PALAE0PELAG0S SPECIAL PUBLICATION 1, 1994, Roma. Proceedings of the 3rd Pergola International Symposium: 17 - 40.

Some early Middle Jurassic ammonites of Tethyan affinities from the Aalenian of southern England

John H. Callomon* & Robert B. Chandler** 'University College London, 20 Gordon Street, London WC1H OAJ **Riddlesdown High School, Purley, Surrey CR2 1EX

A bstract - The ammonites of the early Middle Jurassic Aalenian Stage in Britain are dominated by the family Graphoceratidae, whose habitat was predominantly in extra^Alpine Europe. New collections, particularly from the Scissum Bed and Zone exposed in temporary sections near Burton Bradstock, Dorset, contain however a significant proportion of Mediterranean Tethyan elements, some of which are described. They indude Erycites cf. fallif ax Arkell and E. exulatus sp. nov. of the subfamily Erycitinae Spath, 1938; Hammatoceras lorteti (Dumortier). H. cf. or aff. procerinsigne Vacek, Planammatoceras planinsigne (Vacek) [M] and P. tenellum sp. nov. [m] (from the Murchisonae Zone of Horn Park) of the Hammatoceratinae Hyatt, 1867: Csernyeiceras verpillierense (Roman & Boyer) of the Haugiinae Buckman. 1905; and Tmetoceras scissum (Vacek) in several transients from Lower to Upper Aalenian. These species occupy important positions in the evolutionary histories of their families, which are discussed.

K ey w o r d s : Jurassic, Aalenian, Dorset, Scissum Bed, ammonites, Tethyan, biostratigraphy, systematics.

INTRODUCTION

The ammonite biostratigraphy of the Aalenian the ultimate units, the distinguishable ammonite faunal must be one of the most intensively studied and best horizons that could be recognized in the northern understood of any Stage of the Jurassic. Detailed Jura by Contini was twelve. In Dorset it is currently successions have been worked out at localities ranging sixteen. widely across Europe, beginning with the classical Nevertheless, this impressive picture of the early work of Buckman in Dorset (1887-1907). ammonite biostratigraphy was until recently highly recently brought up to date by the present authors incomplete. It is strongly biased through the (Callomon & Chandler 1990), and extending via dominance, both in numbers and persistence, of the northern Germany (Hoffmann 1913, Althoff 1940), one family, the Graphoceratidae, in what happened to Swabia (Rieber 1963), eastern France (Contini 1969- be, historically, the cradle of classical biostratigraphy 70, Caloo 1970, -71) to Iberian and Betic Spain and biochronology in extra-Alpine northern Europe. (Ureta Gil 1983, -85; Linares, Ureta & Sandoval In Britain, Germany and the Jura, the Graphoceratidae 1989). Illustrations of stratigraphically less extensive make up 95% or more of the Aalenian faunas. The or less well-controlled collections are to be found in remainder provided intriguing glimpses of an almost innumerable other works. The evolutionary alternative culture living “somewhere else". There homotaxis of the dominant elements of the faunas, were therefore indications of bioprovincjalism in the Graphoceratidae. across the whole of this large Aalenian ammonites as in those of other Stages, but area is remarkable. It has therefore been used as the it seemed to be much less important. The biostratigraphical' base for a standard Graphoceratidae, although dominant in the north, did chronostratigraphy that is almost everywhere extend over the Mediterranean as far as North Africa, immediately applicable^ This is shown in Figure 1. Sicily, the Italian Apennines and the Balkans. The (Although there is general agreement on the sequence clear-cut. mutually exclusive, faunal segregations of stratigraphical units in this scale, agreement on “found in the Upper Jurassic, enshrined in the many points of nomenclature has still to be worked traditional division of the world into Boreal and out, as have formal typological definitions in boundary Tethyan Realms, seemed to be lacking. The exotic stratotype sections). More locally, biostratigraphical minor elements of the faunas were therefore regarded subdivision can be taken even further. The number of as curiosities. As the Graphoceratidae were

17 Notes on Figure 1. English faunal 1. Brauns 1865, based on northern Germany. The Zones Subzones horizons 5 holotype of the index came however from an unknown horizon in Franconia. It is lost, and there are as yet neither topotypes nor a neotype. G. fo rmo sum Aa-15,16 The attachment of the name opalinum to these Graphoceras early forms, well known and abundant almost concavum everywhere else, including northern Germany, is G. concavum Aa-13,14 therefore conventional. A typical example is illustrated in the Treatise (Arkell 1957, p.L263, fig.298.4). Buckman, on the contrary, believed B. gigantea Aa-11,12 that the type horizon of L. opalinum lay higher, in Brasilia the Scissum Zone. He therefore renamed the forms bradfordensis of the Opalinum Zone L. opaliniforme. His B. bradfordensis Aa.8,9,10 opaliniforme hemera, or Opaliniforme Zone, is 4 therefore a synonym of Opalinum Zone. 2. Neumayr 1871, and Buckman. Partly replaced by a L. murchisonae Aa-6,7 Comptum Zone by Contini (1969), following biostratigraphical indications of Rieber (1963) and Gabilly (Gabilly & Rioult 1974); Lineatum Ludwigia L. obtusiformis Aa-5 Subzone left by him as a faunal horizon or Subzone murchisonae in the Opalinum Zone. 3. An alternative subzonation sometimes used in L. haugi 3 Aa-4 Germany is based on a succession of Staufenia. The boundaries of the Opalinoides, Sinon, Sehndensis and Staufensis Subzones differ L. comptum Aa-3 considerably from those given here, however, the Tmetoeeras last mentioned reaching well up into the scissum Bradfordensis Zone. 7 L. lineatum Aa-2 4. Used until recently only as a Subzone of the Murchisonae Zone, but the faunas are so Leioceras x distinctive and widely recognizable that promotion L. opalinum Aa-1 to full zonal status seems justified. opalinum 5. Callomon & Chandler, 1990.

Figure 1. - Zonal classification of the Aalenian in Britain.

sufficiently abundant to solve the main geological around Lake Garda and Cap San Vigilio described by problems of stratigraphical correlation, problems Benecke (1865) and Vacek (1886). It was for a long arising from bioprovincialism did not excite much time almost the sole arbiter of the Tethyan Aalenian, interest. but even in his reanalysis of 1956, Arkell (p. 176) Bioprovincialism becomes important, however, deduced the probable ages of the forms represented in attempts to solve the biological problems of the by correlation and analogy rather than from primary ammonites themselves. Leading amongst these stratigraphical evidence, of which there was problems is that of working out the pattern of evolution effectively none. Ironically, perhaps, for an equally as basis for phylogenetic classification. From this long time the best examples of the latter case, of can follow discussions of diversities, rates of turnover faunas from isolated horizons, lay in Buckman's and extinction. Finally come speculations on causes descriptions (1887-1929) of the exotic elements in - the relationships between evolution and the faunas of Dorset: genera such as Asthenoceras, environment, currently a popular topic in Vacekia, Bredyia, Haplopleuroceras, Fontannesia, palaeobiology, ammonites included. Planammatoceras, Eudmetoceras, •Euaptetoceras, The difficulties in the Aalenian have been largely Abbasites and Tm etoeeras itself. circumstantial. Known localities yielding good Since then there has been considerable progress, Tethyan faunas have been few. Either material was largely through the careful study of new successions. relatively abundant and well-preserved but In Europe, the most notable additions have been in stratigraphically doubtful, or it was well localized Hungary (Geczy 1966-7) and Spain (Ureta, 1983, - stratigraphically but confined to isolated horizons, 85; Linares, Ureta & Sandoval, 1989). A number of without obvious ancestors or descendantsj The most the genera listed above, as well as others such as "“famous example of the former is the fauna from the Erycites and Zurcheria, have acquired ranges within highly condensed succession in the Venetian Alps the Aalenian. Perhaps’ even more important, some

