Early Meraspid Research Articles

A revised ontogeny of the early Ordovician trilobite Leptoplastides salteri (Callaway, 1877)

ABSTRACTThe ontogeny of the pelturine olenid trilobite Leptoplastides salteri (Callaway, 1877) from the Shineton Shales, Shropshire, England, was first described in 1925 by Frank Raw. Since that time, scanning electron microscopy and other new technologies have revealed many more details of structure, of early developmental stages in particular, than were available to Raw. Whereas protaspides are not preserved and the state of preservation is less than perfect for the smallest meraspides, we have established that the latter had an array of delicate, long thoracic and pygidial spines, as well as paired procranidial spines, which disappear by meraspid degree 8. Raw's reconstructions of early meraspides, and his measurements of the early stages in development, are here amended in the light of new information. Dorsal spines in the adult are much more highly developed than have been documented in any other olenid. The hypostome is preserved in place in several specimens. Initially conterminant (attached to the doublure), it becomes natant (free) in late meraspid to early holaspid stages of development, with its anterior contour fitting exactly to that of the glabella. The ecology of the widespread Leptoplastides is best known from very extensive sections in South America, which provide a useful basis for comparison. It was well adapted to a range of environments, both oxygenated and dysoxic, and is usually the dominant taxon in the biofacies in which it is found.

Early post-embryonic development inEllipsostrenua(Trilobita, Cambrian, Sweden) and the developmental patterns in Ellipsocephaloidea

AbstractThis study documents the early post-embryonic developmental stages (protaspides and early meraspides) of the Cambrian trilobiteEllipsostrenua granulosa(Ahlberg, 1984) from the Gärdsjön Formation of Jämtland, Sweden. The early protaspid stage is characterized by a circular outline of the exoskeleton, two pairs of fixigenal spines, a short preglabellar field, a genal swelling, and prominent bacullae. The late protaspid stage differs only in having the trunk portion discernible. Early meraspid cranidia are sub-rectangular with prominent palpebral lobes, a wide anterior margin, a proportionally long anterior branch of the facial suture, and intergenal spines. Meraspid pygidia tentatively assigned to this species possess comparatively long macrospines. Small hypostomes associated withE.granulosabear at least four pairs of marginal spines. A comparison of the early developmental stages ofE.granulosawith some other species of Ellipsocephalidae and with species of the closely related Estaingiidae reveals several similarities. The conservative morphology of the early protaspid stage with only two pairs of fixigenal spines, the timing of the development of the trunk portion, and the presence of genal swellings and prominent bacullae could be phylogenetically informative. The range of size variation of the early protaspid stages in two families may be related either to taxonomical differences between Ellipsocephalidae and Estaingiidae, or to environmental differences in various paleogeographic settings.

Morphological assessment of the Cambrian trilobites Oryctocephalus indicus (Reed 1910) from China and Oryctocephalus ‘reticulatus’ (Lermontova 1940) from Siberia

Oryctocephalus indicus is a widespread trilobite species described from the lower–middle Cambrian (provisional Cambrian Stage 5) of south China, North Korea, India, USA and possibly North Greenland. Principal component analysis (PCA) and thin-plate splines (TPSs) based on a pooled sample of 359 specimens from four sections in the Guizhou Province, south China, demonstrated that the shape of this species is very constant, and only a small difference is detected in specimens from deeper part of the basin. Most of the variation is taphonomically controlled, and only the specimens from Sanwan Section show a modest natural difference due to a slightly different depositional environment. A comparison between the Chinese specimens and Oryctocephalus ‘reticulatus’ from the Molodo Section, Siberia, has been carried out. PCA and TPS show that O. ‘reticulatus occupies the same morphospace of O. indicus. However, the canonical variates analysis and the analysis of similarities detect small differences between the Siberian and Chinese populations, indicating a minor geographical variation caused by different environmental settings. The ontogenic variation is also described from early meraspids to holaspids. The most substantial changes take place during the first period of the early meraspid development, in which the glabella changes from a bell-like shape to a cylindrical shape. The ocular ridge changes from poorly defined in early meraspid to well developed in late merapids. The results indicate that O. ‘reticulatus’ is a junior synonym of O. indicus, suggesting that the base O. indicus of Siberia can be correlated with the O. indicus Zone of south China.

