Devonian Trilobites Research Articles

A Spectacular Devonian Trilobite Specimen, Dalmanites pratteni, From Illinois Helps Shed Light on How Trilobite Eyes Worked

In 1912, the Field Museum purchased Henry Pratten's collection of fossils. One of the specimens was a dalmanitid trilobite with large eyes (Fig. 1) that Pratten collected from the Devil’s Backbone. In 1933, this specimen was described as a new species of trilobite, Dalmanites pratteni (P 16704) (Roy 1933). Delo (1935) described a new genus of trilobite, Dalmanitoides and assigned it to a new family, Synphorinae. He noted Dalmanites pratteni has similar ornamentation to this genus. Delo (1940) later places D. pratteni in the genus Odontochile. Other authors refer to it as Dalmanites pratteni (Clarkson and Levi-Setti 1975;Levi-Setti 1975; Frankie et al. 2008). Holloway and De Carvalho (2009) refer to it as ‘Dalmanites’ pratteni and state that this species “probably belongs to the Synphoriinae”. The stratigraphic position of this specimen was not recorded. Seid et al. (2009) published a detailed geologic map of the Devil’s Backbone. Most of the ridge is Middle Devonian Grand Tower and St. Laurent formations. However, the southern end of the ridge is faulted, and the Lower Devonian Backbone Limestone and Crystal Creek Chert (Emsian) is exposed. Frankie et al. (2008) and Devera et al. (2020) report Dalmanites pratteni occurring from the Crystal Creek Chert, indicating that the original specimen may have been collected here. One of the most remarkable features of this fossil is the record number of lenses for a Phacopida. Roy (1933) reports 42 rows of eyes, however: “The exact number of lenses cannot be determined, as not all of them are preserved, nor are the areas which they occupied distinctly outlined. It is, however, certain that there are not less than 770 lenses on each eye.” (Roy 1933). I used images of the eyes and illustration software to estimate the number of lenses by filling in the geometric pattern they exhibit. I counted 730 lenses on the right eye and 712 lenses on left eye, which is missing a sizable piece (Fig. 2). The structure of some individual lenses in this specimen can be seen due to differential weathering. Clarkson and Levi-Setti (1975) reported the large round lenses were composed of a doublet structure that followed the principles established by Descartes (1637) and Huygens (1690) to eliminate spherical distortion. This doublet structure allowed the lens to gather more light and focus it on a single point, and strongly indicates that these trilobites had better vision then previously established (Clarkson and Levi-Setti 1975).

