Lucas, S.G., et al. eds., 2013, The Carboniferous-Permian Transition. New Mexico Museum of Natural History and Science, Bulletin 60. 161 XENACANTH SHARKS AND OTHER VERTEBRATES FROM THE GERALDINE BONEBED, LOWER PERMIAN OF TEXAS

GARY D. JOHNSON

Shuler Museum of Paleontology, Institute for the Study of Earth and Man, Southern Methodist University, PO Box 750274, Dallas, Texas 75275-0274; email: [email protected]

Abstract—The Geraldine Bonebed occurs in the Nocona Formation (Wichita Group, Sakmarian age) in Texas. It has historically yielded a large number of mostly complete skeletons of four tetrapod taxa, for which it is famous, and also a diverse flora as well as other vertebrates. Bulk samples of matrix were recently screen-washed and sorted to produce a variety of vertebrate microfossils, including sharks, especially xenacanths. The non-xenacanth sharks are rare and include a petalodont tooth (Janassa?), Helodus sp. (4 teeth) and one partial hybodont tooth. These are all considerably more common higher in the Wichita Group. Only the petalodont and possibly the hybodont and Helodus represent a marine component in the fauna, but the marine faunas are more extensive higher in the Wichita. Also new to the fauna are acanthodians, actinopterygians, Cardiocephalus and Ophiacodon. Among the xenacanths are two typically small Xenacanthus sp. occipital spine fragments, two Orthacanthus sp. occipital spine frag- ments (one small, one very small) and hundreds of Orthacanthus teeth. Orthacanthus texensis teeth are much more common than O. platypternus teeth. Teeth of O. texensis and O. platypternus are comparable in size distributions, as determined by statistical analyses of the tooth-base measurements, to those higher in the Wichita Group. With one possible exception (the exact locality cannot be confirmed), O. texensis and O. platypternus are not known to occur below the Nocona Formation in Texas, nor are they anywhere older than Sakmarian age.

INTRODUCTION Group) in central Archer County (Fig. 2) and recognized four types of The purpose of this study is to add additional taxa to the previ- associated deposits. One of these, a catastrophic event bonebed, is rep- ously known fauna of the Geraldine Bonebed with emphasis on the resented by the Geraldine Bonebed, but Sander’s (1989) primary intent xenacanth sharks, obtained by bulk processing of matrix to yield a verte- was to describe four occurrences of floodplain pond bonebeds. All four brate microfossil component (Johnson et al., 1994). This bonebed, dis- of these probably contain a more diversified vertebrate fauna than does covered by A. S. Romer in 1932 in central Archer County, probably the Geraldine Bonebed (three of the faunal lists were updated by Johnson, represents the most prolific source of articulated tetrapod skeletons in 2007, 2012). The other two types of deposits recognized by Sander the Lower Permian of North America (Sander, 1987). These include 11 (1989) are isolated skeletons and lag bonebeds. mostly articulated skeletons of Archeria crassidisca, an embolomerous In his description of the pond bonebeds, Sander (1989) did not amphibian; 15 or more associated or articulated skeletons of the laby- recognize any evidence of marine incursions. Hentz (1988, figs. 11-12) rinthodont amphibian Eryops megacephalus; 14 or more partial to com- presented a broad overview of the paleogeography of north-central Texas plete skeletons of the herbivorous synapsid Edaphosaurus boanerges; during the time of deposition of the Archer City Formation (Asselian and three associated skeletons of a carnivorous synapsid, Dimetrodon age). Based on this, Sander’s (1989) pond bonebeds occurred in the natalis. Sander (1987) provided a history of collecting these specimens upper part of a lower coastal plain. This could reasonably explain the together with pertinent associated details. He also provided a detailed presence of marine taxa in these bonebeds under varying circumstances, study of the sedimentology, flora (some two dozen taxa) and taphonomy although their occurrence in the Geraldine Bonebed is more problematic. of the bonebed. It is of Sakmarian (Wolfcampian) age and occurs in the GERALDINE BONEBED VERTEBRATE FAUNA Nocona Formation, Wichita Group (Figs. 1-2). Sander (1987) noted the low diversity of the vertebrate fauna with only three amphibian taxa Taxa in addition to those listed by Sander (1987, table II), includ- (including Diadectes sp.) and three amniote taxa (including Bolosaurus ing indeterminate partial bones and teeth plus tooth and bone fragments striatus) from the bonebed proper, plus two more amphibians that were obtained by bulk processing of matrix from the bonebed, are (Trimerorachis insignis and Zatrachys sp.) and one additional synapsid cataloged as SMU 76693-76753 (Shuler Museum of Paleontology, South- (Ophiacodon uniformis) from the same vicinity. Among the fishes, only ern Methodist University Locality 161). Additional surface-collected one shark (Orthacanthus texensis) and one crossopterygian fossils (SMU 69461-69472, 69499) did not add any taxa to those listed (Ectosteorachis nitidus) were recorded from the bonebed, plus one lung- by Sander (1987). The screen-washed bulk samples (two sites several fish (Sagenodus sp.) from nearby. meters apart within the bonebed) produced the following taxa (catalog Sander (1987) concluded that the Geraldine Bonebed and related numbers in parentheses; the xenacanths are treated separately below; sediments and flora constituted a floodbasin of a small meandering river * taxa not listed in the bonebed proper by Sander, 1987): system. The vertebrate-bearing facies contain only a minor fine-grained sandstone with ripple bedding in what otherwise is mudstone (Sander, Class Chondrichthyes 1987, fig. 3), which he interpreted to represent a freshwater pond in an Subclass Elasmobranchii overall swamp environment. Although he presumed the presence of ox- *hybodontid indet. (partial tooth, 76713) bow lakes in the region, he did not specify such an occurrence for the Orthacanthus texensis bonebed, presumably because of the geometry of the facies distribution. *O. platypternus Sander (1989) provided an analysis of the sedimentology of a portion of *Xenacanthus sp. the Nocona Formation and subjacent Archer City Formation (Bowie Subclass Holocephali *Helodus sp. (4 teeth, 76714) 162