18 genera previously thought to be characteristic of the Freshwater, the mouth of the River Bride (formerly overlying Bajocian, such as Stephanoceras, have had Bredy); and at Manor Farm, on the SW slopes of their ranges extended downwards into the Aalenian. Burton village. The succession in the Scissum Bed is Several previously held views on phyletic roots have the same as that at Burton cliff, which is reproduced had to be modified and some cryptogenic genera can here in Fig.2. now be assigned to their proper phyletic places. The term “Scissum-Beds” was first introduced in Finally, probably the strongest new impulse has come England by Richardson (1904, p.67) as from the New World, in which rich faunas presumed lithostratigraphical term for beds in the Cotswolds to be of Aalenian age have been described along the “laid down during the hemera scissi - the characteristic length of the Eastern Pacific rim, from Alaska to the ammonite, Tmetoceras scissum, being most distinctive southern Andes (see e.g. Westermann 1964; Imlay but rare.” Its use was extended by him to Dorset 1973; Westermann & Riccardi 1972). These pose an somewhat later, and his description of Burton cliff additional problem. The Graphoceratidae are wholly (Richardson 1928, p.63 and Fig.4) has formed the absent in the Pacific and even the primary attempts at liasis of all subsequent accounts. The Scissum Zone correlation with the European standard are dependent in any kind of chronostratigraphical sense seems to on the common presence in both regions of western go back to Neumayr (1871, p.509), albeit for the Tethyan groups. It is especially here that a better “Mediterranean” region, especially Cap San Vigilio. knowledge of the Tethyan genera and their ranges is It was extended to Britain by Buckman (1898a, Table needed. I) as hemera, and thence transformed into a standard The present work is prompted by some new Zone by Arkell (1933, p~-189 and"l~956, p.34). It1 discoveries in temporary sections in Dorset, corresponds to the Comptum Zone and highest faunal particulary in the Scissum Bed of Burton Bradstock. horizon of the Opalinum Zone of Contini (1969). This, the lowest member of the Inferior Oolite, is (Zonal boundaries remain formally to be defined, but usually rather hard and massive. Hence, although one in any case the range o f Tmetoceras scissum - its of the most widespread and persistent units in the biozone - is irrelevant to its function as zonal index.)' formation, its faunas, besides the dominant Scissum Bed at Burton is best seen in the Graphoceratidae, were until now among the least section at the Freshwater Caravan Park. It consists well understood. Pipe-trenches, widening of farm- there of two parts, separated by an indistinct parting, tracks and ground clearance for holiday caravans in when weathered, but inseparably welded together recent years led to extensive excavations of the when fresh, as in the fallen blocks at Burton Cliff. Scissum Bed at places where it had weathered near The lower part (bed 6a in figure 2) is a very fine­ the surface. This made it possible to recover large, grained calcareous sandstone, deeply and intensely well-preserved specimens, often complete with test burrowed. It is sparsely fossiliferous, the main andbodychamber. The fauna turned out to be relatively elements being very large Camptonectes and rich in Tethyan elements, perhaps surprisingly so in ammonites embedded at all angles, consisting almost view of the high palaeolatitude of Dorset: certainly wholly of large Leioceratids, L. opaliniforme so in'comparison with Lorraine, the Jura and the Buckman [M] and [m], preserved as internal moulds. Franco-Swabian basins. The cause may have been The upper part (bed 6b) grades upwards into an trophic, for besides ammonites, the Scissum Bed, in intensely hard, shelly, oolitic and micritic sandy common with most of the rest of the Inferior Oolite, limestone, also intensely bioturbated. Small to has arich and diverse benthos of bivalves, brachiopods medium-sized ammonites are embedded at all angles, and gastropods, as well as the bioturbation of a fauna but large shells are flat-lying and seem to retain some of vigorous crustaceans. We describe now a number layering: Bredyia subinsignis marks a consistent of these new discoveries, together with a few related pavement at a level 5-10 cm from the top. The bed is forms from slightly higher beds. A description of the terminated by a sharp erosion-plane, which is considerable number of Hammatoceratinae from the somewhat diachronous: at Burton Cliff, the top has Murchisonae-Concavum Zones that have accumulated been planed off to a level at or just below the Bredyia is beyond the scope of the present work. level. Most of the Tethyan ammonites described below also came from this level The Leioceratinae in beds 6a and 6b are distinct. STRATIGRAPHY The abundant new collections from 6b confirm Rieber’s (1963) and Contini’s findings (1969-70) The localities from which the present material that apparently two quite separate groups are present, came all lie within less than a kilometre of the famous each dimorphic: coastal section at Burton Cliff, Burton Bradstock; at Freshwater Caravan Park, 400 m NNE of Burton

19 BURTON BRADSTOCK

Bathonian Fullers Earth © Bt-4 g Bt-3 The Scroff fiL.Bt’1,2__ p Zigzag Bed ____ Burton Limestones

@ Bj-28? ► - First Bed

@ Bj-28? Sponge Bed

® Bj-28 - Second Bed @ Bj-28 i © Bj-27b - Third Bed: @ Bj-27a Truellei Bed Astarte obliqua Bed. "Vesulian unconformity Red Conglomerate - upper Red Bed

- lower Snuff-boxes Yellow Conglomerate Blue Bed Scissum Bed

Foxy Bed

Bridport Sands Upper Toarcian (Aalensis Subzone)

Figure 2. - The section through the Inferior Oolite at Burton Bradstock, Dorset. (Beds 3-11 based on Freshwater Caravan Park, beds 12-19 on Burton Cliff).

20 Subfamily Leioceratinae Spath, 1936 SD Loczy 1915, p.381; non Amm. gonionotus Benecke, Genus Leioceras Hyatt, 1867 [= Lioceras Bayle, 1878] des, Roman 1938, p.138]

L. (Cypholioceras) lineatum Buckman, 1899 [M] (incl. Erycites cf. fa l l if ax Arkell, 1957 L. grave, parti turn, plectile, plicatellum : type (Pl.l, figs 1,2,3) localities and horizons all Burton Bradstock). L. (Leioceras) opalinum Buckman non auctt., nec cf. 1865 Ammonites fallax Benecke (non Gueranger), p. 171. pl.6. Reinecke ? [m] (= L. undulatum Buckman, 1899). figs 1-3. non 1874 Ammonites fallax (Benecke): Dumortier, pi.55, figs 3,4. cf. 1886 Hammatocerasfallax Benecke: Vacek, p.93, pi. 15, figs 1- Subfamily Staufeniinae Maubeuge, 1950 9 (topotypes) Genus Cylicoceras Buckman, 1899 cf. 1904 Erycites fallax Benecke: Prinz, p.89, pi.25, fig.l ? 1922 Erycites sphaeroconus Buckman: pi.315 1957 Erycites fallifax Arkell, p.L267, fig.308.3a,b (Benecke's C. (Cylicoceras) uncinatum Buckman, 1899 [M] (incl. fig.l reproduced: holotype). C. uncum: both types from Burton). cf. 1966 Erycites fallifax fallifax Arkell: Geczy, p. 106. pi.30, figs 2- C. (Costiceras) subcostosum Buckman, 1899 [m] ( = 5, pi.3 I, fig.3 Amm. opalinus costosus Quenst., preoccupied), 1966 Erycites fallifax flexuosus: Geczy, p. 11 0. pi.31, fig.3 cf. 1989 Erycites fallifax Arkell: Linares, Ureta & Sandoval 1989. tortumBuckman, 1899 [m] (lectotype Suppl. pl.l 1, pl.l, fig.8 figs 1-3; type species of Rhaeboceras Buckman, 1899, non Meek, 1876). Material - One nearly complete adult (RBC 524) C. (Costiceras)paucicostatum Rieber, 1963 [m] (type and one nucleus (RBC 525). Scissum Bed, Burton species of Costiceras Contini, 1969). Bradstock.

The duality goes back into the Opalinum Zone Type - Benecke founded the species on the basis of below, as illustrated by Buckman from his some 40 syntypes. There was no holotype. Only one opaliniforme hemera, and probably lower, into the of his three figures gave a side-view of a complete Toarcian. Upwards, Cylicoceras can be followed specimen (Pl.6, fig.l), and this has been taken by effortlessly into Staufenia, Leioceras into some authors to imply that it was the type (e.g. Vacek Ancolioceras. Cylicoceras is relatively rare at Burton 1886, p.93 and Geczy 1966, p. 108) even though the Bradstock. other two figures were derived from two other The Leioceratinae of bed 6a appear to differ from syntypes. No confusion has arisen, however, and in those in beds 4 and 5 below only in size, although not any case the matter was settled when Arkell (1957, in enough have yet been collected from bed 4 to quantify the Treatise p.L267) renamed the species E. fallifax, this. Such an upward increase in size of what appear to resolve the junior homonymy with Amm. fallax otherwise to be very similar forms of Leioceras has Gueranger, 1865, and chose Benecke's fig.l to be been noted also in the Opalinum Zone on the holotype of the species.jaomg/? novum. The type was Continent. In Swabia, it occurs in the "Opalinus- said by Vacek to represent an unusually small variant Ton", up to 100 m thick. In France, it has been and appears to be lost. According to Hantken in Prinz formally expressed in terms of two successive faunal (1904, p.89) the type-series was kept in Strasbourg, horizons or Subzones, those of L. subglabrum Buck, where Benecke was professor. Enquiry at Strasbourg below and of L. opaliniforme Buck, above. The in 1974 elicited the reply from Mile Marguerite Wolf, position of the true L. opalinum (Reinecke) itself conservateur, that the whole of the collection of types remains uncertain, for the type material is lost and was destroyed in a fire in 1967, but that the types of there appear to be no topotypes on which to base a Amm. fallax had not been among them. There was new interpretation, including its stratigraphical evidence that it had remained in Benecke’s private horizon. The Opalinum Zone at Burton is therefore collection which was dispersed after his death in taken to be beds 4-6a inclusive, and the Scissum Zone 1917 and cannot be further traced.'An old plaster-cast to be represented by bed 6b only. has however recently been discovered in the Vacek collection at the Geologische Bundesanstalt in Vienna (JHC 1991). Nevertheless, a neotype may have to be SYSTEMATIC DESCRIPTIONS selected.

