Trilobites!: testigos de la evolución by Richard Fortey, , available at Book Depository with free delivery worldwide. A revision of the Devonian Malvinokaffric dalmanitid trilobite Dalmanitoides Delo, , Formación Punta Negra: análisis secuencial y evolución de la Cuenca. This paper reviews the methods which have been used to deduce the life habits of trilobites. The most reliable conclusions are those that satisfy.
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Author biographies Plain-language and multi-lingual abstracts PDF version. In light of new information on holotypes and additional material from the Lower Devonian type areas from Argentina, the dalmanitid trilobite Dalmanitoides Delo,is rediagnosed and considered a dalmanitine rather than a synphoriine.
A revision of the Devonian Malvinokaffric dalmanitid trilobite Dalmanitoides Delo,on the basis of new data from Argentina. Pioneering geological and paleontological surveys were carried out in western Argentina during the 19th and early 20th centuries.
Dalmanitoides drevermanni Thomas,was erected on the basis of a single specimen composed of a cephalon, pygidium and a few fragmentary thoracic segments associated in a single carbonate nodule. This holotype housed in Germany is from an undetermined stratigraphic level and was poorly illustrated.
No more specimens were collected, nor were further details on its occurrence provided, except in a recent brief treatment of the type specimen by Holloway and Carvalho Dalmanitoides boehmi Knod, is based on a nearly complete and outstretched articulated specimen preserved in a sandstone slab collected originally by Hauthal.
This specimen was never illustrated photographically and until now, it lacked a diagnosis, detailed description, precise stratigraphic occurrence data, and repository information. Apart from discussions on Gamonedaspis Edgecombe,both species have been of interest in discussing several other closely related dalmanitid taxa such as Amazonaspis Carvalho and Fonseca, and Fenestraspis Holloway and Carvalho, However, the lack of sufficient material, revised diagnosis, and exhaustive descriptions, has precluded a reappraisal of their systematic, phylogenetic, and paleobiogeographic significance.
In this contribution, we report several additional specimens of both taxa coming from Loma de los Piojos and from some other localities of the Precordillera Basin of San Juan Province; as well as repository information of the holotype of D.
On the basis of this new material, with stratigraphic and geographic data, a complete description is provided for each species, and the diagnoses are emended to allow better systematic comparisons and to provide new insights on the biostratigraphic rank of the taxa. The new information sheds light on the systematic, phylogenetic, and paleobiogeographic proposals discussed for related Malvinokaffric Devonian trilobites.
File:Fósil de trilobite en el Museo de la Evolución de Puebla – Wikimedia Commons
Aspects of the geologic setting relevant here have been adequately treated in several previous works B aldis, ; Astini, ; Herrera,a, b; Edgecombe et al. Fossils studied come from the Talacasto Formation Padula et al. This Lower Devonian unit is composed of a marine succession of intensely bioturbated greenish-gray mudstones with intercalated beds of sandstone.
It starts with dark muddy levels basally, passing upwards into sandy levels with fossiliferous nodules Figure 2. The Talacasto Formation reaches a maximum thickness of more than m in the northern part of the basin. It represents a muddy shelf depositional system developed during a highstand, and overlies the mainly Silurian shelf sequence of the Los Espejos Formation Astini, The stratigraphic record of the Silurian-Devonian boundary in Central Precordillera is poor due to the presence of a discontinuity between Los Espejos and Talacasto Formations.
According to the studies of the brachiopod fauna Herrera,Racheboeuf and Herrera,Herrera and Bustos, the Talacasto Formation spans the early Lochkovian-Emsian. The top of the unit is considered diachronous, with late Pragian to earliest Emsian levels recorded in the southern sections and younger late Emsian levels found in the northernmost sections.
File:Fósil de trilobite en el Museo de la Evolución de Puebla 1.jpg
This can be recognized in the field, thanks to a distinctive latest Pragian to earliest Emsian stratigraphic light marker horizon, observed initially by Keidel and then by Astiniwhich is continuous for more than km, from the Talacasto Creek Herrera and Bustos,p.
