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The ancestory of the Cephalopoda. From Helcionella to Plectronoceras
... Many helcionelloids have septa in the apical region (Rasetti 1957, Kobayashi 1958, Yochelson et al. 1973, Brock & Paterson 2004, Parkhaev 2006. The ontogenetic and evolutionary implications of these structures are unresolved (e.g., Jacquet & Brock 2016), but are significant because of their possible homology with the septa of cephalopod shells (e.g., Kobayashi 1958, 1987, Yochelson et al. 1973, Runnegar & Pojeta 1974, Peel 1991a, 1991b. ...
... In summary, therefore, we suggest that Hampilina and Coreospira could be distinguishable by the presence of complex curviplanar versus simple convex septa, respectively (Fig. 7J), with Coreospira additionally manifesting a tubular 'siphuncle-like' structure. A possible ancestral relationship between helcionelloids and cephalopods could thus be supported by: (1) the presence of multiple septa (Kobayashi 1958, 1987, Yochelson et al. 1973) as in Dorispira pacifica (Fig. 7K, L); (2) a 'snorkel' in some helcionelloids which may equate into a 'siphuncle' (Jell 1978, Pojeta 1980, 1987; and (3) endogastric coiling (Peel 1991a(Peel , 1991b, which is identical to ammonites and nautiloids (Monks & Palmer 2002). ...
... In summary, therefore, we suggest that Hampilina and Coreospira could be distinguishable by the presence of complex curviplanar versus simple convex septa, respectively (Fig. 7J), with Coreospira additionally manifesting a tubular 'siphuncle-like' structure. A possible ancestral relationship between helcionelloids and cephalopods could thus be supported by: (1) the presence of multiple septa (Kobayashi 1958, 1987, Yochelson et al. 1973) as in Dorispira pacifica (Fig. 7K, L); (2) a 'snorkel' in some helcionelloids which may equate into a 'siphuncle' (Jell 1978, Pojeta 1980, 1987; and (3) endogastric coiling (Peel 1991a(Peel , 1991b, which is identical to ammonites and nautiloids (Monks & Palmer 2002). ...
Helcionelloids from the Korean Peninsula are revised based on a re-examination of type specimens and new material collected from the Cambrian Mungyeong Group of South Korea. The fauna comprises Coreospira rugosa, Hampilina goniospira, Dorispira pacifica, cf. Igorella coreanica, and Helcionelloid indet. Coreospira and Hampilina are distinguished from other helcionelloids by their angular junction between dorsal and lateral surfaces, and from each other by the presence or absence of a rounded ridge along the junction, respectively. The Korean helcionelloids range stratigraphically from the base of Maochuangian to the lower Hsuchuangian using the chronostratigraphical scheme from North China; this correlates with upper Stage 4 to the lower Wuliuan Stage. Unusual septal features, such as complex suture lines in Hampilina and a central circular structure in the simple convex septa of Coreospira, occur in the apical region of the Korean helcionelloids, and could have implications for univalved molluscan evolution.
Yeongju Oh [yjoh@kopri.re.kr], Department of Earth and Environmental Sciences, Chungbuk National University, Cheongju, Chungbuk 28644, Republic of Korea; Dong-Chan Lee [dclee@chungbuk.ac.kr], Department of Earth Science Education, Chungbuk National University, Cheongju, Chungbuk 28644, Republic of Korea; Dong-Jin Lee [lichenaria@daum.net], College of Earth Sciences, Jilin University, Changchun 130061, China; Jeong-Gu Lee [leejg0310@korea.kr] Gwacheon National Science Museum, Gwacheon 13817, Republic of Korea
... It is currently widely accepted that cephalopods evolved from monoplacophorans with a relatively high-coned shell. The origin of cephalopods was discussed in most detail by Kobayashi (1987) and Dzik (1981). The origin of the cephalopodan archetype began with the appearance of the septa and siphuncle in the apical part of the shell, the features that allowed the development of the gaseous-fluid float and colonization of the pelagic zone, then a new adaptive zone, at that time inaccessible for other groups of mollusks. ...
... The origin of the cephalopodan archetype began with the appearance of the septa and siphuncle in the apical part of the shell, the features that allowed the development of the gaseous-fluid float and colonization of the pelagic zone, then a new adaptive zone, at that time inaccessible for other groups of mollusks. Continuous septa are present in the apical parts of the shell of many groups of gastropods, and also in the fossil groups Hyolitha and Tentaculita, which are sometimes placed together in the molluscan class Coniconchia, and in the Cambrian monoplacophorans Helcionella and Knightoconus ) (Yochelson et al., 1973;Kobayashi, 1987). According to Kobayashi (1987), Helcionella , with its taller high-coned shell is a more appropriate candidate for the role of a morphological ancestor of cephalopods than Knightoconus , with its low-coned shell. ...