Family Phymatoceratidae Hyatt, 1867 Description and comparisons - Although the [nom. corr. pro Phymatoidae Hyatt, 1867: ICZN Opinion 575, 1959] species is widespread and locally abundant in the Subfamily Erycitinae Spath, 1928 Mediterranean area - Vacek claimed to have had Genus Erycites Gemmellaro. 1886 some 700 specimens from San Vigilio - few good [Type species Amm.fallaxBenecke, 1865 (non Gueranger), specimens have been figured, making it difficult to

21 assess the considerable variability. A topotype is The other species described by him, E. sphaeroconus, therefore shown here for comparison in pi.I, fig.2, is said to have the whole of its last whorl, maximum kindly donated by Sr. Luigi Ambrosi of S. Ambrogio, diameter only 30 mm, consisting of bodychamber. Its Verona. It came from the Scissum bed of Capitello horizon is also unknown, although at the place at quarry, San Vigilio (Sturani 1964, p.9, fig.2, bed s), which it was found, Marston Road Quarry (Buckman the top member of the Oolite of San Vigilio, varying 1893, p.490), the Scissum Bed is well represented. It from 15 to 65 cm in thickness across the quarry, is best regarded as an indeterminable juvenile Erycites bounded at top and bottom by sharp erosion planes, s.s. and its name treated as a nomen dubium. and locally packed with ammonites in fresh The type horizon of E. fallifax at Cap San Vigilio preservation (observations made in 1988). The appears to be firmly dated as upper Comptum Subzone topotype is partly deformed, in that the bodychamber (see also Linares et al. 1989, p. 198). The Leioceras has been displaced sideways and is now somewhat comptum found in intimate association with E. fallifax askew, but this does not detract from what is otherwise and Tmetoeeras scissum (confirmed in 1988), a reliable representation of a typical variant. A including the specimens figured by Vacek. appears to terminal adult constriction is still partly preserved on be correctly identified, as confirmed by Rieber ( 1963). the venter at the end of the bodychamber. The Dorset specimens would seem therefore to be The larger specimen from Burton shares most of slightly older. Perhaps this would explain their slightly the major features of sculpture with the topotype: the more “ancestral" morphology. adult maximum size; the inflated, involute inner Forms that are most probably ancestral have been whorls, becoming evolute and compressed on the abundantly described from the Mediterranean region. outer whorl; the dense, sharp, fine ribbing; and the Two that are worth citing are E. subquadratus Geczy vestigial break in the secondary ribbing on a perfectly (1966, p.95, pi.27, fig. 1) from the topmost Toarcian, round venter. The dimensions are: maximum diameter which has already the tightly involute coiling of E. 85 mm, septate to 67 mm, 0.4 whorl bodychamber fallifax in its inner whorls but retains hammatoceratid preserved, umbilical seam indicating 0.75 whorl ribbing on its bodychamber as in the specimens from bodychamber when complete. At 67 mm: whorl-height Dorset; and thence E. elaphus Merla (1934, p.25, h. 0.37; whorl-breadth b , 0.40; umbilical width u, pi.4, fig.5), from the Dumortieria meneghinil 0.34; 36 ribs per whorl. The principal difference lies pseudoradiosa Zone. in the style of the ribbing, particularly on the bodychamber. The Burton specimens have straighter Erycites exulatus sp. nov. primaries, more accentuated at the umbilical margin, (PI.II. figs 1,2) slightly flexuous, dividing relatively low on the whorl- ? 1874 Ammonites gonionotus Benecke: Dumortier 1874, pi,56, side. The general impression is still more fig.5 only (from La Verpilliere). Hammatoceratid, less Stephanoceratid, than the 71886gammatoceras (Erycites) barodiscux Gemmellaro, p.205, Mediterranean forms. partim (syntypes in Palermo). Ages - These are so far the only specimens of the group found in Britain, and hence we know it from M aterial - Holotype, PI.II, fig.2 (RBC 528), only a single horizon, in the lower Scissum Zone. In paratype 1, pi.II, fig. 1; paratypes II (RBC 536) and III the Mediterranean region it has some range. Geczy (RBC 537). not figured, and a septate nucleus possibly (1966) has distinguished a series of successive belonging to this species; all macroconchs. transients, as subspecies: E. fallifax fallifax (upper Description - Measurements: Comptum Zone or Subzone, see fig.l) fallifax excavatus (Opalinoides Subzone, equivalent to the HT PT I PT II PT III lowest, Haugi Subzone of the Murchisonae Zone) -E. (PI.11,fig.2) (PI.II,fig.l) fallifax flexuosus (the same, somewhat higher) - E. Max.diameter (mm) 138 fallifaxarkeHi (?Concavum Zone). In Spain, Linares, 105 140 no

Ureta and Sandoval (1989) give the genus Erycites septate diameter (mm 85 91. 80 65 almost exactly the same range, although they do not subdivide it further into species. A typical example of bodychamber (whorl 0.8, p 0.8, p 0.8, p 0.85, p (p: peristome) E. fallifax s.s. has recently been described also from

the Comptum Subzone in the southern Beaujolais Diameter (mm) 125 85 100 65 125 85 100 65 (Rhone) by Elmi & Rulleau (1993, pi.2, fig.3). That whorl-height, h 0.34 0.39 0.31 0.36 0.34 0.36 0.32 0.37 the genus as a whole ranges upwards is known to be whorl-breadth. b 0.35 0.45 0,35 0.51 0.36 0.44 0.38 0,51 umbilicus, u 0.39 0.31 0.42 0.40 the case also in Britain, where a specimen of Erycites 0.40 0.36 0.41 0.36 Number of ribs 28 24 34 30 30 27 29 28 partschi Prinz was already figured by Buckman (1921, pi.246). Its probable horizon, as deduced from several Comparison of pis. II and I shows that the new subsequent finds, is Aa-8, lowest Bradfordensis Zone. species mirrors E. fallifax in all major features of

22 morphology, with consistent small differences. E. in the general style of ribbing, but the shell was even exulatus is bigger -c. 140 mm against c. 95 mm - and bigger and the inner whorls are strikingly more much more strongly and coarsely ribbed. The adult evolute. In this respect there is some similarity with bodychamber retains strong hammatoceratid ribbing E. gonionotus (Benecke) (1865, p.172, pi.7, fig.3), to the end. unlike that in E. fallifax which modifies but this is outweighed by other differences. In E. strongly and fades. The nucleus appears to be gonionotus the coverage of the flanks of the inner spheroconic as in E. fallifax, from which it may be whorls is so light that the secondary ribbing is partly indistinguishable; and the specimen shown in PIT, visible. This is also the case in the specimens figured fig.3 may belong to E. exulatus rather than to E. under the name by Vacek (1886, pi. 16, fig. 10, a fallifax. Septal sutures are barely visible but appear nucleus) and Geczy (1966, pi.29, fig.3). In the English to be typically complex. specimen the secondary ribbing, as well as being coarser, is fully covered on the inner whorls. Lastly, Comparisons - There are very few figures in the there is no guarantee that either Benecke's figured literature that resemble the present forms at all closely. lectotype or Geczy’s Hungarian specimen came from The nearest seems to be the one given by Dumortier, the Scissum Zone. They could be older. although it is incomplete. It may have additional One of the characters that remains to be explored direct relevance through its place of origin. La more closely, in both the Erycitinae and the Verpilliere. There appears to be no detailed Hammatoceratinae, is the significance and stratigraphy at this locality (cf. Arkell 1956, p. 103), intraspecific variability of the involuteness of the but it is one of the few to have yielded some of the coiling. In some descendants, e.g. Sonninia s.s.. other forms now being described from the Scissum material is sufficient to leave no doubt that the Bed of Dorset, such as “Hammatoceras” verpillieren.se umbilical width, usually the most direct measure of (see below). “involuteness”, can vary enormously. This could be The closest match may turn out to be with Erycites the case in Erycites; and the possibility that the barodiscus Gemmellaro. We are indebted to Dr present specimen is merely an extreme variant of E. Stefano Cresta (Rome) for showing us some exulatus cannot be ruled out. Much more material photographs of the type material in Palermo. There would be needed before we could tell. appear to be at least three syntypes, which resemble the Dorset forms in most respects - size, coarseness General remarks on Erycites. At the generic level, of ribbing and bodychambers. As Gemmellaro never Erycites occupies by common consent a central completed the projected monograph of the faunas of position in the phylogeny of the ammonites of the Monte San Giuliano and gave no figures, his species Middle and Upper Jurassic. Its roots as an independent was not taken up by subsequent authors. Its name has lineage lie somewhere in the Phymatoceratidae in the been ignored in the hundred years since. Neither were Upper Toarcian, for the very typical E. elaphus was the indications of stratigraphy sufficiently detailed to already fully differentiated from Hammatoceras s.s. permit comparisons of age with the precision needed in the Tethyan Pseudoradiosa/Meneghini Zone, in the present context. It seems best therefore to immediately above the Insigne Zone (equivalent to regard the name of the Sicilian species as a nomen the lowest part of the NW European Levesquei Zone). oblitum for the time being and not to let it introduce It persisted with little change at least into the uncertainty into the description of well-localized new Bradfordense Zone of the Upper Aalenian (E . partschi, material from another very distant locality, Dorset. intermedins) or even the Concavum Zone (Linares. Ureta & Sandoval 1989). But it branched at least E rycites aff. exulatus sp. nov. three times. One branch had already separated in the (PI.I, fig.4) Scissum Zone: Spinammatoceras - Malladaites - Zurcheria (and Haplopleuroceras?) (Linares & Material - One complete phragmocone (RBC 526). Sandoval 1986. Fernandez-Lopez, Mouterde & Rocha 1989). For this branch, as clear an example of Description and comparisons - Measurements: proterogenetic evolution as could be wished for, the maximum diameter 122 mm, septate to 120 mm, name Zurcheriinae Hyatt 1900 would be available. bodychamber just beginning, umbilical seam The second branch led in the Murchisonae Zone to indicating a former bodychamber of 0.85 whorl, A bbasites, with the involute spheroconic coiling which, with a spiral half-whorl constant of 1.27 would already seen in E. fallifax, and thence presumably to have given an adult diameter of 175 mm. Dimensions: Docidoceras - Emileia of the Otoitidae, all the at 120 mm, h = 0.30, b = 0.32 and u = 0.47. Ribs: 28 Sphaeroceratidae, etc. The third branch led to at 120 mm, 31 at 80 mm, 31 at 50 mm. No septal Stephanoceras of the Stephanoceratinae not later than sutures visible. the Murchisonae Zone, for typical St. longalvum There is a strong overall resemblance to E. exulatus (Vacek) (often still referred to as Docidoceras) occurs

