Agraulos ceticephalus ( Barrande, 1846 )

Unger, Tanja, Hildenbrand, Anne, Stinnesbeck, Wolfgang & Austermann, Gregor, 2022, Biostratigraphy and taxonomy of polymerid trilobites of the Manuels River Formation (Drumian, middle Cambrian), Newfoundland, Canada, Geodiversitas 44 (33), pp. 1051-1087 : 1056-1058

Agraulos ceticephalus ( Barrande, 1846)

( Figs 4 ; 5 )

Arion ceticephalus Barrande, 1846: 12 , 13; 1852b: 405-412.

Agraulos ceticephalus – Hawle & Corda 1847: 27; 1848: 143. — Miller 1889: 527. — Pompeckj 1896: 548, pl. 17, figs 12, 13. — Grönwall 1902: 158, 159, pl. 4, fig. 25. — Lorenz 1906: unnamed text fig. p. 67 upper right corner. — Walcott 1913: pl. 15, figs 1, 1a, b. — Wurm 1925: 87, 88, pl. 3, figs 16, 17. — Roch 1930: 132 (?). — Thoral 1935: 50, 51, pl. 3, fig. 12. — Prantl 1952: 262, 263, unnamed fig. p. 264. — Hupé 1953: fig. 120.1; 1955: fig. 96.2. — Šnajdr 1958: 174-177, fig. 37; pl. 36, figs 1-13; 1990: 106, unnamed fig. p. 107. — Horný & Bastl 1970: pl. 4, fig. 9. — Fletcher 1972b: pl. 69, figs 3, 4, 5a-c, 6, pl. 70, figs 1a, b, 2; 2006: pl. 34, fig. 35.; 2017: 11-19, figs 5G-I, 6A-P, 7A-S, 8A-E, H-L, 16B, J, L (partim). — Whittington 1988: 594, text-fig. 14, pl. 55, figs 2, 4, 5, 8, 9; 1992: pls 7, 51. — Fatka 1990: unnamed fig. p. 13 upper right corner; 2011: fig. 17.6. — Müller 1994: 529, fig. 619. — Rudolph 1994: 217, pl. 24, fig. 5. — Cotton 2001: pl. 2, figs 4, 5. — Fletcher et al. 2005: 330, 331, figs 11.1-7. — Fatka et al. 2015: figs 4C, G.

Arionellus ceticephalus – Barrande 1852a: pl. 10, figs 6, 8-21; pl. 11, fig. 7 (partim). — de Verneuil & Barrande 1860: 526, 527, pl. 6, figs 13-17. — Gürich 1908: 19, pl. 5, fig. 2.

Arionellus longicephalus Hicks, 1872: 176 , pl. 5, figs 20-26.

Agraulos longicephalus – Lake 1932: 157-159, pl. 20, figs 2, 7, 10. — Sdzuy 1961: 620-622, figs 32, 33. — Fletcher 1972b: pl. 68, figs 5a-d, 7-11; pl. 69, figs 1, 2; 2006: pl. 34, fig. 34; 2017: figs 22A, B. — Courtessole 1973: 138-140, pl. 10, figs 5, 6, 8-10; pl. 16, figs 12, 13. — Martin & Dean 1988: 21, 22, pl. 3, figs 10, 12, 13 (partim). — Rees et al. 2014: figs 1.8g, h. — Weidner & Nielsen 2014: 47, 48, figs 41A-F; 2015: 5-7, figs 3, 4A-L.

Agraulos longicephalus longicephalus – Liñan & Gozalo 1986: 78, pl. 35, figs 11-14; pl. 36, figs 4, 5 (partim).

Agraulos longicephalus brevilimbarus – Liñan & Gozalo 1986: 78, 79, pl. 35, figs 6-12; pl. 37, figs 1-8.

Agraulos (A.) ceticephalus – Schoenemann & Clarkson 2011: figs 5H, I.

Agraulos affinis – Fletcher 2017: fig. 11F.

Agraulos lewisi Fletcher, 2017: 19-21 , figs 3A-C, 8F, G (partim), n. syn.

Agraulos socialis – Fletcher 2017: 23-27, figs 5J-L, 12A, K-Q, 13I- K, M, N, 14D, G, H, J, 16A, C.

Agraulos 1 – Fletcher 2017: figs 13D, E, 14A, 16F.

Agraulos 2 – Fletcher 2017: figs 14I, 15A-C, 16E (partim).

Skreiaspis punctatissimus – Fletcher 2017: figs 18S, U, W.

