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Middle Jurassic ammonoid jaws (anaptychi and rhynchaptychi) from Dagestan, North Caucasus, Russia
Abstract
The Middle and Upper Jurassic stage of evolution of the anaptychus-type ammonoid jaw apparatus is relatively poorly known due to a small number of findings and uncertainty of their taxonomic position. All previously found anaptychi of this age are preserved either in flattened and dissolved shells or separately from ammonoid conchs. Rhynchaptychus-type jaws were still hitherto unknown from Jurassic deposits. In this paper we describe three-dimensionally preserved ammonoid lower jaws from the Bajocian/Bathonian boundary (Middle Jurassic) beds of Dagestan, Russia. These findings demonstrate a wide variety of their shape and structure. One specimen, consisting only of organic matter which is considered as anaptychus sensu stricto, is located in situ in the body chamber of Lytoceras (Dinolytoceras) zhivagoi (Besnosov). Three specimens which likely belonged to any Phylloceratiadae (Adabofoloceras, Holcophylloceras, or Pseudophylloceras which are presented in the ammonoid assemblage) contain prominent calcareous conchorhynchs, and the outer organic lamellae of these jaws were initially covered with a thin calcareous layer. The last lower jaw, probably from Nannolytoceras, has also a small calcareous conchorhynch in its tip despite a lack of coating. These findings are the first direct evidence of the existence of rhynchaptychus-type lower jaws in the Middle Jurassic. A variety in the shape and structure of the studied lower jaws indicates a variation in the mode of life and feeding behavior of Middle Jurassic ammonoids.
... Findings of isolated calcite elements of the jaw of cephalopods (rhyncholites) are known starting from the Upper Triassic, but they most likely belonged to nautilids (Riegraf and Luterbacher, 1989;Riegraf and Schmitt-Riegraf, 1995). The oldest rhyncholites, presumably belonging to ammonoids, are known starting from the Pliensbachian (Riegraf and Luterbacher, 1989), and the earliest rhynchaptychus jaws are found in the Middle Jurassic (Bajocian) of the Northern Caucasus (Mironenko and Gulyaev, 2018). The Middle Jurassic stage of the evolution of cephalopod jaws remained poorly understood for a long time. ...
... Finds of Middle Jurassic anaptychi were limited to two specimens (Quilty, 1970;Westermann et al., 1999), and in the former case it was not certain that the specimen belonged to the cephalopod jaw apparatus. However, in the last two decades, many new studies have been published on Middle Jurassic aptychi (Rogov and Gulyaev, 2003;Rogov, 2004;Mitta and Keupp, 2004;Mitta, 2009Mitta, , 2017bDietze et al., 2012;Keupp and Mitta, 2013;Mitta and Schweigert, 2016;, as well as on anaptychi and rhynchaptychi (Mironenko and Gulyaev, 2018). New discoveries of jaws of Middle Jurassic coleoids have also been described (Keupp and Mitta, 2013). ...
... The elements of the cephalopod jaw apparatus described above belong to representatives of two subclasses of cephalopods: Ammonoidea and Coleoidea. To date, ammonoid jaws belonging to four different types of jaw apparatuses have been described from the Bajocian of the Northern Caucasus: aptychus type (Mitta, 2017b), anaptychus and rhynchaptychus types (Mironenko, Gulyaev, 2018), and phyllaptychus known so far from only one specimen (Mitta and Schweigert, 2016). Most of the findings described in this work belong to the anaptychus-type lower jaws of ammonoids (anaptychi), which belonged to ammonoids of the suborders Phylloceratina and Lytoceratina. ...
New finds of cephalopod jaw apparatuses from the upper part of the Niortense Zone and the lower part of the Parkinsoni Zone (Upper Bajocian) from the interfluve of the Kuban and Urup rivers (Northern Caucasus) are described. Two isolated valves of aptychi which are considered to be ammonoid lower jaws are assigned to the superfamilies Haploceratoidea and Stephanoceratoidea. Two upper jaws likely belonged to ammonites with aptychus-type jaw apparatus (Ammonitida). The seven anaptychus-type jaws are assigned to the orders Phylloceratida and Lytoceratida. A well-preserved upper jaw of coleoid affinity is described for the first time from the Mesozoic of the Northern Caucasus.
... Находки изолированных кальцитовых элементов челюстей головоногих моллюсков (ринхолитов) известны, начиная с верхнего триаса, но они, скорее всего, принадлежали наутилидам (Riegraf, Luterbacher, 1989;Riegraf, Schmitt-Riegraf, 1995). Древнейшие ринхолиты, предположительно принадлежавшие аммоноидеям, известны, начиная с плинсбаха (Riegraf, Luterbacher, 1989), а самые древние на сегодняшний день челюсти ринхаптихового типа найдены в средней юре (байос) Северного Кавказа (Mironenko, Gulyaev, 2018). ...
... Находки среднеюрских анаптихов ограничивались двумя экземплярами (Quilty, 1970;Westermann et al., 1999), причем в первом случае при-надлежность находки к челюстным аппаратам цефалопод вызывает сомнения. Однако в последние два десятилетия опубликовано множество новых работ, посвященных среднеюрским аптихам (Рогов, Гуляев, 2003;Рогов, 2004;Mitta, Keupp, 2004;Митта, 2009Dietze et al., 2012;Keupp, Mitta, 2013;Mitta, Schweigert, 2016;Митта, Шерстюков, 2018;Mitta et al., 2018), а также анаптихам и ринхаптихам (Mironenko, Gulyaev, 2018). Также были описаны новые находки челюстей среднеюрских колеоидей (Keupp, Mitta, 2013). ...
... Элементы челюстных аппаратов головоногих моллюсков, описанные выше, принадлежат представителям двух подклассов цефалопод: Ammonoidea и Coleoidea. К настоящему времени из байоса Северного Кавказа были описаны челюсти аммоноидей, относящиеся к четырем различным типам челюстных аппаратов: аптиховому (Митта, 2017б), анаптиховому и ринхаптиховому (Mironenko, Gulyaev, 2018), и известному пока только по одному экземпляру филлаптиховому (Mitta, Schweigert, 2016). Большинство находок, описываемых в данной работе, относятся к нижним челюстям аммоноидей анаптихового типа (анаптихам), которые принадлежали аммоноидеям подотрядов Phylloceratina и Lytoceratina. ...
Описываются новые находки остатков челюстных аппаратов цефалопод из верхней части зоны Niortense и нижней части зоны Parkinsoni междуречья Кубани и Урупа. Изолированные створки двух аптихов, трактуемых как нижние челюсти аммонитов, отнесены к надсемействам Haploceratoidea и Stephanoceratoidea. Две верхние челюсти предположительно принадлежали также аммонитам с аптиховым типом челюстного аппарата (Ammonitida). Семь челюстей анаптихового типа отнесены к отрядам Phylloceratida и Lytoceratida. Впервые из мезозоя Северного Кавказа описана хорошо сохранившаяся верхняя челюсть колеоидеи.