23 already in the Bradfordensis Zone of Portugal (JHC of Prinz's attempt. They introduced Hammatoceras coll. 1987). It seems fully justified therefore to revive vaceki “nov. sp.” for a species whose syntypes the subfamily Erycitinae Spath 1928 for at least the included Vacek’s figured specimens and four main stem of E rycites, to differentiate it from the specimens in their own collection from the Rhone Hammatoceratinae. valley. This name is thus doubly preoccupied. The At the specific level, it is perhaps a little puzzling homonymy was resolved by Elmi (1963, p.89) w'ho that the new material from Dorset should be so similar renamed Roman & Boyer's species Planammatoceras overall to its contemporaries in the Tethys, and yet so rom ani “nom. mut.” [nom. nov.] and took as type one different in some respects, mainly size. Could this be of Roman & Boyer's specimens. Vacek’s specimens a reflection merely of geographic subspeciation? Are are therefore at best paratypes of H. romani (Elmi, the Dorset forms representatives of Erycites that have 1963) and are not very closely related to H. vaceki been exiled (banished, exulati) to the bioprovincial, Brasil, 1895. periphery of Durnovaria, as in the days of Imperial Rome? If so, they lived rather well. A ge - The type of H . lorteti came also from the condensed iron-ore deposits of La Verpilliere (Isere). — Subfamily Hammatoceratinae Buckman, 1887 The Dorset specimen serves therefore now firmly to Genus Hammatoceras Hyatt, 1867 establish the age of the species as (lower) Scissum Zone, Lineatum Subzone. Hammatoceras lorteti Dumortier. 1874 (P1.1II, fig.l) Hammatoceras cf. or aff. procerinsigne Vacek (Pl.V, fig.l) 1874 Ammonites lorteti Dumortier, p.262, pi.54, figs 1,2 (holotype by monotypy). cf. 1886 Hammatoceras procerinsigne Vacek, p.89 [33]. pi.14, figs 11.12 (lectotype, here designated) M aterial - One complete phragmocone (RBC 529), and some fragments. Scissum Bed, Burton Bradstock. M aterial - One complete adult (RBC- 531) and a fragment. Scissum Bed, Burton Bradstock. Description - Within even a quite narrowly acceptable range of variability, the resemblance of Description - Maximum diameter 150 mm. septate the Dorset specimen to the holotype is astonishing: to 95 mm, nearly 0.9 whorl bodychamber, peristome the protograph of the type is reproduced on pi.Ill, partly preserved. Dimensions: at 130 mm: h = 0.32, b fig.2, and pi.IV, fig.2. The high keel, coiling and = 0.21, it = 0.42; at 90 mm: h = 0.33, b = 0.27, u = 0.44. nodose ribbing are all typical of Hammatoceras s.s. Ribs: at 150 mm, 36; 100: 34; 60; 32; 40: 30; 25: 23; The Dorset specimen has a diameter of 165 mm with 15: 16. The characteristic features are relatively small about a tenth of a whorl of bodychamber. The complete size; the evolute coiling, especially on the inner adult must therefore have exceeded 200 mm in whorls; the compressed whorl-section; and the diameter. Its dimensions are: at 100 m: h = 0.29, b ~ persistence of tubercles into the middle whorls up to 0.21'0.25, u = 0.47; at 100 mm; h - 0.30, b = 0.24- diameters around 60 mm. The keel on the phragmocone 0.29, u = 0.33. The holotype has a diameter of 151 is floored and high, but not excessively so, very much mm, but there are no indications whether it retains as shown by Vacek. On the bodychamber it is only any bodychamber. It differs from the Dorset specimen quite moderately prominent, leaving only a somewhat mainly in having 4-6; fewer ribs per whorl. acutely fastigiate carina on the internal mould.

Comparisons - The name lorteti has been widely Comparisons and discussion - Of all the forms used but none of the specimens figured under the illustrated by Vacek, his H. procerinsigne comes name is ex&ctly like the .type, in retaining the closest to the Dorset form in size, coiling and characteristic tubercles to such large diameters. The sculpture. The main difference lies in the density of first to use the name was Vacek himself (1886, pi. 16, the ribbing in the tuberculate stage, which also persists figs 5-9) for material from San Vigilio. His specimens to relatively large diameters. were renamed Hammatoceras subinsigne vaceki by The question arises of generic assignment. The Prinz (1904). But Hammatoceras vaceki was present form also has many of the features of what is preoccupied by Brasil (1895), used for a species from today placed in a separate genus Planammatoceras the Murchisonae Zone of Normandy whose holotype (see below). The characteristics of its type species (pi.2, figs 1,2) he compared with Vacek's H. are the involute, compressed coiling on the inner planinsigne rather than with H. lorteti, which is not whorls and the dense, rather fine ribbing with subdued mentioned. A second attempt to rename Vacek's forms primaries on the middle and outer whorls, a tuberculate was made by Roman & Boyer (1923, p.32), unaware stage, if present, being confined to the innermost

24 whorls. The outer whorls of the Dorset specimen already at 45 mm diameter. The keel was high and could therefore be well placed in Planammatoceras, sharp, as shown in all of Vacek’s figures and in the but the inner whorls not. Except for the much higher photograph of the lectotype, and hollow and floored density of ribbing, their affinities appear to lie closer on the phragmocone. The Dorset specimen agrees to H. lorteti, and we prefer to regard the present with the lectotype in almost all details. The latter was specimen as being more closely related to the group also still wholly septate, at a diameter of 150 mm, so of the latter for the time being. Whether it might in the species was a large one. The septal suture also has fact be merely an extreme variant of the same species the typically high complexity, with long, multiply remains once again an open question that only more incised spidery lobes densely covering almost the material could resolve. whole of the whorl-side. Vacek’s illustrations do give the impression that three distinct groups are represented at San Vigilio: D iscussion - The forms from the Scissum Zone (a) the group of H lorteti (= rom ani Elmi) and differ only in detail from the type-species of the procerinsigne, as discussed above; (b) the group of genus, P. planiform e (Buckman 1922, pi.356), which H. planinsigne and tenuinsigne, placed by common probably came from the Murchisonae Zone and consent into Planammatoceras; and (c) the group of Subzone. New' finds range upwards into the lower H. subinsigne (Oppel), today placed in Bredyia (see Bradfordense Zone. The specimen figured under this below). That apparently both groups (a) and (b) are name by Elmi, together with another referred to in the separately recognizable also in Dorset is shown in the text, appears also to have come from the Murchisonae next section. Group (a) has not so far been given a Subzone and could equally well be assigned either to separate generic name. It could be accommodated planiform e or to planinsigne. It seems therefore that under the names either of its probable ancestors or these forms of Planammatoceras ranged almost descendants. The only plausible name available among unchanged at least from low'er Scissum to low'er the latter could be Parammatoceras Buckman, 1925, Bradfordense Zones, making the genus a well-defined as interpreted by Elmi (1963). His P. boyeri and P. independent phyletic entity. A similar range is cited auerbachense from the Murchisonae Zone seem to in Spain (Linares et al. 1989). belong to the same group as H lorteti. But the type of Parammatoceras, P. obtectum , from the upper Bradfordensis Zone, is rather different. We prefer Planammatoceras tenellum sp. nov. [m] therefore to retain the name from below, (PI.VI, fig.2a,b) Hammatoceras itself. 1886 Hammatoceras tenerum Vacek, p.90 [34J, pi.12, fig.5,5a only Genus Planammatoceras Buckman, 1922 18S7 Hammatoceras (?) tenerum Vacek: Haug. p. 128. pi.5, fig.7a.b