FIGURE 1. Stratigraphic section of western North-Central Texas; from Johnson (2011), based on Hentz and Brown (1987). Abbreviations: Pcj, Coleman Junction Formation; Psb, Santa Ana Branch Shale; Pse, Sedwick Formation; Pmo, Moran Formation; Ppb, Pueblo Formation; lPP, Pennsylvanian- Permian; lPPh, Harpersville Formation. 163 Subclass Incertae Sedis In addition, there are a variety of fish teeth including *Janassa? (single incomplete petalodont tooth, actinopterygians (SMU 76621, 76723, 76724), amphibian teeth (76732) 76717) and a reptile caudal? vertebra (76737) and claw (76738). Three small Class Incertae Sedis Acanthodii coprolites (76739) are present; the smallest (6 mm) has a spiral structure *Acanthodes sp. (partial fin spines and scales, not and the other two contain palaeoniscoid scales. A variety of partial bones, common, 76715, 76716) isolated teeth and fragments are present (76740-76745), some of which Class Osteichthyes are probably identifiable. Subclass Actinopterygii *palaeoniscids indet. (scales and teeth common, XENACANTH SHARKS IN THE GERALDINE BONEBED 76718, 76719) Three species of xenacanths (Xenacanthiformes Berg, 1937, 1940; *Platysomus? (single “button tooth,” 76720; see Xenacanthodii Olson, 1946?; Xenacanthida Glikman, 1964) occur in the Johnson and Zidek, 1981) bonebed. Orthacanthus texensis is represented by teeth (SMU 76693- Subclass Sarcopterygii 76702) as is O. platypternus (SMU 76703-76707). Two Orthacanthus crossopterygian indet. (skull fragments, scales sp. small to very small occipital spine fragments (SMU 76709) were common, 76722) recovered. Also, two small spine fragments of Xenacanthus sp. (SMU Sagenodus sp. (5 partial tooth plates, 76725) 76710) occur in the fauna, but Xenacanthus teeth were not recovered, Class Amphibia similar to the faunas in the Archer City Bonebed 3 and Conner Ranch Order Temnospondyli Bonebed (Fig. 2; Johnson, 2012). Xenacanths are also represented by Trimerorhachis sp. (teeth and partial jaws denticles and prismatic cartilage (SMU 76711, 76712). uncommon, 76729) Orthacanthus texensis teeth are very common (total of 1808) in Eryops sp. (skull and jaw fragments common, 76728) the Geraldine fauna. Besides normal teeth, 13 teeth are germinal (under- Order Anthracosauria developed; Johnson, 2005) and three are deformed (Johnson, 1987) (SMU Archeria sp. (6 vertebrae, 76726) 76697, 76698). Of the remaining teeth, 141 were measured (Fig. 3A). A Order Microsauria statistical analysis is summarized in Table 1. The anteromedial-postero- *Cardiocephalus sp. (3 teeth, 76731) lateral (length of tooth base) dimension is taken as the independent Class Reptilia variable because it is usually easier to measure in Orthacanthus teeth. Order Parareptilia The measured population may be skewed toward the lower range (Fig. Bolosaurus sp. (14 teeth, partial jaw, 76730) 3A) because nearly all of the larger teeth were probably removed by Class Synapsida earlier surface collecting. Forty-nine teeth were surface-collected (SMU *Ophiacodon sp. (teeth common, 76735) 69461), but they are incomplete with some badly worn or weathered. Dimetrodon sp. (neural spine fragments and teeth Sander (1987, p. 228) noted that the teeth are smaller than those from common, 76733, 76734) other localities in the vicinity of Geraldine. However, the comparison Edaphosaurus sp. (neural spine fragments common?, shown in Table 1 with the next stratigraphically highest measured sample 76736) (Rattlesnake Canyon, Fig. 2) shows little difference. Teeth from the Briar Creek Bonebed (Fig. 2) have been collected (SMU 69473, 69571, 69572, 76628-76635, 76637-76641, including other xenacanth species) but not analyzed. Orthacanthus texensis teeth typically have a base wider (labio- lingual) than long (anteromedial-posterolateral), a thick base as seen in labial view and serrated principal cusps (Johnson, 1999). In some larger teeth higher in the Wichita Group, both carinae on each principal cusp may be serrated, but none of the Geraldine teeth, where a determination can be made, have serrations on the medial carinae (Fig. 4; what appears to be medial serrations are an artifact of preservation combined with preparation of the photographs; only the lateral carinae are serrated). However, about 2.5% of nearly 1000 isolated cusps (SMU 76699, 76700) have serrations on both carinae. The problem is that very few of the teeth have intact cusps. This also prevents a determination of the extent of heterogeneity of the teeth (compare with Johnson, 1999, p. 233-234). An exception is the occurrence of 14 probable posterior teeth (SMU 76696) that are very small and lack an intermediate cusp; however, the principal cusps bear serrations on their lateral carinae. Typically, O. texensis posterior teeth lack serrations (Johnson, 1999, p. 233), and such is the case for a 15th tooth, which has an intermediate (broken) cusp, shown in Fig. 5. Orthacanthus platypternus teeth are much less common (total of 88) at Geraldine, similar to the rest of the Wichita Group (out of 54 faunas, there is but one exception; Johnson, 1999, table 1). One of these teeth is a germinal tooth (SMU 76705; Johnson, 2005), otherwise the rest are normal. O. platypternus teeth are typically longer than wide FIGURE 2. Sketch of Archer County, Texas, geology from Hentz and Brown, (Table 1, Fig. 3B), have a thin base as seen from the labial side (compare 1987. Abreviations: AC, Archer City Bonebed 3; BC, Briar Creek Bonebed; Figs. 6B, E, H with 4B, E, G), nonserrated principal cusps and the base CR, Conner Ranch Bonebed; G, Geraldine Bonebed; RC, Rattlesnake Canyon sometimes has a distinct anterior extension or flange (Fig. 6B, H; Johnson, Bonebed (all indicated by letters in circles with arrows); Pac, Archer City 1999, p. 236-237). Formation; Pn, Nocona Formation; Pp, Petrolia Formation; see Fig. 1. Some of the Geraldine Orthacanthus teeth are unusual. Three O. 164 TABLE 1. Measurements of Orthacanthus teeth from the Geraldine Bonebed; O. texensis (SMU 76746, n = 1-137; SMU 76747-76750, n = 138-141) and O. platypternus (SMU 76603, n = 1-32; SMU 76751-76753, n = 33-35). For comparison, the previously available stratigraphically lowest measure- ments (Johnson, 1999, table 2) are included.

