Significance of intermediate forms in phyletic reconstructionof ammonites: Early Jurassic Phricodoceras case study JEAN−LOUIS DOMMERGUES and CHRISTIAN MEISTER Dommergues, J.−L. and Meister, C. 2013. Significance of intermediate forms in phyletic reconstruction of ammonites:Early Jurassic Phricodoceras case study. Acta Palaeontologica Polonica 58 (4): 837–854.
This paper discusses the phyletic interpretation of the genus Phricodoceras and its taxonomic classification at thesubfamily, family, and superfamily levels from an historical and critical perspective. First a review of the latest find−ings on this taxon is presented and the grounds for the attribution of Phricodoceras to the Schlotheimiidae(Psiloceratoidea) are summarized and illustrated. This review is a synthesis grounded on evolutionary (e.g.,heterochronies, innovations), eco−ethological (e.g., assumed shell hydrodynamic capacities) and spatio−temporal pat−terns (e.g., bio−chronostratigraphy, palaeobiogeography). Then, the main stages of understanding the taxonomy ofPhricodoceras since the early nineteenth century are reviewed. Two main taxonomic concepts alternate over time. Thefirst is based on the "overall resemblance" of Phricodoceras to some coeval Eoderoceratoidea leading to the genus be−ing included in its own family or subfamily (e.g., Phricodoceratinae) among the Eoderoceratoidea. The second hypoth−esis, recently confirmed by the discovery of an intermediate form (i.e., Angulaticeras spinosus), clearly includesPhricodoceras within the Schlotheimiidae (Psiloceratoidea). Comparison of these two very different conceptions re−veals how "overall resemblance" can be misleading and shows that the discovery of intermediate forms is often the keyto phyletic reconstructions in ammonites.
K e y w o r d s : Cephalopoda, Ammonoidea, stratigraphy, paleobiogeography, taxonomy, character, homology, ontogeny,adaptation, Jurassic.
Jean−Louis Dommergues [Jean−Louis.Dommergues@u−], UFR Sciences Vie, Terre et Environnement,Université de Bourgogne, CNRS/uB, UMR 5561, Biogéosciences Dijon, 6 Boulevard Gabriel, F−21000 Dijon, France;Christian Meister [christian.meister@ville−], Muséum d'Histoire Naturelle de Genève, Département de Géologie etde Paléontologie, 1 Rte de Malagnou, cp 6434, CH−1211 Geneva, Switzerland. Received 18 September 2011, accepted 8 March 2012, available online 20 March 2012.
Copyright 2013 J.−L. Dommergues and C. Meister. This is an open−access article distributed under the terms of the Cre−ative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, pro−vided the original author and source are credited.
latest discoveries and their taxonomic implications; second,to recapitulate the main steps of the taxonomic practices in− Phricodoceras is a homogeneous and unambiguously de− volving Phricodoceras since the early nineteenth century; fined group among the late Sinemurian and Pliensbachian and third, to examine the grounds for the major changes ammonites. Although generally scarce, Phricodoceras has in the interpretation of the relationships of Phricodoceras been actively collected and studied since the early nine− among the Sinemurian and Pliensbachian ammonites. Spe− teenth century because of its attractive and unusual tubercu− cial attention is also paid to why the misleading phyletic hy− late ornamental pattern. As a result, despite its rarity, it is pothesis by which the genus Phricodoceras was ascribed to discussed in a hundred or so publications. It is surprising the Eoderoceratoidea should have proved so resilient in the therefore that its relationships and consequently its taxo− literature. The case of Phricodoceras is discussed here to nomic attribution should recently have been seriously exemplify what is a common bias in ammonite taxonomic questioned (Dommergues 1993, 2003; Dommergues and practices. Taxonomic groupings grounded on some "over− Meister 1999; Meister 2007; Dommergues et al. 2008) and all resemblance" combined with stratigraphic control are finally reconsidered at the superfamily level (Edmunds et usually evidence. Unfortunately, later this may become al. 2003; Meister et al. 2010, 2011; Blau and Meister 2011).
"coarse" evidence and/or may be found to be homeo− This edifying late taxonomic revision illustrates the surpris− morphy, as is shown here for Phricodoceras. The impor− ing immovability of questionable practices in ammonite tance of transitional forms in convincingly defining the pri− taxonomy. The aim of this work is, first, to summarize the mary homologies is also clearly illustrated in the example Acta Palaeontol. Pol. 58 (4): 837–854, 2013 ACTA PALAEONTOLOGICA POLONICA 58 (4), 2013 studied. Thus, beyond Phricodoceras, the present work canbe viewed as a "case study" and a possible source of ideas for ammonite taxonomy.
Institutional abbreviations.—UBGD, University of Burgundy.
Other abbreviations.—M, macroconch; m, microconch; t1, latero−umbilical position; t2, latero−ventral position; t3, peri− siponal position; us, umbilical seam; vb, ventral band (see also Stratigraphic and geographic The stratigraphic and paleobiogeographic frameworks of thegenus Phricodoceras have been extensively and accurately described by Meister (2007: figs. 12, 14, 16, 17). The results of that key work are summarized here and supplemented schematically by more recently published data (Figs. 1, 2).
The stratigraphic range of Phricodoceras is objectively docu− INEMURIAN turneri mented from the base of the Echioceras raricostatum Chrono− zone (Crucilobiceras densinodulum Subchronozone) to the top of the Pleuroceras spinatum Chronozone (Pleuroceras hawskerense Subchronozone). In the Mediterranean Tethys the last Phricodoceras (Phricodoceras aff. cantaluppii Fantini Sestini, 1978) are associated with Emaciaticeras (Meister et al. 2010). The earliest representatives of the genus Phricodo− NGIAN Alsatites ceras (Echioceras raricostatum Chronozone) belong to the group of Phricodoceras gr. taylori (Sowerby, 1826)–P. lamel− H planorbis losum (Orbigny, 1844). They exhibit from the outset all of the impressive diagnostic features of the genus. Convincingly,Phricodoceras roots among the genus Angulaticeras and A.
