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1

New location of the well-known Ordovician trilobite Asaphus expansus (Wahlenberg, 1821) from north-western Poland

100%

Borowski T. , Daniszewski P.

World News of Natural Sciences

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2021

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tom 34

82-87

EN

This report documents the new location of the representative Ordovician trilobite Asaphus expansus. This well-known trilobite was discovered in the “Storkowo” Mining Plant in the central part of the West Pomeranian Province in Poland.

2

Trilobite faunal dynamics on the Devonian continental shelves of the Ardenne Massif and Boulonnais (France, Belgium)

84%

Bignon A. , Cronier C.

Acta Palaeontologica Polonica

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2015

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tom 60

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nr 4

EN

During the Devonian the sedimentation on the continental shelves of Ardenne Massif and Boulonnais has changed from a mixed siliciclastic-carbonate ramp (Eifelian), through a carbonate barrier reef (Givetian) and then to a detritic influx with local mud-mounds (Frasnian). Here we analysed the faunistic dynamics of the trilobite associations through the changing environment. We used multivariate analyses (clustering and ordering) to discriminate the trilobite associations within 67 different samples. Three previously known communities and one new were recognised: the Eifelian Mixed association, the Givetian Dechenella association and the two Frasnian Bradocryphaeus and Scutellum-Goldius associations. These trilobite faunas present a progressive ecological specialisation. The Mixed association occurs both in the ramp or carbonated (local reef developed on the ramp) facies without any significant difference in its composition. The Dechenella fauna occurs preferentially close to barrier reefs, but can also survive during short periods of detrital input. The two Frasnian communities show a strong relationship with their environment. The Scutellum-Goldius association is only found in reef systems, whereas the Bradocryphaeus flourishes exclusively in lateral facies.

3

Upper Cambrian trilobite ichnocoenosis from Wielka Wisniowka (Holy Cross Mountains, Poland)

84%

Radwanski A. , Roniewicz P.

Acta Palaeontologica Polonica

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1963

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tom 08

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nr 2

EN

Description is given of the Upper Cambrian trilobite ichnocoenosls, i.e. a trace assemblage of the various life activities of trilobites, from the shallow-water marine deposits at Wielka Wiśniówka in the Holy Cross Mountains (Góry Świętokrzyskie). These traces occur either on the upper sides of layers (true traces) or on the lower sides of layers covering grooves made by trilobites on the sea bottom (sole markings = hieroglyphs). Hieroglyphs are the more common forms. Out of them, Rusophycus sp., Cruziana sp., Diplichnites sp. and Dimorphichnus sp. have been described in greater detail. Bergaueria perata Prantl and Diplocraterion sp. hieroglyphs are also encountered in the trilobite ichnocoenosis here reported.