In Pursuit of the Iconic Devonian Trilobite Eldredgeops (Phacops) rana

In Pursuit of the Iconic Devonian Trilobite Eldredgeops (Phacops) rana

Devonian Harpetidae from the central and eastern Anti–Atlas, Morocco

The systematics of 37 new species of Devonian Harpetidae from the central and eastern Anti–Atlas Mountains, Morocco, are described. The new material comes from the Dra—Tafilalet region and the province of Tata. A cladistic study was undertaken involving 138 taxa with the objective of assigning the new taxa to the appropriate genera, which are, as far as possible, monophyletic. In order to identify the widespread homoplasy present amongst harpetid taxa, which has proven so problematical for systematics in the past, many additional morphological characters were coded in the data matrix, totaling 111. In addition to the new material, all those described harpetid species from the Devonian and Silurian in which at least 10% of characters could be reliably coded were included in the study. The parsimony analysis using 20 different seeds identified 636 shortest trees; the consensus tree recognised 10 monophyletic clades to accommodate Devonian species. While the node support was weak the topology of the consensus tree is a substantial improvement on those of previous phylogenetic studies which have tended to be pectinate. The new species were assigned to 10 genera. Four genera (Harpes, Lioharpes, Kielania and Eskoharpes) are redefined and Globoharpes is reduced to a junior synonym of Eskoharpes. Three further genera are recognised, Declivoharpes, Fritchaspis and Helioharpes, which have been misinterpreted in the past and the new genera Maghroharpes, Pinnuloharpes and Stoloharpes established. The new species are assigned as follows: to Harpes, H. boudibensis, H. lahceni, H. lentigo, H. oudris, H. prescheri, H. sphenocephalus and H. supercilium; to Lioharpes, L. ammari; L. galea, L. morocconensis, L. saredra, and L. scopulum; to Fritchaspis, F. edgecombei; to Helioharpes, H. aougili; to Kielania: K. tumula; to Eskoharpes, E. sicarius; to Maghroharpes, M. azmamarensis, M. forteyi, M. hammii, M. ihmadii, M. laatchanensis, M. minutipunctus, M. oufatenensis, M. terridus, and M. zguidensis; to Pinnuloharpes, P. apteros, P. chaperon, P. hannabouensis, P haustrum, P. igaouii, P. merzaneensis; P. segaouii. and P. torquis; Stoloharpes, S. calceolus, S. capricornus, S. retiarius, and S. rissaniensis. Decllivoharpes, is also recognised as a genus, although no new species has been assigned to it. The cladogram produced very few synapomorphies and there are no unique diagnostic characters available to determine genera. To assist in the process of assigning species in the future to the correct genera a working guide using combinations of characters and character states used in the study has been prepared. The name Helioharpes perradiatus has been widely used with regard to harpetids from the Anti Atlas. This study shows that this has been a ‘portmanteau’ name for at least three distinct species. All are very different from the type material of H. perradiatus, which was recovered from the Western Meseta to the north of the Atlas Mountains, and has not been found to occur in the Anti-Atlas. The new material figured herein has provided additional information on the eyes of Devonian harpetids of the Anti-Atlas. Typically, each eye lobe has two lenses which vary considerably in shape from species to species and are very different from the symmetrical multi lensed eyes of other Devonian trilobites. Probably in response to environmental changes a small third eye lens appeared for a short time twice, first in the upper Pragian/lower Emsian and then again in the Eifelian. The shape of the Pragian/Emsian lens was circular whereas that of the Eifelian lens was similar to the shape of the two larger accompanying eye lenses.

Function of flow wakes for queuing trilobites: Positioning rather than drag reduction – Criteria for drag force assessment in palaeontological CFD simulations

Trilobites are one of the most important invertebrate clades in the Palaeozoic, with significant disparity in morphology and behaviour, the latter including intriguing instances of queueing. Previous studies employed Computational Fluid Dynamics (CFD) to investigate queuing behaviour in the Devonian trilobite Trimerocephalus chopini and found drag reduction effects. Novel calculations that define a ratio between drag force and Apparent Gravity (W), along with the Submerged Froude Number (Frsub), however, reveal that the obtained drag force was practically negligible in terms of the underwater mobility of trilobites. A trilobite would start to experience difficulty in forward walking only when the relative flow speed was over 42 cm/s, which is inconsistent with the interpreted palaeoenvironment or the predicted moving speed of trilobites. Nevertheless, according to the proposed cantilever model, a trilobite had the ability to sense very minute change in fluid velocity (>7.16 μm/s). High-sensitivity mechanical sensors distributed along the body, either on the exoskeleton or limbs, empowered queuing individuals to discern the fixed self-similar pattern of the wake generated by their predecessors in the queue. In general, if a trilobite were out of the wake, the asymmetrical velocity and pressure field would aid in repositioning itself, facilitating the maintenance of migratory queues. This permitted blind trilobites to securely sense their companions, compensating for lack of long-range visual capability. This paradigm of force assessment is suitable to Computational Fluid Dynamic analyses in other extinct animal-environment interactions, offering a framework to evaluate whether drags and wakes impact more on organism's mobility (W≫0.1,Frsub≫1) or their mechanical sensors, and provides a unique cross-scale insight into animals' adaptation to palaeohydrodynamic variation.

Coupling of taxonomic diversity and morphological disparity in Devonian trilobites?

ABSTRACT Morphological disparity and taxonomic richness are two major aspects of evolution used to understand biodiversity changes. These metrics are often decoupled in time, particularly during the early history of clades. To assess the pervasiveness of this pattern during the post-acme of a clade, both morphological disparity and taxonomic diversity of the well-documented Devonian trilobites from North Africa were analysed. Morphospace occupancy and body size were estimated and compared to genus richness through time. This study highlights that, during the Early Devonian, morphological disparity of the pygidium and the cephalon strongly increased, whereas cranidium disparity remained low. Interestingly, the pygidium and cephalon morphological dynamics were decoupled. Taxonomic diversity also increased. Then, the Middle Devonian anoxic events affected the trilobite communities with simultaneous drastic loss of both morphologies and taxonomic richness. This coupling between diversity and disparity dynamics could be explained by either the intensity of extinctions or strong internal constraints. Finally, the weak Famennian recovery of both disparity and diversity did not reach the Early Devonian levels, thus making trilobites a ‘dead clade walking’ during their late evolutionary history. Devonian trilobite families are thus identified as ‘Bottom-Heavy Clades’, characterised by a diversity peak at the end of their history.