fore the stratigraphic position, of this locality have not been successful, but it probably occurs in extreme southwestern Archer County (Fig. 2). Although the evidence is meager (one petalodont tooth fragment), the Geraldine Bonebed may have been closer to the marine paleoshore than Sander (1987) realized. Carroll (1988, p. 80) suggested that Helodus was freshwater, but Johnson (1990) considered it (referring to helodonts) as marine; Carpenter et al. (2011) listed it as marine (p. 651) or brackish- water (p. 653). The single hybodont tooth fragment listed above is dif- ferent from all of the teeth described by Johnson (1981); it may repre- sent a new species, but could be part of an unrecognized morphotype in the heterodont dentition of an established species. Species of hybodonts found higher in the Wichita Group (Johnson, 1981) were at least in part marine, given the widespread occurrence of Lissodus (Polyacrodus) zideki (discussed in Johnson, 2011, p. 31), the occurrence of three species of Wichita hybodonts in the Kaibab Formation in Arizona (Hodnett et al., 2011) and a species similar to one of yet another Wichita species in the Upper Permian of Iran (Hampe et al., 2011, 2013). The presence of Xenacanthus spines, but not teeth, suggests that it may have been re- stricted to a nearshore marine habitat as discussed in Johnson (2012, p. 370-371). Also, cladodont teeth (Glikmanius occidentalis) occur in much of the Wichita Group (Johnson, 2008, table 1). And finally, the strange but common occurrence of iniopterygians at Rattlesnake Canyon (Fig. 2; FIGURE 3. Linear regression plots of measured Orthacanthus texensis teeth Johnson, 2006), together with the petalodonts, cladodonts and hybodonts, (A) and O. platypternus teeth (B) from the Lower Permian Geraldine suggest many of the Wichita faunas were in close proximity to the marine Bonebed, Archer County, Texas. See Table 1. paleoshore. Parrish (1978, p. 212) thought that the Thrift Bonebed probably ?texensis teeth (SMU 76702) have relatively thin bases suggestive of O. occurred at a stratigraphic level roughly coincident with the Bead Moun- platypternus, but otherwise bear little resemblance to the latter species. tain Formation (marine facies) to the south. Based on Hentz and Brown Another O. ?texensis tooth (SMU 76701) is worn, but resembles the (1987) and the discussion by Hentz (1988, p. 22), he was essentially possibly symphyseal teeth assigned to O. ?compressus (Johnson, 2012, correct, as that bonebed lies very close to the contact between the Petrolia p. 373-375) from the Archer City Bonebed 3 (Fig. 2). One O. ?platypternus Formation and overlying Waggoner Ranch Formation with the Beaverburk tooth (SMU 76707) has a typically thin base, but otherwise is sugges- Limestone at its base (Fig. 1). Parrish (1978, p. 235) concluded that this tive of O. texensis, although the cusps are broken. lag bonebed (Sander, 1989, p. 2) was produced by a catastrophic tropical DISCUSSION storm surge, as the animals (six taxa, strongly dominated by Trimerorhachis insignis) and one shark taxon (listed as Xenacanthus, but The Geraldine fauna includes the earliest known occurrence of is very likely Orthacanthus texensis) inhabited mudflat ponds that were Orthacanthus texensis and O. platypternus teeth. Their supposed pre- only one kilometer from the paleoshoreline (Parrish, 1978, p. 233-234). cursor, O. ?compressus, occurs in the next older known faunas in Archer Although no marine vertebrates were recovered by Parrish (1978), it City Bonebed 3 and Conner Ranch Bonebed (Fig. 2; Johnson, 2012). seems likely that they would occur in the fauna as it is one of the best- However, the first two species also occur at the Benson’s pasture local- documented near-marine faunas in the Wichita Group, perhaps second ity, which may occur in the upper Archer City Formation (discussed in only to that described by Berman (1970). Although the Geraldine Bonebed Johnson, 2012). Efforts to establish the geographic position, and there- is much lower in the Wichita, it is not unreasonable to conclude that it 165

