THE SONNINIID AMMONITE EUHOPLOCERAS FROM THE MIDDLE JURASSIC OF SOUTH-WEST ENGLAND AND SOUTHERN SPAIN

by JOSEÂ SANDOVAL and ROBERT B. CHANDLER

ABSTRACT. A biostratigraphical and taxonomic revision of the genus Euhoploceras is presented using new material collected from the Upper Aalenian±Lower Bajocian of south-west England and the Betic Cordillera (Spain). Euhoploceras is shown to range from the uppermost Aalenian (Concavum Zone, Limitatum Subzone) to the Lower Bajocian (Laeviuscula Zone). S. S. Buckman's 69 species of Sonninia are grouped into three macroconch morphospecies: Euhoploceras acanthodes (Buckman), strongly ornamented, with tubercles and strong ribs throughout ontogeny; Euhoploceras marginatum (Buckman) with tuberculate inner whorls and relatively strong ribs persisting to the outer whorls, and Euhoploceras modestum (Buckman) with ribbed, sometimes slightly tuberculate inner whorls, becoming smooth or only slightly ornamented in later stages of coiling. Euhoploceras adicrum (Waagen) is a younger species with a type horizon in the Laeviuscula Zone. Dimorphism and possible polymorphism are present in both English and Spanish faunas. Euhoploceras subspinosum (Buckman) probably represents dwarf forms of E. acanthodes [M] and is included as a junior synonym of the latter; likewise, E. subdecoratum (Buckman) may belong with E. marginatum [M], although they are described separately herein. Some of the microconchs of Euhoploceras [M] are probably represented by Nannoceras. Similarities between English and Betic Euhoploceras con®rm that during late Aalenian±earliest Bajocian times, the English and Spanish palaeobiogeographical regions were connected. The ammonite assemblages revised here come from the Concavum to Ovalis zones.

T HE ®rst recorded sonniniid ammonites appear suddenly, without any close plausible ancestor, in strata of latest Aalenian (Mid Jurassic) age. A revision of the early members of the family is presented here based on new research from two different palaeogeographical provinces: the Northwest European Province (Page 1996) represented by Dorset and Somerset in southern England, and the Mediterranean Province represented by the Betic Cordillera of southern Spain. The results of this study have taxonomic, evolutionary, biostratigraphical and biogeographical signi®cance. In the taxonomic part of this work, we attempt to clarify the position regarding the many different `species of Sonninia s.l.' ®gured and described by Buckman (1887±1907). Almost all the Sonninia species described in that monograph are now placed in the genus Euhoploceras Buckman, 1913, which he considered to be the earliest sonniniid, representing the transition between Hammatoceratidae and Sonniniidae (Buckman 1889). Members of the genus are useful biostratigraphical indicators in rocks of late Aalenian±early Bajocian age. Bed-by-bed sampling carried out at several localities in both regions enabled us to determine the vertical ranges of Buckman's nominal species of Euhoploceras. We postulate the probable biospeci®c composition of successive faunas over a wide geographical area and consider the biogeographical relationship between the two regions during the Late Aalenian and Early Bajocian.

Repository of material and abbreviations. The English Euhoploceras number hundreds of specimens, many of which have not yet been completely prepared. Figured and cited examples have been cleaned and allocated specimen numbers, and will be deposited in the Sedgwick Museum, Cambridge. The Spanish material is located in the Departmento de EstratigrafõÂa y PaleontologõÂa, University of Granada. Specimen numbers for Euhoploceras ®gured herein accompany the plate legends. In this work, we include as many of Buckman's nominal (morpho-) species as can be identi®ed in the faunas. Nominal species of other authors are used where no suitable match can be found in Buckman's

[Palaeontology, Vol. 43, Part 3, 2000, pp. 495±532, 13 pls] q The Palaeontological Association 496 PALAEONTOLOGY, VOLUME 43

TEXT-FIG. 1. Sketch map showing the outcrop of the Inferior Oolite in southern England. Diagonal shading to the west: pre-Jurassic rocks. Diagonal shading to the east: post-Jurassic rocks. BA, Bradford Abbas; BB, Burton Bradstock Cliff; Br, Bruton; Ch, Quarry Hill, Chideock; HP, Horn Park, near Beaminster; LH, Louse Hill; MF, Mapperton Farm; Se, Seavington St Mary; WH, Waddon Hill. Modi®ed from Callomon and Chandler (1990). Cockroad Farm (CF) is situated about 1 km east of HP.

work. One of the authors (RBC) has studied a number of Buckman's original specimens located at the Sedgwick Museum, Cambridge and the British Geological Survey, Keyworth, Nottinghamshire. In addition, the authors have seen a number of topotypes and chorotypes in both museum and private collections. The following abbreviations are used: T.A., Buckman 1909±30, Type Ammonites, vols 1±7; HT, holotype; [M]/[m], macro/microconch respectively; U/D, diameter of umbilicus as proportion of shell diameter. Symbols and abbreviations used in the systematics are standard and follow Matthews (1973). For ease of reference, successive faunal horizons are labelled and numbered according to Callomon (1995), with each horizon bearing a letter code followed by a number (Aa- and Bj- for Aalenian and Bajocian respectively). The insertion of additional letters (a±c) indicates horizons discovered since the ®rst list was made (Callomon and Chandler 1990) and does not imply a reduction in rank or SANDOVAL AND CHANDLER: MIDDLE JURASSIC AMMONITE 497

TEXT-FIG. 2. Geographical and geological sketch map of the Betic Cordillera (southern Spain) showing the different palaeogeographical domains and the position of some key localities. 1, Sierra del Ahillo; 2, RõÂo FrõÂo; 3, Montillana; 4, Alta Coloma; 5, Cerro MeÂndez; 6, RõÂo Fardes.

importance (Callomon and Cope 1995). Faunal horizons shown in parenthesis are provisional. The standard zonal scheme is used (see, for example, Callomon and Cope 1995) although the Limitatum Subzone is used in preference to the Formosum Subzone for the upper part of the Concavum Zone (Ureta 1985). The names of English localities have been abbreviated to letter codes to avoid repetition. From south to north, these are M-MF, Mapperton, Manor Farm (SY496999); SK-WH, Stoke Knap, Waddon Hill (ST445016); Be-CF, Beaminster, Cockroad Farm (ST470018); Be-Hp, Beaminster, Horn Park (ST458022); Ye-Se, Yeovil, Seavington St Mary (ST387145); BA-rc, Bradford Abbas, railway cutting (ST595145); BA-EH, Bradford Abbas, East Hill quarry (ST591149); Sh-LH, Sherborne, Louse Hill (ST611161); Br-LC, Bruton, Lusty Cutting (ST680345). The names of Spanish localities have been abbreviated to a letter-number code and a national map (1:50,000) reference is given for each. From west to east, these are JAL1, Sierra del Ahillo, Alcaudete, province of JaeÂn (map 18±39, Alcaudete); JOT, RõÂo FrõÂo section, province of JaeÂn (19±38, JaeÂn) (see Text-®g. 7); MOD, Montillana D section, Montillana, province of Granada (19±40, Iznalloz); JAC6, La Tejera sectioÂn, Noalejo, province of JaeÂn (19±39, ValdepenÄas de JaeÂn); JAC3, La Jarropa section, JAC4, La Jarropa second section, JAC11, La Torquilla section, JAC13, Barranco de Cagasebo sectioÂn, JAQ1 and JAQ2, Barranco de Agua Larga, sections 1 and 2, Alta Coloma area, Campillo de Arenas, province of JaeÂn (19±39, ValdepenÄas de JaeÂn) (see Text-®g. 6); CM3, Cerro MeÂndez, Alamedilla, province of Granada (20±39, Huelma); RF1, RõÂo Fardes, province of Granada (21±40, Benalua de Guadix). Plates have been prepared showing specimens at ´ 1 magni®cation for the smaller individuals and ´ 0.5 for larger ones. A star indicates the position of the last preserved septum. Before photography, specimens were coated with ammonium chloride. 498 PALAEONTOLOGY, VOLUME 43

TEXT-FIG. 3. Diagrammatic section showing occurrences of Euhoploceras in the Inferior Oolite at East Hill Quarry, Bradford Abbas; modi®ed from Chandler and Sole (1996). Wavy line indicates zone or zones missing. L indicates probable type horizon of species.

PREVIOUS STUDIES Literature on British Aalenian and Bajocian ammonites is dominated by the name of S. S. Buckman whose geological contributions span some 50 years (Buckman 1878, 1881, 1887±1907, 1889, 1891, 1902, 1909± 1930). In addition, he produced a number of works dealing primarily with stratigraphical matters (Buckman 1889, 1891, 1893, 1895, 1896, 1897, 1901); these included lists of ammonites and descriptions of new species. With regard to Sonniniidae, two of Buckman's works stand apart; his Monograph of the ammonites of the `Inferior Oolite Series' (Buckman 1887±1907), which still remains the most compre- hensive atlas of early sonniniid ammonites, and Type Ammonites (Buckman 1909±1930), in which species were ®gured but accompanied by inadequate descriptions and seldom much stratigraphical detail. Numerous contributions have followed, but few modern accounts make any detailed study of sonniniids. Arkell (1957) and Donovan et al. (1981) dealt with the classi®cation of the group whilst Parsons (1974, 1980) and Senior et al. (1970) listed or discussed sonniniid ammonites in more general papers. Often species are mentioned only by name and are unaccompanied by ®gures; thus it is impossible to make comparison with primary type material. Specimens may be localized down to the bed from which they SANDOVAL AND CHANDLER: MIDDLE JURASSIC AMMONITE 499

TEXT-FIG. 4. Diagrammatic section showing occurrences of Euhoploceras in the Inferior Oolite at Horn Park, near Beaminster; modi®ed from Chandler (1997). Wavy line indicates zone or zones missing. L indicates probable type horizon of species. came but more usually only to zonal level. Westermann (1966) attempted to classify the sonniniids in Buckman's (1887±1907) monograph and Morton (1973, 1975) has researched Sonniniidae of the Isle of Skye, Scotland. Most recently, Callomon and Chandler (1990), Callomon (1995), Callomon and Cope (1995) and Chandler and Sole (1996) have identi®ed the horizons from which most of the type specimens of Buckman's Euhoploceras came; the majority are believed to be from the famous East Hill Quarry (see Text-®g. 3), one of the classic localities around Bradford Abbas in north Dorset recollected by Chandler and Sole (1996). These authors dismantled each bed and collected the fauna on a ten millimetre scale. Each assemblage was then assigned to a faunal horizon following the scheme of Callomon (1995). It was possible in nearly every case to match and identify the type horizon of almost all Buckman's specimens of Euhoploceras. They occur in the middle and upper third of the Bradford Abbas Fossil Bed (see Text-®g. 3). A detailed lithological description has been made and a new, more detailed section drawn up for comparison with Buckman's original of 1893 (updated and modi®ed here). The ®rst Euhoploceras occur rarely in the Limitatum Subzone (ammonite faunal horizon Aa-15). In the Betic Cordillera (southern Spain), studies of the biostratigraphy and ammonite assemblages of the Aalenian and Bajocian have been carried out by Linares (1979), Sandoval (1979, 1983, 1990), Linares and Sandoval (1981, 1990, 1993), Linares et al. (1988) and Henriques et al. (1996). Middle 500 PALAEONTOLOGY, VOLUME 43

TEXT-FIG. 5. Diagrammatic section showing occurrences of Euhoploceras in the Inferior Oolite at Cockroad Farm, near Beaminster. Wavy line indicates zone or zones missing. L indicates probable type horizon of species.

Jurassic ammonites from the Subbetic region have been studied by Sandoval (1983, 1985, 1986) and Linares and Sandoval (1986, 1988, 1992, 1996) but despite the extensive literature, Subbetic Sonniniidae have not, until now, been studied in detail. Only a few sonniniid specimens (mostly Euhoploceras) from the Betic Cordillera have previously been ®gured (Linares and Sandoval 1990; Sandoval 1990, 1995; HernaÂndez-Molina et al. 1991) although they are relatively abundant, especially in the Median Subbetic domain.

