MY ABSTRACTS 1
Lerosey-Aubril, R. and R. Feist. 2005. Journal of Paleontology, 79: 702-718. full version (text only)
The recovery of well-preserved silicified larvae from the early Tournaisian of Montagne Noire, southern France, allows the first description of the early ontogeny of proetoid trilobites, survivors of the end-Devonian Hangenberg extinction event. The fauna comprises various taxa that can only partly and tentatively be assigned to the genera Liobolina, Diacoryphe, and Pedinocoryphe without specific attribution. The close resemblance of these larvae to previously described proetoid larvae from the Ordovician and Devonian emphasizes the ontogenetic homogeneity of this superfamily. Moreover, it supports the view that the Proetida is composed of two clades: the Aulacopleuroidea/Bathyuroidea group and the Proetoidea. The Carboniferous anaprotaspides exhibit an unusually wide size-range that may provide evidence of the acquisition of an extended planktonic period in the early ontogeny of at least some Carboniferous proetoids. This change in the ontogenetic strategy may have enabled proetoid trilobites to survive during the end-Devonian biocrises.
Lerosey-Aubril, R. and R. Feist. 2005. Senckenbergiana Lethaea, 85(1): 119-130.
The almost complete post-protaspid ontogenetic sequence and the hitherto unknown hypostome of a Late Devonian blind proetid, Helioproetus costifusus, are described. The silicified meraspid remains were recovered from the lower part of the Upper Clymenien-Schichten of late Famennian (Dasbergian) age from Breternitz near Saalfeld, Thuringia. The course of the facial suture in H. costifusus is in early ontogenetic stages similar to that of adults of the younger H. carintiacus, present in the upper part of the same section. This observation suggests an ancestor-descendent relationship between the two species, implying processes of heterochrony. The smallest cranidia of H. costifusus also exhibit a particular overall morphology and a remnant of a straight palpebral suture indicating that this species may have had an oculated cyrtosymboline ancestor. The Early Carboniferous Pedinocoryphe is considered to have evolved in a convergent way from a common rootstock.
Die fast vollstandige post-protaspide ontogenetische Entwicklungsabfolge und das bisher unbekannte Hypostom eines spat-devonischen blinden Proetiden, Helioproetus costifusus, werden beschrieben. Die verkieselten meraspiden Reste stammen aus dem unteren Teil der Oberen Clymenien-Schichten (Oberdevon, Dasbergium) von Breternitz bei Saalfeld in Thüringen. Der Verlauf der Gesichtsnaht in früh-ontogenetischen Stadien von H. costifusus gleicht demjenigen adulter Stadien des jungeren H. carintiacus, der im oberen Teil desselben Profils auftritt. Diese Beobachtung lässt auf ein Ahnen-Nachfolger-Verhaltnis zwischen den beiden Arten schließen, das auf die Beteiligung von Prozessen der Heterochronie hinruhrt .Die kleinsten Cranidia von H. costifusus zeigen zudem eine besondere Gesamt-Morphologie sowie einen Rest von Palpebralsutur, die auf mögliche augentragende cyrtosymboline Vorläufer hinweisen. Die früh-carbonische Pedinocoryphe wird als Konvergenzentwicklung aus einer gemeinsamen Wurzel gedeutet.
Lerosey-Aubril, R. and R. Feist. 2005. Acta Palaeontologica Polonica, 50(3): 449-464. full version (pdf)
Abundant trilobite remains were recovered from late mid-Famennian marlstones from various sites in Eastern Tafilalet, southeast Morocco. All belong to a single taxon 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 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.
Feist, R. and Lerosey-Aubril, R. 2005. Acta Palaeontologica Polonica, 50(3): 465-475. full version (pdf)
The hitherto poorly known type species of Cyrtosymbole, i.e., Dechenella escoti, is redescribed on the basis of an abundant new material recovered from the early Famennian Lower Griotte Limestone Formation at La Tourière, near Cabrières, southern France. It includes sclerites (hypostome, librigenae, thoracic segments and external surface of the pygidium) that previously were either unknown, or represented by poorly preserved and incomplete specimens, together with a full suite of post-protaspid growth stages. The latter has revealed that certain characters, in particular the preglabellar region and postocular facial sutures, show marked changes between the early and late holaspid stages. In the past, some species have been based on immature specimens; for example the lectotype of C. escoti is an early holaspis, and the characters that it displays have been regarded as diagnostic of the genus. For confident specific assignments in cyrtosymboline trilobites it is important, therefore, to have to hand sufficient material, including late holaspids. A revised diagnosis of Cyrtosymbole is given, and only those species that share diagnostic adult characters with C. escoti are assigned to it. Insights into early growth development exemplified by C. escoti and allies corroborate the attribution of the Cyrtosymbolinae to the Proetidae.
