The Strophomenide Brachiopod Ahtiella Öpik in the Ordovician Of

1 The strophomenide brachiopod Ahtiella Öpik in the Ordovician of

2 Gondwana and the early history of the plectambonitoids

Q13 Juan L. Benedetto

4 Centro de Investigaciones en Ciencias de la Tierra (CICTERRA), Consejo Nacional de Investigaciones Cientíﬁcas y Técnicas (CONICET) and 5 Universidad Nacional de Córdoba, Vélez Sarsﬁeld 1611, X5016GCA Córdoba, Argentina 〈[email protected]〉

76 Abstract.—The Precordilleran species Ahtiella argentina Benedetto and Herrera, 1986 is redescribed and illustrated 8 and Monorthis coloradoensis Benedetto, 1998 from northwestern Argentina is reassigned to the genus Ahtiella Öpik, 9 1932. Ahtiella famatiniana new species from volcaniclastic rocks of the Famatina range (western Argentina) and 10 Ahtiella tunaensis new species from the Precordillera basin (Cuyania terrane) are proposed. Paleogeographic and strati- 11 graphic evidence strongly suggests that Ahtiella originated in the Andean region of Gondwana to further migrate to 12 Avalonia, Baltica, and Cuyania. Contrary to previous assumptions, the fossil record from the Famatina volcaniclastic 13 succession suggests that the plectambonitoid Ahtiella famatiniana n. sp. evolved from the hesperonomiid orthoid 14 Monorthis transversa Benedetto, 2003 that always occurs in the underlying strata. Phylogenetic analysis of Ahtiella 15 species shows that A. famatiniana n. sp. and the Peruvian A. zarelae Villas in Gutiérrez-Marco and Villas, 2007 are not 16 only the earliest species of the genus but also are morphologically intermediate between Monorthis Bates, 1968 and the 17 later and more derived species of Ahtiella from Baltica and Cuyania. If, as empirical evidence presented here shows, 18 Ahtiella originated from Monorthis through a series of minor transformations, then the impressive morphological gap 19 between orthides and strophomenides was bridged through short-time cladogenesis events, suggesting that it might not 20 have a deﬁnite discontinuity between the species level evolution and the origin of higher taxa (macroevolution).

21 UUID: http://zoobank.org/4b8c5442-ea2c-41b2-97f7-4c0a8b0384a2

22 23 24 Introduction One of the objectives of this study is to update the tax- 49 onomy of the genus Ahtiella from the three major Ordovician 50 25 The genus Ahtiella Öpik, 1932 is a distinctive resupinate and basins of Argentina: Precordillera, Famatina, and Central 51 26 variably geniculate plectambonitoid brachiopod described ori- Andes. This includes: (1) the redescription of the Precordilleran 52 27 ginally from the Baltic region (Öpik, 1932, 1933; Hessland, species Ahtiella argentina Benedetto and Herrera, 1986, on the 53 28 1949) but subsequently recognized in Wales (Bates, 1968) and basis of extensive collections made in the past twenty years from 54 29 central Newfoundland (Neuman, 1976). In South America, the upper part of the San Juan Formation, as well as the proposal 55 30 Ahtiella is very common in the lower − middle Darriwilian of a new species of Ahtiella from the somewhat younger Las 56 31 carbonate-ramp deposits of the Precordillera basin of west-central Chacritas Formation; (2) the first description of the Ahtiella 57 32 Argentina where it defines the uppermost of the six brachiopod specimens from volcaniclastic rocks of the Famatina Range; and 58 33 biozones recognized through the San Juan Formation (Herrera (3) the reassignment to the genus Ahtiella of Monorthis color- 59 34 and Benedetto, 1991; Benedetto, 2002, 2007). Later, Ahtiella was adoensis Benedetto, 1998b, from northwestern Argentina. 60 35 reported from the Floian-Dapingian volcaniclastic succession of Evidence presented here aims to shed light on the long- 61 36 the Famatina Range (Benedetto et al., 2003; Benedetto 2003a) standing and not yet resolved issue of the origin of plectambo- 62 37 but these specimens remain undescribed. Its presence in southern nitoid brachiopods. Although parsimony analysis constitutes an 63 38 Peru (Gutiérrez-Marco and Villas, 2007), together with its record indispensable tool for unravelling the phylogeny of fossil groups, 64 39 in the central Andean Basin of northwestern Argentina (this the most difficult task is to corroborate in the fossil record the 65 40 paper) and probably Bolivia (described as Valcourea sp. by phyletic lineages predicted in such analyses, and even more 66 41 Havlíček and Branisa, 1980), indicate that this genus not only problematic is to detect those morphological transitions leading to 67 42 attained a wide geographic range in South America but also the origin of new taxa. According to the punctuated equilibrium 68 43 experienced a significant speciation event encompassing at least hypothesis (Eldredge and Gould, 1972; Gould and Eldredge, 69 44 five species. As Gutiérrez-Marco and Villas (2007) pointed out, 1977; Benton and Pearson, 2001), this can be explained by the 70 45 the records of Ahtiella in the Floian of Peru and Dapingian of conjunction of the rapidity as cladogenesis events occur and the 71 46 Famatina are the oldest known of the genus, strongly suggesting relatively small size and geographic restriction of populations 72 47 that it originated on the Andean margin of Gondwana and later undergoing phenotypic change. In this respect, the continuous 73 48 migrated to other regions. and richly fossiliferous volcanosedimentary succession of the 74 1 2 Journal of Paleontology

75 Famatina Range provides an invaluable frame to establish well- 76 resolved phylogenies based on the fossil record. In this paper, 77 evidence is presented suggesting that Ahtiella originated from the 78 hesperonomiid orthoid Monorthis transversa Benedetto, 2003b, 79 which always occurs in strata below those bearing Ahtiella 80 famatiniana new species (described herein). A general trend of 81 morphological change through time emerges from the compara- 82 tive morphology of Ahtiella species and its putative ancestor 83 Monorthis. Relevant for our phylogenetic hypothesis is the fact 84 that the earliest species of Ahtiella recorded in Gondwana exhibit 85 transitional characteristics between Monorthis and the typical 86 Ahtiella species from younger strata of Cuyania and Baltica. 87 Finally, a phylogenetic analysis is presented herein to investigate 88 the evolutionary relationships among the Gondwanan species of 89 Ahtiella and those from Cuyania, Baltica, and Avalonia.

90 Stratigraphic provenance and age

91 The early Paleozoic geodynamic history of southern South 92 America involved three main sedimentary domains (Fig. 1), 130 93 which were inhabited at different times by species of Ahtiella. 94 They are: (1) the autochthonous Central Andean Basin devel- 95 oped around the Brazilian craton through Peru, Bolivia, and 131 96 northwestern Argentina; (2) the volcanosedimentary Famatina 97 Basin, which together with the Puna volcanic arc developed 98 peripheral to the active pre-Andean Gondwana margin; and 132 99 (3) the Precordillera Basin developed on the Laurentian-derived 100 Cuyania terrane, which accreted to Gondwana during the early 101 Paleozoic (for a comprehensive review of the Ordovician basins 133 102 of Argentina, see Astini, 2003).

103 Central Andean Basin.—The southern part of the large Central 134 104 Andean Basin is widely exposed in the Cordillera Oriental of 105 northwestern Argentina, where the uppermost Cambrian to 106 Lower Ordovician siliciclastic succession of the Santa Victoria 135 107 Group attains 3,800 m in thickness. In the study area of Los 108 Colorados (Fig. 2), it is overlain by a succession of reddish Figure 1. Map of central-western South America showing the main 109 purple sandstones named the Alto del Cóndor Formation, which Ordovician sedimentary basins discussed in the text (gray shading). 136 110 is succeeded by fossiliferous greenish mudstones and marls. 111 This interval, which was referred to as the ‘Green Member of the 112 Sepulturas Formation’ by Astini (1994) and as the Sepulturas deposited in a retroarc basin almost synchronously with the 137 113 Formation by Astini et al. (2004a), is well exposed at Quebrada emplacement of crust-derived magmatism along the proto- 138 114 Chamarra and Quebrada del Cardonal (Fig. 2). Brachiopods Andean margin (Pankhurst et al., 2001; Dahlquist et al., 2005). 139 115 consist of Monorthis coloradoensis (reassigned herein to Marine intervals are well exposed to the north of the basin in the 140 116 Ahtiella) and rare specimens of Paralenorthis sp., Dinorthis? Chaschuil area (Catamarca Province), and to the south in the 141 117 sp., and small dalmanellids. Trilobites are represented by Cachiyuyo-Saladillo rivers area (La Rioja Province) (Fig. 3). In 142 118 Neseuretus sp., a trinucleid of the Anebolithus-Incaia group the Chaschuil area, a regressive volcanosedimentary sequence 143 119 (personal communication, B.G. Waisfeld, 2017), and a new acummulated on a high-gradient narrow platform ﬂanking the 144 120 species of Hoekaspis, the latter recorded elsewhere in the Sub- volcanic chain (Mángano and Buatois, 1996, 1997). Its lower 145 121 andean Ranges of northwestern Argentina from beds not older part, ~ 150 m thick, was referred to the Loma del Kilómetro 146 122 than the upper Darriwilian (Waisfeld and Vaccari, 2003). Member of the Suri Formation; it has been interpreted as 147 123 Albanesi and Astini (2002) reported from interbedded deposited in a storm- and mass ﬂow-dominated shelf, whereas 148 124 carbonate-rich layers a conodont assemblage consisting of the upper Punta Pétrea Member is a coarse-grained volcani- 149 125 Erraticodon, Erismodus, and Plectodina, as well as micro- clastic wedge that records the progradation of a fan delta system 150 126 remains of the agnathan Sacabambaspis considered of late onto the shelf sediments. The Dapingian age of the Loma del 151 127 Darriwilian age. Kilómetro Member, containing Monorthis transversa (dis- 152 cussed below) and other brachiopods (Benedetto, 1994), is 153 128 Famatina Basin.—The Famatina Range is characterized by a based on conodonts of the Baltoniodus navis Biozone (Albanesi 154 129 thick succession of sedimentary and volcanosedimentary rocks and Vaccari, 1994) and the Baltoniodus triangularis Biozone 155 Benedetto—The strophomenide brachiopod Ahtiella in Gondwana 3

Figure 2. Geological map of the Los Colorados area of the Central Andean Basin (modiﬁed from Astini et al., 2004a) showing fossil locations (stars) and integrated stratigraphic column of the study area showing levels yielding Ahtiella coloradoensis.1= Quebrada Chamarra; 2 = Quebrada Cardonal.

156 (Carlorosi et al., 2017) recovered from the upper shell beds of famatiniana n. sp. (this paper). This succession is partially 162 157 this member. That age is consistent with the Whitlandian British interbedded with (Cisterna, 2001), or is unconformably overlain 163 158 regional stage suggested by the underlying trilobite fauna by (Astini and Dávila, 2002), the Sierra de Las Planchadas 164 206 238 159 (Vaccari and Waisfeld, 1994). The Punta Pétrea Member, which rhyolite, which provided a Pb/ U SHRIMP age of 165 160 crops out between Agua del Médano and Puesto Chaschuil, 468.3 ± 3.4 Ma (Baldo et al., 2003), i.e., close to the Dapingian- 166 161 yielded an undescribed species of Famatinorthis and Ahtiella Darriwilian boundary. 167 4 Journal of Paleontology

Figure 3. Location of the Famatina Range showing sampled areas (circled numbers), stratigraphic columns, and fossiliferous horizons. 1 = Chaschuil River area; 2 = Central Famatina Range (Cachiyuyo-Saladillo rivers area).

