Peedeeaster sandersoni, Mah, 2022

Mah, Christopher L., 2022, A new genus and species of Goniasteridae, Peedeeaster sandersoni, and the first occurrence of Sclerasterias (Asteriidae) from the Cretaceous Peedee Formation of North Carolina, Zootaxa 5138 (5), pp. 533-548 : 539-545

Peedeeaster sandersoni nov. gen, n. sp.

Figures 3A–H , 4A–B , 5A–B

Etymology. The species epithet honors the specimens’ original collector Mr. David Sanderson of Cary, North Carolina.

Diagnosis. Goniasterid species with low columnar, hourglass shaped abactinal plates, round in cross-section, each covered by round granules. Marginal plates trapezoid to quart in shape, approximately four per interradius with enlarged triangular to trapezoid-shaped pre-terminal superomarginals and inferomarginals, covered with coarse round granules. Actinal surface covered by round, coarse granules. Furrow spines two, these blunt, cylindrical. Single subambulacral spine, large, twice thickness of furrow spines, pointed.

Description. Body pentagonal to weakly stellate ( Fig. 3A–B , 4A–B , 5A–B ) but specimens show some distortion. (R/r=approximately 1.1–1.8). The most flattened specimen (USNM PAL 618276) shows R/r=1.25. Interradial arcs weakly curved. Armtips blunt.

Abactinal plates squat, columnar, round in cross-section, hourglass-like in overall shape ( Fig. 3C–D ) with abactinal and coelomic-facing surface of individual plate identical in size and weakly developed curve on central waist. Each abactinal plate surface with coarse granules, eight to 20 (mostly 12–15) ( Fig. 3D ). Granules widely spaced. Individual plate surface was textured but it was unclear if granular pitting on plate surface was present. Specimen USNM PAL 618276 shows approximately 12 plates in radial series ( Fig. 4A ) on two arms from primary circlet to where enlarged superomarginals are abutted. Approximately three shorter parallel ordered plate series adjacent to the central radial series along arm. Abactinal plates are mostly jumbled on USNM 618274 and 618275 ( Figs 3A–B , 5A ). Fasciolar grooves present but extent of development (i.e. shallow, strongly developed) is unclear. Superomarginal plates form prominent border around abactinal surface, occupying approximately 25% (width of superomarginal/r= 0.4/1.6) of the abactinal surface ( Fig. 3A , 4A , 5A ). Madreporite teardrop shaped approximately 3.0 mm in length, well developed sulci.

Marginal plates four per interradius ( Fig. 3A, E , 4A , 5A ). Distalmost superomarginal and inferomarginal plates enlarged, abutted at arm tip, rectangular to trapezoidal in shape, about 1.5 to twice the size of marginal plates present interradially ( Fig. 3E , 4B , 5B ). Two superomarginals and inferomarginals per interradius in the type specimens. Interradial superomarginal plates are trapezoidal to quadrate in shape with wide end in contact with the abactinal surface. Interradial superomarginal plates wide, with dimensions ranging from width only slightly greater than length to distinctly wider than long. Marginal plate surface covered by coarse, round granules, approximately three to four counted along a 1.0 mm line. Granules distributed uniformly over plate surface but irregularly becoming denser closer to contact with disk. No differentiation of granules on plate surface region. Where granules have been removed, weakly convex pitting is present, although on some marginals this pitted surface seems to have been eroded to a rough surface.

Actinal surface partially complete on one specimen (USNM PAL 618275 ) showing partial actinal interradius with complete actinal and adambulacral plate series. USNM PAL 618276 with little to no actinal surface present ( Fig. 3G ). Individual actinal plates diamond to polygonal in shape, present (based on partial series) in approximately four chevron-like rows ( Fig. 3H ). USNM PAL 618274 shows round to pointed, bullet-shaped, granules, two to twelve present on each plate surface, widely spaced. Plates on USNM PAL 618275 without surficial accessories.

Adambulacral plates, approximately 30–35, from mouth to arm tip based on near complete series in USNM PAL 618275 and USNM PAL 618276. Individual plates wide (width>length) and narrow, rectangular in shape with indented edges. Furrow spines two, cylindrical, pointed. Subambulacral spine twice as thick as furrow spines, blunt and pointed ( Fig. 3F ). Oral plates with thick furrow spines, three to five, quadrate in cross-section, plate surface obscured by matrix.

Ambulacral ossicles, approximately 25 partially visible via ambulacral grooves in holotype with elongate shaft and well developed alveolus (following terminology of Turner and Dearborn 1972).

