Canadian Journal of Earth Sciences
ALBANERPETONTIDS (LISSAMPHIBIA, ALBANERPETONTIDAE) FROM THE AGUJA FORMATION (LOWER CAMPANIAN) OF WEST TEXAS, USA.
Journal: Canadian Journal of Earth Sciences
Manuscript ID cjes-2020-0071.R2
Manuscript Type: Article
Date Submitted by the 19-Jul-2020 Author:
Complete List of Authors: Wick, Steven; Texas Vertebrate Paleontology Collections
Lissamphibia, Texas, Albanerpeton, early Campanian, Aguja Formation, Keyword: Aquilan Draft Is the invited manuscript for consideration in a Special Not applicable (regular submission) Issue? :
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1 ALBANERPETONTIDS (LISSAMPHIBIA, ALBANERPETONTIDAE) FROM THE AGUJA
2 FORMATION (LOWER CAMPANIAN) OF WEST TEXAS, USA.
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4 Steven L. Wick¹
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6 ¹Texas Vertebrate Paleontology Collections, 10100 Burnet Road, Austin, TX 78758
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24 Abstract
25 The Lowerverse local fauna of West Texas, USA, preserves a rare, early Campanian
26 assemblage of microvetebrates from Laramidia. The recovery of 137 fragmentary specimens
27 reveals that albanerpetontids were locally abundant here and also widespread throughout much
28 of the Western Interior of North America by early Campanian time. Both gracile- and robust-
29 snouted species are represented within the assemblage. Among these, the occurrence of
30 Albanerpeton nexuosum is consistent with its occurrence in paracontemporaneous deposits
31 elsewhere in the Western Interior. The referral of two specimens to Albanerpeton sp., cf. A.
32 galaktion strongly suggests that this long-lived taxon was far more widespread during the early
33 Campanian than previously known and its likely occurrence in West Texas represents a
34 significant geotemporal range extensionDraft for the species. However, Albanerpeton gracile is
35 seemingly restricted to Judithian ‘age’ deposits in North America and was not identified at
36 Lowerverse. The Lowerverse assemblage supports the current paradigm involving the
37 occurrence of these three named albanerpetontids during middle Campanian–Maastrichtian time
38 in the Western Interior of North America.
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40 Keywords: Lissamphibia, Albanerpeton, Texas, Early Campanian, Aguja Formation
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48 Introduction
49 The present report involving albanerpetontid amphibians is the latest in a series of reports
50 documenting the Lowerverse local fauna. The Lowerverse locality (TMM 45947) is located on
51 private property just west of Big Bend National Park, Texas, USA (Fig. 1). The site is situated
52 within the lower shale member of the Aguja Formation (Lehman 1985). Small theropod
53 dinosaurs from this site were described previously by Wick et al. (2015), mammals by Brink
54 (2016), lizards and snakes by Wick and Shiller (2020). Frogs are currently under study by Wick
55 (in review). Larger dinosaurs and mesoreptiles from elsewhere in the lower shale were described
56 by Lehman et al. (2019). A few albanerpetontid fossils and species from the Big Bend region
57 have previously been reported from the Draftupper shale member of the Aguja Formation (e.g.,
58 Standhardt 1986; Langston et al. 1989; Rowe et al. 1992; Sankey 1998, 2008; Gardner 2000).
59 However, many of these were taxonomically indeterminate and have provided but an impression
60 of middle to upper Campanian albanerpetontid diversity in West Texas. The present report is the
61 first documenting an extensive albanerpetontid assemblage from a single locality but in older
62 (early Campanian) strata of the Aguja Formation.
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64 Geologic context and age of the Lowerverse locality
65 The Lowerverse locality site is situated within the middle of the lower shale member of
66 the Aguja Formation. It preserves a multi-dominant, high-diversity macro- and microverebrate
67 assemblage (sensu Eberth et al. 2007) consisting of both terrestrial and aquatic species. Deposits
68 here consist primarily of dark lignitic clayshale intervals with discontinuous whitish sandstone
69 lenses. Poor quality coal seams are also present in the area (e.g., Henry et al. 1989). All of these
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70 were deposited in paralic environments dominated by peritidal, estuarine, and coastal marsh and
71 swamp habitats (Lehman 1985). A few fossilized logs and in-situ stumps at Lowerverse
72 (representing both conifer and dicotyledonous trees) are further evidence that lower shale
73 habitats were sporadically forested (e.g., Wheeler and Lehman 2000; 2005). At Lowerverse, they
74 typically have a diameter of ~12 inches or less (pers. obs. by the author) and suggest the former
75 presence of trees with low to moderate crown heights. Inter-bedded remains of marine organisms
76 (e.g., ostreid bivalve shells, decapod chelae, and chondrichthyan teeth) indicate intermittent
77 deposition in brackish aquatic habitats. The fundamental stratigraphy of the lower shale was
78 more thoroughly characterized by Lehman (1985) and Lehman et al. (2019) and so the reader is
79 referred to those works for additional information regarding depositional context.
80 Radiometric dates have yet to beDraft obtained for the lower shale member. However,
81 ammonite biostratigraphy indicates that the uppermost interval of the underlying Pen Formation
82 pertains to the Scaphites hippocrepis III zone (ca. 82 Ma) whereas deposits in the overlying
83 Rattlesnake Mountain sandstone member of the Aguja Formation pertain to the Baculites
84 maclearni zone (ca. 80 Ma) (Waggoner 2006). The respective ages for these intervals indicate
85 that the intervening lower shale member is early Campanian in age. Hence, the Lowerverse
86 assemblage belongs to one of only a few early Campanian terrestrial microvertebrate faunas
87 known from the Western Interior of North America and is likely contemporaneous with those of
88 the lower Wahweap Formation of southern Utah and Menefee Formation of northwestern New
89 Mexico but slightly younger than those of the Milk River Formation of Alberta (e.g., Fox 1975;
90 Eaton 1990; Payenberg et al. 2002; Heckert et al. 2007; Larson 2008; Jinnah et al. 2009; Nydam
91 2013; Seymour and Fielding 2013).
