1048
Journal of Paleontology
elongate than is typical of large individuals of K. perfectus suggests that the specimen could belong to a mature individual of A. gregorii. However, the skull possesses features that are not diagnostic of the taxon, including: (1) a deep otic notch, (2) an occiput that projects posteriorly, and (3) a relatively wide cul- triform process (Hunt, 1993; Spielmann and Lucas, 2012). Furthermore, a histological analysis of two intercentra belon- ging to this specimen as part of a broader survey of North American metoposaurid intercentra (Gee et al., 2017) reveals that these intercentra belong to a relatively immature individual. Given that cranial features are more phylogenetically informative than postcranial features, such as intercentra, which may be influenced significantly by habitat and general ecology, we tentatively assign the specimen to K. perfectus (Hunt, 1993; Long and Murry, 1995). Regardless of the taxonomic affinities, this material is not referable to A. gregorii.
Geologic setting
Locality information.—PEFO 35392 was collected in 2008 from locality PFV 215 (Zuni Well Mound) in the Petrified Forest National Park, Arizona, USA. Exact locality information is protected from disclosure by the Paleontological Resources Protection Act of 2009, but is available to qualified researchers from the Resource Management Division at the PEFO, see Figure 1.
Stratigraphic information.—PEFO 35392 was collected from the middle portion of the Petrified Forest Member (middle Norian) of the Chinle Formation (sensu Woody, 2006). The quarry is situated at the top of the Painted Desert Sandstone #4 (Parker and Martz, 2011), ~30m below the Black Forest Bed of the Petrified Forest Member. The Black Forest Bed is a sandstone unit dominated by reworked tuffaceous material (Ash, 1992) and has provided a U/Pb date (sample BFB) of 209.926±0.072Ma from detrital zircons (Ramezani et al., 2011). This provides a minimum age for the quarry. The maxi- mum age at the northern end of the PEFO is set by sample KWI, which is from the Brown sandstone (Billingsley, 1985) and which has a date of 213.870±0.078Ma(Ramezani et al., 2011). The Brown sandstone is ~120m below the quarry (Parker and Martz, 2011). Thus the estimated age of the quarry is closer to 211 Ma (Nordt et al., 2015). Other taxa found at this locality include phytosaurs (PEFO
36745), large-bodied metoposaurids (PEFO 31173), drepano- saurids (PEFO 36743), the archosauriform Vancleavea campi Long and Murry, 1995 (PEFO 34035; Parker and Barton, 2008), a rauisuchid paracrocodylomorph (PEFO 36740), the aetosau- rian Typothorax coccinarum Cope, 1875 (PEFO 16668), the pseudosuchian Revueltosaurus callenderi Hunt, 1989 (PEFO 16671), and a theropod dinosaur (PEFO 36741). Numerous small, elongate metoposaurid intercentra from this locality have been previously assigned to Apachesaurus gregorii (e.g., PEFO 31209; Parker and Martz, 2011), but these identifications are less certain given the conclusions of the present study. Typothorax coccinarum and R. callenderi are index taxa of the Revueltian biozone (Parker and Martz, 2011).
Materials and methods
PEFO 35392 was discovered by Katie Loughney (then of the University of Rhode Island) on May 30, 2008 during geological and paleontological investigations of PFV 215. The skull and associated vertebrae were found adjacent to where a partial skeleton of the archosauriform Vancleavea campi had been collected in 2004 (Parker and Barton, 2008). The bones from this locality are extremely friable and often ‘explode’ once uncovered. The intercentra were collected individually; how- ever, the skull was badly weathered and was collected as a separate jacket. Before jacketing, the specimen was con- solidated with heavy amounts of very thin Vinac™ (polyvinyl acetate beads dissolved in acetone). The skull was jacketed using several layers of plaster bandages on August 1, 2008 by WGP and it was noted at the time that the specimen consisted of the rear of the skull and that it was badly preserved ventrally (unpublished field notes at the PEFO, W.G. Parker, 2008). Upon collection, the specimen was assigned the field number WGP 08/48-3. The skull was prepped by Kenneth Bader in October of 2010 at the PEFO. Matrix was removed with pin vise and brushes. Thick Paraloid B-72 (Rohm and Haas) was used as the adhesive, and thin Paraloid B-72 was used as a consolidant to treat areas where the inner bone surface was highly fragmented. The anterior portion of the skull was recovered as a mass of matrix and shattered fragments. This area is held together by consolidant, but no features can be determined in these areas (labeled “mbf” in Fig. 2.2, 2.4). For the histological analysis, the intercentra were first
cleaned using a toothbrush and water to remove excess matrix before being consolidated with thin Paraloid B-72. All speci- mens were molded and casted according to the PEFO museum standards (National Park Service, 2007), with Carbowax (molecular weight 4000; Dow) added to stabilize cracks and other fragile areas. After creating two-part molds using Platsil 73-25 silicone rubber, the Carbowax was removed using a brush and warmwater. All specimens were impregnated in a polyester resin mixture of CastoliteTM AC and hardener (Eager Polymers) at a ratio of one ounce of CastoliteTM to 12 drops of hardener. The specimens were placed in a vacuum chamber to evacuate gas from the resin and then allowed to cure for a minimum of 24 hours. Both sagittal cuts (down the midline in the antero- posterior axis) and transverse cuts (at the mid-length along the mediolateral axis) were made based on the amount of ontoge- netic information that could be derived from the different planes in the analysis of Konietzko-Meier et al. (2013). All specimens were cut using an automated IsoMet 1000 Precision Saw (Buehler). The cut surface of the desired block and its respective plexiglass slide were prepared by polishing each with a 600- mesh silicon carbide on a glass plate. Both surfaces were rinsed with ethanol and then attached using Scotch-Weld Instant Adhesive (CA40; 3M). The sections were allowed to dry for a minimum of 1 hour. All sections were cut to a height of 0.7mm using the IsoMet 1000 Precision Saw. All specimens were then polished with a Hillquist 1010 grinding cup, followed by manual polishing on glass plates using a succession of 600 mesh grit, 1000 mesh grit, and 1 micron grit. The thin sections were gradually ground down with repeated examination under a compound microscope to evaluate their optical clarity.
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