(Angulaticeras) spinosus Meister, Schlögl, and Rakús, 2010, Fig. 1. Bio−chronostratigraphic framework of the six genera belonging tothe Schlotheimiidae as this family is understood in the present paper. The a recently discovered species with a Phricodoceras−like juve− ranges are referred to the standard chronostratigraphic scale (stages and nile stage, comes from a condensed Carpathian fauna suggest− chronozones) so that relevant global comparisons can be made. The proba− ing a period from the Arietites bucklandi to the Caenisites ble age of Angulaticeras spinosus is starred. Radiochronologic ages of the turneri chronozones (Meister et al. 2010). The condensed con− stage boundaries from Ogg et al. (2008). The height of the chronozone text of this unusual fossiliferous locality must be underlined boxes varies with the stage duration in Myr.
because the sedimentary processes often associated with con−densation can explain the presence of an episode that is usu− Phricodoceras obviously reflects the persistence of only a few ally missing at the regional level (e.g., long lasting submarine but striking ornamental diagnostic traits (autapomorphies).
exposure and/or erosion) (Olóriz 2000; Cecca 2002; Olóriz On the contrary, such flagrant features are missing among the and Villaseñor 2010). Even if an age somewhere in the Caeni− earliest representatives of the family and the genus diagnoses sites turneri Chronozone is plausible for A. (A.) spinosus are clearly less constrained as a result. So comparisons of ge− (Fig. 1), there remains an undocumented stratigraphic gap in nus durations are perhaps weakly significant in evolutionary Phricodoceras history corresponding approximately to the duration of the Asteroceras obtusumOxynoticeras oxynotum In paleobiogeographic terms Phricodoceras is a taxon Chronozones. Fig. 1 shows that Phricodoceras is clearly the chiefly known in the Mediterranean and NW European con− longest−surviving genus of the Family Schlotheimiidae. In fines of the Western Tethys (Fig. 2). Thus, of the just over one point of fact, the genus durations have a propensity to increase hundred publications featuring, to some extent, the genus throughout the history of the family, and this tendency appar− Phricodoceras, 37 concern the Mediterranean faunas (includ− ently peaks with Phricodoceras. Obviously, like all taxo− ing the Pontides, Northern Turkey), 41 discuss the NW Euro− nomic groupings, genera are partly subjective and their dura− pean faunas, and only 7 refer to other parts of the world. In tion may be influenced by taxonomic practice, which widely fact, very few specimens are cited outside the Mediterranean depends on human perception. Thus the long duration of Tethys, NW Europe and the Pontides (Fig. 2). Moreover, the DOMMERGUES AND MEISTER—PHYLETIC RECONSTRUCTION OF EARLY JURASSIC AMMONOID approximate NW European vs. Tethyan faunal Angulaticeras spinosus Asterocera boundary during the Early Pliensbachian Phricodoceras from the Echioceras raricostatum Chronozone Phricodoceras from the Uptonia jamesoni Chronozone Mediterranean Tethys Phricodoceras from the Tragophylloceras ibex Chronozone Pontides (Northern Turkey) Phricodoceras from the Prodactylioceras davoei Chronozone Phricodoceras from the Amaltheus margaritatus Chronozone Timor (Roti Island) Phricodoceras from the Pleuroceras spinatum Chronozone Western North America (British Columbia, Oregon) Phricodoceras from the Early Pliensbachian sensu lato Fig. 2. Schematic distribution of Angulaticeras spinosus Meister, Schlögl, and Rakús, 2010 and Phricodoceras at the global scale. The approximate bound−ary between the NW European and Tethyan (Mediterranean) faunas is suggested by a dotted line. Paleogeographical reconstruction from Vrielynck andBouysse (2001), modified.
specimens from Western North America, Northern Chile and More generally, the Mediterranean Tethys seems to be the Eastern Himalayas are unconvincing or questionable. The the only known sustained "hot spot" of Phricodoceras di− only reliable representative of the genus Phricodoceras from versity. By contrast, only a few species related to the group outside the Mediterranean and NW European confines of the of P. taylori sensu lato are known in NW Europe and almost Western Tethys is a finely preserved specimen from the Timor all of the many specimens known in this area are associated area close to the Australian Tethyan margin (Krumbeck with a brief dramatic acme in the lower part of the Uptonia 1922). Ideally, it would be best to consider the stratigraphic jamesoni Chronozone. Paradoxically, the Phricodoceras sensu lato and sedimentological frameworks so as to counter− are never common in the Mediterranean Tethys but both balance this crude palaeobiogeographical data, which can their taxonomic diversity and their morphological disparity yield a partly biased picture of reality. Unfortunately, though, remain persistently high in this area where the genus is the present synthesis is grounded on such heterogeneous liter− recurrently observed from the Echioceras raricostatum ature that the consideration of stratigraphic and sedimento− Chronozone to the base of the Pleuroceras spinatum logical data is no more than an ideal. Nevertheless—as previ− Chronozone (Figs. 1, 2). We must also emphasize that ously demonstrated for the Early Pliensbachian by Dom− Angulaticeras (Angulaticeras) spinosus, a possible ances− mergues et al. (2009: fig. 6)—despite a similar study effort (at tor of Phricodoceras, is to date only known in the Mediter− least in terms of number of publications), the Mediterranean ranean Tethys (i.e., Austroalpine). In terms of diversity Tethys palaeobiodiversity is clearly richer than that of NW (i.e., comparison of the number of species during the Echio− Europe, although it is still undersampled in comparision.
ceras raricostatum and Uptonia jamesoni chronozones) the ACTA PALAEONTOLOGICA POLONICA 58 (4), 2013 Pontides area occupies an intermediate position between ner whorls of the macroconch and microconch at all onto− the Mediterranean Tethys and NW Europe.
genetic stages (e.g., P. taylori) are quite distinctive and pre− In this paper, the binominal italicized names of chrono− clude any confusion. At small diameters Phricodoceras may zones result from the policy of the journal that any names display one of the most impressively tuberculate ornamenta− derivative of biological species should be written in this tions among the Early Jurassic ammonites, notably an excep− tional peri−siphonal (t3) row of tubercles or spines (Figs. 4,5). The inner mould of the phragmocones exhibits only thebases of the spines, which in this case look like truncated tu− Morphology, dimorphism, bercles or bullae (Fig. 4), but some well−preserved speci−mens display prominent spines especially in peri−siphonal ontogeny, and adaptation (t3) and latero−ventral (t2) positions (e.g., Buckman 1911: pl.