... Such a type of ammonoid jaw, similar to the nautiloid one, is referred to as the rhynchaptychus type (Tanabe et al., 2015). For a long time, rhynchaptychi were known exclusively from the Upper Cretaceous of Japan and Far East Russia (Sakhalin); however, recently, they have been recovered also from the Middle Jurassic of the northern Caucasus (Mironenko and Gulyaev, 2018). ...
... To date, ammonoid jaws of the rhynchaptychus type have been described from the Upper Cretaceous (TuronianeCampanian) of Japan and Sakhalin Tanabe et al., 1980Tanabe et al., , 2015Kanie, 1982) and from the Middle Jurassic (BajocianeBathonian) of Dagestan (Mironenko and Gulyaev, 2018). Dissociated calcitic elements of lower jaws (Tillicheilus obtusus), according to Riegraf and Schmitt-Riegraf (1995), occur in western Europe in the Lower Cretaceous (ValanginianeHauterivian). From Crimea, T. obtusus has also been described to date from the uppermost Jurassic(?) and Lower Cretaceous (Tithonianelower Berriasian, upper Hauterivian and upper Barremianelower Aptian; see Komarov, 2005Komarov, , 2008. ...
... For several decades such jaws were known only from the Upper Cretaceous (TuronianeCampanian) deposits of Japan and Sakhalin Tanabe et al.,1980Tanabe et al., , 2015Kanie, 1982). Recently, they have also been recovered from the Middle Jurassic of Dagestan, Russia (Mironenko and Gulyaev, 2018). In the present paper calcitic ammonoid conchorhynchs are described from uppermost Jurassic(?) and Lower Cretaceous (Tithonianelower Berriasian, upper Hauterivian and upper Barremianelower Aptian) strata of Crimea, together with well-preserved lower jaws with calcitic tips from Cenomanian beds of the same region. ...
The jaws of Cretaceous nautiloids and some ammonoids (Phylloceratina and Lytoceratina) contain calcareous elements, namely rhyncholites in the upper jaws and conchorhynchs in the lower. Until now, only several types of numerous rhyncholites have been described from the Cretaceous deposits of Crimea, but lower jaw elements have never been reported from this region. Here we present the first finds of ammonoid lower jaws from the Cenomanian of Crimea that comprise well-preserved calcitic elements. The shape of these conchorhynchs and the ratio of their size to dimensions of the jaw vary in the different specimens. This difference may indicate a variety of food strategies amongst ammonoids with rhynchaptychus-type jaws, whereas all of them were likely durophagous. This assumption is confirmed by longitudinal scratches on the dorsal surface of these conchorhynchs. Amongst dozens of Crimean rhyncholites, specimens which belong to the form genus Tillicheilus have been described previously. Tillicheilus differs fundamentally from other rhyncholites by its shape. A comparison of the conchorhynchs from jaws with Tillicheilus rhyncholites has shown that these calcitic elements are identical, i.e., Tillicheilus constitutes lower jaw elements (conchorhychs, rather than rhyncholites as interpreted earlier. Finds from Crimea significantly expand the stratigraphical and geographical distribution of Cretaceous rhynchaptychus-type ammonoid jaws.
... Each jaw of living cephalopods (coleoids and nautilids) and of extinct ammonoids consists of two lamellaethe outer and the inner, whose sizes greatly vary among taxa (see Tanabe et al. 2015). Nautilids, starting from the Middle Triassic,and some of the Jurassic and Cretaceous ammonoids have additional calcareous elements in the jaws (Klug 2001;Riegraf & Moosleitner 2010;Tanabe et al. 2015;Mironenko & Gulyaev 2018). Nevertheless, in general, the jaws of coleoids, nautilids and ammonoids share the same general structural plan. ...
... In the course of the evolution of cephalopods, calcareous elements of their jaw apparatus evolved repeatedly and independently. Calcitic pointed tips of jaws (rhyncholites and conchorhynchs) independently appeared in Triassic nautilids (Riegraf & Moosleitner 2010) and Jurassic ammonoids, moreover, likely they evolved independently and at different times in Jurassic ammonoid suborders Phylloceratina and Lytoceratina (Mironenko & Gulyaev 2018). A calcitic layer on the surface also independently arose in the jaws of Jurassic ammonites and in Aptychopsis. ...
Cephalopoda is the only class of molluscs in which virtually all its modern representatives have a pair of powerful jaws. There is little doubt that jaws have contributed to the evolutionary success of cephalopods, but their origin still remains a mystery. Though cephalopods appeared at the end of the Cambrian, the oldest unequivocal jaws have been reported to date from the Late Devonian, though they were initially interpreted as phyllopod crustaceans of the suborder Discinocarina. After their relation with ammonoids was proven, they were considered as opercula, and only later their mandibular nature was recognized and widely accepted. Finds of discinocarins from Silurian deposits are still considered as opercula of ammonoid ancestors ‐ nautiloids of the order Orthocerida. However, according to modern ideas, there is no place within their soft body for the location of such large opercula. Moreover, the repeated appearance of very similar structures in the same evolutionary line at least twice, but in different places of the body and for different purposes seems highly improbable. A new hypothesis is proposed herein, in which the Silurian fossils, earlier assigned to Discinocarina, are not specialized opercula, but protective shields, to defend orthocerids not from the predators, but from their own prey. The chitinous plates around the mouth likely appeared in the Silurian orthocerids for protection from such damage and later, during Silurian and Devonian, most likely gradually evolved into the jaws.
... Remains of a black organic layer without calcite elements are preserved. The organic layer has a characteristic reticulate microstructure, which is also observed in other anaptychi from the Northern Caucasus (Mironenko and Gulyaev, 2018;Mironenko and Mitta, 2020). The described specimen is distinct in its size, as this anaptych is several times larger than all the published Middle Jurassic anaptychi. ...
An unusually large anaptychus is described from the lower part of the Upper Djangura Subforma-tion (Upper Bajocian Garantiana baculata Subzone of the Strenoceras niortense Zone) on the Kyafar River (Karachay-Cherkessia, Northern Caucasus). Judging by the shape and size, it belonged to a representative of Lytoceras (Thysanolytoceras) (family Lytoceratidae). The wings of the anaptychus are partially deformed and asymmetrical; most ridges and flexures have no cracks or fractures. This may indicate synsedimentary deformation and lifetime elasticity of at least the peripheral part of the anaptychus.
... Baculites) and likely juveniles of other ammonoid taxa preyed on small planktic crustaceans (Kruta et al., 2011;Tanabe et al., 2015). Calcareous tips of the jaws of lytoceratid and phylloceratid ammonoids (rhyncholites and conchorhynchs) could have been used for breaking solid prey shells, including crustacean carapaces (Tanabe et al., 1980(Tanabe et al., , 2015Mironenko and Gulyaev, 2018;Mironenko and Rogov, 2018), as well as analogous calcitic structures in the jaws of modern nautilids are currently used for hunting crabs and hermit crabs (Saunders et al., 1978;Ward, 1981;Tanabe et al., 2015). ...
