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New paleocene sepiid coleoids (cephalopoda) from Egypt: evolutionary significance and origin of the sepiid 'rostrum'.

Košťák M, Jagt JW, Speijer RP, Stassen P, Steurbaut E - PLoS ONE (2013)

Bottom Line: The occurrence of the new genus near the Selandian/Thanetian boundary suggests an earlier origin of belosaepiids, during the early to Middle Paleocene.These earliest known belosaepiids may have originated in the Tethyan Realm.From northeast Africa, they subsequently spread to western India, the Arabian Plate and, probably via the Mediterranean region, to Europe and North America.

View Article: PubMed Central - PubMed

Affiliation: Institute of Geology and Palaeontology, Faculty of Science, Charles University, Prague, Czech Republic.

ABSTRACT
New coleoid cephalopods, assignable to the order Sepiida, are recorded from the Selandian/Thanetian boundary interval (Middle to Upper Paleocene transition, c. 59.2 Ma) along the southeastern margin (Toshka Lakes) of the Western Desert in Egypt. The two genera recognised, Aegyptosaepia n. gen. and ?Anomalosaepia Weaver and Ciampaglio, are placed in the families Belosaepiidae and ?Anomalosaepiidae, respectively. They constitute the oldest record to date of sepiids with a 'rostrum-like' prong. In addition, a third, generically and specifically indeterminate coleoid is represented by a single rostrum-like find. The taxonomic assignment of the material is based on apical parts (as preserved), i.e., guard, apical prong (or 'rostrum-like' structure), phragmocone and (remains of) protoconch, plus shell mineralogy. We here confirm the shell of early sepiids to have been bimineralic, i.e., composed of both calcite and aragonite. Aegyptosaepia lugeri n. gen., n. sp. reveals some similarities to later species of Belosaepia, in particular the possession of a distinct prong. General features of the phragmocone and protoconch of the new form are similar to both Belocurta (Middle Danian [Lower Paleocene]) and Belosaepia (Eocene). However, breviconic coiling and the presence of a longer ventral conotheca indicate closer ties with late Maastrichtian-Middle Danian Ceratisepia. In this respect, Aegyptosaepia n. gen. constitutes a link between Ceratisepia and the Eocene Belosaepia. The occurrence of the new genus near the Selandian/Thanetian boundary suggests an earlier origin of belosaepiids, during the early to Middle Paleocene. These earliest known belosaepiids may have originated in the Tethyan Realm. From northeast Africa, they subsequently spread to western India, the Arabian Plate and, probably via the Mediterranean region, to Europe and North America.

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Mineralogical composition of the sheath, showing original presence of aragonite (A), recorded calcite also contains a Mg-element.(B) Mineralogical composition of the prong showing pure calcite. X-ray diffraction (X´Pert Pro, PANalytical B.V., Almelo).
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pone-0081180-g009: Mineralogical composition of the sheath, showing original presence of aragonite (A), recorded calcite also contains a Mg-element.(B) Mineralogical composition of the prong showing pure calcite. X-ray diffraction (X´Pert Pro, PANalytical B.V., Almelo).

Mentions: The shell of the Recent cuttlefish Sepia is composed of principally inorganic (predominantly aragonite and some calcite and hydroxyapatite) and some organic (β-chitin and proteins) matter [45]. A similar composition is seen in extinct representatives of the Sepia stem lineage, in particular in Ceratisepia, Belocurta, Belosaepia and Anomalosaepia. Recently, extremely well-preserved cuttlebones of Mississaepia have been recorded [29,46] that revealed a similar inorganic-organic sepiid cuttlebone composition. However, the sepiid shells described herein are strongly recrystallised (Figures 5–6). Yet, some important microstructural data are preserved thanks to mineral pseudomorphosis (substitution), clearly documenting the original mineral composition and the original composition has been detected using RTG (X-ray diffraction ) methods. X-ray diffraction (Figure 9) has shown the original composition of the guard to have been bimineralic, i.e., composed of both calcite and aragonite (Figures 6C–F, 7D–F), a feature which is also well visible in crystal differentation (i.e. Figures 6E-F, 7G-H). Our analysis has revealed that the first layer covering the conotheca is composed of aragonite (however, due to strong recrystallisation, Mg-calcite forms a dominant, yet secondary component). It forms radial fans, which have also been recorded in the Eocene Anomalosaepia [28]. In this respect, this layer should be considered the equivalent of the primordial rostrum of belemnoids (see below). The second layer, forming the guard and prong, are composed of poor calcite, with no traces of aragonite and magnesium. The phragmocone is poorly preserved and only a few parts of the protoconch and ventral part of the siphonal tube are preserved as semi-transparent, brownish to yellowish remains located closely to the mural parts. Probably, originally less mineralised septa (?chitinous) are not preserved.