The strata overlying this guide horizon, which are mainly recorded in the thicker northernmost sections of the basin, are overall considered of Emsian age. Devonian materials studied herein derive from classical sections of the Talacasto Formation, in San Juan Province, as follows Figure 1: The holotype of D. Emended diagnosis of the genus. According to illustrations by Edgecombethis species shares with Dalmanitoides all of characters mentioned in the emended diagnosis of this latter genus above.
Therefore we interpret Gamonedaspis as a junior synonym of the genus Dalmanitoides. The diagnosis of Dalmanitoides put forward by Delop. This diagnosis comprises a unique character combination rather than an exhaustive list of generic apomorphies.
The recognition and definition of subfamilies within Dalmanitidae has been long discussed, and brief reviews of the literature focused on Malvinokaffric dalmanitidscan be found in Carvalho and Fonseca and Holloway and Carvalho Herein, we follow considerations given by Campbell and Hollowaytogether with additional taxonomic criteria drawn by Holloway and Carvalho Besides previously available illustrations of D.
Dalmanitoides drevermanni is now interpreted as a dalmanitine, based on the distance between S1 and S2 apodemes being less than 1. Contrasting opinions on the subfamilial status of this species may be due to intraspecific variability together with a slightly different morphological expression of anatomical structures between internal and external moulds, observed for example between the exfoliated left side and the well-preserved right side of the holotype pygidium illustrated by Holloway and Carvalhofigure 3 G ; as well as in Figure 5 herein.
However, the intersegmental fenestrae, very tall eyes with a very different lens formula, a conspicuous palpebral rim, morphology and arrangement of glabellar lobes and furrows, almost straight morphology of pygidial pleural ribs, conspicuous indentations of the apodemal pits exsagitally along the pygidial axis, among many other differences with Dalmanitoides cited by Holloway and Carvalhop.
So many similarities suggest a sister taxon relationship rather than a convergence between Dalmanitoides and Fenestraspis.
Nevertheless, since Dalmanitoides including Gamonedaspis is reliably considered a dalmanitine, whereas Fenestraspis has most recently been interpreted as a synphoriine, our reasoning presents a major systematic problem: Certainly, Fenestraspis exhibits synphoriine characters i.
Unraveling this major taxonomic issue evolucoon an exhaustive revision of dalmanitids, which is beyond the aim of the present contribution, but which should be eolucion in future works. Dalmanitoides exhibits a high intraspecific variability, and the overlapping wide range of morphologies complicate the recognition of species. Hence, most useful characters separating species of Dalmanitoides include: Loma de los Piojos: Dalmanitoides with paired anterior spiny projections medially and little spiny crenulations anterolaterally on anterior border, stout median spine on occipital ring and each thoracic axial ring with a couple of additional spines located laterally; small spines on the posterior border; glabella variably exhibiting paired large tubercles or spines on its median part; pygidial axial rings bearing paired spines most frequently on strongly swollen rings 1, 3 and 4, 7 or 8, 12 and 16; large spinose tubercles or spines on posterior pygidial pleural bands irregularly disposed but tending to define bilateral symmetry.
Cephalon Figure 3 widely subtriangular in outline, with length sag.
Anterior cephalic border approximately twice as long sag. Glabella excluding occipital ring approximately as long sag.
Axial furrow wide tr. Preglabellar furrow short sag. LO occipital ring moderately long sag. SO occipital furrow moderately deep and long sag. L1 moderately narrow, shorter sag. S1 of overall concave forwards shape, very weak sagittally, longer exsag. L2 longer sagittally than L1, approximately as long as the sagittal length of the occipital ring; with medial part separated from the lateral parts by an elongated and weak shallow depression anteromedially-posterolaterally oriented, bearing coarse to spinose tubercles with one larger tubercle usually present ; lateral part barely oriented backwards, longest exsag.