The ontogeny of Ellipsocephalus (Trilobita) and systematic position of Ellipsocephalidae

Laibl, L., Fatka, O., Budil, P., Ahlberg, P., Szabad, M., Vokáč, V. & Kozák, V., 24.3.2015. The ontogeny of Ellipsocephalus (Trilobita) and systematic position of Ellipsocephalidae. Alcheringa 39, 477–487. ISSN 0311-5518.Well-preserved early holaspid stages of the Cambrian Series 3 trilobites Ellipsocephalus hoffi (Schlotheim, 1823) and Ellipsocephalus polytomus Linnarsson, 1877 have been discovered in the Příbram-Jince Basin (Czech Republic) and Jämtland (Sweden), respectively. Both species show remarkable morphological changes during late ontogeny. The earliest holaspides share long genal spines, and long macrospines on the second thoracic segment. Whereas macrospines disappear abruptly in later stages, genal spines are progressively shortened. Consequently, the ontogeny of trilobites of Ellipsocephalidae is revised. The morphology of early meraspid cranidia and ontogenetic patterns in the disappearance of macrospines suggest that this family is closely related to members of Redlichiida rather than Ptychopariida.Lukáš Laibl [lukaslaibl@gmail.com] and Oldřich Fatka [fatka@natur.cuni.cz], Charles University, Institute of Geology and Palaeontology, Albertov 6, 128 43, Prague 2, Czech Republic; Petr Budil [petr.budil@geology.cz], Czech Geological Survey, Klárov 3, Prague 1, 118 21, Czech Republic; Per Ahlberg [per.ahlberg@geol.lu.se], Department of Geology, Lund University, Sölvegatan 12, SE-223 62 Lund, Sweden; Michal Szabad [geosz.pb@seznam.cz], Obránců míru 75, 261 02 Příbram VII, Czech Republic; Václav Vokáč [lichas@seznam.cz], Ke Kukačce 21, 312 00 Pilsen, Czech Republic; Vladislav Kozák [vlada.kozak@tiscali.cz], K Moravině 11/1689, 190 00 Prague 9, Czech Republic.

Ontogeny of the redlichiid trilobiteEoredlichia intermediatafrom the Chengjiang Lagerstätte, lower Cambrian, southwest China

A detailed investigation of the morphology and ontogeny of the redlichioid trilobite Eoredlichia intermediata (Bulletin of the Geological Society of China, 3–4, 1940, 333) from the lower Cambrian Yu'anshan Member of the Heilinpu Formation, in Kunming, Yunnan Province, southwest China, is presented. The new material comprises a relatively complete ontogenetic series ranging from the early meraspid to the holaspid period, which reveals more details on morphological variation such as the appearance of bacculae in some holaspid specimens, contraction and disappearance of fixigenal spines, and macropleural spines of the first and second thoracic segments, which are all documented for the first time and can also be used as developmental markers defining ontogenetic phases. Two distinct morphotypes, possibly an expression of intraspecific variation or sexual dimorphism, are distinguished by the morphology of pleural spines of the second thoracic segment in meraspid degree 14 and holaspides. The trunk segmentation schedule of E. intermediata is also discussed and conforms to the protarthrous developmental mode. The distinction of the thoracic region into two portions can be observed during late meraspid and early holaspid periods, which might be considered as a reference for a better understanding on the relationship of tagmosis and growth segmentation among the Cambrian redlichiid trilobites.

Morphology and ontogeny of the eodiscoid trilobite Sinodiscus changyangensis from the lower Cambrian of South China