Planammatoceras planinsigne (Vacek, 1886) [M] M aterial - The holotype only (RBC 533), from (PI.IV, fig.l) Horn Park quarry, bed 3c, horizon Aa-7, Murchisonae Zone and Subzone (Callomon & Chandler 1990, p.90, 1886 Hammatoceras planinsigne Vacek, p.89 [33], pi. 13, figs 1 fig-3). (lectotype), 2-6. ? 1923 Hammatoceras tenuiinsigne Vacek: Roman & Boyer, p.33, pi.7, fig.l. Description - Maximum diameter 43 mm, complete ? 1963 Planammatoceras planiforme (Vacek): Elmi. p.82, pi. 11, phragmocone with the beginnings of the bodychamber; fig. 1 a,b. internal cast, no test preserved. Coiling evolute, 1982 Planammatoceras (P.) planinsigne (Vacek): Weslermann compressed, with acutely carinate venter, the keel & Riccardi, p.19, text-fig.3 (lectotype refigured). not floored and hollow. Dimensions: at 40 mm, h = 0.32, b = 0.21, u - 0.44. The ribbing is dense, subdued M aterial - One complete phragmocone (RBC 530), and relatively delicate (tenellate), the primaries from the Scissum Bed of Burton. bifurcating irregularly at the shallow umbilical edge or remaining simple with intercalatory secondaries; Description - Maximum diameter 220 mm, wholly ribs about 26 per w'horl on the outer whorl, 35 at septate: estimated diameter of complete adult 350 diameter 25 mm. The septal sutures are well incised mm. Dimensions at 210 mm: h = 0.35, b = 0.18, u = but relatively simple and w-ell-spaced, with long 0.38; at 120 mm: h = 0.39, b = 0.22, u = 0.36. The test ventral and lateral lobes (E > L), only vestigial has been largely lost and the innermost whorls have accessory lobes and the simplest of short umbilical been broken, so that all that can be seen of the ribbing lobes, barely retracted. The last two sutures are at is its impression on the internal mould. But it clearly best only slightly approximated but show a consisted of very subdued primaries and dense, fine simplification indicating adult maturity. Assuming a secondaries that persisted, even on the inner whorls former length of bodychamber of three quarters of a

25 whorl, the complete adult would have been about 65 were found mm in diameter. Size and suture therefore point Senior used the same name for the forms both of strongly to a microconch, and the non-tuberculate, the Opalinum and Scissum Zones. The lectotype of B. compressed, sharply keeled coiling strongly suggests subinsignis in the Oppel collection came from the the microconch of Planammatoceras planiforme. “Torulosus-Schichten” of Swabia, lowest Opalinum Zone. The holotype of B. crassornata came from the Comparisons - The present specimen matches in Scissum Bed of Burton Bradstock. The microconch, almost ail details one of the four syntypes of with lappets, appears not to have been given a separate Hammatoceras tenerum from San Vigilio, the one name in the past. The main areas of distribution seem shown in Vacek’s pi. 12, fig.5, as well as the topotype to lie in the more temperate shelf-seas away from the figured by Haug. The second syntype figured by Tethys - Europe and the southern Andes (Hillebrandt Vacek (fig.4) is significantly different. The septal & Westermann 1985) - which may account for one of suture, shown at a diameter of 55 mm. has the same the generic characteristics, a relatively simple septal plan as that of the Dorset specimen but is much more suture compared with those of the other Lower incised, with strongly retracted umbilical lobe. There Aalenian Hammatoceratids. is no indication whether it is the last, and its complexity suggests not. The ribbing has also wholly Subfamily Haugiinae Buckman, 1905 (p.cxcviii) faded. One cannot therefore exclude the possibility Genus Csernyeiceras Geczy, 1966 (p.83) that the specimen is merely the nucleus of what was (Type species Hammatoceras verpillierense Roman & a much larger specimen, presumably then a Boyer, 1923] macroconch. A lectotype has not so far been unambiguously designated, Geczy ( 1966, p.55) states Csernyeiceras verpillierense (Roman & Boyer, 1923) en passant that “ Au cours de sa morphogenese le type (PI.VI, fig.l; pi.VII, fig.la-c; pi.VIII. fig.la-c) perd completement son ornamentation...”, suggesting Vacek’s figure 4. and tentatively assigns his fig.5 to ? 1386 Oppelia subaspidoides Vacek, partim. p.84 [28], pi. 10. fig.7 only a new subspecies szoerenyiae whose type (Geczy, 1923 Hammatoceras verpillierense Roman & Boyer, p.34. pi.8, pi. 10, fig.4) is however quite different. To avoid fig.l (holotype by monotypy, reduced x 0.88) further confusion we stabilize Geczy's intention by 1963 Euapletoceras verpillierense (Roman & Boyer): Elmi. p.73. now formally designating Vacek's fig.4 lectotype of 5 966 Hammatoceras (Csernyeiceras) verpillierense (Roman & Boyer): Geczy, p.83, pi.22; pl.41, fig.2 H. tenerum, even though it leaves the interpretation of this species somewhat uncertain. It is then a logical M aterial - Two complete phragmocones (RBC step to introduce a new name for those specimens 341, 534), an incomplete phragmocone showing inner whose morphological interpretation as well as age whorls, and fragments; all from the Scissum Bed of are not in doubt. Burton. The apparent rarity of the microconchs of both the Erycitinae and Hammatoceratinae more generally is D im ensions something of a mystery. The exception is the genus

B redyia, whose undoubted microconchs are common Diameter, h b u and well documented (see below). D/mm

