Echidnacaris briggsi ( Nedin, 1995 ), 2023

Paterson, John R., Garc ́ ıa-Bellid, Diego C. & Edgecomb, Gregory D., 2023, The early Cambrian Emu Bay Shale radiodonts revisited: morphology and systematics, Journal of Systematic Palaeontology (2225066) 21 (1), pp. 1-29 : 15-21

publication ID	https://doi.org/ 10.1080/14772019.2023.2225066
publication LSID	lsid:zoobank.org:pub:AEFDB294-AE8F-426D-9805-FC701798A986
DOI	https://doi.org/10.5281/zenodo.10987558
persistent identifier	https://treatment.plazi.org/id/039B87D4-FF8F-AE26-B15F-ACB46F87FAE8
treatment provided by	Felipe
scientific name	Echidnacaris briggsi ( Nedin, 1995 )
status

Treatment

Echidnacaris briggsi ( Nedin, 1995)

( Figs 7C, D View Figure 7 – 16 View Figure 16 )

1992 Anomalocaris sp. ; Nedin: 221.

1993 Anomalocaris sp. ; McHenry and Yates: 77–81, 84–85, figs 2–8.

1995 Anomalocaris briggsi Nedin : 31–35, figs 1, 3A.

1997 Anomalocaris briggsi Nedin ; Nedin: 134.

1999 Anomalocaris briggsi Nedin ; Nedin: 989.

2002 Anomalocaris briggsi Nedin ; Hagadorn: 98.

2006 Anomalocaris briggsi Nedin ; Van Roy and Tetlie: 240, 244, fig. 1A.

2006 Anomalocaris briggsi Nedin ; Paterson and Jago: 43.

2008 Anomalocaris briggsi Nedin ; Hendricks, Lieberman, and Stigall: table 1.

2008 Anomalocaris briggsi Nedin ; Paterson, Jago, Gehling, Garćıa-Bellido, Edgecombe, and Lee: 320.

2009 Anomalocaris briggsi Nedin ; Garćıa-Bellido, Paterson, Edgecombe, Jago, Gehling, and Lee: 1221.

2010 Anomalocaris briggsi Nedin ; Daley and Peel: 354.

2011 Anomalocaris briggsi Nedin ; Jago and Cooper: 239.

2011 Complex arthropod eyes; Lee, Jago, Garćıa-Bellido, Edgecombe, Gehling, and Paterson: 631, figs 1a–c, 2, SI figs 1–3.