Lerosey-Aubril, R. 2006. Geological Magazine, 143(1): 83-104. full version (pdf)
Numerous silicified and calcareous sclerites of various sizes, recovered from the latest Famennian of Thuringia (Germany), allow the description of the first complete growth series of a blind proetoid trilobite: Drevermannia richteri. In addition, the partial ontogenetic development of Drevermannia antecurvata sp. nov. and undetermined species, Drevermannia sp. 1, are described. The proetoid anaprotaspides, associated with D. richteri, illustrate that a marked increase in larval size occurred prior to the terminal Devonian extinction event. Considering the homogeneity of larval size in older Devonian proetoids, it is interpreted as evidence that the developmental strategy of these trilobites significantly modified. Though largely speculative, two alternative hypotheses are proposed to explain this modification. Finally, all three ontogenetic sequences show that ocular structures never develop externally in Drevermannia, but also illustrate that the development of optical nerves is not completely lost in this group. This suggests that blindness in the Drevermannia lineage followed a centripetal mode of eye reduction.
Lerosey-Aubril, R. and R. Feist. 2006. Palaeontology, 49(5): 1053-1068.
A new species, Cyrtosymbole rectifrons sp. nov., from Famennian marlstones in the south-eastern vicinity of Erfoud (Tafilalt, Morocco), is described. Silicified sclerites of various sizes allow the description of its late growth sequence, which demonstrates that some characteristic features of the Cyrtosymbolinae are acquired during late ontogeny. Precise examination of exceptionally well-preserved material enables reconstruction of the in situ position of the adult hypostome, together with a reconsideration of its relation to the dorsal exoskeleton and its morphofunctional capacity for movement. The natant hypostomal condition inferred for C. rectifrons suggests that it is not always possible to deduce the nature of hypostomal attachment from the dorsal morphology alone.
Lerosey-Aubril, R. 2007. Bulletin de la Société Géologique de France, 178 (3): 197-200.
The late Emsian middle Member of the Bissounel Formation (Montagne Noire, France) has yielded a highly diverse silicified trilobite fauna. Among the thousands of disarticulated sclerites discovered, two protaspid specimens were found that display morphological characteristics of planktonic larvae of calymenid trilobites. The presence of calymenid protaspides within a non-calymenid trilobite fauna is noted. The two specimens are very similar to the first planktonic larval stage of the Ordovician Flexicalymene senaria (Conrad, 1841), and are of comparable size. This indicates that, as in F. senaria, a second planktonic larval stage might have occurred in the ontogeny of this undetermined calymenid. Thus, some post-Ordovician calymenids might have retained the ancestral developmental strategy with a two-stage planktonic period. The discovery of these two protaspides constitutes the first evidence of a calymenid trilobite in the Devonian of the Montagne Noire.
Lerosey-Aubril, R., R. Feist & B.D.E. Chatterton. in press. Geological Magazine.
A new otarionine trilobite Otarionella rastrum sp. nov., from the late Emsian Mont Peyroux Formation (Montagne Noire, France), is described. Silicified remains, recovered from the underlying Bissounel Formation (early to late Emsian), are also attributed to this new species. These isolated silicified sclerites represent metaprotaspid to young holaspid growth stages, which enables the almost complete ontogeny of an otarionine trilobite with a spinose adult morphology to be described for the first time. Comparison with associated larval and juvenile growth stages of Cyphaspis reveal that the pattern of juvenile cranidial spine distribution in Otarionella rastrum sp. nov. differs from all patterns described so far in the Otarioninae, in particular that characterizing the tribe Otarionini.
A second species, Otarionella lkomalii sp. nov., known only from a complete articulated specimen discovered in the early Eifelian of southern Morocco, is also described. Like the middle Eifelian Otarionella chamaeleo (Basse, 1997), this new species has only ten thoracic segments, with the fourth and the sixth segments each bearing a long axial spine.
In the light of the new elements provided by the ontogenetic sequence of O. rastrum sp. nov. and the adult specimens of this species and O. lkomalii sp. nov., the putative synonymy of Otarionella and Otarion is rejected and a restricted concept of the genus Otarionella is defined.