RBC 341 (Pl.VI, fig.l) max. 250; Genus Bredyia Buckman at 240: 0.47 0.16 0.23 [Type species Bredyia crassornata Buckman, 1910; =Amm. 180: 0.46 0.16 0.21 subinsignis Oppel, 1856 (subj,)] 125: 0.46 0.18 0.19 [= Pseudammatoceras Elmi. 1963. type species Amm. subinsignis Oppel. 1856] RBC 534 (PI.VII, fig.l) max. 240; at 240: 0.42 0.15 0.26 170: 0.42 0.16 0.25 Bredyia subinsignis (Oppel) [M] and [m] 120: 0.43 0.18 0.25 • ^ The species has been exhaustively described by RBC 535 (PI.VIII, fig.l) max. 120: Senior (1977), who designated a lectotype and at 120: 0.48 0.17 0.23 "discussed the numerous synonyms. The new collections from the Scissum Bed include several Description and comparisons - The species is specimens, but they add little to what was known large. There is no evidence as to the length of the before and we cite the species here only to complete bodychamber, but assuming it to have been 0.5-0.75 the list of Hammatoceratinae from the Scissum Bed. whorls, the unusually high spiral half-whorl constant "It seems there is a level 5-10 cm below the top of the of around 1.5 would extrapolate to an adult maximum | bed at which the species forms a la^er, for several diameter of 370-450 mm. The keel is very high and razor-sharp, hollow, with a broad flat floor giving the rather distinct: through Praestrigitespraenuntius (sic) internal cast of the phragmocone a tabulate venter Buckman (1924, pi.466), the earliest, from the upper (see pi. VIII, fig. 16, lower edge}. The ribbing fades in Bradfordensis Zone (probably horizon A a-11), on the mid-height on the whorl-side, leaving the dense, one hand; or through “O ppelia” subaspidoides Vacek straight primaries and secondaries accentuated at the (precise age unknown), or Hebetoxyites clypeus umbilical and external margins respectively. Buckman (1924, pl.496A only) of the early Occasionally the secondaries divide again high on Laeviuscula Zone, horizon Bj-8, on the other (see the whorl-side, giving short, irregular tertiaries. And Geczy 1967. p.222). But much later still, all the perhaps most interestingly, the test shows distinct characters of Csernyeiceras strikingly reappear in traces of spiral strigation (see pi.VIII, fig.la). The Strigoceras dorsocavatum (Quenstedt) (1886, pl.69, septal sutures are only partially discernible but agree fig-6) of the Lower Bathonian. The last known member in dense spidery complexity with that shown in ot the Strigoceratidae is a Phlycticeras from the Geczy’s pi.41, fig.2, and appear to have similarly LIpper Callovian. Csernyeiceras seems therefore long, broad-based external lobes. They must be among partly to fill a gap in what is beginning to appear to the most complex of any ammonite. The long, thin have been a long lineage going back from the top of ancillary lobelets of second, third and even fourth the Middle Jurassic to the ancestors of Haugia in the rank fill almost all the space available. The tips of Lower Toarcian. principal lobes run well into the stems of the preceding lobes, and ancillary lobes totally fill all saddles. Age - The Dorset forms are firmly dated to the There is no part of the whorl-side not covered by lower Scissum Zone. The type from Verpilliere came sutures. from condensed Lower Aalenian and could also be The agreement between the Dorset, French and from the Scissum Zone. The precise age of the. Hungarian specimens is very close, indicating that Hungarian material is similarly uncertain. New the variability of the species is quite siuajl. But records from the neighbourhood of Ly^onjrvthe Rhone except for the presence of a septicarinate keel, these valley are firmly assigned to the Comptum Subzone forms have almost nothing in common with their (Elmi & Rulleau 1993, p. 154). But a second specimen contemporary Hammatoceratinae. Going back in time, from the Jura cited by Elmi (1963, p.77) seems to be they do, however, bear a striking resemblance to securely dated as Murchisonae Zone and Subzone. Haugia of the upper Middle Toarcian Variabilis Zone, The species has therefore been recorded over some such as the splendid Haugia variabilis, jugosa, beani range in the Lower Aalenian. andphillipsi from France illustrated by Gabilly (1976, pis. 11 -15), or the Haugia grandis from the Cotswolds already figured by Buckman (1890, pi.24, pi.25 fig. 1). Family Hildoceratidae Hyatt. 1867 The size, coiling, sculpture, high hollow keel and Subfamily Tmetoceratinae Spath, 1936 characteristic complex suture are already all there (Buckman 1889, pi.A, figs 34,48). There cannot be Genus Tm etoceras Buckman, 1892 much doubt that the roots of Csernyeiceras lie in H augia, even if the two are currently still separated Tmetoceras scissum (Benecke, 1865) by a considerable faunal gap. But the very discovery (Pl.V. figs 2,3; pi.VI, fig.3; pi.VIII. fig.2.3,4) of Csernyeiceras itself has shown the danger of attaching any great weight to faunal gags. Such gaps 1865 Ammonites scissus Benecke, p,170, pl.6. fig.4 (lectotype des. are negative evidence at best and vulnerable to quite Roman 1938; lost) 1874 Am m oni/es regleyi (Tholliere MS) Dumortier, p. 119, pl.31, figs modest increases in collections, as the present example 8,9. has shown. To underline the independent phyletic 1883 Cosmoceras hollandae Buckman, p. 141. pi. 1, fig. 2a,b (lectotype), position of Csernyeiceras, we have revived the pi.2, fig.2a.b. subfamily Haugiinae. Going forward in time, it seems 1886 Sim oceras scissum (Benecke): Vacek, p .103; pi.16. figs 15-17. 1892 Tmetoceras scissum (Benecke): Buckman, p.273. pl.48. figs 1- a plausible hypothesis to see in Csernyeiceras the 10. roots of the hitherto cryptogenic family 1904 Parkinsonia (Tmetoceras)scissa (Benecke): Prinz. p. 130, pi, 16, Strigoceratidae. This was already proposed and fig.2. pi.20, fig.3 (both refigured by Geczy 1967). examined by Geczy (1966, p.84), who drew particular 1905 Tmetoceras circulare Buckman, p.clxx (type Buckman 1892, vide sup., pl.48, figs 1-3) attention to the close similarities in the characteristic 1933 Tmetoceras scissum (Benecke): Arkell, pi.33, fig.4,4a. basic plan of the septal sutures. The tall septicarinate 1964 Tmetoceras scissum (Benecke): Westermann. p.428, pi.72, figs venter of the majority of the Strigoceratidae has 1,2, always been regarded as one of their leading 1967 Tmetoceras scissum (Benecke): Geczy, p. 160, pi.35, figs 3-7; pi.64, figs 73.74, characters. Precjse details of the connection remain 1990 Tmetoceras scissum (Benecke): Callomon & Chandler, pl.l, unclear, because two plausible routes of descent are fig.la.b.

27 Discussion - Tmetoeeras is fairly common in the Tmetoeeras is dimorphic. The first example clearly to Scissum Bed and there is abundant material in the bfe demonstrated was in Alaska: T. kirki Westermann, collections. Complete, well-preserved specimens are 1964 [M] - T. tenue Westermann [m] of the Upper rather rarer, however, because of the hardness of the Aalenian. (For consistency, Westermann introduced rock as ordinarily met with. We take this opportunity anew subgeneric name Tmetoites for the microconch.) merely to illustrate some good new specimens that The macroconchs have a size-range of c.45-60 mm, have become available. the microconchs c.20-30 mm. The microconchs have The genus Tmetoeeras and its relation to other clearly-developed lappets. Both dimorphs are groups have received lengthy discussion in the past, isocostate, with minor modification of the ribbing most recently by Geczy (1967). It was, and still is, near the end of the adult bodychamber, so that maturity something of a curiosity, for it stands well apart from can be easily recognized. Except for the lappets, the any of its contemporaries both in morphology, dimorphism is thus inconspicuous. No specimens distribution and evolution. There were the usual early with lappets have so far been figured in Europe, attempts to distinguish separate species on the basis which is probably the reason why dimorphism has of morphological differences. But when material was escaped notice. We have seen fragments of abundant, as in the case of the collection from San bodychambers with well-developed lappets in the Vigilio studied by Vacek, these species all appeared Scissum Bed at Burton Bradstock, and it seems that to intergrade. Stratigraphical information indicated the dimorphism in T. scissum takes the same form as that the genus did have some range but was in T. kirki. insufficiently precise to see whether there were any The three specimens on PI.VIII appear to be systematically detectable changes with time. The microconchs of transient Aa-2. Scissum Zone. They general conclusions were that in Europe at least, the are essentially complete, as indicated by the umbilical assemblages from any one horizon were monospecific; seams, but unfortunately the actual peristomes have that the variability within one isochronous assemblage been lost. Fig.4 shows a specimen that raises several was targe, larger than tne ditterences Detween interesting questions. It has a terminal constriction successive assemblages; that the genus w'as therefore and the last five septa are strongly approximated. o f little value as biochronological guide-fossil, even There can be little doubt, therefore, that it is a complete though it had its “acme'’ in one zone, the Scissum adult. Yet the bodychamber occupies only a quarter Zone; and hence that one might as well use the one yof a whorl, compared with the half whorl that is more name, T. scissum , for the lot. usual. This must be the shortest bodychamber in an Further progress should now be possible on two ammonite yet found. Together with the simplicity of counts. Firstly, as stratigraphically precisely dated the septal suture, does this indicate a passive mode of assemblages are becoming available, the changes of life similar to that of some heteromorphs? Was the morphology with time should be reassessed. The shell only partly external? precise characterization of successive transients could Pl.V, fig.2 is somewhat younger: Aa-6, be important in correlating the Aalenian of the East Murchisonae Zone and Subzone. It appears to be a Pacific margins, from Alaska to the Andes, with the macroconch, with a broad, shallow terminal European standards. Tmetoeeras is abundant, for constriction and a simple sinuous peristome on the instance, in Alaska (Westermann 1964). We make a obverse side. It bears a strong resemblance to three of start by indicating the “vertical'1 position of English the specimens figured by Geczy (1967, pi.35, figs 3- material in the systematic nomenclature explicitly. 5), all of which are clearly also macroconchs. One of tne ways in which the Rules of Nomenclature Unfortunately, their precise age is unknown, but could allow this to be done is to treat successive transients be the same. This transient may therefore turn out to as (chrono-)subspecies within the species-group^This have a distinct and easily recognizable morphology. would however mean the introduction of new trivial?, itPI.VI, fig. y ^ x e presents a second specimen from the names that would forever be in possible conflict w ith y ^ l ower Comfavum Zone, A a-12/13, the youngest form existing names (see synonymy) of taxa of uncertain so far found in Britain. It is very similar to the one age, and vulnerable to differences of opinion between described by us previously (1990, pl.l, fig.la.b) of authors. Instead we prefer to use the existing Linnean the same age. Both are very evolute with broad ventral name T. scissum for all forms, as is the current smooth band and, by analogy, probably microconchs. practice, and to indicate the transient by an additional Tntra-subSpecmc label, that of its faunal horizon as liste< "previously (.Callomon & Chandler 1990; and CONCLUSION see Fig.l). The known range in Britain is therefore Aa-2 T o Aa-13, lower Scissum to lower Concavum The Tethyan ammonites of the Aalenian occupy a 2ones. key position in the evolutionary history of many Secondly, account must be taken of the fact that important Middle Jurassic lineages whose roots, long

28 regarded as cryptogenic, are beginning to emerge in well-preserved, but Tethyan ammonites are the Toarcian. The difficulties in past attempts to relatively rare. Persistent collecting over the years unravel these phyletic histories have been largely has however yielded enough of them to contribute stratigraphic. In the Tethys, where these ammonites significantly to our understanding of their evolution. are dominant, the successions consist largely of highly With the help of the new material described in this incomplete or condensed pelagic limestones. Fossils account, some venerable Tethyan species are now' are often sparse, poorly preserved or hard to extract. fully characterized for the first time - on the basis In extra-Tethyan Britain, in contrast, the stratigraphy of collections from Dorset. is now well understood, fossils are abundant and