Material Examined. HOLOTYPE: USNM PAL 618274 , Rocky Point Member , Peedee Formation, Pender County, NC, R =2.0 r=~1.8 (body distorted but with complete furrow spination),

PARATYPES: USNM PAL 618275 , Rocky Point Member , Peedee Formation, Pender County , NC, R =2.0 r=1.1 (partial actinal/adambulacral series).

USNM PAL 618276, Rocky Point Member, Peedee Formation, Pender County , NC., R =2.0 r=1.6 (no actinal surface).

USNM PAL 618277, Rocky Point Member, Peedee Formation, Pender County , NC. (armtip and disk fragment), R =~1.3, disk incomplete.

USNM PAL 618278, Rocky Point Member, Peedee Formation, Pender County, NC . (intact on matrix).

Taxonomic Affinities. Peedeeaster nov. gen. displays characters which are reminiscent of several extant goniasterid genera but could not be reconciled with any extant or extinct taxon. Argumentation for Peedeeaster ’s status is considered within the context of the problematic nature of goniasterid fossil taxonomy as outlined by Blake & Portell (2009).

The relatively few, interradial, trapezoidal-shaped marginal plates and the enlarged, triangular-shaped pre-terminal superomarginal and inferomarginal plates are comparable to Tosia australis but differ in that Peedeeaster ’s marginal plate surfaces are covered by coarse granules. Abactinal and marginal plate surfaces in Tosia australis are smooth and lack granules. The abactinal plates are columnar and hourglass-like in shape unlike Tosia or any of the Pentagonaster -like goniasterids which have flat, smooth plates ( Mah 2007).

Peedeeaster ’s body shape invites immediate comparison with other similar pentagonal Goniasteridae with granular coverings and similarly columnar and hourglass-like abactinal (also called tabulate) plates, these including Ceramaster , Sphaeriodiscus , and Peltaster . These three genera display unclear taxon limits and it is likely that several species or possibly one or two of these genera might better be treated as synonyms (Mah 2011). Comparisons between Peedeeaster and exemplars from these three genera shows several differences between them, including a greater number of marginal plates in the extant genera (approximately six to ten from armtip to armtip) compared to consistently four per interradius (armtip to armtip) at a comparable size ( R =~1.1–1.8). Marginal plate shape also differs in that Peedeeaster displays trapezoid to quadrate shaped plates whereas the other three genera, especially Sphaeriodiscus displays evenly quadrate marginal plates( Fig. 4A–B, E–F ).

Pillsburiaster has an extensive coarse granular covering but its abactinal plates are flattened rather than columnar and hourglass-like in shape. Genera such as Plinthaster ( Fig. 4A–B, 4C–D ), Glyphodiscus and members of the Pentagonasterinae ( Mah 2005b, 2007), show flattened and abutted abactinal plates rather than the columnar, hourglass shaped plates in Peedeeaster .

Comparisons with other Fossil Genera. Comparisons within the field of fossil Asteroidea and especially the Goniasteridae , within the context of biology-based taxonomy requires a brief introduction to the practice and systematic usage of ossicles versus whole body fossils. Many, if not most, described fossil asteroid taxa are based on individual ossicles rather than complete body fossils. The use of individual ossicles has found significant use among paleontologists for inferring phylogenetic trends, paleoecology, and taxonomy (e.g., Villier 1999, Villier et al. 1997, Villier et al. 2004). Blake & Portell (2009) have re-emphasized the caution accompanying interpretation and use of individual ossicles in systematic work. Ossicle-based species utilized for comparison should be considered within this context.

Published North American Cretaceous Goniasteridae do not appear to be abundant in the literature. Peedeeaster sandersoni n. gen, n.sp. invites comparison with other Cretaceous North American goniasterid taxa. Two pentagonal shaped goniasterid species, Crateraster texensis ( Adkins & Winton 1920) and Formalhautia hortensae ( Adkins & Winton 1920) were outlined in Blake & Reid (1998) from the Cretaceous of Texas. Both of these species however display very pronounced wide, almost rectangular interradial superomarginals (W>L) relative to those present in Peedeeaster n. gen. which display much less disparity between width and length and whose plates are more trapezoid-like in shape. Codellaster from the Cretaceous Codell Sandstone Member in Colorado displays extremely wide (W>L) but very narrow interradial superomarginals relative to Peedeeaster . In all three instances of the North American Goniasteridae compared above, there are also greater numbers of interradial superomarginals present, as counted from armtip to armtip compared to Peedeeaster .