GEOGRAPHICAL AND GEOLOGICAL FRAMEWORKS The counties of Dorset and Somerset in south-west England have within their limits one of the ®nest outcrops of highly fossiliferous Lower±Middle Jurassic rocks in the world. The Inferior Oolite, of mainly Aalenian±Bajocian age, crops out in a narrow disrupted band running from the coast near Burton Bradstock in the east and Chideock in the west, northwards with a roughly SSW-NNE strike towards Bristol (Text-®g. 1). It has been the subject of intermittent intense study for well over one hundred years (Buckman 1887±1907, 1893, 1909±1930, 1910a±b; Richardson 1916, 1928; Parsons 1974, 1976, 1980; Cope 1980; Callomon and Chandler 1990, 1994; Callomon 1995; Chandler and Sole 1996; Chandler 1997). In south Dorset, much of the Upper Aalenian and Lower Bajocian is absent as a result of erosion and/or non-deposition. Little material of this age appears to be preserved south of Beaminster other than some thin, irregular, oncolitic beds of the Discites-Sauzei zones (including the famous `snuff boxes'), the Red Bed and the Yellow Conglomerate at Burton Bradstock, where most of the Upper Aalenian and Discites Zone of the Lower Bajocian are represented by a few tens of millimetres of rock. Wilson et al. (1958) gave details of the succession. The most southerly exposed strata containing good Euhoploceras faunas occur in the region of Mapperton where localised lenses and thin beds of ironshot SANDOVAL AND CHANDLER: MIDDLE JURASSIC AMMONITE 501

TEXT-FIG. 6. Lithological succession and ammonite ranges in the Barranco de Agua Larga section, near MontejõÂcar, Alta Coloma area, Median Subbetic domain. Asterisks indicate occurrences of Euhoploceras; modi®ed from Linares and Sandoval (1996). 502 PALAEONTOLOGY, VOLUME 43

TEXT-FIG. 7. Lithological succession and ammonite ranges in the RõÂo FrõÂo section, External Subbetic domain. Modi®ed from Sandoval (1983). oolite often wedge out over distances of a few metres within outliers of Inferior Oolite resting upon soft Bridport Sand (`Upper Lias'). Excellent exposures around Beaminster include the famous Horn Park Quarry (Text-®g. 4) and Stoke Knapp (Waddon Hill) sections, and a new locality at Cockroad Farm (Text-®g. 5).

EXPLANATION OF PLATE 1 Fig 1. Euhoploceras adicrum (Waagen, 1869) [M]. 1, X27876; Cockroad Farm, Beaminster, Dorset; Bed 3b, Ovalis Zone, horizon (Bj-6); lateral view; ´ 1. Figs 2±3. Euhoploceras acanthodes (Buckman, 1889) [M]. X27875; Horn Park, Beaminster, Dorset; Bed 5e; Concavum Zone, horizon Aa-16; lateral and ventral views; ´ 0´5. PLATE 1

SANDOVAL and CHANDLER, Euhoploceras 504 PALAEONTOLOGY, VOLUME 43 Between Seavington St Mary and Sherborne, good faunas have been recorded in the past from a number of quarries almost all of which have now disappeared. In the vicinity of Bradford Abbas, east of Yeovil, a number of former quarries were made famous by the research of S. S. Buckman (Buckman 1893), and later descriptions by Richardson (1916, 1928). Recent contributions include those by Parsons (1974), Callomon and Chandler (1990), Callomon and Cope (1995) and Chandler and Sole (1996). To the north, around Bruton, exposures are restricted. However, excellent collections have recently been made from the road cutting near Pitcombe and at Lusty railway cutting. Further north at Dundry Hill and in the Cotswolds, Aalenian-Lower Bajocian faunas have been recorded (Parsons 1979) but are beyond the scope of the present study. The Subbetic domain (Text-®g. 2) constitutes the central part of the external zones of the Betic Cordillera, extending from the CaÂdiz to Murcia provinces. It is the only Betic domain with more or less continuous pelagic or hemipelagic sedimentation during the Late Aalenian and Early Bajocian (Con- cavum±Humphriesianum zones). The best sections with fossiliferous Aalenian±Bajocian sediments are located in the central sector of the Median Subbetic, speci®cally in the areas of Montillana and Sierra de Alta Coloma (provinces of JaeÂn and Granada) (Text-®g. 6). Bed-by-bed sampling is possible from the different sections in the uppermost Aalenian±lowermost Bajocian parts of the succession and most of the Subbetic Euhoploceras come from them. Further specimens occur in the other Subbetic areas of Cerro MeÂndez, Median Subbetic (provinces of Granada and JaeÂn), Sierra del Ahillo and the RõÂo FrõÂo area [External Subbetic, province of JaeÂn (Text-®g. 7)] and the RõÂo Fardes area (province of Granada) (Text-®g. 2), but are scarce.

SYSTEMATIC PALAEONTOLOGY

Order AMMONOIDEA Zittel, 1884 Suborder AMMONITINA Hyatt, 1889 Superfamily HILDOCERATACEAE Hyatt, 1867 Family SONNINIIDAE Buckman, 1892

Genus EUHOPLOCERAS Buckman, 1913

Type species. (by original designation) Sonninia acanthodes Buckman (1889, HT ®gured by Buckman 1892, pl. 60, pl. 63, ®g. 1).

Synonymy. Alaskoceras 1969 Westermann, p. 102.

Description. Evolute to moderately involute sonniniids with rectangular (sometimes almost square) to ovate, slightly compressed whorl-sections. The venter is subtabulate, often slightly bisulcate and possesses a low hollow keel. The inner whorls have weak primary ribs and many specimens have well-developed tubercles or spines. The degree to which the spinose/tuberculate stage persists is highly variable and it is not uncommon to ®nd strong ribbing continuing beyond the end of the phragmocone; in this case, the body-chamber commonly has single or, more rarely, some bifurcate ribs, which extend as far as the peristome. In others, tubercles give way to ribs which progressively fade, the body-chamber becoming striated or completely smooth. On the other hand, many specimens lack strong ornamentation throughout ontogeny with tiny spines present only on the earliest inner whorls of some shells. Secondary ribs range

EXPLANATION OF PLATE 2 Fig. 1. Euhoploceras adicrum (Waagen, 1869) [M]. 1, X27876, Cockroad Farm, Beaminster, Dorset; Bed 3b, Ovalis Zone, horizon (Bj-6); lateral view; ´ 1. Figs 2±7. Euhoploceras acanthodes (Buckman, 1889) (morphotype subspinosum Buckman, 1893) [m?]. 2±3, X27863; East Hill Quarry, Bradford Abbas, Dorset; Bed 6biii, Discites Zone, horizon Bj-1; lateral and ventral views; ´ 1. 4±5, X27868; Waddon Hill, Stoke Knap; Bed 5f, Ovalis Zone, horizon Bj-4; lateral and ventral views; ´ 1. 6±7, X27874; Lusty Cutting, Bruton; Bed 3c, Discites Zone, horizon Bj-3; lateral and ventral views; ´ 1. PLATE 2

SANDOVAL and CHANDLER, Euhoploceras 506 PALAEONTOLOGY, VOLUME 43 from strong to feeble. The septal suture is relatively complex, although simple compared to hammatoceratids, with a rami®ed deep L, and slightly retracted U2 ±U5 lobes. Complete macroconchs have simple, only very slightly constricted peristomes, which appear to be rather weak and consequently are rarely preserved.

Dimorphism. Euhoploceras appears to exist in at least two macroconch adult size groups. We have found small forms with lappets, which may be the microconchs of the smaller macroconchs, but no undisputed microconchs of larger size with lappets. Small specimens (the Euhoploceras `subdecoratum and subspinosum' groups) are scarce in Spain but relatively common in England. Their size is around 20 per cent. of the diameter of the corresponding macroconchs of otherwise similar morphology. These shells are commonly incomplete and dif®cult to discriminate from the inner whorls of larger forms. Available Spanish specimens do not have their peristomes intact, but some English examples are beautifully preserved, complete with mouth-borders and show signs of maturity such as approximated sutures, eccentric coiling of the last whorl, modi®cation of the ribbing on the last third of the body-chamber and constriction of the peristome. The mouth borders of these `dwarf' forms are plain and do not possess lappets. Westermann (1966) thought that such specimens were the probable microconchs of Euhoploceras. In England and Spain, there are also specimens of around 20 mm diameter that have lappets and modi®ed coiling of the last whorl. These `Pelekodites-style' ammonites are moderately common, and range from rare spinose forms to more common ribbed shells. We believe that Nannoceras nannomorphum Buckman (T.A. 5, pl. 445) is a variant of this microconch lineage, a form occurring in ammonite faunal horizons Aa-16±Bj-1, and agree with the view of FernaÂndez- LoÂpez (1985, p. 94) that Nannoceras is the microconch counterpart of Euhoploceras. Both Euhoploceras [M] and Nannoceras [m] have identical stratigraphical ranges and both can be shown to occur in the Discites Zone and above. The genus may be polymorphic with respect to size, and sexually dimorphic with the pairing of Euhoploceras [M] and Nannoceras [m]. These ®ndings are consistent with the trend identi®ed in other ammonite genera (Westermann and Riccardi 1972; Pavia 1983; FernaÂndez-LoÂpez 1985; Linares and Sandoval 1986), including the Middle Jurassic forms Erycites fallifax [M] ± Spinammatoceras pugnax [m], Eudmetoceras [M] ± Rhodaniceras [m], Dorsetensia [M] ± Nannina [m].

Remarks. The ®rst appearance of the family Sonniniidae, represented by the genus Euhoploceras, occurs both in England and the Subbetic towards the upper part of the Concavum Zone, Limitatum Subzone. As yet, no clear ancestry has been recognised. Accounts of the occurrence and distribution of Euhoploceras have been sporadic, beginning in England with Buckman (1887±1907) who ®gured 69 species which he included in the genus Sonninia Bayle. These illustrations represent the best available record of the variability to be found in these early Sonniniidae. In most cases, their stratigraphical position is given simply as `Concavum Zone', with little further reference to their precise horizons, and localities for the majority of them are given as just `Bradford Abbas'. Most of the ®gured material was collected by James Buckman and later described by his son S. S. Buckman, who in a number of cases may not have had direct knowledge of the exact locality or stratigraphy which is notorious for rapid changes over small distances. Although it is probable that the majority of specimens came from East Hill Quarry adjacent to the Buckman's home (Chandler and Sole 1996), other nearby localities were also available at the time. Buckman (1889) considered the possible route by which sonniniids had evolved, and investigated the similarity between them and the hammatoceratids. Later, he erected the genus Euhoploceras to include the forms described in his monograph (Buckman 1887±1907) and selected as type Sonninia acanthodes Buckman, 1889 (Buckman 1913). Various authors have since contributed studies on European sonniniids, including Euhoploceras (Dorn 1935; Gillet 1937; Hiltermann 1939; Maubeuge 1951; Oechsle 1958), but little has appeared concerning English or Spanish specimens. Westermann (1966) studied the plates and descriptions in Buckman's (1887±1907) monograph alongside the actual specimens now in the Sedgwick

EXPLANATION OF PLATE 3 Figs 1±4. Euhoploceras acanthodes (Buckman, 1889) [M]. 1±2, X27866; East Hill Quarry, Bradford Abbas, Dorset; Bed 6bii(b), Concavum Zone, horizon Aa-16; lateral and ventral views; ´ 0´5. 3±4 (morphotype irregularium Buckman, 1892), X27865; East Hill Quarry, Bradford Abbas, Dorset; Bed 6bii(b), Concavum Zone, horizon Aa-16; lateral and ventral views; ´ 0´5. PLATE 3

SANDOVAL and CHANDLER, Euhoploceras 508 PALAEONTOLOGY, VOLUME 43 Museum, Cambridge and concluded that the specimens ®gured by Buckman together with other European forms could be assigned to a single co-variable species Sonninia (Euhoploceras) adicra (Waagen). Morton (1975) and FernaÂndez-LoÂpez (1985) have carried out detailed taxonomic studies of Bajocian ammonites including descriptions of Euhoploceras. According to these authors, Sherbornites Buckman (1923, T.A. 4, pl. 411) is a synonym of Euhoploceras. Although we are in agreement that Sherbornites is derived from Euhoploceras, or is a late form of it, it already differs in a number of important respects, in particular the marked Shirbuirnia-type venter and having the maximum whorl breadth close to the dorsal part of the whorl. It is rather younger than the groups we discuss here, but may well be very close in age to E. adicrum. Recently collected new material (RBC) from the post-Discites Zone of the Beaminster area includes E. adicrum and specimens that can be used to demonstrate the intraspeci®c variability of Sherbornites (which also includes some species previously included in the genus Shirbuirnia). Another genus, Stiphromorphites Buckman (1923, T.A. 4, pl. 398) was considered a synonym of Euhoploceras by Morton (1975) but, in the opinion of FernaÂndez-LoÂpez (1985, p. 66), it represents a typical Witchellia with a simple septal suture. It has also been recorded (by RBC) from the Laeviuscula Zone of Sherborne. Typical Euhoploceras are distinguished from Sonninia (`sensu stricto') by having broader and more subquadrate to subtabulate whorl-sections, sometimes with a bisulcate venter, and a less well-developed keel. Fissilobiceras, which co-exists with Euhoploceras over part of its stratigraphical range, is another related genus probably evolving directly from hammatoceratids (J. H. Callomon, pers. comm.). It has a similar whorl-section, but differs from Euhoploceras in having smooth middle and outer whorls, a far more complex septal suture, and lacking a keel on the last whorl.