Trilobite tridents demonstrate sexual combat at 400 Mya

The Devonian trilobite Walliserops carries a remarkable anterior cephalic trident posing a challenge to functional interpretation. A unique teratological specimen of Walliseropstrifurcatus showing four, rather than three tines, is inconsistent with possible hypotheses connecting the trident to feeding techniques and suggests a sexually selected function. Malformations in a variety of living organisms support this conclusion. Morphometric comparisons to similar structures used for intraspecific combat in dynastine beetles show that the trident occupies a comparable shape space consistent with the hypothesis that it was a sexual combat weapon, the oldest reported example of its kind. This lends further credibility to the idea that some trilobites may have been strongly sexually dimorphic.

Morphological disparity trends in Devonian trilobites from North Africa

AbstractThe Devonian was a time of drastic environmental change that shaped the morphology of trilobites. This study aims to investigate their morphological evolution and to show the influence of some abiotic and biotic factors (bathymetry, feeding habits and visual abilities) on their shape. A dataset was compiled to investigate the shape of three structures (cephalon as a whole, central part of the cephalon, and pygidium) of Devonian trilobites from North Africa, using a geometric morphometric approach. Based on empirical morphospaces, the morphological changes were quantified through the Devonian stages. The results reveal important variations in the morphological disparity of the glabella shape, the facial suture location, the pygidial length and the presence of spines. In the Lochkovian, morphological disparity was low, subsequently increased in the Pragian with numerous innovations, and reached a maximum in the Emsian. If the morphospace occupancy remained until the Eifelian, a severe loss of disparity occurred in the Givetian, a time known for important environmental changes. Disparity then remained low in the Late Devonian. The shapes inherited from the Silurian persisted throughout the Devonian whereas Pragian novelties were most affected by losses. These persistent shapes were more versatile for environmental adaptation, helping those trilobites to survive the environmental events. Similarly, the trilobite orders that survived Devonian events had a wide morphological spectrum and were better adapted to withstand environmental change.

The influence of palaeogeography and tectonic events on trilobite distributions in Morocco and northwestern Algeria

AbstractThe effects of sea-level changes and anoxia on Devonian trilobites have been studied for a long time, but the importance of palaeogeographic and tectonic events in this key-period is still not well understood. In the Devonian Period, trilobites invaded many different marine environments and areas in North Africa where important palaeogeographic changes occurred. Distribution patterns of trilobites through time and space have been analysed using a hierarchical cluster analysis and diversity indices. Our examination of the literature suggests that trilobites were scarce during Lochkovian time before an important diversification in Pragian time. Trilobites flourished in many North African regions without there being important taxonomic differences between basins, because of free migration in relatively flat palaeo-topography and homogeneous environments. During Middle Devonian time, early Variscan tectonic movements transformed the eastern Anti-Atlas area into a basin with a platform topography. Geographical barriers such as deep basins prevented trilobite migrations. At the beginning of Eifelian time, the reduction in migration between the different regions of this area coincided with a decrease in diversity. Consequently, tectonic events played an important role in the decline of trilobites during Middle Devonian time, especially when these were combined with sea-level changes and anoxic/hypoxic events. A recovery occurred in Famennian time involving only new genera. As at the global scale, cyrtosymbolines developed in shallow seas, whereas phacopids evolved in deeper environments. The basin and platform system still hampered migrations, although sea-level variations led to episodic exchanges. The late Famennian regression reduced trilobite diversity dramatically in the study area.