... Continuous septa are present in the apical parts of the shell of many groups of gastropods, and also in the fossil groups Hyolitha and Tentaculita, which are sometimes placed together in the molluscan class Coniconchia, and in the Cambrian monoplacophorans Helcionella and Knightoconus ) (Yochelson et al., 1973;Kobayashi, 1987). According to Kobayashi (1987), Helcionella , with its taller high-coned shell is a more appropriate candidate for the role of a morphological ancestor of cephalopods than Knightoconus , with its low-coned shell. Thus, the development of septa is not a feature unique to cephalopods, whereas the appearance of the siphuncle is a fundamentally new character, as of a part of the body that remains in the chambers and is capable of controlling the buoyancy of the animal. ...
... Known as charismatic, attractive, colorful and intelligent, cephalopods have existed in the oceans for hundreds of millions of years, thus undergoing impressive evolution and diversification over time approximately 530 million years ago (mya) in the Early Cambrian (Kobayashi, 1987). The evolutionary history of some ancient cephalopods is well documented due to the fact that most forms had a mineralized shell that has been easily preserved in the fossil record. ...
La identificación precisa de los cefalópodos ha sido un desafío histórico debido a la diversidad de especies y las dificultades de clasificación. Uno de los muchos problemas es su morfología variable, ya que presentan una amplia gama de formas, tamaños y colores, lo que dificulta una identificación visual precisa, especialmente en etapas tempranas de desarrollo o cuando las muestras están dañadas. Además, algunas especies tienen biodiversidad críptica: algunas son morfológicamente similares, pero genéticamente diferentes, lo que hace que distinguirlas
usando caracteres morfológicos sea muy difícil o imposible. Por último, pero no menos importante, la convergencia evolutiva entre especies no relacionadas ha conducido a morfologías similares, lo que complica aún más la identificación basada en caracteres morfológicos. Por lo tanto, la aplicación de códigos de barras de ADN ha revolucionado la identificación de cefalópodos al proporcionar una herramienta fiable y efectiva para superar los desafíos asociados con la morfología variable y las similitudes morfológicas entre especies. Esta técnica ha mejorado nuestra comprensión de la biodiversidad de cefalópodos y ha tenido importantes aplicaciones en la investigación y conservación marina de este tipo de moluscos. El objetivo de este estudio fue explorar los patrones de biodiversidad de la clase Cephalopoda utilizando secuencias previamente publicadas de la subunidad 1 de la citocromo oxidasa c mitocondrial (comúnmente abreviada como cox1 o COI), como un código de barras para la identificación y diferenciación interespecífica. Con esta información, estudié la diversidad específica de los diez órdenes de cefalópodos y la representación geográfica de los códigos de barras de cefalópodos disponibles en las bases de datos genéticos.
... Mazurek & Zatoń reduce cephalopod origins to a 'known and logical sequence of events', but the reality is somewhat more complicated. There are at least four possible ancestries for Plectronoceras, the earliest siphunculate cephalopod (Yochelson et al. 1973;Dzik 1981Dzik , 2010Kobayashi 1987;Peel 1991), notwithstanding disputed alternatives (Jell 1976;Teichert 1988). The characters that tie miscellaneous Cambrian shelly taxa to the cephalopod lineage are few in number, and are prone to both convergence and controversy; their interpretations should be regarded with suspicion. ...
Book Description
Ammonites are an extinct and charismatic lineage that persisted for over 300 million years. They were used, with other fossils, to corroborate the principle of faunal succession and launch the field of biostratigraphy. Despite intense research, many important questions remain unanswered. Furthermore, outdated hypotheses persist. Many new findings include a better understanding of their appearance in life, their locomotion, and their role in long gone ecosystems. And, of course, there are still controversies; e.g. why did shell complexity increase during evolutionary history. This richly illustrated book describes the full range of ammonoids and their fascinating evolutionary history.
Key Features
Documents the early history of paleontology and the role played by ammonoids
Describes the basic anatomy of a diverse and long persisting lineage
Summarizes the classification and diversity of ammonoids
Lavishly illustrated with beautiful reconstructions
Highlights recent findings and outstanding controversies
Late Cambrian gastropod and monoplacophoran faunas from western Antarctica, eastern and mid-western North America, and northern China, are diverse and provide some insight into palaeogeography and faunal distribution. The oldest of these, a well-preserved trilobite-mollusc fauna from the Ellsworth Mountains, Antarctica is dated as latest Dresbachian (Idamean); the Antarctic fauna is not unlike a slightly younger one (Franconian) from east-central Minnesota, USA. Slightly younger Franconian-age rocks from north China contain the first authentic cephalopods. A Trempealeauan fauna from eastern New York, USA, is closely comparable to another Trempealeauan fauna from north China.