Distribution. In the type area around Bradford Abbas and in other areas of Dorset and Somerset, we now know that the genus Euhoploceras ranges from the Concavum Zone of the Upper Aalenian to the Laeviuscula Zone of the Lower Bajocian. It ®rst appears rarely in a predominantly graphoceratid-dominated fauna in ammonite faunal horizon Aa-15 (Chandler and Sole 1996) but is fairly common in Aa-16. The genus increases in abundance across the Aalenian±Bajocian stage boundary and co-dominates with the graphoceratids, almost to the top of the Discites Zone, after which the ®nal graphoceratids, represented by Hyperlioceras, linger into the Ovalis Zone as extreme rarities as in Germany (Dietl and Etzold 1977). Euhoploceras can be traced upwards into the Ovalis/Laeviuscula zones of the Lower Bajocian where the ®nal members of the group co-exist with abundant true Sonninia and Witchellia. The genus is also reported from Scotland where it is rare and seldom well preserved (Morton 1975, 1994) but it apparently ®rst appears a little higher in the succession, and is represented by slightly later forms, than in Dorset/Somerset (see Morton 1994, p. 88). In the Subbetic, Euhoploceras ®rst occurs in the upper part of the Concavum Zone, Limitatum Subzone (Upper Aalenian) and ranges up to the Ovalis Zone. The genus has frequently been cited and ®gured from western Tethys (Mediterranean, Submediterranean and Northwest European provinces), the western Paci®c: Andes (Westermann and Riccardi 1972), West Interior, USA, (Imlay 1973; Taylor 1988), Alaska (Imlay 1964; Westermann, 1969), southern Tibet (Morton pers comm.) and Australia (Arkell and Playford 1954; Hall, 1989).

Euhoploceras acanthodes (Buckman, 1889) [M] Plate 1, ®gures 2±3; Plate 2, ®gures 2±7; Plate 3, ®gures 1±4; Plate 4, ®gures 1±4; Plate 5, ®gure 1 1889 Sonninia acanthodes Buckman, p. 658. v 1892 Sonninia crassispinata Buckman, p. 317, pl. 48, ®gs 16±17; pl. 50, ®gs 16±22; pl. 57, ®gs 1±2; pl. 65, ®gs 3±5; pl. 93, ®g. 7.

EXPLANATION OF PLATE 4 Figs 1±4. Euhoploceras acanthodes (Buckman, 1889) [M]. 1±2 (morphotype magnispinatum Buckman, 1892), X27864; East Hill Quarry, Bradford Abbas, Dorset; Bed 6bii(b), Concavum Zone, horizon Aa-16; lateral view ´ 0´5, and ventral view ´ 0´6. 3, JO1.5.3; RõÂo FrõÂo section, External Subbetic domain; Discites Zone, lateral view; ´ 1. 4 (morphotype crassispinatum Buckman, 1892); JAQ1.(-53).1; Agua Larga section, Alta Coloma area, Median Subbetic domain; Concavum Zone, Limitatum Subzone; lateral view; ´ 1. PLATE 4

SANDOVAL and CHANDLER, Euhoploceras 510 PALAEONTOLOGY, VOLUME 43 v 1892 Sonninia multispinata Buckman, p. 317, pl. 50, ®gs 11±13. v*1892 Sonninia acanthodes Buckman, p. 319, pls 58±60; pl. 63, ®g. 1 HT. v 1892 Sonninia irregularis Buckman, p. 320, pl. 61; pl. 98, ®g. 6. v 1892 Sonninia ptycta Buckman, p. 332, pl. 73, ®g. 1; pl. 96, ®g. 7. v 1892 Sonninia spinocostata Buckman, p. 337, pl. 73, ®gs 4±6. v 1892 Sonninia magnispinata Buckman, p. 341, pl. 76, ®gs 1±6; pl. 98, ®gs 1±3. 1892 Sonninia sp. Buckman, pl. 77, ®gs 6±9. v 1893 Sonninia biplicata Buckman, p. 345, pl. 78. v 1893 Sonninia crassiformis Buckman, p. 348, pl. 79, ®gs 1±6. v 1893 Sonninia crassibullata Buckman, p. 353, pl. 80, ®gs 1±3. v 1893 Sonninia subspinosa Buckman, p. 358, pl. 84, ®gs 4±6. v 1893 Sonninia diversa Buckman, pl. 83, ®gs 1±4. 1893 Sonninia spinosa Buckman, p. 365, pl. 81, ®gs 7±9. v 1893 Sonninia nodata Buckman, p. 369, pl. 89, ®gs 1±5. v 1893 Sonninia duplicata Buckman, p. 402, pl. 99, ®gs 1±3. 1894 Sonninia spinea, Buckman, p. 405, pl. 86, ®gs 4±6. v 1894 Sonninia magnispinata Buckman, p. 413, pl. 98, ®gs 1±3. 1894 Sonninia gibbera Buckman, p. 421, pl. 87, ®gs 4±5; pl. 88, ®gs 1±3. v 1894 Sonninia locuples Buckman, p. 431, pl. 92, ®gs 1±4; pl. 103, ®g. 4. v 1894 Sonninia reclinans Buckman, p. 421, pl. 98, ®g. 4; pl. 103, ®g. 21 (see S. crassispinata Buckman 1892); pl. 48, ®gs 16±17; pl. 65, ®gs 3±4. v 1894 Sonninia multispinata Buckman, p. 425, pl. 103, ®g. 3. 1894 Sonninia subirregularis Buckman, p. 426, pl. 77, ®gs 6±9; pl. 88, ®g. 4 (Sonninia sp.); pl. 98, ®gs 4±5. 1935 Sonninia spinosa S. Buckman; Dorn, p. 33, pl. 11, ®g. 1. ?1951 Sonninia crassispinata Buckman; Maubeuge, p. 17, pl. 9, ®g. 3. 1951 Sonninia pseudogibbera Maubeuge, p. 24, pl. 16, ®g. 1. 1973 Sonninia (Euhoploceras) cf. S. (E.). adicra (Waagen); Imlay, p. 65, pl. 13, ®gs 8±9. 1973 Sonninia (Euhoploceras) adicra (Waagen); Imlay, p. 65. pl. 13, ®gs 10, 12; pls 14±16. 1988 Euhoploceras westi Taylor, p. 132, pl. 3, ®gs 1±2. 1988 Euhoploceras transiens Taylor, p. 132, pl. 3, ®g. 3. v 1990 Euhoploceras sp. cf. E. crassispinatum (Buckman); Linares and Sandoval, pl. 2, ®g. 3. 1990 Euhoploceras sp., Rocha et al. pl. 1, ®g. 11. 1990 Euhoploceras acanthodes (Buckman); Cresta and GalaÂcz, p. 168, pl. 5, ®g. 2; pl. 12, ®g. 2. 1997 Euhoploceras crassispinatum (Buckman); Groupe FrancËais EÂ tude Jurassique, pl. 14, ®g. 2.

Material. English: Tens of specimens from the following localities and beds: M-MF Bed 3a-b, Be-HP Bed 5d-5eii (Text-®g. 4), Be-CF Bed 2a-c (Text-®g. 5), SK-WH Bed 5d-f, Ye-Se Beds 2b-3, BA-EH Bed 6bi-6c (Text-®g. 3), BA-rc Bed 6b-c, Sh-LH Bed 5a-d, Br-LC Bed 3a-c. Spanish: Eight specimens: JOT1.5.3 (Text-®g. 7), JAQ1.(-53).1 (Text-®g. 6), JAQ1.(-45).8, JAQ1.(-43).1, MOD.x.194, MOD.x.195, MOD.x.196, JAC4.24.1.

Description. A relatively large platycone-discoidal macroconch, with diameters up to 250 mm, this species is distinguished by its persistent spines through to late stages of development. The coiling is evolute and slightly eccentric with U/D ratios higher than 0´40. The inner whorls have oval-subsquare, sometimes depressed whorl- sections, a tabulate or slightly bisulcate venter with moderately convex ¯anks and maximum whorl width between the well-developed sharp spines. At this stage of development, the primary ribs are widely spaced, scarcely raised, and originate near the umbilical wall. Later ribs are slightly rursiradiate and develop strong spines located approximately three/®fths up the whorl ¯ank. Later, lateral tubercles give rise to two or three weak radial or, more

EXPLANATION OF PLATE 5 Fig. 1. Euhoploceras acanthodes (Buckman, 1889) [M], (morphotype irregularium Buckman, 1892). MOD.x.196; Montillana D section, Median Subbetic Domain; Concavum or Discites zones; lateral view; ´ 1. Fig. 2. Euhoploceras marginatum (Buckman, 1892) [M]. JAC13.R.1; Barranco de Cagasebo section, Alta Coloma area, Median Subbetic domain; Discites Zone; lateral view; ´ 1. PLATE 5

SANDOVAL and CHANDLER, Euhoploceras 512 PALAEONTOLOGY, VOLUME 43 frequently, slightly forward-projecting secondary ribs; these divide and ®nish just beyond the edge of the venter which is marked by a prominent undercut hollow keel, bordered by depressed zones. Throughout ontogeny, the whorl-section may become subsquare or slightly rectangular and compressed with almost ¯at ¯anks and a broad subtabulate venter. The primary ribs become stronger and single, often alternating tuberculate and simple. On the anterior portion of the phragmocone, all the ribs may become single, very strong, gently concave prorsiradiate and completely lacking tubercles. In most specimens, the peristome is not preserved. The septal suture is relatively less complex than that of related species.

Remarks. Many of Buckman's (1887±1897) species have as common characters a very well developed and persistent tuberculate, and later strongly ribbed stage, evolute coiling and subsquare whorl-section. These nominal species represent morphotypes of the Euhoploceras acanthodes group and are included here as synonyms of E. acanthodes. The English material is abundant and ranges from the Concavum Zone, Limitatum Subzone to the upper Discites Zone (ammonite faunal horizons Aa-15±Bj-3). The horizon of the holotype is Aa-16 (Limitatum Subzone) at which level specimens have a very distinctive and characteristic morphology. Forms with slightly different morphology, but considered here as part of the same species, occur both higher and lower in the succession. Euhoploceras marginatum (Buckman) is a close relative of E. acanthodes but is slightly more involute, with a less well-developed tuberculate stage, and almost radial, only ventrally projected ribs. Some strongly tuberculate morphotypes that we include in E. marginatum (e.g. S. alternata Buckman) may be very similar to E. acanthodes, and could represent intermediates between these two morphospecies. The status of the small and strongly tuberculate `Sonninia subspinosa' (Buckman 1893, p. 358, pl. 84, ®gs 4±6) is unresolved; it could be a microconch (Westermann 1966) or, more probably, a dwarf form of E. acanthodes, so we tentatively include it in this species. The type of Euhoploceras adicrum (re-®gured by Dorn 1935, pl. 10, ®g. 7 and Schlegelmilch 1985, pl. 17, ®g. 1) appears to have only slightly tuberculate inner and middle whorls and has very widely spaced ribs on its outer whorls. It is certainly different in age and must be regarded as a different species, not directly related to the material considered here. Euhoploceras westi Taylor and E. transiens Taylor, from the Tuberculatum Zone, Westi Subzone (equivalent to the Discites Zone) of Oregon, USA, are very similar to some European morphotypes of E. acanthodes and they are here regarded as junior synonyms of the latter.