2011 Anomalocaris briggsi Nedin ; Paterson, Garćıa-Bellido, Lee, Brock, Jago, and Edgecombe: 239, SI fig. 2.

2012 Anomalocaris briggsi Nedin ; Jago, Gehling, Paterson, Brock, and Zang: 252.

2013 Anomalocaris briggsi Nedin ; Q. Liu: 339, 340.

2013 Anomalocaris briggsi Nedin ; Daley, Budd, and Caron: 782.

2013 Anomalocaris briggsi Nedin ; Daley, Paterson, Edgecombe, Garćıa-Bellido, and Jago: 972–973, figs 1, 2, 4.

2014 Anomalocaris briggsi Nedin ; Vinther, Stein, Longrich, and Harper: 497, 498, ext. data fig. 6b.

2014 Anomalocaris briggsi Nedin ; Daley and Edgecombe: 90.

2014 Anomalocaris briggsi Nedin ; Lerosey-Aubril, Hegna, Babcock, Bonino, and Kier: 275, fig. 3.

2014 Anomalocaris briggsi Nedin ; Cong, Ma, Hou, Edgecombe, and Strausfeld: ext. data fig. 4.

2015 Anomalocaris briggsi Nedin ; Van Roy, Daley, and Briggs: ext. data fig. 10.

2016 Anomalocaris briggsi Nedin ; Paterson, Garćıa-Bellido, Jago, Gehling, Lee, and Edgecombe: 3, 5, fig. 4a, b.

2016 Anomalocaris briggsi Nedin ; Jago, Garćıa-Bellido, and Gehling: 549.

2017 Anomalocaris briggsi Nedin ; Zeng, Zhao, Yin, and Zhu: 2.

2017 Anomalocaris briggsi Nedin ; Pates and Daley: 468.

2018 Anomalocaris briggsi Nedin ; Bicknell and Paterson: 769.

2018 Anomalocaris briggsi Nedin ; Cong, Edgecombe, Daley, Guo, Pates, and Hou: 615, 619.

2018 Anomalocaris briggsi Nedin ; Lerosey-Aubril and Pates: 4, 5, fig. 3b.

2019 Anomalocaris briggsi Nedin ; Guo, Pates, Cong, Daley, Edgecombe, Chen, and Hou: 100, 105, 107.

2019 Anomalocaris briggsi Nedin ; Pates, Daley, and Butterfield: 3, 4, 8.

2019 Anomalocaris briggsi Nedin ; Pates and Daley: 1235, 1237, 1239, 1240, 1242, fig. 6e.

2019 ‘ Anomalocaris ’ briggsi Nedin ; Moysiuk and Caron: 8.

2020 ‘ Anomalocaris ’ briggsi Nedin ; Paterson, Edgecombe, and Garćıa-Bellido: 2–8, figs 1, 2, 5A, B.

2021 Anomalocaris briggsi Nedin ; Pates, Daley, Edgecombe, Cong, and Lieberman: 237, 252.

2021 Anomalocaris briggsi Nedin ; Wu, Fu, Ma, Lin, Sun, and Zhang: 209–211, 216–219, fig. 4e.

2021 ‘ Anomalocaris ’ briggsi Nedin ; Jiao, Pates, Lerosey-Aubril, Ortega-Herńandez, Yang, Lan, and Zhang: 263, 267–271.

2021 Anomalocaris briggsi Nedin ; Moysiuk and Caron: 718.

2021 ‘ Anomalocaris ’ briggsi Nedin ; Caron and Moysiuk: 13–14.

2022 ‘ Anomalocaris ’ briggsi Nedin ; Wu, Pates, Ma, Lin, Wu, Zhang, and Fu: 9.

2023 Anomalocaris briggsi Nedin ; Zeng, Zhao, and Zhu: 14, 15.

2023 ‘ Anomalocaris ’ briggsi Nedin ; Potin and Daley: 8, 11, 12, 18, figs 5C, 6I–K.

Holotype. SAMA P40180 About SAMA ; frontal appendage ( Fig. 8 View Figure 8 ). Originally referred to as AUGD 1046-630 View Materials by Nedin (1995, fig. 1A).

Paratype. SAMA P40763 About SAMA ; frontal appendage. Originally referred to as AUGD 1046-335 ( Nedin, 1995, fig. 1C).

Additional material. Frontal appendages: SAMA P48371 ( Fig. 12C, D View Figure 12 ), P48975 ( Fig. 10 View Figure 10 ), P49151 ( Fig. 12A, B View Figure 12 ), P54790 ( Fig. 11 View Figure 11 ), P54876 ( Fig. 9 View Figure 9 ), in addition to other specimens listed by Daley, Paterson et al. (2013, suppl. information) and Paterson et al. (2020, table S4) as Anomalocaris briggsi or ‘ A. ’ briggsi , respectively. Head elements: SAMA P45911 ( Fig. 13B, C View Figure 13 ), P51380 ( Fig. 13A View Figure 13 ). Oral cones: SAMA P48195 ( Fig. 14D View Figure 14 ), P52881 ( Fig. 15C, D View Figure 15 ), P55433 ( Fig. 16D, E View Figure 16 ), P55600 ( Fig. 16A, B View Figure 16 ), P55646 ( Fig. 14C View Figure 14 ), P55650 ( Fig. 16C View Figure 16 ), P57415 ( Fig. 15A, B View Figure 15 ), P57418 ( Fig. 14A, B View Figure 14 ), in addition to SAMA P31956 (previously illustrated by McHenry & Yates, 1993, fig. 8 and Daley, Paterson et al., 2013, fig. 4), P48319, P48343, P48373, P49777, P52899, and P54231. Compound eye specimens are listed by Paterson et al. (2020, table S3) as ‘Acute zone-type’.

