The Graphoceratid Ammonite Succession in the Aalenian and Lowest Bajocian (Middle Jurassic) at Horn Park, Dorset, UK ROBERT B

Home , Graphoceras, Hyperlioceras, Ludwigia (ammonite)

The Graphoceratid Ammonite Succession in the Aalenian and lowest Bajocian (Middle Jurassic) at Horn Park, Dorset, UK ROBERT B. CHANDLER Riddlesdown High School, Purley, Surrey, CR8 lEX Summary In 1990 Callomon and Chandler set out a scheme of 16 faunal horizons for the Aalenian-Lower Bajocian of Dorset and Somerset based principally on graphoceratid ammonites. One locality, Horn Park, stands apart in displaying strata from almost all the horizons identified in that work. Yet little material from it has ever been figured. Here a section is given together with exhaustive tables of existing nominal morphospecies collected at each level and with figures that allow the variability of the successive, probably in most cases, monobiospecific assemblages to be assessed. A revised generic classification of the Graphoceratidae is presented.

them precludes almost any satisfactory discussion of phyletic relationships and hence of the overall evolution The highly discontinuous, condensed and rapidly of the group. varying development of the Inferior Oolite in southern England was first perceived by S.S. Buckman (e.g. 1891, The biostratigraphy of the Graphoceratidae has now 1893, 1910) during his attempts to correlate sections by been rather well documented, for example by Rocha et means of ammonites. Leading amongst these in al. (1990), Henriques (1992; et al. 1994) in Portugal; the Aalenian part of the succession are the Linares and Sandoval (1990) in Spain, Sadki (1994) in Graphoceratidae, including such well known genera as Morocco. In Britain, Morton (1990; 1994) and Morton Leioceras, Ludwigia, Brasilia, Graphoceras and and Hudson (1995) have described the succession in Hyperlioceras. Scotland and compared it with Dorset (Morton and Chandler 1994). In Dorset it is represented in terms of An enormous number of these ammonites have been a succession of faunal horizons, the modern successors described over the years. The first extensive treatment to Buckman's hemerae, based on the closest-spaced suc- was that of the collections made by the Buckmans in cession of distinguishable faunal assemblages Dorset, in S. S. Buckman's Monograph of the Ammonites (Callomon and Chandler 1990; 1994, Callomon 1995; of the Inferior Oolite Series (1887-1907). Descriptions of Callomon and Cope 1995; Chandler and Sole 1995). A equally rich faunas in other parts of Europe soon fol- full list of the fauna along with figures of characteristic lowed, notably in works by Hoffmann (1913), Althoff ammonites on which the scheme is based has not so far (1940) and Spiegler (1966) from northern Germany; been published. It is now possible to pinpoint the exact Horn (1909) and Rieber (1963) for southern Germany; horizon from which the majority of Buckman's grapho- Contini (1969) for eastern France; Geczy (1967) for ceratids came, based on large new collections, number- Hungary; and Ureta (1983) for Spain. ing hundreds of specimens, made carefully level by level Yet despite this profusion of described material, at the classical locality of Horn Park in southern Dorset. many uncertainties remain. Firstly, the majority of They include perfect matches of the types of almost all existing nominal species were based on type series of Buckman's nominal species, types whose precise whose horizons are not precisely known. This applies horizons were mostly hitherto unknown and which in particularly to Buckman's species, for he was discover- some cases remained to be selected from syntype series. ing and working out the stratigraphical refinements These findings allow a revised classification to be pre- hand in hand with the description of the material over a sented, based now on accurately collected new material. period of many years. His earlier descriptions therefore In 1990 the known ammonite faunal horizons num- lacked the precision of his subsequent stratigraphical bered in total 16 for the Aalenian and 20 for the Lower knowledge. Elsewhere, few accounts were based on Bajocian. Of these 36, 14 of the Aalenian and two of the stratigraphical evidence of comparable precision at all, Lower Bajocian can be seen at Horn Park and 15 of relying heavily on material in old collections in the them contain Graphoceratidae. Subsequent addition of museums. Secondly, previous classifications were further newly discovered horizons (Callomon 1995) has almost always in conventional, purely morphological not so far necessitated any modification in the Aalenian. terms. It is therefore very difficult to assess the true, natural, relationships between existing nominal species: The Inferior Oolite has been quarried at Horn Park to distinguish differences representing merely morpho- intermittently for many years. Previous descriptions logical variation within single biospecies from differ- were given by Richardson (1928), Bomford (1948), and ences of age, and hence from genuine evolutionary Senior, Parsons and Torrens (1970), and were sum- development. Such ambiguities have in the past led to marised by Parsons in Cope (1980). Their bed-number- both taxonomic and stratigraphical misidentifications, ing is retained here, modified by further subdivision of often locked in circular argument, and failure to resolve some of the beds in the lower part of the succession Murchisonae-Concavum Zones. The top is planed off

