Abertella miskellyi Kroh et al., 2013

Mooi, Rich, Martínez, Sergio A., Del Río, Claudia J. & Ramos, Maria Inês Feijó, 2018, Late Oligocene - Miocene non-lunulate sand dollars of South America: Revision of abertellid taxa and descriptions of two new families, two new genera, and a new species, Zootaxa 4369 (3), pp. 301-326 : 318

Abertella miskellyi Kroh et al., 2013

2013 Abertella miskellyi Kroh et al. : 371–376, figs. 2–6.

Diagnosis. Abertella with strongly heterogeneous interambulacral basicoronal plates (small in interambulacrum 5, largest in interambulacra 2 and 3); oral interambulacra discontinuous by involvement of two adjacent ambulacral plates (rather than one as in other Abertella ) in at least one of the oral interambulacra; apparent "violation" of Lovén's Rule in oral ambulacrum III.

Type material studied. Holotype MB E.7463, paratype MB E.7462.

Description. See Kroh et al. (2013).

Occurrence. A. miskellyi is recorded only from the (possibly early) Miocene of Chubut Province, southern Argentina in the Camarones Formation ( Fig. 1 ).

Remarks. This species is unique among Abertella in that the posterior interambulacral basicoronal plate is much smaller than that in each of the paired interambulacral basicoronals. It is also the only Abertella in which specimens are known to have a discontinuity involving more than one postbasicoronal plate in a given halfambulacrum. An unusual feature of one of the known specimens of A. miskellyi is that ambulacral basicoronal III at first seemed longer in the "a" column than in the "b" column, suggesting violation of Lovén's Rule (sensu David et al. 1996) until a small plate was detected, wedged between the basicoronal plates of ambulacrum III to re-establish the Lovénian pattern ( Kroh et al. 2013).

Figures

FIGURE 1. Localities for taxa discussed in the text. Inset at lower left centers on the Santa Cruz region of Patagonia. Numbered occurrences correspond to unequivocal Iheringiella patagonensis localities (inside boxed region in main map): 1. Pampa Castillo, Chile (Andre Wyss, pers. comm.); 2. Cañadón El Lobo, Santa Cruz, Argentina (CPBA 16493-95); 3. Oven Point/Sholl's Tomb, Santa Cruz, Argentina (Ortmann 1902), Punta Cuevas, Santa Cruz, Argentina (MACN 4586 and Cuitiño 2011), Playa La Mina, Santa Cruz, Argentina (Cuitiño 2011); 4. Meseta Chica, Bajo de San Julián, Santa Cruz, Argentina (MACN 5144 and Cuitiño 2011); 5. Upper Rio Chalia, Santa Cruz, Argentina (Ortmann 1902); 6. Puerto Santa Cruz, Santa Cruz, Argentina (ROM 5433M, 5468M, 5469M); 7. Sector Flamenco, Tierra del Fuego, Chile (Larrain 1984)—reported to be from Eocene strata, but this is questionable (Mooi et al. 2000).