New paleocene sepiid coleoids (cephalopoda) from Egypt: evolutionary significance and origin of the sepiid 'rostrum'.

Košťák M, Jagt JW, Speijer RP, Stassen P, Steurbaut E - PLoS ONE (2013)

Mineralogical composition of the sheath, showing original presence of aragonite (A), recorded calcite also contains a Mg-element.(B) Mineralogical composition of the prong showing pure calcite. X-ray diffraction (X´Pert Pro, PANalytical B.V., Almelo).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3860988&req=5

pone-0081180-g009: Mineralogical composition of the sheath, showing original presence of aragonite (A), recorded calcite also contains a Mg-element.(B) Mineralogical composition of the prong showing pure calcite. X-ray diffraction (X´Pert Pro, PANalytical B.V., Almelo).
Mentions: The shell of the Recent cuttlefish Sepia is composed of principally inorganic (predominantly aragonite and some calcite and hydroxyapatite) and some organic (β-chitin and proteins) matter [45]. A similar composition is seen in extinct representatives of the Sepia stem lineage, in particular in Ceratisepia, Belocurta, Belosaepia and Anomalosaepia. Recently, extremely well-preserved cuttlebones of Mississaepia have been recorded [29,46] that revealed a similar inorganic-organic sepiid cuttlebone composition. However, the sepiid shells described herein are strongly recrystallised (Figures 5–6). Yet, some important microstructural data are preserved thanks to mineral pseudomorphosis (substitution), clearly documenting the original mineral composition and the original composition has been detected using RTG (X-ray diffraction ) methods. X-ray diffraction (Figure 9) has shown the original composition of the guard to have been bimineralic, i.e., composed of both calcite and aragonite (Figures 6C–F, 7D–F), a feature which is also well visible in crystal differentation (i.e. Figures 6E-F, 7G-H). Our analysis has revealed that the first layer covering the conotheca is composed of aragonite (however, due to strong recrystallisation, Mg-calcite forms a dominant, yet secondary component). It forms radial fans, which have also been recorded in the Eocene Anomalosaepia [28]. In this respect, this layer should be considered the equivalent of the primordial rostrum of belemnoids (see below). The second layer, forming the guard and prong, are composed of poor calcite, with no traces of aragonite and magnesium. The phragmocone is poorly preserved and only a few parts of the protoconch and ventral part of the siphonal tube are preserved as semi-transparent, brownish to yellowish remains located closely to the mural parts. Probably, originally less mineralised septa (?chitinous) are not preserved.

Bottom Line: The occurrence of the new genus near the Selandian/Thanetian boundary suggests an earlier origin of belosaepiids, during the early to Middle Paleocene.These earliest known belosaepiids may have originated in the Tethyan Realm.From northeast Africa, they subsequently spread to western India, the Arabian Plate and, probably via the Mediterranean region, to Europe and North America.

View Article: PubMed Central - PubMed

Affiliation: Institute of Geology and Palaeontology, Faculty of Science, Charles University, Prague, Czech Republic.

ABSTRACT
New coleoid cephalopods, assignable to the order Sepiida, are recorded from the Selandian/Thanetian boundary interval (Middle to Upper Paleocene transition, c. 59.2 Ma) along the southeastern margin (Toshka Lakes) of the Western Desert in Egypt. The two genera recognised, Aegyptosaepia n. gen. and ?Anomalosaepia Weaver and Ciampaglio, are placed in the families Belosaepiidae and ?Anomalosaepiidae, respectively. They constitute the oldest record to date of sepiids with a 'rostrum-like' prong. In addition, a third, generically and specifically indeterminate coleoid is represented by a single rostrum-like find. The taxonomic assignment of the material is based on apical parts (as preserved), i.e., guard, apical prong (or 'rostrum-like' structure), phragmocone and (remains of) protoconch, plus shell mineralogy. We here confirm the shell of early sepiids to have been bimineralic, i.e., composed of both calcite and aragonite. Aegyptosaepia lugeri n. gen., n. sp. reveals some similarities to later species of Belosaepia, in particular the possession of a distinct prong. General features of the phragmocone and protoconch of the new form are similar to both Belocurta (Middle Danian [Lower Paleocene]) and Belosaepia (Eocene). However, breviconic coiling and the presence of a longer ventral conotheca indicate closer ties with late Maastrichtian-Middle Danian Ceratisepia. In this respect, Aegyptosaepia n. gen. constitutes a link between Ceratisepia and the Eocene Belosaepia. The occurrence of the new genus near the Selandian/Thanetian boundary suggests an earlier origin of belosaepiids, during the early to Middle Paleocene. These earliest known belosaepiids may have originated in the Tethyan Realm. From northeast Africa, they subsequently spread to western India, the Arabian Plate and, probably via the Mediterranean region, to Europe and North America.

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Related in: MedlinePlus