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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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Thin section (A-B) illustrating Ceratisepia-like structures at ventral part of phragmocone (?conellae) in specimen IGP-BDA 09/04.Scale bars equal 0.3 mm (A) and 1 mm (B). (C) Polished section of specimen IGP-BDA 09/05, showing dorsal part of phragmocone with preserved remains of dorsal septa, aragonite fans (primordial rostrum) and calcitic (partially limonitised) guard (rostrum proper). Scale bar equals 0.5 mm. (D) Thin section of specimen IGP-BDB 09/01, illustrating alveolus infilled by sediment, bordered by conotheca, aragonite fans (primordial rostrum) and calcitic guard (rostrum proper). Scale bar equals 1 mm. (E–F) Thin section of specimen IGP-BDB 09/01, showing details of aragonite fans forming sheath (primordial rostrum). Scale bar equals 1 mm. Abbreviations: c – conotheca; phr – phragmocone; g – guard; sd – remains of dorsal septa; af – primordial rostrum (sheath), aragonite fans; lg – calcitic, partly limonitised guard; pf – planktic foraminifera.
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pone-0081180-g006: Thin section (A-B) illustrating Ceratisepia-like structures at ventral part of phragmocone (?conellae) in specimen IGP-BDA 09/04.Scale bars equal 0.3 mm (A) and 1 mm (B). (C) Polished section of specimen IGP-BDA 09/05, showing dorsal part of phragmocone with preserved remains of dorsal septa, aragonite fans (primordial rostrum) and calcitic (partially limonitised) guard (rostrum proper). Scale bar equals 0.5 mm. (D) Thin section of specimen IGP-BDB 09/01, illustrating alveolus infilled by sediment, bordered by conotheca, aragonite fans (primordial rostrum) and calcitic guard (rostrum proper). Scale bar equals 1 mm. (E–F) Thin section of specimen IGP-BDB 09/01, showing details of aragonite fans forming sheath (primordial rostrum). Scale bar equals 1 mm. Abbreviations: c – conotheca; phr – phragmocone; g – guard; sd – remains of dorsal septa; af – primordial rostrum (sheath), aragonite fans; lg – calcitic, partly limonitised guard; pf – planktic foraminifera.

Mentions: The phragmocone is incompletely preserved and only a few morphological features are visible. One of the most relevant macroscopic morphological features is the coiling of the phragmocone. In comparatively better-preserved specimens, i.e., IGP-BDA 09/4 and IGP-BDA 09/7, most of the apical part of the phragmocone, inclusive of the protoconch part, is preserved (Figure 5). Phragmocone coiling corresponds to that of Belocurta and Belosaepia. No complete dorsal septa are preserved, with the exception of their attachments parts (Figure 6C) in the dorsal mural part of the phragmocone. The ventral septa are well preserved in specimen IGP-BDA 09/4 (Figure 5E), in which they form a strong planar deck structure [27]. The thickness of the deck amounts to 0.3–0.4 mm. In this area, septa are recurved and attached to the conotheca at an obtuse angle. The ventral wall of the phragmocone is relatively long, comparable to the situation seen in Ceratisepia (Figure 5C-D). However, these conical structures (compare [1]; see Figure 6A-B herein) have been observed in thin section only; these might represent conellae, well known in other extinct coleoid cephalopods, in particular belemnites. The thickness of the conotheca increases (c. 1.5 mm from the protoconch: 0.1–0.2 mm) towards the protoconch (0.4 mm, at the protoconch). The ventral phragmocone wall (conotheca) continuously effaces from the protoconch towards the anterior part. Approximately 4–5 mm from the protoconch, the conotheca fuses into a very thin layer (?membrane) and continues posteriorly in an irregular manner. From this point onwards, the ventral phragmocone wall does not follow phragmocone coiling. The siphuncle band has well-developed, typically undulate margins. The bases of the ventral septa appear to be covered by a thin layer (Figure 5E), possibly equating with the ?lamello-fibrillar nacre (sensu [29]). However, a very thin layer also covers their strongly recurved dorsal parts (?connecting strips sensu [45]). Ventral septa are visible only in a 4-mm-long segment adhering to the protoconch.