Among other North American Goniasteridae , which invited comparison, was the sole, currently accepted Metopaster species from North America, Metopaster tenesseensis Wade 1926 , known only from marginal ossicles. Wade’s (1926: Fig. 1 ) shows marginal plate ossicles which are wider than large, which immediately distinguishes them from Peedeeaster but furthermore, the presence of granules appears isolated to a convex surface of the plate with a distinct border, rather than evenly occurring on the plate surface as in Peedeeaster . As with Metopaster parkinsoni , this appears to be a character identifying Metopaster rather than individual species. A related genus Fredaster , described by Breton & Néraudeau (2004) also displays this distinct granulated convex surface flanked by a distinct border, ruling out affinities between Fredaster and Peedeeaster .

Peedeeaster was also compared with a whole body fossil of Metopaster parkinsoni ( Forbes 1848) ( Fig. 5C–D , USNM PAL 772335) as an exemplar of Metopaster , the genus of Cretaceous fossil Goniasteridae , which includes the greatest number of species. Most prominent is the difference in abactinal plates, which in M. parkinsoni ’s are flat and polygonal ( Fig. 5C ) but in Peedeeaster are squat and columnar with an overall hourglass shape ( Fig. 3C–D , 5A–B ), comparable to plates in modern Sphaeriodiscus or Peltaster . Similarities between Metopaster parkinsoni and Peedeeaster include the granule covered superomarginal plate surface and the pentagonal body shape. However, as with Metopaster tenesseensis the pattern of marginal plate granulation is limited to a discrete, raised surface area with a peripheral edge whereas Peedeeaster shows granulation evenly across the complete plate surface. Interradial superomarginal plates in Peedeeaster were also compared and found to be different between the two species, with Peedeeaster demonstrating much fewer and more elongate (L>W) shaped, blockier superomarginal plates relative to Metopaster parkinsoni which shows many more and much wider (W>L) superomarginal plates. Adambulacral plates in Peedeeaster were also compared against figures of adambulacral plates in Metopaster parkinsoni i n Wright (1863, Pl. 12, fig. 4) which shows plates in Peedeeaster as much narrower and less blocky than those in M. parkinsoni .

Peedeeaster was also compared with the European Cretaceous Weitschataster and Parametopaster , which both had a uniform covering of granules ( Neumann & Girod 2018) similar to that observed on Peedeeaster . Superomarginal plates on these two genera displayed greater width (W>L) and was much more quadrate than trapezoid as it is in Peedeeaster . Pedicellariae are conspicuously absent in Peedeeaster , but present in Weitschataster and Parametopaster .

Taxonomic Trends in Enlarged Pre-Terminal Plates. One of the most evident characters in Peedeeaster sandersoni n. gen, n. sp., which invites comparison between other fossil and living Goniasteridae is the enlarged penultimate or pre-terminal superomarginal plates ( Figs. 4A–F , 5A–D ). Although this character is observed in other families within the Valvatacea, such as the Odontasteridae and the Asterodiscididae , it is most commonly observed within the Goniasteridae . Its functional significance is unclear but Blake (1983) has argued for their use as protection for soft-tissue against predators, specifically citing the enlarged distal superomarginals in Pentagonaster duebeni Gray 1847 .

The presence of an enlarged pre-terminal superomarginal and/or inferomarginal plate is a character, which when observed in the Goniasteridae , seems associated almost exclusively with those taxa displaying a pentagonal or weakly stellate body form (i.e., a relatively low R /r ratio), such as Pentagonaster , Plinthaster or Sphaeriodiscus among living taxa, or Metopaster among fossil taxa. Peedeeaster joins the known fossil genera which display this character. Stellate goniasterids (approximately R /r ratio> 2.0), have yet to be shown exhibiting this character. The shape of these plates, even within a single species, such as the Atlantic Peltaster placenta has been shown to display significant variation ( Tortonese 1984).

The enlarged pre-terminal plates observed in P. sandersoni show a wide, almost triangular shape in outline ( Fig. 3B, C, F , 4B , 5A ) which is similar to the fossil Cretaceous Metopaster parkinsoni as well as species in the living genus Plinthaster ( Fig. 4C–D ), such as Plinthaster lenaigae , from Madagascar. In spite of the shared similarity in pre-terminal plates, other characters in Peedeeaster , such as the possession of low, tabulate abactinal plates and granulation on the abactinal and marginal plate surface are more similar to those of living goniasterids such as Peltaster or Sphaeriodiscus ( Fig. 4C ). Those with more triangular pre-terminal plates, such as Metopaster and Plinthaster show more polygonal shaped, smooth, flat abactinal plates, devoid of surficial granules. Peedeeaster has a more comparable body form with modern goniasterids such as Peltaster and Sphaeriodiscus , their enlarged pre-terminal superomarginal plates are wider and quadrate in shape rather than elongate and triangular ( Fig. 4 ).