Abstract: A large number of complete specimens together with numerous disarticulated sclerites of the eodiscinid trilobite Sinodiscus changyangensis Zhang inZhou et al., 1977 have been collected from the lower Cambrian Shuijingtuo Formation in Changyang, Hubei Province, South China. An ontogenetic series is established based on the immature and mature exoskeletons including the previously unknown protaspides and meraspides, in particular. No further substages can be differentiated in the protaspid specimens herein. Changes that took place during the meraspid period include the addition of postcephalic segments and prominent pygidial larval notches in early meraspid development which became progressively less distinct and disappeared in degree 2. Two holaspid stages are recognized based on the addition of a new pygidial segment, indicating that the start of the holaspid phase preceded the onset of the epimorphic phase and accordingly, its developmental mode is attributed to the protarthrous pattern. The trunk segmentation schedule of S. changyangensis is discussed, which is similar to other primitive eodiscoid trilobites, that is, as the boundary between the thorax and pygidium migrated posteriorly, there is no change in the number of the trunk segments. The processes of liberation of the thoracic segment and segment insertion into the pygidium are separated from one another, and the two different mechanisms, somitogenesis and tagmosis, progress independently during the ontogenetic development of the postcephalic region of these primitive eodiscinids.

Ontogeny of the Upper Cambrian (Furongian) Olenid trilobite Protopeltura aciculate (Angelin, 1854) from Skåne and Västergötland, Sweden

Abstract: The ontogeny of the trilobite Protopeltura aciculata (Angelin, 1854) is described on the basis of material from the upper Cambrian (Furongian) of Andrarum (Skåne) and Hjelmsäter (Västergötland), Sweden. P. aciculata is present in the Parabolina brevispina and Parabolina spinulosa zones. Protopeltura aciculata is represented by all stages of growth, from early protaspides to holaspides, although most of the specimens are disarticulated and precise degrees are unknown. The cranidia have therefore been allocated to five morphological groups. Cuticular sculpture of the cranidia changes throughout ontogeny. Large tubercles are present in earlier stages, disappear gradually in middle meraspid stages and are replaced with a very faint granulation. The transitory pygidium, relatively large and shield‐shaped with upwardly and backwardly directed marginal spines in early meraspides, later becomes very small, triangular‐shaped and lacking spines as a late meraspid and holaspid. The development of hypostomes and librigenae is also described. Protopeltura aciculata shows major intraspecific variations throughout development, especially regarding the pygidium where variation is much less constrained than in many other olenids. This high developmental plasticity may be a survival strategy for a trilobite living in a stressed environment. Protopeltura inhabited a dysoxic environment, possibly unusually prone to localised spreading of anoxic or toxic water. Some morphs may have been less vulnerable than others to such stresses, surviving by chance and thus enabling the species to continue.

THE LOWER CAMBRIAN EODISCOID TRILOBITECALODISCUS LOBATUSFROM SWEDEN: MORPHOLOGY, ONTOGENY AND DISTRIBUTION

Abstract: Several thousand disarticulated remains together with a few complete enrolled specimens of the lower Cambrian eodiscoid trilobiteCalodiscus lobatus(Hall, 1847) have been collected at two outcrop areas in Sweden. The material reveals new details of morphology and morphogenesis during ontogenetic development. Size‐frequency analyses show that the material from the Fånån rivulet in Jämtland, central Sweden, represents a natural population dominated by juveniles, whereas the material from Gislövshammar in Scania, southern Sweden, has been sorted during postmortem transport. Three stages of protaspid development can be traced and defined as well as all subsequent ontogenetic stages for the cephalon, hypostome and pygidium. The early meraspid pygidium has a pronounced larval notch, which persists, though becoming progressively less distinct in later meraspides. The number of axial rings in the transitory pygidium increases throughout meraspid development until a third and final thoracic segment is liberated. During ontogeny the articulating half‐rings are strongly developed, and both meraspides and holaspides were capable of full sphaeroidal enrollment and outstretched postures. The hypostome undergoes some dramatic modifications; in M0 the anterior margin is axe‐shaped, by M1 the area of attachment greatly decreases and the hypostome becomes more elongated and pear‐shaped, before attaining its adult form, which has an overall resemblance to that of polymerid trilobites. During ontogeny, the hypostome changes from a conterminant attachment to a natant condition, thereby mirroring hypostomal evolution within trilobites generally. The morphology, ontogeny, enrollment, hypostomal development and the presence of calcified protaspides suggest polymerid rather than agnostoid affinities of the eodiscoids.