The discovery of a hermit crab (superfamily Paguroidea) preserved in the likely immature shell of an ammonite, Craspedites nekrassovi is reported from the Upper Jurassic of Moscow, Russia. This is the oldest undoubtable symmetrical hermit crab to date which is known from non-reefal environments. This new occurrence combined with the documentation of numerous sublethal and lethal injuries on ammonite shells in the same beds (probably produced by such paguroids), all suggest that the hermit crabs not only lived in ammonite shells but also hunted these animals. The proportion of damaged shells (including healed ones) varies in different Upper Jurassic ammonite genera from 1.2% in Kachpurites up to 9.3% in Craspedites. Among damaged Kachpurites only 6.25% survived attacks whereas among Craspedites the percentage of survivors was 87.5%. These data imply that Craspedites likely lived near the sea bottom and often encountered hermit crabs, whereas Kachpurites likely lived in the water column.
... 70 ? 8.2 have also been reported from the Middle Jurassic in the North Caucasus by Mironenko and Gulyaev (2018), who assigned their taxonomic relationships to the Phylloceratidae. Hence, this specimen can be identified as a species belonging to either Lytoceratina or Phylloceratina. ...
Two exceptionally large cephalopod jaws collected from the Upper Cretaceous marine deposits of the Hidaka area, Hokkaido (Yezo Group), and Awaji Island, Southwest Japan (Izumi Group), respectively, are described. Further, their taxonomic relationships and functional morphologic aspect for feeding are discussed. Based on a comparison to counterparts of modern and extinct cephalopods, they were identified as the lower jaws of ammonoids. Owing to the development of a thick calcareous tip in the large outer chitinous lamella, the lower jaw from the Yezo Group is classified as a rhychaptychus-type known from the Cretaceous Lytoceratina and Phylloceratina. The lower jaw from the Izumi Group lacks a sharply pointed calcareous tip and is characterized by a posteriorly elongated outer chitinous lamella, whose outer surface is sculptured by a median furrow in the anterior portion. These features categorize it as an intermediate-type lower jaw shared by the Cretaceous Desmoceratoidea. As determined from the co-occurring ammonoids and the relationship between the dimensions of in situ lower jaws and conchs for ammonoids previously described, the two lower jaws from the Yezo and Izumi groups were, respectively, thought to belong to large gaudryceratid and pachydiscid specimens, both of which have shell diameters greater than 40 cm. The overall shape and structure of the two lower jaws suggest a scavenging-predatory feeding habit for the gaudryceratid and a passive microphagous habitat for the pachydiscid.
Ammonoids – cephalopod molluscs with external shells that existed from the Early Devonian up to the end of the Cretaceous – had well-developed jaws. During ammonoid evolution, several different types of their jaw apparatus arose, the study of which is of undoubted interest since it allows researchers to draw conclusions about the feed-ing strategies of ammonoids and their position in trophic chains. However, there is a lack of findings relating to the evolution of ammonoid jaws during the Permian. Here we describe a collection of almost thirty of cephalopod jaws from the Divjinskian Formation (Artinskian Stage, Cisuralian, Lower Permian), from the Sverdlovsk region of Russia. Most likely, these jaws belong to goniatitid ammonoid Uraloceras, the most abundant cephalopod mollusc in the Divjinskian (Divya) Formation. Uraloceras lower jaws are typical ammonoid anaptychi which have a rounded, wide and convex shape with smooth or slightly ribbed surface. They have a large inner lamella with a trapezoidal platform in the central part. One of the jaws bears a possible bite trace of a predator or scavenger. The upper jaws, described here for the first time, are slightly smaller than the lower jaws, their shape is narrow and pointed. Originally, both jaws were completely organic without calcareous elements. The absence of sculpture, consisting of frequent ribs and growth lines, characteristic of the more ancient Carboniferous goniatitid jaws, makes the jaws of the Uraloceras closer to the structure of the jaw apparatus of Triassic ammonoids. Judging by the pointed shape of the tips of both jaws, Uraloceras were active predators.
A single, atypical conchorhynch (calcitic tip of a cephalopod lower jaw), recovered from the uppermost Meerssen Member (Maastricht Formation, upper Maastrichtian) at the former ENCI-HeidelbergCement Group quarry, south of Maastricht, is described as a new parataxon, Conchorhynchus illustris sp. nov. The specimen can be differentiated from all previous conchorhynch records on account of its large size, elongated shape and, in particular, of the structure of its apical part which is smooth and forwardly elongated. During the Late Cretaceous, conchorhynchs formed part of the jaw apparatus of nautilids and of two ammonoid suborders, Phylloceratina and Lytoceratina. Since conchorhynchs are most often found separated from jaws, establishing to which group of cephalopods their bearer belonged can be complicated. Here, for the first time, we propose a set of morphological criteria to differentiate clearly between nautiloid and ammonoid conchorhynchs. Although Conchorhynchus illustris sp. nov. is distinct from all currently known nautilid conchorhynchs, the sum of its morphological features is indicative of assignment to that cephalopod group. The upper portion of the Maastricht Formation in the Maastricht area (Nekum and Meerssen members) has yielded internal and external moulds of shells of the nautilid Eutrephoceras Hyatt, 1894 and the hercoglossid Cimomia Conrad, 1866. The new conchorhynch type described herein most likely belonged to one of these shell-based taxa. Judging from its unusual shape, the feeding strategy of its bearer must have differed from that of modern nautilids, in that it held and pierced prey rather than crushed sturdy shells.
Until now thefindingsof rhyncholites from the Jurassic marine sediments of Crimea were very scarce. In both the Oxfordian and Kimmeridgian of Crimea, rhyncholites were never found despite the fact that in Western and Central Europe they are very numerous in Middle and Upper Jurassic marine sediments. We have described five new findings of rhyncholites from Crimea whose age ranges from the Upper Callovian to the Kimmeridgian. They belong to the five different species (including three new ones) of the genus Gonatocheilus Till, 1907, which was never previously described in Crimea. We also discuss the taxonomy of rhyncholites and argue that the genus Palaeotheutis Till, 1906 is unavailable according to article 33 of International code of zoological nomenclature and the genus Gonatocheilus Till, 1907 should be used instead of it.
We introduce high-resolution synchrotron radiation X-ray tomography for nondestructive, three-dimensional reconstruction of the jaw apparatus preserved within the body chamber of the Late Cretaceous phylloceratid ammonoid, Phyllopachyceras ezoensis, for the first time. Analysis of the X-ray images using linear absorption coefficient estimation reveals that the upper jaw consisted mainly of inner and outer lamellae composed of carbonate apatite, which originally might have been a chitin-protein complex, with angulated rims of thick calcareous material. The morphological features indicate that the jaw apparatus of this species is the rhynchaptychus-type. The three dimensional architecture of the jaw apparatus of this species is similar to that of other ammonoids, except for the development of a thick calcified deposit in both upper and lower jaws, which can be considered to support the predatory-scavenging feeding habits of the species. The jaw features of this species appear to have been constrained by both phylogenetic and functional morphological factors.
