A new Cambrian catillicephalid trilobite from the Shallow Bay Formation of western Newfoundland, Canada

A new Cambrian catillicephalid trilobite from the Shallow Bay Formation of western Newfoundland, Canada. Acta Palaeontologica Polonica 67 (1): 27–33. Species of Catillicephala are known from sites around the mid-Cambrian margin of Laurentian North America, including Vermont, Quebec, Newfoundland and North Greenland. Catillicephala cifellii sp. nov. is from the Downes Point Member of the Shallow Bay Formation (Cow Head Group) in western Newfoundland. It occurs in three shelf margin-derived boulders in debris flow conglomerates that accumulated in a continental slope setting. The associated trilobites and agnostoid arthropods, including Ptychagnostus aculeatus and Megagnostus glandiformis , indicate a correlation with the Lejopyge laevigata Zone. As such, C. cifellii is among the oldest representatives of the genus, and is early Guzhangian in age. which per-mits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.


Introduction
The Cow Head Group of western Newfoundland (James and Stevens 1986) is a succession of Cambrian to Lower Ordovician continental slope strata that includes debris flow conglomerates (assigned to the Shallow Bay Formation) containing carbonate boulders that yield abundant trilobites (Kindle and Whittington 1958;Kindle 1982). Along with fossiliferous boulders from Quebec (e.g., Rasetti 1946Rasetti , 1948, the conglomerates provide a record of the faunas of a Laurentian shelf-margin that was destroyed during the Taconic orogeny, and have been characterized as the remnants of a "lost faunal realm" (Pohler et al. 1987).

Geological setting
The study area lies in the Cow Head region of western Newfoundland. The trilobites were collected from three boulders (BPS 458,467,468) in a 20-m-thick interval of amalgamated debris flow conglomerates exposed along the shore to the south of Broom Point (Broom Point South section of James and Stevens 1986). Westrop et al. (1996: fig. 4) provided a locality map and stratigraphic column that shows where the boulders were collected. The conglomerate beds are part of the oldest Downes Point Member of the Shallow Bay Formation (see James and Stevens 1986, for an exhaustive account of the stratigraphy and sedimentology of the Cow Head Group, including the Shallow Bay Formation).
The boulders that yielded Catillicephala cifellii sp. nov. also contain agnostoid arthropods (Westrop et al. 1996) that provide a constraint on the age of the species. It is associated with Ptychagnostus aculeatus (Angelin, 1851), in BPS 458, with Megagnostus glandiformis (Angelin, 1851), in BPS 468, and with Kormagnostus cf. K. seclusus (Walcott, 1884), in BPS 467 and BPS 468. These indicate a correlation with the Lejopyge laevigata Zone (Westrop et al. 1996), which is the oldest zone (Peng et al. 2009) of the Guzhangian (Miao lingian; Zhao et al. 2019). Associated trilobites that have been named in recent papers include Hysteropleura (Verditerrina) adraini Ludvigsen, 2000, in BPS 468, andHolmdalia lata Westrop andDengler, 2017, in boulders BPS 458, 467, 468. Numerous other trilobites remain to be documented from these boulders, including undescribed species of Bynumia Walcott, 1924, Prolonchocephalus Palmer in Palmer and Peel, 1981, and Onchonotopsis Rasetti, 1946 The other records of Catillicephala comes from material from shelf margin sites of Laurentia, including boulders in conglomerate beds in Vermont (Shaw 1952), Quebec (Rasetti 1946;Westrop and Dengler 2014a) and Newfoundland (Westrop and Dengler 2014a), as well as in situ specimens from Greenland in shallow (Palmer in Palmer and Peel 1981) and deep subtidal  settings. Catillicephala cifellii sp. nov. is most likely the oldest known species from shelf-margin derived boulders, and an indeterminate species from deep subtidal facies in Greenland (= C. rotundata of Robison 1988; see Westrop and Dengler 2014a: 97) is also from the Lejopyge laevigata Zone.