33; Hoffmann 1982: pl. 14: 3; Edmunds et al. 2003: fig. 20.5) The diagnostic features of Phricodoceras and especially the (Fig. 5E). Within the groups of P. taylori (m)–P. lamellosum "juvenile" ornamental features are very unusual for Early Ju− (M) and of P. bettoni (m) Géczy, 1976–P. urkuticum (M) rassic ammonites and the genus has always been regarded as (Géczy, 1959) at least, up to three rows of tubercles can be forming both a highly distinctive and a homogeneous taxon.
observed, though briefly, during the most strongly orna− Even the most morphologically derived forms (e.g., tiny Late mented growth stage (Meister 2007: fig. 11). The positions Pliensbachian microconchs or large Early Pliensbachian of these three rows of tubercles are indicated in Fig. 4.
macroconchs) can be fairly easily attributed to the genus. As Among the genus Phricodoceras the latero−umbilical (t1) a result, the synonymy of the genus is limited to a single row of tubercles is often missing and the latero−ventral (t2) taxon (i.e., Hemiparinodiceras Géczy, 1959) and there is no row is sometimes absent, even in the group of P. taylori subgenus to suggest possible groupings within the twenty or (m)–P. lamellosum (M) (e.g., Phricodoceras aff. cornutum so nominal species. Despite its apparent homogeneity, the [Simpson, 1843]) (Fig. 3D). Conversely the peri−siphonal genus Phricodoceras is not a simple lineage but, as evi− (t3) row of tubercles remains visible, during a brief growth denced by Meister (2007: fig. 15), a clade with a rather com− stage at least. The permanence of this trait is strong evidence plex internal structure. The concept of "species complex" that the peri−siphonal tubercles or shoulder (t3 or s3) of Phri− might be helpful in putting the clade topology into words.
codoceras are homologous with the sudden peri−siphonal in− Even if the phenomenon tends to decrease with time, a usu− terruption of the ribs or shoulders (s3) of Angulaticeras, ally obvious microconch (m)/macroconch (M) dimorphism which is also a very permanent juvenile trait (Figs. 4–6).
characterizes the Phricodoceras as exemplified by the pair of Although less distinctive, the suture lines of Phricodoceras nominal species P. taylori (m)–P. lamellosum (M) in Fig. 3.
also have informative features which can be contrasted with Dimorphism seems to have peaked in this group close to the Angulaticeras on the basis of a comparative study of septal base of the Early Pliensbachian in NW Europe and therefore suture ontogenies. The pointed, often slender and trifid in a palaeobiogeographical context suggesting a briefly suc− (sometimes sub−triangular) lateral lobe of Phricodoceras is cessful northward faunal ingression. The extent of this strik− the most obvious similarity (Fig. 7), and despite many appar− ing dimorphism is difficult to quantify because the largest ent differences, the suture line of Phricodoceras can be un− known P. lamellosum (M) are all incomplete phragmocones derstood as a simplified version of that observable in Angu− (e.g., Fig. 3A), and their adult body chambers are unknown.
laticeras with wider saddles and chiefly without any clear re− However, a ratio of about one to ten in diameter can be rea− tracted suspensive lobe, as is usual in Angulaticeras. Many sonably suspected. The intermediate and outer whorls of the of these differences and especially the lack of an obvious sus− large macroconch forms have rather involute and compres− pensive lobe are probably partially correlated with different sed shells with slightly curved flanks and a rounded ventral shell morphologies. At the same diameters, shells are clearly area. The transition between the umbilical area and the base more involute and compressed in Angulaticeras than in Phri− of the flanks is rounded without shoulders, although faint codoceras whose inner whorls, at least, often have sub− peri−siphonal shoulders (s3), inherited from juvenile peri− circular sections and barely overlap the successive whorls, siphonal tubercles (t3), may persist at relatively large dia− thus providing less space for the retraction of the umbilical meters (e.g., Fig. 3A, B). The ornamentation of crowded, lobes. Conversely, the suture lines of Phricodoceras are very fine, subdivided and slightly flexuous ribs is rather discreet different from those of both the Lytoceratoidea and Eodero− and often somewhat irregular (e.g., Fig. 3A). At large diame− ceratoidea whose bifid or trifid lateral lobes are invariably ters the ribs may cross the ventral area. Thus, the pre−adult adapically broad but abapically often narrow (Fig. 8).
and probably also the adult (body chamber) habitus of the The evolution of Phricodoceras is, as demonstrated by macroconch is coarsely comparable, at the same diameter, to Meister (2007: fig. 11), basically controlled by ontogenetic that of Angulaticeras. Actually, at large diameters Phricodo− heterochronies in the "size−based" or "allometric" and not ceras lamellosum (M) looks similar to Angulaticeras al− "age−based" sense of the term. Fig. 9 summarizes and sim− though with a less compressed shell and a wider and more plifies the model proposed by Meister (2007) for Phricodo− rounded ventral area. In contradistinction, the traits of the in− ceras and extends it to a broader taxonomic framework

DOMMERGUES AND MEISTER—PHYLETIC RECONSTRUCTION OF EARLY JURASSIC AMMONOID Fig. 3. Microconch (m) / macroconch (M) dimorphism expressed by scholtheimiid ammonoid Phricodoceras exemplified by the NW Europe forms in the
Uptonia jamesoni to Tragophylloceras ibex chronozones. A. Phricodoceras lamellosum (Orbigny, 1844) (M), UBGD 277451, Mazenay, Saône et Loire,
France, probably early Uptonia jamesoni Chronozone, in apertural (A1), lateral (A2), and ventral (A3) views. B. Phricodoceras lamellosum (M), Kircheim unter
Teck, Baden−Würtemberg, Germany, Early Pliensbachian (from Schlegelmilch 1976: pl. 27: 4, modified; original from Quenstedt 1884: pl. 28: 24), in apertural
(B1), lateral (B2), and ventral (B3) views. C. Phricodoceras taylori (Sowerby, 1826) (m), Corbigny, Nièvre, France, Uptonia jamesoni Chronozone,
Phricodoceras taylori Subchronozone (from Dommergues 2003: pl. 1: 4), in lateral view. D. Phricodoceras aff. cornutum (Simpson, 1843) (m), Fresnay−
le−Puceux, Calvados, France, Early Pliensbachian (from Dommergues et al. 2008: pl. 3: 6, modified), in ventral (D1) and lateral (D2) views. E. Phricodoceras
(m), Fresnay−le−Puceux, Calvados, France, Early Pliensbachian (from Dommergues et al. 2008: pl. 3: 5, modified), in ventral (E1) and lateral (E2) views.
The two specimens corresponding to A, B are incomplete phragmocones (juvenile or immature shells) but the three corresponding to C–E are adult microconchs
with the major part of the body chamber. The end of the phragmocone is starred. Notice the progressive ontogenetic transformation from tubercle (t3) to faint
shoulder (s3) in specimen B. Abbreviations: t2, tubercle in latero−ventral position; t3, tubercle in peri−siphonal position; s3, shoulder peri−siphonal position.
including Angulaticeras, with A. boucaultianum (Orbigny, bachian). The first step (A. boucaultianum to A. spinosus) 1844) (Early Sinemurian) for comparison and A. spinosus involves a "juvenile innovation" sensu Dommergues et al.
(Late Sinemurian) as a possible ancestor or at least the sister (1986) and Dommergues (1987), a phenomenon that is not a group of Phricodoceras (Late Sinemurian to Late Pliens− heterochony sensu stricto but which immediately precedes

ACTA PALAEONTOLOGICA POLONICA 58 (4), 2013 case, retardation is accompanied by a dramatic enhance−ment of the juvenile features and the tuberculated ornamen−tation reaches a maximum in the group of P. taylori (m)–P.