A nearly complete radula with seven elements per row preserved inside of an isolated, bivalved, calcitic lower jaw (= aptychus) of the Late Jurassic ammonite Aspidoceras is described from the Fossillagerstätte Painten (Bavaria, southern Germany). It is the largest known ammonite radula and the first record for the Perisphinctoidea. The multicuspidate tooth elements (ctenodont type of radula) present short cusps. Owing to significant morphological differences between known aptychophoran ammonoid radulae, their possible function is discussed, partly in comparison with modern cephalopod and gastropod radulae. Analogies between the evolution of the pharyngeal jaws of cichlid fishes and the ammonoid buccal apparatus raise the possibility that the evolution of a multicuspidate radula allowed for a functional decoupling of the aptychophoran ammonoid jaw. The radula, therefore, represents a key innovation which allowed for the evolution of the calcified lower jaws in Jurassic and Cretaceous aptychophoran ammonites. Possible triggers for this morphological change during the early Toarcian are discussed. Finally, we hypothesize potential adaptations of ammonoids to different feeding niches based on radular tooth morphologies.
The body chamber of an ammonoid of the genus Calliphylloceras (Suborder Phylloceratina) containing its lower jaw is reported from the Upper Bajocian (Strenoceras niortense Zone) of the Northern Caucasus. The arrangement, state of preservation, and size of the lower jaw suggest preservation in situ. The general morphology of the lower jaw strongly resembles the chitinous inner lamella of the aptychus-type lower jaws, because it is divided into two almost symmetric parts by a median harmonic midline joint termed symphysis. However, outer bivalved calcitic plates (apytchus sensu stricto) cannot be recognized in the present lower jaw. Early Jurassic Phylloceratina are known to have had lower jaws of the anaptychus-type, whereas Late Cretaceous taxa had lower jaws of the rhynchaptychus-type. It appears that in the Middle Jurassic a third morphotype of lower jaws was present in Phylloceratina, for which we introduce the new term ‘phyllaptychusʼ.
The field guide provides data on the Jurassic deposits of the Mountain Dagestan, including information on ammonite zonal biostratigraphy in five reference sections, located in Kazikumukhskoe Koisu river valley
More than 30 isolated nautilid jaws have been discovered in washed samples of late Cretaceous (turonian) nearshore/ shallow water deposits located in the southern part of the Bohemian Cretaceous Basin (BCB). Upper and lower jaws discovered in genetically-similar early turonian deposits are described in detail herein. the nautilid jaw apparatuses comprise rhyncholites (upper jaws) assigned to Nautilorhynchus simplex (Fritsch), and conchorhynchs (lower jaws) assigned to Conchorhynchus cretaceus Fritsch. some rhyncholites show signs of abrasion and corrosion, and may also form a substrate for sessile organisms. in one specimen, signs of acid digestion in the stomach of a predator were recognized. N. simplex is synonymized with "Rhyncholithus" bohemicus (till), "R." curvatus (till), "R". rectus (till) and "R". curtus (till). the significant morphological variability observed in N. simplex is supported by biometric data. although the jaws were not found associated with body chambers, it is inferred from the extremely low nautilid biodiversity across the Cenomanian/turonian boundary interval in the BCB, and from the range and relative abundance of the only early turonian nautilid taxon present, that the jaws are probably referable to the genus Eutrephoceras hyatt and specifically to the common and long-ranging species E. sublaevigatum (d'orbigny).
This two-volume work is a testament to the abiding interest and human fascination with ammonites. We offer a new model to explain the morphogenesis of septa and the shell, we explore their habitats by the content of stable isotopes in their shells, we discuss the origin and later evolution of this important clade, and we deliver hypotheses on its demise. The Ammonoidea produced a great number of species that can be used in biostratigraphy and possibly, this is the macrofossil group, which has been used the most for that purpose. Nevertheless, many aspects of their anatomy, mode of life, development or paleobiogeographic distribution are still poorly known.
Themes treated are biostratigraphy, paleoecology, paleoenvironment, paleobiogeography, evolution, phylogeny, and ontogeny. Advances such as an explosion of new information about ammonites, new technologies such as isotopic analysis, tomography and virtual paleontology in general, as well as continuous discovery of new fossil finds have given us the opportunity to present a comprehensive and timely "state of the art" compilation. Moreover, it also points the way for future studies to further enhance our understanding of this endlessly fascinating group of organisms.
Table of Contents:
PART I – Conch
1 Describing ammonoid conchs
Christian Klug, Dieter Korn, Neil H. Landman, Kazushige Tanabe,
Kenneth De Baets and Carole Naglik
2 Colour patterns
Royal H. Mapes and Neal L. Larson
3 Ammonoid septa and sutures
Christian Klug and René Hoffmann
4 Cameral membranes, pseudosutures, and other soft tissue imprints in ammonoid shells
Kristin Polizzotto, Neil H. Landman and Christian Klug
PART II - Ontogeny
5 Ammonoid embryonic development
Kenneth De Baets, Neil H. Landman and Kazushige Tanabe
6 Theoretical modelling of the molluscan shell: what has been learned from the comparison among molluscan taxa?
Severine Urdy
7 Mature modifications and sexual dimorphism
Christian Klug, Michał Zatoń, Horacio Parent, Bernard Hostettler and
Amane Tajika
8 Ammonoid shell microstructure
Cyprian Kulicki, Kazushige Tanabe, Neil H. Landman and Andrzej Kaim
9 Ammonoid intraspecific variability
Kenneth De Baets, Didier Bert, René Hofmann, Claude Monnet,
Margaret M. Yacobucci and Christian Klug
PART III - Anatomy
10 Ammonoid buccal mass and jaw apparatus
Kazushige Tanabe, Isabelle Kruta and Neil H. Landman
11 Ammonoid radulae
Isabelle Kruta, Neil H. Landman, and Kazushige Tanabe
12 Soft-part anatomy of ammonoids:
reconstructing the animal based on exceptionally preserved specimens and
actualistic comparisons
Christian Klug and Jens Lehmann
13 Soft-part anatomy of the siphuncle in ammonoids
Kazushige Tanabe, Takenori Sasaki and Royal H. Mapes
14 Muscle scars in ammonoid shells
Larisa A. Doguzhaeva and Royal H. Mapes
15 The additional external shell layers indicative of “endocochleate experiments” in some ammonoids
Larisa A. Doguzhaeva and Harry Mutvei
PART IV – Habit and habitats
16 Ammonoid buoyancy
René Hoffmann, Robert Lemanis, Carole Naglik and Christian Klug
17 Ammonoid locomotion
Carole Naglik, Amane Tajika, John A. Chamberlain and Christian Klug
18 Ammonoid habitats and life history
Alexander Lukeneder
19 Isotope signature of ammonoid shells
Kazuyoshi Moriya
20 Parasites of ammonoids
Kenneth De Baets, Helmut Keupp and Christian Klug
21 Ammonoid paleopathology
Helmut Keupp and René Hoffman
Tanabe, K., Landman, N.H. & Kruta, I. 2011: Microstructure and mineralogy of the outer calcareous layer in the lower jaws of Cretaceous Tetragonitoidea and Desmoceratoidea (Ammonoidea). Lethaia, Vol. 45, pp. 191–199.
