Peru 2010 "Prehistorical animals – Thalassocnus"

<prev

back to index

next>

Issue Date	21.09.2010
ID	Michel: Bl. 70 (2485); Scott: 1748; Stanley Gibbons: ; Yvert et Tellier: 61; Category: pR
Design	Cristian Alvarez M. – SERPOST S.A.
Stamps in set	1
Value	S/. 10.00 -Thalassocnus littoralis: fossil on stamp and reconstruction in margin
Emission/Type	commemorative
Issue place	Lima
Size (width x height)	stamp: 30 mm x 40 mm, Souvenir-Sheet: 80 mm x 100 mm
Layout	Souvenir-Sheet with 1 stamp
Products	FDC x1
Paper
Perforation	13.50 x 14
Print Technique	Offset
Printed by	Thomas Grag and Sons, Peru
Quantity	10.000
Issuing Authority	Servicios Postales del Peru SA

On September 21^st, 2010, the Post Authority of Peru - Servicios Postales del Peru SA (Serpost) - continued the series started in 2004, “Prehistoric Animals” (Animales Prehistoricos - Fosiles). These stamps show fossils discovered in the country of Peru.
This year the Souvenir-Sheet shows scientific reconstruction and fossils of a prehistoric sloth - Thalassocnus littoralis.
The reverse side of the Souvenir-Sheet is numbered.

When you think of marine mammals, sloths are probably the last thing you’d expect to take to the water. But from the Late Miocene (7-8 million years ago) to the Late Pliocene (3-1.5 million years ago), several species of giant ground sloths in the genus Thalassocnus did indeed evolve to take advantage of the aquatic environment. However even some modern sloths can swim.

The text below is translation of brochure produced by Serpost in 2010. The text was written by Rodolfo Salas Gismondi, Curator of Vertebrate Paleontology Department of Natural History Museum in Lima (UNMSM).

"If there is something amazing about paleontology it is a capacity to show us that the life on the Earth, such as we know it nowadays, is the result of constant changes.
Even the English naturalist Charles Darwin sketched his primordial ideas about the biological evolution inspired by fossilized bones of giant sloths and Glyptodonts, the ancestors of little tree sloths and armadillos in South America. The theory of evolution developed 150 years ago in Darwin’s “The origin of the species” - is the concept that integrates all the sciences of life, now with the help of genetics and molecular biology. As in Darwin’s time, fossils are still critical to understanding evolution.
Millions of years ago, the desert area of Sacaco, north to Arequipa, was a littoral marine environment. In its sands lie hundreds of fossils of whales, dolphins, seals, penguins and sharks in excellent state of preservation. In 1967, French paleontologist Robert Hoffstetter visited the area, and was greatly surprised to find a terrestrial intruder: a sloth between aquatic species. It was initially assumed that the sloth lived on land, near the littoral. Hoffstetter thought that their bodies were transported to the sea by an Andean paleo-river, where they were buried and preserved with aquatic species. However, something was wrong: the skeletons were always found articulated and complete, as if buried in the same place of their death - in the sea. What if it really was an aquatic sloth? This possibility, though wild, encouraged paleontologists Christian de Muizon and Greg McDonald to observe every bone's detail to look for revealing clues. In 1995, Muzion and McDonald announced in Nature Magazine, the existence of a 4-million-year old aquatic sloth in Peru. Some details of its anatomy, such as the shape of the premaxilla, femur and caudal vertebrae (the bones that make up the tails of tailed animals), are more similar to certain aquatic mammals that to others extinct sloths. Various scientists were skeptical though.

After almost 15 years and many discoveries made by Mario Urbina, 5 species of the aquatic sloth Thalassocnus were described, all of them found in marine deposits nearby Sacaco, but in rocks belonging to successive epochs from 9 to 2,5 million years ago.

Thalassocnus skeleton - image from Wikipedia, Photographer: FunkMonk.

This only record, let us track the first splashes in its linneage evolution, and also observe the way that certain adaptations to the aquatic environment were progressively accentuated through time. Thalassocnus was a sloth the size of a large dog, with long tail and powerful claws. It had simple teeth with no enamel. Since the most ancient species (Thalassocnus antiquus) to the most modern (Thalassocnus yaucensis) several changes were observed, especially an increase in the length and width of the muzzle’s posterior region, related to obtaining aquatic grass as a new source of food. The radius bone morphology shows substantial differences in the mode of locomotion. While Thalassocnus antiquus has a long radius bone with a reduced supinator crest, typical of terrestrial sloth, in Thalassocnus yaucensis the radius bone is short and the supinator crest is highly developed as observed in seals and sea lions. Today there is no doubt that Thalassocnus was an aquatic sloth which spent a long time feeding into the sea; but what could have incentivized it to leave its quiet life on land to adventure amongst waves infested with sharks? Good question. It is known that the Peruvian coast was already arid in that epoch. Possibly the scarce vegetation in the coasted desert led to the search for alternative resources such as algae exposed during low tide. After many generations, some of them ventured into the sea to look for algae and marine grasses. As this survival strategy was good enough, those individuals who had small anatomical advantages to live and feed in the sea –therefore the more suitable - had more opportunities to reproduce and fix their genes in their offspring. The mechanism of evolution proposed by Darwin – natural selection - was on the road.
In 2008, more work on these fossils was published in the Journal of Vertebrate Paleontology. This work focused on the first remains of Thalassocnus discovered outside of Sacaco, nearly 1500 km away in rocks of marine origin at Bahia Inglesa, in northern Chile. The broadening of the geographic range of these fossils suggests that these animals dominated a vast littoral territory. These fossils were also found with whale and dolphin remains. Another site where Thalassocnus was found recently, was at Ica, 180 km north of Sacaco.
The evolutionary journey of the aquatic sloth, Thalassocnus ended 2 million years ago. The quiet, warm water bays that these animals lived in for millions of years changed to the more agitated seas that we find in this area today. The wide region of sea grass meadows disappeared and the Thalassocnus lineage went extinct. Instead, other terrestrial sloths evolved to become the largest mammals that lived in South America.

Products and associated philatelic items

FDC	First-Day-of-Issue Postmark	Example of circulated cover

References

• Technical details and stamps presentation:
  Serpost Brochure colnect
• Thalassocnus:
  Nocturnalsea (the article does not exist anymore) Laalaps
• Museum of Natural History, Lima
  official website, Wikipedia

Acknowledgements

• Many thanks to fellow stamp collector Romina Aimar from Argentina, for her help translating Serpost's brochure text from Spanish to English.
• Many thanks to Dr. Peter Voice from Department of Geological and Environmental Sciences, Western Michigan University, for reviewing the draft page and his very valuable comments.

<prev

back to index

next>