168 The thicker and more continuous volcanosedimentary the Suri Formation and the base of the overlying Molles 189 169 succession exposed in the central Famatina Range has been Formation contain conodonts referable to the upper part of the 190 170 referred to the Famatina Group, encompassing the Suri and Oepikodus evae Biozone of Floian age (late Fl2 stage slice of 191 171 Molles formations (Harrington and Leanza, 1957). Both units Bergström et al., 2009) (Albanesi and Astini, 2000). Lehnert 192 172 are profusely fossiliferous, containing rhynchonelliform et al. (1997) reported from the Molles Formation conodonts of 193 173 (Benedetto, 2003b, 2008, 2013) and lingulate brachiopods the Paroistodus originalis Biozone of middle Dapingian age. 194 174 (undescribed), bivalves (Sánchez and Babin, 1993; Sánchez, The Molles Formation is unconformably overlain by a 195 175 1997), trilobites (Harrington and Leanza, 1957; Vaccari and 720 m thick volcanosedimentary succession named the Cerro 196 176 Waisfeld, 1994), and graptolites (Toro and Brussa, 1997). The Morado Group, which starts with acidic volcanics and 197 177 up to 2,000 m thick succession reflects deposition on a high- ignimbrites (Portillo Formation) and culminates with silicified 198 178 gradient, mixed siliciclastic-volcaniclastic platform (Astini and tuffs, pyroclastic flows, and bioturbated fossiliferous green 199 179 Benedetto, 1996; Astini, 1999, 2003; Mángano et al., 2002). shales interbedded with coquina layers (La Escondida Forma- 200 180 The Suri Formation displays a shallowing-upward trend ranging tion) (Astini and Dávila, 2002) (Fig. 3). The fauna is dominated 201 181 from dark shales deposited in relatively deep oxygen-deficient by Famatinorthis turneri (Benedetto, 2013), a distinctive taxon 202 182 waters to shallow platform facies. The Molles Formation of the underlying Molles Formation. A volcanosedimentary unit 203 183 consists of fossiliferous grey mudstones alternating with probably equivalent to the La Escondida Formation crops out to 204 184 silicified tuffs, volcanogenic sandstones, and reddish sandstones the north of the Cachiyuyo River at Las Pircas anticline. These 205 185 with evidence of tidal action. Concerning the age, the lower part levels yielded an undescribed Skenidioides? sp. , Paralenorthis 206 186 of the Suri Formation yielded graptolites that indicate the Floian sp., and Ahtiella sp. (Benedetto et al., 2003), the last described 207 187 Baltograptus deflexus and Didymograptellus bifidus biozones herein as A. famatiniana n. sp. The age of this interval, in 208 188 (Toro and Brussa, 1997), whereas the shell beds from the top of absence of conodont data, is still poorly constrained, but given 209 Benedetto—The strophomenide brachiopod Ahtiella in Gondwana 5

210 that in the Chaschuil area the levels of A. famatiniana n. sp. are et al., 2001, and references therein), and numerous brachiopods 268 211 interbedded with isotopically dated volcanic rocks (see above), not yet described, including Skenidioides? sp. and Ahtiella 269 212 a middle-late Dapingian age seems most likely. tunaensis new species (this paper). Several conodont studies led 270 to the recognition the Y. crassus Zone in the lower part of the 271 213 Precordillera Basin (Cuyania terrane).—There is a general Las Chacritas Formation, the Eoplacognathus pseudoplanus 272 214 agreement that the up to 2,500 m thick, passive-margin carbo- Biozone from 36 m above the base, and the Eoplacognathus 273 215 nate succession started to accummulate during the Cambrian suecicus Biozone near the top (Albanesi and Astini, 2000; 274 216 Series 2 on the Laurentian continental margin, a segment of Heredia et al., 2011; Mestre and Heredia, 2012, 2013; Serra 275 217 which subsequently rifted from the Ouachita Embayment ori- et al., 2015). Accordingly, A. tunaensis n. sp. can be confidently 276 218 ginating the Cuyania terrane (Astini et al., 1995; Thomas and dated as middle Darriwilian (Dw2). 277 219 Astini, 1996, 2003; Astini, 1998; Benedetto, 1998a, 2004; 220 Ramos, 2004; but see Finney, 2007, for a para-autochthonous Remarks on the biogeography of Ahtiella and related 278 221 Gondwanan hypothesis). Cuyania became part of the Gond- ahtiellins 279 222 wana continent since its accretion to the proto-Andean margin 223 by Middle Ordovician or more probably Late Ordovician times. The earliest known representative of the genus is Ahtiella zarelae 280 224 Depositional environments evolved from tidal flats, shoals, Villas in Gutiérrez-Marco and Villas, 2007 from the upper Floian 281 225 shallow subtidal settings, and restricted subtidal settings during San José Formation of southern Peru (Gutiérrez-Marco et al., 282 226 the Cambrian − early Tremadocian, to open shelf settings by late 2008). The slightly younger A. famatiniana n. sp. occurs in vol- 283 227 Tremadocian-Darriwilian times (Cañas, 1999; Keller, 1999, caniclastic rocks of the Famatina Range of middle-late Dapingian 284 228 2012; Gómez and Astini, 2015). The carbonate succession age. In Anglesey (northwestern Wales), Ahtiella is represented by 285 229 referred to the San Juan Formation consists of ~ 350 m of A. quadrata Bates, 1969, from the Expansograptus hirundo 286 230 burrowed skeletal wackestones and packstones capped by a Biozone, which in the Atlantic Province encompasses the 287 231 25 − 30 m thick interval of mid-outer ramp nodular limestones Dapingian and the base of Darriwilian (Zalasiewicz et al., 2009), 288 232 bearing a rich benthic fauna dominated by rhynchonelliform and A. concava Bates, 1969, from the slightly younger Bob Dei- 289 233 brachiopods and sponges, with trilobites, bryozoans, gastro- niol Formation. Ahtiella paucirugosa Neuman, 1976 has been 290 234 pods, crinoids, and linguliforms as secondary components reported from the lower Darriwilian Summerford Group of New 291 235 (Carrera, 2003; Waisfeld et al., 2003; Sorrentino et al., 2009; World Island, central Newfoundland. These volcaniclastic rocks 292 236 Carrera and Ernst, 2010; Lavié and Benedetto, 2016) (Fig. 4). were interpreted as recording intra-Iapetus volcanic islands related 293 237 The brachiopod association from these beds encompasses the to the Avalonian paleocontinent (Neuman, 1976, 1984; Neuman 294 238 Ahtiella argentina Biozone, which is the uppermost of the six and Harper, 1992; Harper et al., 1996). Monorthis coloradoensis 295 239 biozones recognized through the San Juan Formation (Herrera occurs in the Cordillera Oriental of northwestern Argentina from 296 240 and Benedetto, 1991; Benedetto, 2002, 2007). This interval is beds probably not older than mid-Darriwilian. Ahtiella is common 297 241 particularly well exposed along the western slope of Cerro in the carbonate or mixed carbonate-clastic rocks of Baltica and 298 242 Viejo, ~ 20 km northeast of the city of San José de Jáchal, where Cuyania. In Sweden and Estonia, Ahtiella encompasses the 299 243 the San Juan Formation forms a westward-dipping homoclinal Kunda and Asseri regional stages, the latter reaching the middle 300 244 succession. The A. argentina specimens described herein were Darriwilian Pterograptus elegans Biozone and E. suecicus Zone 301 245 collected mainly at Quebrada Los Gatos and the adjacent (Tolmacheva et al., 2003; Suyarkova and Koren, 2009). As sta- 302 246 Quebrada Honda stratigraphic sections from a 10 − 12 m thick ted above, in the Precordillera basin, Ahtiella ranges from the 303 247 package of nodular limestones lying immediately below the lower Darriwilian (A. argentina) to the middle Darriwilian (A. 304 248 contact with the Los Azules Formation black shales (Fig. 4). tunaensis n. sp.) but does not reach the E. suecicus Zone. Such a 305 249 The age of this interval is well constrained by conodonts of the distribution led Gutiérrez-Marco and Villas (2007) to infer that 306 250 Paroistodus horridus Subzone within the Lenodus variabilis Ahtiella migrated eastward from the mid-latitude (~30–40°) 307 251 Biozone (Albanesi and Ortega, 2002; Ortega et al., 2007) and Andean region into Avalonia and Baltica, and simultaneously 308 252 the lower part of the succeeding Yangtzeplacognathus crassus moved into the low-latitude Cuyania taerrane. It should be noted 309 253 Biozone (Mestre and Heredia, 2013; Serra et al., 2015). that Gutiérrez-Marco and Villas (2007, fig. 8) adopted the 310 254 According to the time-slices schema proposed by Bergström paleogeographic reconstruction of Aceñolaza et al. (2002) and 311 255 et al. (2009), the A. argentina beds fall mostly within Dw1 Finney (2007) and placed Cuyania into the gap delimited by 312 256 reaching the lower part of Dw2. southern South America, South Africa, and Antarctica. Because 313 257 At Sierra de la Trampa, near 40 km south of the city of San neither tectonostratigraphic (Astini and Rapalini, 2003; Ramos, 314 258 José de Jáchal, a ~ 60 m thick succession of nodular limestones 2004; Thomas et al., 2004) nor paleontological evidence (Ben- 315 259 crops out at Quebrada Las Chacritas and Quebrada La Tuna edetto, 2004) supports such a para-autochthonous Gondwanan 316 260 (Fig. 4). This package was originally referred by Espisúa (1968) origin, Cuyania is located here fairly closer to, and at approxi- 317 261 to the ‘upper member’ of the San Juan Formation, then to the mately the same paleolongitude as the Famatina-Puna volcanic 318 262 ‘Las Tunas calcareous unit’ by Carrera (1997), and finally to the arc (Fig. 5). Perhaps the major weakness—but not the only 319 263 Las Chacritas Formation by Astini (1998), which was formally one—of the Finney (2007) reconstruction is the complete 320 264 defined by Peralta et al. (1999). The thin bedded wackestones, absence in the Cambrian carbonate rocks of the Precordillera of 321 265 bioclastic grainstones, and mudstones of the Las Chacritas Redlichiid-realm trilobites, which, as it is known, are distinctive 322 266 Formation have yielded rich poriferan assemblages (Carrera, of Australasia and Antarctica. Instead, the Cambrian- 323 267 1997), excellently silicified trilobite larval stages (Waisfeld Tremadocian trilobites from Cuyania (Astini et al., 1995; 6 Journal of Paleontology

Figure 4. Outcrops of Ordovician rocks in the Precordillera mountain belt, sampled areas (circled numbers), and stratigraphic columns showing fossiliferous horizons. 1 = Cerro Viejo (Qebrada Los Gatos and Qebrada Honda); 2 = Sierra de la Trampa (Quebrada Las Chacritas and Quebrada La Tuna).

324 Vaccari, 1995; Benedetto, 2004; Benedetto et al., 2009), as well with Cuyania, e.g., Skenidiodes Schuchert and Cooper, 1931; 331 325 as brachiopods (Benedetto and Foglia, 2012) and other fossil Paralenorthis Havlíček and Branisa, 1980; Productorthis 332 326 groups (Carrera and Rigby, 1999; Carrera, 2003; Astini et al., Kozlowski, 1927; Monorthis Bates, 1968; Ffynnonia Neuman 333 327 2004b) display indisputable Laurentian afﬁnities. On the other and Bates, 1978; Hesperonomia Ulrich and Cooper, 1936; 334 328 hand, the Early Ordovician brachiopod faunas of Famatina— Hesperonomiella Ulrich and Cooper, 1936; Camerella Billings, 335 329 with a strong Celtic province signature (Benedetto, 2004; Harper 1859; and Rugostrophia Neuman, 1971. This indicates that by 336 330 et al., 2009)—share several genera (though not the same species) the Darriwilian, Cuyania was separated from Gondwana by a 337 Benedetto—The strophomenide brachiopod Ahtiella in Gondwana 7