Based on the differences in their relative size, overall shape, structure and the degree of development of an outer calcified covering, lower jaws of the Ammonoidea have been classified into four morphotypes: normal, anaptychus, aptychus and rhynchaptychus types. However, detailed microstructural and mineralogical comparison of these morphotypes has not yet been addressed. This article documents the results of SEM and XRD observations of the lower jaws of three Late Cretaceous ammonoid species belonging to the Tetragonitoidea (Anagaudryceras limatum) and Desmoceratoidea (Pachydiscus kamishakensis and Damesites aff. sugata), based on excellent material preserved in situ within the body chamber, and retaining an aragonitic shell wall. The lower jaws of the three species are assigned to an intermediate form between anaptychus and aptychus types for the first two species and the rhynchaptychus type for the third species. Their black, presumably originally chitinous outer lamella is wholly covered with a calcareous layer. The calcareous layer is composed of aragonite in D. aff. sugata and A. limatum, and calcite in P. kamishakensis. The microstructure of the outer calcareous layer differs among the three species, i.e. granular in A. limatum, spherulitic prismatic in D. sugata, and prismatic in P. kamishakensis, all of which can be distinguished from the lamellar and spongy structure of the outer-paired calcitic plates of the typical aptychus-type lower jaws in some Jurassic and Cretaceous Ammonitina and Ancyloceratina. Our study suggests that most Jurassic and Cretaceous ammonoids possessed an outer calcareous layer in their lower jaws, although its mineralogy, microstructure and relative thickness vary among different taxa. □Ammonoidea, Cretaceous, Desmoceratoidea, lower jaw, microstructure, Tetragonitoidea.
190 species of the Late Bajocian and Bathonian are described.
Klug, C. 2001. Functional morphology and taphonomy of nautiloid beaks from the Mid-dle Triassic of southern Germany. -Acta Palaeontologica Polonica 46, 1,43-68. New records of nautiloid beak elements conventionally classified as 'Rhyncholithes hirundo (Biguet, 18 19)' and 'Conchorhynchus avirostris (von Schlotheim, 1820)' with carbonised (originally chitinous) three-dimensionally preserved appendages from the Upper Muschelkalk (Middle Triassic) of northern Wiirttemberg (Southwest Germany) enable restoration of the complete beak of Germanonautilus. In three specimens, the lower mandible is embedded within the living chamber of Germanonautilus conchs. Beak elements of Germanonautilus differ from those of Recent Nautilus in the more elongate appendages of the fossil lower mandibles and the weaker sculpture on the origi-nally chitinous parts. Furthermore, the dorsal sculpture of the fossil conchorhynchs con-sists of ridges rather than denticles and the ventral sculpture of the fossil rhyncholiths dis-plays ridges in places where the Recent rhyncholiths have a smooth surface. Addi-tionally, the fossil beak elements attained a larger size than their Recent counterparts. During transport of 'Rhyncholithes hirundo', the light chitinous parts served as a sail and the heavier conchorhynch anchored in the sediment causing alignment. In contrast to the irregularly embedded isolated rhyncholiths, the conchorhynchs usually settled with their ventral side up. From the study of 407 fossil nautiloid beak-elements, a significant vari-ability of the hard parts is evident. Consequently, the assignment of specific morpho-logies to the species of Germanonautilus is impossible. Key w or d s : Conchorhynch, rhyncholith, functional morphology, taphonomy, Muschel-kalk, Triassic, Germany. Christian Klug [christian. klug @ uni-tuebingen.de], Institut und Museum fur Geologie und Palaontologie, SigwartstraJe 10,D-72076 Tiibingen, Germany.
The jaw apparatuses of two species of Late Cretaceous Phylloceratina (Ammonoidea), Hypophylloceras subramosum and Phyllopachyceras ezoensis, are described on the basis of well-preserved in situ material from Hokkaido, Japan. Gross morphological and X-ray CT observations reveal that the upper and lower jaws of the two species are essentially similar in their overall structure. Their upper jaws consist of a shorter outer lamella and a pair of larger, wing-like inner lamellae that become narrower and join together in the anterior portion, as in those of other ammonoids. The upper jaws of the two phylloceratid species are, however, distinguishable from those of other known ammonoids by the presence of a thick, arrowhead-shaped calcified rostral tip. The lower jaws of the two species consist of a short, reduced inner lamella and a large, gently convex outer lamella covered with a thin calcareous layer, the features of which are common with the rhynchaptychus-type lower jaws of the Cretaceous Lytoceratina. In the presence of a sharply pointed, thick calcareous tip on upper and lower jaws, the jaw apparatuses of the Phylloceratina resemble those of modern and fossil nautilids, suggesting that they were developed to serve a scavenging predatory feeding habit in deeper marine environments. This and other studies demonstrate that at least some Mesozoic rhyncholites and conchorhynchs are attributable to the Phylloceratina and Lytoceratina.
Jaw morphologies of 19 Cretaceous ammonoid genera that are distributed in the suborders Phylloceratina, Lytoceratina, Ammonitina, and Ancyloceratina were compared. The upper jaws known from seven genera of the Ammonitina and Ancyloceratina are essentially similar in having horny reduced outer and large paired inner lamellae, both of which are united in the anterior portion forming a sharp rostral tip. These features have also been recognized in the upper jaws of Goniatitina and Ceratitina, suggesting the morphological conservatism of the upper jaws in the Ammonoidea. The lower jaws of Cretaceous ammonoids, by contrast, exhibit remarkable taxonomic variation in their relative size to the upper jaws, overall morphology, and the degree of development of the outer calcitic covering. They may fall into either rhynchaptychus- or anaptychus- or aptychus-types, but intermediate forms are present among them. The anaptychus-type lower jaw in some Ammonitina and Ancyloceratina with a large outer horny lamella with a median "hinge" and paired calcite plates may have acquired a secondary function as an operculum.
