Nobiliasaphus nobilis BARRANDE 1846

 

Nobiliasaphus nobilis is one the most frequently encountered asaphids of the Armorican Llanvirn (Brittany, France). It can be found in the Spanish Ordovician, as this is the case for the first specimen of that page. Even if my pictures don't show it that well, this is odd to remark that the 2 specimens do have exactly the same delicate golden color :)

 

Specimen description :

  • Almost complet specimen.
  • Lack of left genal spine.
  • On matrix.
  • Total size : 22 mm
  • Lower Middle Ordovician - Llandeilian.
  • Calzada de Calatrava.
  • Ciudad Real, Spain.
Dorsal view of the positive.
Ventral view of the negative.

 

Diagnosis :

 

Order

 

Asaphida

 

 

SALTER 1864

 

 

 Order including 1/5 of all the species of Trilobites, it mostly regroup librostoms of various morphology, in which the most advanced families do present a ventral median suture early visible in the ontogeny ( "asaphoïd" protaspid larvæ).

Occurrence : Middle-Upper Cambrian boundary to upper Ordovician-lower Silurian.

  • Cephalon : Opisthoparian.
  • Often equal / subequal to pygidium (e.g., Asaphoidea), but some not so (e.g., Trinucleioidea).
  • Usually with a high degree of cephalic effacement so glabellar furrows are faint or not visible.
  • Eyes usually large (some forms secondarily blind).
  • Preoccipital glabellar tubercle in late forms.
  • Cephalic doublure often wide, with terrace ridges.
  • Librigenæ are typically separated by a median ventral suture.
  • Dorsal anterior facial sutures often curve adaxially to meet in front of the glabella.
  • Hypostome conterminent or impendent, with only primitive forms (e.g., the Anomocaroidea) natant.
  • Thorax : Typically 5 – 12 segments, but 2 - 3 in a few Trinucleioidea, 13+ in some Anomocaroidea, up to 30 in an Alsataspidid (Trinucleioidea).
  • Pygidium: Typically large (subisopygous to macropygous).
  • Wide doublure.

Superfamily

Asaphoidea

BURMEISTER 1843

Occurrence: Middle Cambrian to Ordovician.

  • Cephalon : Preoccipital glabellar tubercle.
  • Glabella elongate, subparallel to tapering forward.
  • Defined occipital ring.
  • Curved, apostrophe-like pair of basal glabellar furrows isolated within glabella.
  • Hypostome conterminant, fixed to the doublure (rarely impendent)
  • Thorax : 6 - 9 segments, typically 8.
  • Pygidium : Typically rounded.
  • Typically without spines, sometimes with a terminal spine or pair of spines (e.g., Thysanopyginae).

Family

 

Asaphidæ

BURMEISTER 1843

Family tends toward loss of apparent segmentation of cephalon and pygidium, obsolescence of axial furrows and deep notching of posterior margin of hypostoma.

  • Cephalon : Librigenæ separated anteriorly by a median suture.
  • Asaphoïd with well defined to obsolete glabella, considerably longer than frontal area.
  • Lateral glabellar furrows mostly weaks or absent.
  • Most genera with distinct glabellar tubercule.
  • Eyes generally somewhat distant from axial furrows.
  • Faint, almost obsolete eye ridges only know in 2 genera.
  • Doublure commonly broad.
  • Genal spines generally short and with a wide basis.
  • Posterior margin of hypostoma varying from pointed (later forms) to deeply notched and/or with panderian openings.
  • Thorax : 8 segments.
  • Pleural furrows generally diagonal, if present.
  • Panderian organs developped as notches or separate openings, but absent in some (e.g., Ogygiocaridinæ, Symphysurininæ).
  • Pygidium : External margin varying from rounded to pointed.
  • Some genera with terminal spine.

Subfamily

 Asaphinæ

BURMEISTER 1843
  • Cephalon : Glabella commonly expanded in front of eyes.
  • Posterior lateral furrows commonly strong, obliquely directed, mostly deeper than part of axial furrows laterally delimiting posterior lateral glabellar lobe.
  • Glabellar tubercle situated immediately in front of occipital furrows or of area corresponding to this furrow.
  • Posterior border furrow generally distinct.
  • Panderian organs developped as notches or separate openings.
  • Anterior wings of hypostoma broad (tr.), more or less quadrangular in outline.
  • Posterior margin of hypostoma with deep notch (except Aulacoparia).
  • Pygidium : Ribs of pleural field unfurrowed, if present, or rarely with faint furrows.
  • Posterior margin rounded.
  • Without spine.

Genus

Nobiliasaphus

PRIBYL & VANEK 1965
  • Cephalon : Glabella well defined (sag. and tr.).
  • Median glabellar lobe linguoidal.
  • Preglabellar area large, equivalent to 2/5 of the cephalic length.
  • Anterior branches of the facial sutures semi-circular, intramarginal, forming an angle of 40 to 70° with the sagital axis.
  • Pygidium : Parabolic.
  • Sometimes median marginal spine.
  • 17 axial rings.
  • 16 pairs of pleural ribs max.
  • The inner part of the rings and the inter-ring furrows have a broad "V" shape.
  • Terrace lines quasi-parallel to the pygidial border.

Species

nobilis

BARRANDE 1846

 
  • Cephalon : Glabella slightly convex, 2/3 of the cephalic length.
  • Anterior branches of the facial sutures forming an angle of 70° with the sagital axis.
  • Pygidium : Parabolic.
  • No marginal spine.
  • spindle-shaped axis, ¾ of the pygidial length.
  • 6 - 7 distinct axial rings.
  • 8 - 9 pairs of ribs.

 

Complementary pictures :

 

Synthetogram of the cephalon (D'après P. Lebrun, 2002)

 

Specimen of Brittany, France :

Trilobite found in the synclinorium of Laval.

 

ventral view of the positive part.
Zoom on the terrace lines of the cephalic border.

 

Diagnosis of Nobiliasaphus delessei (DUFET 1875) :

In Brittany, Nobiliasaphus delessei (DUFET 1875) can be collected in the Abereidian of the formation d'Angers.

Species

delessei

DUFET (1875)

 
  • Cephalon : Glabella long, slightly convex, 3/4 of the cephalic length..
  • Preglabellar area narrow.
  • Anterior branches of the facial sutures forming an angle of 55° with the sagital axis.
  • Pygidium : Axial length of ¾ of the pygidial length.
  • 5 - 6 distinc axial rings.
  • 6 - 7 pairs of pleural ribs that don't reach the marginal border.
  • Long fine median marginal spine, of circular section.
  • Doublure covering more of half of the surface of the pygidium.

So, the important differential diagnostic point is the lack of median marginal pygidial spine for Nobiliasaphus nobilis.

Synthetogram of Nobiliasaphus delessei. (After P. lebrun 2002).

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