Other goniasterids, such as Tosia or Pentagonaster showing enlarged pre-terminals are dissimilar in shape, being more round and strongly convex rather than triangular and flat (see Mah, 2006). Although these species share similar shaped pre-terminal, enlarged superomarginals, they differ in that their abactinal plates are smooth and flat compared to Peedeeaster which are covered by granules and form low tabular plates and have a coarse granular cover on their marginal plate surface.

Feeding Mode. Although Peedeeaster sandersoni n. gen., n. sp. invites comparison with several taxa of pentagonal-shaped Goniasteridae , feeding and life modes for these species is varied but suggests predation on sessile taxa, such as sponges, and various types of cnidarians. Mah (2020) documented several instances of sponge and coral predation, as well as various types of organic debris, by Ceramaster grenadensis , Plinthaster dentatus and Peltaster placenta , which are all pentagonal in shape. West tropical Atlantic Peltaster placenta were reported mainly feeding on sponges, but Bo et al. (2018) reported Mediterranean Peltaster placenta feeding on antipatharians (black coral). Shallow-water analogs, such as Tosia australis are also reported as also feeding on sponges and other epizoic invertebrates ( Shepherd 1968, Keough & Butler 1979, Marsh & Fromont 2020).

Figures

FIGURE 1. Sclerasterias sp. USNM PAL 618279. Fossil material figured unless otherwise noted. A. Armtip fragment showing transverse ribs and carinal series. Scale bar=2.0 mm. B. Sclerasterias contorta, USNM E12922 Armtip. Abactinal view showing transverse ribs along carinal series. Scale bar=1.0 mm. C. Abactinal view of arm fragment showing carinal and transverse ribs. D. Sclerasterias contorta USNM E12922 Abactinal view of arm fragment showing carinal and transverse ribs. E. Sclerasterias contorta USNM E34058 showing superomarginal and inferomarginal plates. F. Superomarginal, inferomarginal and adambulacral plates. Abbreviations:Ad= Adambulacral plate, CAR=Carinal plate, CAR-SP=Carinal spine, Pap=papular space, Trv=Transverse rib, SM=Superomarginal plate. IM sp.=Inferomarginal spine, SM sp.=Superomarginal spine.

FIGURE 3. Peedeeaster sandersoni n. gen, n. sp. A. USNM PAL 618274 holotype. Abactinal surface. Scale Bar=5.0 mm. B. Closeup abactinal surface, pre-terminal superomarginal plates. Scale Bar=2.5 mm. C. Columnar-hourglass abactinal plates from USNM 618274. Top-side view (right) scale=1.0 mm and USNM 618275 side view, abactinal, top side (left) scale=0.5 mm. D. Superomarginal plates from interradius showing granular cover. Scale= 2.5 mm. E. Lateral view, inferomarginal plates. Scale Bar=3.0 mm. F. Furrow spines, actinal details. Scale Bar=5.0 mm. G. USNM PAL 618275, paratype. Closeup of actinal surface showing adambulacral plates and other details. Scale Bar=2.0 mm. H. Actual surface. Scale Bar= 3.0 mm.

FIGURE 4. Comparison of Peedeeaster sandersoni n. gen., n. sp. with enlarged pre-terminal superomarginals in living taxa. A. Abactinal, USNM PAL 618276. Scale Bar=10.0 mm. B. Closeup of enlarged pre-terminal superomarginals. Scale Bar=5.0 mm. C. Plinthaster lenaigae Mah 2018, Holotype IE-2013-7003. Scale Bar=5.0 mm. D. Armtip showing enlarged preterminal superomarginal plates. Scale bar=5.0 mm. E. Sphaeriodiscus mirabilis A.M. Clark 1976, USNM 1116242, Abactinal surface. Scale Bar=5.0 mm. F. Closeup of pre-terminal superomarginal plates. Scale Bar=5.0 mm.

FIGURE 5. Comparison of Peedeeaster sandersoni n. gen., n. sp. with enlarged pre-terminal superomarginals in fossil taxa. A. USNM PAL 618275 abactinal. Scale Bar=5.0 mm. B. Closeup showing enlarged superomarginal plates. Scale Bar=3.0 mm. C. USNM PAL 772335, Metopaster parkinsoni, abactinal. Scale Bar=3.0 mm. D. same. armtip. Scale Bar=3.0 mm.