Agraulos Explained

Agraulos is a genus of Solenopleuridae^[1] trilobites that lived during the Middle Cambrian in North America and Europe, particularly the Czech Republic. The genus was named by Hawle & Corda in 1847.^[2]

Etymology

Agraulos is derived from the Greek Greek, Ancient (to 1453);: Ἄγραυλος, "country woman", wife of Kekrops.^[3]

Type species

Type species (designated by Miller 1889).^[4] Arion ceticephalus Barrande, 1846 ^[5] from the Cambrian Eccaparadoxides pusillus Zone in the Skryje Member of the Buchava Formation, within the Skryje–Tyrovice Basin, Bohemia.

Diagnosis

Agraulinae with cephala generally domed; glabella isosceles-trapezoidal, i.e. with truncate front and base angles of the forward-converging lateral margins/flanks more than 15°; occipital ring mesially swollen backwards, with or without a medial node or spine; preglabellar field relatively long (sag.); posterolateral projection of fixigena narrow (tr.); librigenal spines short to long, with some deflected outwards. Thorax of up to 16 segments with first anterior axial rings marked by terrace lines immediately succeeded in some species by rings bearing incipient median nodes or incipient/prominent spines; thoracic segments finely punctate or granulate. Pygidium, small and transverse (Fletcher, 2017, pp, 9,10).

Distribution

• A. ceticephalus (= Arionellus longicephalus Hicks, 1872) ^[6] occurs in the Middle Cambrian Jince Formation of the Czech Republic.^[7] The species was first described from the Skryje Member of the Buchava Formation (Clupáč et al. 1998; Fatka et al. 2011) ^{[8] [9]} on the slopes of the river Berounka in the Týřovice-Luh-Skryje area between Prague (Praha) and Pilsen (Plzen) in the Skryje-Týřovice Basin. The species has been recovered also from the Menevia Formation of St. David's, South Wales (Fletcher, 2017, Fig. 8, I, J, K and Fig. 9, A-C) and, as its junior subjective synonym "Agraulos longicephalus" (Hicks, 1872), from the Nant-y-big Formation (Hypagnostus parvifrons Biozone) of Porth Ceiriad, North Wales (Young et al., 2002; Young et al., 1994, p. 343),^{[10] [11]} the Manuels river formation of Eastern Newfoundland (Martin and Dean, 1988, p. 21, pl.3, figs. 9, 11, 12; non figs. 10 & 13),^[12] and Spain (Sdzuy, 1961, pl.23, ?figs. 8-11, 15).^[13] Fletcher (2017, p. 26) observed that specimens described by Weidner and Nielsen (2015, pl. 41A–F; Fig. 22B) as Agraulos longicephalus ^[14] (from the Middle Cambrian Paradoxides paradoxissimus Superzone of the Alum Shale Formation and within the lower and upper parts of the Ptychagnostus s.l. atavus Zone as well as in the Ptychagnostus punctuosus Zone), are in fact "marked by a conspicuous small median projection on the occipital ring, quite different from any species recorded elsewhere".
• A. socialis (Billings, 1872) occurs in the Manuels River Formation (Drumian Stage) of Eastern Newfoundland where localities include the eastern side of chapel arm in Trinity Bay, Deep Cove in St Mary's Bay, and the Manuels River Section near St John's (Fletcher, 2017, p. 25). Fletcher also observed (op. cit. pp. 25, 26) that "of all the specimens referred to longicephalus, the exoskeleton from the Montagne Noire figured by Courtessole (1973, pl. 10, fig. 5; Fig. 22P) ^[15] appears to be very close to A. socialis, as are Sdzuy's 1961 illustrations of associated Spanish cranidia and a thoracic axis without notable nodes or spines".
• A. affinis (Billings, 1872) derives from the Big Gulley Member green mudstone of the Chamberlain's Brook Formation in the coastal cliffs of the greater Branch Cove on both sides of the Branch River estuary, St Mary's Bay, Newfoundland, originally as part of the Geological Survey of Newfoundland Collection (Fletcher, op. cit, p. 21). The species occurs in association with the Scandinavian taxa Condylopyge carinata Westergärd, 1936 and Parasolenopleura gregaria [''Solenopleura cristata'' Linnarsson, 1877] ^[16] indicating a zonal position about that of Ptychagnostus praecurrens (Fletcher, op.cit.) and Eccaparadoxides oelandicus.
• A. lewisi Fletcher, 2017 (p. 19, fig. 9D-I) is recorded from the Menevia Formation of Porth-y-rhaw, St. David's, Wales and derives from the Hypagnostus parvifrons Biozone (Localities PR-4 and PR-16 of Rees et al., 2014).^[17] The species is also recorded from the parvifrons Zone in the Harlech Dome of North Wales, Clogau Formation, above Rhaiadr Bridge (Fletcher, op. cit. Fig. 8, F & G).

Remarks

Arionellus quadrangularis Whitfield (1884), originally collected from the mid-Cambrian Braintree Formation at Old Hayward Quarry, Quincy, Massachusetts, US, had previously been assigned to Agraulos by Walcott and others.^[18] McMenamin (2002), however, erected Skehanos to accommodate the species as Skehanos quadrangularis.^[19]

Scandinavian species attributed by Westergård (1953)^[20] to Agraulos [i.e. ''A. difformis'', ''A. aculeatus'', ''A. acuminatus'' (all Angelin, 1851), and ''A. anceps''] were transferred by Ahlberg & Bergström (1978)^[21] to Proampyx^[22] although several Lower Cambrian forms they also assigned to Proampyx would later be allocated to various other genera.