S2 posterolaterally directed, starting adaxially as a deep commissural apodemal pit convex forwards defining an exsagittal small convex projection coming from the most adaxial part L2 forwardthen progressively weakening to become inconspicuous laterally at junction with axial furrow. L2 and L3 tending slightly to be fused and swollen. L3 with medial part approximately as long sag. S3 forming an angle of about 60—70 degrees between each branch, long exsag. Frontal lobe approximately rhombic in outline tending to be of symmetrical anterior and posterior aspects, comprising more than half sagittal length of glabella including the occipital ring, of width tr.
Tubercles of various sizes rather densely distributed on frontal lobe, very coarse in general and frequently tending to be elliptical in outline, coarser and moderately dense in two elongated zones anterolaterally-posteromedially oriented, coarsest and more densely disposed posteromedially, smaller and sparsely developed in the sagittal along the delicately depressed median bandanterior and anterolateral zones, and particularly small and subdued on the entire periphery adjacent to the edge of frontal lobe.
Eye situated with posterior edge opposite of L1, and anterior edge opposite of outer end of S3. Palpebral furrow deep and broad tr. Palpebral lobe elevated with respect to palpebral area, convex in transverse and exsagittal profile, slightly taller in the posterior part; palpebral rim weakly defined. Visual surface outline as a semicircle in dorsal view, inclined and slightly convex in frontal view; composed of ?
Anterior section of facial suture running subparallel to and just laterally of axial furrow near lateral corner of frontal lobe of glabella; posterior section as a convex curve forwards, crossing the genal field towards the inner edge of lateral border opposite posterior part of the eye, then deflected obliquely backwards to reach the cephalic margin in front of genal angle, with a shallow furrow-like depression associated anteriorly.
Base of the eye limited by a moderately deep and short tr. Anterior portion of fixigena vestigial; interocular fixigena strongly reduced to a slopping and very narrow tr. Posterior border moderately narrow exsag. Posterior border furrow deep and relatively broad exsag. Librigenal field steeply sloping, moderately narrow tr. Lateral border weakly concave, approximately as broad tr. Epiborder furrow conspicuous, wide tr.
Lateral border furrow broad tr. Base of genal spine bearing a longitudinal, posterolaterally directed ridge which is a continuation of the anterior edge of the posterior border furrow, and the effaced extension of lateral border furrow, herein abruptly interrupted.
The trilobite Dalmanitoides
Genal spine flattened, evolicion narrow tr. Cephalic doublure incompletely known yet apparently composed of a slightly inflated anterior band and a more depressed posterior region.
Thorax Figure 4 composed of 11 segments. Axial ring short sag. Spiny tubercles evolucjon two median files adjacent to the sagittal plane, continuing along pygidial axis, although more irregularly. Articulating half-ring separated from axial ring by a deep and moderately short sag. Axial furrow shallow and moderately narrow tr.
Pleurae slightly oriented backwards with respect of the axis, with subhorizontal adaxial part wider tr. Anterior pleural band ridge-like, much shorter exsag. Deep and wide exsag. Posterior pleural band convex-topped, long exsag. Distal part of pleurae acuminate. Articulating facet smooth and barely concave anterolaterally. Pygidium Figure 5approximately as long sag.
Total of distinguishable axial rings, convex to barely flattened, egolucion two longitudinal rows of subrounded projections defined by the evoulcion inflated portions of axial rings located immediately adjacent to the sagittal plane, which develop spines in some axial rings. Paired spines on axial rings distributed variably on axial rings 1, 3 to 5, 7 to 9, 11 or 12, and 16; most frequently present on rings 1, 3 and 4, 7 or 8, 12, and Strongly marked axial segmentation evoluciob in the last few effaced axial rings.
Inter-ring furrows moderately long sag. Elongated dorsal sagittal band of effaced segmentation present on the last axial rings, which is progressively broader tr. Terminal piece of effaced ornamentation trilobitess as a long sag. Axial furrows broad tr.