Diagnosis. As for the genus, by monotypy.

Description. Frontal appendages are Ĺ 175 mm in length along the dorsal margin, consisting of a non-segmented base and a claw of 13 podomeres (Cp1–13). The single podomere of the base appears bilobate in the proximal region, with the holotype ( SAMA P40180) and SAMA P48975 showing a notch in the proximal margin that separates a large dorsal lobe from a smaller ventral lobe ( Figs 8 View Figure 8 , 10); in SAMA P54876 ( Fig. 9 View Figure 9 ), only the dorsal lobe is preserved, which has a straighter dorsal margin. The base is at least four times as long as the adjacent podomere (Cp1), with a subtle dorsal kink at the articulation of the base and Cp1 ( Fig. 10 View Figure 10 ). The base endite located at the distal corner is relatively long (length ~95–100% the height of the distal-most portion of the associated podomere), oriented posteriorly, with at least seven evenly spaced anterior auxiliary spines along its length and a single posterior auxiliary spine situated near the tip of the endite ( Figs 8–10 View Figure 8 View Figure 9 View Figure 10 ). Claw podomeres have a sub-rectangular outline in lateral view, with dorsal margins slightly longer than ventral margins, and the overall size of podomeres gradually decreasing distally; observed length:height ratios are ~0.5–0.8 for Cp1–8, ~1.0 for Cp9, ~1.2 for Cp10, ~1.8–2.4 for Cp11–12, and ~1.3 for Cp13. The proximal and distal margins of podomeres Cp1 to Cp12 are straight to slightly curved. Arthrodial membrane is occasionally preserved as narrow recessive triangular regions between podomeres (e.g. Figs 8 View Figure 8 , 10, 11). Claw endites are paired (e.g. Figs 8 View Figure 8 , 12; Daley, Paterson et al. 2013, fig. 1C, D), straight to slightly curved, oriented posteriorly, and of approximately equal length up to En11; observed ratios of endite length to associated podomere height range from ~1.2 (En1:Cp1) to ~4.4 (En9:Cp9), then decrease to ~3.1 (En11:Cp11) ( Figs 8 View Figure 8 , 11). En1 bears at least eight evenly spaced anterior auxiliary spines along its length and one posterior auxiliary spine near the tip of the endite ( Figs 8–10 View Figure 8 View Figure 9 View Figure 10 ). En2 has at least eight evenly spaced anterior auxiliary spines, but only one posterior auxiliary spine has been observed in available specimens ( Figs 8– 10 View Figure 8 View Figure 9 View Figure 10 ). En3 to En11 each have several evenly spaced auxiliary spines on both margins, with up to 13 and seven observed on the anterior and posterior margins, respectively ( Figs 8 View Figure 8 , 9, 11, 12A, B; Daley, Paterson et al., 2013, fig. 1C, D). En12 length is ~1.4 times the height of the associated podomere, with the angle between the endite and the ventral margin of the podomere being ~30 ǫ, possibly with posterior auxiliary spines ( Figs 8 View Figure 8 , 11). En13 length is ~1.4 times the height of the associated podomere, possibly with posterior auxiliary spines ( Figs 8 View Figure 8 , 11). Spinules extend from the proximoventral margin of the podomere onto the basal portion of the posterior margin of endites on En1 to En11; with up to 10 spinules per podomere ( Figs 8–11 View Figure 8 View Figure 9 View Figure 10 View Figure 11 , 12B, C). Dorsal spines are present on Cp11–13 and are slightly curved, with the one on Cp11 being short (~25% the remainder of the dorsal margin of the podomere; Fig. 11 View Figure 11 ), and those on Cp12 and Cp13 being very long (i.e. of length equal to or greater than the dorsal margin of the associated podomere) ( Figs 8 View Figure 8 , 11).

Head elements are represented by two isolated ovate sclerites that are gently convex (sag., tr.): SAMA P51380 (83.2 mm long, 61.1 mm wide; Fig. 13A View Figure 13 ); and SAMA P45911 (85.2 mm long, c. 54 mm wide; Fig. 13B, C View Figure 13 ). The inferred anterior margin forms a rounded apex. A narrow marginal rim is defined around the circumference. A few sub-marginal concentric folds are observed in both specimens; the surface is otherwise smooth.