(M). The spines reach outstanding proportionsand three rows of tubercles are usual. The third (P. lamel−losum to P. urkuticum) and fourth (P. urkuticum to P.
[Bettoni, 1900]) steps follow a reversal and an in−crease in complexity of the heterochronic pattern. Theselast two steps in Phricodoceras history witness a sustained contraction and weakening of the juvenile tuberculate stageand a correlative progressive decline in adult size. Thiscomplex pattern suggests the combination of two distinctpolarities, one peramorphic (by acceleration of growth) andthe other paedomorphic (by hypomorphosis), although"phyletic dwarfism" is another possibility because size isnot necessarily a proxy of age. In palaeobiogeographicalterms the late tiny or at least smallish (possibly dwarf ?)Phricodoceras are rare, or even very rare, strictly Tethyanspecies; however, relations with the palaeoenvironmental conditions remains obscure.
In terms of adaptation and traits of life history only as− sumptions are possible. Nevertheless, the importance of pat− Fig. 4. Position and terminology of the tubercles, spines and/or bullae on terns chiefly related with juvenile stages (i.e., juvenile inno− Phricodoceras shells (juvenile and/or microconch. A, B. Normal view. C, D.
vation and paedomorphosis by deceleration) suggests that Shaded view with indication of the main ornamental structure outlines (white the evolutionary history of Phricodoceras was a phenome− lines). Abbreviations: t1, latero−umbilical position; t2, latero−ventral posi− non partly associated with changes in juvenile living condi− tion; t3, peri−siphonal position; us, umbilical seam; vb, ventral band.
tions (Fig. 10). It seems reasonable to assume that the spec−tacular tuberculate ornamentation ensured an effective pas− evolutionary phenomena chiefly controlled by heterochro− sive protection both for the juvenile macroconchs and for nies. In the case of A. spinosus, the innovation is the possi− the microconchs throughout their growth. In this sense, the bly rapid emergence of an obviously tuberculated ornamen− emergence of a tuberculate growth stage in Phricodoceras, tation in the innermost whorls only. Conversely, the subse− and therefore within the Schlotheiimidae, could be under− quent and merely ribbed growth stages of this species are stood as a convergence with the plentiful and diversified Late usual for Angulaticeras. Truncated tubercles in (t2) posi− Sinemurian and Early Pliensbachian tuberculated Eodero− tion are clearly visible up to an umbilical diameter of 11 mm ceratoidea (Fig. 11B, C). Conversely, it is possible that the (Fig. 5A1, A2). They are similar to the tubercles in the same living conditions of the post−juvenile macroconchs of Phri− position and at the same diameter in Phricodoceras (Fig.
codoceras were little changed from those of Angulaticeras.
5B1) so, and although the ventral area is concealed by whorl Differences in lifestyle between juvenile macroconchs and overlap, it is plausible that tubercles also exist in peri− microconchs (assumed to have been not very mobile but pas− siphonal position in the inner whorls of A. spinosum. The sively protected) and adult macroconchs (assumed to have second step (A. spinosus to P. lamellosum) is chiefly a had better hydrodynamic abilities and mobility, as suggested paedomorpic pattern of heterochony with an obvious decel− by the more compressed shell, with weaker and more flexu− eration of growth sensu Reilley et al. (1997). As is often the ous ornamentation) are therefore perhaps the key to the spe− Fig. 5. Comparison of morphological and ornamental patterns of scholtheimiid ammonoid Angulaticeras spinosus Meister, Schlögl, and Rakús, 2010 and ®
Phricodoceras gr. taylori (Sowerby, 1826) (m)–Phricodoceras lamellosum (Orbigny, 1844) (M). A. Angulaticeras (Angulaticeras) spinosus (M?), holotype,
Chtelnica, Male Karpaty Mts., Western Carpathians, Slovakia, Sinemurian condensed bed (from Meister et al. 2010: fig. 34, a, b, modified), in lateral (A1, A2)
and apertural (A3) views. B. Phricodoceras taylori (m?), Corbigny, Nièvre, France, Uptonia jamesoni Chronozone, Phricodoceras taylori Subchronozone
(from Dommergues 2003: pl. 1: 2, modified), in lateral (B1, B2) and ventral (B3) views. C. Phricodoceras lamellosum (M), Hinterweiler, Baden−Würtemberg,
Germany, Early Pliensbachian (from Schlatter 1980: pl. 6: 6, modified), incomplete phragmocone showing the transition between the juvenile tuberculate stage
and the late merely ribbed stage, in lateral (C1) and ventral (C2) views. D. Phricodoceras taylori (m), Corbigny, Nièvre, France, Uptonia jamesoni Chronozone,
Phricodoceras taylori Subchronozone (from Dommergues 2003: pl. 1: 4), in lateral view. E. Phricodoceras taylori (m), Fresnay−le−Puceux, Calvados, France,
Early Pliensbachian (from Dommergues et al. 2008: pl. 3: 5, modified), in lateral (E1) and ventral (E2) views. To facilitate comparisons at small diameters,
A1 and B1, respectively corresponding to A2 and B2, are twice magnified. The three specimens corresponding to A–C are incomplete phragmocones (juvenile
or immature shells) but the two specimens corresponding to D, E are adult microconchs with the major part of the body chamber. The end of the phragmocone
is indicated by a star. Some noticeable ornamental elements are indicated by arrows: smooth ventral band (vb), tubercle in latero−ventral position (t2), tubercle
or shoulder in peri−siphonal position (t3 or s3).

DOMMERGUES AND MEISTER—PHYLETIC RECONSTRUCTION OF EARLY JURASSIC AMMONOID ACTA PALAEONTOLOGICA POLONICA 58 (4), 2013 cific features of Phricodoceras. This hypothesis, summa− 1996). Such a pattern, however, is not rare among the extant rized in Fig. 10, is partly speculative, though, because eco− ethological considerations derived from shell type and sculp−ture with respect to "abilities" for swimming and/or maneu− Geographic and stratigraphic range.—Chiefly NW Europe verability are interesting but unfortunately limited for all and Mediterranean Tethys including Pontides (Turkey). The ectocochleate cephalopods (Westermann and Tsujita 1999).
presence of Phricodoceras is also attested in Timor (Indone−sia) but is doubtfull in British Columbia (Canada), Oregon Systematic palaeontology (USA), and Chile. Phricodoceras ranges from Late Sine−murien to Late Pliensbachian.