New dalmanitid trilobite taxa from the Lower Devonian of Argentina: comments on spinosity in endemic taxa from southern high paleolatitudes

Three new Lower Devonian dalmanitid trilobite taxa are recognized from the Talacasto Formation in the Precordillera Basin, Argentina, which includes two monospecific genera (Ivanites leonorae n. gen., n. sp. and Aguaditaspis mediaspina n. gen., n. sp.), and one additional new genus and species left in open nomenclature. These taxa combine characters of the subfamilies Dalmanitinae Vogdes, 1890 and Synphoriinae Delo, 1935, challenging their taxonomic distinction. Forty percent of the dalmanitids from high paleolatitudinal basins from southwestern Gondwana (Malvinokaffric) exhibit non-homologous dorsal spinosity. Aguaditaspis mediaspina n. gen., n. sp. shares similar spines with Trypaulites calypso (Hall, 1861). The unnamed new genus resembles the spinosity of endemic Malvinokaffric dalmanitids, like Dalmanitoides Delo, 1935 and Fenestraspis Braniša & Vaněk, 1973. Considered defensive, the recorded spinosity along with putative sublethal-attack marks, suggest higher predation pressure than previously thought at high paleolatitudes. This evidence is in accordance with some hypothesis on rising predation pressure in the mid-Paleozoic marine ecosystems.

A preliminary account on Devonian trilobites from Arabian Plate, SE Turkey

Recently, several Devonian localities and the related biota occurring from the southeastern Turkey were reinvestigated. Although, the Hakkari-Çukurca and the Diyarbakır-Hazro areas of the Arabian Plate are considered as an important source of the Devonian macrofossils from the north Arabian sector of Gondwana, the existing record of Devonian trilobites in these regions was hitherto unknown. We here report and illustrate for the first time Lower and Middle Devonian trilobites represented by three proetid pygidia and one calymenid pygidium. The morphological features of these pygidia suggest that they can be assigned to undetermined species of Gravicalymene (Calymenidae) and Podoliproetus (Proetidae), two genera known in the Lochkovian; and Pseudodechenella (Proetidae), a genus known in the Givetian.

A 390 million-year-old hyper-compound eye in Devonian phacopid trilobites

Trilobites, extinct arthropods that dominated the faunas of the Palaeozoic, since their appearance c 523 million years ago, were equipped with elaborate compound eyes. While most of them possessed apposition compound eyes (in trilobites called holochroal eyes), comparable to the compound eyes of many diurnal crustaceans and insects living today, trilobites of the suborder Phacopina developed atypical large eyes with wide lenses and wide interspaces in between (schizochroal eyes). Here, we show that these compound eyes are highly sophisticated systems—hyper-compound eyes hiding an individual compound eye below each of the big lenses. Thus, each of the phacopid compound eyes comprises several tens, in cases even hundreds of small compound eye systems composing a single visual surface. We discuss their development, phylogenetic position of this hyper-compound eye, and its neuronal infrastructure. A hyper-compound eye in this form is unique in the animal realm.

Computational fluid dynamics confirms drag reduction associated with trilobite queuing behaviour

AbstractQueuing behaviour has been documented in marine arthropods from Cambrian to modern oceans. It was previously hypothesized that this behaviour provided energy savings through hydrodynamic drafting, with trilobites in following positions hypothesized to produce less drag than those leading. In this study, we evaluate the hydrodynamics of queuing behaviour in the Devonian trilobite Trimerocephalus chopini using computational fluid dynamics. The results show that the drag forces of the trilobites following in the queue were substantially lower than those produced by the leader (˜65–79% lower at velocities of 0.5–2 cm s−1). Drag reduction was positively correlated with the movement speed of the trilobites, but decreased with increasing distance from the leader, and there was essentially no drag reduction at all for the first following trilobite when the following distance was greater than about six times its body length. This agrees with fossil evidence preserving trilobites in queues in close proximity to each other. The results also show that drag reduction was still significant (˜86.8% at 2 cm s−1) even for the longest queues preserved in the fossil record. Our findings support the hypothesis that the queuing behaviour of trilobites was an adaptation for reducing hydrodynamic drag. This drag reduction effect compensated for the energy cost of movement, which would have been particularly advantageous during migration.