@ by a slightly unconformable erosion-plane of Bajocian @ Bathonian age, Sauzei Zone, but extension of the working has o revealed the preservation locally of the lowermost part @ of the Discites Zone. The succession will be described in order of distinguishable faunal assemblages. The level of each of these assemblages constitutes a 'faunal horizon' in the sense that has become widely used in recent times (Callomon 1995). The faunal content of a horizon may be regarded for all practical purposes as representing the sampling of an instant in time; horizons are therefore not neces- sarily contiguous subdivisions of chronostratigraphical Zones or Subzones, and will in general be separated by faunal gaps equivalent to time-durations of unknown extent. Thus, faunal horizons at other localities may well come to be inserted between those at Horn Park. (The time-equivalent of a faunal horizon thus closely resembles one of Buckman's 'hemerae', shorn of all con- notations relating to ranges or acmes of anyone particular species.) The assemblage of Graphoceratidae from each horizon are listed in a set of faunal tables. As the purpose is to classify English biostratigraphy, no attempt is made to carry out a systematic revision with extensive synonymies, which would in any case be a Aa-10 major undertaking well beyond the scope of the present Aa-9 work. The species listed in the tables therefore include Aa-8 as many of Buckman's nominal (morpho-) species as can be identified in the faunas. Nominal species of @ Aa-7 other authors are added where no suitable match can be (9 Aa-5 found in Buckman's work, together with a reference to at least one figure and its type status, if any, There may @> Aa-4 be additional notes as appropriate. Many of Buckman's species are also type-species of nominal genera, and @ Aa-3 these will be indicated by asterisks. In addition, the fol- lowing abbreviations are used: Mon.: Buckman 1887-94, @ Aa-2 Monograph of the Ammonites of the Inferior Oolite Series; Supp.: supplement, ibid., 1898-1907; T A: Buckman 1909-30, Type Ammonites, vols.III-VII; HT, holotype; HT (mon), id., by monotype; ST, syntype; LT, lectotype; TT, topotype; CT, chorotype (same horizon, different but neighbouring locality). [M], [m]: macro/micro- Figure 1: Diagrammatic section through the Inferior Oolite at Horn Park, near Beaminster conch, respectively. R, 0, C,: rare, occurs, common. +: probable horizon from which the type came. Generic (Chandler 1982; Callomon and Chandler 1990). The names cited in square brackets are those of nominal most recent account of the present quarry (G.R. ST genera created by Buckman and regarded here as junior 458022) is that of Callomon (in Callomon and Cope synonyms. Names placed in round brackets are retained 1995). The standard zonal classification followed here is as subgenera. that of Callomon and Chandler (1990; 1994). A weath- Each horizon is labelled with the name of one of its ering profile of the section is reproduced in Fig. I. nominal species, preferably one of which it is the type-horizon; and if there are more than one of these, The lowest bed with ammonites at Horn Park, bed 2, the nomenclaturally senior among them, which would forms the base of the quarry and is not worked. It survive if the others were put in synonymy. belongs to the Scissum Zone; and because it has yielded rather little material and is much better known else- For ease of reference, successive horizons will be where (e.g. Bridport: Callomon and Chandler 1994), it labelled and numbered according to the practice adopt- will not be described here in detail. The main part of the ed by Callomon and Chandler (1990), with each horizon succession consists of beds 3-5 and includes the Horn bearing a letter code followed by a number (Aa- and Bj- Park Ironshot (Parsons 1980), which spans the for Aalenian and Bajocian respectively). In addition to graphoceratid ammonites, many other Chandler (1990) and Callomon and Cope (1995) and important species have been recorded from Horn Park. will not be repeated here. These have been already listed by Callomon and