PL

Osady górnego kambru Wielkiej Wiśniówki w Górach Świętokrzyskich, które były przedmiotem opracowań sedymentologicznych Dżułyńskiego i Żaka (1960) oraz autorów (Radwański & Roniewicz, 1960), zawierają charakterystyczny zespół bardzo różnorodnych śladów związanych z działalnością trylobitów i innych zwierząt. Niektóre z tych śladów zostały już pokrótce opisane przez wymienionych autorów. Niniejsza praca jest próbą szczegółowego rozpatrzenia zagadnień związanych z licznym występowaniem całego zespołu śladów ogranicznych, czyli ichnocenozy (Dawitaszwili, 1945). Rozpatrzono również zagadnienia dotyczące trybu życia trylobitów, których ślady są najbardziej charakterystycznym składnikiem tej ichnocenozy, jak również warunki umożliwiające zachowanie się wszystkich śladów zwierzęcych w osadzie. Najczęstszymi śladami związanymi z działalnością trylobitów są hieroglify (terminologia poszczególnych śladów, w zależności od ich położenia na dolnych lub górnych powierzchniach ławic, została podana na tabeli, s. 264), wśród których wyróżniono: hieroglify śladów spoczynku - Rusophycus sp. (pl II), śladów pełzania po dnie połączonego z jego rozgrzebywaniem - Cruziana sp. (pl. IV-VII), śladów stąpania po dnie - Diplichnites sp., śladów kroczenia lub pływania bokiem tuż ponad dnem, w czasie którego trylobit dotykał dna - Dimorphichnus sp. (pl. VIII), oraz niewyraźnych śladów grzebania. Wymienione ślady, jak widać z ilustracji, miały bardzo zmienne kształty, co - pominąwszy późniejsze deformacje, głównie pogrzęzanie - wywołane było różnym zachowaniem się zwierząt w czasie wykonywania poszczególnych czynności. Z tego też względu autorzy stosują nazwy specjalne: Rusophycus sp., Cruziana sp., Diplichnites sp., Dimorphichnus sp. - w dość szerokim zakresie, nie tyle dla czterech rodzajów śladów o ściśle zdefiniowanym kształcie, co dla czterech grup śladów związanych z czterema wyżej wymienionymi czynnościami życiowymi trylobitów, które można obecnie interpretować na podstawie materiału kopalnego. Zebrany materiał autorzy traktują jako jedną całość - czyli ichnocenozę, którą nazywają ichnocenozą trylobitową ze względu na dominujący udział śladów pozostawionych przez trylobity. Obok tych śladów, w obrębie ichnocenozy spotyka się ślady związane prawdopodobnie z działalnością ukwiałów (hieroglify Bergaueria perata Prantl; pl. IX, fig. 1, 2) oraz zwierząt mułożernych, być może pierścienic (hieroglify Diplocraterion sp., pl. X, fig 1). Istnieją także drobne hieroglify zagadkowego pochodzenia (pl. X, fig. 2). Na podstawie ichnocenozy trylobitowej z Wielkiej Wiśniówki można spróbować wyciągnąć pewne wnioski co do trybu życia trylobitów w morzu górno-kambryjskim Gór Świętokrzyskich. Fakt występowania dużej ilości śladów spoczynku, a stosunkowo mniejszej śladów pełzania, oraz obecność śladów pozostawionych przez trylobity pływające tuż ponad dnem i chwilami zawadzające o nie, z drugiej zaś strony brak wyraźnych śladów grzebania w osadzie, - zdają się wskazywać, że trylobity tutaj żyjące należały raczej do form pływających, a przebywających na dnie przede wszystkim w celu spoczynku. Można również zauważyć, że jako miejsce spoczynku trylobity wybierały dno nie zanieczyszczone gnającymi substancjami organicznymi, gdyż wyraźnie unikały ciemnych osadów, w których tak charakterystyczne są ślady żerowania zwierząt mułożernych (hieroglify Diplocraterion sp.). Aczkolwiek nie można rozstrzygnąć, czy były to trylobity należące do różnych gatunków, rodzajów i rodzin, można z dużym prawdopodobieństwem przypuścić, że były to formy o podobnym trybie życia i podobnych wymaganiach życiowych, co oczywiście w znacznej mierze wywołane było przystosowaniem do panujących warunków środowiskowych. Być może, że przyszłe badania w Wielkiej Wiśniówce pozwolą dokładniej ustalić warunki występowania ichnocenozy trylobitowej, jej skład, zmienność i zależność od warunków facjalnych, co z kolei może rzucić większe światło na interesujące problemy dotyczące samych trylobitów.