ACKNOWLEDGMENTS

We are greatly indebted to David Sole (Lyme preparation of some of the specimens of Tmetoeeras. Regis) for generously making available to us some of One of us (J.H.C.) acknowledges with pleasure some the fine specimens from the Freshwater Caravan Park valuable discussions of Tethyan biostratigraphy with excavations at Burton Bradstock that he had collected Stefano Cresta (Rome), and the guidance during a and prepared. They are cited in the legends to the brief visit to San Vigilio in 1988 of Giulio Pavia plates. We also acknowledge with gratitude once (Torino) and Luigi Ambrosi (S. Ambrogio. Verona), again the enthusiastic help of Andrew G. England and who also kindly donated some specimens from his William J.E. Jones on numerous occasions in the collection. field. We thank Hans Rieber (Zurich) for the careful

REFERENCES

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29 (Hildocerataceae, Ammonitina) de la region de nordostlichen Bakony. Mitt. Jahrb. k. Ung. geol. Thouars. stratotype du Toarcien. Mem. Soc. geol. Anst., 15, 1-142, pis 1-38. France, N.S., 54; Mem. 124, 196 p., 36 pis. Q u e n s t e d t , F.A., (1886) - Die Ammoniten des schwabischen G abilly, J. & R ioult, ML, (1974) - Le Bajocien inferieur et Jura. II. Der Braune Jura, Lief, x-xiii, 441-672, pis le Toarcien superieur sur les bordures du massif 55-79. Schweizerbart, Stuttgart. Amoricain. Mem. Bur. Rech. Geol. Min.. Fr., 75, R ic h a r d so n , L., (1904) - A handbook to the geology of 385-96. Paris. Cheltenham and neighbourhood. Cheltenham, G e c z y , B.. (1966) - Ammonoides jurassiques de Csernye, Norman, Sawyer & Co., xii + 303 p., 19 pis. Montagne Bakony. Hongrie. Par tie I, R ich a rd so n , L., (1928) - The Inferior Oolite and contiguous Hammatoceratidae. Geol. Hungarica, 34, 276 p., 44 deposits of the Burton Bradstock - Broadwindsor pis. districts. Proc. Cotteswold Nat. Field Club, 23, 35- Geczy. B., 1967 - Ammonoides jurassiques de Csernye, 68, pis 2-6. Montagne Bakony, Hongrie. Partie II, excl. R ieb er . H.. (1963) - Ammoniten und Stratigraphie des Hammatoceratidae. Geol. Hungarica. 35,413 p., 65 Braun jura 6 der schwabischen Alb. pis. Palaeontographica, A122. 1-89, pis 1-8. G e m m ella r o . G.G., (1886) - Sul Dogger inferiore di Monte R o m a n , F., (1938) - Les ammonites Jurassiques et Cretacees: Giuliano (Erice). Bull. Soc. Sci. nat. econ. Palermo, essai de genera. 554 p., 53 pis. Masson, Paris. 17, 197-212. R o m a n , F. & B o y e r , P., (1923) - Sur quelques ammonites Haug, E.. (1887) - Uber die “Polymorphidae”, eine neue de la zone a Ludwigia murchisonae du Lyonnais. Ammonitenfamilie aus dem Lias. N. Jahrb.f. Min. Tray. Lab. Geol. Fac. Sci. Lyon. 4, 48 p., 9 pis. Geol. P a ld o n t 1887, ii, 89-163, pis 4.5. S en io r , J.R.. (1977) - The Jurassic ammonite Bredyia Hillebrandt, A. v o n & Westermann, G.E.G.. (1985) - Buckman. Palaeontology, 20, 675-93. pis. 81-4. Aalenian (Jurassic) ammonite faunas and Zones of S pa th . L.F.. (1928) - Revision of the Jurassic cephalopod the southern Andes. Zitteliana, 12, 3-55. pis 1-10. fauna of Kachh (Cutch). Palaeont. Indica, N.S., 9, H o f f m a n n , G., (1913) - Stratigraphie und Ammoniten- Mem. 2, pt. ii, 73-161, pis. 8-19. Fauna des unteren Doggers in Sehnde bei Hannover. S t u r a n i, C., (1964) - La successione delle faune ad Schweizerbart, Stuttgart, vi + 202 p., 18 pis, ammoniti nelle formazione mediogiurassiche delle H y a tt, A., (1867) - The fossil cephalopods of the Museum Prealpi Venete Occidentali (regione tra il Lago di of Comparative Zoology. Bull. Mus. comp. Zoo!., Garda e la Valle del Brenta). Mem. 1st. Geol. Mineral. Harvard, 1, 71-102. Univ. Padova, 24, 63 p., 6 pis. Im la y , R.W., ( 1973) - Middle Jurassic (Bajocian) U r eta G il . M.S., (1983, 1985) - Bioestratigrafia y ammonites from eastern Oregon. U.S. Geol. Survey. paleontologia (Ammonitina) del Aaleniense en el Prof. Paper 756. iv + 100 p., 47 pis. chart. sector noroccidental de al Cordillera Iberica. L in a r es. A. & S a n d o v a l , J.. {1986) - Malladaites nov. gen. Memoria Doct. Ciencias geol., Univ. Complutense et Spinammatoceras (Hammatoceratidae, Madrid, viii + 452 p., 34 pis (1983); Tesis Doctoral Ammonitina) de l’Aalenien de la zone subbetique, 158/85, Universidad Complutense de Madrid sud de l'Espagne. Geobios, 19, 207-24, pis 1,2. (printed, 1985). L in a r es, A., U r e t a , M.S. & S a n d o v a l , J., (1989) - Vacek, M.. (1886) - Uber die Fauna der Oolithe von Cap S. Comparison between the Aalenian ammonite Vigilio. Abh. k. k. geol. Reichsanst. Wien. 12, no. 3, associations from the Betic and Iberian Cordilleras: 57f 11-212[156], pis 1-17. elements of correlation. In: Rocha. R.B. & Zeiss, W est er m a n n , G .E .G ., (1964) - The ammonite fauna of the A., eds, 2nd International Symposium on Jurassic Kialagvik Formation at Wide Bay, Alaska Peninsula. Stratigraphy, Lisbon 1987, 193-208, pis 1.2. Part I: Lower Bajocian (Aalenian). Bull. Amer. M erla, G., (1933) - Ammonita Giuresi dell'Appennino Paleont., 47, 329-503, pis 44-76. Centrale. II: Hammatoceratidae. Palaeont. Italica, W est er m a n n , G .E .G . & R icca rd i, A.C., (1972) - Middle 34, 1 -29, pis 1-4. Jurassic ammonoid fauna and biochronology of the N e u m a y r , M.. (1871) - Jura-Studien. V. Der penninische Argentine-Chilean Andes. Part I: Hildocerataceae. Klippenzug. Jahrb. k. k. geol. Reichsanst. Wien, 21, Palaeontographica, A140, 1-116, pis 1-31. 451-536. Westermann, G.E.G. & R ic c a r d i, A.C., (1982) - Ammonoid O ppel, A., (1856) - Die Juraformation Englands, Frankreichs fauna from the early Middle Jurassic of Mendoza und des sUdwestlichen Deutschlands. Lief, i-v, 1- Province, Argentina. Jl Paleontology, 56, 11-41, 438. Stuttgart. pis 1 -6. P rinz, G., (1904) - Die Fauna der alteren Jurabildungen im

30 EXPLANATION OF THE PLATES

All figures natural size except where stated. Asterisks mark onset of bodychamber, where visible.

Plate I

Figs 1,3. - Erycites cf .fallifax Arkell. la.b: adult, test largely preserved with umbilical seam indicating former extent of bodychamber of 0.75 whorl, estimated maximum diameter 96 mm (RBC 524, David Sole Coll.). 3a.b: nucleus (RBC 525). Both Scissum Bed, Freshwater Caravan Park, Burton Bradstock. Fig.2. - Erycites fallifax Arkell. Complete adult, internal cast, with part of terminal constriction and peristome preserved on the venter; somewhat distorted, the bodychamber displaced obliquely outwards (JHC 1240, leg. Luigi Ambrosio). Topotype, Scissum Bed. Capitello quarry. Cap San Vigilio. Fig.4. - Erycites aff. exulatus sp.nov. Complete phragmocone. umbilical seam indicating 0.75 whorl former bodychamber, estimated maximum diameter 150-160 mm (RBC 525). Scissum Bed. near top, Manor Farm, Burton Bradstock.

Plate II

Figs 1,2. - Erycites exulatus sp.nov. la.b.c: paratype I. complete adult with test and peristome preserved. A L. opal in uni is embedded in the matrix (RBC 527, David Sole coll.). 2a,b; holotype. nearly complete adult, test preserved, peristome partly preserved on the obverse side as indicated, transposed. Another L. opalinum embedded in the matrix. (RBC 528). - Both specimens from the Scissum Bed, at Freshwater Caravan Park and Manor Farm respectively.

Plate III

Figs 1,2. - Hammatoceras lorteti (Dumortier). 1: complete phragmocone with test preserved (RBC 529. David Sole coll.). For side view, see pi.IV. fig.2. Scissum Bed. Freshwater Caravan Park. Burton Bradstock. 2: Dumortier's original figure of the holotype, side view (1874, pi.54, fig.l): for section, see pi.VI, fig.4. Condensed ironstones. La Verpilliere (Isere), 28 km ESE of Lyon.