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93 Methods
94 Around 450 kg of bulk matrix was collected from the Lowerverse site. The material was
95 then water screened through (stacked) 6 mm and 0.8 mm screens. This process resulted in the
96 production of ~70 kg of residual concentrate in two size fractions. This modest volume of
97 concentrate produced thousands of vertebrate specimens, among which 137 pertain to
98 albanerpetontids. Almost all of these albanerpetontid specimens are very fragmentary and most
99 pertain to jaws. However, 15 specimens are diagnostically informative and provide the
100 foundation for this report. After water screening, further preparation was generally not needed. A
101 few specimens were soaked in household vinegar to help remove adhering matrix. After it had
102 been initially photographed, one of these (TMM 45947-624) was inadvertently left submerged
103 overnight resulting in considerable degradationDraft of the specimen. Furthermore, two specimens
104 (TMM 45947-627 and -629) were sputter coated with gold during an unrelated test project
105 involving scanning electron microscopy. Otherwise, most specimens were imaged using visible
106 light. Imaging was conducted via a binocular microscope using a mounted Apple® iPhone 8.
107 Multiple images of each specimen were then focus stacked and adjusted in Photoshop®
108 Elements 9.0+ to improve image quality. To produce figure scales, specimen measurements were
109 made using a standard graduated microscope reticle and 1 mm calibration slide. Osteological
110 terminology generally follows Gardner (1999a, b) and in some instances Matsumoto and Evans
111 (2018). For the sake of readability, listed specimen numbers are sometimes shortened to the last
112 three digits unique to a particular specimen in order to avoid unnecessary repetition of the
113 locality number (TMM 45947).
114 Lowerverse specimens and locality data are housed at the Vertebrate Paleontology
115 Laboratory at the Jackson School Museum of Earth History (TMM), University of Texas at
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116 Austin, Texas, USA. The following institutional abbreviations are also used: OMNH, Oklahoma
117 Museum of Natural History, Norman, Oklahoma, USA; UALVP, University of Alberta
118 Laboratory for Vertebrate Paleontology, Edmonton, Alberta, Canada; UCMP, University of
119 California Museum of Paleontology, Berkeley, California, USA.
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121 Specimen Descriptions
122 Three named albanerpetontids are currently recognized from Late Cretaceous (middle
123 Campanian–Maastrichtian) deposits of the Western Interior of North America (e.g., Gardner
124 2000; Gardner and Böhme 2008; Gardner and DeMar 2013). Among Gardner’s (2000) ‘robust 125 and gracile-snouted clades’, AlbanerpetonDraft nexuosum (amended from A. nexuosus by Folie and 126 Codrea 2005) is included in the former clade and A. gracile (amended from A. gracilis by Folie
127 and Codrea 2005) and A. galaktion in the latter (e.g., Gardner 1999c, 2000, 2002; Folie and
128 Codrea 2005; Gardner and Böhme 2008; Matsumoto and Evans 2018). For the purposes of
129 efficiency, the following comparative descriptions focus principally on diagnostic elements (i.e.,
130 jaws and skull roof bones) that can be referred to those three recognized species.
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132 SYSTEMATIC PALEONTOLOGY
133 Subclass LISSAMPHIBIA Haeckel, 1866
134 Order ALLOCAUDATA Fox and Naylor, 1982
135 Family ALBANERPETONTIDAE Fox and Naylor, 1982
136 Genus Albanerpeton Estes & Hoffstetter, 1976
137
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138 Albanerpeton nexuosum (=A. ‘nexuosus’ of Estes, 1981; in part = ‘Prodesmodon copei’ Estes
139 1964, referred jaws subsequently assigned by Estes 1981 to A. ‘nexuosus’)
140 Referred material: TMM 45947-626 (fragmentary left dentary) (Fig. 4g, h), TMM45947-
141 628 (middle portion of right maxilla) (Fig. 4d, e), TMM 45947-630 (fragmentary left
142 premaxilla) (Fig. 3d–f), TMM 45947-636 (fragmentary left frontal) (Fig. 2a, b).
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144 Albanerpeton sp., cf. A. galaktion Fox and Naylor, 1982
145 Referred material: TMM45947-629 (fragmentary left premaxilla) (Fig. 3a–c),
146 TMM45947-631 (fragmentary right premaxilla) (Fig. 3 g–i).
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148 Albanerpeton sp. indet. Draft
149 Referred material: TMM 45947-623 (fragmentary left maxilla) (4a, b), TMM 45947-624
150 (fragmentary right maxilla) (Fig. 4c), TMM 45947-625 (fragmentary right maxilla) (Fig.
151 4f), TMM 45947-627 (fragmentary left dentary) (Fig. 4i, j), TMM 45947-632,
152 (fragmentary atlantal centrum) (Fig. 5a–c), TMM 45947-633 (axis) (Fig. 5d), TMM
153 45947-634 (articular) (Fig. 5e, f), TMM 45947-635 (fragmentary ?right parietal) (Fig 2f–
154 h), TMM 45947-637 (fragmentary right frontal) (Fig. 4c–e).