margin. Several recent paleontological discoveries provided 369 evidence supporting that both the Central Andean Basin and the 370 arc-related Puna-Famatina Basin operated simultaneously as 371 centers of evolutionary radiation (‘centers of origin’) and spe- 372 cies pump regions (sensu Harper et al., 2013) from which new 373 taxa spread to neighboring areas (Benedetto and Sánchez, 2003; 374 Muñoz and Benedetto, 2016; Benedetto and Muñoz, 2017). 375 Such temperate Gondwana basins acted as sites of origination, 376 as did the equatorial shallow-water shelves of Gondwana and 377 peri-Gondwanan terranes, which have been identified by Bassett 378 et al. (2002) as the main source of the precursors to the Ordo- 379 vician radiation. For instance, the earliest known punctate 380 orthide Lipanorthis Benedetto in Benedetto and Carrasco, 2002 381 from the upper Tremadocian of northwestern Argentina was not 382 an immigrant from the tropical belt, as Harper et al. (2004) 383 suggested, but probably originated from a Protorthisina-like 384 plectorthoid ancestor inhabiting the Central Andean Basin in the 385 latest Cambrian (Benedetto, 2013). Furthermore, based on cla- 386 distic analysis, Benedetto and Muñoz (2017) showed that plec- 387 torthoids not only underwent an important diversification in the 388 Central Andean Basin during the Tremadocian and Floian but 389 Figure 5. Early − Middle Ordovician paleogeography map (modified from also could have been a source for the heterorthids, which 390 Cocks and Torsvik, 2002 and Popov et al., 2009), showing global distribution through the Ordovician spread along the western Gondwanan 391 of the genus Ahtiella (stars). Paleogeographic map. ATA = Armorican Terrane shelves (Peru, northern Africa) and peri-Gondwanan terranes 392 Assemblage; CAB = Central Andean Basin; CNF = Central Newfoundland (placement based on Neuman, 1984). (Avalonia, Armorica). 393 The Puna-Famatina volcanic arc (Fig. 5) was another sig- 394 338 remnant ocean not large enough to prevent faunal dispersion nificant center of origin during the Early to Middle Ordovician. 395 339 (Benedetto et al., 2003; Benedetto, 2004). It seems likely that As it has been already noted, its shelly faunas exhibit a high 396 340 brachiopod dispersion from Famatina to Cuyania was facilitated level of endemicity, in particular bivalves (Sánchez and Babin, 397 341 by the gradual approximation of the Cuyania terrane to the 1993; Sánchez, 1997) and brachiopods (Benedetto, 2003b; 398 342 Gondwana margin combined with a generalized sea-level rise Benedetto and Sánchez, 2003). Volcanic islands and archipe- 399 343 (Carrera and Astini, 1998; Cañas, 1999; Astini, 2003). lagos have long been recognized as important evolutionary 400 344 An interesting feature is that diversification of the sub- centers of modern biota (e.g., MacArthur and Wilson, 1967), but 401 345 family Ahtiellinae was centered mainly in Avalonia, Cuyania, their role in promoting faunal diversification in the past was not 402 346 and Baltica (Fig. 5). The Welsh Treiorwerth Formation yielded fully acknowledged until Neuman (1984) proposed that the 403 347 Inversella (Reinversella) monensis Bates, 1969 (Neuman and distinctive Celtic faunas from the Ordovician volcaniclastic 404 348 Bates, 1978), whereas the Central Newfoundland Summerford rocks of the Caledonian-Appalachian folded belt inhabited 405 349 Group contains the ahtiellins Schedophyla potteri Neuman, intra-Iapetus volcanic islands. Also relevant was the subsequent 406 350 1971, Inversella sp., and the endemic Guttasella gutta Neuman, study by Webby (1992) on the low-latitude Ordovician faunas 407 351 1976. In the Cuyanian Precordillera Basin, Ahtiella argentina from the volcaniclastic rocks of New South Wales. Harper et al. 408 352 co-occurs with I. (R.) arancibiai Herrera and Benedetto, 1987 (2009) emphasized the role of such volcanic chains as cradles 409 353 (Benedetto et al., 2008) and the endemic ahtiellin Sanjuanella and centers of origin contributing to the increase of γ-diversity 410 354 plicata Benedetto and Herrera, 1987. In Estonia, Ahtiella lirata during the Great Ordovician Biodiversification Event. 411 355 Öpik, 1932 is approximately coeval with I. (Inversella) borealis 356 Öpik, 1933. Outside the Baltic and Celtic faunal provinces, the Current ideas about the origin of Plectambonitoidea 412 357 only ahtiellins reported are Borua Williams and Curry, 1985 358 from Ireland, and two species of Schedophyla Neuman, 1971 The general statement that the order Strophomenida evolved 413 359 from southern China (Xu and Liu, 1984; Zhan et al., 2006). from the early to middle Cambrian Nisusiidae of the class 414 360 However, as noted below, the placement of Schedophyla among Kutorginata (Williams and Hurst, 1977) or, alternatively, from 415 361 the ahtiellinis requires further confirmation. The Norwegian an ancestor similar to Billingsella Hall and Clarke, 1892 at the 416 362 Rutrumella Harper in Bruton and Harper, 1981 is a poorly Cambrian-Ordovician transition, has been based essentially on 417 363 known genus that has been referred questionably to the sub- the presence in all these groups of an apically perforated pseu- 418 364 family (Cocks and Rong, 2000). dodeltidium (Cocks and Rong, 1989; Williams et al., 1996). 419 However, no further compelling evidence has been presented to 420 365 The Andean region as a center of origin support such ancestor-descendant relationships for all members 421 of the order. According to Bassett et al. (2001), bilingsellides 422 366 As Gutiérrez-Marco and Villas (2007) previously noted, and and kutorginates share the well-developed perforate pseudo- 423 367 regardless of the chosen paleogeographic scenario, it is apparent deltidium and the lack of dental plates, but differ in that sockets 424 368 that Ahtiella originated along the proto-Andean Gondwana and socket plates have a different origin in billingsellides and 425 8 Journal of Paleontology

426 strophomenides, concluding that their phylogenetic links still alternatively, could be an homoplastic feature that appeared and 484 427 remain unclear. Subsequently, Bassett et al. (2008) and Bassett became lost at different times in different clades. In fact, in 485 428 and Popov (2017), based on a study of the ontogeny of the certain basal plectambonitoids, e.g., Plectella Lamansky, 1905, 486 429 orthotetide Coolinia Bancroft, 1949, inferred an early diver- Ingria Öpik, 1930, Aporthophyla Ulrich and Cooper, 1936, 487 430 gence of strophomenates and rhynchonellate brachiopods. Tourmakeadia Williams and Curry, 1985, and Pelonomia 488 431 At the superfamily level, it has been assumed that Stro- Cooper, 1956, the pseudodeltidium is rudimentary or lacking. In 489 432 phomenoidea was derived from the Plectambonitoidea during any cases, this structure is not as phylogenetically informative as 490 433 the Early Ordovician. Spjeldnaes (1957) did not identify the previously supposed. 491 434 group of plectambonitoideans that gave rise to the strophome- Noteworthily, the widely splayed, rodlike socket ridges 492 435 noideans and left open the possibility that the latter group is running almost parallel to the hinge line of billingselloids are 493 436 polyphyletic. According to Cocks and Rong (1989, 2000), closely comparable to those of the family Plectambonitidae 494 437 strophomenoideans originated from plectambonitoideans by a (e.g., Plectella, Plectambonites Pander, 1830, and Ingria). Such 495 438 transformation of the cardinal process from simple to bifid, an arrangement is quite different from the typically orthoid 496 439 suggesting as potential ancestor a leptellinid like Apatomorpha cardinalia seen in taffiids. Therefore, it is not surprising that in 497 440 Cooper, 1956 or Toquimia Ulrich and Cooper, 1936. Recent the parsimony analysis carried out by Congreve et al. (2015), 498 441 discoveries demonstrated that the three basic types of stropho- Plectambonites appears as monophyletic only if it is excluded 499 442 menoid cardinalia were already differentiated in the oldest from all other ‘plectambonitoids’ and placed in a separate 500 443 known members of the clade recorded in the Dapingian of superfamily. In this context, it is worth noting the close resem- 501 444 southern China (Zhan et al., 2015), supporting that the Stro- blance between the billingsellide (?) Kozhuchinella Severgina, 502 445 phomenoidea originated in the Floian from an unknown ‘stro- 1967 and the oldest known probable plectambonitoid Akelina 503 446 phomenide stem group’ shortly after the first appearance of Severgina, 1967, both from the upper Tremadocian Algan For- 504 447 plectambonitoids. Dewing (2004) challenged the hypothesis of mation of Kuznetz-Altai, Altai Mountains, Siberia (Severgina, 505 448 the plectambonitoid derivation of strophomenoids based on 1967). Despite the poor preservation of the latter (reillustrated 506 449 their different shell structure (laminar in the former and fibrous by Cocks and Rong, 1989, figs. 13–17), both genera share a 507 450 in the latter). Unlike the a priori assumption that shell structure is concavoconvex profile; parvicostellate ornamentation (typical 508 451 homoplastic (Cocks and Rong, 2000), i.e., evolved indepen- billingsellides are multicostellate or ramicostellate); the absence 509 452 dently in different clades, Dewing (2004, fig. 3) proposed a of dental plates; a prominent dorsal median ridge; a simple 510 453 phylogenetic scenario in which the Strophomenoidea arose from knob-like cardinal process; long, widely divergent socket rid- 511 454 a Cambrian laminar-shelled billingselloid, whereas the common ges; and a well-developed dorsal subperipheral rim. Accord- 512 455 ancestor of both the fibrous-shelled Plectambonitoidea and ingly, Akelina and Kozhuchinella are likely related forms, which 513 456 Clitambonitoidea was left with interrogation. On the contrary, could be considered either as early members of the ‘plectam- 514 457 the parsimony analysis performed by Congreve et al. (2015) bonitoid’ clade or, alternatively, as derived billingselloids (the 515 458 indicated that plectambonitoideans and strophomenoideans are presence of pseudopunctae has not yet been demonstrated in 516 459 phylogenetically related but, in contrast to previous inferences, these genera). This raises the possibility that only the plectam- 517 460 plectambonitoideans do not constitute a monophyletic group but bonitoid clade sensu stricto (the subfamily Plectambonitinae in 518 461 a paraphyletic grade of the strophomenoidean clade. Sig- the current classification) evolved from a billingselloid ancestor, 519 462 nificantly, in the phylogeny presented by Congreve et al. (2015, and that ahtiellins (and probably other taffids) had a different 520 463 fig. 4), Taffia Butts, 1926, Railtonella Laurie, 1991, and ancestor, which should be sought among the Orthoidea, as 521 464 Ahtiella, all currently included in the family Taffiidae, cluster as discussed below. 522 465 basal forms to all other Strophomenida, as Spjeldnaes (1957) 466 intuitively depicted in his phylogenetic tree sixty years earlier. Searching for the Ahtiella ancestors 523 467 The absence or extreme paucity of undisputed plectambo- 468 nitoids in the Tremadocian, along with their sudden diversifi- In his outstanding morphological study of Middle Ordovician 524 469 cation around the Floian-Dapingian transition, suggests that this strophomenides from Norway, Spjeldnaes (1957, fig. 42) pre- 525 470 superfamily originated in the Early Ordovician rather than deep sented a diagrammatic evolutionary tree of Strophomenida 526 471 in the Cambrian. In my opinion, billingselloids are too derived starting with two main branches, one of them lacking descen- 527 472 morphologically to be considered direct ancestors of plectam- dants including Plectambonites and allied forms, and the other 528 473 bonitoids (excepting the family Plectambonitidae, as discussed including the ‘ahtiellinids’ (Ahtiella, Inversella Öpik, 1933, and 529 474 below). Since their first appearance in the middle Cambrian, Ukoa Öpik, 1932), which albeit with a question mark, were 530 475 billingsellides developed a proportionally high planar ventral placed at the origin of the strophomenoid stock. A third, short- 531 476 interarea leading in the late Tremadocian to the hemipyramidal lived basal branch was represented by Taffia. In their compre- 532 477 shells that characterize most polytoechioids, e.g., Protambo- hensive revision of plectambonitoid classification, Cocks and 533 478 nites Havlíček in Havlíček and Josopait, 1972 and Tritoechia Rong (1989, p. 83, fig. 5) also placed the Taffiidae at the base of 534 479 Ulrich and Cooper, 1936, which form a consistent monophyletic the plectambonitoid tree “because we regard the absence of side 535 480 clade (Benedetto, 2009; Topper et al., 2013). The apically per- septa as representing a more primitive state than their presence 536 481 forated pseudodeltidium—the main feature linking bill- (as in the Plectambonitidae),” and also that the “oldest plec- 537 482 ingsdelloids and plectambonitoids—could be a plesiomorphic tambonitacean[s] ... are essentially indistinguishable from their 538 483 condition of basal rhynchonelliforms already present in some of orthide (probably billingselloid) ancestors except by their 539 the earliest members of the clade (e.g., Nisusioidea) or, pseudopunctate shell.” In fact, basal plectambonitoids share 540 Benedetto—The strophomenide brachiopod Ahtiella in Gondwana 9