Notes and References

1. ANGELIN, N. P. (1854). Paleontologica Scandinavica. Pars 2. Crustacea formationis transitionis. Academiae Regiae Scientiorum Suecanae (Holmiae): I-IX + 21-92).
2. HAWLE, J. & CORDA, A. J. C. 1847. Prodrom einer Monographieder bohmischen Trilobiten. 176 pp. J. G. Calve, Prague
3. J.. VANĚK. J.. VALIČEK. V.. VOKÁČ. 1999. Plutonides hicksi (Salter) from the Middle Cambrian of Skryje - Týřovice Area (Czech Republic). Palaeontologica Bohemiae. 6. 36–38. 2015-01-04.
4. MILLER, S. A. 1889. North American geology and palaeontology for the use of amateurs, students and scientists, 664 pp. Western Methodist Book Concern, Cincinnati, OH.
5. BARRANDE, J. 1846. Notice pre Âliminaire sur le syste Áme silurien et les trilobites de Bohême. Leipzig, 97 pp,
6. HICKS, H. 1872. On some undescribed fossils from the Menevian Group with a note on the Entomostraca by Prof. T. Rupert Jones. Quarterly Journal of the Geological Society of London, 28, 173–185.
7. Web site: Trilobites of the Jince Formation, Czech Republic. S.M. GON III. 2015-01-04.
8. CHLUPÁČ, I., FATKA, O., PROKOP R. J., and TUREK V. 1998. Research of the classical palaeontological locality "Luh" in the Cambrian of Skryje (Barrandian area, Czech Republic). Journal of the Czech Geological Society. 43 (3), 169-174 (in Czech).
9. FATKA, O., MICKA, V., SZABAD, M., VOKÁČ V., VOREL T. 2011. Nomenclature of Cambrian lithostratigraphy of the Skryje-Týřovice Basin, Bulletin of Geosciences 86 (4): 841 - 85
10. YOUNG, T. P., GIBBONS, W., DEAN, W. T. and McCARROLL, D. 2002. Geology of the Country around Pwllheli. Memoir of the British Geological Survey, 1:50,000 Geological Sheet 134 (England and Wales). The Stationery Office, London
11. YOUNG, T. P., MARTIN, F., DEAN W. T. & RUSHTON, A. W. A. 1994. Cambrian stratigraphy of St Tudwal's Peninsula, Gwynedd, northwest Wales, Geo!. Mag. 131 (3), 1994, pp. 335-360
12. MARTIN, F. and DEAN, W. T. 1988. Middle and Upper Cambrian acritarch and trilobite zonation at Manuels River and Random Island, Eastern Newfoundland. Geological Survey of Canada Bulletin, 381, 1-91
13. SDZUY, K. 1961. Das Kambrium Spaniens, Teil II: Trilobiten. Abhandlungen der Mathematisch-Naturwissenschaftlichen Klasse, 8, 597 – 693 [315 – 411]. Akademie der Wissenschaften und der Literatur, Mainz & Wiesbaden
14. WEIDER, T. & NIELSEN, A. T. 2015. Agraulos longicephalus and Proampyx? depressus (Trilobita) from the Middle Cambrian of Borggård, Øle on Bornholm, Denmark. Bulletin of the Geological Society of Denmark, Vol. 63, pp. 1–11
15. COURTESSOLE, R. 1973. Le Cambrien Moyen de la Montagne Noire, Biostratigraphie. Imprimerie d' Oc, Toulouse, 248 pp)
16. LINNARSSON, J. G. O. 1877. Om faunan i lagren med Paradoxides Ölandicus. Geologiska Föreningens i Stockholm Förhandlingar, 3 (12), 352–375.
17. REES, A. J., THOMAS, A. T., LEWIS, M., HUGHES, H. E. & TURNER, P. 2014. The Cambrian of SW Wales: Towards a United Avalonian Stratigraphy. Geological Society, London, Memoirs, 42, 1–30.
18. WALCOTT, C. D. 1884. On the Cambrian faunas of North America. Preliminary studies. United States Geological Survey Bulletin 10, 289-355
19. McMenamin . M.A.S. . 2002 . The ptychoparioid trilobite Skehanos gen. nov. from the Middle Cambrian of Avalonian Massachusetts and the Carolina Slate Belt, USA . Northeastern Geology & Environmental Sciences . 24 . 4 . 276–281.
20. WESTERGÅRD, A. H. 1953. Non-agnostidean trilobites of the Middle Cambrian of Sweden. III. Sveriges Geologiska Undersökning 526, 1 – 58.
21. AHLBERG, P. & BERGSTRÖM, J. 1978. Lower Cambrian Ptychopariid trilobites from Scandinavia. Sveriges Geologiska Undersökning Ca 49, 1 – 41.
22. FRECH, F. 1897, Lethaea geognostica oder Beschreibung und Abbildung der für die Gebirgs-Formationen bezeichnendsten Versteinerungen. I. Theil. Lethaea Palaeozoica. 2. Band. 788 pp. E. Schweizerbarth'sche Verlagshandlung, Stuttgart.