Class Cephalopoda Cuvier, 1798Subclass Ammonoidea Zittel, 1884 The phylogenetic and taxonomic Order Phylloceratida Arkell, 1950 (sensu Hoffmann 2010)Suborder Psiloceratina Housa, 1965 Phricodoceras in the literature.—Since 1826, a hundred
(sensu Guex 1987 = Ammonitina Arkell, 1950, or so publications have dealt, at least in part, with Phricodo− sensu Hoffmann 2010) ceras. Most of them contain illustrations (drawings or pho− Superfamily Psiloceratoidea Hyatt, 1867 tographs). All these publications are considered in Fig. 12with a view to summarizing the taxonomic opinions of their (sensu Guex 1995) authors (Sowerby 1826; Zieten 1830; Orbigny 1844; Quen− Family Schlotheimiidae Spath, 1923 stedt 1846, 1849, 1883; Oppel 1853, 1856; Hauer 1861; Remarks.—In view of the close relationships between Angu− Wright 1880; Fucini 1898, 1908; Bettoni 1900; Del Cam− laticeras and Phricodoceras with A. spinosus as a convinc− pana 1900; Hyatt 1900; Buckman 1911, 1921; Krumbeck ing intermediate form, it appears convenient to include Phri− 1922; Schröeder 1927; Höhne 1933; Gérard and Théry codoceras in the Schlotheimiidae and to abandon the sub− 1938; Roman 1938; Spath 1938; Otkun 1942; Venzo 1952; family and family terms Phricododeratinae and Phricodo− Fantini Sestini and Paganoni 1953; Donovan 1954; Arkell ceratidae. This classification has already been adopted by et al. 1957; Géczy 1959, 1979, 1998; Dean et al. 1961; Meister et al. (2011). Its main advantage is that it is readily Fantini Sestini 1962, 1978; Schindewolf 1962; Bremer supported by the comparative anatomy within the Psilo− 1965; Cantaluppi and Brambillia 1968; Frebold 1970; ceratoidea and is founded on an odd morpho−ornamental fea− Wiedmann 1970; Tintant et al. 1975; Schlegelmilch 1976; ture (i.e., the "Phricodoceras habitus") the complexity of Schlatter 1977, 1980, 1990, 1991; Dommergues 1978, which greatly reduces the risk of convergences.
1993, 2003; Dubar and Mouterde 1978; Alkaya 1979;Linares et al. 1979; Wiedenmayer 1980; Donovan et al.
1981; Hoffmann 1982; Venturi 1982; Braga 1983; Genus Phricodoceras Hyatt in Zittel, 1900 Mouterde et al. 1983; Büchner et al. 1986; Meister and = Hemiparinodiceras Géczy, 1959 Sciau 1988; Smith et al. 1988; Dommergues and Meister Type species: Ammonites taylori Sowerby, 1826; Early Pliensbachian, 1990, 1999; Dommergues et al. 1990, 2000, 2008; Cope from a boulder in glacial till at Happisburgh, Norfolk, England, by origi− 1991; Ferretti 1991; Sciau 1991; Tipper et al. 1991; Page nal designation.
1993, 2008; Dommergues and Mouterde 1994; Mouterde Remarks.—21 nominal species can be attributed to the genus and Dommergues 1994, Alkaya and Meister 1995; El Hariri Phricodoceras. Nine of them are based on NW European et al. 1996; Faraoni et al. 1996; Smith and Tipper 1996; specimens and 11 on Tethyan sensu lato forms. In a recent re− Géczy and Meister 1998, 2007; Rakús 1999; Macchioni vision of the genus, Meister (2007) retains only 11 valid spe− 2001; Venturi and Ferri 2001; Howarth 2002; Rakús and cies, three of which are NW European while seven are Guex 2002; Donovan and Surlyk 2003; Edmunds et al.
Tethyan. These proportions are representative of the high di− 2003; Meister et al. 2003, 2010, 2011; Hillebrandt 2006; versity of the genus Phricodoceras in Tethyan and especially Meister 2007; Yin et al. 2007; Venturi and Bilotta 2008; Mediterranean faunas. According to Meister (2007), three Venturi et al. 2010; Blau and Meister 2011).
m–M pairings can be suspected while four small or tiny spe− In all, 162 specimens are figured in these publications, in− cies (one NW European and three Mediterranean) cannot cluding 78 for NW Europe and 84 for the Tethyan realm readily be considered microconchs despite their small size.
sensu lato. Compared with other taxa, such a large number of In fact, despite its indisputable success in the palaeonto− illustrations is not in proportion to the relative scarcity of logical literature, the m–M model is often far from evidence.
Phricodoceras in the fossil record but partly reflects the spe− The possibility of small species without or at least without cial interest shown by authors in this morphologically aston− significant m–M dimorphism is rarely considered as a valu− ishing and taxonomically challenging group. In fact, the il− able alternative hypothesis for ammonites (Davis et al.
lustrated specimens correspond to a significant portion of the

DOMMERGUES AND MEISTER—PHYLETIC RECONSTRUCTION OF EARLY JURASSIC AMMONOID Fig. 6. Habitus of some specimens belonging to scholtheimiid ammonoid Agulaticeras, the genus which represents the root of Phricodoceras.
A. Angulaticeras (Sulciferites) charmassei (Orbigny, 1844), Stuttgart−Vaihingen, Baden−Würtemberg, Germany, Arietites bucklandi Chronozone,
Coroniceras rotiforme Subchronozone (from Bloos 1988: pl. 11, modified), in lateral (A1) and apertural (A2) views. B. Angulaticeras (Boucaulticeras)
boucaultianum (Orbigny, 1844), Chtelnica, Male Karpaty Mts., Western Carpathians, Slovakia, Sinemurian condensed bed (from Meister et al. 2010: fig.