RU

Отложения верхнего кембрия Велькой Висьнювки в Свентокржиских Горах, которые были предметом седиментологических исследований Джулыньского и Жака (1960), а также авторов настоящей статьи (Радваньски и Роневич, 1960), содержат характерный комплекс весьма разнообразных следов связанных с деятельностью трилобитов и других животных. Некоторые из них уже вкратце описаны упомянутыми авторами. Настоящая работа является попыткой подробного рассмотрения вопросов связанных с многочисленным выступанием целого комплекса органических следов или ихноценоза (Давиташвили, 1945). Рассмотрены также вопросы касающиеся образа жизни трилобитов, которых следы яв ляются наиболее характерной частью этого ихноценоза, равным образом как и условия позволяющие на сохранение следов животных в отложениях. Наиболее часто встречаемыми следами связанными с жизнедеятельностью трилобитов являются иероглифы (терминология отдельных следов в зависимости от их расположения на нижних или верхних поверхностях пластов показана на таблице, стр. 264), среди которых выделено: иероглифы следов покоя - Rusophycus sp. (пл. II), следов ползания по дну с его разгребанием - Cruziana sp., (пл. IV-VII), следов ступания по дну - Diplichnites sp., следов шагания или плавания боком непосредственно над дном, во время которого трилобит касался дна - Dimorphichnus sp. (пл. VIII), и неотчетливых следов рытья. Перечисленные следы, как видно на иллюстрации, имели очень изменчивую форму, что кроме позднейших деформации, главным образом связанных с увязанием, было вызвано разным поведением животных при выполнении разных действий. Потому авторы применяют особые названия; Rusophycus sp., Cruziana sp., Diplichnites sp., Dimorphichnus sp. в довольно широких границах, не для четырех видов следов точно определенной формы, но для четырех групп следов связанных с четырьмя выше перечисленными проявлениями жизнедеятельности трилобитов, которые можно теперь интерпретировать на ископаемом материале. Собранный материал рассматривается авторами как целое или ихноценоз, который называют трилобитовым в виду преобладания следов оставленных трилобитами. Рядом с этими следами, в пределах ихноценоза встречаются следы связанные по всей вероятности с деятельностью актиний (иероглифы Bergaveria perata, Prantl - пл. IX, фиг. 1, 2,) и мулоедов, вероятно аннелид (иероглифы Diplocraterion sp. - пл. X, фиг. 1). Существуют тоже небольшие иероглифы загадочного происхождения (пл. X, фиг. 2). На основании трилобитового ихноценоза из Велькой Висьнювки можно попытаться сделать некоторые выводы относительно образа жизни трилобитов в верхне-кембрийском море Свентокржиских Гор. Наличие большого количества следов покоя, а относительно менее многочисленных следов ползания, далее - присутствие следов оставленных трилобитами плавающими тут же над дном и иногда прикасающимися к нему, а с другой стороны отсутствие отчетливых следов рытья в осадке, указывает повидимому на то, что живущие тут трилобиты были плавающими формами пребывающими на дне прежде всего для отдыха. Можно также заметить, что для отдыха трилобиты выбирали дно незагрязненное гниющим органическим веществом, так как несомненно избегали темных осадков, в которых характерными являются следы просверленные животными поедающими донный осадок (иероглифы Diplocratenon sp.). Хотя невозможно решить, были ли это трилобиты принадлежащие разным видам, родам или семействам, очень правдоподобно предположение, что были это формы со сходным образом жизни и сходными жизненными требованиями, что конечно в большой степени было вызвано приспособлением к господствующим условиям среды. Возможно, что дальнейшие исследования в Велькой Висьнювке позволят установить более подробно условия Еыступания трилобитового ихноценоза, его состав, изменчивость и зависимость от фациальных условий, что в свою очередь может бросить больше света на интересные вопросы касающиеся самих трилобитов.

4

Upper Cambrian trilobite biostratigraphy and taphonomy at Kakeled on Kinnekulle, Vastergotland, Sweden

84%

Terfelt F.

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2003

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tom 48

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nr 3

EN

A section through the Upper Cambrian black shales and limestones at Kakeled on Kinnekulle, Västergötland, Sweden, extends from the lower–middle part of the Agnostus pisiformis Zone into the Peltura scarabaeoides Zone. Fossils are usually preserved only in the stinkstones, but in the A. pisiformis Zone trilobites can be found also in the shales. Lithologically, the stinkstones can be subdivided into primary coquinoid limestone, which include the majority of the fossils, and early diagenetically formed limestone. The orientation of cephala and pygidia of A. pisiformis were measured on four shale surfaces and one stinkstone surface. The majority of the shields were deposited with the convex side up and showed a preferred orientation, suggesting that their positions were affected by currents. Above the A. pisiformis Zone the section comprises the Olenus/Homagnostus obesus Zone (0.30 m), the upper part of the Parabolina spinulosa Zone (0.05 m), the Peltura minor Zone (1.15 m), and the Peltura scarabaeoides Zone (2.50 m). The Leptoplastus and Protopeltura praecursor zones are missing. The Olenus/H. obesus Zone is represented only by the O. gibbosus and O. wahlenbergi subzones, whereas the O. truncatus, O. attenuatus, O. dentatus, and O. scanicus subzones are missing.

5

Phosphatised olenid trilobites and associated fauna from the Upper Cambrian of Vastergotland, Sweden

84%

Ahlberg P. , Szaniawski H. , Clarkson E. N. K. , Bengtson S.