Taphonomy and palaeoecology of the emuellid trilobite Balcoracania dailyi (early Cambrian, South Australia)

Monospecific assemblages of the trilobite Balcoracania dailyi occur in lower Cambrian strata within the Adelaide Geosyncline in South Australia. Biostratinomic data from single bedding plane assemblages within the Warragee and Coads Hill Members of the Billy Creek Formation and White Point Conglomerate reveal a range of taphonomic signatures from census to within-habitat, time-averaged assemblages. These assemblages are interpreted as having inhabited protected, shallow, marginal marine environments. Size–frequency distributions, coupled with taphonomic data, show that the Warragee Member census assemblage represents a living population in a physically stressful environment within a tidally-influenced lagoon, while the original population structure of the Coads Hill Member and White Point Conglomerate assemblages has been lost due to varying degrees of taphonomic overprinting. Integration of taphonomic, stratigraphic and sedimentological data supports the interpretation of B. dailyi as representing an opportunistic species. A preserved body cluster from the Warragee Member assemblage is considered to characterise a congregation formed for the purpose of synchronous reproduction and ecdysis, representing one of the oldest examples of gregarious behaviour in the arthropod fossil record. Furthermore, by analogy with modern horseshoe crabs, the high number of juveniles (i.e., protaspides and early meraspides) within the same assemblage are believed to be constituents of a nursery within the intertidal zone, with adults migrating into the shallows to copulate and spawn. Preserved moult ensembles from the Coads Hill Member and White Point Conglomerate have enabled the description of exuviation techniques for B. dailyi.

Structure, ontogeny, and moulting of the olenid trilobite Ctenopyge (Eoctenopyge) angusta Westergård, 1922 from the upper Cambrian of Västergötland, Sweden

The genus Ctenopyge is known mainly from disarticulated sclerites and from rare complete specimens flattened in shales. Hitherto, very few specimens have been found preserved intact and in three dimensions. In a recently discovered fauna, however, in the Peltura minor Subzone in Västergötland, central Sweden, there occur several species of Ctenopyge, of which many are complete and superbly preserved; moreover they occur at all stages of growth. Of these the abundant Ctenopyge (Eoctenopyge) angusta Westergård, 1922 is described and reconstructed here as an adult, and the entire ontogeny is documented for all post–protaspid growth stages. Many characters typical of the adult, such as the long genal spines and the caudal spine, develop very early in ontogeny, and the relative dimensions of the cranidium do not greatly change during growth. Macropleural spines, however, develop later. The transitory pygidium, relatively large and shield–shaped in the early meraspid, later becomes very small as the ten thoracic segments are liberated; a median spine develops on the last thoracic segment only at the holaspid stage. Instar groupings can be clearly distinguished for the early stages. Recurrent associations of sclerites are interpreted as moulting configurations. As reconstructed, the genal spines are horizontal and parallel with the extended thorax; an adaptation which presumably allowed the trilobite to rest on the sea floor.

Ontogeny of the Late Cambrian trilobiteOlenus asiaticus Kobayashi, 1944 from the Machari Formation of Korea

Ontogeny of the Late Cambrian trilobiteOlenus asiaticus Kobayashi, 1944 was examined based on the material from theGlyptagnostus reticulatus Zone of the Machari Formation in Yongwol area, Korea. Protaspides are differentiated into anaprotaspid and metaprotaspid stages. Anaprotaspides are represented by circular dorsal shields with faintly segmented axis, while meta-protaspides have five axial rings, eye ridges, and a differentiated protopygidium. Most of meraspides, represented by disarticulated cranidia, are further divided into six morphological groups. The Group 1 is assumed to represent the meraspid degree 0, whereas the remaining groups are subdivided in convenience to describe the morphological development of cranidia. Morphological changes within the meraspid stages are gradual in general. The glabella is parallel-sided or tapers rearwards in the early meraspides, whereas it tapers forwards in the later forms. The preglabellar field appears in the Group 3 and becomes progressively longer in the later meraspid stages. The holaspid cranidia are distinct in having a subquadrate glabella with three pairs of lateral glabellar furrows.