Class Trilobita in the Wocklum Limestone of the northern Rhenish Massif east of the Rhine (late Famennian, Late Devonian) – Part 1. Phillipsiidae and Proetidae

In 1926, Rudolf & Emma Richter published the first and so far only monograph of the Late Devonian trilobites. Most of these are in need of revision for technical reasons. In recent years there has been some interesting progress in connection with research on the Devonian- Carboniferous boundary and the Hangenberg Event. The trilobites of the latest Famennian Wocklum Limestone, which belong to the Proetoidea and Phacopinae, are locally the last before the event. They are ex- tensively investigated only by sites at Apricke. The combination of corresponding data with new and updated old information from all other important sites provides for the first time a modern overview of the trilobite fauna. This is important for understanding aspects of the event. The Proetoidea is first in- vestigated in detail. On the basis of previously unpublished finds, the type species of Pseudo waribole and Waribole are documented relatively extensively for the first time. The exact knowledge of their morphology is important for phylogenetic examinations. Eowinterbergia effenbergensis sp. nov. is the first proof for this genus for the German Late Devonian. The demarcation of the Wocklum Limestone against the underlying Dasberg Limestone is only possible faunistically. Species of Helio proetus seem suitable for this, as an example shows. Balvibole kaufmanni gen. et sp. nov. from the Dasberg Limestone is another eyeless cyrtosymboline in the late Famennian.

Early Devonian (Lochkovian) trilobites and brachiopods from the west Balkhash Region, Kazakhstan and their significance for regional terrane dynamics

A moderately diverse Early Devonian (Lochkovian) trilobite and brachiopod association has been recovered from the lower part of the volcano-sedimentary Shakshagaily Formation, exposed on the western side of Lake Balkhash in central Kazakhstan. Its discovery demonstrates the presence of Lower Devonian marine deposits in the region. The trilobite assemblage includes representatives of six genera: the dalmanitid Kasachstania alperovichi nov. sp. is the dominant taxon, with other components being Ananaspis?, Leonaspis?, Maurotarion, Trimerus (Edgillia), and Warburgella. Associated brachiopods include species of Glossoleptaena, Leptaena, Protolepstostrophia, Pseudostrophochonetes, and Resserella. Whilst a significant proportion of these taxa show distinct links with the contemporaneous trilobite and brachiopod faunas of the north Balkhash Region, the occurrence of Trimerus (Edgillia) aff. kinglakensis Gill, 1949 suggests a possible link with the Lochkovian trilobite fauna of the Australasian sector of Gondwana. The west Balkhash Region preserves an extensive record of late Silurian to Early Devonian island arc volcanism, slope-rise sedimentation and olistostrome formation, which has invariably been ignored in models favouring early amalgamation of the Kazakhstanian terranes into a single continent by the end of the Ordovician.

The paleobiogeographical significance of the Silurian and Devonian trilobites of Japan

AbstractSix major groups of trilobites from the Silurian and Devonian of Japan are evaluated for their paleobiogeographical signature. Silurian illaenids and scutelluids show four generic‐level and at least two species‐level links with the Australian segment of the Gondwana paleocontinent; encrinurids also indicate two generic‐level links with Australia and also the South China paleocontinent; whilst Devonian phacopids, and possibly proetids, suggest at least two generic‐level links with the North China paleocontinent. These different patterns may reflect the fragmentary biostratigraphical record of Japanese trilobites, but they also appear to reflect paleoenvironmental parameters associated with lithofacies, and paleoecology. Thus, Japanese assemblages of proetids and phacopids occurring in deep‐water clastic lithofacies have counterparts in similar settings in North China, and Japanese scutelluids and illaenids are strongly associated with shallow marine carbonate lithofacies that are similar to those of their occurrences in Australia. Japanese encrinurids occur in carbonate rocks indicative of shallow marine settings in the Kurosegawa Terrane, and they demonstrate a consistent paleobiogeographical affinity with Australia and South China. Larval ecology cannot be directly assessed for Japanese trilobite groups. However, proetids have consistently been shown to have planktonic protaspides, whereas illaenids, scutelluids, and encrinurids have benthic protaspides. Planktonic protaspides would have a greater propensity for distribution in ocean currents than benthic ones, and therefore may be of more limited paleobiogeographical utility. The combined data from the six different groups indicates that the complex paleobiogeographical patterns of the Japanese trilobite assemblages need to be interpreted with caution, and similarity of taxa does not necessarily denote paleogeographical proximity to other regions.

Spirits of Yokokurayama: shrine of the Japanese trilobites

‘We are such stuff as dreams are made on, and our little life is rounded with a sleep’. So sleep the trilobites of Yokokurayama, a sacred mountain hidden within the beautiful landscape of Japan’s Shikoku’s island. And though Prospero may have been speaking to his daughter and her fiancé (in William Shakespeare’s The Tempest), he might well have been contemplating the magnificent trilobite fossils of Yokokurayama. Japan may be better known for its sweeping volcanic landscapes, majestic castles, Shinto shrines and bullet trains, but it is also home to important collections of Silurian and Devonian trilobites.