Distribution. E. acanthodes is commonly recorded in the Upper Aalenian (Concavum Zone, Limitatum Subzone) and Lower Bajocian (Discites Zone) faunas of western Tethys: England (Buckman, 1889, 1887±1894; Parsons 1979; Callomon 1995; Callomon and Chandler 1990, 1994; Chandler and Sole 1996), France (Gillet 1937; Maubeuge 1951), Belgium (Maubeuge 1951), Portugal (Rocha et al. 1990), Spain (Sandoval 1983, 1990; Linares and Sandoval 1990), Italy (Cresta and GalaÂcz 1990), Hungary (Cresta and GalaÂcz 1990; GalaÂcz 1991), Morocco (Sadki 1996). Also occurs in West Interior, Oregon, USA (Imlay 1973; Taylor 1988).

Euhoploceras marginatum (Buckman, 1892) [M] Plate 5, ®gure 2; Plate 6, ®gures 1±4; Plate 7, ®gures 1±3; Plate 8, ®gures 1±4 v*1892 Sonninia marginata Buckman, p. 321, pl. 62 HT; pl. 63, ®g. 2; pl. 64; pl. 65, ®gs 1±2; pl. 96, ®g. 6. v 1892 Sonninia dominans Buckman, p. 322, pl. 66; pl. 67, ®gs 1±2; pl. 69; pl. 94, ®gs 1±2; pl. 95, ®g. 1; pl. 97, ®g. 4. 1892 Sonninia, intermediate form between marginata and dominans, Buckman, p. 322, pl. 67, ®gs 3, 5; pl. 87, ®g. 4.

EXPLANATION OF PLATE 6 Figs 1±4. Euhoploceras marginatum (Buckman, 1892) [M]. 1±2, X27872; Cockroad Farm, Beaminster, Dorset; Bed 2b, Discites Zone, horizon Bj-2b; lateral and ventral views; ´ 0´5. 3±4 (morphotype dominans Buckman, 1892), X27871; Cockroad Farm, Beaminster, Dorset; Bed 2b, Discites Zone, horizon Bj-2b; lateral and ventral views; ´ 0´5. PLATE 6

SANDOVAL and CHANDLER, Euhoploceras 514 PALAEONTOLOGY, VOLUME 43 v 1892 Sonninia revirescens Buckman, p. 324, pl. 70, ®g. 1. v 1892 Sonninia submarginata Buckman, p. 329, pl. 71, ®gs 1±3. 1892 Sonninia subcostata Buckman, p. 330, pl. 71, ®gs 4±5. v 1892 Sonninia obtusiformis Buckman, p. 333, pl. 72, ®gs 3±5. 1892 Sonninia spinigera Buckman, p. 335, pl. 50, ®g. 14; pl. 74, ®gs 4±6. v 1892 Sonninia spinocostata Buckman, p. 33, pl. 73, ®gs 4±6. v 1892 Sonninia costata Buckman, p. 338, pl. 74, ®g. 1; pl. 75, ®gs 1±2. v 1893 Sonninia brevispinata Buckman, p. 343, pl. 75, ®gs 6±8. v 1893 Sonninia semispinata Buckman, p. 343, pl. 77, ®gs 1±2. 1893 Sonninia alternata Buckman, p. 343, pl. 76, ®gs 7±9; pl. 77, ®gs 3±5. 1893 Sonninia diversa Buckman, p. 355, pl. 81, ®gs 5±6 (non pl. 83, ®gs 1±4) v 1893 Sonninia omphalica Buckman, p. 363, pl. 83, ®gs 5±9. v 1893 Sonninia palmata Buckman, p. 372, pl. 90, ®gs 7±9. 1893 Sonninia scalpta Buckman, p. 376, pl. 87, ®gs 1±3. v 1894 Sonninia dominatrix Buckman, p. 392, pl. 94, ®gs 3±4. 1894 Sonninia tridactyla Buckman, p. 393, pl. 101, ®gs 1±3. v 1894 Sonninia regularis Buckman, p. 395, pl. 96, ®gs 3±5. 1894 Sonninia umbilicata Buckman, p. 397, pl. 84, ®gs 1±3. v 1894 Sonninia diversa Buckman, p. 399, pl. 103, ®g. 8. v 1894 Sonninia camura Buckman, p. 403, pl. 99, ®gs 4±6. v 1894 Sonninia dominata Buckman, p. 408, pl. 97, ®gs 1±3. 1894 Sonninia dominica Buckman, p. 410, pl. 69, ®gs 1±3; pl. 103, ®g. 14. 1894 Sonninia multicostata Buckman, p. 410, pl. 86, ®gs 1±3. v 1894 Sonninia plicata Buckman, p. 415, pl. 97, ®gs 6±8. 1894 Sonninia spinifera Buckman, p. 418, pl. 100, ®gs 1±4 (non pl. 74, ®gs 4±6) v 1894 Sonninia cymatera Buckman, p. 420, pl. 100, ®gs 5±7. v 1894 Sonninia alternata, Buckman, p. 424, pl. 103, ®g. 7. v 1894 Sonninia costigera Buckman, p. 428, pl. 102, ®gs 1±3. v 1894 Sonninia renovata Buckman, p. 433, pl. 93, ®gs 1±6. v 1894 Sonninia dominans Buckman, p. 435, pl. 94, ®gs 1±2; pl. 95, ®g. 1; pl. 97, ®g. 4. 1894 Sonninia sp. Buckman, p. 438, pl. 103, ®g. 24 (see Buckman 1892, pl. 67, ®gs 1±2). 1894 Sonninia sp. Buckman, p. 438, pl. 103, ®g. 20 (see Buckman 1892, pl. 67, ®gs 3±5). 1966 Sonninia (Euhoploceras) adicra (Waagen); Westermann p. 310 (pars). 1973 Sonninia (Euhoploceras) dominans Buckman; Imlay, p. 63, pl. 63, ®gs 11±12. 1975 Euhoploceras (Euhoploceras) marginatum (Buckman); Morton, p. 46, pl. 6, ®gs 2±3. 1975 Euhoploceras (Euhoploceras) dominans (Buckman); Morton, p. 48, pl. 7, ®gs 1±2. 1983 Euhoploceras (Euhoploceras) marginatum (Buckman); Pavia, pl. 3, ®g. 1. v 1985 Euhoploceras (Euhoploceras) dominans (Buckman); FernaÂndez-LoÂpez, p. 24, pl. 1, ®g. 1; pl. 2, ®g. 2. 1988 Euhoploceras crescenticostatum Taylor, p. 130, pl. 2, ®gs 5±6. 1988 Euhoploceras grantense Taylor, p. 131, pl. 2, ®gs 3±4. 1990 Euhoploceras marginatum (Buckman); Rocha et al., pl. 2, ®g. 2. 1990 Euhoploceras sp. Rocha et al., pl. 2, ®g. 18. v 1990 Euhoploceras dominans (Buckman); Sandoval, pl. 1, ®g. 2. v 1990 Euhoploceras cf. multicostatum (Buckman); Linares and Sandoval, pl. 2, ®g. 5. 1990 Euhoploceras marginatum (Buckman); Cresta and GalaÂcz, p. 170, pl. 2, ®g. 2. v 1995 Euhoploceras dominans (Buckman); Sandoval, pl. 1, ®g. 2.

Material. English: Tens of specimens from the following localities and beds: M-MF Bed 3a-b, Be-HP Bed 5d-e (Text- ®g. 4), Be-CF Bed 2a-c (Text-®g. 5), SK-WH Bed 5d-f, Ye-Se Bed 2b-3, BA-EH Bed 6bi-6c (Text-®g. 3), BA-rc Bed

EXPLANATION OF PLATE 7 Figs 1±3. Euhoploceras marginatum (Buckman, 1892) [M], (morphotype cymaterum Buckman 1894). 1, X27862; Waddon Hill, Stoke Knap; Bed 5d-e, Discites Zone, horizon Bj-2b; lateral view; ´ 1. 2±3, X27870; East Hill Quarry, Bradford Abbas, Dorset; Bed 6bii(b), Concavum Zone, horizon Aa-16; lateral view; ´ 1. PLATE 7

SANDOVAL and CHANDLER, Euhoploceras 516 PALAEONTOLOGY, VOLUME 43 6b-c, Sh-LH Bed 5a-d, Br-LC Bed 3a-d. Spanish: Nine specimens: JAL1.10.7, JOT1.5.4 (Text-®g. 7), JOT1.6.5, JAQ1.(-46) (Text-®g. 6), JAC11.3.1, JAC13.R.1, JAC13.R.2 (=A4.9.1.31), MOD.x.197, CM3.70.1.

Description. Medium to large size (up to 300 mm in diameter) Euhoploceras that are relatively evolute, discoidal- platycones (U/D ratios vary from 0´34 to 0´40 in the Subbetic specimens and can reach up to 0´45 in English material). The whorl-section varies throughout ontogeny from compressed-ovate on the inner whorls to compressed subrectan- gular on the middle and outer whorls with an oblique to subvertical umbilical wall. The umbilical edge is rounded and slightly convex, sometimes with almost ¯at ¯anks. The venter is rounded on the inner whorls, becoming subtabulate on the anterior phragmocone and body-chamber, and there is a low hollow keel. On the inner whorls, all ribs are strongly tuberculate up to diameters of 25±30 mm. Up to 60±70 mm diameter, the mid-¯ank is ornamented by strong tuberculate ribs alternating with narrow simple ribs, some of which tend to join together near the umbilical edge. In later whorls, tubercles are absent and the ornament consists of single ribs that are radial or slightly concave prorsiradiate. In some examples, the ribs become broad and widely spaced, especially on the last part of the phragmocone (e.g. S. costata Buckman 1887±1907, pl. 74, ®g. 1), while other forms develop thinner, denser ribbing throughout ontogeny. The peristome is preserved in some English material but not on the Spanish specimens. The suture line is similar to other contemporary species of Euhoploceras.

Remarks. Euhoploceras marginatum is similar in coiling, whorl-section and possession of a spinose (tuberculate) stage to the holotype of Ammonites polyacanthus Waagen which is, however, much younger. It also exhibits important differences: more persistent and less dense ribbing which is prorsiradiate on the venter, more persistent and well-developed tubercles, and a smaller adult size. In A. polyacanthus, the ribbing is rather straight and fades to give a smooth area on the whorl shoulders, and the ventral aspect of some ribs is marked by a slight anterior-posterior `pinching'. We consider it a different species, possibly a direct descendant representing the `marginatum' morphology at the `polyacanthum' level. Many of Buckman's (1887±1907) species (see synonymy) coming from ammonite faunal horizons Aa-16±Bj-3 can be considered simply as morphotypes of `Sonninia marginata' Buckman, and therefore they are regarded here as junior synonyms of Euhoploceras marginatum (Buckman). The small Euhoploceras subdecoratum (Buckman) (here described separately) has very similar coiling, ribbing, tubercles and ontogenic development and therefore could be a morphotype (dwarf or microconch) of E. marginatum [M]. Euhoploceras crescenticostatum Taylor and E. grantense Taylor, from the Concavum or Discites zones of Oregon, USA (Taylor 1988), are very similar to the European specimens and they are here regarded as junior synonyms of Euhoploceras marginatum.

Distribution. The species ranges from the Upper Aalenian (Concavum Zone, Limitatum Subzone) to the Lower Bajocian (Ovalis Zone) of numerous European and North African localities: France (Pavia 1983), Hungary (Cresta and GalaÂcz 1990; GalaÂcz 1991), Italy (Cresta and GalaÂcz 1990), Portugal (Rocha et al. 1990), Morocco (Sadki 1994, 1996), Scotland (Morton 1975), Iberian Cordillera, Spain (FernaÂndez LoÂpez 1985), Betic Cordillera, Spain (Linares and Sandoval 1990; Sandoval 1990, 1995). The species also occurs in the Lower Bajocian of the Western Interior, USA (Imlay 1973; Taylor 1988). The new material cited here and collected in situ from Spain is from the Discites Zone and rarely the Ovalis Zone; the English material ranges from ammonite faunal horizon Aa-15 to Bj-3.