The ontogeny ofTaihungshania miqueli(Bergeron, 1893) from the Arenig of the Montagne Noire, southern France

AbstractThe very large trilobiteTaihungshania miquelioccurs abundantly in siliceous nodules in the Ordovician of the Montagne Noire, southern France, but in these, larval individuals are not preserved. At a new locality at Peret, near Cabrières, protaspid and early meraspid growth stages occur in great abundance, together with a few complete specimens belonging to meraspid degrees 1, 2, 3, 5 and 7, and a single young holaspis. Although this material is largely flattened, and the originally globular protaspides crushed, it is still possible to establish the development of several axial rings before the transitory pygidium becomes liberated. In the degree 0 meraspis, the cephalon and transitory pygidium are about the same size, and the presence of a partially enrolled degree 3 meraspis indicates that protective coiling was possible by this early stage. Palpebral lobes are incipient in degree 2 meraspides, and fully formed by degree 7, otherwise the morphology of the cephalon becomes quite adult-like by degree 4. The pygidial spines begin to appear in degree 5, at which stage there are about 10 axial rings; there are about 13 in a degree 7 meraspis, and in the adult, where the posterior contour is semi-elliptical, there are some 22. The smallest hypostomes present belong to a degree 6 meraspis, and these are morphologically similar to those of adults. Observations on the later growth stages were made on material from another locality (Caramaou), as well as that from Peret. In the eye the upper lenses are large and slightly separated, but those towards the base are much diminished in size; this is a function of an unusual growth geometry.At Peret, all stages of development, at least as far as young adults, are represented, albeit often in a fragmentary state. As with other asaphines, the protaspides are assumed to be planktic, andT. miquelipresumably left the plankton and became benthic between the protaspid and meraspid periods.

Ontogeny of the trilobiteOlenus wahlenbergiWestergård, 1922 from the upper Cambrian Alum Shales of Andrarum, Skåne, Sweden

AbstractThe upper Cambrian trilobiteOlenus wahlenbergiWestergård, 1922 occurs abun- dantly in stinkstone concretions in the Alum Shales at Andrarum, in Skåne, southern Sweden (Olenus/Homagnostus obesusZone). All growth stages from anaprotaspis onwards are represented, though the early stages are comparatively uncommon and complete specimens are rare. Fine details of structure are preserved, suitable for scanning electron microscopic study.The protaspis has five axial rings, which in the adult become divided transversely and reduced to three, and the preglabellar field expands markedly in the holaspis. The librigena broadens during development and the eye, with its widely separated lenses is retained on the librigena throughout meraspid development. The visual surface dehisces during ecdysis from the early holaspid onwards, due to emplacement of the ocular suture. The hypostome apparently changes from a conterminant to a natant condition in the early holaspis, which is consistent with the growth of the preglabellar field at this stage. The transitory pygidium has a slightly serrated margin throughout development, but becomes entire when all thoracic segments have been liberated.Cuticular sculpture changes dramatically throughout ontogeny. Large (Type A) tubercles appear on the fixigena in early meraspides; these become prominent and coalesce by the end of meraspid development. They are abruptly replaced by smaller (Type B) tubercles in the early holaspid, which link to form a rough network in mature specimens. Comparable Type A tubercles in early meraspid librigenae give rise to a strong polygonal caecal sculpture in holaspids, while a radial sculpture on the broadening anterior border develops independently. The significance of these cuticular changes remains obscure. A median occipital organ is described for the first time in the Olenidae.

Protaspid and early meraspid growth stages of the eodiscoid trilobitePagetia ocellataJell, and their implications for classification

During recent investigations of the Middle Cambrian phosphate deposits south of Duchess in the Burke River Structural Belt, Georgina Basin, western Queensland, large numbers of the early growth stages of trilobites have been recovered by acid etching of samples from the Monastery Creek Phosphorite Member of the Beetle Creek Formation. Among these a late protaspid growth stage is recognised as belonging to Pagetia ocellata Jell 1970, described earlier from the same formation. The morphogenesis of this and the earliest meraspid growth stage are described, and their development compared to that of an associated agnostoid referred to Peronopsis. The differences between eodiscoid and agnostoid trilobites are reviewed in the light of much recently published information. A taxonomic separation of at least ordinal magnitude is advocated. If miomeran arthropods are related to polymeroid trilobites, then the eodiscoids are the closer of the two groups.