FIGURE 4. Orthacanthus texensis teeth from the Lower Permian Geraldine Bonebed, Archer County, Texas. A, Lingual, B, labial, and C, aboral views of SMU 76747; D, lingual-occlusal, and E, labial views of SMU 76748; and F, lingual-occlusal, G, labial, and H, aboral views of SMU 76749. Scale bars equal 3 mm (A-E) and 2 mm (F-H).

FIGURE 5. Probable posterior tooth of Orthacanthus texensis from the Lower Permian Geraldine Bonebed, Archer County, Texas. A, Lingual-occlusal, B, labial, and C, aboral views of SMU 76750. Scale bar equals 1 mm. 166

FIGURE 6. Orthacanthus platypternus teeth from the Lower Permian Geraldine Bonebed, Archer County, Texas. A, Lingual-occlusal, B, labial, and C, aboral views of SMU 76751; D, lingual-occlusal, E, labial, and F, aboral views of SMU 76752; and G, lingual-occlusal, H, labial, and I, aboral views of SMU 76753. Scale bars equal 3 mm (A-C) and 2 mm (D-I). was close to the marine paleoshore, given the constantly changing sea- ACKNOWLEDGMENTS level changes that continued into the Sakmarian (Stanley and Powell, 2003). W. (Bill) May (Norman, Oklahoma) helped collect field samples The assumption that all of the tetrapods in the Geraldine Bonebed on a hot day and identified some of the Geraldine fossils. D. Winkler were freshwater-terrestrial is assumed, given the presence of the associ- (Shuler Museum) provided assistance with preparation of the illustra- ated synapsids and flora. But some late Paleozoic amphibians may have tions, entered cataloged descriptions into the Shuler Museum database tolerated a marginal marine habitat, as reviewed in Laurin and Soler-Gijón and his comments on an earlier draft improved a later draft. Reviews by (2010). Furthermore, this bonebed fauna is somewhat comparable to R. Soler-Gijón (Berlin) and H.-P. Schultze (University of Kansas) made that described by Carpenter et al. (2011) in which a fish-dominated significant improvements, which are appreciated. J. Zidek (Praha) and R. assemblage occupied brackish water in an estuarine environment (R. Soler-Gijón provided suggestions on attempts to locate the origin of Soler-Gijón, personal commun. 2012). “Xenacanthodii.” F. Stangl (Midwestern State University, Wichita Falls, Texas) and E. Lundelius (University of Texas at Austin) are thanked for their attempts to locate any information regarding Benson’s pasture locality (see Johnson, 2012). 167 REFERENCES

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