EXPLANATION OF PLATE 8 Figs 1±4. Euhoploceras marginatum (Buckman, 1892) [M]. 1, (morphotype diversum Buckman, 1893), A4.9.1.31; Alta Coloma area, Median Subbetic domain; Discites Zone; lateral view; ´ 1. 2, JO1.6.5, (immature specimen), RõÂo FrõÂo Section, External Subbetic domain; Ovalis Zone; lateral view; ´ 1. 3, (morphotype dominans Buckman, 1892), immature? specimen, JAC11.3.1; La Torquilla section, Alta Coloma area, Median Subbetic domain; Discites Zone; lateral view; ´ 1. 4, (morphotype multicostatum Buckman, 1894), immature? specimen, JAQ1.(-46).1; Agua Larga section, Alta Coloma area, Median Subbetic domain; Discites Zone; lateral view; ´ 1. PLATE 8

SANDOVAL and CHANDLER, Euhoploceras 518 PALAEONTOLOGY, VOLUME 43 Euhoploceras subdecoratum (Buckman, 1893) Plate 9, ®gures 1±5 v 1893 Sonninia decorata Buckman, p. 360, pl. 84, ®gs 7±8. v*1893 Sonninia subdecorata Buckman, p. 361, pl. 84, ®gs 9±11. 1893 Sonninia decora Buckman, p. 361, pl. 84, ®gs 12±14. v 1966 Sonninia subdecorata group Buckman; Westermann, p. 301 (pars). 1983 Euhoploceras (m) cf. decorum (Buckman); Pavia, pl. 3, ®g. 5.

Material. English: Eight specimens from the following localities and beds: M-MF Bed 3b, Be-CF Bed 2b-c (Text-®g. 5), BA-EH Bed 6biii-c (Text-®g. 3), Br-LC Bed 3b-c. Spanish: Seven specimens: MOD.x.198, MOD.x.199, MOD.x.200, JAC6.33.1, JAC3.19.2, JAC3.20.5, JAC11.R.3 (=TT1.75).

Description. The shells are small, relatively evolute platycones with slightly eccentric coiling (U/D varies from 0´35 to 0´40). The whorl-section varies from slightly compressed-ovate on the inner whorls to almost compressed and rectangular on the body-chamber. Specimens have oblique to almost vertical umbilical walls, a rounded umbilical edge, and convex to almost ¯at ¯anks, which vary throughout ontogeny. Shells have a rounded to subtabulate ventral area and a low hollow keel. On the inner whorls (up to 10±15 mm in diameter), there are radial primary ribs which project almost to the keel and which have a mid lateral spine or tubercle. Each lateral tubercle divides into two or three secondary ribs, which project forward slightly beyond the primaries. On the middle whorls, the tubercles are rather impersistent, being interspersed with single, feebly developed ribs. The body-chamber has only gently convex or radial single simple ribs, which are commonly con®ned to the upper third of the ¯ank. Here, bifurcation may occur at variable positions on the whorl ¯ank and faint ribbing without tubercles can persist up to the end of the shell. Peristomes are not preserved on the Spanish specimens, but a number of English examples are almost complete and exceptionally well preserved. Modi®cations of the ribbing on the last third of the body-chamber indicate that these shells are probably adults.

Remarks. From among more than 110 specimens of `Sonninia' from Bradford Abbas ®gured by Buckman (1887±1907), only four of them (Buckman 1893, pl. 84, ®gs 4±14) are possible microconchs; they are small and exhibit adult characters (Westermann 1966). Some Betic specimens, in particular those coming from the Discites Zone, are very similar to Buckman's species `S. subdecorata-S. decorata-S. decora', although the tuberculate stage is slightly less well developed. The specimen ®gured by Pavia (1983), from the Beaumont section (Digne area, France), is similar to the type of `S. decora' and also some Betic specimens. E. subdecoratum could represent the microconch partner of E. marginatum but it is far more likely that these specimens are dwarf polymorphs [M] of that morphospecies.

Distribution. The English material comes from the upper Concavum±Discites zones. Three of the Subbetic specimens are ex situ and come from the upper Concavum or Discites zones of the Montillana D section; all the Subbetic in situ specimens were collected from the Discites Zone. The specimen ®gured by Pavia (1983) comes from the Discites Zone of Beaumont, Digne (France).

EXPLANATION OF PLATE 9 Figs 1±5. Euhoploceras subdecoratum (Buckman, 1893) [m?]. 1, TT1±75; La Torquilla section, Alta Coloma area, Median Subbetic domain; Discites Zone; lateral view; ´ 1. 2, MOD.x.199 and 3, MOD.x.198; Montillana D section, Median Subbetic domain; Concavum or Discites zones; lateral views; ´ 1. 4, JAQ1. (-38).1; Agua Larga section, Alta Coloma area, Median Subbetic domain; Discites Zone; lateral view; ´ 1. 5, JAC3.19.2; Barranco de la Jarropa section, Alta Coloma area, Median Subbetic domain; Discites Zone; lateral view; ´ 1. Figs 6±7. Euhoploceras adicrum (Waagen 1867) [M]. X27861; Lusty Cutting, Bruton; Bed 4, Ovalis Zone, horizon Bj-5; lateral and ventral views; ´ 0´5. PLATE 9

SANDOVAL and CHANDLER, Euhoploceras 520 PALAEONTOLOGY, VOLUME 43 Euhoploceras adicrum (Waagen, 1867) Plate 1, ®gure 1; Plate 2, ®gure 1; Plate 9, ®gures 6±7 v*1867 Ammonites adicrus Waagen, p. 591, pl. 25, ®g. 1 HT. 1926 Sherbonites adicrus Waagen; Buckman, pl. 669. v*1935 Sonninia adicra Waagen; Dorn, p. 37, text-®g. III, 1±2; pl. 6, ®g. 1; pl. 10, ®gs 1, 7 [HT re-®gured]. 1935 Sonninia berckhemeri Dorn, p. 31, pl. 21, ®g. 1; in text, pl. 2, ®gs 1±2. 1939 Sonninia adicra (Waagen); Hiltermann, p. 150, text-®gs 20±24; pl. 6. ®g. 1 1958 Sonninia adicra (Waagen); Oechsle, p. 85, pl. 10, ®gs 5±9; pl. 11, ®g. 2; pl. 18, ®gs 3±4. 1966 Sonninia (Euhoploceras) adicra (Waagen); Westermann, p. 310 (pars). 1973 Sonninia (Euhoploceras) adicra (Waagen); Imlay, p. 65, pl. 13, ®gs 5±12; pls 14±17. 1985 Euhoploceras adicrum (Waagen); FernaÂndez-LoÂpez, p. 23, pl. 2, ®g. 1. v*1985 Sonninia adicra (Waagen, 1867) Schlegelmilch, p. 60, pl. 17, ®g. 1 [HT re-®gured]. 1985 Sonninia berckhemeri Dorn 1935; Schlegelmilch, pl. 15, ®g. 3 [HT re-®gured].

Material. English: 14 specimens from the following localities and beds: M-MF Bed 3b, Be-CF Bed 3b-4 (Text-®g. 5), Br-LC Bed 4.

Description. The shells are medium to very large (500 mm) platycones that are rather depressed and moderately evolute. Early whorls have fairly dense primary ribs, every third or fourth of which bears stout-based, large, long spines, which lie against the dorsal wall of the next whorl in a retrosiphonate direction. The venter is subtabulate to oval and possesses a strong, slightly bisulcate keel on the inner whorls. A diagnostic character is the gradual replacement of the spines by distant strong broad ribs, which fade before the venter. Where outer whorls are preserved, the body-chamber is completely smooth with a round to oval, rather in¯ated venter lacking a keel. It is terminated by a simple mouth border.

Remarks. The type (Waagen 1867), re®gured by Dorn (1935) and Schlegelmilch (1985), is an internal mould and has rather poorly preserved inner whorls. It is dif®cult to assess the strength of the spinose stage but it is clear that were the shell intact, the spines would be more prominent. Descriptions of the type area of the species around Nenningen in southern Germany were given by Oechsle (1958). Dietl (1980) gave a faunal list in which he identi®ed E. adicrum with E. polyacanthum in the Laeviuscula Subzone. Both these species occur together in the same bed and their type horizon is in the Laeviuscula Zone. Since the types of neither E. adicrum nor E. polyacanthum come from the Discites Zone, it is unlikely that Buckman's Concavum±Discites faunas from Bradford Abbas could be synonymous with E. adicrum.

Euhoploceras modestum (Buckman, 1892) Plate 10, ®gures 1±4; Plate 11, ®gures 1±2; Plate 12, ®gures 1±3; Plate 13, ®gures 1±4 v*1892 Sonninia modesta Buckman, p. 325, pl. 68; pl. 70, ®g. 5 HT. v 1892 Sonninia simplex Buckman, p. 326, pl. 70, ®gs 2±4. v 1892 Sonninia substriata Buckman, p. 330, pl. 70, ®gs 6±7; pl. 71, ®gs 6±8. v 1892 Sonninia parvicostata Buckman, p. 339, pl. 75, ®gs 3±5. v 1893 Sonninia papilionacea Buckman, p. 36, pl. 90, ®gs 1±3 v 1893 Sonninia nuda Buckman, p. 352, pl. 82, ®gs 3±4. v 1894 Sonninia attrita Buckman, p. 371, pl. 90, ®gs 4±6. 1894 Sonninia parvicostata Buckman, p. 396, pl. 103, ®g. 22. v 1894 Sonninia inaequa Buckman, p. 400, pl. 101, ®gs 4±6.

EXPLANATION OF PLATE 10 Figs 1±4. Euhoploceras modestum (Buckman, 1892) [M]. 1±2, (morphotype inaequaum Buckman, 1894), X27873; Halfway House, Sherborne; Bed 5c, Discites Zone, horizon Bj-2; lateral and ventral views; ´ 0´5. 3±4, (morphotype parvicostatum Buckman, 1894), X27867; East Hill Quarry, Bradford Abbas, Dorset; Bed 6ci, Discites Zone, horizon Bj-2b/3; lateral and ventral views; ´ 0´5. PLATE 10

SANDOVAL and CHANDLER, Euhoploceras 522 PALAEONTOLOGY, VOLUME 43 v 1894 Sonninia contusa Buckman, p. 409, pl. 88, ®gs 5±7. v 1894 Sonninia modesta Buckman, p. 422, pl. 95, ®gs 3±5; pl. 96, ®gs 1±2. v 1894 Sonninia subsimplex Buckman, p. 427, pl. 95, ®gs 6±8. v 1894 Sonninia loculosa Buckman, p. 437, pl. 92, ®gs 5±7. 1935 Sonninia substriata Buckman; Dorn, p. 55, pl. 5, ®g. 6; text-®gs 6±7. 1939 Sonninia modesta Buckman; Hiltermann, p. 153, pl. 10, ®gs 5±6; pl. 11, ®g. 1. 1951 Sonninia (Euhoploceras) mussonense Maubeuge, p. 25, pl. 2, ®g. 3 1958 Sonninia modesta modesta Buckman; Oechsle, p. 111, pl. 13, ®g. 7; pl. 14, ®g. 8; pl. 16, ®g. 5. 1958 Sonninia modesta substriata Buckman; Oechsle, p. 111, pl. 13, ®g. 6; pl. 14, ®g. 7; pl. 19, ®g. 3. 1958 Sonninia modesta nenningensis Oechsle, p. 111, pl. 13, ®g. 5; pl. 14, ®g. 6; pl. 18, ®g. 1 1966 Sonninia adicra (Waagen); Westermann, p. 310 (pars) 1973 Sonninia (Euhoploceras) modesta Buckman; Imlay, p. 62, pls 7±10. 1985 Euhoploceras parvicostatum (Buckman); FernaÂndez-LoÂpez, p. 26, pl. 1, ®g. 2. 1988 Sonninia burkei Taylor, p. 130, pl. 1, ®gs 11±12. 1988 Sonninia washburnensis Taylor, p. 130, pl. 2, ®gs 1±2. 1990 Euhoploceras sp. group modestum (Buckman); Rocha et al. pl. 1, ®g. 1. 1990 Euhoploceras sp. Rocha et al., pl. 1, ®g. 3; pl. 2, ®g. 3. v 1990 Euhoploceras modestum (Buckman); Linares and Sandoval, pl. 2, ®g. 2.