541 with orthoids a simple, not undercut cardinal process, the Famatina (Benedetto, 2003b) was described as having a widely 596 542 absence of side septa, and the absence of a bema, a structure open delthyrium. However, a slightly arched pseudodeltidium 597 543 interpreted as a lophophore support and/or for providing muscle can be observed in a few conjoined shells (Fig. 6.1). Its absence 598 544 attachment. A more elaborated trifid, often undercut cardinal in most specimens is likely due to postmortem breakage by 599 545 process, a variably elevated and bilobed bema, paired dorsal hydrodynamic action, but could also reflect ecophenotypical 600 546 valve septa, hinge-line denticles, and more or less prominent variation within a population, ranging from absent to nearly 601 547 internal papillae and/or septules are all features that gradually complete according to specific (but unknown) environmental 602 548 appear in different combinations in younger, more derived constraints. A careful revision of the Precordilleran specimens of 603 549 plectambonitoids. M. cumillangoensis Benedetto, 2001, perhaps the better-known 604 550 Among taffiids, the ahtiellins—exemplified by the type species of Monorthis worldwide (Benedetto, 2001), revealed the 605 551 genus Ahtiella—display such a combination of internal features presence of an apparently imperforated pseudodeltidium cover- 606 552 that, in absence of pseudopunctae, they are virtually indis- ing the apical region of the delthyrium (Fig. 6.15). A closely 607 553 tinguishable from certain basal orthoids (e.g., hesperonomiids). comparable structure is also present in Ahtiella coloradoensis 608 554 For instance, the inclusion among the ahtiellins of Schedophyla (Fig. 11.9). Ahtiella zarelae possesses a small apical pseudo- 609 555 potteri, whose shell structure remains unknown, was cast in deltidium that is hardly visible in the illustrated specimens 610 556 doubt by Cocks and Rong (1989, p. 97) who stated that “it is (Gutiérrez-Marco and Villas, 2007, fig. 4E, F), but in Ahtiella sp. 611 557 possible that the genus is an orthid.” Laurie (1991) also noted from slightly older strata of the same formation of Peru, it is better 612 558 the orthoid dorsal cardinalia and musculature of Schedophyla. developed, almost attaining the delthyrium midlength. Ahtiella 613 559 Recently Harper et al. (2017, p. 624) noted that “…questions famatiniana n. sp. always possesses a well-developed pseudo- 614 560 remain regarding the placement of a number of groups such as deltidium covering one-half to two-thirds of the delthyrium (Fig. 615 561 the toquimiids, that apparently possess orthoid characters.” 10.9, 10.14). In the younger species A. argentina (Fig. 9.3) and A. 616 562 Perhaps the best example of such a difficulty is the conflicting tunaensis n. sp. (Fig. 10.5), the pseudodeltidium covers the 617 563 taxonomic position of ‘Monorthis’ coloradoensis, from the pedicle opening almost entirely at all growth stages, suggesting a 618 564 Central Andean Basin, which is hardly differentiable from general trend from nearly absent to fully developed. 619 565 unquestionable species of Ahtiella such as A. zarelae Villas in 566 Gutiérrez-Marco and Villas, 2007 and A. famatiniana n. sp. Muscle scars.—The ventral muscle field of Monorthis trans- 620 567 (described herein). Originally, the species ‘coloradoensis’ was versa is subtriangular and confined to the delthyrial cavity 621 568 ascribed to the hesperonomiid Monorthis, on the basis of its (Fig. 6.7) as in younger individuals of Ahtiella famatiniana n. 622 569 convexoplanar, slightly resupinate profile, carinate ventral fold, sp. (Fig. 10.15). In mature specimens of the latter species 623 570 multicostellate ornamentation, and orthoid cardinalia and mus- (Fig. 10.16, 10.18), as well as in A. coloradoensis (Fig. 11.3, 624 571 cle scars (Benedetto, 1998b). Such an assignment was further 11.8) and the Peruvian species A. zarelae (Fig. 11.18), the 625 572 supported by the lack of evidence of pseudopunctae and pseu- ventral muscle field becomes larger and more or less sub- 626 573 dodeltidium (Benedetto, 2003b), both considered apomorphic pentagonal in outline. The Precordilleran A. tunaensis n. sp. is 627 574 features of plectambonitoids. The shell structure, however, unique in having a large bilobed muscle field (Fig. 10.4). The 628 575 could not be verified because available shells are entirely dec- dorsal muscle field of M. transversa is quadripartite, with 629 576 alcified, so that its nonpunctate condition was inferred from the anterior and posterior scars nearly equal in size. A persistent 630 577 lack of evidence of pseudopunctae on internal molds, even feature in most specimens of M. transversa is the presence of a 631 578 though many undisputable strophomenoids do not show internal pair of slightly divergent ridges bounding laterally or bisecting 632 579 traces of them. longitudinally the adductor field (Fig. 6.4, 6.5). Remarkably, 633 these ridges are also present in A. famatiniana n. sp., A. color- 634 580 Comparative morphology of Monorthis and Ahtiella adoensis, and A. zarelae (Figs. 10.23, 11.14). In the Welsh 635 species A. concava, such ridges extend along the entire length of 636 581 The orthoid ancestor hypothesis of Ahtiella finds empirical muscle scars (Bates, 1968, pl. 7, figs. 16, 19). 637 582 support from the comparison of the species Monorthis trans- 583 versa (Fig. 6.1–6.12) and Ahtiella famatiniana n. sp. (Fig. 10.9– 584 10.24), which occur in successive strata of the Famatina Basin. Cardinalia.—There are only minor differences between the 638 cardinalia of Monorthis (Fig. 6.5, 6.12) and Ahtiella (Figs. 9.17, 639 585 Shell shape and ornament.—Overall, the slightly resupinate, 10.20, 10.24, 11.10, 11.15). Monorthis transversa shows some 640 586 carinate, transversely elongate, alate shells of Monorthis trans- degree of intraspecific variation in the cardinal process, ranging 641 587 versa and Ahtiella famatiniana n. sp. are closely comparable. from bladelike to a ridge moderately enlarged anteriorly, occu- 642 588 Shells of M. transversa are rather smaller and more transverse pying the entire length of a raised subtriangular notothyrial 643 589 than A. famatiniana, resembling the juvenile to medium-sized platform. The cardinalia of M. transversa are nearly identical to 644 590 specimens of the latter. Although ornamentation in M. transversa those of A. famatiniana n. sp. and A. coloradoensis, whereas in 645 591 is slightly coarser than in A. famatiniana n. sp., it is subequally the Peruvian A. zarelae and Ahtiella sp., the cardinal process 646 592 multicostellate in both species. tends to be more robust and ovoid in outline. Ahtiella argentina 647 is characterized by a bladelike to slightly enlarged cardinal 648 593 Pseudodeltidium.—Specimens of Monorthis transversa from process erected on a gently convex notothyrial platform 649 594 Chaschuil—originally referred to as Monorthis aff. M. menapiae (Fig. 9.20, 9.22). The subtriangular to suboval, anterolaterally 650 595 (Davidson, 1868) by Benedetto, 1994—and from Central open sockets excavated on the valve floor and partially under the 651 10 Journal of Paleontology Benedetto—The strophomenide brachiopod Ahtiella in Gondwana 11

652 dorsal interarea of Monorthis and Ahtiella, as well as the slen- distal portion of mantle canals is well marked on the anterior 700 653 der, distally enlarged socket ridges, are also closely comparable. third of the ventral valve (Fig. 10.22). Adult stages of 701 A. argentina and A. paucirugosa always display a deeply 702 impressed mantle canal system of the saccate type, with pos- 703 654 Subperipheral rims and platforms.—Despite the redefinition of teriorly directed branches of vascula media enclosing large 704 655 these terms by Cocks and Rong (1989), some imprecision per- gonadal pouches (Fig. 9.10, 9.18). 705 656 sists in the literature, with the term ‘platform’ having been 657 applied to both dorsal and ventral valves (not only to the dorsal 658 one, as these authors proposed), and the two structures are often Trends of morphological change.—From the above compar- 706 659 not easy to differentiate on the basis of their morphology. To isons, the following trends can be recognized through the 707 660 avoid confusion, ‘platform’ ( = ‘diaphragm’) is used here to inferred Monorthis transversa (and its putative ancestor 708 661 designate a low to high, somewhat undercut elevation of the Hesperonomiella arcuata Benedetto, 2003b)–Ahtiella argen- 709 662 ventral and/or dorsal valve floor originating at or near the car- tina lineage (Fig. 7): (1) the nongeniculated ventral valve mar- 710 663 dinal angles and not related to external geniculation, the internal gin of M. transversa progressively thickens, originating in 711 664 disc, or any kind of valve thickening. On the other hand, fol- Ahtiella an internal geniculation, which is low in the species 712 665 lowing Cocks and Rong (1989), the term ‘peripheral rim’ (or from Wales (A. quadrata, A. concava) and northwestern 713 666 ‘subperipheral rim’) is applied to a raised rim running at or near Argentina (A. coloradoensis), intermediate in the Famatinan 714 667 the variably thickened valve margin. When a more or less pro- (A. famatiniana n. sp.) and Peruvian (A. zarelae) forms, and 715 668 minent peripheral rim has developed in the ventral valve, it can more prominent in the Darriwilian species from Cuyania and 716 669 be mirrored in the dorsal valve by a similar structure that is often Baltica. In the latter (e.g., A. lirata, A. jaanussoni Hessland, 717 670 related to an internal deflection of the valve. 1949), the main trend is toward a strongly convex gibbous 718 671 According to the original diagnosis of Monorthis (see dorsal valve; (2) the pseudodeltidium is absent or incipient in 719 672 Bates, 1968), platforms are absent in both valves. Valve margins Monorthis, is restricted to the apical region of delthyrium in the 720 673 of the Famatinan M. transversa are crenulated but not thickened oldest known species (A. zarelae) as well as in the Welsh spe- 721 674 (Fig. 6.9), whereas the large ventral valves of the Precordilleran cies, and reaches almost two-thirds in the later species from 722 675 M. cumillangoensis show variably thickened margins and an Precordillera and Baltica; (3) external ornamentation evolved 723 676 internal geniculation, which is nearly identical to that seen in from equally multicostellate in Monorthis (retained in the 724 677 Ahtiella zarelae (cf. Figs. 6.14, 11.18). The ventral valves of younger A. coloradoensis) to ramicostellate in the Floian A. 725 678 A. famatiniana n. sp. and A. coloradoensis exhibit a conspic- zarelae, becoming unequally multicostellate to incipiently par- 726 679 uous thickening along the geniculation; in both species, vicostellate in the Dapingian A. famatiniana, and definitely 727 680 however, it is absent in juvenile individuals (Fig. 10.15), parvicostellate in the Darriwilian species; (4) the dorsal platform 728 681 suggesting that this structure developed progressively by is absent in Monorthis, is variably developed in the early species 729 682 peramorphy. In A. argentina, the whole ventral valve margin A. zaleae and A. famatiniana n. sp., and becomes more promi- 730 683 is geniculated, forming a prominent internal disc deeply incised nent in the younger Cuyanian and Baltic species; (5) the mantle 731 684 by the vascula terminalia (Fig. 9.9), like in the Baltic A. lirata. canal system is indistinct or confined to the valve margin in 732 685 A corresponding discontinuous platform-like structure is Monorthis, has well-impressed distal branches on the margin of 733 686 usually present in the dorsal valve of A. famatiniana n. sp. disc and trail in the Floian-Dapingian species of Ahtiella, and 734 687 (Fig. 10.20). On the contrary, in A. coloradoensis, it is poorly culminates in A. argentina and A. paucirugosa with a deeply 735 688 developed or even absent (Fig. 11.10). Unlike other Gondwanan impressed mantle canal system on the entire surface of adult 736 689 species, the large dorsal valves of A. argentina display a series specimens. 737 690 of curved, roughly radial ridges that can be interpreted as a 691 platform-like structure (Fig. 9.20, 9.22). Ahtiella baltica Öpik, Phylogenetic analysis 738 692 1932, as can be seen in the specimen figured by Öpik (1933, pl. 693 4, fig. 6), possesses a continuous undercut platform, but it is Cladistic analysis of Ahtiella species.—Comparative morphol- 739 694 faint or absent in A. lirata. ogy makes evident that differences between Monorthis and 740 basal species of Ahtiella are subtle, which makes them difficult 741 695 Vascular system.—Vascular trunks are not discernible in to distinguish from each other. The question is whether such 742 696 Monorthis cumillangoensis in part due to the strong internal similarities reflect homologies and therefore reveal phylogenetic 743 697 impression of the external ornamentation, whereas in M. trans- affinities or, on the contrary, they can be viewed as cases of 744 698 versa, a series of short anastomosing canals can be present along extreme morphological convergence along two independent 745 699 valve margins (Fig. 6.4, 6.8). In Ahtiella famatiniana n. sp., the lineages. Given the striking resemblance in multiple external 746

Figure 6. (1 − 9) Monorthis transversa Benedetto, 2003b; Loma del Kilometro Member of the Suri Formation (Chaschuil) and Molles Formation, Famatina Range: (1) latex cast of ventral valve exterior, CEGH-UNC 19628a; (2) latex cast of dorsal valve exterior, CEGH-UNC 19628b; (3) latex cast of ventral valve, CEGH-UNC 19628a, showing incipient delthyrium cover; (4, 5) internal mold (4) and latex cast (5) of dorsal valve, CEGH-UNC 19635; (6) internal mold of dorsal valve, CEGH-UNC 19632; (7) internal mold of ventral valve, CEGH-UNC 19625; (8, 9) internal mold of ventral valve (8) and latex cast (9), CEGH-UNC 10962. (10 − 18) Monorthis cumillangoensis Benedetto, 2001; San Juan Formation, siliciﬁed specimens from Cerro Cumillango and Cerro La Chilca, Precordillera: (10) ventral valve exterior, CEGH-UNC 17915; (11) ventral valve exterior, CEGH-UNC 17917; (12) dorsal valve interior, CEGH-UNC 17920; (13) ventral valve interior, CEGH-UNC 17933; (14, 15) ventral valve interior (14) and detail of incipient delthyrium cover (15), CEGH-UNC 17948; (16) ventral valve interior, CEGH-UNC 21152; (17) dorsal valve exterior, CEGH-UNC 21153; (18) dorsal valve interior, CEGH-UNC 17942. All specimens dusted with ammonium chloride. Scale bars = 5 mm. 12 Journal of Paleontology

Figure 8. Phylogenetic relationships of taxa analyzed calibrated to chronostratigraphic scale. Apomorphies deﬁning numbered nodes are discussed in the text.