Relatively high taxonomic diversity suggests tropical to sub-tropical marine environments for all these faunas. Plate tectonic position as interpreted from palaeomagnetism supports this interpretation. The occurrence of these molluscs on separate continents, and the presumed widely separated position of these continents in the Late Cambrian, makes it likely that the distribution mechanism for the molluscs was long-lived larval forms.
A key member of the Antarctic faunule is the monoplacophoran Knightoconus which has been considered representative of a group directly ancestral to the oldest cephalopod Plectronoceras . This view is reconsidered in the light of criticisms and alternatives proposed during the last 15 years; these occupy the bulk of the paper. Reaffirmation of evolution from the Antarctic Knightoconus is supported both by refutation of the criticisms and by ontogenetic studies of new topotypical material of the genus.
Twenty-eight species of fifteen genera of Middle Cambrian molluscs are described from tiny phosphatic moulds or silica replicas of the shells. The molluscs were etched from limestones at two sites: one in the earliest Middle Cambrian Coonigan Formation of the Mootwingee area, 130 km northeast of Broken Hill, New South Wales; and another in the middle Middle Cambrian Currant Bush Limestone of the Thorntonia area, 150 km northwest of Mt Isa, Queensland. These unusually diverse collections show that many different kinds of molluscs lived in the tropical Australian seas of the Middle Cambrian and provide new information on the way the molluscan classes Cephalopoda, Gastropoda, Rostro- conchia, and Pelecypoda evolved.In other sections, we discuss the problems of classifying and naming Cambrian molluscs; define a number of terms that can be used to describe shell form (including a new adjective, gyrogastric); reclassify the Class Monoplacophora after incorporating the helcionellacean and bellerophontacean “gastropods”; and outline the early record and history of the Mollusca. New taxa are: the Families Scenellidae (nom. transl. ex Scenellinae Wenz 1938) and Yochelcionellidae; the genera Eotebenna (Yochelcionellidae), Mellopegma (Procarinariidae), and ProtoweneHa (Multifariidae); and the species Helcionella terraustralis, Latouchella accordionata, L. merino, L. penecyrano, Yochelcionella daleki, Y. ostentata, Eotebenna pontifex, E. papilio, Mellopegma georginensis, Stenotheca tepee, S. pojetai, Protowenella flemingi, Pelagiella deltoides, P. corinthiana, and Myonai? queenslandica.
Stasek theorized that the extant mollusks are the progeny of three separate lineages that separated before the phylum was well established. He wrote that no known intermediate forms, fossil or living, bridge the "enormous gaps between any two of the three lineages," and therefore treated each as a separate subphylum. These subphyla are (i) the subphylum Aculifera Hatscheck 1891, containing only the class Aplacophora, derived from the most primitive ancestors of the Mollusca; (ii) the subphylum Placophora von Jhering 1876, containing only the class Polyplacophora, and emphasizing the pseudometamerism of its more advanced premollusk ancestor; and (iii) the subphylum Conchifera Gegenbaur 1878, containing the Monoplacophora and the other classes derived from it.
We point out that the Polyplacophora may be derived from the Monoplacophora instead of a more primitive ancestral stock. We also suggest that the Conchifera can be separated into two major lineages, each worthy of the rank of subphylum. The fossil record indicates that the Monoplacophora gave rise to the Gastropoda, Cephalopoda, Rostroconchia, and possibly Polyplacophora, and that the Pelecypoda and Scaphopoda are derived from the Rostroconchia. These last three classes thus form a lineage that diverged from the Monoplacophora in the Early Cambrian. They emphasized a shell form that in all groups is primitively open at both ends, allowing the gut to remain relatively straight, with an anterior mouth and posterior anus. They became burrowing (infaunal) deposit or filter feeders. We coin the term Diasoma (through-body) for the subphylum containing these three classes (Rostroconchia, Pelecypoda, and Scaphopoda). The remaining three classes (Monoplacophora, Gastropoda, and Cephalopoda) emphasize a conical univalved shell, usually twisted into a spiral. The relatively small single aperture forces the anus to lie close to the mouth, and the gut is bent into a "U." Most are surface-dwelling (epifaunal) grazers or carnivores. We coin the name Cyrtosoma (hunchback-body) for the subphylum containing these three classes. Strictly speaking, the cyrtosomes are the ancestors of the diasomes but, in fact, both subphyla appeared and began to diversify within a few million years in the Early Cambrian.
Note added in proof : After proofs were corrected we were informed that the new genus Opikella is preoccupied by (pikella = Oepikella) Thorslund 1940, an Ordovican ostracod. We rename the mollusk genus Oepikila.