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156 Frontoparietal complex (Fig. 2a–h)
157 Two cranial fragments pertain to a frontal and a third to a parietal. Although these
158 fragments may pertain to multiple species, the three fragments represent different portions of the
159 bone and so permit a generalized description of it. The larger fragmentary frontal, TMM 45947-
160 636, is from the left posterior part of the element (Fig. 2a, b). The dorsal surface exhibits
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161 anastomosing ridges and interstitial polygonal pits typical of albanerpetontid frontals. A posterior
162 portion of the interdigitating sutural surface for contact with the parietal is preserved in addition
163 to the parietal facet. The posterior portion of the orbital margin is also preserved. The
164 ventrolateral crest in TMM 45947-636 is relatively wide and its ventral surface more concave
165 dorsally similar to the condition in Albanerpeton nexuosum, in contrast to the narrower and flat
166 surface seen in A. galaktion or A. gracile (Fox and Naylor 1982, fig.1e; Gardner 2000, figs. 6G,
167 J, K and 8B, C, E). Given these similarities, TMM 45947-636 is tentatively referred herein to A.
168 nexuosum.
169 The second frontal fragment (TMM 45947-637, fig. 2c–e) is from the right side of the
170 element and is similarly sculptured as in TMM 45947-636. The fragment is broken anteriorly at
171 the base of the anterolateral process andDraft posteriorly through the anterior portion of the orbital
172 margin. A conspicuous lateral facet is present (Fig. 2e), which likely represents the posterior slot
173 for the prefrontal. The facet resembles that illustrated for the frontal of Celtedens ibericus (=
174 lacrimal facet of McGowan 1998a, fig. 4). The ventral surface of TMM 45947-637 (Fig. 2d)
175 exhibits a distinct ridge trending posteromedially from the broken anterolateral process which is
176 interpreted as the anterior portion of the ventrolateral crest. As such, the fragment likely pertains
177 to the medial right side of the bone (Fig. 2 cranial schematic). This portion of the crest in TMM
178 45947-637 is more pronounced than in A. galaktion and so the specimen is more likely referable
179 to A. nexuosum. The dorsal sculpture and style of preservation is also identical to the tentatively
180 referred fragment TMM 45947-636 (Fig. 2a) and it is possible that both belong to the same
181 individual bone.
182 The third cranial fragment (TMM 45947-635, Fig. 2f–h) pertains to a parietal. It exhibits
183 a dorsal sculpture similar to the other cranial fragments, but the anastomosing ridges are
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184 narrower and the enclosed pits better defined. A portion of the un-sculptured occipital shelf is
185 also preserved, but very little of it remains so its original form cannot be fully determined (Fig.
186 2f; and see Matsumoto and Evans 2018, fig. 42 for several examples of this variable feature
187 among taxa). Two intact margins bearing sutural contacts are present on the specimen. The first
188 consists of a long, straight, and narrowly slotted margin (Fig. 2h). The second is positioned at a
189 right angle to the first and is more unevenly sutured (Fig. 2g), and more closely resembles that
190 preserved in the presumed posterior frontal exemplar (TMM 45947-636; fig. 2a). Hence, the
191 favored interpretation is that TMM 45947-635 represents an anteromedial portion of a right
192 parietal with the slotted margin representing the contact with the opposite parietal (Fig. 2 cranial
193 schematic fav.). Furthermore, the orientation of the shallowly vaulted ventral surface of the bone
194 seems more consistent with its presumedDraft position on the right side (for comparison see
195 Shirerpeton in Matsumoto and Evans 2018, figs. 12, 13). If so, the lateral margin is apparently
196 fractured just medial to the transverse crest (e.g., Fig 2g versus right parietal of Albanerpeton
197 inexpectatum of Estes and Hoffstetter 1976, plate VIII). Alternatively, if rotated 90 degrees
198 clockwise the specimen could pertain to the anterior part of the left parietal (Fig. 2 cranial
199 schematic alt.), but this interpretation is less likely for the aforementioned reasons. If the favored
200 interpretation is correct, then the parietal portion bearing the unnamed process for contact with
201 the frontal (e.g., fap in Fig. 2b) is not preserved. In any case, TMM 45947-635 could be referred
202 to any one of the three currently recognized albanerpetontids from the Campanian of North
203 America.
204
205 Premaxilla (Fig. 3a–g)
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206 Three premaxillary fragments in the Lowerverse sample are taxonomically informative.
207 As in other albanerpetontids, marginal teeth are pleurodont, non-pedicellate, chisel-like, and with
208 weakly tricuspid crowns. The first specimen (TMM 45947-629) (Fig. 3a–c) consists of the bulk
209 of the ventral portion of a left premaxilla which preserves five complete teeth, a single
210 incomplete tooth, and space for a seventh which has broken off. Most of the pars dorsalis is
211 missing due to breakage. As preserved, the specimen differs from TMM 45947-630 (below) in
212 that the suprapalatal pit appears to have been relatively large with a wide, straight basal margin
213 (Fig. 3b). However, it cannot be determined if the pit was triangular as in the holotype of
214 Albanerpeton galaktion (UALVP 16203: Fox and Naylor 1982, figs. 1b, 2a; Gardner 2002, fig.
215 4b; Gardner 2002, character states 10:2, 11:1). In lingual view, the suprapalatal pit in TMM
216 45947-629 is separated from the medialDraft margin of the bone by a narrow flange rather than a wide
217 strut as in TMM 45947-630 (Fig. 3b versus 3e). Apart from having several intermittent nutritive
218 foramina, the external surface of the fractured pars dorsalis in TMM 45947-629 is nearly smooth.
