|ID||Michel: Scott: Stanley Gibbons: Yvert: UPU: MA012.15 Category: pF|
|Stamps in set||4|
|Value||3.75 - Stromatolite
3.75 - Marrellomorph
9.00 - Aegirocassis
9.00 - Tissint_meteorite
|Size (width x height)||40mm x 30mm ; 30mm x 40mm|
|Layout||Sheets of 25 stamps
|Perforation||13 x 13
|Printed by||philaposte France|
|Issuing Authority||Barid Al-Maghrib|
stromatoliths are layered bio-chemical accretionary structures formed
in shallow water by the trapping, binding and cementation of
sedimentary grains by biofilms (microbial mats) of microorganisms,
especially cyanobacteria. Fossilized stromatolites provide ancient
records of life on Earth by these remains, which might date from more
than 3.5 billion years. Lichen stromatolites are a proposed mechanism
of formation of some kinds of layered rock structure that is formed
above water, where rock meets air, by repeated colonization of the rock
by endolithic lichens.
A variety of stromatolite morphologies exists, including conical, stratiform, branching, domal, and columnar types. Stromatolites occur widely in the fossil record of the Precambrian, but are rare today. Very few ancient stromatolites contain fossilized microbes. While features of some stromatolites are suggestive of biological activity, others possess features that are more consistent with abiotic (non-biological) precipitation. Finding reliable ways to distinguish between biologically formed and abiotic stromatolites is an active area of research in geology.
There are only two more stamps and one commemorative with Stromatolite issued today: definitive set of Angola 1970 (face value 3#00), Canada 1990 (green stamp), India 2015
The stamp shows Marrellomorph
arthropod from Zagora region of Morocco, discovered by
Mohamed Benmoulai, local
collector and it is the first time when fossilized
soft tissue of the specie is found which is very rare
Marrella itself is a small animal, 2 cm or less in length. The head shield has two pairs of long rearward spikes. On the underside of the head are two pairs of antennae, one long and sweeping, the second shorter and stouter. Marrella has a body composed of 24–26 body segments, each with a pair of branched appendages. The lower branch of each appendage is a leg for walking, while the upper branch is a long, feathery gill. There is a tiny, button-like telson at the end of the thorax. It is unclear how the unmineralized head and spines were stiffened. Marrella has too many antennae, too few cephalic legs, and too few segments per leg to be a trilobite. It lacks the three pairs of legs behind the mouth that are characteristic of crustacea. The legs are also quite different from those of crustaceans. The identification of a diffraction grating pattern on well-preserved Marrella specimens proves that it would have harboured an iridescent sheen—and thus would have appeared colourful. Dark stains are often present at the posterior regions of specimens, probably representing extruded waste matter.
On March 12 2015, Sci
Tech Daily website reports about newly discovered
fossils of an extinct sea creature named Aegirocassis benmoulae provide
key evidence about the early evolution of arthropods.
The new animal, named Aegirocassis benmoulae in honor of its discoverer, Mohamed Ben Moula, attained a size of at least 2 meters, ranking it among the biggest arthropods that ever lived.
It was found in southeastern Morocco and dates back some 480 million years.
“Aegirocassis is a truly remarkable looking creature,” said Yale University paleontologist Derek Briggs, co-author of a Nature paper describing the animal. “We were excited to discover that it shows features that have not been observed in older Cambrian anomalocaridids — not one but two sets of swimming flaps along the trunk, representing a stage in the evolution of the two-branched limb, characteristic of modern arthropods such as shrimps.”
The recent discovery of Aegirocassis benmoulae bring new details at arthropods story. The new animal shows that anomalocaridids in fact had two separate sets of flaps per segment. The upper flaps were equivalent to the upper limb branch of modern arthropods, while the lower flaps represent modified walking limbs, adapted for swimming.
Furthermore, a re-examination of older anomalocaridids showed that these flaps also were present in other species, but had been overlooked. These findings show that anomalocaridids represent a stage before the fusion of the upper and lower branches into the double-branched limb of modern arthopods.
Aegirocassis benmoulae is also remarkable from an ecological standpoint, note the researchers. While almost all other anomalocaridids were active predators that grabbed their prey with their spiny head limbs, the Moroccan fossil has head appendages that are modified into an intricate filter-feeding apparatus. This means that the animal could harvest plankton from the oceans. “Giant filter-feeding sharks and whales arose at the time of a major plankton radiation, and Aegirocassis represents a much, much older example of this — apparently overarching — trend,” said Dr. Van Roy is one of the authors of a new study that has shed light on the early evolution and development of arthropod limbs.
Latest update 09.11.2017
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