Acta Palaeontologica Polonica

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2005

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tom 50

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nr 3

EN

Secondarily phosphatised olenid trilobites from organic−rich limestones (orsten) in the Furongian (Upper Cambrian) of Västergötland, south−central Sweden, are described and illustrated. All trilobites originate from the Peltura scarabaeoides Zone and were collected on the western slope of Kinnekulle. Only the dorsal exoskeletons have become secondarily phosphatised, and the ventral appendages are not preserved. Yet the material is otherwise remarkably well preserved and reveals the morphology of the olenid trilobites in greater detail than hitherto known. Species belonging to the genera Ctenopyge, Sphaerophthalmus, Parabolina, and Peltura are identified, and several juvenile specimens are present in the material. The material is disarticulated and fragmentary, and it has only been possible to identify a few specimens to species level. In addition to chaetognaths and conodonts, the trilobites are associated with pelmatozoan columnals, a possible camaroid, and fossils of uncertain affinities. These fossils, along with a probable conulariid fragment from the Peltura minor Zone, are also described and discussed. The presence of a benthic fauna of pelmatozoans, and possible conulariids and camaroids, indicates that at least parts of the Peltura zones were deposited during dysoxic rather than anoxic periods. Moreover, the sea floor must have been firm enough to allow colonisation by sessile organisms.

6

Trilobites from the latest Frasnian Kellwasser crisis in North Africa [Mrirt, Central Moroccan Meseta]

84%

Feist R.

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nr 2

EN

Latest Frasnian trilobites are recorded for the first time from North Africa. They occur in oxygenated limestones between the Lower and Upper Kellwasser horizons at Bou Ounabdou near Mrirt, central Moroccan Meseta. The faunas are very close to the contemporaneous associations in European sections both by their taxonomic composition and by patterns of evolutionary behavior towards eye reduction. Two new taxa are described: Gondwanaspis mrirtensis gen. et sp. nov., which is the last known representative of the Odontopleuridae before its extinction at the base of the Upper Kellwasser horizon, and Pteroparia ziegleri maroccanica subsp. nov., a geographical variant of the nominal subspecies from Sessacker in the Rhenish Slate Mountains.

7

Systematics, morphology, and appendages of an Early Ordovician pilekiine trilobite Anacheirurus from Fezouata Shale and the early diversification of Cheiruridae

67%

Perez-Peris F. , Laibl L. , Vidal M.

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tom 66

|

nr 4

8

Ordovician ostracods from East Central Iran

67%

Ghobadi Pour M. , Williams M. , Vannier J. , Meidla T. , Popov L. E.

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2006

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tom 51

|

nr 3

EN

Ordovician ostracods are described for the first time from Iran, enhancing the record of this group from the Lower Palaeozoic of the Middle East. The ostracods occur in the Shirgesht Formation, in the east central part of the country, and comprise Ogmoopsis achaemenid sp. nov., Cerninella aryana sp. nov., Ordovizona amyitisae sp. nov., cf. Aechmina? ventadorni, Vogdesella sp., and podocope taxa tentatively identified as species of Longiscula, Pullvillites, and Rectella. These taxa were hitherto unknown from this region. The ostracod−bearing interval is associated with trilobites (Neseuretinus) and brachiopods (Nicolella) that suggest a late Middle Ordovician age. Although the ostracod fauna is small, it demonstrates biogeographical links at genus−level, and possibly at species−level, with the fauna of the late Middle Ordovician Travesout Formation of western France, which also lay in a peri−Gondwanan palaeogeographical setting. It also suggests the potential use of some ostracods as stratigraphical tools for correlating Ordovician rock successions between Europe and the Middle East.

9

A new Cambrian catillicephalid trilobite from the Shallow Bay Formation of western Newfoundland, Canada

67%

Westrop S. R. , Dengler A. A.

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tom 67

|

nr 1

10

Red Devonian trilobites with green eyes from Morocco and the silicification of the trilobite exoskeleton

67%

Klug C. , Schulz H. , De Baets K.

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nr 1

117-123

EN

Latest Emsian (Early Devonian) sediments at the famous mud−moundand trilobite−locality Hamar Laghdad (Tafilalt, Morocco) yielded some red−coloured remains of phacopid trilobites. Closer examination revealed that the eyes of these phacopids are often greenish in colour. EDX−analyses showed that the lenses retained their original calcitic composition, possibly greenish due to Feand Mn−impurities, while most of the exoskeleton was silicified. The silicified parts contain elevated concentrations of iron which causes the red colour. This phenomenon is explained by the porosity of the exoskeleton in contrast to the homogeneous and massive construction of the lenses and their Mg−content. These incompletely silicified trilobites enabled a reconstruction of the silicification process in trilobites. Their diagenetic alteration probably occurred as a result of events associated with the Cretaceous transgression.

11

New genus of dimeropygid trilobites from the earliest Ordovician of Laurentia

67%

Adrain J. M. , Westrop S. R.