219 The dimensions of what remains of it imply that it was somewhat narrower than in A. nexuosum
220 (as figured by Gardner 2000, fig. 5A, B, D) – especially as reflected by the curvature of the
221 external narial margin (Fig. 3b, c). The pars palatinum bears a modestly-sized ?palatal foramen
222 (Fig. 3a). It is considerably larger than analogous foramina of A. nexuosum or A. gracile but not
223 nearly as large as that in A. galaktion (e.g., Gardner 2000, compare figs. 4H, I versus figs. 5F, G,
224 H, and 7E). For example, the foramen is not as expansive as that in UALVP 16212 (Gardner
225 2000, see fig. 4H) where the palatal foramen is described as being one and a third to two times
226 that of the bases of medial teeth. It is also possible that what is herein tentatively identified as the
227 palatal foramen in TMM 45947-629 may actually be a smaller unnamed foramen that typically
228 occurs in this area in most albanerpetontid premaxillae (J. Gardner pers. comm.). If so, the
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229 palatal foramen may be missing due to breakage in this fragmentary specimen. In any case, the
230 somewhat enlarged ?palatal foramen and widely open suprapalatal pit in TMM 45947-629 are
231 more consistent with A. galaktion than A. nexuosum or A. gracile. Given these observations, this
232 specimen is herein referred to Albanerpeton sp., cf. A. galaktion. The enlargement of the
233 suprapalatal pit and palatal foramen in A. galaktion is probably linked as they involve feeding
234 and/or olfaction (Gardner 2000; character state 14:1 of Gardner 2002).
235 A second, more robust specimen (TMM 45947-630) consists of a medial section of a left
236 premaxilla (Fig. 3d–f). It preserves three complete teeth and the lower portion of the sutural
237 contact with the contralateral premaxilla. The outer surface of the pars dorsalis is slightly
238 roughened and perforated with tiny nutritive foramina. On its inner surface, only the medial
239 portion of the suprapalatal pit is preserved.Draft The outline of its margin suggests that the
240 suprapalatal pit was likely oval as in Albanerpeton nexuosum (Gardner 2002, character 11:0), as
241 opposed to the triangular or slit-like shape seen in A. cifellii, A. gracile, and A. galaktion
242 (Gardner 2002, character 11:1). Furthermore, the pit in TMM 45947-630 is separated widely
243 from the medial margin of the bone, whereas the suprapalatal pit in A. galaktion closely
244 approaches it (Fig. 3b, e). In A. gracile, this margin is intermediate in width compared to that in
245 both A. nexuosum and A. galaktion. Although a medial portion of the pars palatinum is
246 preserved, the palatal foramen is not. The teeth in TMM 45947-630 are large but not unusually
247 so considering the relative size of the specimen, and they do not appear any stouter than those
248 preserved in the other specimens described here from Lowerverse. Overall, as preserved, this
249 specimen most closely resembles the premaxilla of A. nexuosum.
250 The third specimen (TMM 45947-631) is small and fragmentary (Fig 3g–i). The external
251 surface is slightly roughened and perforated by several nutritive foramina. In lingual view, the
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252 specimen bears remnants of eight teeth; however, none are intact. TMM 45947-631 resembles
253 TMM 45947-629 (above) in having a large suprapalatal pit, a wide base, and is separated from
254 the medial portion of the bone by a narrow strut (Fig. 3h). However, the suprapalatal pit is
255 incompletely preserved in TMM 45947-631 and it cannot be determined if it was triangular in
256 shape as in A. galaktion. However, its preserved form suggests that it was neither oval as in A.
257 nexuosum nor slit-like as in A. gracile or the holotype (OMNH 25400) of A. cifellii (Gardner
258 1999c, fig. 3G; Gardner 2000, figs. 5B, D, J, K and 7B, D, F, G, H). As preserved, the palatal
259 foramen is large and its diameter increases posteriorly, a condition owing (at least in part) to
260 breakage. Of note is that the palatal foramen in TMM 45947-631 is much larger than that in
261 TMM 45947-629 and, as preserved, conforms more closely to that described for A. galaktion by
262 Gardner (2000). As TMM 45947-631 seeminglyDraft exhibits the autapomorphic condition of A.
263 galaktion (i.e., presence of both a large, suprapalatal pit and enlarged palatal foramen), it is
264 tempting to refer TMM 45947-631 to that species. However, given that both features are
265 incompletely preserved (as they are in TMM 45947-629, above), TMM 45947-631 is
266 conservatively referred herein as Albanerpeton sp. cf. A. galaktion.
267
268 Maxilla (Fig. 4a–f)
269 Among the several fragmentary maxillae recovered from Lowerverse, four are
270 taxonomically informative. In all of them (as in other albanerpetontids) the marginal teeth are
271 pleurodont, non-pedicellate, with chisel-like and weakly tricuspid crowns. The first specimen
272 (TMM 45947-623) consists of the medial portion of a left maxilla including a portion of the
273 nasal process and nine teeth (Fig. 4 a, b). The teeth do not exhibit the same degree of size
274 heterodonty seen in those of Albanerpeton nexuosum, but more closely resemble those of both A.
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275 galaktion and A. gracile (Gardner 2000). The tip of the nasal process has broken away, and
276 although the base of the premaxillary lateral process is preserved, the specimen is nonetheless
277 missing the anteromedially positioned, premaxillary dorsal process. Matrix obscures part of the
278 inner surface. The pars palatinum is separated from the nasal process by a shallow trough for
279 articulation with a portion of the palate. The labial surface is smooth aside from several nutritive
280 foramina. In lateral view, the ventral margin of the pars dentalis is horizontal along its preserved
281 length. Although the ventral margin of the pars dentalis below the nasal process is broken, as
282 preserved, the more posterior part bears no evidence of becoming ventrally convex (= “sinuous”
283 of some authors) as in the maxilla of A. nexuosum where this area is conspicuously convex,
284 matching the similarly sinuous condition of the dentary (e.g., Gardner 2000, figs. 2D, 3A).
285 Hence, among Campanian albanerpetontidsDraft from North America, the specimen seemingly
286 pertains to a member of the gracile-snouted clade, but it cannot be confidently referred to a
287 specific taxon.