Material. English: Tens of specimens from the following localities and beds: M-MF Bed 3a-b, Be-HP Bed 5e (Text-®g. 4), Be-CF Bed 2b-c (Text-®g. 5), SK-WH Bed 5d-f, Ye-Se Bed 3, BA-EH Bed 6bii-6c (Text-®g. 3), BA-rc Bed 6b-c, Sh-LH Bed 5b-c, Br-LC Bed 3b-c. Spanish: 15 specimens: JAQ1.(-46).6 (Text-®g. 6), JAQ1.(-40).3, JAQ1.(-36).1, JAQ1.(-36).2, JAQ1.(-36).3. JAQ1.(-36).4, JOT1.6.2 (Text-®g. 7), JOT1.6.3, MOD.x.186, MOD.x.188, MOD.x.189, MOD.x.190, MOD.x.191, MOD.x.192, MOD.x.193.

Description. Euhoploceras with discoidal, medium sized shells that have maximum diameters ranging from 160 to 250 mm. Coiling is usually involute (U/D ˆ 0´20) on the inner whorls becoming more evolute and eccentric with growth. The U/D ratio can be as much as 0´40 at the aperture. The whorl-section is subrectangular-compressed and may be ventrally convergent, especially on the inner whorls. Shells have a near vertical umbilical wall, which has an abruptly rounded umbilical edge. The ¯anks are ¯at or very slightly convex and the venter is rather rounded or subrectangular. The hollow keel is less strongly developed than in other species of the genus. In some of the `species' ®gured by Buckman (1887±1907) (`S. simplex', pl. 70, ®gs 2±4; `S. substriata', pl. 71, ®gs 6±8), which are here considered synonyms of E. modestum, the keel fades completely on the last part of the body-chamber. At diameters smaller than 15 mm, there may be a tuberculate stage (specimens from Bed BA-6c and MOD.x.192, MOD.x.193) but in some E. modestum, the inner whorls are completely smooth or have vestigial spines. On the inner whorls, the ribs are ®ne and dense, often dividing near the umbilical edge to produce a slightly sigmoidal curve (e.g. typical modestum). On later whorls, the ribs become single, radial, spaced, and only very slightly developed such as seen in E. simplex, parvicostatum and nudum. The middle and outer whorls become completely smooth or have only growth-lines. In complete and adult specimens, the body-chamber occupies approximately three-®fths of the last whorl and the peristome is simple. Septal sutures are typical of Euhoploceras, being very divided, with a deep lateral lobe and slightly retracted umbilical lobes.

Remarks. Imlay (1973) carried out a detailed analysis of Euhoploceras modestum including synonymies. All Buckman's species included here as synonyms of E. modestum have an eccentric and moderately involute style of coiling. However, this character is more strongly developed in some morphotypes (`S.' modestum,`S.' simplex,`S.' nudum). The abruptly rounded umbilical edge, the densely and ®nely ribbed inner whorls, the very reduced or absent tuberculate stage and the very weakly ornamented or even smooth outer whorls are common to all members of the group. Subbetic and English specimens included in this species show all these characters and in addition we include some very involute and presumably non-

EXPLANATION OF PLATE 11 Figs 1±2, Euhoploceras modestum (Buckman, 1892) [M], (morphotype contosum Buckman, 1894); X27869; Cockroad Farm, Beaminster; Bed 2b, Discites Zone, horizon Bj-2b; lateral and ventral views; ´ 1. PLATE 11

SANDOVAL and CHANDLER, Euhoploceras 524 PALAEONTOLOGY, VOLUME 43 tuberculate forms (JAQ1.-(40).3, JAQ1.(-36).1,2,3), together with MOD.x.191 and MOD.x.193, which are slightly more evolute and have tuberculate inner whorls up to 15 mm diameter. Those specimens of E. polyacanthum that lack strong ornament show similarities to the strongly ornamented varieties of E. modestum, but the former is more evolute, has a better developed tuberculate stage and more strongly ribbed inner whorls. Some species of the genus Fissilobiceras [F. gingense (Waagen) and F. ®ssilobatum (Waagen)] resemble the smooth and involute morphotypes of E. modestum, but species of this genus are more involute, smoother and lack a keel on the last whorl. The suture is complex and similar to that of Hammatoceratidae, the probable ancestor. Sonninia washburnensis Taylor, from the Tuberculatum Zone, Ochocoense Subzone (equivalent to the Ovalis Zone), and S. burkei Taylor, from the Burkei Zone (equivalent to the Laeviuscula Zone) of Oregon (Taylor 1988), are very similar to some ribbed morphotypes of Euhoploceras modestum, and are here regarded as possible junior synonyms.

Distribution. E. modestum is a common species in the Discites Zone of both the Subbetic domain (Betic Cordillera) and Dorset/Somerset. Some rare, rather atypical specimens occur in the Concavum Zone (Limitatum Subzone) of both regions. Some of the smooth varieties represented in the Ovalis and Laeviuscula zones may also be closely related. E. modestum has been recorded from the following regions: Mediterranean: Betic Cordillera (Sandoval, 1983, 1990; Linares and Sandoval 1988), Morocco (Sadki 1994, 1996), Submediterranean: Spain (FernaÂndez-LoÂpez, 1985), Portugal (Rocha et al. 1990; Mouterde 1991). E. modestum has also been recorded in the Western Interior, Oregon, USA (Imlay 1973; Taylor 1988). Subbetic and Dorset specimens representing E. modestum are recorded from the Upper Aalenian (Concavum Zone, Limitatum Subzone, Aa-15) to Lower Bajocian (Discites to Laeviuscula zones).

Euhoploceras? sp. A [M?] Plate 12, ®gure 4

Material. A single specimen: JAQ1.(-54).1

Description. A specimen that has a small, relatively involute shell (55 mm diameter including a half whorl of body- chamber). The whorl-section is subrectangular compressed with an almost vertical umbilical wall, gently rounded umbilical edge, slightly convex ¯anks and convergent venter, which has a hollow and poorly developed keel. Ribbing is ®ne, dense (34 per half whorl), radial or slightly sigmoidal, and is simple or more frequently bifurcating near the umbilical edge. On the inner whorls, some slightly stronger ribs support a small tubercle at the point of bifurcation. The septal suture has characters intermediate between that of Sonniniidae and Hammatoceratidae with slightly retracted umbilical elements.

Remarks. This is the oldest sonniniid recorded in the Betic Cordillera. The specimen has characters intermediate between Hammatoceratidae (Euaptetoceras) and weakly ornamented Sonniniidae (E. mod- estum). The closest species are E. marginatum (morphotype `S.' multicostatum Buckman) and some ribbed morphotypes of E. modestum. E. marginatum has a better developed tuberculate stage, E. modestum has weaker ribbing and both species are slightly younger (Concavum Zone, Limitatum Subzone±Laeviuscula

EXPLANATION OF PLATE 12 Fig. 1±3. Euhoploceras modestum (Buckman, 1892) [M]. 1, JAQ1.(-36).3 (juvenile); Agua Larga section, Alta Coloma area, Median Subbetic domain; Discites Zone; lateral view; ´ 1. 2, (morphotype simplex Buckman, 1892, adult with peristome), MOD.x.186; Montillana D section, Median Subbetic domain; Discites Zone; lateral view, ´ 0´5. 3, (morphotype nudum Buckman, 1892), MOD.x.187; Montillana D section, Median Subbetic domain; Ovalis? Zone; lateral view; ´ 1. Fig. 4. Euhoploceras sp. A [M?], JAQ1.(-54).1; Agua Larga section, Alta Coloma area, Median Subbetic domain; Concavum Zone, Limitatum Subzone; lateral view; ´ 1. PLATE 12

SANDOVAL and CHANDLER, Euhoploceras 526 PALAEONTOLOGY, VOLUME 43 Zone), whereas this specimen comes from what may be a slightly earlier horizon in the Concavum Zone. This form may represent the transition between Hammatoceratidae (Euaptetoceras) and scarcely ornamented Sonniniidae such as E. modestum.

Distribution. Upper Aalenian (Concavum Zone; Limitatum Subzone), Agua Larga section.

Euhoploceras sp. B [m?] or dwarf Plate 13, ®gure 5

Material. Three specimens: JAC11.4.1, MOD.x.200, MOD.x.201.

Description. Small Euhoploceras (36 mm maximum diameter) that are very evolute (U/D ˆ 0´46 at maximum diameter for complete specimens). The whorl-section is subrectangular and slightly compressed with slightly convex ¯anks. The venter has a small keel bordered by shallow sulci. The inner and middle whorls have single, almost radial, unequally spaced primary ribs (12±14 per whorl) terminating in relatively strong tubercles on the ventro-lateral shoulder. On the last whorl, the ribs become stronger and denser (24±29) and some tend to join together (two by two) near to the umbilical edge. At this stage, `clavi'-like tubercles occur on some ribs, but not on the last third of the whorl. The peristome and septal suture are not preserved in the Subbetic specimens.

Remarks. Although the aperture and the suture are not preserved, the very evolute coiling and modi®cation of the ornament (ribs and tubercles) are typical of mature material. We believe that this small species could represent a Euhoploceras microconch, possibly corresponding to the E. acanthodes group, but it varies signi®cantly from typical Nannoceras [m].

PALAEOBIOGEOGRAPHICAL RELATIONSHIPS The Euhoploceras species occurring in Dorset and Somerset have an almost identical age-range to those from the Betic Cordillera. Difference in size is a signi®cant character separating the Betic and English specimens. The latter are bigger, compared with specimens of the same species and morphotype from the Betic Cordillera. Such size differences could be due to palaeoecological or palaeogeographical controls. Factors such as food availability are important parameters in¯uencing the growth of individuals and food is likely to have been more abundant on the shallow marine shelf (or in the epicontinental shelf seas), where the Inferior Oolite of Dorset and Somerset was deposited, than in the Tethyan oceanic basin of the Subbetic (Betic Cordillera). Taphonomic and palaeoecological analyses show that macroconch, microconch, juvenile and adult forms coexist in both Betic and Inferior Oolite domains but there are big differences in relative abundances, which ¯uctuate from level to level. This implies that during late Aalenian±earliest Bajocian times, Euhoploceras populations lived and reproduced in both epicontinental shelf seas (England) and in Tethyan oceanic basins (Betic).

EXPLANATION OF PLATE 13 Fig. 1±4. Euhoploceras modestum (Buckman, 1892). 1, JAQ1.(-40).3 (complete macroconch with peristome); Agua Larga section, Alta Coloma area, Median Subbetic domain; Discites Zone; lateral view, ´ 1. 2, 4, MOD.x.189 and MOD.x.191 (juvenile); Montillana D section, Median Subbetic domain; Concavum Zone, Limitatum Subzone, or Discites Zone; lateral views, ´ 1. 3, JAQ1.(-40).3 (juvenile, ®nely ribbed); Agua Larga section, Alta Coloma area, Median Subbetic domain; Discites Zone; lateral view; ´ 1. Fig. 5. Euhoploceras sp. B [m?] or dwarf; MOD.x.201; Montillana D section, Median Subbetic domain; Concavum or Discites zones; lateral view; ´ 1. PLATE 13