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2006

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tom 51

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nr 3

EN

The new genus Tulepyge includes a type species, T. tulensis nov., from the Barn Canyon Member of the House Formation, western Utah, USA, and T. paucituberculata from the Broom Point Member of the Green Point Formation, western Newfoundland, Canada. Both species are earliest Ordovician in age, with occurrence immediately above the Cambrian–Ordovician boundary. Together with the hystricurid taxon Millardicurus, the new genus is likely to serve as an indicator fossil for the Cambrian–Ordovician boundary in Laurentia, as it is already known from different biofacies on opposite margins of the continent. Tulepyge is not closely comparable with contemporaneous taxa assigned to Hystricuridae but in its dorsally convex and coarsely tuberculate exoskeleton it resembles taxa which have been referred to Dimeropygidae, most of which are considerably younger in age.

12

First report on the occurrence of Neseuretinus and Ovalocephalus trilobites in the Middle Ordovician of Iran

67%

Ghobadi P. M. , Popov L. E.

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nr 1

125-133

EN

In the Derenjal Mountains of east Central Iran, the upper part of the Shirgesht Formation (uppermost Darriwilian) contains a distinct trilobite assemblage that includes Neseuretinus birmanicus and Ovalocephalus aff. obsoletus among others. Both genera were previously unknown in Iran. The occurrence of Ovalocephalus represents the earliest sign of westward taxon migration from China towards higher latitudes along the West Gondwanan margin, which may be related to global warming, after a short episode of cooler climate in the early to mid Darriwilian. Patterns of biogeographical distribution of Ovalocephalus and Neseuretinussuggest that Central Iran was part of an “overlap zone” where tropical and high latitude benthic taxa mingled.

13

Morphology and developmental traits of the trilobite Changaspis elongata from the Cambrian Series 2 of Guizhou, South China

67%

Du G.-Y. , Peng J. , Wang D.-Z. , Wang Q.-J. , Wang Y.-F. , Zhang H.

Acta Palaeontologica Polonica

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2019

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tom 64

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nr 4

EN

The morphology and ontogeny of the trilobite Changaspis elongata based on 216 specimens collected from the Lazizhai section of the Balang Formation (Stage 4, Series 2 of the Cambrian) in Guizhou Province, South China are described. The relatively continuous ontogenetic series reveals morphological changes, and shows that the species has seventeen thoracic segments in the holaspid period, instead of the sixteen as previously suggested. The development of the pygidial segments shows that their number gradually decreases during ontogeny. A new dataset of well-preserved specimens offers a unique opportunity to investigate developmental traits after segment addition is completed. The ontogenetic size progressions for the lengths of cephalon and trunk show overall compliance with Dyar’s rule. As a result of different average growth rates for the lengths of cephalon, trunk and pygidium, the length of the thorax relative to the body shows a gradually increasing trend; however, the cephalon and pygidium follow the opposite trend. Morphometric analysis across fourteen post-embryonic stages reveals growth gradients with increasing values for each thoracic segment from anterior to posterior. The reconstruction of the development traits shows visualization of the changes in relative growth and segmentation for the different body parts. The new dataset and growth gradient of the trunk suggest that the thoracic segment growth dynamics of early Cambrian to Silurian trilobites follow the same general continuous, steady-state growth gradient decreasing from posterior to anterior.

14

Revision of the late Ordovician trilobite Holotrachelus punctillosus [Tornquist, 1884] from Dalarna, Sweden

67%

Suzuki Y.

|

2001

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tom 46

|

nr 3

EN

Holotrachelus punctillosus from the Boda Limestone (Ashgill, Upper Ordovician) of Sweden is redescribed. The systematic position of this problematic species is discussed. Its distinctive morphology appears to be the result of an adaptation towards illaenid life habits. The pygidial morphology, with the extra-fulcral field developed as segmental pleural spines, makes an assignment possible to only four Ordovician groups, namely the Remopleuridioidea, Odontopleuroidea, Lichoidea and Cheiruroidea. Of these, the former three are so different that a direct affiliation is out of the question. Similarities with the Cheiruroidea are the more persuasive, particularly after a misinterpretation of the facial suture is corrected and some other problems are sorted out. It is suggested that the Holotrachelinae are placed within the Cheiruridae, where it may have special affinities to the Sphaerexochinae.