Plate IV

Fig.la.b. - Planammatoceras planinsigne (Vacek). Complete phragmocone, internal cast, x 0.76. Note remains of high, sharp keel at point of emergence of last whorl (RBC 530). Scissum Bed, Freshwater Caravan Park. Fig.2. - Hammatoceras lorteti (Dumortier). Ventral view of specimen on pi.Ill, fig.l.

Plate V

Fig. la.b. - Hammatoceras cf. or aff. procerinsigne Vacek. Complete adult with test preserved on inner whorls (RBC 531. David Sole coll.). Scissum Bed, Freshwater Caravan Park, Burton Bradstock. Fig.2a,b. - Tmetoeeras scissum Benecke Aa-6 [MJ. Complete adult with peristome (RBC 509). Quarry Hill, Chideock, bed 4 (Callomon & Chandler 1990, p.91, fig.2), Murchisonae Zone and Subzone, horizon of Ludwigia patellaria (Aa-6). Fig.3a,b. - Tmetoeeras scissum Benecke Aa-2 [M?]. Complete adult with simple peristome on obverse side. (RBC 510). Locality and horizon as fig.l.

Plate VI

Fig.l. - Csernyeiceras verpillierense (Roman & Boyer). Complete phragmocone, x 0.76, test partly preserved (RBC 341). Scissum Bed. Freshwater Caravan Park, Burton Bradstock. Fig.2a,b. - Planammatoceras tenellum sp.nov. [m], Holotype, complete phragmocone, internal cast (RBC 533). Horn Park, bed 3c. Murchisonae Zone and Subzone, horizon Aa-7 (Callomon & Chandler 1990, p.92, fig.3). Fig.3a.b. - Tmetoeeras scissum (Benecke )Aa-l2ll3 [m?J. Nearly complete adult, former extent deduced from umbilical seam, test preserved, no sutures visible (RBC 532). Horn Park, bed 5c. Concavum Zone and Subzone. Fig.4. - Hammatoceras lorteti (Dumortier). Dumortier's figure of the cross-section of the holotype: cf. pi.Ill and pi.IV, fig.2.

31 Plate VII

Fig.la-c. - Csernyeiceras verpillierense (Roman & Boyer). Complete phragmocone, x 0.76. test partly preserved (RBC 534). Note the razor-sharp keel. Scissum Bed. Freshwater Caravan Park, Burton Bradstock.

Plate VIII

Fig.la-c. - Csernyeiceras verpillierense (Roman & Boyer). Septate inner whorls, test partly preserved (RBC 535. David Sole coll.). Note the hint of strigation on the whorl-side (la), the high, sharp keel at the point of emergence of the exposed whorl, and the broad, tabulate venter on the internal cast made by the floor of the hollow keel (lb. lc, bottom). The second ammonite in the matrix is a Cylicoceras (Costiceras) subcostosum (Buckman) [m], Scissum Bed. Freshwater Caravan Park, Burton Bradstock. Figs 2-4. - Tmetoceras scissum (Benecke) Aa-2 [m]. Three complete adults. Note the very short bodychamber in 4a (RBC 512, David Sole coll.). (2a,b: RBC 514; 3a,b: RBC 517). Locality and horizon as fig.l.

32 Plate I

All figures natural size except where stated. Asterisks mark onset of bodychamber, where visible. Figs 1,3. - Erycites cf .fa l l i f a x Arkell. la.b: adult, test largely preserved with umbilical seam indicating former extent of bodychamber of 0.75 whorl, estimated maximum diameter 96 mm (RBC 524, David Sole Coll.). 3a.b: nucleus (RBC 525). Both Scissum Bed, Freshwater Caravan Park, Burton Bradstock. Fig.2. - Erycites fallifax Arkell. Complete adult, internal cast, with part of terminal constriction and peristome preserved on the venter; somewhat distorted, the bodychamber displaced obliquely outwards (JHC 1240, leg. Luigi Ambrosio). Topotype, Scissum Bed. Capitello quarry. Cap San Vigilio. Fig.4. - Erycites aff. exulatus sp.nov. Complete phragmocone. umbilical seam indicating 0.75 whorl former bodychamber, estimated maximum diameter 150-160 mm (RBC 525). Scissum Bed. near top, Manor Farm, Burton Bradstock. Plalc II

All figures natural size except where stated. Asterisks mark onset of bodychamber, where visible. Figs 1,2. - Erycites exulatus sp.nov. la,b,c: paratype I, complete adult with test and peristome preserved. A L. opalinum is embedded in the matrix (RBC 527, David Sole coll.). 2a,b: holotype, nearly complete adult, test preserved, peristome partly preserved on the obverse side as indicated, transposed. Another L. opalinum embedded in the matrix. (RBC 528). - Both specimens from the Scissum Bed, at Freshwater Caravan Park and Manor Farm respectively. Plalc 111

All figures natural size except where stated. Asterisks mark onset of bodychamber, where visible. Figs 1,2. - Hammatoceras lorteti (Dumortier). 1: complete phragmocone with test preserved (RBC 529, David Sole coll.). For side view, see pi.IV, fig.2. Scissum Bed, Freshwater Caravan Park, Burton Bradstock. 2: Dumortier’s original figure of the holotype, side view (1 874, pi.54, fig. 1): for section, see pi.VI, fig.4. Condensed ironstones, La Verpilliere (Isere), 28 km ESE of Lyon. Plalc IV

All figures natural size except where stated. Asterisks mark onset of bodychamber, where visible. Fig.la,b. - Planammatoceras planinsigne (Vacek). Complete phiagmocone, internal cast, x 0.76. Note remains of high, sharp keel at point of emergence of last whorl (RBC 530). Scissum Bed, Freshwater Caravan Park. Fig.2. - Hammatoceras lorteti (Dumortier). Ventral view of specimen on pi.Ill, fig.l. Plate V

All figures natural size except where stated. Asterisks mark onset of bodychamber, where visible. Fig. la.b. - Hammatoceras cf. or aff. procerinsigne Vacek. Complete adult with test preserved on inner whorls (RBC 531. David Sole coll.). Scissum Bed, Freshwater Caravan Park, Burton Bradstock. Fig.2a,b. - Tmetoeeras scissum Benecke Aa-6 [MJ. Complete adult with peristome {RBC 509). Quarry Hill, Chideock, bed 4 (Callomon & Chandler 1990, p.91, fig.2), Murchisonae Zone and Subzone, horizon of Ludwigia patellaria (Aa-6). Fig.3a,b. - Tmetoeeras scissum Benecke Aa-2 [M?]. Complete adult with simple peristome on obverse side. (RBC 510). Locality and horizon as fig.l. Plalc VI

All figures natural size except where stated. Asterisks mark onset of bodychamber, where visible. Fig.l. - Csernyeiceras verpillierense (Roman & Boyer). Complete phragmocone, x 0.76, test partly preserved (RBC 341). Scissum Bed. Freshwater Caravan Park, Burton Bradstock. Fig.2a,b. - Planammatoceras tenellum sp.nov. [m], Holotype. complete phragmocone, interna) cast (RBC 533). Horn Park, bed 3c. Murchisonae Zone and Subzone, horizon Aa^7 (Callomon & Chandler 1990, p.92, fig.3). Fig.3a.b. - Tmetoceras scissum (Benecke) Aa-12/13 [m?J. Nearly complete adult, former extent deduced from umbilical seam, test preserved, no suturesVisible (RBC 532). Horn Park, bed 5c. Concavum Zone and Subzone. Fig.4. - Hammatoceras lorteti (Dumortier). Dumortier's figure of the cross-section of the holotype: cf. pi.Ill and pi.IV, fig.2. Plate VII

All figures natural size except where stated. Asterisks mark onset of bodychamber, where visible. Fig.la-c. - Csernyeiceras verpillierense (Roman & Boyer). Complete phragmocone, x 0.76, test partly preserved (RBC 534). Note the razor-sharp keel. Scissum Bed, Freshwater Caravan Park, Burton Bradstock, Plalc VIII

All figures natural size except where stated. Asterisks mark onset of bodychamber, where visible. 40 Fig.la-c. - Csernyeiceras verpillierense (Roman & Boyer). Septate inner whorls, test partly preserved (RBC 535, David Sole coll.). Note the hint of strigation on the whorl-side (la), the high, sharp keel at the point of emergence of the exposed whorl, and the broad, tabulate venter on the internal cast made by the floor of the hollow keel (lb. lc, bottom). The second ammonite in the matrix is a Cylicoceras (Costiceras) subcostosum (Buckman) [m], Scissum Bed. Freshwater Caravan Park, Burton Bradstock. Figs 2^4. - Tmetoceras scissum (Benecke) Aa-2 I'm]. Three complete adults. Note the very short bodychamber in 4a (RBC 512, David Sole coll.). (2a,b: RBC 514; 3a,b: RBC 517). Locality and horizon as fig.l.