SANDOVAL and CHANDLER, Euhoploceras 528 PALAEONTOLOGY, VOLUME 43 Most of the morphospecies included here in Euhoploceras are relatively common in both regions. Sonniniids are never the dominant taxa among the ammonite assemblages studied, although in Dorset they share almost equal dominance with the graphoceratids in the Lower Bajocian (ammonite faunal horizons Bj-1±Bj-3). They represent approximately 2±3 per cent. of the ammonites recorded from the Betic uppermost Aalenian±lowermost Bajocian (Limitatum Subzone±Discites Zone), whereas the Erycitidae (including Haplopleuroceras) constitute approximately 35 per cent., and the Graphoceratidae almost 40 per cent. The families Hammatoceratidae, Phylloceratidae, Otoitidae (including Riccardiceras) and Haploceratidae are each more abundant than the Sonniniidae. In Dorset and Somerset, the situation is very different. The Graphoceratidae dominate the Aalenian and early Lower Bajocian, sometimes attaining abundances close to 100 per cent. Sonniniidae, represented by Euhoploceras, appear in the upper Concavum Zone as extreme rarities in ammonite faunal horizon Aa-15. In Aa-16, they are abundant enough (about 10 per cent.) to constitute good guide fossils and were chosen by Callomon and Chandler (1990) to label ammonite faunal horizon Aa-16 Euhoploceras acanthodes. Euhoploceras increases in abundance in the Lower Bajocian to co-dominate with the graphoceratids of the upper Discites Zone (Bj-3) and continues into the Ovalis Zone as a common element. The Aalenian±Lower Bajocian ammonite fauna of Dorset and Somerset has yielded a number of Tethyan migrants, but they are relatively rare compared to the graphoceratids (Callomon and Chandler 1994). Erycitidae constitute less than 1 per cent. of the Aalenian±Lower Bajocian ammonite fauna, although Haplopleuroceras [M] is locally more common (2±5 per cent.) in the Bradford Abbas area and is accompanied by Fontannesia [M and m] (about 5 per cent.) in ammonite faunal horizon Bj-1. Hammatoceratidae constitute about 5 per cent. throughout, while Phylloceratidae are extremely rare and Otoitidae (Riccardiceras and Docidoceras) occur as rarities but increase to about 1 per cent. in the Discites Zone. Lytoceratidae occur throughout and are relatively common, but never constitute a high proportion of the fauna. During Aalenian±Bajocian times, the connection between the oceanic Betic Basin (located in the Mediterranean Province, western Tethys) and the western part of the European epicontinental shelf-seas basin (which includes Dorset and Somerset) could have been continuous through the Iberian-Basque- Cantabrian basins, or through the Lusitanian Basin (Ziegler 1982). The nature of the Lusitanian Aalenian ammonite assemblages, which display an intermediate character between Dorset/Somerset and the Subbetic, supports a probable Subbetic-Lusitanian-Dorset/Somerset connection during this part of the Mid Jurassic. Such a connection may have allowed the migration of ammonites between the two domains (Henriques et al. 1996). Mediterranean taxa, such as Tmetoceras, Erycites, Riccardiceras, Haplopleuroceras, Abbasitoides, migrated northward to England where they became relatively common in Dorset and Somerset (Callomon and Chandler 1990, 1994), although they hardly reached the German Basin (Sandoval et al., in press). Subboreal taxa (e.g. Leioceratinae and Graphoceratidae) migrated southwards, colonizing Tethys. Similarities between the English and southern Spanish Euhoploceras provide evidence that appears to support migrations between both regions. The occurrence of Euhoploceras on an almost pandemic scale is supported by records from numerous well-scattered locations including Scotland (Morton 1975), France and Belgium (Maubeuge 1951), Germany (Oechsle 1958; Dorn 1935), Hungary (GalaÂcz 1991), South America (Westermann and Riccardi 1972), North America (Imlay 1964, 1973; Westermann 1969; Taylor 1988) and Western Australia (Arkell and Playford 1954; Hall 1989).

Acknowledgements. We thank Dr N. Morton, Prof. J. H. Callomon and an anonymous reviewer for comments on an earlier version of the manuscript and for making suggestions and recommendations that served to improve the text. J. Sandoval acknowledges the support of his PB94±0786 (DGICYT) project grant. We thank the Wessex Cephalopod Club (A. and R Chiarini, V. Dietze, A. G. England, B. Huber, W. J. E. Jones, H. Rieber, R. RuÈegg, D. T. C. Sole, N. Schaffeld and S. Udall) for their assistance in various aspects of the preparation of this work. We acknowledge the cooperation of English Nature for allowing access to localities of SSSI status and the site owners and tenants Sherborne Castle Estates, Winchester College, T. and G. Gibbs, M. Higgins, B. and L. Lock, R. and H. Loxton, J. Sibley, D. Tolley and A. N. Wells. We thank J. Huxtable for introducing us to the locality at Cockroad Farm. SANDOVAL AND CHANDLER: MIDDLE JURASSIC AMMONITE 529 REFERENCES

ARKELL, W. J., KUMMEL, B. and WRIGHT, C. W. 1957. Mesozoic Ammonoidea. L80±L490. In MOORE R. C. (ed.). Treatise on invertebrate paleontology. Part L. Mollusca 4, Cephalopoda. Geological Society of America, Boulter, and University of Kansas Press, Lawrence, xxii + 490 pp. ÐÐ and PLAYFORD, P. E. 1954. The Bajocian ammonites of Western Australia. Philosophical Transactions of the Royal Society of London, Series B, 237, 547±605. BUCKMAN, S. S. 1878. On the species of Astarte from the Inferior Oolite of the Sherborne district. Proceedings of the Dorset Natural History and Archaeological Field Club, 2, 81±92. ÐÐ 1881. A descriptive catalogue of some species of ammonites from the Inferior Oolite of Dorset. Quarterly Journal of the Geological Society, London, 37, 588±608. ÐÐ 1887±1907. A monograph of the ammonites of the `Inferior Oolite Series'. Monographs of the Palaeonto- graphical Society, London, 456 + 103 pp. (1887±1894); supplement 24 + 262 pp. (1898±1907). ÐÐ 1889. The descent of Sonninia and Hammatoceras. Quarterly Journal of the Geological Society, London, 45, 651±663. ÐÐ 1891. Ammonite zones of Dorset and Somerset. Report of the English Association Meeting, Cardiff, p. 655, and Geological Magazine, 7, 502±503. ÐÐ 1893. The Bajocian of the Sherborne district: its relations to subjacent and superadjacent strata. Quarterly Journal of the Geological Society, London, 49, 479±522. ÐÐ 1895. The Bajocian of the mid-Cotteswolds. Quarterly Journal of the Geological Society, London, 51, 388± 462. ÐÐ 1896. Dundry Hill: its upper portion, or the beds marked as Inferior Oolite (G5) in the maps of the Geological Survey, Quarterly Journal of the Geological Society, London, 52, 669±720. ÐÐ 1897. Deposits of the Bajocian age in the northern Cotteswolds; the Cleeve Hill Plateau. Quarterly Journal of the Geological Society, London, 53, 607±629. ÐÐ 1901. Bajocian and contiguous deposits in the North Cotteswolds: the Main Hill-Mass. Quarterly Journal of the Geological Society, London, 57, 126±155. ÐÐ 1902. The term ``hemera''. Quarterly Journal of the Geological Society, London, 9, 554±557; 10, 95±96. ÐÐ 1907. On the correlation of the Bath-Doulting Strata with those of Dorset. Quarterly Journal of the Geological Society, London, 63, 424±426. ÐÐ 1909±1930. Type ammonites. Wheldon and Wesley, London. Vols 1±7, 790 pls. Reprint (1972±1976), Historia Naturalis Classica, 93 (1). Cramer Verlag and Wheldon and Wesley, Lehre and Codicote. ÐÐ 1910a. Certain Jurassic (Lias-Oolite) strata of South Dorset. Quarterly Journal of the Geological Society, London, 66, 52±89. ÐÐ 1910b. Certain Jurassic (Inferior Oolite) species of ammonites and Brachiopoda. Quarterly Journal of the Geological Society, London, 66, 90±108. CALLOMON, J. H. 1995. Time from fossils: S. S. Buckman and Jurassic high-resolution geochronology. 127±150. In LE BAS, M. J. (ed.). Milestones in geology. Memoir of the Geological Society, London, 16, 127±150. ÐÐ and CHANDLER, R. B. 1990. A review of the ammonite horizons of the Aalenian±Lower Bajocian stages in the Middle Jurassic of southern England. Memorie Descrittive della Carta Geologica d'Italia, 40, 85±112. ÐÐ ÐÐ 1994. Some early Middle Jurassic ammonites of Tethyan af®nities from the Aalenian of southern England. Paleopelagos, Special Publication, 1, 17±40. ÐÐ and COPE, J. C. W. 1995. The Jurassic geology of Dorset. 51±103. In TAYLOR, P. D. (ed.). Field geology of the British Jurassic. Geological Society, London, 286 pp. CHANDLER, R. B. 1982. The ®rst record of Staufenia (Staufenia) sehndensis (Hoffman) in Britain. Proceedings of the Geologists' Association, 93, 301±304. ÐÐ 1997. The graphoceratid ammonite succession in the Aalenian and lowest Bajocian (Middle Jurassic) at Horn Park, Dorset, UK. Proceedings of the Dorset Natural History and Archaeological Society, 118 (for 1996), 84±106. ÐÐ and SOLE D. T. C. 1996. The Inferior Oolite at East Hill Quarry, Bradford Abbas, Dorset. Proceedings of the Dorset Natural History and Archaeological Society, 117 (for 1995), 101±108. COPE, J. C. W. (ed.) 1980. A correlation of Jurassic rocks in the British Isles. Part two: Middle and Upper Jurassic. Geological Society, London, Special Report, 15, 109 pp. CRESTA, S. and GALACZ, A. 1990. Mediterranean basal Bajocian ammonite faunas. Examples from Hungary and Italy. Memorie Descrittive della Carta Geologica d'Italia, 40, 165±198. DIETL, G. 1980. UÈ ber die sowerbyi-Zone (ˆ Laeviuscula-Zone, Unter-Bajocium, Mittl. Jura) im einen Pro®l bei Nenningen (oÈstl. SchwaÈb. Alb). Stuttgarter BeitraÈge zur Naturkunde B, 60, 1±11. ÐÐ and ETZOLD, H. 1977. The Aalenian at the type locality. Stuttgarter BeitraÈge zur Naturkunde B, 30, 1±39. 530 PALAEONTOLOGY, VOLUME 43