septa), resulting in destabilization of the relationships among 762 other taxa. Hesperonomiella was chosen as the outgroup for 763 rooting the phylogenetic tree because it exhibits an ensemble of 764 765 Figure 7. Generalized trend of morphological change through selected taxa nonderived internal features, and lacks the majority of apo- from the Floian-Dapingian volcanosedimentary succession of Famatina. morphies present in the group analyzed here. This, along with its 766 Ventral internal molds at left, dorsal internal molds at right. Hesperonomiella first appearance in the middle Cambrian, suggests it as a 767 arcuata Benedetto, 2003b): left, CEGH-UNC 15740; right, CEGH-UNC 19078. Monorthis transversa Benedetto, 2003b: left, CEGH-UNC 19095; potential ancestor of the taxa considered in this study. A heur- 768 right, CEGH-UNC 19623. Ahtiella famatiniana n. sp.: left, CEGH-UNC istic search of the data matrix in which all characters were 769 27140; right, CEGH-UNC 27135b. At the top of the succession, A. argentina unordered and equally weighted produced four minimal length 770 Benedetto and Herrera, 1986 illustrates a more derived species of Ahtiella from the Darriwilian of Precordillera (left, CEGH-UNC 27111; right, CEGH- trees 52 steps long, with consistency index of 0.692 and reten- 771 UNC 21118b). tion index of 0.754. The strict consensus tree (Fig. 8) is pre- 772 sented here with branch length calibrated to the age of the first 773 747 and internal details along with gradation in some features, con- appearance datum of each taxon. As the phylogenetic tree 774 748 vergence seems highly improbable. To investigate whether the shows, the basal member of the Ahtiella clade is Monorthis 775 749 trends deduced from comparative morphology are phylogen- transversa, which possesses ancestral features such as multi- 776 750 etically significant, a cladistic analysis of Ahtiella species was costellate ornamentation, absence of a dorsal platform, an 777 751 performed using TNT (Tree Analysis Using New Technology) unthickened periphery of the ventral valve, an open delthyrium, 778 752 version 1.5 (Goloboff and Catalano, 2016), selecting the heur- and an unmodified notothyrium. Monorthis transversa has in 779 753 istic search option with multiple random addition sequences and common with the Ahtiella species a resupinate and alate shell 780 754 the tree bisection reconnection (TBR) branch-swapping algo- (node 1), and cardinalia and muscle scars of the orthoid type. 781 755 rithm holding 10 trees in each addition sequence. A total of 23 The Welsh species A. quadrata is expressed as the most basal 782 756 characters comprising internal and external features were member of the Ahtiella clade displaying vestigial or incipient 783 757 included within the Ahtiella analysis (Table 1). The 23-character pseudodeltidium and chilidium and a slightly thickened ventral 784 758 matrix was analyzed for 10 taxa (Table 2). The Welsh species valve margin (node 2). The apomorphy that defines the 785 759 A. concava was not considered because it possesses some fea- remaining Ahtiella species (node 3) is the presence of a dorsal 786 760 tures atypical for the genus (e.g., apparently smooth exterior, platform, which varies from low and discontinuous in the older 787 761 elongate oval anterior adductor scars each flanked by prominent species to variably developed in the younger species. The 788 Benedetto—The strophomenide brachiopod Ahtiella in Gondwana 13

789 Gondwanan species A. coloradoensis, A. zarelae, and A. fama- quadrata and, eventually, of the ‘anomalous’ species A. 848 790 tiniana n. sp., which each retain ancestral uniform or nearly concava. It seems likely that cases of parallel evolution in 849 791 uniform radial ornamentation and an incipient apical pseudo- brachiopods, and thus the existence of paraphyletic genera, 850 792 deltidium, appear as basal to the more derived species from might be more frequent than previously thought. 851 793 Baltica, Cuyania, and Newfoundland. In addition, it should be In summary, available evidence from the Gondwanan 852 794 noted that the presence of pseudopunctae has not been demon- material supports, contrary to previous assumptions, that the 853 795 strated in any of these Gondwanan species. Among them, A. basal plectambonitoid Ahtiella could have evolved from the 854 796 famatiniana n. sp. is slightly more advanced by having a com- hesperonomiid orthoid Monorthis transversa, and that A. 855 797 paratively larger pseudodeltidium and chilidium, a more pro- famatiniana n. sp. and A. zarelae are not only the earliest 856 798 minent dorsal platform, a deeply impressed vascular system on species of the genus, but also are morphologically intermediate 857 799 the disc/trail deflection, and ornamentation tending to be inci- between M. transversa and the more derived species of Ahtiella 858 800 piently parvicostellate. The Famatinan species clusters with the from the Darriwilian of Cuyania and Baltica (Fig. 8). 859 801 group that includes A. tunaensis n. sp., A. lirata, A. jaanussoni, 802 A. argentina, and A. paucirugosa, characterized by a well- Some macroevolutionary implications.—There is a general 860 803 defined disc and a dorsally directed trail in the interior of ventral consensus that the peculiar strophomenide shell architecture 861 804 valve (node 4). This group shares unequally parvicostellate and concomitant anatomical and physiological changes were 862 805 ribbing, a well-developed pseudodeltidium and chilidium, and a adaptations (key innovations) allowing invasion of a new eco- 863 806 relatively large pseudopunctae (node 5). Ahtiella jaanussoni and logical niche or adaptive zone, which was essentially the 864 807 A. lirata form a cluster based on a gibbous shell profile and acquisition of an ambitopic or permanent liberosessile life 865 808 prominent rugae or corrugations covering most of the valve strategy linked to the colonization of low-energy, offshore 866 809 surface, and likely reflect local radiation of the genus in the marine environments (Bassett, 1984). Over time, such mor- 867 810 Baltica paleocontinent (node 6). This group of species served phological changes became so marked that they led to the 868 811 originally to define the genus Ahtiella. On the other hand, A. recognition of a separate higher taxon, the order Strophome- 869 812 argentina and A. paucirugosa form a sister group of Baltic nida, which together with other groups was lumped into the 870 813 species by sharing deeply impressed mantle canals on the entire large and quite heterogeneous class Strophomenata. Although 871 814 valve interior and curved ridges in the floor of dorsal valve higher taxa are often viewed as artificial, nonmonophyletic, 872 815 (node 7). subjective entities, a number of quantitative studies have con- 873 816 Our species-level phylogenetic tree shows that since its firmed the taxic metrics as an adequate proxy for assessing 874 817 origin in the Floian, the genus Ahtiella underwent successive morphological disparity (Erwin, 2007, p. 59). If, as evidence 875 818 speciation events along the Andean margin of Gondwana where presented here suggests, Ahtiella originated from Monorthis 876 819 the common ancestor would likely have inhabited, and through a series of minor transformations, then the impressive 877 820 subsequently dispersed and continued speciating as new morphological gap among ‘typical’ orthides and strophome- 878 821 geographic areas were colonized. The diversification of the nides was bridged through a brief cladogenetic event. At first, 879 822 Ahtiella clade appears to have occurred by cladogenesis because such a transition indicates that there is not a definite dis- 880 823 A. coloradoensis, a conservative species closely related continuity between species-level evolution (processes that 881 824 morphologically to Monorthis, persisted in the Central Andean occur within a species or lead to a new species) and the origin of 882 825 Basin until the late Darriwilian. Perhaps the main conflict posed higher taxa (macroevolution). Central to this statement is the 883 826 by the phylogenetic hypothesis of Figure 7 is that A. quadrata is assumption that higher taxa are evolutionary entities char- 884 827 shown as a basal member of the clade because the Welsh species acterized by a significant morphological disparity achieved over 885 828 retains some traits ancestral to A. zarelae and A. famatiniana n. a long period of time, then the greater the time elapsed since 886 829 sp. A possible explanation is that A. quadrata originated from a their origin from a common ancestor, the larger morphological 887 830 Gondwanan ancestor and then migrated along Gondwanan disparity. In the present case study, it would be expected that the 888 831 shelves to reach the colder Avalonian waters. However, to date highly plesiomorphic basal forms (i.e., ahtiellins) of a given 889 832 no records of morphologically related forms are known from higher taxon (i.e., strophomenides) are more similar to their 890 833 Gondwana, which could be due either to a lack of extensive putative ancestors (i.e., hesperonomiids) than they are to the 891 834 sampling in the still poorly known Bolivian and Peruvian more derived (apomorphic) end-members of the same clade 892 835 sectors of the Central Andean Basin or to the absence of this (i.e., sowerbyellids, aegiromenids). In other words, morpholo- 893 836 species in the Andean region. An alternative interpretation is gical discontinuity becomes minimal at a point closer to the 894 837 that A. quadrata evolved independently in the Avalonian initial divergence of two phylogenetically related higher taxa. A 895 838 paleocontinent from a local species of Monorthis. The consequence of this is that assignation of basal forms to one or 896 839 possibility of parallel evolution at the generic level as well as another higher taxon can be difficult in the lack of a well- 897 840 its possible causes were discussed in a previous paper supported phylogeny. The need of a ‘shoehorn’ to classify such 898 841 (Benedetto, 2008) to account for the nearly simultaneous record earliest members of a given higher taxon into a specified order 899 842 of the genus Productorthis in Baltica and the Famatinan or suborder has also been noted in other groups of marine 900 843 volcanic arc, with underlying strata in both regions of the benthic organisms. For instance, the clade Bivalvia includes a 901 844 ancestral genus Panderina Schuchert and Cooper, 1931. In our number of early representatives of Tremadocian-Floian age that 902 845 case, the Welsh species M. menapiae of ‘lower Arenigian’ lack certain apomorphies defining more derived crown groups. 903 846 (Floian) age (Bates, 1969) closely resembles the Famatinan In this respect, it has been suggested that such basal taxa can be 904 847 species M. transversa and could be a potential ancestor of A. classified as plesions, i.e., paraphyletic groups having a number 905 14 Journal of Paleontology Benedetto—The strophomenide brachiopod Ahtiella in Gondwana 15

906 of symplesiomorphic traits but morphologically close to a given 2009 Ahtiella argentina; Benedetto et al., fig. 9f. 947 907 higher taxon (Fang and Sánchez, 2012). In the case of bra- 908 chiopods, as Carlson (2016, p. 421) stated, numerous higher Holotype.—CORD-PZ 8283, a conjoined specimen from the 948 909 taxa had been thought to represent grade-level taxa, i.e., not upper San Juan Formation, Quebrada Los Gatos, Cerro Viejo, 949 910 clades, and our evidence indicates that this could be the case of San Juan Province, Argentina (Benedetto and Herrera, 1986). 950 911 strophomenides. Diagnosis.—Shell transversely semielliptical (mean length/ 951 912 Materials and methods width ratio 0.39) with acute cardinal extremities; profile variably 952 resupinate with carinate ventral median fold and corresponding 953 913 Repository and institutional abbreviations.—CEGH-UNC, subangular dorsal sulcus reaching anterior margin. Radial 954 914 Centro de Investigaciones en Ciencias de la Tierra CONICET ornamentation unequally parvicostellate. Ventral muscle field 955 915 and Universidad Nacional de Córdoba, Argentina; CORD-PZ, short, triangular, extending up to 25% of valve length. Ventral 956 916 Museo de Paleontologia, Universidad Nacional de Córdoba, valve strongly thickened marginally, defining internal disc and 957 917 Argentina; MGM, Museo Geominero, Madrid, Spain. trail. Dorsal valve with strong rounded median ridge originating 958 in front of notothyrial platform. Internal surface with elongated 959 918 Systematic paleontology pustules coalescing to form irregular, roughly radial ridges. 960 Both valves with deeply impressed saccate mantle canal system. 961 919 The systematic classification follows that of the Treatise on — 920 Invertebrate Paleontology (Cocks and Rong, 2000). Following Occurrence. Uppermost levels of the San Juan Formation, 962 – 921 Congreve et al. (2015), the genus Ahtiella is referred to the Precordillera, San Juan Province, Argentina. Darriwilian (Dw1 963 922 ‘Plectambonitoidea’ with the quotation marks denoting that the Dw2). 964 923 superfamily is paraphyletic (Wiley, 1979). Description.—Shell to 23 mm width, transversely semielliptical 965 924 Order Strophomenida Öpik, 1934 in outline; mean length/width ratio 0.39 (N = 18); profile 966 ‘ ’ 925 Superfamily Plectambonitoidea Jones, 1928 strongly concavoconvex, mature specimens up to 45% as deep 967 fi 926 Family Taf idae Schuchert and Cooper, 1931 as long. Maximum width at hinge line. Cardinal extremities 968 927 Subfamily Ahtiellinae Öpik, 1933 auriculate or alate in juvenile to medium-sized specimens, 969 928 Genus Ahtiella Öpik, 1932 becoming acute (40–45°) in mature specimens. Ventral valve 970 resupinate, gently convex at umbonal area, becoming broadly 971 929 Type species.—Ahtiella lirata Öpik, 1932 from the Darriwilian concave anteriorly; ventral median fold initially carinate, 972 930 (Middle Ordovician) of Tsitri, Estonia, by original designation. becoming broader and rounded toward anterior margin where it 973 attains 15–20% of valve width, flanked by strongly concave 974 931 Diagnosis (emended).—Shell resupinate, variably geniculate; areas. Ventral interarea planar, steeply apsacline to almost 975 932 ornamentation subequally multicostellate, ramicostellate or parvi- catacline, attaining height equivalent to 15% of shell length. 976 933 costellate, often with posterolateral rugae. Dental plates widely Pseudodeltidium well developed, semiconical, covering near 977 934 spaced converging to valve floor, enclosing posteriorly sub- two-thirds of delthyrium. Dorsal valve moderately to strongly 978 935 triangular to subquadrate ventral muscle field. Interior of ventral convex with deep angular median sulcus becoming wide and 979 936 valve with thickened margin defining disc and trail. Cardinal pro- shallow anteriorly. Dorsal interarea anacline, planar, three to 980 937 cess simple. Dorsal median ridge broad, rounded. Dorsal platform four times lower than ventral. Notothyrium covered almost 981 938 variably developed. Saccate mantle canal system usually strongly entirely by large convex chilidium. Ornamentation unequally 982 – fi 939 impressed either along shell margin or whole interior. parvicostellate, with 6 8 rst-order rounded costellae originat- 983 – fi 940 ing at umbonal area and 4 8 subequal ner parvicostellae 984 941 Ahtiella argentina Benedetto and Herrera, 1986 intercalated between them, some of which can attain size equal 985 942 Figure 9.1–9.23 to primaries on anterior third of valve; costellae 10–12 per 2 mm 986 (counted at 5 mm growth stage). Fine, evenly spaced, concentric 987 943 1986 Ahtiella argentina Benedetto and Herrera, p. 114, pl. 1, fila (~18 per mm). Posterolateral margins with up to six faint 988 944 figs. 4 − 21. rugae strongly oblique to hinge line. 989 945 2002 Ahtiella argentina; Benedetto, p. 114, pl. 2, figs. 20, 21. Ventral interior with small subtriangular teeth bearing well- 990 developed, slit-like crural fossettes on medial faces, supported 991 946 2003a Ahtiella argentina; Benedetto, p. 201, pl. 9, figs. 9–12. by short thick dental plates slightly converging to valve floor 992