The uppermost Bajocian to lowermost Bathonian ammonoid succession has been studied in the Bas Auran area in view of choosing one of its sections as the Global Stratotype Section and Point (G.S.S.P.) of the Bathonian Stage. The Bas Auran ammonite assemblages display exceptional values of record quality. The stratigraphic distribution of 629 specimens referred to 63 species and 35 genera, collected during the last forty years from three sections (Ravin du Bes, Ravin d'Auran, Ravin des Robines), is plotted and analysed, bed by bed. Over 85 stratigraphic levels, through 9 in in thickness, have been studied at the top of the "Marno-calcaires Cancellophycus" formation, ranging from the latest Bajocian (Parkinsoni Zone, Bomfordi Subzone) to the earliest Bathonian (Zigzag Zone, Convergens Subzone) and the base of the Macrescens Subzone. Ammonoid assemblages arc composed of Northwest European and Mediterranean elements, associated with Sub-Mediterranean ones, allowing chrono-correlation between the Northwest European Convergens Subzone and the Sub-Mediterranean Parvum Subzone. The basal boundary of the Zigzag Zone and of the Bathonian Stage is placed at the base of Sturani's bed 23 in the Ravin du Bes section and is identified by the first occurrence of Gonolkites convergens, and coincides with the lowest occurrence of Morphoceras parvum. Features of the ammonoid Succession indicate relatively homogeneous and good record quality, gradual biostratigraphic change and high degree of taxonomic similarity between the Bomfordi and Convergens subzones. Palaeontological criteria also indicate relatively high values of palaeontological and stratigraphic completeness at the base of levels RB070-RB071 (= level 23 in Sturani 1967) which corresponds to the Bajocian/Bathonian boundary. The Ravin du Bes Section, with forty-six successive ammonoid fossil-assemblages of the Convergens Subzone belonging to three biohorizons through five metres of thickness, shows maximum values of biostratigraphic and biochronostratigraphic completeness, being one of the most complete in the world. Therefore, the Ravin du Bes Section should be chosen as the Global Stratotype Section and Point for the base of the Bathonian Stage. Two biostratigraphic logs summarize the ammonite content from the uppermost Bomfordi to basal Macrescens subzones. Three plates illustrate the most characteristic ammonoid taxa at the Bajocian-Bathonian passage in the Bas Auran succession.
Lytoceratites together with Phylloceratites are often described as “conservative”. However, the origin and monophyly of lytoceratid
ammonites as well as their role in the evolution of all ammonites is under constant debate. In this work, the Lytoceratoidea investigated
on generic level for the presence of a septal lobe. Included into this investigation is the verification of relevant literature and the
registration of the collected literature in a database system. Furthermore material from public and private collections was studied.
The investigation reveals that all Lytoceratoidea are characterised by the presence of a septal lobe which constitutes their monophyly
(cp. Arkell et al., 1957). The septal lobe represents a consistent morphological character that appeared in the lowermost Jurassic and
is present in the uppermost Cretaceous members of Lytoceratoidea. It was noticed that the septal lobe appeared earlier in ontogeny and
was stronger developed in most of the stratigraphical younger representatives compared to Jurassic members (acceleration). In addition,
further characters have been investigated and tested for their phylogenetic significance. It turned out that most of these characters e. g.
whorl section, course and number of constrictions are homoplastic or highly variable within one genus. Finally, six characters (septal
lobe, parabolic ribs, fimbriation, shape of adult lateral lobe, primary suture, jaw type) have been kept for stratocladistic analyses.
With this method the phylogeny within the Lytoceratoidea was enlightened as far as possible. Within the family Lytoceratidae five
monophyletic subfamilies are retained : Ectocentritinae, Pleuroacanthinae, Lytoceratinae, Alocolytoceratinae and Megalytoceratinae.
The monophyly of the second family Tetragonitidae is based on the distribution of the quinque- and sixlobate primary suture line and
the development of a rhynchaptychus (Engeser & Keupp, 2002). Within the Tetragonitidae two subfamilies (Gaudryceratinae and
Tetragonitinae) and one tribus Gabbioceratini are retained. This work has been the first critical-systematical review for the whole group
within the last forty years. As a main result of this investigation fifteen genera have been excluded from Lytoceratoidea, seventeen
genera have been regarded as junior subjective synonyms. A sexual dimorphic couple is presented for Anagaudryceras (M) and
Anagaudryceras (Zelandites [m]) for the first time in addition to the two well known of Lytoceras (M). Thirty genera have been retained
as valid lytoceratid taxa. For some genera e. g. Lobolytoceras and Protetragonites the stratigraphic distribution has been extended
significantly. “Trachyphyllites” costatus is included into Analytoceras hermanni and represents a typical Lower Jurassic lytoceratid
member. It appears that the Lytoceratoidea are derived from psiloceratids at the Triassic-Jurassic-boundary as already stated by Guex
(1987).
The author assents the statement of Guex (1987) and regards the Lytoceratoidea as members of Ammonitina. Tetragonitidae are
derived from Protetragonites. Both taxa develop non-fimbriate ribs in contrast to contemporary lytoceratids. Protetragonites fraasi
from the Oxfordian (Upper Jurassic) represents the oldest member of that genus. Judging from the two characters sixlobate primary
suture and septal lobe, discussed above, Lytoceratoidea represent the most advanced ammonoid group.
In the second part of this thesis the functional significance of the septal lobe was investigated. It was planned to calculate the ratio of
chamber volume against its surface. For this purpose a Gaudryceras specimen in hollow preservation was scanned using computer
tomography at the “Bundesanstalt für Materialforschung und -prüfung” (Berlin). The ammonite was digitalised at “Konrad-Zuse-
Institut” (Berlin) using AM IRA®. Unfortunately, the resolution was too low for the project. The positive effect of the ratio of chamber
volume against its surface caused by the septal lobe can therefore only be assumed. It is supposed that the septal lobe increases the
efficiency of the hydrostatic apparatus.