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)

Thin section (A-B) illustrating Ceratisepia-like structures at ventral part of phragmocone (?conellae) in specimen IGP-BDA 09/04.Scale bars equal 0.3 mm (A) and 1 mm (B). (C) Polished section of specimen IGP-BDA 09/05, showing dorsal part of phragmocone with preserved remains of dorsal septa, aragonite fans (primordial rostrum) and calcitic (partially limonitised) guard (rostrum proper). Scale bar equals 0.5 mm. (D) Thin section of specimen IGP-BDB 09/01, illustrating alveolus infilled by sediment, bordered by conotheca, aragonite fans (primordial rostrum) and calcitic guard (rostrum proper). Scale bar equals 1 mm. (E–F) Thin section of specimen IGP-BDB 09/01, showing details of aragonite fans forming sheath (primordial rostrum). Scale bar equals 1 mm. Abbreviations: c – conotheca; phr – phragmocone; g – guard; sd – remains of dorsal septa; af – primordial rostrum (sheath), aragonite fans; lg – calcitic, partly limonitised guard; pf – planktic foraminifera.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0081180-g006: Thin section (A-B) illustrating Ceratisepia-like structures at ventral part of phragmocone (?conellae) in specimen IGP-BDA 09/04.Scale bars equal 0.3 mm (A) and 1 mm (B). (C) Polished section of specimen IGP-BDA 09/05, showing dorsal part of phragmocone with preserved remains of dorsal septa, aragonite fans (primordial rostrum) and calcitic (partially limonitised) guard (rostrum proper). Scale bar equals 0.5 mm. (D) Thin section of specimen IGP-BDB 09/01, illustrating alveolus infilled by sediment, bordered by conotheca, aragonite fans (primordial rostrum) and calcitic guard (rostrum proper). Scale bar equals 1 mm. (E–F) Thin section of specimen IGP-BDB 09/01, showing details of aragonite fans forming sheath (primordial rostrum). Scale bar equals 1 mm. Abbreviations: c – conotheca; phr – phragmocone; g – guard; sd – remains of dorsal septa; af – primordial rostrum (sheath), aragonite fans; lg – calcitic, partly limonitised guard; pf – planktic foraminifera.
Mentions: The phragmocone is incompletely preserved and only a few morphological features are visible. One of the most relevant macroscopic morphological features is the coiling of the phragmocone. In comparatively better-preserved specimens, i.e., IGP-BDA 09/4 and IGP-BDA 09/7, most of the apical part of the phragmocone, inclusive of the protoconch part, is preserved (Figure 5). Phragmocone coiling corresponds to that of Belocurta and Belosaepia. No complete dorsal septa are preserved, with the exception of their attachments parts (Figure 6C) in the dorsal mural part of the phragmocone. The ventral septa are well preserved in specimen IGP-BDA 09/4 (Figure 5E), in which they form a strong planar deck structure [27]. The thickness of the deck amounts to 0.3–0.4 mm. In this area, septa are recurved and attached to the conotheca at an obtuse angle. The ventral wall of the phragmocone is relatively long, comparable to the situation seen in Ceratisepia (Figure 5C-D). However, these conical structures (compare [1]; see Figure 6A-B herein) have been observed in thin section only; these might represent conellae, well known in other extinct coleoid cephalopods, in particular belemnites. The thickness of the conotheca increases (c. 1.5 mm from the protoconch: 0.1–0.2 mm) towards the protoconch (0.4 mm, at the protoconch). The ventral phragmocone wall (conotheca) continuously effaces from the protoconch towards the anterior part. Approximately 4–5 mm from the protoconch, the conotheca fuses into a very thin layer (?membrane) and continues posteriorly in an irregular manner. From this point onwards, the ventral phragmocone wall does not follow phragmocone coiling. The siphuncle band has well-developed, typically undulate margins. The bases of the ventral septa appear to be covered by a thin layer (Figure 5E), possibly equating with the ?lamello-fibrillar nacre (sensu [29]). However, a very thin layer also covers their strongly recurved dorsal parts (?connecting strips sensu [45]). Ventral septa are visible only in a 4-mm-long segment adhering to the protoconch.

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.

Show MeSH
Related in: MedlinePlus