Ammonoid Paleobiology: From anatomy to ecology

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Abstracts from Volume 43, 2015 (subscription)

Soft Part Anatomy of Ammonoids: Reconstructing the Animal Based on Exceptionally Preserved Specimens and Actualistic Comparisons
Christian Klug, Jens Lehmann pp 507-529

Soft-tissue preservation is very rare in ammonoids. The reconstruction of the internal anatomy relies on few specimens with exceptional preservation, comparisons with recent cephalopods, and inferences based on the extant phylogenetic bracket. Herein, we describe the current knowledge of the soft part-anatomy of ammonoids. Of the digestive tract, the buccal mass, oesophagus, crop, stomach and caecum are rarely preserved. Stomach contents have become known from eleven species. Remains of the cephalic cartilage are scarce and suggest the presence of a simple lens eye. Only little has become known of ammonite gill anatomy. Unequivocal imprints of arm crowns have not been discovered yet, but we reinterpreted a baculitid that possibly preserves an arm crown with (?) ten short and thin retractable arms. An ink sac was absent, while a hyponome was present. There is no evidence for a hood in ammonoids.
The Body Chamber Length Variations and Muscle and Mantle Attachments in Ammonoids
Larisa A. Doguzhaeva, Royal H. Mapes pp 545-584
Abstract
The varying body chamber lengths and the different attachment of muscles and mantle to conch wall belong to the major adaptations to their diverse modes of locomotion. Therefore, these traits are indirect indicators of different life styles. The sparse record of ammonoid body chamber lengths and attachment marks has impeded the understanding of this aspect of ammonoid paleobiology. The examination of body chamber length revealed that the decrease of the ammonitella body chamber lengths shows is the long-term trend characterizing the evolutionary development of the Goniatitida–Prolecanitida–Ceratitida–Phylloceratida branch of the Ammonoidea. The analysis of the body chamber lengths and the attachment marks leads to conclusion that a precondition for the jet-powered swimming of ammonoids is less than one whorl body chamber length and the position of the attachment marks in sites from where the cephalic retractor and funnel retractor muscles would be able to extend straight across to the head and to the funnel. This is the case of goniatitids and ammonitids possessing moved forward large ventrolateral muscle marks; jet-powered swimming is highly probable for them. None of the universal small dorsal, umbilical and ventral marks may be left in the attachment sites of the cephalic retractor and funnel retractor muscles. In the hook-shaped terminal body chambers of heteromorph ammonoids, like Audouliceras, the long tongue-like umbilical marks perhaps indicate the moved forward strong umbilical muscles adapted for regular change of the mantle cavity volume for sucking and filtering seawater. This suggests that such ammonoids fed on fine plankton or suspended organic rich substance. Their irregular coiled spiral shells, best suited to floating and perhaps vertical (diurnal) migrations, support the view above. The fossilized mantle so far described in the ceratitid ammonoid Austrotrachyceras has a laminated structure fibrous seen in internally shelled Jurassic belemnotheutis and Loligosaepia.
The Additional External Shell Layers Indicative of “Endocochleate Experiments” in Some Ammonoids
Larisa A. Doguzhaeva, Harry Mutvei pp 585-609

Abstract
The present chapter is a review on the aberrant shell wall structures of some ammonoids characterized by additional external layers. Secondary deposits of shell on the outside of the conchs of some ammonoid species suggest that the body exceeded the body chamber volume and the mantle coated the shell.

Ammonoid Locomotion
Carole Naglik, Amane Tajika, John Chamberlain, Christian Klug pp 649-688

Abstract
Because ammonoids have never been observed swimming, there is no alternative to seeking indirect indications of the locomotory abilities of ammonoids. This approach is based on actualistic comparisons with the closest relatives of ammonoids, the Coleoidea and the Nautilida, and on the geometrical and physical properties of the shell. Anatomical comparison yields information on the locomotor muscular systems and organs as well as possible modes of propulsion while the shape and physics of ammonoid shells provide information on buoyancy, shell orientation, drag, added mass, cost of transportation and thus on limits of acceleration and swimming speed. On these grounds, we conclude that ammonoid swimming is comparable to that of Recent nautilids and sepiids in terms of speed and energy consumption, although some ammonoids might have been slower swimmers than nautilids.
Ammonoid Buoyancy
René Hoffmann, Robert Lemanis, Carole Naglik, Christian Klug pp 649-688

Abstract
The buoyancy of ammonoids is one of the most controversial issues of ammonoid paleobiology. This chapter gives a short historical review about attempts made to clarify the potential function of the cephalopod chambered shell (phragmocone) and ammonoid life habits either as benthic crawler or as free swimmers in the water column. In order to understand efficiency of buoyancy control and the mode of life of the extinct ammonoids decoupling of cameral liquid, process of osmotic pumping including local osmosis, pre-septal gas, and the role of the siphuncle and cameral liquid were discussed extensively. It is accepted that processes like osmotic pumping and local osmosis act in ammonoids due to similar architecture of the extant relatives including the presence of a siphuncle. Additionally, the calculation of buoyancy represents a major task which depends on exact reconstructions of volumes and densities for shell and soft body. With the rise of 3D-imaging techniques the determination of volumes were enhanced and now represent an important step towards more precise buoyancy calculations.
Isotope Signature of Ammonoid Shells
Kazuyoshi Moriya pp 793-836
Abstract
Geochemical analyses of ammonoid shells provide an independent and objective data set to evaluate life and habitat of the animal. This uniformitarian consideration, in combination with functional morphology and physical evidence for ecology or physiology, potentially delivers a significant advantage for new insights in paleoecology. One difficulty is that ammonoids as a proxy carrier are assumed to be mobile organisms. In contrast to stationary proxy carriers like benthic bivalves, it is difficult to impossible to estimate absolute depth or locality in which a certain proxy was recorded. Although the temperature proxy is very informative, it could indicate alternative scenarios; shallower calcification depth or calcification in the warmer season. When the calcification temperature is calibrated against the thermal structure of the water column, the proxy records would be fully understood. Therefore, providing the external frame of references is significantly important for getting better insights from geochemical signatures on ammonoids.
Parasites of Ammonoids
Kenneth De Baets, Helmut Keupp, Christian Klug pp 837-875

Abstract
Extant cephalopods are commonly infested by parasites making it plausible that ammonoids also had parasites. We review the fossil evidence of parasitic infestations in ammonoids, which, due to low preservation potential of soft-tissues in ammonoids and parasites, are mainly recorded as shell pathologies on the external shell interpreted to be caused by parasites. Extant nautilids are of little help to interpret these structures as they only harbor parasitic copepods. Pathologies analogous to those found in ammonoids that are caused by parasites are common in extant bivalves and gastropods. The position of these features might reveal their parasitic nature. The restriction of these structures to certain ammonoid lineages suggests both the influence of phylogeny and the potential role of ecology (feeding, mode of life) on infestation risks. Other long-term associations with detriment to ammonoids such as epizoa and bioeroders as well as their possible confusion with parasitism are briefly discussed.
 
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