We describe upper and lower jaws of Placenticeras Meek, 1876, from the Upper Cretaceous (upper Campanian) Bearpaw Shale and Pierre Shale of the Western Interior of North America and lower jaws of the related ammonite Metaplacenticeras Spath, 1926, from the Campanian Yasukawa Formation of Hokkaido, Japan. One lower jaw is preserved inside the body chamber of Placenticeras costatum Hyatt, 1903. The other jaws are isolated but are generally associated with fragments of placenticeratid shells. The jaws from North America are attributed to Placenticeras meeki Böhm, 1898, and P. costatum, while those from Japan are attributed to Metaplacenticeras subtilistriatum (Jimbo, 1894). All of the jaws are presumed to be from adults. The jaws of Placenticeras attain lengths of up to 95 mm. They are preserved as steinkerns with a thin film of black material, representing diagenetically altered chitin. X-ray diffraction analysis of samples of this material indicates that it consists of magnesium-rich calcite, pyrite, and amorphous material (organic compounds). The upper jaw is approximately the same length as the lower jaw and is U-shaped, with narrow wings that converge anteriorly to a dome-shaped hood. The lower jaw is composed of two lamellae. The outer lamella is broad and consists of two wings terminating in a bilobate posterior margin. The inner lamella is one-half the length of the outer lamella. The two lamellae are separated except in the apical region and along the sides. The junction between the lamellae appears as a U or V-shaped outline on the anterior portion on the ventral surface of the jaw. This junction is especially conspicuous in specimens in which part of the inner lamella has eroded away. In crushed specimens, the lower jaw is subquadrate in shape. In specimens that retain some or all of their original curvature, the central portion is gently convex and the sides bend steeply dorsally. The rostrum projects slightly anteriorly and dorsally and there is a thickened rim of chitin along the anterior margin where the two lamellae are doubled over. A small indentation appears at the apical end and, in most specimens, develops into a midline slit that extends posteriorly 10–15 mm. However, as shown in well-preserved specimens and based on comparisons with the jaws of closely related ammonites, this slit represents the remnants of a narrow ridge on the ventral side of the inner lamella. This ridge is surrounded by an elongate boss of thickened chitin, which corresponds to a depression on the dorsal side. The ventral surface of the outer lamella bears a midline ridge with a central groove, which essentially forms a continuation of the ridge on the inner lamella. The ventral surface of the outer lamella is ornamented with thin, radial striations and irregular broad undulations paralleling the posterior margin. The posterior end is generally incomplete, probably as a result of predation or postmortem degradation, and the lateral margins are commonly creased, indicating postmortem plastic deformation. The lower jaws of Metaplacenticeras subtilistriatum are much smaller than those of Placenticeras but are otherwise similar in morphology. However, they retain pieces of a very thin, fibrous outer layer comprising two plates. X-ray diffraction analysis of samples of this layer indicates that it consists of calcite enriched in magnesium. Each plate covers the ventral surface of one of the wings and terminates at the midline ridge. Based on the close affinity of Metaplacenticeras and Placenticeras, and in comparison with published descriptions of placenticeratid jaws from elsewhere, we hypothesize that similar plates covered the lower jaws of all placenticeratids, although these plates have not been found in any Placenticeras material from North America. The thin nature and fibrous microstructure of this layer would have made it susceptible to mechanical breakage and chemical dissolution. Furthermore, jaws are internal structures embedded in the buccal bulb. The micro-environment within this bulb may have promoted dissolution of the outer calcitic layer of the lower jaw. The presence of a pair of calcitic plates (aptychi) and a midline ridge with a central groove on the outer lamella of the lower jaw are unique features of the lower jaws of the Aptychophora Engeser and Keupp, 2002. Although differences in preservation obscure this similarity, the lower jaws of placenticeratids conform to the description of aptychus-type jaws. However, unlike the thick calcitic aptychi of other Ammonitina, the thin calcitic aptychi of placenticeratids probably did not function as opercula and would have served simply to strengthen the lower jaw. The jaws of placenticeratids were probably designed for biting and cutting food rather than for passively collecting and straining plankton. Other data about the habitat and mode of life of placenticeratids are consistent with this interpretation. These ammonites probably inhabited surface waters and were capable of pursuing and attacking sluggish prey. An ecological analog of placenticeratids may be the modern ocean sunfish Mola mola (Linnaeus, 1758), which inhabits surface waters and feeds on gelatinous zooplankton.
Documentation of repaired injuries and abnormalities on the jaws ofmodern nautilus sheds light on the ecology and behavior of these animals. It also helps elucidate the function of ammonite aptychi, which are traditionally interpreted as opercula. We examined 219 pairs of jaws belonging to Nautilus belauensis, N. mucmmphulus, N. pompilius, and Allonautilus scrobiculatus. Abnormalities occur in 68% of the sample and are only present on the lower jaw. The abnormalities consist of I) repaired fractures, 2) small depressions, 3) radial grooves and ridges, and 4) flexures in the chitin. These abnormalities arc cither the result of injury or growth pathology. Injuries may be due to accidents during feeding (e.g., biting down on a hard crustacean carapace) or from predatory attacks. Alternatively, they may have been sustained during mating behavior or fighting between males. Most abnormalities occur on the left side of the lower jaw. This may be related to the fact that in male nautilus, the jaws are displaced to the right side of the midline, so that during mating, for example, the apex of the jaws of the male lines up with the left side of the jaws of the female. The presence of injuries and other abnormalities on the jaws of nautilus suggest that similar features on aptychi may have been produced during the normal use of the jaws, and do not necessarily imply an opercular function. Alternatively, aptychi may have served to strengthen and reinforce the lower jaw.
The present state of knowledge concerning the function of anaptychi, aptychi, and opercula of ammonoids is reviewed. The jaw apparati found associated with the lytoceratid generaGaudryceras andTetragonites by Kanie et al. (1978) and Tanabe et al. (1980) and classified as rhynchaptychus type of ammonoid jaws by Lehmann (1981) are re-interpreted. Morphologically, they are very similar toNautilus jaws. Their interpretation as allochthonous nautiloid jaws is discussed and considered probable. However, beccublast cell impressions inGaudryceras and recentNautilus differ considerably. Further investigations are deemed necessary concerninga.
the nature of the anaptychi in Palaeozoic anaptychus assemblages, whether they are opercula or jaw elements;
b.
the function of the laevaptychi. Their jaw nature is still open to doubt;
c.
the autochthony of the rhynchaptychus-type lower jaws found in lytoceratid Upper Cretaceous ammonites in Japan.
A newly discovered fossil cephalopod jaw apparatus that may belong to Permian representatives of the Endocochlia is described. Permorhynchus dentatus n. gen. n. sp. is established on the basis of this apparatus. The asymmetry of jaws in the Ectocochlia may be connected with the double function of the ventral jaw apparatus, and the well‐developed, relatively large frontal plate of the ventral jaw should be regarded as a feature common to all representatives of ectocochlian cephalopods evolved from early Palaeozoic stock. Distinct features seen in the jaw apparatus of Upper Permian endocochlians include the pronounced beak form of both jaws and the presence of oblong wings on the ventral mandible.
Nine proposals of aptychus (sensu stricto) function have been published (in historical order): operculum, micromorphic males, lower mandible, protection of gonades, ballast for lowering of aperture, flushing of benthic prey, filtering microfauna, pump for jet propulsion, and active stabilizer against rocking produced by the pulsating jet during forward foraging and backward swimming. Some ammonites bear thick, laevaptychus- and lamellaptychus-type aptychi (aspidoceratids and haploceratoids) that may have improved lowering of the aperture as part of a mobile cephalic complex, enabling many of these functions. Aptychi were multifunctional, most commonly combining feeding (jaw, flushing, filtering) with protection (operculum), and/or with propulsion (ballast, pump, diving and stabilizing plane). Multifunctionality would have been a strong constraint in ontogeny and evolution as shown by the limited diversity of aptychi with respect to the wide variety of shell morphologies known in the Mesozoic Ammonitina. Calcification of aptychi in the Jurassic Ammonitina is known from the Early Toarcian Hildoceras which is also the first ammonite with males bearing well-formed lateral peristomatic projections or lappets. Calcification allowed aptychi to be involved in functions, which would have improved, in different degrees and combinations, feeding, propulsion and protection. It is herein suggested that multifunctional calcareous aptychi allowed the gradual development of a wide variety of new life-styles. These new life-styles would have led to the origin and early evolution of haploceratids and stephanoceratids producing the wide diversification of the Ammonitina observed from the Early Aalenian.