288 The second specimen (TMM 45947-624) is taphonomically deformed and so is difficult
289 to evaluate (Fig. 4c). It bears 15 complete teeth and likely represents the anterior two thirds of
290 the maxilla. As preserved, the more mesial teeth become progressively longer as in homologous
291 portions of the maxilla in Albanerpeton nexuosum: as such, TMM 45947-624 could be referred
292 to that taxon. Conversely, the labial side of TMM 45947-624 is too damaged and otherwise
293 obscured by matrix to determine if the ventral margin of the pars dentalis is markedly convex as
294 in A. nexuosum. Given these observations, TMM 45947-624 is best considered an indeterminate
295 genus and species of albanerpetontid.
296 The third specimen (TMM 45948-628) represents the middle portion of a robust right
297 maxilla (Fig. 4d, e). The labial side of TMM 45947-628 exhibits a few nutritive foramina but is
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298 otherwise smooth. The lingual side is damaged and the premaxillary dorsal process and pars
299 palatinum are fractured and uninformative. The specimen bears three preserved teeth and a
300 fourth partial one; however, only the base of the nasal process remains. The three preserved teeth
301 exhibit notably disparate lengths and the ventral margin of the pars dentalis also exhibits a
302 considerable steepness. These character states imply that the ventral margin of the pars dentalis
303 may have been strongly convex similar to that seen in A. nexuosum (Fig. 4d schematic and
304 overlay). Given these similarities, TMM 45948-628 is herein referred to that taxon (e.g., see
305 Gardner 2000, fig. 3a).
306 The last exemplar (TMM 45947-625) is fragmentary and abraided (Fig 4f). It consists of
307 the posterior portion of the bone and seemingly bears remnants of 12 teeth. It represents about
308 one half of the element from a very smallDraft individual.
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310 Dentary (Fig. 4g–j)
311 Two taxonomically informative dentaries are included in the current sample. Both
312 specimens exhibit marginal teeth that are pleurodont, non-pedicellate, and with chisel-like,
313 weakly tricuspid crowns. Several additional (and unfigured) specimens in the Lowerverse
314 assemblage exhibit the interdigitating (= ‘mortise and tenon’ of some authors) mandibular
315 symphysis typical of albanerpetontids.
316 The smaller of the two specimens (TMM 45947-626) is from the anteriormost part of a
317 left dentary (Fig. 4 g, h). Although the area of the symphysis is fragmented, all of the mesial
318 tooth positions can be accounted for. The labial surface is smooth with several nutritive foramina
319 but is otherwise unremarkable. In its overall anatomy, TMM 45947-626 bears characteristics
320 seen in robust-snouted albanerpetontid species like A. nexuosum (Estes 1964, 1981; Gardner
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321 2000) or cf. A. nexuosum (Gardner 1999c). For example, the teeth in TMM 45947-626 exhibit an
322 abrupt increase in height as they trend distally and exhibit significant size heterodonty as a result.
323 This condition results in the dental parapet having a sinuous margin to match the convex ventral
324 margin of the pars dentalis in the maxilla of this species (e.g., see TMM 45948-628 above). In
325 TMM 45947-626 the more robust tooth crowns extend well above the level of the dental parapet
326 to a maximum height seemingly at tooth position 7 (however, the tooth at position 6 is missing).
327 This condition is similar to that seen in UCMP 49538 and 49547 (Estes 1964, figs. 43e, 44c,
328 respectively). Estes (1964, p. 92) noted that the tooth crowns in A. nexuosum reach their greatest
329 height at tooth 4 or 5 with a subsequent decrease in height thereafter. However, Estes’ (1964,
330 figs. 43e and 44c) illustrations of UCMP 49538 and 49547 indicate that dentary tooth height
331 reached a maximum extent at tooth positionDraft 7, a fact later confirmed by Gardner (2000, p. 367)
332 who observed that dentary teeth in A. nexuosum are tallest typically at the “sixth to ninth loci on
333 the dentary”. Posterior to tooth position 7, the teeth and associated dorsal margin of the pars
334 dentalis in TMM 45947-626 become reduced, giving the dental parapet a sinuous profile in labial
335 aspect (character states 18:1 and 19:1 of Gardner 2002). Given these observations, TMM 45947-
336 626 is herein referred to A. nexuosum. It is also worth mentioning that the presence of these
337 features in small individuals indicates that they are not simple ontogenetic expressions but are
338 reliably diagnostic for that species (sensu Gardner 2000, p. 353).
339 The second specimen, TMM 45947-627, preserves the anterior portion of a left dentary
340 that is larger than TMM 45947-626 (Fig. 4i, j). The symphysis is not preserved. On its broken
341 surface, the Meckelian canal appears as only a small pore. The labial surface of the dentary is
342 smooth, with multiple nutritive foramina. Thirteen teeth are partially or completely preserved,
343 with most of these in the region of the dentary that has highest degree of size heterodonty among
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344 albanerpetontids. In this regard, there is a notable increase in mesiodistal tooth height among the
345 preserved crowns in TMM 45947-627 similar to that exhibited by A. nexuosum. However, the
346 increase in size is not as abrupt as in TMM 45947-626 which is referred to that species (above).
347 In TMM 45947-627, the teeth increase more gradually in height to a maximum height and
348 robustness at tooth position 10 or 11, similar to that seen in A. galaktion, A. gracile, and the
349 Aptian-Albian species A. arthridion (e.g., Gardner 2000, figs. 2J–M, 7O; Gardner 1999b, fig.
350 2H–J). Furthermore, the increase in tooth height seen in TMM 45947-627 differs slightly from
351 the condition in A. nexuosum where maximum crown height occurs more mesially at around
352 tooth position 6 to 9 (e.g., compare TMM 45947-626 referred to A. nexuosum above with a
353 topotypic dentary [UCMP 49538] of the species figured in Estes 1964, fig. 43e). Furthermore,
354 TMM 45947-627 does not exhibit an abruptDraft rise of the anterior dorsal margin of the pars dentalis
355 in this area as in A. nexuosum. However, the margin is not straight; rather it exhibits a convexity
356 suggestive of the sinuous condition in A. nexuosum. Given the range of characteristics exhibited
357 by TMM 45947-627, this indeterminate specimen could pertain to any one of the three
358 recognized Campanian albanerpetontids in the Western Interior Basin of North America and so
359 is regarded here as being from an indeterminate albanerpetontid.