LECTOTYPE. — Specimen NM L 12581 (former ČC 345, No. 85 from SBNM collection Barrande), National Museum, Prague, Czech Republic, originally figured by Barrande (1852a) and designated as the lectotype by Šnajdr (1958). From the Buchava Formation, Skreyje Member, Eccaparadoxides pusillus Zone from Skryje-Týřovice Basin , Bohemia, Czech Republic.

DIAGNOSIS. — Portion in front of cranidium domed; front of glabella rounded to truncate; eyes distant at anterior half of glabella; pair of eye ridges expands from front of glabella towards eye lobes (based on Miller 1889; Fletcher 2017, with modifications).

MATERIAL EXAMINED. — 537 cranidia of Agraulos ceticephalus (for NFM numbers see Appendix 1) . 24 specimens are attached to the thorax and seven have at least one librigena attached. The specimens are well to very well-preserved as internal casts and moulds. Some are pyritized and in a few the exoskeleton is preserved . All specimens range between 1.94 and 9.11 m ( Fig. 2 ) of the Manuels River Formation, type locality, Conception Bay South, Newfoundland, Canada.

OCCURRENCE. — Agraulos ceticephalus is a common middle Cambrian trilobite and has been documented from southeastern Canada, eastern Newfoundland, in the Tomagnostus fissus to Ptychagnostus atavus zones ( Fletcher et al. 2005), Ptychagnostus atavus to Hypagnostus parvifrons zones ( Fletcher 2017), and Paradoxides hicksi Zone ( Fig. 2 ). It has also been reported from the United Kingdom in Wales ( Hypagnostus parvifrons zone ; Rees et al. 2014), Denmark ( Acidusus atavus zone ; Weidner & Nielsen 2014, 2015), in Bornholm ( Ptychagnostus punctuosus zone ; Rudolph 1994), France ( Thoral 1935), Germany ( Wurm 1925), the Czech Republic ( Eccaparadoxides pusillus zone ; e.g., Šnajdr 1990; Fletcher et al. 2005), and Spain ( Pardailhania and Solenopleuropsis zones; Liñan & Gozalo 1986).

DESCRIPTION

The cranidia range from 3.0 mm to 16.0 mm in width and from 2.0 mm to 11.0 mm in length. The shape of the glabella varies from slightly trapezoidal to more equal-sided, with a rounded to truncate front. Three to four pairs of glabellar furrows are preserved mainly in larger-sized specimens.In small-sized specimens, the glabella is steeply domed, while it is flatter in largesized specimens.Nevertheless, the glabella is always more domed than the cheeks.Eye ridges, if preserved, initiate near the front of the glabella and connect with the eye lobes in a horizontal line, some line in a backwards angle towards the sides. The occipital ring points backwards roughly triangularly and the length of the spine varies with size. Some moulds of cephala connected to the thorax spare spines to nodes on up to five axial segments. These and an ornamentation are usually preserved on moulds. Several cephala show up to three variably pronounced grooves. One of these reaches from the front of the glabella to the anterior margin.The other two are developed towards the sides, varying in position. The front of the cranidium is highly domed but a lateral view and microscope measurements indicate that this is an optical illusion and it is still rather flattened domed.

REMARKS

Agraulos ceticephalus and Agraulos longicephalus are closely related species (e.g., Hicks 1872; Lake 1932; Sdzuy 1961; Weidner & Nielsen 2015) and both show a wide range of intraspecific variations, e.g. regarding the front of glabella or size and projection of the occipital spine ( Barrande 1852b; Lake 1932; Sdzuy 1961). Barrande (1852b) documented ontogenetic changes in Ag. ceticephalus . He emphasized an increase in depth of the occipital furrow and dorsal furrows, less domed genal regions, and an increase in the thickness of exoskeletons in adult forms. The latter was also identified in Ag. longicephalus by Lake (1932). Accordingly, the development of glabellar, axial and other furrows as well as the occipital ring are not considered to be reliable diagnostic characteristics. Also, specimens with a preserved exoskeleton may show morphological details not identified in internal casts ( Lake 1932; Sdzuy 1961). Despite the numerous descriptions and discussions about differences between Ag. ceticephalus and Ag. longicephalus , differentiation is hence questionable and this work agrees with Weidner & Nielsen (2014) that the genus Agraulos requires revision.

