612


Journal of Paleontology 92(4):611–633


classification places Pleuromyidae phylogenetically distant from Pholadomyidae, which is counter to molecular data (Harper et al., 2006; Bieler et al., 2014). Pleuromyidae ranged fromEarly Triassic to the end of the Cretaceous (Carter et al., 2011) as did Pleuromya (Global Biodiversity Information Facility [GBIF], 2016). Pleur- omya diversified during the Jurassic, especially during Middle and Late Jurassic (Duff, 1991) and became widespread latitudinally from Antarctica to Russia and Greenland (GBIF, 2016); it was less common during the Early Cretaceous. These families are grouped in the megaorder Poromyata Ridewood, 1903 by Carter et al. (2011) and in the subclass Anomalodesmata Dall, 1889 by Newell (1965), Cox et al. (1969), Morton (1981), Harper et al. (2006), and Bieler et al. (2014). Albian–lower Cenomanian Comanchean Series species


of Pholadomyoidea have been neglected as biostratigraphic markers and paleoecological indicators. Some 22 fossil species have been described (Akers and Akers, 2002). These species have been classed with Pholadomya, Homomya, Pachymya, Myopholas Douvillé (1907), Panopea Ménard de Groye (1807), and Pleuromya. Species of these genera are rather large and readily collected. Specimens are generally preserved as external


casts that show external features of their uncomplicated shell morphology; internal features are rarely preserved. These Comanchean infaunal suspension feeders (Stanley,


1970, 2015) are found in lime mud carbonate strata that represent muddy calcareous substrates in shallow shelf environments (Fig. 1).Modern Pholadomya occupies inshore waters and is a passive deep burrower that feeds on sediment detritus by extending its foot through the anterior gape, pedal feeding (Morton, 1981, 1985). Ferdinand Roemer discovered and named the first species,


Homomya alta, from the Fredericksburg Group during his exploration travels along the Texas Balcones escarpment and up the transecting rivers (Roemer, 1852). Roemer also noted a specimen that he placed in H. Panopea sp. and compared it to the European species Panopea regularis d’Orbigny (1843, v. 3, pl. 360, figs. 1, 2). Roemer (1852) named Pholadomya pedernalis from Fredericksburg strata. Subsequent explorers discovered similar specimens in west Texas (Conrad, 1857; Shumard, 1860), in the El Paso area (Böse, 1910), and in north Texas (Cragin, 1893, 1894, 1905; Hill, 1893), and central Texas (Whitney, 1937). This species group ranges from the upper Aptian–lower Albian Glen Rose Formation of the Trinity Group


Figure 1. Middle Albian paleogeographic map of the Comanche Shelf, Texas, and surrounding areas (from Scott, 2007). Tan areas represent shallow-water carbonate; light blue is shelf carbonate; dark blue is intrashelf basin or deeper-water carbonate. Location of type localities of Homomyid species: 1. Burnett County; 2. Parker County; 3. Travis County; 4. Grayson County; 5. El Paso County; 6. Comal County; 7. Coahuila, Mexico; 8. Tarrant County.


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