The compound eyes of Echidnacaris briggsi have been previously described in detail by Lee et al. (2011) and Paterson et al. (2020) and this will not be reiterated here.

The oral cone is sub-circular in outline, reaching a diameter of ~ 77 mm in available specimens. It has a triradial symmetry, with three large plates separated by eight or nine medium-sized plates of variable width, and a small central opening into which the large plates sometimes project. The large plates are oriented ~100 ǫ and 125–130 ǫ from each other, are of sub-equal size, and have gently convex lateral margins, conferring greatest width at their midlength ( Figs 14A–C View Figure 14 , 15A, B View Figure 15 ). Medium-sized plates have an anastomosing fold in their outer portions towards the oral cone margin ( Figs 14A, B View Figure 14 , 15A, B View Figure 15 ). Three ( Fig. 15D View Figure 15 ) or four ( Daley, Paterson et al., 2013, fig. 4) teeth are present on the inner margins of large plates; two teeth are observed on the inner margin of a medium-sized plate adjacent to a large plate in SAMA P55650 ( Fig. 16C View Figure 16 ). The large- and medium-sized plates bear relatively numerous nodes on their inner halves, with as many as 30 nodes on large plates ( Fig. 14 View Figure 14 ); on large plates, larger nodes are concentrated inwards of small nodes; the medium-sized plates bear more uniformly sized small nodes. The nodes have an asymmetrical surface profile, with the raised tips directed towards the centre of the oral cone. The outer half to third of the oral cone surface appears to be smooth in mature specimens. Folding of specimen SAMA P55600 ( Fig. 16A, B View Figure 16 ) shows that the oral cone was pliable. A small oral cone (~ 10 mm in diameter; Fig. 16D, E View Figure 16 ) shows that the large plates are of a similar size to the medium plates (in contrast to mature specimens), suggesting allometric growth of large plates throughout ontogeny; this specimen also exhibits more pervasive tuberculation, especially near the outer margins of all plates.

Remarks. The synonymy of Echidnacaris briggsi above indicates the recognition that its classification as Anomalocaris was inappropriate, as phylogenetic analyses consistently allied it with Tamisiocaris rather than with Anomalocaris canadensis , and it has been classified in Tamisiocarididae rather than Anomalocarididae since that family was established (Pates & Daley, 2019). Assignment to ‘ Anomalocaris ’ in recent works reflected the need for generic reassignment, formalized herein with the naming of Echidnacaris . Affinities of E. briggsi with Tamisiocaris rather than Anomalocaris were first signalled by frontal appendages ( Vinther et al., 2014), and striking differences between E. briggsi and Anomalocaris were revealed in eye morphology ( Paterson et al., 2020). The diagnosis and description of E. briggsi add more characters for distinguishing this species from Anomalocaris , drawing on the oral cone, eyes and head elements.

The assignment of the pervasively tuberculate oral cone to E. briggsi is largely based on it being the only other morphotype known from the EBS, with the A. daleyae oral cone identified by direct association with frontal appendages. This is further reinforced by relative abundance data in the EBS, with the tuberculate form being far more common (15 isolated oral cones) than specimens of A. daleyae (five oral cones, including appendage associations), echoing frontal appendage counts of both species (see Paterson et al., 2020).

Body flaps (described below) cannot be confidently assigned to either of the two EBS species, but based on relative abundance at horizons in which Echidnacaris briggsi is the more common of the two species, much of the body flap material is likely to be that species. The body flaps are similar in outline and in the arrangement of transverse lines to those of the only tamisiocaridid with well-known body flaps, Houcaris saron ( Hou et al., 1995, figs 4, 5). Below, we interpret a sharply delimited inner attachment margin of the flaps as representing a suture. If this is correct and these flaps are those of E. briggsi , this is another potential autapomorphy of the genus and/or species, if not shared with other tamisiocaridids.