42f, g, modified), in lateral (B1) and ventral (B2) views. C. Angulaticeras (Boucaulticeras) gr. deletum (Canavari, 1882), Jbel Bou Hamid, Central Hight At−
las (Rich), Morocco, Late Sinemurian (from Guex et al. 2008: pl. 4: 6, modified), in apertural (C1) and lateral (C2) views. D. Angulaticeras (Boucaulticeras)
gr. rumpens (Oppel, 1862), Chtelnica, Male Karpaty Mts., Western Carpathians, Slovakia, Sinemurian condensed bed (from Meister et al. 2010: fig. 40c, d,
modified), in ventral (D1) and lateral (D2) views. E. Angulaticeras (Sulciferites) chtelnicaense Meister, Schlögl, and Rakus, 2010, holotype, Chtelnica,
Male Karpaty Mts., Western Carpathians, Slovakia, Sinemurian condensed bed (from Meister et al. 2010: fig. 32d, e, modified), in ventral (E1) and lateral
(E2) views. A, C (and possibly B) are incomplete phragmocones (juvenile or immature shells) but the two specimens corresponding to D, E have a signifi−
cant part of the body chamber intact. The age of D is doubtful but E is probably an adult. The end of the phragmocone is indicated by a star. The ornamenta−
tion of Angulaticeras is chiefly constituted by usually crowded, fairly flexuous and divided ribs which suddenly break up just before reaching the venter. At
least at small diameters (juveniles, microconchs) the ventral area bears a narrow smooth and more or less depressed ventral band (vb). The abrupt endings of
the ribs look like shoulders in peri−umbilical position (s3). Shoulders may vanish progressively with growth (B). Moreover, some rare species may exhibit
unusual peri−umbilical projections from the ribs (ppr), which partially obstruct the umbilicus (E). Such projections are not true tubercles or spines.
samples collected in the NW European faunas and encom− Hypotheses, discussions, and facts.—From Sowerby (1826)
pass almost all of the samples recovered in Tethyan sensu to Hauer (1861), the early authors described and depicted lato areas. In this context, the literature is probably very rep− some convincing specimens belonging to the group of Phri− resentative of the material collected over some two centuries, codoceras taylori under the generic name Ammonites without and largely housed in museums.
any indication of possible relationships within this huge genus ACTA PALAEONTOLOGICA POLONICA 58 (4), 2013 A. martinschmidti (wh = 180 mm) P. urkuticum (wh = 20 mm) P. taylori (wh = 7 mm) A. charmassei (wh = 40 mm) P. taylori (wh = 6 mm) A. densilobatum (wh = 32 mm) P. taylori (wh = 5 mm) A. lacunatum (wh = 4,5 mm) P. gr. taylori (wh = 5 mm) A. rumpens (wh = 3 mm) Fig. 7. Septal suture lines of several Schlotheimiidae belonging to the genera Phricodoceras (AE) and Angulaticeras (FJ). A. Phricodoceras urkuticum
(Géczy, 1959) (from Géczy 1976: fig. 49, modified). B. Phricodoceras taylori (Sowerby, 1826) (from Dommergues 2003: fig. 6A, modified).
C. Phricodoceras taylori (from Dommergues 2003: fig. 6B, modified). D. Phricodoceras taylori (from Schlegelmilch 1976: 61, modified). E. Phricodo−
gr. taylori (Sowerby, 1826) (from Schlatter 1990: fig. 3, modified). F. Angulaticeras martinischmidti (Lange, 1951) (from Schlegelmilch 1976: 38,
modified). G. Angulaticeras charmassei (Orbigny, 1844) (from Schlegelmilch 1976: 38, modified). H. Angulaticeras densilobatum (Pompeckj, 1893)
(from Schlegelmilch 1976: 39, modified). I. Angulaticeras lacunatum (J. Buckman, 1844) (from Schlegelmilch 1976, 38, modified). J. Angulaticeras
(Oppel, 1862) (from Schlegelmilch 1976: 39, modified). For each suture line the whorl height (wh) is indicated, if known. The main elements of
the suture line are indicated by following abbreviations: E, external lobe; L, lateral lobe; U1, U2, umbilical lobes; I, internal lobe.
(Fig. 12). Publications during the subsequent period from presence of tubercles and/or spines. At that same time, Hyatt Wright (1880) to Del Campana (1900) still lack explicit infor− (1900: 586–587) proposed the genus name Phricodoceras.
mation about the possible relationships of the Phricodoceras Curiously this author included his new taxon in the "Cosmo− at the family level. Nevertheless, the arrangement of the illus− ceratidae" family with some Middle Jurassic forms (i.e., Kos− trated specimens on the plates (e.g., Quenstedt 1883–1885) moceras and Sigaloceras) and surprisingly, at an informal and/or the use of genus names such as Aegoceras or Dero− higher taxonomic level, in the "Cosmoceratida" with some ceras (e.g., Wright 1880; Bettoni 1900) suggest that the au− Cretaceous taxa (e.g., Douvillieiceras). The grouping at fam− thors suspected possible relationships with certain taxa cur− ily level proposed by Hyatt (1900) is based on obvious orna− rently attributed to the Eoderoceratoidea (e.g., Liparocera− mental convergences and it is currently rejected as strongly tiadae). This pre−family position is clearly supported by the polyphyletic. Only Gérard and Théry (1938) followed Hyatt's DOMMERGUES AND MEISTER—PHYLETIC RECONSTRUCTION OF EARLY JURASSIC AMMONOID Zagouanites (wh = ?) Epideroceras (wh = 30 mm) Eolytoceras (wh = 18 mm) Xipheroceras (wh = 15 mm) Xipheroceras (wh = 8.5 mm) Pleuroacantithes (wh = ?) Analytoceras (wh = 10 mm) Eoderoceras (wh = 8.6 mm) Fig. 8. Septal suture lines of several Lytoceratoidea (AD) and Eoderoceratoidea (EH) for comparisons with those of the scholtheimiid ammonoids
Angulaticeras and Phricodoceras (Fig. 7). A. Zaghouanites arcanum (Wiedenmayer, 1977) (from Rakús and Guex 2002: fig. 54e, modified). B. Eolyto−
ceras tasekoi
Frebold, 1967 (from Wiedmann 1970: text−fig. 9c, modified). C. Pleuroacanthites biformis (Sowerby in De La Beche, 1831) (from Canavari
1888: text–fig. 2.3, modified). D. Analytoceras gr. articulatum (Sowerby in De La Beche, 1831) (from Wiedmann 1970: text–fig. 8a, modified). E. Epi−
deroceras planarmatum
(Quenstedt, 1856) (from Schlatter 1980: beil. 15a, modified). F. Xipheroceras rasinodum (Quenstedt, 1884) (from Schlegelmilch
1976: 57, modified). G. Xipheroceras ziphus (Zieten, 1830) (from Schlegelmilch 1976: 56, modified). H. Eoderoceras bisbinigerum (Buckman, 1918)
(from Schlegelmilch 1992: 62, modified). For each suture line the whorl height (wh) is indicated, if known. The main elements of the suture line are indi−
cated by following abbreviations: E, external lobe; L, lateral lobe; U1, U2, umbilical lobes; I, internal lobe.