Figure 9. Ahtiella argentina Benedetto and Herrera, 1986; Upper San Juan Formation, Cerro Viejo, Precordillera: (1) latex cast of ventral valve exterior, CEGH-UNC 27121; (2, 7) latex cast of dorsal valve exterior (2) and profile view (7), CEGH-UNC 27119; (3) posterior view of conjoined specimen showing presudodeltidium and chilidium, CEGH-UNC 16328; (4) early juvenile ventral internal mold, CEGH-UNC 27118; (5) juvenile ventral internal mold, CEGH- UNC 27153; (6) internal mold of small adult ventral valve, CEGH-UNC 27072; (8, 9) internal mold (8) and latex cast (9) of ventral valve, CEGH-UNC 27111; (10) internal mold of ventral valve, CEGH-UNC 27181; (11, 12) external (11) and internal (12) views of silicified ventral valve, CEGH-UNC 21963; (13, 14) ventral (13) and dorsal (14) views of silicified conjoined specimen, CEGH-UNC 21964; (15) internal mold of juvenile dorsal valve, CEGH-UNC 27160; (16, 17) internal mold (16) and latex cast (17) of dorsal valve, CEGH-UNC 27108; (18) internal mold of ventral valve, CEGH-UNC 21995; (19, 20) internal mold (19) and latex cast (20) of dorsal valve, CORD-PZ 8295; (21, 22) internal mold (21) and latex cast (22) of dorsal valve, CEGH-UNC 27075; (23) dorsal internal mold, CEGH-UNC 21118b. All specimens dusted with ammonium chloride. Scale bars = 3mm(3, 4); 5 mm (remainder). 16 Journal of Paleontology Benedetto—The strophomenide brachiopod Ahtiella in Gondwana 17

993 and diverging from each other at 80–90°. Lateral delthyrial 22075, 27104–27130, and 27160–27162 from Cerro Viejo 1041 994 cavities of adult specimens partially to completely filled with (Quebrada Los Gato). 1042 995 secondary deposits. Ventral muscle field short, triangular in 996 outline, extending ~ 20–25% of valve length, enclosed poster- Remarks.—This species clearly differs from Ahtiella lirata in its 1043 997 olaterally by dental plates, delimited anterolaterally by low more transverse shell outline and less convex, uniformly curved 1044 998 arcuate ridges; diductor scars elongate, almost three times shell profile lacking abrupt geniculation. Moreover in A. lirata, 1045 999 longer than wide, not clearly differentiated from wider the dorsal sulcus is very shallow and confined to the posterior 1046 1000 subtriangular adductor field. Mantle canal system saccate, region of the valve and the corresponding ventral fold is 1047 1001 deeply impressed in mature individuals; vascula media broad, inconspicuous, whereas in A. argentina, the sulcus is deeper and 1048 1002 straight, diverging forward at 60°, extending from anterior ends always attains the anterior margin, and the ventral fold is well 1049 1003 of diductors to approximate valve midlength where they defined and carinate posteriorly. Internally, the Precordilleran 1050 1004 bifurcate, with one branch directed posterolaterally and the species can be distinguished by having smaller subtriangular 1051 1005 other directed medially, each becoming repeatedly dichoto- ventral muscle field, which in the type species tends to be sub- 1052 1006 mized at disc margin (Fig. 9.10, 9.18). Surface between vascular quadrate and extends to approximately one-third of the valve 1053 1007 trunks covered by pustules. Gonadal areas subtriangular to length; there are deeply impressed vascular trunks on the inter- 1054 1008 suboval in outline, faintly striated radially, variably pitted. nal surface of both valves, but especially in the ventral one. The 1055 1009 Valve margin strongly thickened, geniculated, with well- slightly older species A. baltica, from the Rögo Sandstone of 1056 1010 defined disc and trail deflected dorsally, forming angle of Estonia, resembles A. argentina in its more transverse shell 1057 1011 ~ 40° with respect to disc surface. Low rounded to subangular outline but differs in having a longer bilobed ventral muscle 1058 1012 subperipheral rim occasionally present along entire disc margin. field of lirata-type. The dorsal interior, even though exhibiting 1059 1013 External ribbing not reflected on valve interior except in features of the genus, shows a quite atypical continuous, ante- 1060 1014 juvenile individuals. riorly free dorsal platform (Öpik, 1933, pl. 4, fig. 6). Ahtiella 1061 1015 Dorsal interior with small cardinalia extending ~ 10% of arenaria Öpik, 1933 is a poorly known Estonian species (only a 1062 1016 valve length. Cardinal process high, bladelike, slightly enlarged dorsal exterior and a ventral interior have been illustrated, by 1063 1017 anteriorly, erected on moderately elevated slightly convex Öpik, 1933, pl. 4, figs. 7, 8) recovered from the same beds and 1064 1018 notothyrial platform merged anteriorly with strong, rounded localities as A. baltica to which it strongly resembles. Of the 1065 1019 median ridge, usually extending to valve midlegth or slightly species from Sweden (Island of Öland) described by Hessland 1066 1020 beyond, but reaching disc margin in some specimens. Socket (1949), only A. jaanussoni is known from dorsal interiors 1067 1021 ridges rodlike, free distally, diverging from each other at 95– (ventral interiors are unknown). Its dorsal valve is reminiscent 1068 1022 100°, bounding deep semiconical sockets excavated below and of A. lirata, but the shell is somewhat more transverse, the 1069 1023 partially on interarea. Muscle field faintly impressed, quad- posterolateral rugae are more pronounced, and the dorsal inter- 1070 1024 ripartite, with subcircular posterior adductor scars and larger ior possesses a long prominent median ridge. As Cocks and 1071 1025 suboval anterior adductor scars. Saccate dorsal mantle canal Rong (1989) stated, the rest of the Ahtiella species described by 1072 1026 system with broad, well-impressed vascula media divided Hessland (1949) can only be questionably assigned to the genus 1073 1027 immediately in front of anterior extremity of muscle field in because internal morphology remains unknown. Among them, 1074 1028 two branches, one of them running subparallel to median ridge, A.? oelandica Hessland, 1949 is the most similar to A. argentina 1075 1029 the other directed anterolaterally, both originating numerous in its transverse shell outline, uniformly curved dorsal valve 1076 1030 small canals perpendicular to valve margin. Valve interior with profile, and especially in the presence of a well-developed dorsal 1077 1031 elongated papillae, in large specimens coalescing to form median sulcus reaching the anterior margin. The main external 1078 1032 irregular roughly radial ridges, which are more conspicuous at difference lies in the coarser and more prominent rugae in the 1079 1033 valve midlength on both sides and at end of median ridge. Swedish species. It is unclear whether such differences in size, 1080 1034 Small, closely spaced papillae between peripheral vascular shell outline, definition of disc and trail, and strength of pos- 1081 1035 trunks. terolateral rugae are taxonomically significant because these 1082 features show gradation between species and are quite variable 1083 1036 Materials.—In addition to the material listed and illustrated by even in individuals of the same species. Clearly, a revision of the 1084 1037 Benedetto and Herrera (1986), the following new specimens Baltic species is needed to clarify this issue. 1085 1038 have been included in the present study: CEGH-UNC 21960– Ahtiella concava from the Bob Deiniol Formation of 1086 1039 21965, 21981, and 21994–21995 from Cerro Viejo (Quebrada Anglesey (Wales) resembles A. argentina in its moderately 1087 1040 Honda); CEGH-UNC 10561–10564, 16319–16321, 22070– convex and uniformly curved dorsal valve profile, acute cardinal 1088

Figure 10. (1 − 8) Ahtiella tunaensis n. sp.; Las Chacritas Formation, Sierra de la Trampa, Precordillera: (1 − 3, 5) paratype, conjoined specimen, CEGH-UNC 21084, in ventral (1), dorsal (2), and proﬁle (3) views, and detail of interarea (5) showing pseudodeltidium and chilidium; (4) holotype, interior of ventral valve, CEGH-UNC 21083; (6) paratype, ventral view of conjoined specimen, CEGH-UNC 27172; (7) detail of ventral valve, CEGH-UNC 27174, showing pseudopunctae; (8) paratype, dorsal internal mold, CEGH-UNC 27171. (9 − 24) Ahtiella famatiniana n. sp.; Punta Pétrea Member of the ‘Suri’ Formation (Chaschuil), and volcaniclastic beds exoposed at Las Pircas anticline (Central Famatina Range): (9) paratype, latex cast of ventral valve exterior, CEGH-UNC 27149; (10, 11) external mold (10) and latex cast (11) of ventral valve, CEGH-UNC 27131; (12 − 14) ventral (12) and dorsal (13) views of conjoined specimen, CEGH-UNC 27163, and detail of pseudodeltidium (14); (15) juvenile ventral internal mold, CEGH-UNC 27158; (16, 17) paratype, internal mold (16) and latex cast (17) of ventral valve, CEGH-UNC 27135a; (18, 21) holotype, internal mold (18) and latex cast (21) of ventral valve, CEGH-UNC 27137; (19, 20) internal mold (19) and latex cast (20) of dorsal valve, CEGH-UNC 27135b; (22) internal mold of ventral valve, CEGH-UNC 27140; (23, 24) internal mold (23) and latex cast (24) of dorsal valve, CEGH-UNC 27141, showing detail of cardinalium. All specimens dusted with ammonium chloride. Scale bars = 1mm(7); 3 mm (5, 14); 5 mm (remainder). 18 Journal of Paleontology Benedetto—The strophomenide brachiopod Ahtiella in Gondwana 19

