Diplorrhina

Diplorrhina is a genus of trilobites, a well known class of extinct marine arthropods. It lived during the early Middle Cambrian (Amgan and Mayan stages) in what are now the Czech Republic and the North Siberian plateau. Like all agnostina it has a headshield (or cephalon and tailshield (or pygidium of approximately the same shape and size (or isopygeous), and two thorax segments. Like other members of the Peronopsidae family, it lacks a furrow connecting the furrow surrounding the central raise area of the cephalon (or glabella) and the furrow that defines the border of the cephalon. Both the cephalon and the pygidium lack spines. It is difficult to distinguish from many other peronopsids.[2]

Diplorrhina
Temporal range: early Middle Cambrian earliest Amgan to latest Mayan
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Scientific classification
Kingdom:
Animalia
Phylum:
Arthropoda
Class:
Trilobita
Order:
Agnostida
Suborder:
Agnostina
Superfamily:
Agnostoidea
Family:
Peronopsidae
Genus:
Diplorrhina

Hawle & Corda, 1847[1]
species
  • D. triplicata Hawle & Corda, 1847 (type)
  • D. cuneifera (Barrande, 1846) synonyms Battus cuneiferus, Peronopsis cuneifera
  • D. lata (Shabanov, 1972) synonym Peronopsis lata
  • D. redita Pek et Vanek, 1971
  • D. recta (Pokrovskaya et Jegorova, 1972) synonym Peronopsis recta
Synonyms

Mesospheniscus

Taxonomy
Schematic showing the relationship between the genus Diplorrhina (light green) with other Peronopsid genera (darker green).

The ancestor of Diplorrhina is most likely one of the Siberian species of the genus Archaeagnostus. D. recta is the most primitive species and it gave rise to D. cuneifera, which was in turn ancestral to Diplorrhina triplicata.[2]

Species previously assigned to Diplorrhina

Distribution
  • D. triplicata is known from the early Middle Cambrian of the Czech Republic (Eccaparadoxides pusillus and P. gracilis-zones, Skryje Beds, pod hruskou, near Tyrovice and near Ginetz).[1]
  • D. cuneifera has been collected from the early Middle Cambrian of the Czech Republic (Eccaparadoxides pusillus-zone Skryje Beds, near Tyrovice).
  • D. redita occurs in the early Middle Cambrian of the Czech Republic (Paradoxides gracilis-zone, Jince Formation).
  • D. recta was excavated from the early Middle Cambrian of Eastern Siberia (Ovatoryctocara-zone, Molodo River, Olenek Uplift, and Kounamkite-zone, Nekekit River and Amidai River, all Western Jakutia).
  • D. lata is found in the Middle Cambrian of Eastern Siberia (Kounamkites-zone, Nekekit River).[2]

Description

Both the border and the border furrow of the cephalon are relatively narrow. The furrow that divides the glabella in an anterior and posterior part (or transglabellar furrow) is straight or bent slightly rearwards. The posterior lobe is parallel sided, has two pairs of lateral furrows in shape of prominent grooves, or pits small basal lobes, and no median node. The pygidium has a border that is flattened and widened. The pygidium is not entirely subcircular, because posterolateral corners are somewhat developed, but without spines. The lobes of the rhachis are separated by narrow groves (or transaxial furrows) that reach the median node but do not cross the rhachis. The distance between the tip of the rhachis and the border furrow is short or these even touch, but there is no furrow midline that connects the furrows defining the rhachis and the pygidial border.[2]

Differences with Peronopis

Diplorrhina differs from members of the subgenus Peronopsis (Peronopsis) in the better developed transaxial furrows, better developed lateral furrows of the glabella, larger basal lobes, and in the trend towards the formation of a transverse depression of the axis.[2]

gollark: Not necessarily; you could allow doing it without an error.
gollark: And it's not really better than just having tuples and things which are not tuples.
gollark: Nothing stops you from assigning to part of a tuple.
gollark: Not necessarily...
gollark: You could have mutable tuples.

References
  1. Whittington, H. B. et al. Part O, Treatise on Invertebrate Paleontology. Revised, Volume 1 – Trilobita – Introduction, Order Agnostida, Order Redlichiida. 1997
  2. Naimark, E.B. (2012). "Hundred species of the Genus Peronopsis Hawle et Corda, 1847". Paleontological Journal. 46 (9): 945–1057. doi:10.1134/S0031030112090018.
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