360
361 Additional elements (Fig. 5a–f)
362 A few additional elements from Lowerverse are also reported here for the purpose of
363 documentation. An isolated atlantal centrum and axis are represented by TMM 45947-632 and -
364 633, respectively (Fig. 5a–c, and 5d) and a left articular (TMM 45947-634) represents one of
365 several recovered (Fig. 5e, f). These specimens so closely resemble their homologues in other
366 albanerpetontids which have been described or figured in detail elsewhere (e.g., Estes and
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367 Hoffstetter 1976; Estes 1981; McGowan 1998b; Gardner 1999a, b, c; Gardner 2000; Rees and
368 Evans 2002; Folie and Codrea 2005; Sweetman and Gardner 2013) that they require no further
369 description here.
370
371 Results
372 The taxonomically informative elements recovered at Lowerverse support recent
373 hypotheses that suggest the occurrence of only three currently named albanerpetontids during
374 middle Campanian–Maastrichtian time in the Western Interior (e.g., Gardner 2000 see fig. 1;
375 Gardner and Böhme 2008; Gardner and DeMar 2013 see figs. 5, 6, and 8). As Albanerpeton
376 nexuosum was a temporally long-ranging species with a wide distribution within the Late
377 Cretaceous Western Interior (including Draftthe middle Campanian portion of the Aguja Formation)
378 (Rowe et al. 1993; Gardner 2000; Gardner and DeMar 2013), its occurrence at Lowerverse is
379 unsurprising.
380 Two specimens (TMM45947-629 and -631) compare favorably with Albanerpeton
381 galaktion. According to Gardner‘s (2000) revision of Late Cretaceous albanerpetontids from
382 western North America, premaxillae of A. galaktion are best diagnosed on the basis of two
383 unique features: a relatively large suprapalatal pit that is nearly right-triangular in lingual outline,
384 and a relatively large palatal foramen. However strongly TMM 45947-629 and -631 may
385 (collectively) support the presence of A. galaktion at Loweverse, the fact that neither specimen
386 conclusively exhibits both of the aforementioned features makes a definitive taxonomic referral
387 unjustifiable. Yet, as preserved, their combined attributes strongly suggest that A. galaktion is
388 indeed present in the Aguja Formation. Although A. galaktion was reported to co-occur with A.
389 gracile in the upper shale of the Aguja Formation by Gardner (2008, p. 197) this reference was
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390 obviously a simple error because Gardner’s (2000) descriptions and figures clearly indicate that
391 A. nexuosum is the correct taxon intended (e.g., also see Gardner and DeMar 2013, tab.4). In any
392 case, the (presumed) occurrence of A. galaktion at Lowerverse (J. Gardner pers. comm.) as well
393 as its occurrence in the slightly older Milk River Formation of Alberta (Fox and Naylor 1982)
394 suggests that this long-lived species was widespread throughout the Western Interior by early
395 Campanian time and persisted into the late Maastrichtian of Wyoming and Montana (Gardner
396 2000, 2005; Gardner and DeMar 2013; Wilson et al. 2014). Although indeterminate
397 albanerpetontids are known from multiple localities within the lower Campanian Wahweap
398 Formation of Utah (Gardner 2000; Gardner and Böhme 2008; Gardner and DeMar 2013), A.
399 galaktion has yet to be reported there (Gardener and DeMar 2013, tab. 3). Its occurrence in the
400 overlying Kaiparowits Formation (e.g., DraftGardner 2000) as well as in contemporaneous strata both
401 north and (likely now) south of Utah suggests that it will eventually turn up in the Wahweap. In
402 fact, the Wahweap Formation is rather similar to the Aguja lower shale in that it preserves
403 abundant carbonaceous mudrock, coalified wood, lenticular tidal channels, and brackish water
404 trace fossils (e.g., Teredolites) suggestive of having developed within comparable paralic
405 environments (see Jinnah and Roberts 2011 and references therein). The absence of A. galaktion
406 in the (middle Campanian) upper shale member of the Aguja Formation and its probable
407 occurrence both at the Lowerverse locality and certainly elsewhere within younger (Judithian
408 NALMA) deposits throughout the Western Interior implies that it also occurs in the upper shale
409 as well but has yet to be identified.
410 Previous accounts suggesting that Albanerpeton gracile occurs exclusively within
411 Judithian deposits remain uncontested here (Gardner 2000; Gardner and DeMar 2013). Although
412 it is logical to assume an earlier and more localized origin for such a geographically widespread
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413 taxon, given the fragmentary condition of the Lowerverse specimens, and because A. gracile
414 exhibits a combination of primitive and derived features with no recognizable autapomorphies
415 (Gardner 2000), it is likely that only well-preserved specimens would allow for its confident
416 identification. For now, if A. gracile has a pre-Judithian origin, it seems to have occurred
417 elsewhere.
