What Is An Asspect Of A Redlichia Takeoonesis Trilobites

plate 52

OLENELLUS Billings, 1861 (= Fremontia Raw, 1936; Mesonacis Walcott, 1885; Paedumias Walcott, 1910), Olenellus fremonti Walcott (x7.2). Lower Cambrian of British Columbia. Bonnia-Olenellus assemblage zone in the St. Piran Sandstone (Peyto Limestone Member). (Gift of J. R. Evans to UCWM; loaned by FMNH; id. RLS.) The classification of the Olenellidae has undergone extensive revision in recent years (Fritz 1972; Bergstrom 1973b). Having changed generic affiliation several times, Olenellus fremonti is presently reinstated within the original denomination given by Walcott, 1910. This trilobite typically has fourteen thoracic segments. Note exaggerated development of the pleural lobe of the third thoracic segment, said to be macropleural The irregular fractute along the axis is probably due to compression. The axial spine is hollow.

Juvenile form of Olenellus fremonti Walcott (xlO), from the same sample which yielded the preceding example (RLS coll., id.; now at FMNH.) In (a) the specimen, whitened with magnesium oxide, is photographed by standard technique, while in (b) the specimen is photographed while immersed in xylene. The optical contact of this medium (index ot refraction n = 1.5) with the surface crystalline layers of the sample provides a much better representation of the anatomical features than in (a). Note that the axial spine is as long as the entire carapace.

Cambrian Families

Exuviae of a large specimen of Olenellus fremonti W a l c o 11 (x2 ) from the Lower Cambrian Latham Shale of the Marble Mountains, San Bernardino County, California (RLS coll., id.). As a commonly encountered outcome of the molting process, the cranidium slipped backward, overlapping the first two thoracic segments. The genal, pleural, and axial spines of the trilobites from this locality are often replaced by limonite and appear in brightly colored hues of yellow, red, and black, as is the case in this example.

External impression of the exuviae of the trilobite Olenellus clarki (Resser) (x2.8), also from the Latham Shale of the Marble Mountains (RLS coll., id., now at FMNH). This trilobite was previously assigned to the genus Paedumias Walcott, 1910 (see synonyms mentioned for plate 52) and bears great resemblance to

Olenellus transitans

(Walcott) of the Atlantic faunal province. Note wide frontal area anterior to glabella, marked by median ridge, and third segment macropleurae. The latter, however, are not as wide as in O. fremonti (Walcott). The opisthothorax (the posterior extension of the thorax) is partially exposed in this graceful example; the presence of this extension of the rachis is characteristic of the Olenellidae.

Particularly well preserved, although partially disarticulated, exuviae of another specimen of Olenellus clarki (Resser) from the Latham Shale (x4.7)(RLS coll., id.). The only functional sutures in the cranidium of this ttilobite are those that rerain the visual surface. This is genetally released during molting or after death of the individual, leaving a gap between the palpebral lobe and the librigena, as is cleatly occutring in this example. A peculiar fractute and displacement of part of the macropleural third tetgite causes an apparent misalignment of the right and left side of the latter. Axial nodes are present on most axial rings. The axial spine and opistothorax are missing.

Olenellus clarki (Res ser) (x6.3). Lower Cambrian of Pioche, Nevada. Pioche Shale, D Member. Specimen collected by Afton Fawcett during a field trip with the author (RLS coll., id., now at FMNH). Part of a slab containing four partially complete individuals. Specimen whitened with magnesium oxide. The eyes of this individual are somewhat longer than the norm.

This somewhat stretched, yet captivating example of OUnellus clarki

(Resser) originates from the Nopah range of Southern California (x4.1). Specimen collected by Thomas Johnson (RLS coll., id.)

Olenellus mohavensis (Resser) (x7.3), another olenellid species found in the Latham Shale of the Marble Mountains of Southern California (RLS coll., id.). A disproportionate swollen macropleura of the third thoracic tergite and an advanced genal angle characterize this trilobite at all stages of growth.

The characters noted in the preceding example become even more pronounced in Bristolia bristolensis Resser (x3.9) from the same Lower Cambrian locality. External imptession (RLS coll., id.).

plate 61

Cranidia of several olenellid species found in the Lower Cambrian Latham Shale of the Marble Mountains of Southern California (RLS coll., id.). An evolutionary trend toward a forward shift of the genal angle is noted in the sequence of short-eyed olenellids that starts with Olenellus jremonti (Walcott) (a)(x2.3) and includes Olenellus mohavensis

(Resser)(b)(x2.5), B ristolia bristolensis Re sser (c) (x2. 0), and Bristolia insolens Resser (d)(x3.0). All of these species have the glabella extending to the frontal rim of the cranidium. By contrast, the long-eyed form Olenellus clarki (Resser)(e)(xl.8), with its wide frontal brim, does not seem to belong with this sequence.