Barrande (1852a) illustrated several specimens of Ag. ceticephalus . The articulated specimens figured by the author on pl. 10, figs 1-5, and the cranidium on pl. 10, fig. 7, do not show the characteristic long preglabellar area of the genus Agraulos and are here excluded from Ag. ceticephalus , and even the genus. An enrolled specimen illustrated in lateral view of Barrande (1852a: pl. 10, fig. 21) shows no diagnostic characteristics and assignment to Agraulos is questionable. Hicks (1872) first described Ag. longicephalus based on a longer form and a more domed genal region than seen in Ag. ceticephalus . However, all cranidia figured by Hicks (1872), some attached to the thorax, are deformed, some elongated, and others compressed in length, as already mentioned by Fletcher (2017). The longer form of the cephalon is here interpreted as a result of tectonic deformation and the more domed genal region may also represent a preservational artefact. All seven type specimens illustrated byHicks (1872) are here assigned to Ag. ceticephalus . Roch (1930) also referred to the similarity of Ag. ceticephalus and Ag.longicephalus . He compared specimens from Morocco and Algeria to Ag. ceticephalus from the type locality in Central Europe. Nevertheless, the assignment of the material to Ag. ceticephalus is questionable as no illustrations were presented byRoch (1930) and no information given regarding the number of studied specimens. Lake (1932) also discussed the morphological differentiation of Ag. longicephalus and Ag. ceticephalus . According toLake (1932) Ag. longicephalus has an occipital ring ending in a triangular point and a more truncate glabella.However, Sdzuy (1961) suggested that the form of the occipital spine, or occipital node, is a variable characteristic and unsuited to define Agraulos . We here follow this latter view and interpret the more truncate glabella to fall within the intraspecific variation of Ag. ceticephalus . The presented specimens are here assigned to this latter species.

Sdzuy (1961) described a variable shape of the occipital ring of Ag.longicephalus , stating the shape as non-diagnostic. He followed Lake (1932) in that Ag.longicephalus is closely allied to Ag. ceticephalus but that the glabella of Ag. longicephalus is slightly more narrowed towards the front,and mentioned a more domed genal region. We rather suggest that the domed genal region of Ag. longicephalus results from preservational bias and that the narrowed front of the glabella ranges within the intraspecific variation of Ag. ceticephalus . Hence, all cranidia illustrated by Sdzuy (1961) are here assigned to Ag. ceticephalus . Cranidia assigned to Ag.longicephalus byFletcher (1972b) andCourtessole (1973) also show the characteristics of Ag. ceticephalus and are here assigned to this species. Liñan & Gozalo (1986) described two subspecies of Ag. longicephalus based on a more extended, respectively narrower preglabellar area compared to the border. These variations are also interpreted here as an intraspecific variation of Ag. ceticephalus and both subspecies are considered to be synonyms of the latter species. This interpretation includes cranidia, some attached to the thorax, illustrated by Liñan & Gozalo (1986: pl. 35, figs 11-14, pl. 36, fig. 4, pl. 36, fig. 5), whereas cranidia illustrated by the authors in plate 36, figs 1-3, do not show the long preglabellar field typical for Agraulos and are here excluded from the species and even the genus.Specimens documented by Martin & Dean (1988) as Ag. longicephalus are here assigned to Ag. ceticephalus , except for pl. 3, figs 9 and 11. These images display the same cranidium devoid of a wide preglabellar field and are therefore atypical for Agraulos . Fletcher (2006) displayed Ag.ceticephalus and Ag.longicephalus . The two cranidia figured by the author have distant eyes and a rounded to truncate glabella; the cranidium illustrated on pl. 34, fig. 34, is here assigned to Ag. ceticephalus . Specimens presented by Rees et al. (2014) and Weidner & Nielsen (2014, 2015) as Ag. longicephalus show the characteristics of Ag. ceticephalus and are hence assigned to this species.