(1900) proposal. On the contrary, Buckman (1911, 1921) ex− superfamily level, the authors tend to conform to the position plicitly includes Phricodoceras within the Liparoceratidae of Arkell et al. (1957) even if the family and subfamily levels thereby clarifying and formalizing the implicit hypothesis of are sometimes challenged. For example, the grouping of Phri− many previous authors. From that time until fairly recently— codoceras and Epideroceras within the Phricodoceratinae even if Spath (1938) creates the subfamily Phricodoceratinae proposed by Arkell et al. (1957) is abandoned by several au− (within the Eoderoceratidae)—Phricodoceras was under− thors (e.g., Cope 1991; Schlatter 1991; Dommergues and stood, usually unreservedly, as belonging to the Eoderocera− Meister 1999). Nevertheless, it was not until 1991 that the in− toidea. The single notable exception is Wiedmann (1970: clusion of Phricodoceras in the Eoderoceratoidea was seri− 1002) who proposes that Phricodoceras is a possible relative ously challenged by Kevin Page (personal communication to of Adnethiceras within the Lytoceratoidea. In fact, at the Dommergues 1993) and that convincing relationships with the

ACTA PALAEONTOLOGICA POLONICA 58 (4), 2013 late involute only ribbed stage transition between the evolutetuberculated stage and theinvolute only ribbed stage evolute coarse tuberculated stage,usually three rows of tuberclessensu lato (rows 1, 2, and 3) juvenile evolute tuberculated stage,usually two rows of tubercles Phricodoceras paronai (M) approximate adult size of the microconch Phricodoceras urkuticum (M) Phricodoceras lamellosum (M) Angulaticeras spinosus (M) Angulaticeras boucaultianum (M) Fig. 9. Some illustrative steps—in terms of morphological ontogeny—in the intricate evolutionary trend from the Sinemurian scholtheimiid genus
Angulaticeras to the late Pliensbachian Phricodoceras (i.e., Phricodoceras paronai [Bettoni, 1900]). For simplicity, the complex and more or less gradual
ontogenetic transformations are reduced to just four stages (see A–C for an illustration of the last three). The length and the place of a given stage in the
ontogenetic cartouches depend on its duration and position during ontogeny. The overall length of the cartouche is proportional to adult size. Ontogenies of
the macroconchs (M) alone are depicted in the cartouches and the adult sizes (complete shells) of the microconchs (m) are suggested by black triangles (grey
if doubtful). AC. Scholtheimiid ammonoid Phricododeras lamellosum (Orbigny, 1844), Rote Island, East Nusa Tenggara, Indonesia, probably Early
Pliensbachian (from Krumbeck 1922: pl. 17: 5, modified), in ventral (A), lateral (B), and apertural (C) views.
Schlotheimiidae within the Psiloceratoidea were considered but with some reservations. Such an alternative was discussed for the first time to be at least a plausible hypothesis. Despite also by Venturi and Bilotta (2008) and Venturi et al. (2010), this first serious challenge to the traditional taxonomic attribu− and their choice of a doubtful superfamily classification for tion, most authors until Yin et al. (2007) continued to consider the Phricodoceratidae was due to the lack of decisive data. The Phricodoceras as member of Eoderoceratoidea with no fur− proof that Phricodoceras belongs to the Schlotheimiidae was ther discussion. In spite of this taxonomic inertia, several pub− ultimately provided by Meister et al. (2010), who described a lications have understood Phricodoceras as an unresolved new Angulaticeras (i.e., A. spinosus) whose inner whorls are taxon and two to four credible but rival hypothesis have been virtually indistinguishable from those of Phricodoceras gr.
suggested (Dommergues 1993, 2003; Dommergues and tayloriP. lamellosum at the same diameter. Since this publi− Meister 1999; Meister 2007; Dommergues et al. 2008). In all cation, all subsequent works have placed the Phricodoceras these papers, the possibility of the Schlotheimiidae and Phri− within the Psiloceratoidea and close to or within the Schlo− codoceras being closely related is seriously considered but theimiidae (Blau and Meister 2011; Meister et al. 2011).
Edmunds et al. (2003) were clearly the first to propose this tax−onomic option unreservedly albeit unfortunately without any Characters, assumed relationships, and taxonomic prac−
compelling evidence. Later, Page (2008) took up this position tice.—The history of taxonomic practice is rarely considered
DOMMERGUES AND MEISTER—PHYLETIC RECONSTRUCTION OF EARLY JURASSIC AMMONOID for itself, especially for ammonites (Donovan 1994). This isregrettable because such historical approaches may help to re− fine taxonomic practices empirically by highlighting some misleading but consensual traditions. The case of Phricodo−ceras is particularly instructive in this respect because a widely accepted hypothesis, herein rejected, has affected thetaxonomic understanding of this remarkable group of am−monites. This confusing but successful hypothesis is based ona dual argument grounded on both the concepts of "overall re− semblance" and of "stratigraphic consistency". Indeed, Phri− codoceras and especially the emblematic P. taylori, which islocally not rare in the Uptonia jamesoni and Tragophylloceras ibex chronozones (Early Pliensbachian), can be roughly com− pared with some Late Sinemurian and/or Early PliensbachianEoderoceratoidea (e.g., Eoderoceratidae, Polymorphitidae,Liparoceratidae). Some of these more of less markedly tuberculated forms have subplatycone, subplanorbicone orsubsphaerocone shells with usually rounded and keelless ven−tral areas. The habitus of such Early Pliensbachian Eodero− ceratoidea (Fig. 11) are not very close to those of Phri− codoceras (Figs. 3–5) (e.g., lack of peri−siphonal tubercles but usually presence of ventral secondary and intercalary ribs be−tween the ventro−lateral rows of tubercles in Eoderoceratoideabut not in Phricodoceras), but all these forms are roughly co− juvenile growth stages minor ontogenetic change eval and the presence of tubercles and/or spines was long re− post-juvenile growth stages major ontogenetic change garded as a diagnostic trait confined or pretty much so to theEoderoceratoidea among the Pliensbachian ammonites. Con− late growth stages trariwise, Schlotheimiidae were understood until recently as Fig. 10. Schematic representation and comparison of the ontogenies of an forms unable to produce true tubercles and/or spines. Thus, in Angulaticeras macroconch (A. boucaultianum) and of a Phricodoceras addition to the age (chiefly Early Pliensbachian), the presence macroconch (P. lamellosum) in a simplified diagram taking into account the of tubercles, the keelless smooth ventral area and the rather assumed mobility (x−axis) and the assumed passive shell protection (y−axis).
