Mesonacis wileyi
- Dataset
- New olenelloid trilobites from the Northwest Territories, Canada
- Rank
- SPECIES
- Published in
- Gapp, I. Wesley, Lieberman, Bruce S. (2014): New olenelloid trilobites from the Northwest Territories, Canada. Zootaxa 3866 (4): 479-498, DOI: 10.11646/zootaxa.3866.4.2
Classification
- kingdom
- Animalia
- phylum
- Arthropoda
- class
- Trilobita
- order
- Redlichiida
- family
- Olenellidae
- genus
- Mesonacis
- species
- Mesonacis wileyi
description
Description. Anterior cephalic border developed as a raised ridge, length (sag.) directly anterior of LA is approximately 0.5 times length (sag.) LO; small preglabellar field; anterolateral margin of LA directed posteriorly at approximately 45 degrees; LA length (sag.) equal to the combined length (sag.) of LO and L 1; ocular furrow present; ocular lobes extend back to SO; S 3 convex anteriorly, conjoined adaxially; abaxial margins of L 2 adaxial of abaxial margins of L 3; S 1 and SO both conjoined adaxially; L 1 length (sag.) approximately length (sag.) of LO; abaxial margins of L 1 adaxial to abaxial margins of LO; posterior margin of LO convex posteriorly; extraocular area relatively wide, with prominent anastomosing ridges; posterior border between intergenal angle and LO is parallel to a transverse line; intergenal angle deflected anteriorly at 45 to 50 degrees; genal spine narrow, developed opposite L 1 or S 1, extends back to T 5 or T 6; prothorax consists of 13 (?) segments and opisthothorax about 5 or 6; pleural spines long and directed posteriorly; T 3 is macropleural with spines extending posterior of pygidium; axial spine is present, questionably on T 13, approximately the length (sag.) of the thorax.
diagnosis
Diagnosis. LA does not contact anterior cephalic border furrow; width of extraocular area approximately equal to width (tr.) of glabella at L 1; posterior border between LO and intergenal angle parallel to a transverse line; intergenal angle 45 to 50 degrees relative to a transverse line; genal spines terminate posteriorly opposite T 5 or T 6.
discussion
Discussion. This species is assigned to Mesonacis due to the presence of several character states including: the anterolateral margins of LA are not prominently separated from the extraocular area by a furrow; the lateral margins of each prothoracic axial ring converge when proceeding from anterior to posterior. Further, this species can be distinguished from species of Olenellus based on several character states including: the transverse profile of the ocular lobe is convex dorsally; the intergenal angle is directed anteriorly approximately 45 degrees relative to a transverse line; and finally the thoracic pleural spines on all segments but the third are relatively narrow (tr.) compared with those of most species of Olenellus. Lastly, this species is assigned to Mesonacis, rather than Bristolia on the basis of several character states including: the lateral margins of L 2, when proceeding anteriorly, do not bulge relative to LO; the surface of the interocular area does not slope evenly from the tip of the ocular lobe to the glabella; the width of the interocular area is approximately equal to the width of the ocular lobe at its midlength; and the posterior margin of the thoracic pleural furrow on the third segment is directed evenly posterolaterally.
etymology
Etymology. In honour of Edward O. Wiley, University of Kansas, for his fundamental contributions to the field of phylogenetics.
materials_examined
Type material. Holotype KUMIP 355550. Paratypes KUMIP 355551 and PWNHC- 2013.23.4 - 5. Olenellus zone or Waucoban Series, Dyeran stage, sensu Webster (2011 a, b) and Webster et al. (2011), early Cambrian, Sekwi Formation, Mackenzie Mountains, Northwest Territories, Canada, Section 4, 430 – 435 m above the base of section; Section 3, 700 – 800 m above the base of the section.
Name
- Homonyms
- Mesonacis wileyi