Musculus somaliensis

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Musculus somaliensis
Temporal range: Late Jurassic
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Musculus somaliensis 4.jpg
Musculus somaliensis viewed from the side
Scientific classification Red Pencil Icon.png
Kingdom: Animalia
Phylum: Mollusca
Class: Bivalvia
Order: Mytilida
Family: Mytilidae
Genus: Musculus
Species:
M. somaliensis
Binomial name
Musculus somaliensis
Cox, 1935
Synonyms

Modiola aspera, M. autissiodorensis

Musculus somaliensis is an extinct species of small saltwater mussel, a fossil marine bivalve mollusc in the family Mytilidae, the mussels. The size, shape and sometimes color of these fossils are reminiscent of a pistachio nut.

In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. Other ways of defining species include their karyotype, DNA sequence, morphology, behaviour or ecological niche. In addition, paleontologists use the concept of the chronospecies since fossil reproduction cannot be examined.

Fossil Preserved remains or traces of organisms from a past geological age

A fossil is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved in amber, hair, petrified wood, oil, coal, and DNA remnants. The totality of fossils is known as the fossil record.

Bivalvia class of molluscs

Bivalvia, in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. Bivalves as a group have no head and they lack some usual molluscan organs like the radula and the odontophore. They include the clams, oysters, cockles, mussels, scallops, and numerous other families that live in saltwater, as well as a number of families that live in freshwater. The majority are filter feeders. The gills have evolved into ctenidia, specialised organs for feeding and breathing. Most bivalves bury themselves in sediment where they are relatively safe from predation. Others lie on the sea floor or attach themselves to rocks or other hard surfaces. Some bivalves, such as the scallops and file shells, can swim. The shipworms bore into wood, clay, or stone and live inside these substances.

Contents

Distribution

Musculus somaliensis lived during the late Jurassic, possibly throughout the Ethiopian Faunal Province, which consisted of Ethiopia, Somalia, Jordan, Yemen, Kenya, Madagascar, Saudi Arabia, and Tunisia according to Kiessling. [1] Fossils of M. somaliensis are known from the Upper Jurassic of Somalia (Callovian/Oxfordian in Jirba Range, Biyo Dader Tug, [2] Bihendula [3] ), Ethiopia (Callovian in Mt. Guresu, Marda Pass; [4] Late Oxfordian in Antalo Limestone north of Mekele [1] ) and Tunisia (Late Callovian/Oxfordian in Ghomrassen; Middle Callovian/Late Callovian in Ksar Ben Soltane, Krechem el Miit; Callovian/Early Oxfordian in Foum Tataouine Post Optique; Callovian/Oxfordian in Bir Remtha, Faljet Jdar/Ed-Dghaghra [5] ). [6]

The Jurassic period is a geologic period and system that spanned 56 million years from the end of the Triassic Period 201.3 million years ago (Mya) to the beginning of the Cretaceous Period 145 Mya. The Jurassic constitutes the middle period of the Mesozoic Era, also known as the Age of Reptiles. The start of the period was marked by the major Triassic–Jurassic extinction event. Two other extinction events occurred during the period: the Pliensbachian-Toarcian extinction in the Early Jurassic, and the Tithonian event at the end; neither event ranks among the "Big Five" mass extinctions, however.

In the geologic timescale, the Callovian is an age and stage in the Middle Jurassic, lasting between 166.1 ± 4.0 Ma and 163.5 ± 4.0 Ma. It is the last stage of the Middle Jurassic, following the Bathonian and preceding the Oxfordian.

The Oxfordian is, in the ICS' geologic timescale, the earliest age of the Late Jurassic epoch, or the lowest stage of the Upper Jurassic series. It spans the time between 163.5 ± 4 Ma and 157.3 ± 4 Ma. The Oxfordian is preceded by the Callovian and is followed by the Kimmeridgian.

Habitat

The fossil locations cited were tropical shallow seas, [1] where this mussel lived as a stationary epifaunal suspension feeder. [6]

Description

Musculus somaliensis has a modioliform shape with a straight to weakly convex dorsal margin. A rounded carina runs from the umbo to the postero-ventral corner of the shell, forming an angle of c. 45° with the dorsal margin, ventrally followed by a shallow sulcus. The antero-ventral part of the shell is inflated and has a convex antero-ventral margin. Its carina is more strongly curved and in its distal part forms an angle of c. 60–70° with the dorsal margin. A sulcus is absent, the antero-ventral part is low and limited by a concave antero-ventral margin. [1]

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References

  1. 1 2 3 4 W. Kiessling, D. K. Pandey, M. Schemm-Gregory, H. Mewis, and M. Aberhan. 2011. "Marine benthic invertebrates from the Upper Jurassic of northern Ethiopia and their biogeographic affinities". Journal of African Earth Sciences 59:195-214
  2. L. R. Cox. 1935. "Jurassic Gastropoda and Lamellibranchia". The Mesozoic Palaeontology of British Somaliland, Geology and Palaeontology of British Somaliland, II 148-197
  3. H. M. Muir-Wood. 1935. "Jurassic Brachiopoda". The Mesozoic Palaeontology of British Somaliland, Geology and Palaeontology of British Somaliland, II 75-147
  4. D. Jaboli. 1959. "Fossili Giurassici dell'Harar (Africa Orientale): Brachiopodi, Lamellibranchi e Gasteropodi" / "Jurassic fossils from Harar (Eastern Africa): brachiopods, lamellibranchs and gastropods". Missione Geologica dell'Azienda Italiana Petroli (AGIP) nella Dancalia Meridionale e sugli Altipiani Hararini 4(1):3-100
  5. S. Holzapfel. 1998. Palökologie benthischer Faunengemeinschaften und Taxonomie der Bivalven im Jura von Südtunesien. Beringeria - Würzburger geowissenschaftliche Mitteilungen (22)1-199
  6. 1 2 Paleobiology Database