418
419 Conclusions
420 Although this report documents albanerpetontids from a single microvertebrate locality,
421 they were seemingly abundant in West Texas during early Campanian time. However, none of
422 the Lowerverse specimens exhibit morphological characteristics that refute the taxonomic make-
423 up of the clade as currently recognized duringDraft middle Campanian–Maastrichtian time in the
424 Western Interior of North America (e.g., Gardner 2000). If both TMM 45947-629 and -631
425 pertain to A. galaktion as speculated here, the prior absence of this taxon in West Texas was very
426 likely a sampling artifact. Furthermore, the presence of Albanerpeton nexuosum and likely
427 presence of A. galaktion at the Lowerverse locality indicates that both species were far more
428 widespread during early Campanian time (southern Alberta, Canada to West Texas, USA) than
429 previously known. If A. galaktion is indeed present at the Lowerverse locality, its occurrence in
430 West Texas would also represent a significant geographic range extension for that species.
431
432 Acknowledgements
433 I am grateful to J. Gardner of the Royal Tyrrell Museum of Palaeontology and two
434 anonymous referees whose critical reviews significantly improved the manuscript. I also thank
435 M. Brown and J.C. Sagebiel of the Texas Vertebrate Paleontology Laboratory at the Jackson
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436 School Museum of Earth Sciences at The University of Texas at Austin for their continued
437 support and curation of the specimens reported herein. I appreciate the efforts of A. Brink who
438 assisted both in bulk matrix processing and with the microscopic collection of specimens. A
439 special word of appreciation is extended to J. Wick who assisted with fieldwork and has patiently
440 supported the author’s academic endeavors. T. Lehman and T. Shiller II have been very
441 entertaining over many years involving countless paleontological adventures in Big Bend.
442
443 References
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541 Lehman, T.M., Wick, S.L, Brink, A.A., and Shiller, T.A., II. 2019. Stratigraphy and vertebrate
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591 Sweetman, S.C., and Gardner, J.D. A new albanerpetontid amphibian from the Barremian (Early
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595 Waggoner, K.J. 2006. Sutural form and shell morphology of Placenticeras and systematic
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599 Wheeler, E.A., and Lehman, T.M. 2000. Late Cretaceous woody dicots from the Aguja and
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610 Wick, S.L., and Shiller, T.A., II. 2020. New taxa among a remarkably diverse assemblage of
611 fossil squamates from the Aguja Formation (lower Campanian) of West Texas. Cretaceous
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613 Wick, S.L., Lehman, T.L., and Brink, A.A. 2015. A theropod tooth assemblage from the lower
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618 Wilson, G.P., DeMar, D.G., Jr., and Carter, G. 2014. Extinction and survival of salamander and
619 salamander-like amphibians across the Cretaceous-Paleogene boundary in northeastern Montana,
620 USA, pp. 271–297. In: Wilson, G.P., Clemens, W.A., Horner, J.R., and Hartman, J.H. (eds.),
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623 doi:10.1130/2014.2503(10)
624
625 Figure captions
626
627 Fig. 1.
628 Map depicting the location of the lower DraftCampanian Lowerverse locality TMM 45947 (LV) west
629 of Big Bend National Park, Texas, USA. Modified from Lehman et al. (2019).
630
631 Fig. 2.
632 Albanerpetontid skull roof bones from the Lowerverse locality, Texas, USA. (a, b), TMM
633 45947-636 fragmentary left frontal referred to Albanerpeton nexuosum in dorsal (a) and ventral
634 (b) views; (c–e) TMM 45947-637 fragmentary, taxonomically-indeterminate right frontal in
635 dorsal (c), ventral (d), and right lateral oblique (e) views; and (f–h) TMM 45947-635
636 fragmentary taxonomically-indeterminate ?right parietal in dorsal (f), ventral (g), and medial
637 oblique (h) views. Parietal abbreviations fav. versus alt. indicates parietal fragment favored
638 positional interpretation versus alternative positional interpretation. Dashed line indicates
639 posterior extent of dorsal sculpture. Abbreviations: facet for unnamed parietal process (fap);
640 frontal (fr); frontal suture (fsu); orbital margin (om); parietal occipital shelf (poc); polygonal pit
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641 (pop); posterior slot for prefrontal (ps); parietal suture (psu); ventrolateral crest (vc). Skull
642 schematics based upon Albanerpeton inexpectatum adapted from Matsumoto and Evans (2018).
643 Scale bar = 1 mm.
644
645 Fig. 3.
646 Premaxillae from the Lowerverse locality, Texas, USA. (a–c), TMM 45947-629 fragmentary left
647 premaxilla referred to Albanerpeton sp., cf. A. galaktion in palatal (a), lingual (b), and labial (c)
648 views with visible light image (a) of specimen sputter coated in gold for SEM image (b); (d–f),
649 TMM 45947-630 fragmentary left premaxilla referred to A. nexuosum in medial (d), lingual (e),
650 and labial (f) views; and (g–i), TMM 45947-631 fragmentary right premaxilla referred to
651 Albanerpeton sp. cf. A. galaktion in palatalDraft (g), lingual (h), and lingual oblique (i) views.
652 Abbreviations: external narial margin (enm); medial flange (mf); nutritive foramen (nfo);
653 ?palatal foramen (?pfo); pars dorsalis (pdo); pars palatinum (pp); suprapalatal pit (sp). Dashed
654 white line indicates margin of the suprapalatal pit in TMM 45947-629. White dots indicate width
655 (w) of the area between the suprapalatal pit and the medial margin of the bone. Scale bar = 1
656 mm. SEM image (3b) was cropped and scaled to match specimen size as figured in 3c.
657
658 Fig. 4.
659 Albanerpetontid maxillae and dentaries from the Lowerverse locality, Texas, USA. (a, b) TMM
660 45947-623 indeterminate anterior portion of left maxilla in labial (a) and lingual (b) views; (c)
661 TMM 45947-624 indeterminate posterior portion of right maxilla in lingual view; (d, e) TMM
662 45947-628 medial portion of right maxilla referred to Albanerpeton nexuosum in labial (d) and
663 lingual (e) views; (f) TMM 45947-625 indeterminate posterior portion of right maxilla in lingual
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664 view; (g, h) TMM 45947-626 anterior left dentary referred to A. nexuosum in lingual (g) and
665 labial (h) views; (i, j) TMM 45947-627 indeterminate anterior left dentary in lingual (i) and
666 labial (j) views. Black arrow indicates TMM 45947-628 herein referred to A. nexuosum shaded
667 and overlain on schematic of A. nexuosum based upon UALVP 16242 from Gardner (2000).