1089 angles, and well-developed, carinate ventral fold, but differs dorsal valve; CEGH-UNC 21084 and 27172, two conjoined 1137 1090 from the Precordilleran species in having a catacline to procline specimens. 1138 1091 ventral interarea and a less transverse shell; the width/length 1092 ratio in the specimens measured by Bates (1968, p. 168) is 0.63. Diagnosis.—Shell semielliptical to subrectangular, moderately 1139 1093 According to Bates (1968, p. 167), the ornamentation in the to strongly convexoconcave (mean length/width ratio 0.63) with 1140 “ fi ” 1094 Welsh specimens is too ne to be observed, and posterolateral subrectangular cardinal extremities; ventral median fold low, 1141 1095 rugae are not evident. Internally, A. concava has a subquadrate almost indistinct near commissure; dorsal sulcus shallow pos- 1142 fi 1096 rather than subtriangular ventral muscle eld. The dorsal valve teriorly, impersistent at anterior margin. Radial ribbing sub- 1143 1097 shares with A. argentina a high rounded median dorsal ridge equally to unequally parvicostellate. Ventral muscle field 1144 1098 extending beyond the valve midlength, but in the Welsh species, bilobed with suboval diductor scars extending 40–45% of valve 1145 fi 1099 the muscle eld is strongly elongated and bounded by a pair of length. Valve margin strongly thickened with peripheral rim 1146 1100 conspicuous ridges, a feature atypical of the genus. Ahtiella separating disc and trail. Dorsal median ridge initially low and 1147 1101 quadrata from the Torllwyn Formation of Anglesey is highest at approximately two-thirds valve length. 1148 1102 represented by fragmentary material, but judging from the two 1103 fi illustrated complete ventral valves (Bates, 1968, pl. 8, gs. 2, 3), Occurrence.—Type specimens and other materials considered 1149 1104 the shell is slightly wider than long and coarsely costellate in this study come from the Las Chacritas Formation exposed at 1150 1105 (~6 costellae per 2 mm) than A. argentina. Quebrada La Tuna, Cordón de La Trampa, San Juan Province, 1151 1106 Ahtiella zarelae from the San José Formation of Peru can Argentina; middle Darriwilian. 1152 1107 readily be distinguished from A. argentina by its less transverse, 1108 nonauriculate shell, and its ramicostellate radial ornamentation. Description.—Shell to 16.5 mm in width, semielliptical to sub- 1153 1109 Internally, the Peruvian species possesses a subpentagonal rectangular in outline, with mean length/width ratio 0.63 1154 1110 rather than triangular ventral muscle field, and a higher, septum- (N = 15); lateral profile moderately convexoconcave, slightly 1155 1111 like dorsal median ridge. In addition, the inner surface of both resupinate, typically 38% as deep as long. Cardinal extremities 1156 1112 valves is almost entirely covered by radial ribs lacking vascular subrectangular, slightly acute in juvenile specimens. Ventral 1157 1113 impressions. valve broadly concave with low carinate median fold originat- 1158 1114 Most similar to the Precordilleran species is Ahtiella ing at umbonal area, becoming almost indistinct near commis- 1159 1115 paucirugosa from the volcaniclastic Summerford Group of sure that is slightly sulcate or rectimarginate. Ventral interarea 1160 1116 Newfoundland. Given that the North American specimens are planar, catacline to gently procline, twice as high as dorsal. 1161 1117 tectonically distorted, shell outline is difficult to compare Arched imperforated pseudodeltidium covering one-half to two- 1162 1118 (A. paucirugosa seems to be approximately twice as wide as thirds of delthyrium. Dorsal valve moderately to strongly con- 1163 1119 long). However, they have in common such external features as vex, uniformly curved in lateral profile, with broad rounded 1164 1120 a well-defined dorsal sinus and ventral fold, and moderate shell median sulcus on its posterior third, becoming shallow to 1165 1121 convexity, although posterolateral rugae are less marked in the impersistent at anterior margin. Dorsal interarea planar, steeply 1166 1122 North American species. Internally, the dorsal valve resembles anacline to orthocline. Notothyrium entirely covered by 1167 1123 that of A. argentina in having a broad median ridge almost strongly convex chilidium. Ornamentation varying from sub- 1168 1124 reaching the margin, rows of elongate pustules and septules equally parvicostellate to unequally parvicostellate; accentuated 1169 1125 forming radial crests, and deeply marked mantle canals of the costellae better defined on anterior half of largest individuals, 1170 1126 saccate type. The main difference lies in the ventral muscle field with 6–8 finer parvicostellae between them; costellae 11 or 12 1171 1127 of A. paucirugosa, which is bilobed with longer diductor scars per 2 mm (counted at 5 mm growth stage). Fine, evenly spaced 1172 1128 extending approximately to the valve midlength. concentric fila present on entire shell surface. Posterolateral 1173 1129 fi 1130 Ahtiella tunaensis new species rugae poorly de ned or absent. 1174 1131 urn:lsid:zoobank.org:act:C9CF5CB8-E169-4777-8C0B- Ventral interior with small, transversely triangular teeth 1175 1132 ADEF34A52181 supported by short strongly diverging dental plates partially 1176 fi 1133 Figure 10.1–10.8 masked by secondary deposits. Muscle eld bilobed extending 1177 anteriorly near 40–45% of valve length; diductor scars suboval, 1178 1134 2003a Ahtiella n. sp.; Benedetto, p. 201, pl. 9, figs. 16–18. bounded by ridges arising from anterior ends of dental plates; 1179 adductor field shorter than diductors, not raised, unbounded 1180 anteriorly. Valve margin strongly thickened with rounded 1181 1135 Type specimens.—Holotype, CEGH-UNC 21083, a ventral subperipheral rim separating disc and trail. Vascula media 1182 1136 valve. Paratypes: CEGH-UNC 27171, an internal mold of a straight, initially subparallel, subdivided toward valve margin. 1183

Figure 11. (1 − 15) Ahtiella coloradoensis (Benedetto, 1998); ‘Green Member of the Sepulturas Formation,’ Los Colorados, northwestern Argentina: (1 − 4) holotype, external mold (1), latex cast (2), internal mold (3), and latex cast (4) of ventral valve, CEGH-UNC 13780; (5, 6) latex cast of exterior (5) and internal mold (6) of dorsal valve, CEGH-UNC 13817; (7) latex cast of ventral exterior, CEGH-UNC 13797; (8) ventral internal mold, CEGH-UNC 13802; (9) latex cast of ventral valve, CEGH-UNC 27187, showing incipient delthyrial cover; (10) latex cast of dorsal interior, CEGH-UNC 13808; (11) internal mold of juvenile dorsal valve, CEGH-UNC 13786; (12) internal mold of juvenile ventral valve, CEGH-UNC 13795; (13) dorsal internal mold, CEGH-UNC 13826; (14, 15) dorsal internal mold (14) and latex cast (15) of dorsal valve, CEGH-UNC 13823, showing detail of cardinalium. (16 − 18) Ahtiella zarelae Villas in Gutiérrez- Marco and Villas, 2007; San José Formation, Inambari River, Peru (illustrations from Gutiérrez-Marco and Villas, 2007, p. 552, ﬁgs. 4D, F, and J, reproduced under the Creative Commons Attribution License CC BY 4.0): (16) latex cast of dorsal valve exterior, MGM 5944X; (17) dorsal internal mold, MGM 5945X; (18) latex cast of ventral interior, MGM 5926X. All specimens dusted with ammonium chloride. Scale bars = 5 mm. 20 Journal of Paleontology

Table 1. Characters utilized in phylogenetic analysis. 1. Shell profile. 0 biconvex; 1convexo-concave; 2 resupinate; 3 concavo-convex or planoconvex; 4 dorsal valve strongly arcuate, gibbous. 2. Outline. 0 semilelliptical; 1 transverse; 2 auriculate or alate. 3. Geniculation. 0 absent; 1 present; 2 strong defining disc and trail. 4. Radial ornamentation. 0 multicostellate or ramicostellate; 1 equally parvicostellate; 2 unequally parvicostellate. 5. Concentric fila. 0 absent; 1 present. 6. Rugae. 0 absent, 1 present on posterolateral areas; 2 strong on the entire surface. 7. Ventral fold. 0 absent; 1 present. 8. Dorsal sulcus. 0 absent; 1 present. 9. Ventral interarea. 0 apsacline; 1 catacline to procline. 10. Dorsal interarea. 0 anacline to orthocline; 1 catacline to hypercline 11. Chilidium. 0 absent; 1 short; 2 large. 12. Delthyrial cover: 0 absent; 1 separated into delthyrial plates; 2 pseudodeltidium. 13. Coverage of pseudodeltidium. 0 absent; 1 apical; 2 nearly complete. 14. Dental plates. 0 absent; 1 short recessive; 2 long well defined. 15. Ventral subperipheral rim. 0 absent; 1 low discontinuous; 2 strongly thickened; 3 defining a disc and trail. 16. Dorsal platform. 0 absent; 1 weak or discontinuous; 2 strong complete; 3 coalescing septules forming curved ridges. 17. Ventral muscle field. 0 short confined delthyrial cavity; 1 long and narrow; 2 small bilobed; 3 large subquadrate or subpentagonal; 4 large bilobed. 18. Ventral muscle bounding ridges. 0 absent; 1 present. 19. Dorsal muscle field. 0 indistinct; 1 quadripartite, orthoid. 20. Dorsal median ridge or myophragm. 0 absent or short; 1 prominent, long and rounded; 2 high bladelike. 21. Cardinal process. 0 simple ridgelike; 1 prominent or bulbous. 22. Ventral mantle canal system. 0 indistinct; 1 impressed on the valve margin; 2 strongly impressed on the entire surface. 23. Shell structure. 0 impunctate; 1 pseudopunctate.

1184 Gonadal areas poorly defined, striated. Areas between vascular molds. Its shell outline is reminiscent of A. quadrata,fromwhich 1207 1185 trunks finely pustulose. External ribbing not reflected on valve it differs mainly in its much finer radial ribbing. The large bilobed 1208 1186 interior. ventral muscle field of A. tunaensis n. sp. is comparable to that of 1209 1187 Dorsal interior with high, bladelike cardinal process erected the Baltic species A. lirata, but differs from the latter species in its 1210 1188 on moderately elevated subtriangular notothyrial platform. Socket less convex and smoothly geniculated profile, better defined 1211 1189 ridges thickened distally, diverginganteriorlyfromeachotherat ventral fold and dorsal sinus, and indistinct rugae. The elongate 1212 1190 ~ 100°, bounding semiconical sockets. Median ridge initially low, oval ventral diductors of the Precordilleran species, although 1213 1191 becoming highest at approximately two-thirds valve length, fading rather shorter, resemble those of A. paucirugosa. However, the 1214 1192 near anterior margin. Muscle field indistinct in single available Precordilleran species can be distinguished by its subrectangular 1215 1193 internal mold. Dorsal mantle canal system faintly impressed with shell, broad dorsal median ridge, and more deeply impressed 1216 1194 straight inner branchs of vascula media almost subparallel to mantle canals. The Peruvian species A. zarelae differs in having 1217 1195 median ridge. Internal surface with coarse papillae near margin. uniformly costellate radial ribbing, a more prominent ventral fold 1218 and deeper dorsal sulcus, a proportionally shorter and wider 1219 1196 Etymology.—Named after the original locality, Quebrada subpentagonal ventral muscle field, and strongly marked internal 1220 1197 La Tuna. radial ornamentation at all growth stages. 1221 1222 Ahtiella famatiniana new species 1223 1198 Materials.—CEGH-UNC 27172–27183, 12 conjoined speci- urn:lsid:zoobank.org:act:9AB173B1-73FE-4142-A2AF- 1224 1199 mens; CEGH-UNC 27168–27170, three fragmentary ventral A2DF1FD3ED9C 1225 1200 valves. Figure 10.9–10.24 1226

1201 Remarks.—This new species is readily distinguished from 2003a Ahtiella sp.; Benedetto, p. 210, pl. 18, ﬁgs. 18–20. 1227 1202 Ahtiella argentina by the less transverse subrectangular shell 1203 outline, nonalate cardinal extremities, catacline to procline ventral 1204 interarea, and larger bilobed ventral muscle ﬁeld. In addition, the Type specimens.—Holotype, CEGH-UNC 27137, internal mold 1228 1205 mantle vascular system in A. tunaensis n. sp. is barely impressed, of ventral valve. Paratypes: CEGH-UNC 27135, internal mold 1229 1206 although this could be due to the lack of well-preserved internal of dorsal valve; CEGH-UNC 27149, conjoined specimen. 1230

Q3 Table 2. Character state distribution for taxa included in phylogenetic analysis. 1 234567891011121314151617181920212223 Hesperonomiella 001000000001010000011000 M. transversa 2200001100000100000100010 A.lirata 422212001122223131 01001 A. jaanussoni 42221201111? ???1?? 11001 A. quadrata 22100011101012112031 1100? A. paucirugosa 2221011110121013341011012? A. argentina 22221111001222133000110121 A. tunaensis 12021210110022223141 010011 A. famatiniana 22210001111112223131 0101? A. zarelae 20110001110100211313101001 A. coloradoensis 201100011100?0112131011001? Benedetto—The strophomenide brachiopod Ahtiella in Gondwana 21