Family Holmiidae Hupe, 1953

plate 62

ANDALUSIANA Sdzuy, 1961. Andalusiana sp. (xl.3). Lower Cambrian, Djbel Ougrat, Morocco. (RLS coll., id.) Complete specimens of this trilobite have appeared in the fossil market of recent years in great number, unfortunately mostly defaced by poor preparation or arbitrary reconstruction. The granulated, reticulated surface of the carapace betrays the genuine portions of the specimen figured here, altered only by minor repair. The genus Andalusiana, indigenous of Spain, as the name implies, is known from the type Andalusiana comuta Sdzuy. The Moroccan species bears many similarities with the latter, while differing in some aspects. The palpebral lobes are here about one-third the length of the glabella, versus one-half for Andalusiana cornuta. Noticeable also is the falcate appearance of the broad genal spines, even more pronounced than in the related genus Kjerulfia. The thorax contains sixteen segments. The axial notches or spines become progressively more pronounced, distally tapered and rectangular in cross section, toward the pygidium.

Family Wanneriidae Hupe, 1953

plate 63

Wanneria walcottana (Wanner), Lower Cambrian, Kinzers Formation, Lancaster, PA. (x2.8)(coIlected by M. Thomas, RLS coll.). Although remarkably well preserved in its undistorted entirety, this is an internal impression that does not show surface ornamentation or axial nodes that should be present. Axial spine also not preserved.

Unusual assemblage of complete individuals of Wanneria sp., from the Lower Cambrian of Sweden, at various stages of growth (x0.8). (Loaned through courtesy of Pio Pezzi.)

Family Redlichiidae Poulsen, 1927

Subfamily Redlichiinae Poulsen, 1927

plate 65

REDLICH1A Cossman, 1902. Redlichia forresti (Etheridge Jr.), Early Middle Cambrian, Emu Bay Shale near Big Gully, North Coast of Kangaroo Island, Australia, partially disarticulated exuviae (x4.2). In this trilobite, facial sutures (opisthoparian) separating the glabella from the librigenae appear for the first time. (Photographed by the author at SMNH, through courtesy of Jan Bergstrom.)

Family Dolcrolenidae Kobayashi, 19 51

plate 66

dolerolenus

Leanza, 1949. Dolerolenus z?ppii (Meneghini) (x6.8) Up. L.Cambrian, Nebida Formation, Punta Manna member, Porto di Canalgrande, Sardinia, Italy. In this specimen, the exoskeleton is still replaced by a hard film of hematite, which is more generally altered to limonite. (Photo courtesy of Franco Todde, reproduced by permission.)

Dolerolenus

Dolerolenus z?ppii (Meneghini) (x7.4), from the same locality as preceding plate. Here most of the original hematitic replacement of the exoskeleton is altered to a bright yellow film of limonite. External impression. (Loaned through courtesy of Bruno Corti.)

Family EUipsocephalidae Matthew, 1887

Subfamily Ellipsocephalinae Matthew, 1887

ELLIPSOCEPHALUS Zenker, 1833. Ellipsocepbalus boff (Schlotheim) (xl.8). M. Cambrian, Jinetz, Bohemia. (Loaned by Geological Enterprises, Ardmore,

Oklahoma.) This trilobite commonly occurs in densely populated assemblages, known since the early nineteenth century.

Family Conocoryphidae Angelin, 1854

plate 69

CONOCORYPHE Hawle and Corda, 1847. Conocoryphe sul^eri Schlotheim (xl.8). M. Cambrian (Jinetz Shale), Beroun near Prague, Bohemia. (Loaned by MCZ.) This trilobite was blind. The specimen on the lower left-hand corner is a negative mold, the other two are positive casts (steinkerns).

Conocoryphe sul^eri Schlotheim, as for preceding plate (x3.4). (RLS coll.; courtesy of MCZ, now at FMNH.) What black-and-white photography cannot convey is, of course, the color of some of the trilobite specimens. In this case, the trilobite is coated by a bright yellow-ochre film of limonite that contrasts with the tan matrix background.

BAILIELLA Matthew,

18 85. Bailielk manuelensis (Hutchinson), M. Cambri an,

Eccaparadoxides bennetti beds, Kellygrews, Conception Bay, Newfoundland (x3.6). Blind trilobite. (RLS coll., id.)

CTENOCEPHALUS Hawle and Corda, 1847. C r ani dium of Ctenocephalus howelli Resser, M. Cambrian, Paradoxides davidis beds, east side of Manuels River, Manuels, Newfoundland (x5.9)(RLS coll., id.). This blind trilobite is closely related to Conocoryphe, with fifteen thoracic segments instead of fourteen. The location of the preglabellar boss drifts toward the anterior border in other species. The granulated surface of the convex parts of the cranidium is particularly noticeable and well preserved in this example.

Family

Zacanthoididae Swinnerton,

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  • tarquinio
    What is an asspect of a redlichia takeoonesis trilobites?
    8 years ago

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