668 White arrows indicate dentary tooth position #7. Abbreviations: dental parapet (dp); dentary pars
669 dentalis (dpd); maxillary pars dentalis (mpd); Meckel’s canal (mc); nasal process (np);
670 premaxillary dorsal process (pdp); pars palatinum (pp); trough for articulation with the palate
671 (tr); subdental shelf (sds). Asterisks indicate missing anterior end of each specimen. Scale bar =
672 1 mm.
673
674 Fig. 5. Draft
675 Additional isolated elements from the Lowerverse locality, Texas, USA. (a–c) TMM 45947-632
676 fragmentary atlantal centrum in ventral (a), anterior (b), and left lateral (c) views; (d) TMM
677 45947-633 axis in dorsal and slightly posterior view, and (e, f) TMM 45947-634 left articular in
678 labial (e) and lingual (f) views. Abbreviations: anterior cotyle (ac); dentary facet (df); odontoid
679 process (op); neural canal (nc); articular surface for the quadrate (qar); semicircular projection
680 (sc). Some osteological terms from from Rees and Evans (2002) and Folie and Codrea (2005).
681 Scale bar = 1 mm.
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Draft
Map depicting the location of the lower Campanian Lowerverse locality TMM 45947 (LV) west of Big Bend National Park, Texas, USA. Modified from Lehman et al. 2019.
332x430mm (300 x 300 DPI)
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Draft
Fig. 2. Albanerpetontid skull roof bones from the Lowerverse locality, Texas, USA. (a, b), TMM 45947-636 fragmentary left frontal referred to Albanerpeton nexuosum in dorsal (a) and ventral (b) views; (c–e) TMM 45947-637 fragmentary indeterminate right frontal in dorsal (c), ventral (d), and right lateral oblique (e) views; and (f–h) TMM 45947-635 fragmentary indeterminate ?right parietal in dorsal (f), ventral (g), and medial oblique (h) views. Parietal abbreviations fav. versus alt. indicates parietal fragment favored positional interpretation versus alternative positional interpretation. Dashed line indicates posterior extent of dorsal sculpture. Abbreviations: facet for unnamed parietal process (fap); frontal (fr); frontal suture (fsu); orbital margin (om); parietal occipital shelf (poc); polygonal pit (pop); posterior slot for prefrontal (ps); parietal suture (psu); ventrolateral crest (vc). Skull schematics based upon Albanerpeton inexpectatum adapted from Matsumoto and Evans (2018). Scale bar = 1 mm.
205x149mm (300 x 300 DPI)
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Fig. 3. Premaxillae from the Lowerverse locality, Texas, USA. (a–c), TMM 45947-629 fragmentary left premaxilla referred to Albanerpeton cf. galaktion in palatal (a), lingual (b), and labial (c) views with visible light image (a) of specimen sputter coated in gold for SEM image (b); (d–f), TMM 45947-630 fragmentary left premaxilla referred to A. nexuosum in medial (d), lingual (e), and labial (f) views; and (g–i), TMM 45947- 631 fragmentary right premaxilla referred to Albanerpeton cf. galaktion in palatal (g), lingual (h), and lingual oblique (i) views. Abbreviations: external narial margin (enm); medial flange (mf); nutritive foramen (nfo); ?palatal foramen (?pfo); pars dorsalis (pdo); pars palatinum (pp); suprapalatal pit (sp). Dashed white line indicates margin of the suprapalatal pit in TMM 45947-629. White dots indicate width (w) of the area between the suprapalatal pit and the medial margin of the bone. Scale bar = 1 mm. SEM image (3b) was cropped and scaled to match specimen size as figured in 3c.
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Fig. 4. Albanerpetontid maxillae and dentaries from the Lowerverse locality, Texas, USA. (a, b) TMM 45947-623 indeterminate anterior portion of left maxilla in labial (a) and lingual (b) views; (c) TMM 45947-624 indeterminate posterior portion of right maxilla in lingual view; (d, e) TMM 45947-628 medial portion of right maxilla referred to Albanerpeton nexuosum in labial (d) and lingual (e) views; (f) TMM 45947-625 indeterminate posterior portion of right maxilla in lingual view; (g, h) TMM 45947-626 anterior left dentary referred to A. nexuosum in lingual (g) and labial (h) views; (i, j) TMM 45947-627 indeterminate anterior left dentary in lingual (i) and labial (j) views. Black arrow indicates TMM 45947-628 herein referred to A. nexuosum shaded and overlain on schematic of A. nexuosum based upon UALVP 16242 from Gardner (2000). White arrows indicate dentary tooth position #7. Abbreviations: dental parapet (dp); dentary pars dentalis (dpd); maxillary pars dentalis (mpd); Meckel’s canal (mc); nasal process (np); premaxillary dorsal process (pdp); pars palatinum (pp); trough for articulation with the palate (tr); subdental shelf (sds). Asterisks indicate missing anterior end of each specimen. Scale bar = 1 mm.
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Fig. 5. Additional isolated elements from the Lowerverse locality, Texas, USA. (a–c) TMM 45947-632 fragmentary atlantal centrum in ventral (a), anterior (b), and left lateral (c) views; (d) TMM 45947-633 axis in dorsal and slightly posterior view, and (e, f) TMM 45947-634 left articular in labial (e) and lingual (f) views. Abbreviations: anterior cotyle (ac); dentary facet (df); odontoid process (op); neural canal (nc); articular surface for the quadrate (qar); semicircular projection (sc). Some osteological terms from from Rees and Evans (2002) and Folie and Codrea (2005). Scale bar = 1 mm.
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