DONOVAN, D. T., CALLOMON, J. H. and HOWARTH, M. K. 1981. Classi®cation of the Jurassic Ammonitina. 101±155. In HOUSE, M. R. and SENIOR J. R. (eds). The Ammonoidea. Systematics Association, Special Publication, 18, 593 pp. DORN, P. 1935. Die Hammatoceraten, Sonninien, Ludwigien, Dorsetensien und Witchellien des SuÈddeutschen, insbesondere FraÈnkischen Doggers. Palaeontographica, Abteilung A, 82, 1±124. FERNANDEZ-LOPEZ, S. R. 1985. El Bajociense en la Cordillera IbeÂrica. Unpublished PhD Thesis, Universidad Complu- tense, Madrid. GALACZ. A. 1991. Lower Bajociansonniniid ammonites from the Gerecse Mountains, Hungary. 109±111.In MORTON, N. (ed.). Conference on Aalenian and Bajocian stratigraphy, Isle of Skye. Birkbeck College, University of London, 129 pp. GILLET, S. 1937. Les ammonites du Bajocien d'Alsace et de Lorraine. MeÂmoires du Service de la Carte GeÂologique d'Alsace et de Lorraine, 5, 1±130. GROUPE FRANCAIS E TUDE JURASSIQUE 1997. Biostratigraphie du Jurassique Ouest-EuropeÂen et MeÂditerraneÂen: zonations paralleÁles et distribution des inverteÂbreÂs et microfossiles: 5, AaleÂnien and 6, Bajocien. 37±53. In CARIOU, E. and HANTZPERGUE, P. (Coords). Bulletin du Centre de Recherches Elf Exploration Production, 17, 1±400. HALL, R. S. 1989. Lower Bajocian ammonites (Middle Jurassic; Sonniniidae) from the Newmarracarra Limestone, Western Australia. Alcheringa, 13, 1±20. HENRIQUES, M. H., LINARES, A., SANDOVAL, J. and URETA, M. S. 1996. The Aalenian in the Iberia (Betic, Lusitanian and Iberian Basins). GeoResearch Forum, 1±2, 139±150. HERNA NDEZ-MOLINA F. J., SANDOVAL J., AGUADO R., O'DOGHERTY L., COMAS M. C. and LINARES A. 1991. Olistoliths from the Middle Jurassic in Cretaceous materials of the Fardes Formation: biostratigraphy (Subbetic Zone, Betic Cordillera). Revista de la Sociedad GeoloÂgica de EspanÄa, 4, 79±104. HILTERMANN, H. 1939. Stratigraphie und Palaeontologie der Sonninienschicten von OsnabruÈck und Bielefeld. 1 Teil. Stratigraphie und Ammonitenfauna. Palaeontographica, Abteilung A, 90, 108±209. HYATT, A. 1867. The fossil cephalopods of the Museum of Comparative Zoology. Bulletin of the Museum of Comparative Zoology, Harvard, 5, 71±102. ÐÐ 1889. Genesis of the Arietitidae. Smithsonian Contribution to Knowledge, 673, xi +238 pp. IMLAY, R. W. 1964. Middle Bajocian ammonites from the Cook Inlet Region, Alaska. Professional Paper of the United States Geological Survey, 418B, 1±57. ÐÐ 1973. Middle Jurassic (Bajocian) ammonites from eastern Oregon. Professional Paper of the United States Geological Survey, 756, 1±100. LINARES, A. 1979. El Aalenense de la Zona SubbeÂtica. Cuadernos de GeologõÂa, Universidad de Granada, 10, 413±424. ÐÐ and SANDOVAL, J. 1981. El Dogger en las Cordilleras BeÂticas. LõÂmites y correlaciones. 183±205. Curso de Conferencias sobre Programa Internacional de CorrelacioÂn GeoloÂgica (PICG). Real Academia de Ciencias Exactas, FõÂsicas y Naturales, Madrid, 325 pp. ÐÐ ÐÐ 1986. Malladaites nov. gen. et Spinammatoceras (Hammatoceratidae, Ammonitina) de l'AaleÂnien de la Zone SubbeÂtique, Sud de l'Espagne. Geobios, 19, 207±224. ÐÐ ÐÐ 1988. Asthenoceras y Fontannesia (Grammoceratinae?, Ammonitina) del traÂnsito Aaleniense-Bajociense de la Zona SubbeÂtica (Sur de EspanÄa). Revista EspanÄola de PaleontologõÂa, 3, 3±11. ÐÐ ÐÐ The lower boundary of the Bajocian in the ``Barranco de Agua Larga'' section, (Subbetic Domain, southern Spain). Memorie Descrittive della Carta Geologica d'Italia, 40, 13±22. ÐÐ ÐÐ 1992. El geÂnero Vacekia (Gammoceratinae, Ammonitina) del Aaleniense de la Cordillera BeÂtica. Revista EspanÄola de PaleontologõÂa, Numero Extraordinario, 91±99. ÐÐ ÐÐ 1993. El Aaleniense de la Cordillera BeÂtica (Sur de EspanÄa): anaÂlisis bioestratigra®co y caracterizacioÂn paleobiogeogra®ca. Revista de la Sociedad GeoloÂgica de EspanÄa, 6, 177±206. ÐÐ ÐÐ 1996. The genus Haplopleuroceras (Erycitidae, Ammonitina) in the Betic Cordillera, southern Spain. Geobios, 29, 287±305. ÐÐ URETA, M. S. and SANDOVAL, J. 1988. Comparison between the Aalenian ammonite associations from the Betic and Iberian cordilleras: elements of correlation. 193±208. In ROCHA, R. B. and SOARES, A. F. (eds), 2nd International Symposium on Jurassic Stratigraphy. Centro de Estratigra®a e Paleobiologia da Universidade Nova de Lisboa and Centro de GeoscieÃncias da Universidade de Coimbra, Lisbon, 1, 639 pp. MATTHEWS, S. C. 1973. Notes on open nomenclature and on synonymy lists. Palaeontology, 16, 713±719. MAUBEUGE, P. L. 1951. Les ammonites du Bajocien de la reÂgion frontieÁre Franco-Berge (Bord septentrional du bassin de Paris). Institut Royal des Sciences Naturelles de Belgique, 42, 1±104. MORTON, N. 1973. The aptychi of Sonninia (Ammonitina) from the Bajocian of Scotland. Palaeontology, 16, 195±203. ÐÐ 1975. Bajocian Sonniniidae and other ammonites from western Scotland. Palaeontology, 18, 41±91. ÐÐ 1994. Stratigraphical markers in the Aalenian±Bajocian boundary succession at Bearreraig, Isle Skye, Scotland. Miscellanea del Servizio Geologico Nazionale, 5, 79±90. SANDOVAL AND CHANDLER: MIDDLE JURASSIC AMMONITE 531

ÐÐ and CHANDLER, R. B. 1994. Ammonite biostratigraphy of the Aalenian±Bajocian boundary: comparison of faunal horizons in Dorset/Somerset and Isle of Skye. Miscellanea del Servizio Geologico Nazionale, 5, 91±92. MOUTERDE, R. 1991. DonneÂes paleÂontologiques sur les ammonites de la limite AaleÂnien-Bajocien preÂsenteÂes a Piobicco (1988). 125±129. In MORTON, N. (ed.). Conference on Aalenian and Bajocian stratigraphy, Isle of Skye. Birkbeck College, University of London, 129 pp. OECHSLE, E. 1958. Stratigraphie und Ammonitenfauna der Sonninien-Schichten des Filsgebiets unter besonderer BeruÈcksichtgung der Sowerbyi Zone (Mittlerer Doggers, WuÈttemberg). Palaeontographica, Abteilung A, 111, 47±129. PAGE, K. N. 1996. The ammonoids in space and time. 756±787. In LANDMAN, N. H., TANABE, K. and DAVIS, R. A. (eds). Ammonoid paleobiology. Plenum Press, NewYork, 857 pp. PARSONS, C. F. 1972. A new temporary section in the Inferior Oolite of south Dorset. Proceedings of the Dorset Natural History and Archaeological Society, 87, 117±118. ÐÐ 1974. The sauzei and `so called' sowerbyi Zones of the Lower Bajocian. Newsletters on Stratigraphy, 3, 153± 180. ÐÐ 1975. The stratigraphy of the Stony Head Cutting, Bridport. Proceedings of the Dorset Natural History and Archaeological Society, 96, 8±13. ÐÐ 1976. Ammonite evidence for dating some Inferior Oolite sections in the north Cotswolds. Proceedings of the Geologists' Association, 87, 45±63. ÐÐ 1979. A stratigraphic revision of the Inferior Oolite of Dundry Hill Bristol. Proceedings of the Geologists' Association, 90, 133±151. ÐÐ 1980. Aalenian and Bajocian correlation chart. 3±21. In COPE, J. W. C. (ed.). A correlation of Jurassic rocks in the British Isles. Part two: Middle and Upper Jurassic. Geological Society, London, Special Report, 15, 109 pp. PAVIA, G. 1983. Ammoniti e biostratigra®a del Baiociano inferiore di Digne (Francia SE, Dip. Alpes-Haute-Provence). Monogra®e Museo Regionale di Scienze Naturali, 2, 1±254. RICHARDSON, L. 1916. The Inferior Oolite and contiguous deposits of the Doulting-Milborne Port district (Somerset). Quarterly Journal of the Geological Society, London, 71, 473±520. ÐÐ 1928. The Inferior Oolite and contiguous deposits of the Burton Bradstock-Broadwindsor district, Dorset. Proceedings of the Cotteswold Naturalists' Field Club, 23, 35±68. ROCHA, R. B., HENRIQUES, M. H., SOARES, A. F., MOUTERDE, R., CALOO, B., RUGET, C. and FERNANDEZ-LOPEZ, S. R. 1990. The Cabo Mondego section as a possible Bajocian boundary stratotype. Memorie Descrittive della Carta Geologica d'Italia, 40, 49±60. SADKI, D. 1994. L'AaleÂnien superieur et le Bajocien infeÂrieur du Haut Atlas marocain: reÂvision biostratigraphique et correlations. Miscellanea del Servizio Geologico Nazionale, 5, 177±190. ÐÐ 1996. Le Haut-Atlas Central (Maroc). Stratigraphie et paleÂontologie du Lias SupeÂrieur et du Dogger InfeÂrieur. Dynamique du Bassin et des peuplements. Documents des Laboratoires de GeÂologie, Lyon, 142, 1±245. SANDOVAL, J. 1979. El Bajocense de la Zona SubbeÂtica. Cuadernos de GeologõÂa, Universidad de Granada, 10, 225± 240. ÐÐ 1983. BioestratigrafõÂa y paleontologõÂa (Stephanocerataceae y Perisphinctaceae) del Bajocense y Bathonense de las Cordilleras BeÂticas. PhD thesis (published), Secretariado de Publicaciones, Universidad de Granada, 613 pp., 73 pls. ÐÐ 1985. Los Strigoceratidae (Ammonitina) del Bajocense de la Zona SubbeÂtica (Sur de EspanÄa). Mediterranea, 4, 85±112. ÐÐ 1986. Middle Jurassic Haploceratidae (Ammonitina) from the Subbetic Zone (South Spain). Geobios, 19, 435± 463. ÐÐ 1990. A revision of the Bajocian divisions in the Subbetic Domain (southern Spain). Memorie Descrittive della Carta Geologica d'Italia, 40, 141±162. ÐÐ 1995. BioestratigrafõÂa: aspectos conceptuales e intereÂs biocronoloÂgico de los Ammonoideos. Tierra y TecnologõÂa, 11, 35±41. ÐÐ SCHMIDT-EFFING, R., DIETL, G. and JIMEÂ NEZ, A.P. in press. Ammonitenvergesellschaftungen von Toarcium bis zum Bathonium (Jura) der Betischen Kordillera (S-Spanien) und des deutschen Beckens (CentraleuropaÈisches Becken): Der Ein¯uss der Meeresspiegelschwankungen auf Evolution und Migratiosprocesse. Stuttgarter BeitraÈge zuÈr Naturkunde. SCHLEGELMILCH, R. 1985. Die Ammoniten des suÈddeutschen Doggers. Gustav Fischer Verlag, Stuttgart, 284 pp. SENIOR, J. R., PARSONS, C. F. and TORRENS, H. S. 1970. New sections in the Inferior Oolite of South Dorset. Proceedings of the Dorset Natural History and Archaeological Society, 91, 114±119. TAYLOR, D. G. 1988. Middle Jurassic (late Aalenian and Early Bajocian) ammonite biochronology of the Snowshoe Formation, Oregon. Oregon Geology, 50 (11±12), 123±137. 532 PALAEONTOLOGY, VOLUME 43

TORRENS, H. S. (ed.). 1969. International Field Symposium on the British Jurassic. Excursion N1. 1. Guide for Dorset and south Somerset. University of Keele, 71 pp. URETA, M. S. 1985. Bioestratigra®a y paleontologia (Ammonitina) del Aaleniense en el sector noroccidental de la Cordillera IbeÂrica. PhD thesis (published), 158/85, Universidad Complutense de Madrid. WAAGEN, W. 1867. UÈ ber die Zone des Ammonites Sowerbyi. Geognostische-PalaÈontologie BeitraÈge, 1, 507±668. WESTERMANN, G. E. G. 1966. Covariation and taxonomy of the Jurassic ammonite Sonninia adicra (Waagen). Neues Jahrbuch fuÈr Geologie und PalaÈontologie, Abhandlungen, 124, 289±312. ÐÐ 1969. The ammonite fauna of the Kialagvik Formation at Wide Bay, Alaska Peninsula, Part II, Sonninia sowerbyi Zone (Bajocian). Bulletins of American Palaeontology, 57, 5±226. ÐÐ and RICCARDI, A. C. 1972. Middle Jurassic ammonoid fauna and biochronology of the Argentine-Chilean Andes. Part. I: Hildocerataceae. Palaeontographica, Abteilung A, 140, 1±116. WILSON, V., WELCH, F. B. A., ROBBIE, J.A. and GREEN, G. W. 1958. 77±97. In Geology of the country around Bridport and Yeovil. Memoir of the Geological Survey of Great Britain. ZIEGLER, P. A. 1982. Post Hercynian plate reorganization in the Tethys and Arctic-North Atlantic domains. 711±755. In IVIANSPEIZER, W. (ed.). Triassic±Jurassic rifting, continental breakup and the origin of the Atlantic Ocean and passive margins. Developments in Geotectonics, 22 (B), Elsevier, Amsterdam, 755 pp. ZITTEL, K. A. von 1884. GrundzuÈge der Palaeontologie (Palaeozoologie). R. Oldenbour, Munich-Leipzig, 971 pp.

JOSEÂ SANDOVAL Departamento de EstratigrafõÂa y PaleontologõÂa Universidad de Granada Av. Fuentenueva s/n 18002 Granada, Spain email [email protected].

ROBERT B. CHANDLER Riddlesdown High School Purley, Surrey, CR8 1EX, and Birkbeck College Malet Street Typescript received 20 September 1998 London WC1E 7HX, UK Revised typescript received 27 October 1999 email [email protected].