Fletcher (2017) described and illustrated several species of Agraulos . The cranidium illustrated in fig. 11F was assigned to Agraulos affinis Billings, 1872 , by Fletcher (2017), but the specimen has eyes distant to the glabella. This character disagrees with the diagnosis of Ag. affinis , in which eyes are located close to the glabella. Instead, the position of the eyes matches that seen in Ag. ceticephalus and the specimen is here assigned to this species. Specimens illustrated in fig. 9A-C as Ag. ceticephalus , on the other hand, display cranidia too deformed to determine the species. Specimens figured by Fletcher (2017: figs 9D-I) as Agraulos lewisi Fletcher, 2017 are also too poorly preserved to be assigned specifically. Figures 3A and 8F of Fletcher (2017) reillustrated the same articulate and distorted specimen figured previously by Lake (1932: pl. 20, fig. 3). Fletcher (2017) edited the images using Photoshop ( Fletcher 2017: figs 3B, C, 8G). The figures 3C and 8G show the same image. The single specimen illustrated in figs 3A-C and 8F, G as Ag. lewisi clearly shows the characteristics of Ag. ceticephalus . The diagnosis of Ag. lewisi presented by Fletcher (2017) is not unique to the species, and characteristics as a “librigenal spine extending back to the posterior end of the third thoracic pleura” and “prominent stout median spines on the succeeding five rings” ( Fletcher 2017) cannot be applied to the illustrations. Another characteristic, i.e. the “sharply pointed occipital spine”, is undiagnostic as discussed above. Consequently, Ag. lewisi is here interpreted to be a synonym of Ag. ceticephalus . Cranidia attributed byFletcher (2017) to Ag.longicephalus and illustrated in figs 22A, B show eye ridges characteristic of Ag. ceticephalus and are here assigned to this species. Fletcher’s (2007: figs 5J-L, 12A, K-Q, 13I-K, M, N, 14D, G, H, J, 16A, C) display cranidia, or cranidia attached to the thorax, and were attributed by the author to Agraulos socialis Billings, 1872 . Nevertheless, these illustrated specimens morphologically agree with Ag. ceticephalus and are here assigned to this species.A new species, Agraulos 1 Fletcher, 2017, was introduced without a formal diagnosis or description. Fletcher (2017) only states that the “new species status is marked by the less trapezoidal aspect of the cranium with a longish occipital spine significantly different from associated similar-sized ceticephalus cranidia”. These differences are here interpreted as intraspecific variations of Ag. ceticephalus . Therefore, the cranidia illustrated by Fletcher (2017: figs 13D, E, 14A, 16F) match the characteristics of Ag. ceticephalus and Agraulos 1 is here interpreted as synonym of Ag. ceticephalus . Fletcher (2017) also described the new species Agraulos 2 ( Fletcher 2017: figs 14I, 15A-C, 16E) which is here also interpreted as an intraspecific variation of Ag. ceticephalus , while cranidia illustrated in figures 15D, E are too poorly preserved to be assigned to any species. Fletcher (2017) described Skreiaspis punctatissimus as a new species and illustrated several specimens.Cranidia illustrated in figures 18S, U and W do not show the short preglabellar field characteristic for Skreiaspis , but rather match Ag. ceticephalus .

Figures

FIG. 4. — Agraulos ceticephalus (Barrande, 1846): A, internal cast of a cranidium attached to the thorax with preserved exoskeleton (NFM F-3476 from 5.97 m); B, internal cast of a cranidium attached to the thorax, partly covered with sediment, eye ridges and glabellar furrows slightly visible (NFM F-3951 from 7.10 m); C, internal cast of a cranidium attached to the thorax with preserved exoskeleton, eye ridges present (NFM F-3957 from 3.30 m); D, internal cast of a cephalon attached to the thorax, librigena attached, eye ridges present (NFM F-3621 from 9.08 m); E, mould of a cranidium attached to the thorax, spines on axial rings present,coarse ornamentation on thorax visible (NFM F-3476 from 5.98 m); F, mould of a cranidium attached to the thorax,occipital spine preserved (sedimentary filling laying in glabellar mould), coarse ornamentation on thorax visible (NFM F-3946 from 4.27 m); G, internal cast of a cranidium attached to the thorax, projection of axial spine preserved (NFM F-3831 from 7.43 m); H, internal cast of a cranidium attached to the thorax, eye ridges present (NFM F-2787 from 7.56 m); I, internal cast of a cranidium attached to first thoracic segments, eye ridges and glabellar furrows preserved (NFM F-3778 from 5.96 m). Scale bars: 1 mm.

FIG. 5. — Agraulos ceticephalus (Barrande, 1846): A, internal cast of a cranidium, eye ridges present, two grooves visible (NFM F-2785 from 1.96 m); B, internal cast of a cranidium, one groove visible, occipital ring triangular in shape with projection of spine preserved (NFM F-3062 from 2.10 m); C, internal cast of a cranidium, occipital ring ending in a spine (NFM F-2841 from 2.40 m); D, internal cast of a cranidium, projection of occipital spine preserved (NFM F-2919 from 2.44 m); E, internal cast of a cranidium, eye ridges and occipital spine preserved (NFM F-2846 from 2.53 m); F, internal cast of a cranidium, eye ridges present, projection of occipital spine preserved (NFM F-3321 from 5.52 m); G, internal cast of a cranidium, eye ridges present, projection of occipital spine preserved (NFM F-2863 from 2.52 m); H, internal cast of a cranidium, two grooves visible,profile on the right shows that front is not as domed as it seems in overview (NFM F-3225 from 5.19 m). Scale bars: 1 mm.

FIG. 2. — Lithology of the type locality of the Manuels River Formation, range chart of the here described species. Agnostid biozones from Hildenbrand et al. (2021) and polymerid biozones from Howell (1925).

FIG. 3. — Visualization of measurement terms in cranidia (A) and pygidia (B).

FIG. 8. —Bailiella aequalis (Linnarsson,1882) internal cast of a cranidium (NFM F-3811 from 5.90 m). Scale bar: 1 mm.