Early Middle Devonian trilobites and events in the Nismes – Vireux-Molhain area, southern border of the Dinant Synclinorium (Belgium, northern France)

Well-preserved trilobite specimens are recorded from Eifelian strata between the villages of Nismes (southern Belgium) and Vireux-Molhain (northern France). In the area of study the lower Eifelian Vieux Moulin Member of the Jemelle Formation crops out. The diversified trilobite associations of this unit occur in dark shales and siltstones during a deepening phase and replace the comparatively poorly diversified trilobite fauna of the underlying Eau Noire Formation. This overturn of the local trilobite fauna might, in part, be considered a regional expression of the globally recognised Choteč Event. A marked influx of exotic trilobites in the Vieux Moulin Member is provisionally referred to the local Vieux Moulin Event. Trilobite diversity peaked in the middle Eifelian part (Chavées Member) of the Jemelle Formation before drastically dropping in the upper part of this formation. The manifestations in the Ardennes of the eastern North American Bakoven and Stony Hollow Events can neither be confirmed nor rejected based on the currently available data. New taxa from the early Eifelian part of the Jemelle Formation in the area of study are Asteropyge boeckae sp. nov., Asteropyge eonia sp. nov., Asteropyge filoxenia sp. nov., Cyphaspis insolata sp. nov., Cyphaspis iuxta sp. nov., Diademaproetus pertinax sp. nov., Geesops icovellaunae sp. nov., Gerastos kesselaeri sp. nov., Kettneraspis eftychia sp. nov., Pedinopariops ceuthonymus sp. nov., Pedinopariops richterianus geminus ssp. nov., Scabriscutellum archinalae sp. nov., Septimopeltis akatastasia sp. nov. and Tropidocoryphe insciens sp. nov. Our material includes exceptionally rare, well-preserved specimens from the famous “Mur des douaniers” locality near Vireux-Molhain. Additionally, Astycoryphe rugocauda sp. nov. is described from the lower Eifelian Couvin Formation (southern Belgium) and Gerastos silvicultrix sp. nov. from the uppermost Emsian Heisdorf Formation (German Eifel).

The biogeographical significance of Silurian and Devonian trilobites of Japan: a comparison of different taxonomic groups and discussion of their individual ecological and lithofacies ranges.

The biogeographical significance of Silurian and Devonian trilobites of Japan: a comparison of different taxonomic groups and discussion of their individual ecological and lithofacies ranges.

The rise and fall of Late Devonian (Frasnian) trilobites from Belgium: taxonomy, biostratigraphy and events

1. Introduction The Frasnian was a period of recurrent global eustatic perturbations that had already commenced in the Middle Devonian and led to major faunal crises. Frasnian trilobites, encompassing exclusively benthic and endobenthic inhabitants of the continental shelf, suffered consecutive blows from the worldwide “drowning” of reef ecosystems and a decline of the shallow water environments to which they were confined (Feist, 1991, 1995). The latest Frasnian Kellwasser Event, though not by itself responsible for the demise of Frasnian trilobites, was the “coup de grâce” for many families. This event and its effects on trilobites have been the focus of investigations at various sections located in Germany, France, Morocco and NW Australia, among other countries (e.g. Becker et al., 1989; Feist & Schindler, 1994; Feist, 2002; McNamara & Feist, 2016). Frasnian trilobites from Belgium were described mainly in the monograph on Late Devonian trilobites of Richter & Richter (1926) and in van Viersen & Bignon (2011) and van Viersen & Prescher (2011). Bignon & Crônier (2015) analysed faunal dynamics of Devonian trilobites from Belgium and northern France and recognised two poorly diversified associations in the Frasnian: the Scutellum–Goldius association which they considered to be restricted to reef environments, and the Bradocryphaeus association (Bradocryphaeus, Otarion, Heliopyge) of Crônier & van Viersen (2007) which occurs in lateral shales and limestones below fair-weather

北上山地"早池峰構造帯"東部よりデボン紀三葉虫化石の発見

北上山地"早池峰構造帯"東部よりデボン紀三葉虫化石の発見