A single, conical specimen from the Upper Bathonian of Chacay Melehue, west-central Argentina, displays the characteristic features of ammonoid lower jaws, inner pit and lateral platforms, as well as the beak of the upper jaw. There are no direct taxonomic clues but its large size, circular outline, and associated cephalopod fauna indicate that it belonged to Lytoceratinae, possible Lytoceras.
The occurrence of ammonite jaw apparatuses in situ within concretions from the Sinemurian (Lower Jurassic) of Black Ven Cliff, Charmouth, Dorset, provides evidence of burial of the ammonites with soft parts intact and this is of importance in considering the origin of the concretions. The lower jaws (anaptychi) of arietitid and eoderoceratid ammonites are preserved and three examples of upper jaws are recorded in the species Asteroceras stellare. Although usually accepted as being entirely of organic composition, the anaptychi of A. stellare have an outer calcareous layer.
Ammonites are probably the most famous marine fossil of the Jurassic System, being often abundant and with a virtually global distribution where appropriate fades are preserved. Along with their fundamental role for Jurassic stratigraphy and correlation, this frequency of occurrence and wide distribution can also provide valuable insights into Jurassic marine biogeography as well as into evolutionary and other palaeobio-logical processes. In the Jurassic, up to seven suborders can be recognized: Phylloceratina, Psiloceratina, Ammonitina, Lytoceratina, Haploceratina, Perisphinctina and Ancyloceratina. Each is reviewed, citing a selection of important evolutionary case histories. These suborders range through up to about 20 distinguishable biogeographical provinces and subprovinces distributed through up to seven realm-group biochores. The latter comprise a northern, high latitude Pan-Boreal Realm or Superrealm (including the Arctic, Boreal-Pacific and Boreal-Atlantic realms/subrealms) and the low latitude and southern Pan-Tethyan Realm or Superrealm (including the Mediterran-Caucasian, East Pacific, Indo-Pacific and possibly Austral realms/subrealms).
A newly discovered fossil cephalopod jaw apparatus that may belong to Permian representatives of the Endocochlia is described. Permorhynchus dentatus n. gen. n. sp. is established on the basis of this apparatus. The asymmetry of jaws in the Ectocochlia may be connected with the double function of the ventral jaw apparatus, and the well-developed, relatively large frontal plate of the ventral jaw should be regarded as a feature common to all representatives of ectocochlian cephalopods evolved from early Palaeozoic stock. Distinct features seen in the jaw apparatus of Upper Permian endocochlians include the pronounced beak form of both jaws and the presence of oblong wings on the ventral mandible.
Cephalopod jaws have been recovered from the Etalian (Middle Triassic = Anisian-Ladinian) of New Zealand. The jaws are found as isolated elements in the Tilson Siltstone near Kaka Point, southeast Otago. The structures are interpreted as jaws of ceratitid and phylloceratid ammonoids. Most of the jaws are small, < 10 mm in length, but two specimens are much larger: c. 35 mm in length. The lower jaws conform to the published descriptions of anaptychus type jaws. Each jaw is convex on the ventral side and terminates in a projected apex. The surface is covered with regularly spaced ridges that parallel the posterior margin. The inner lamella is preserved near the anterior margin and in areas where the outer lamella has eroded away. The upper jaws are rarer, with their inner lamella ending in a bilobate posterior margin. The lower jaws are similar to those of Paleozoic ammonoids and contrast with those of the Ancyloceratina and most of the Ammonitina, which are characterised by a midline flange with a central groove and a pair of calcareous plates (aptychi), and the Lytoceratina, which bear calcareous deposits at the apex.
Lehmann, U. & Kulicki, C. 1990 10 15: Double function of aptychi (Ammonoidea) as jaw elements and opercula. Lethaia, Vol. 23, pp. 325–331. Oslo. ISSN 0024–1164.Aptychi are calcitic coverings on the outer surface of organic ammonite lower jaws. They are similar in shape to that of the corresponding ammonite apertures. This observation and additional features of many aptychi are in harmony with their former interpretation as protective opercula. We suggest that they served as opercula in addition to functioning as jaws. The primary function of the lower jaws was thus secondarily extended to that of protective shields when they acquired their calcitic covering, while as lower jaws their importance dwindled to that of a more passive abutment. Phylogenetically, this seems to have started slowly in some anaptychi and became obvious with the first aptychi. ▭Ammonites, aptychus, operculum, jaw apparatus, evolution, function.
Conspicuous calcareous coverings are present in the anterior region of 17 fossil jaws from late Cretaceous rocks of Hokkaido (Japan) and Sakhalin (U.S.S.R.). The jaws were preserved in calcareous nodules either in situ in body chambers of ammonites or in close association with identifiable ammonite conch remains. From the morphologic similarity between in situ and isolated jaws, they may be attributed to Tetragonites glabrus, Gaudryceras tenuiliratum, G. denseplicatum, G. sp., and Neophylloceras subramosum. The jaw apparatus of these species is composed of two three-dimensional black walls of carbonate apatite, which might be a diagenetic replacement of chitinous material. The calcareous coverings in both upper and lower jaws closely resemble those of upper (rhyncholite) and lower (conchorhynch) jaws of modern Nautilus as well as rhyncholite and conchorhynch fossils in their gross morphology, microstructure, and chemical composition. Calcified remains of cephalopod jaws known as rhyncholites and conchorhynchs have been reported from late Paleozoic to Recent. The present discovery of ammonoid rhyncholites and conchorhynchs suggests that at least some previously known late Paleozoic and Mesozoic counterparts belong to the Ammonoidea. The essential similarity of jaw elements of some Late Cretaceous ammonites and modern Nautilus gives reliable information on the feeding habits of the former. The sharp and thick ammonoid rhyncholites and conchorhynchs may have had a special function for cutting up food, similar to those of Nautilus.
The different forms of the aptychi (opercula, homologous with lower jaws) of the Ammonoidea are used for the first time in a phylogenetic analysis of part of the classic Ammonoidea phylogeny. The results indicate that the aptychi-possessing ammonoids form a monophylum for which we propose the informal name Aptychophora nov. Among the Jurassic ammonoids, it is possible to recognize several monophyletic groups. In part, our results support existing superfamilies (e.g. Hildocerataceae, Haplocerataceae) by new synapomorphies. However, the Perisphinctaceae can now be much more clearly differentiated than in the previously established phylogenetic tree. The Upper Cretaceous ammonoid superfamilies cannot be derived from the Haplocerataceae, but are descendants of a ‘primitive’ perisphinctacean possessing a praestriaptychus. Nor can they be derived from the ‘higher’ perisphinctaceans (family Perisphinctidae) because that clade is characterized by granulaptychi. The consequence of these results is that the quadrilobate primary suture of the ‘Ancyloceratina’ must have evolved more than once by reduction from an ancestral quinquelobate primary suture. The Ancyloceratidae have praestraptychi or aptychi types which can be derived from praestriaptychi, whereas the Crioceratitinae have longitudinally striated anaptychi.
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