Material and methods
Illustrated material is housed at the Geological Survey of Canada, Ottawa (GSC). Depth of field was maximized by rendering digital images from stacks of images focused at 200 micron intervals using Helicon Focus 4.0 for the Macintosh.
Proportions expressed in percentages in descriptions and diagnoses are means, with the following pair of numbers indicating the range of values. All measurements were made on digital images of specimens in Figs. 1-3 to the nearest tenth of a millimetre using the Measure Tool of Adobe Photoshop ™.
Remarks.-Catillicephala was revised by Westrop and Dengler (2014a) and their diagnosis is followed here.
Catillicephala cifellii sp. nov. Material.-The type material and two pygidia from boulder BPS 467; two cranidia and two pygidia from boulder BPS 458. All from the type locality.
Pygidium strongly arched, semicircular in outline, length equal to 70% (65-78%) of maximum width, with anterior margin angled back, and conspicuous articulating facet at anterior corner. Axis inflated, rising well above pleural field; gently tapered and well-rounded posteriorly; long, overhanging posterior margin slightly on largest specimens (e.g., Fig. 3A 1 , B 2 ), with width at anteriormost axial ring equal to 37% (34-40%) of maximum pygidial width. Articulating half-ring conspicuous, roughly semielliptical in outline; articulating furrow broad, roughly equal in length to half-ring. Broad, transverse ring furrows generally faint. Up to four rings and a terminal piece comprising at least two segments evident (e.g., Fig. 3A 1 , B 2 ). Pleural field flexed downward; one well-defined pleural furrow expressed on external surface, remainder faint, although better defined on internal moulds. Border furrow faint but clearly defined; border downsloping. External surface save for furrows finely pitted; posterior edge of border with terrace ridges (e.g., Fig. 3B 1 ).
Ontogeny.-A series of differently sized cranidia show that the occipital spine develops during holaspid ontogeny. The smallest cranidium (Fig. 1D) has a short, aspinous LO that occupies only 21% of glabellar length, although there is an ill-defined node present. LO becomes longer (occupying 24% of glabellar length) and more triangular in outline in a somewhat larger specimen (Fig. 1C 1 ) but, although a node may be present, it is not yet spinose. By the time a distinct spine appears, LO accounts for 32% of glabellar length (Fig. 2D), and the incompletely preserved spine of the larger holotype is also part of a very long LO (Fig. 1A 1 ). The axial furrows become increasingly bowed outwards, producing a distinctly barrel-shaped glabellar outline (compare Fig. 1A 1 , B, C 1 , D). Smaller individuals have better defined lateral glabellar furrows (Fig. 1C 1 , D). The pygidial axis is very long in all specimens. It terminates just short of the pygidial margin in smaller specimens (e.g., Fig. 3C 2 ) but extends to overhang the margin slightly in larger individuals (Fig. 3A 1 , B 2 ).
Remarks.-The conspicuous glabella that overhangs a very short anterior border and pygidium with a strongly convex, gently tapered axis ally Catillicephala cifellii sp. nov. with the other members of the genus that were revised by Westrop and Dengler (2014a). The spinous, triangular occipital ring of larger individuals (Figs. 1A, 2D) is unique. Catillicephala cifellii sp. nov. is most like C. rotunda (Rasetti, 1946) from the Grosses-Roches Formation, Métis-sur-Mer area, Quebec. The latter species has a tapered occipital ring with a rounded to bluntly pointed terminus (e.g., Westrop and Dengler 2014a: figs. 3D, 4B, G) that resembles the condition in small specimens of C. cifellii (Fig. 1D), albeit without an occipital node. Unlike C. cifellii, the occipital ring of C. ro tunda does not develop a spine, even in the largest individuals. In addition, C. rotunda has a more bulbous glabella that is well-rounded anteriorly, and has narrower (tr.) posterior area of the fixigena. In the largest pygidia of C. rotunda, the axis terminates short of the posterior margin (e.g., Westrop and Dengler 2014a: fig. 5A-C), whereas similarly sized pygidia of C. cifellii have longer axes that overhang the pygidial margin (e.g., Fig. 3A, B) Compared to C. cifellii, C. impressa (Rasetti, 1946) has a far more rounded preoccipital region of the glabella that is subcircular in outline and usually has a medial backward expansion that constricts the occipital furrow (e.g., Westrop and Dengler 2014a: figs. 7A, I, 8E, 9B). The anterior border furrow of C. impressa is effaced medially across almost the entire width of the glabella (e.g., Westrop and Dengler 2014a: figs. 7D, 8F, I, 9C, F, I), whereas C. cifellii has a shallow but complete border furrow (Figs. 1A 3 , C 3 , 2A 3 ).
Catillicephala shawi Westrop and Dengler, 2014a, differs from C. cifellii in having a subquadrate glabella that expands gently forward, an occipital furrow that shallows medially, and, as in C. impressa, the anterior border furrow is effaced in front of the glabella (e.g., Westrop and Dengler 2014a: figs. 14, 15). Like C. cifellii, the pygidium of C. calva Westrop and Dengler, 2014a, has a convex axis that overhangs the posterior margin. The cranidia of these two species are differentiated readily. In addition to lacking an occipital spine, C. calva has a relatively narrow, forwardly expanding glabella that contrasts with the barrel-shaped glabella of C. cifellii (compare Fig. 1A, B with Westrop and Dengler 2014a: fig. 19).
Stratigraphic and geographic range.-Type locality and horizon only.

Concluding remarks
Studies of the faunas of the Cow Head Group of western Newfoundland continue to expand the diversity of trilobites known from mid-to upper Cambrian paleoenvironments at the edge of the continental shelf of Laurentian North America (e.g., Dengler 2014a, b, 2017). Catillicephala cifellii sp. nov. is the oldest member of Family Catillicephalidae, which may be a large clade with representatives that range throughout the upper Cambrian (e.g., Ludvigsen et al. 1989). on the Cambrian faunas of the Cow Head Group was supported in part by a succession of grants to SRW from the Natural Sciences and Engineering Research Council of Canada and the National Science Foundation (USA).