PL

W pracy przedstawiono redeskrypcję trylobita Holotrachelus punctillosus, pochodzącego ze szwedzkich wapieni Boda (aszgil, górny ordowik) i omówiono pozycję systematyczną tego problematycznego gatunku. Jego charakterystyczna morfologia wydaje sie być związana z przystosowaniem do trybu zycia typowego dla Illaenidae. Morfologia pygidium, z polem pozawidełkowym rozwiniętym w postaci członowanych kolców pleuralnych, umożliwia zaliczenie holotrachelusa do jednej z czterech ordowickich nadrodzin: Remopleuridioidea, Odontopleuroidea, Lichoidea lub Cheiruroidea. Holotrachelus wykazuje najwieksze podobieństwo do Cheiruroidea, zwłaszcza po skorygowaniu mylnej interpretacji szwu policzkowego. Autor sugeruje, że Holotrachelinae należy umieścić w obrębie Cheiruridae, przy czym najbliższe pokrewieństwa mogą je łączyć ze Sphaerexochinae.

15

Enrolment in a Middle Ordovician agnostoid trilobite

67%

Bruton D. L. , Nakrem H. A.

Acta Palaeontologica Polonica

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2005

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tom 50

|

nr 3

EN

Study of silicified material of Trinodus elspethi, from the Edinburg Formation, Virginia, USA, shows there is no gliding of distal parts of segments but an articulating furrow and opposing flange with prongs, acting as apodemes for muscle attachment, allowed cephalon and thorax to move as a single unit. Articulation between thorax and pygidium was more rigid with prongs from the thorax articulating in sockets on the pygidium. Support is given to the view that agnostoids lived partially enrolled with cephalon and pygidium gaping. They are unique in lacking an articulating half−ring between cephalon and thorax and the hinge joint is modified medially to provide an opening for what is interpreted as an exhalatory organ through which water passed during feeding and swimming. Peculiarities of the thorax are connected with the presence of only two thoracic segments articulating as a unit with distal tips directed anteriorly rather than posteriorly. Otherwise articulating half rings are present in the rest of the thorax and pygidium and lack of articulating facets is not unique. It is concluded that agnostoids can be shown to be trilobites.

16

Pellets independent of or associated with Bohemian Ordovician body fossils

67%

Bruthansova J. , Kraft P.

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2003

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tom 48

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nr 3

EN

Clusters of small cylindrical pellets occur sporadically in Ordovician strata in Bohemia. They are assigned to the ichnogenus Tomaculum and occur in lenticular or elongated accumulations. Similar accumulations are associated with body fossils including the cephala of the trilobites Ormathops atavus, Pricyclopyge binodosa, and Parabarrandia crassa. The clusters are situated under the glabella and in the anterior parts of the cephalon but their exact position is variable in different cases. Accumulations of pellets have also been studied inside shells of hyoliths, bellerophontids, and echinoderm thecae. They probably represent the faeces of either scavengers feeding on soft parts or organisms using cephalic shields and other shells as hiding places. An interpretation of these pellets as trilobite eggs is highly improbable.

17

Ontogeny of a new cyrtosymboline trilobite from the Famennian of Morocco

67%

Loresey-Aubril R. , Feist R.

Acta Palaeontologica Polonica

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2005

|

tom 50

|

nr 3

EN

Abundant trilobite remains were recovered from late mid−Famennian marlstones from various sites in Eastern Tafilalet, southeast Morocco. All belong to a single taxon previously identified as Cyrtosymbole (Waribole) prima. This taxon is designated the type species of Osmolskabole gen. nov. A redefinition of this species, including the description of newly discovered, disarticulated exuviae both in limestone and silicified state of preservation, is given. In particular, silicified sclerites of various sizes allow the first complete growth series of a cyrtosymboline proetid to be presented. The close morphological resemblance of its protaspid stages to known proetoid larvae emphasizes the homogeneity of the early ontogeny in this superfamily. The Famennian proetoid anaprotaspis is also of comparable size to that of other Devonian proetoid larvae. However, their size−range is much less than that observed in Carboniferous larvae. This suggests that the survival of proetoid trilobites at the Frasnian−Famennian Kellwasser crisis did not result from a modification of the developmental strategy, as it might have been the case at the terminal Devonian extinction event. Moreover, O. prima possesses a plectrum from the metaprotaspid to the mid meraspid periods. This implies that the natant hypostomal condition is not steadily acquired early in the ontogeny of the Proetida. Thus we preclude the use of this character in the diagnosis of this order.