1231 Diagnosis.—Shell transversely semielliptical (mean length/ trunks. External ribbing weakly impressed only on juvenile 1288 1232 width ratio 0.48), alate to mucronate; ventral valve with strongly interiors. Gonadal areas large, occupying most posterolateral 1289 1233 concave posterolateral areas and prominent carinate median areas, sculptured by roughly radial anastomosing ridges. 1290 1234 fold; corresponding dorsal sulcus narrow and deep posteriorly, Dorsal interior with simple bladelike cardinal process 1291 1235 broader and wider at anterior margin. Ornamentation subequally slightly enlarged anteriorly, erected on elevated subtriangular 1292 1236 multicostellate to incipiently parvicostellate, with primary notothyrial platform. Socket ridges strong, slightly thickened 1293 1237 costellae slightly more accentuated. Ventral muscle field almost and free distally, divergent anterolaterally at ~ 80º, bounding 1294 1238 pentagonal, extending to ~ 32% of valve length, with elongate deep semiconical sockets partially excavated under dorsal 1295 1239 diductor scars bounded laterally by curved ridges and shorter interarea. Broad, rounded median ridge arising in front of 1296 1240 adductor field. Broad rounded dorsal median ridge fading notothyrial platform, fading anteriorly at intersection with 1297 1241 anteriorly. Usually well-defined discontinuos dorsal platform. peripheral rim. Muscle field weakly impressed, slightly wider 1298 1242 Vascular system deeply impressed only on disc margin and trail. than long, extending anteriorly for 30% of valve length, 1299 bounded laterally by low ridges; posterior adductor scars 1300 1243 Occurrence.—Cerro Morado Group, Las Pircas anticline, cen- subcircular, smaller than suboval anterior pair. Dorsal mantle 1301 1244 tral Famatina Range, La Rioja Province. Northern margin of canal system indistinct or feebly impressed; vascula media 1302 1245 Chaschuil River (Loma del Médano), Catamarca Province. broad, divergent, branching toward valve margin. Coarse ridge- 1303 1246 Dapingian. like pustules or endospines coalescing to form well-defined 1304 discontinuous platform, which extends along entire valve 1305 1247 Description.—Shell transversely semielliptical, resupinate in margin except posterolateral extremities. 1306 1248 lateral profile, up to 18 mm in width (mean 13 mm, N = 26), 1249 mean length/width ratio 0.48 (N = 20). Cardinal extremities Etymology.—Named after one of the original localities, the 1307 1250 alate, often projecting in rodlike mucrons (usually incompletely Famatina Range. 1308 1251 preserved). Ventral valve strongly concave with greatest con- 1252 cavity at posterolateral areas; carinate median fold stronger Materials.—CEGH-UNC 27131–17159, 29 specimens from 1309 1253 posteriorly, becoming wider and rounded anteriorly; anterior the volcanosedimentary unit exposed at Anticlinal Las Pircas, 1310 1254 commissure broadly sulcate. Ventral interarea planar, procline north of Cachiyuyo River, central Famatina Range, La Rioja 1311 1255 or occasionally catacline, approximately twice as high as dor- Province; CEGH-UNC 27163–27167, five specimens from the 1312 1256 sal. Delthyrium covered in apical two-thirds by semiconical Chaschuil River, north Famatina Range, Catamarca Province. 1313 1257 pseudodeltidium. Dorsal valve moderately convex, 30–35% as 1258 deep as long, uniformly curved (nongeniculated) in lateral Remarks.—In its size and shell convexity, nearly uniform 1314 1259 profile, with median sulcus initially narrow and deep, becoming costellate ornamentation, high carinate ventral fold, and well- 1315 1260 broader and wider at anterior margin where it attains ~ 25% of developed dorsal peripheral rim, this species strongly resembles 1316 1261 valve width. Dorsal interarea planar, orthocline to steeply A. zarelae from the upper Floian of Peru, but differs in having a 1317 1262 anacline, with triangular notothyrium covered posteriorly by proportionally larger ventral muscle field reaching approxi- 1318 1263 convex chilidium. Radial ornamentation subequally multi- mately one-third of the valve length; broader, rounded, non- 1319 1264 costellate, with rounded primary costellae often slightly more septiform dorsal median ridge; and vascular trunks strongly 1320 1265 accentuated than second order ones giving ribbing a parvicos- impressed on the margin of the ventral disc and especially on the 1321 1266 tellate aspect; costellae increasing in number mainly by inter- trail. The Peruvian Ahtiella sp., which is known only by its 1322 1267 polation in dorsal valve and by interpolation and dichotomy in dorsal valve, can be distinguished from the Famatina species by 1323 1268 ventral valve, typically 9 per 2 mm (counted at 5 mm growth its finer and uniform ribbing, higher and shorter median ridge, 1324 1269 stage). Ribs crossed by prominent, closely and evenly spaced and more continuous, anteriorly excavated platform. Ahtiella 1325 1270 fila (~20 per mm) and by few prominent growth discontinuities. argentina can readily be distinguished from A. famatiniana n. 1326 1271 Posterolateral rugae weakly defined or absent. Shell substance sp. by having a more transverse shell outline, unequally parvi- 1327 1272 apparently impunctate. costellate ornamentation, a smaller triangular ventral muscle 1328 1273 Ventral interior with strong triangular teeth supported by field, and a strongly impressed vascular system. The ventral 1329 1274 short dental plates diverging at ~ 120°; umbonal cavities muscle field of A. famatiniana n. sp. is reminiscent of that of A. 1330 1275 partially filled by secondary deposits. Muscle field proportion- tunaensis n. sp., but in the latter it is more definitely bilobed. 1331 1276 ally large, subpentagonal in outline, generally wider than long, Moreover, the Precordilleran species differs in having sub- 1332 1277 typically extending 32% of valve length (maximum 36%); rectangular cardinal extremities, a less pronounced ventral 1333 1278 diductor scars elongate subtriangular, enclosed laterally and median fold, and unequally parvicostellate ornamentation. 1334 1279 anterolaterally by curved ridges originating in front of dental Ahtiella lirata resembles the Famatinan species in its alate or 1335 1280 plates; adductor field shorter and more deeply impressed than mucronate cardinal extremities and its large subrectangular 1336 1281 diductors, suboval to subrectangular in outline, not enclosed ventral muscle field, but can be distinguished by its unequally 1337 1282 anteriorly by diductors. Valve margin strongly thickened, parvicostellate ornamentation, poorly defined (or absent) dorsal 1338 1283 defining internal disc and trail separated by low, rounded sulcus and corresponding ventral fold, and a strongly convex 1339 1284 peripheral rim. Vascula media broad, weakly impressed, slightly gibbous dorsal valve. Ahtiella paucirugosa externally resembles 1340 1285 divergent; distal region of vascular system coinsisting of A. famatiniana n. sp. in having a well-developed dorsal sinus 1341 1286 numerous radially arranged distal branches deeply cutting disc and ventral fold, moderate shell convexity, and almost indistinct 1342 1287 margin and prolonged on trail; small papillae between vascular posterolateral rugae, but differs internally in its elongate ventral 1343 22 Journal of Paleontology

1344 diductor scars extending to near the valve midlength, its deeply accorded to each character. The species M. coloradoensis is 1395 1345 impressed mantle canals, and its high, septum-like dorsal med- reassigned here to Ahtiella mainly because of the incipient 1396 1346 ian ridge. As far as can be judged from the incomplete material, internal geniculation in the ventral valve defining a low disc and 1397 1347 A. quadrata resembles A. famatiniana n. sp. in its shell outline a trail, the large subquadrate ventral muscle field bounded by 1398 1348 and morphology of its ventral muscle field, but the Welsh spe- widely splayed dental plates, and the presence of a faint dis- 1399 1349 cies differs in its coarser radial ornamentation. Ahtiella concava continuous platform in the dorsal valve. In addition, a revision 1400 1350 clearly differs in having a strongly impressed and longer dorsal of the type material and newly collected specimens of M. col- 1401 1351 muscle field and impersistent (much finer? smooth?) ribbing. oradoensis revealed an incipient apical delthyrial cover, like 1402 1352 some specimens of M. cumillangoensis (Figs. 6.15 and 11.9). 1403 1353 Ahtiella coloradoensis (Benedetto, 1998) Havlíček and Branisa (1980) referred to Valcourea sp. a 1404 – 1354 Figure 11.1 11.15 few ventral valves from supposedly Darriwilian sandstones 1405 exposed along the road Sucre-Potosí at Tambo Acachila, 1406 1355 ?1980 Valcourea sp.; Havlíček and Branisa, p. 23, pl. 2, fig. 7. Bolivia. The single illustrated interior is nearly indistinguishable 1407 1356 1998b Monorthis coloradoensis Benedetto, p. 11, pl. 2, figs. from Ahtiella coloradoensis but without dorsal valves and the 1408 1357 15–28. lack of information of external ornamentation, assignment to 1409 this species must remain provisional. 1410 1358 2003a Monorthis coloradoensis; Benedetto, p. 211, pl. 24, Ahtiella coloradoensis resembles A. famatiniana n. sp. in 1411 fi – 1359 gs. 5 9. its large subrectangular (sometimes subpentagonal) ventral 1412 muscle field extending anteriorly to near one-third of the valve 1413 — 1360Q2 Holotype. CEGH-UNC 13780, internal mold of ventral valve length, its well-defined peripheral ventral thickerning, and its 1414 ‘ ’ 1361 from the Green Member of the Sepulturas Formation, north- incipient dorsal platform. Ornamentation is multicostellate in 1415 1362 west of Los Colorados village, Cordillera Oriental, Jujuy Pro- both species but in A. coloradoensis it is more uniform tending 1416 1363 vince, Argentina. to be ramicostellate in the ventral valve. Ahtiella coloradoensis 1417 mainly differs from the Famatinan species in its planar to gently 1418 — 1364 Diagnosis. Shell semielliptical, convexoplanar to gently con- concave ventral valve profile, its less transverse shell outline, its 1419 1365 vexoconcave (mean length/width ratio 0.63) with right-angled rectangular cardinal extremities, and its indistinct pseudodelti- 1420 1366 cardinal extremities in adult specimens; ventral valve almost dium. It can be distinguished from A. zarelae by its lower and 1421 fi 1367 planar with low median fold and well-de ned corresponding rounded ventral fold, less pronounced geniculation, larger 1422 1368 dorsal sulcus. Ornamentation equally multicostellate, occa- ventral muscle field, and the presence of a conspicuous 1423 – 1369 sionally ramicostellate in ventral valve; ribs 10 12 per 2 mm. peripheral rim in the ventral valve. In addition, internal ribbing 1424 fi 1370 Ventral muscle eld subrectangular to subpentagonal, slightly in the Peruvian species is strongly marked. 1425 1371 wider than long, extending to ~ 31% of valve length, bounded 1372 by strong ridges in adult specimens; variably developed plat- Acknowledgments 1426 1373 form in dorsal valve. Vascular system indistinct excepting on 1374 periphery of each valve. I am especially indebted to my colleagues F. Dávila and 1427 R. Astini who collected material from the Famatina Range 1428 1375 Occurrence.—‘Green Member of the Sepulturas Formation’ (Las Pircas anticline), and B. Waisfeld, who collected speci- 1429 1376 (sensu Astini et al., 2004a), Los Colorados area, western slope mens of Ahtiella coloradoensis, making them available for this 1430 1377 of Cordillera Oriental, Jujuy Province, Argentina. Middle-late? study. The helpful comments of the journal reviewer D.A.T. 1431 1378 Darriwilian. Harper and the Associate Editor Ren-Bin Zhan greatly 1432 improved the original manuscript. The TNT program for phy- 1433 1379 Description.—See Benedetto (1998b). logenetic analysis was made available with sponsorship of the 1434 Willi Hennig Society. Research has been financially supported 1435 1380 Materials.—In addition to the type material listed by Benedetto by CONICET (grant PIP 112-201101-00803). This paper is a 1436 1381 (1998b), new specimens CEGH-UNC 27187–27190 were col- contribution to the International Geoscience Programme (IGCP) 1437 1382 lected from Quebrada Chamarra, northwest of Los Colorados Project 653 ‘The onset of the Great Ordovician Biodiversifica- 1438 1383 village, Jujuy Province, Argentina. tion Event.’ 1439

1384 Remarks.—The overall morphology of the Los Colorados spe- References 1440 1385 cies, in particular its convexoplane shell profile, carinate ventral − 1386 fold, equally multicostellate ornamentation, acute cardinal Aceñolaza, F.G., Miller, H., and Toselli, A.J., 2002, Proterozoic early Paleo- 1441 zoic evolution in western South America—A discussion: Tectonophysics, 1442 1387 extremities, and orthoid cardinalia led Benedetto (1998b) to v. 354, p. 121–137. doi: 10.1016/s0040-1951(02)00295-0. 1443 1388 refer it to the hesperonomiid genus Monorthis. This assignment Albanesi, G.L., and Astini, R.A., 2000, New conodont fauna from Suri Forma- 1444 tion (Early − Middle Ordovician), Famatina System, western Argentina: 1445 1389 was further supported by the lack of evidence of pseudopunctae Reunión Anual de la Asociación Paleontológica Argentina, Mar del Plata, 1446 1390 and pseudodeltidium, both considered diagnostic features of the Abstracts, v. 3, Ameghiniana, v. 37, no. 4, supplement, p. 68. 1447 1391 plectambonitoids. As discussed previously, however, the dif- Albanesi, G.L., and Astini, R.A., 2002, Faunas de conodontes y Sacabambaspis 1448 janvieri (Vertebrata) en el Ordovícico Medio de la Cordillera Oriental 1449 1392 ferences between Monorthis and the basal species of Ahtiella are Argentina: Implicancias estratigráficas y paleobiogeográficas: Congreso 1450 1393 subtle and exhibit transitional characteristics, so that assigne- Argentino de Paleontología y Bioestratigrafía, 8th, Corrientes, Argentina, 1451 1394 ment to one or the other genus depends largely on the weight Abstracts, p. 17. 1452 Benedetto—The strophomenide brachiopod Ahtiella in Gondwana 23

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