary, it is not certain if they belong to the same genus or instead represent a second species of crocodile native to the island.[2]

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