evolute juvenile coiling pattern were all used as arguments These parameters cannot be fully expressed quantitatively. Mobility de− (taxonomic shoehorns) for placing Phricodoceras within the pends mainly on hydrodynamic abilities, which are correlated with shell ge−ometry but also with some aspects of ornamentation. Marked ornamental Eoderoceratoidea. This nearly universally or at least widely traits may play an important role. For example a keel or a ventral groove may accepted argument is in fact circular. It was ultimately over− increase the hydrodynamic stability of the shell and thereby facilitate mobil− turned by the recent discovery by Meister et al. (2010) of a ity, but prominent tubercles and/or spines may significantly increase hydro− clearly tuberculate juvenile growth stage in the inner whorls of dynamic drag thereby reducing mobility. Conversely the prominence of or− a typical Schlotheimiidae (i.e., Angulaticeras spinosus). From namentation (chiefly of tubercles and/or spines) may be an effective passive then on, it becomes easy to understand the genus Phricodo− protection against predators. Although highly schematic and hypothetical, ceras as a close relative of Angulaticeras within the Schlo− such a diagram can be understood as an approximate representation of an"adaptative landscape" in which successive growth stages can be roughly theimiidae and to fundamentally rethink the comparative anat− situated. This "adaptative landscape" can be divided into four quadrants la− omy of these forms. For example, it becomes possible to prove beled A–D. The two studied species occupy only quadrants A (rather poor the peri−siphonal shoulders of the Schlotheimiidae are homol− mobility but good passive shell protection) and C (good mobility but poor ogous with the peri−siphonal tubercles of Phricodoceras. In passive shell protection). In fact, only the juvenile growth stages of Phri− fact, the homologies (e.g., shell morphology, ornamentation, codoceras lamellosum are situated in quadrant A but all the other growth suture line if controlled by ontogenesis) with Angulaticeras stages, of both species, are in quadrant C. This pattern underlines the are so numerous and obvious, throughout the growth stages, adaptative peculiarity of the juvenile growth stages of Phricodoceras.
that it seems unnecessary to use a distinct subfamily or familylevel name to separate the two genera.
they are stratigraphicaly well constrained. In addition, itshows how much an allegedly consensus−based formaliza−tion such as that proposed in the "Treatise of Invertebrate Pa− leontology" (Arkell et al. 1957) may become sterilizing fortaxonomic research. The present synthesis suggests that the The history of taxonomic practice with respect to Phri− understanding of relationships between ammonites, and par− codoceras is edifying because it clearly exemplifies the vul− ticularly between clearly identified and distinct groups, de− nerability of approaches based on "overall similarity" even if pends largely on the discovery of transitional forms and/or

ACTA PALAEONTOLOGICA POLONICA 58 (4), 2013 Fig. 11. Habitus of some nodded, spined and/or tuberculate Lytoceratoidea (A) and Eoderoderatoidea (B–D). A. Analytoceras hermanni (Gümbel, 1861),
Kammerkaralpe, Waidring, Tyrol, Austria, probably Late Hettangian (from Wähner 1894: pl. 3: 3a, b, modified), in ventral (A1) and lateral (A2) views.
B. Epideroceras lorioli (Hug, 1899), St Peter's Field, Radstock, Somerset, UK, Echioceras raricostatum Chronozone, Paltechioceras aplanatum Sub−
chronozone (from Edmunds et al. 2003: fig. 21. 4, modified), in lateral (B1) and apertural (B2) views. C. Tetraspidoceras repentinum Edmunds, 2009, St Pe−
ter's Field, Radstock, Somerset, UK, Uptonia jamesoni Chronozone, Phricodoceras taylori Subchronozone (from Edmunds 2009: pl. 32: 1, modified), in
lateral (C1) and ventral (C2) views. D. Becheiceras bechei (Sowerby, 1821), Golden Cap, Seatown, Dorset, UK, Prodactylioceras davoei Chronozone,
Oistoceras figulinum Subchronozone (from Edmunds 2009: pl. 38: 1, modified), in lateral (D1) and apertural (D2) views. Tubercles and/or spines in (t1)
and/or (t2) positions of the Eoderoceratoidea (B–D) are not homologous with those of Phricodoceras, nevertheless this genus was long understood as a
(borderline) member of this superfamily. In the case of Lytoceratoidea (A) the ornamental features in peri−siphonal position (pn3) are parabolic nodes which
are morphologically clearly distinct from the tubercles or spines of both Eoderoceratoidea and Phricodoceras. The growth stage of the specimen is un−
series in an acceptable stratigraphic context. If heterochroni− tremely rich fossiliferous locality in the western Carpathians, cal processes, possibly associated with innovation, are in− Slovakia (Meister et al. 2010). This locality has yielded sev− volved (as is the case for Phricodoceras), such transitional eral thousand specimens including various Angulaticeras so forms are often informative and easy to interpret in evolu− Angulaticeras spinosus is obviously extremely rare. The sed− tionary and phylogenetic terms. Unfortunately, intermediate imentary context is certainly important. For example, con− forms between obviously distinct groups are usually very densed deposits are probably particularly favorable for the rare and localized. For example, Angulaticeras spinosus, the search of transitional forms. Nevertheless, and despite the key species for the understanding of the relationship between probable scarcity of many transitional forms, field studies Angulaticeras and Phricodoceras, is known by only three still appear to be the most reliable way to resolve many enig− specimens (including the holotype) from a single but ex− matic taxonomic problems and to clarify our knowledge of DOMMERGUES AND MEISTER—PHYLETIC RECONSTRUCTION OF EARLY JURASSIC AMMONOID Mouterde et al.
Büchner et al.
Meister and Sciau Smith et al.
Dommergues and Meister Dommergues et al.
Page (personal commun.) Tipper et al.
Dommergues and Mouterde Alkaya and Meister El Hariri et al.
Faraoni et al.
Geczy and Meister Fantini and Paganoni Dommergues and Meister Arkell et al.
Dommergues et al.
Venturi and Ferri Cantaluippi and Brambill Donovan and Surlyk Edmunds et al.
Meister et al.
Tintan et al.
Geczy and Meister Dommergues et al.
Venturi and Bilotta Meister et al.
Linares et al.
Venturi et al.
Meister et al.
Donovan et al.
Fig. 12. Historical synthesis of the taxonomic interpretation for the genus Phricodoceras from 1826 until today. Six options are considered: H?, no taxo−nomic attribution or attribution deliberately left undetermined; Eo, explicit attribution to Eoderoceratoidea or implicit proximity with some ammonites cur−rently attributed to the Eoderoceratidae; Ko, explicit attribution to the Kosmoceratidae; Ly, explicit attribution to the Lytoceratoidea (in the current sense);Ps, explicit attribution to the Psiloceratoidea and proximity with the Schlotheimiidae; La, enigmatic lazarus taxon. A cross indicates an absence of attribu−tion to a taxon. A single black dot suggests an implicit or explicit but very reserved attribution. Two black dots suggest an explicit but debatable attribution.
Three black dots suggest an unconditional explicit attribution. Four black dots suggest an explicit attribution based on ontogenetic evidence. For easy read−ing, the two columns corresponding to the two most frequent taxonomic interpretations (i.e., Eo and Ps) are shaded.
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