Standard zonation Zones I Subzones Bj-3 Hyperlioceras subsectum I =eo: I "0 Q Bj-2b Hyperlioceras rudidiscites ";- I t Discites Bj-2a Hyperlioceras walkeri =~•• I I ~ Bj-l I Hyperlioceras politum I ~ Aa-16 Euhoploceras acanthodes I I Formosum Aa-15 Graphoceras formosum I I Concavum Aa-14 Graphoceras concavum I t Concavum Aa-13 I Graphoceras cavatum r Aa-12 Bras,ilia decipiens I 1 Gigantea Aa-ll I Brasilia gigantea I Aa-lO I Brasilia bradfordensis, similis [ Bradfordensis Aa-9 Brasilia bradfordensis, baylii Bradfordensis I J Aa-8 I Brasilia bradfordensis, subcornuta , Aa-7 I Ludwigia murchisonae l - Murchisonae Aa-6 Ludwigia patellaria I J Murchisonae Obtusiformis Aa-5 1 Ludwigia obtusiformis I Haugi Aa-4 1 Ancolioceras opalinoides ( Aa-3 Leioceras bifidatum 1 I Scissum Aa-2 I Leioceras lineatum r Aa-l I Leioceras opalinum , Opalinum

Note: the labelling of some horizons with additional letters a, b, c... reflects the insertion of further horizons recognised since the first list was drawn up in 1990, so as not to have to change the main framework of numbering introduced in that list. The letters imply no reduction or other inequality of rank and importance . occur at the centre of variability here; but the precise age of the lectotype is not certain. Some further species stand apart, and are here AALENIAN placed in the genus Cylicoceras, that have strong ribbing Scissum Zone and retain a compressed morphology and relatively Bed 2: Limestone, somewhat sandy, massive, hard; complex suture. They are presumably close relatives of on weathering splits at a parting into two compo- Staufenia, of which the earliest representive Staufenia nents: sinon already occurs here but is very rare. A number of -2a: (Aa-2) massive, white, few fossils, shells with Cylicoceras bear a striking resemblance to this species test preserved. .,,0-40 m (cf. Cylicoceras crassicostatum (Rieber 1963)) but lack the -2b: (Aa-3) somewhat argillaceous, heavily biotur- characteristic, much simplified suture of the German bated, burrows with ochreous infill weathering into type specimen of Staufenia sinon (Bayle 1878, pl.83, fig. cavernous pockets. Highly fossiliferous: very large 1, LT designated. Rieber 1963, 40) and of much other bivalves, including Lima sp., Ceratomya sp., and soli- central European material. Presumably Cylicoceras and tary corals, Montlivaltia delabechi Tomes. ...0·15 m Staufenia share a common ancestor, the central - Sharp boundary; planed erosion surface, base of European population evolving by development of a sim- quarry - ple suture and rare examples finding their way into Murchisonae Zone British waters. Bed 3: Limestone, sandy, more or less ferruginous, is regarded here as the first of the bioturbated, divisible into three courses separated Ludwigia by irregular clay partings: Graphoceratinae and is almost certainly a direct descen- dant of broad, strongly ribbed Cylicoceras, from which Haugi Subzone Ludwigia had already started to differentiate in the -3a: (Aa-4) The Ancolioceras Bed, in part of upper Scissum Zone (cf. Ludwigia praecursor Rieber Richardson (1928-30,41). Limestone, light yellow to 1963, p.66 and Chandler unpublished). Ludwigia is rep- grey, variably ferruginous, hard, micro-oolitic in resented in Aa-4 by ammonites centered on L. parts, echinodermal, bioturbated and heavily bur- rowed, the burrows mainly vertical, filled with [Cosmogyria] [*] obtusa (Buckman, 1899) (non Amm. brown limonitic marl. Many fossils: large bivalves, murchisonae obtusus Quenstedt 1846, nec Amm. obtusus J. decalcified; solitary corals; ammonites preserved as Sowerby 1817); LT Quenstedt, pl.7, fig.l2, designated. internal moulds of bodychambers, inner whorls Rieber 1963 (as 'HT'), lost; = L. haugi Douville 1885 crushed, replaced by marl. .,,0·30 m (LT: Quenstedt 1849, pI. 7, fig.l2, designated Geczy The Graphoceratid fauna consists of (i) Leioceras, 1967, p.l90; from Aalen, lost); includes C. obtusa including forms persisting unchanged from below Buckman 1899, Supp. p.53, pIA, figs.l0-12. (Cypholioceras), fine to moderately strongly ribbed oxy- The macroconchs of Ludwigia are medium-sized to cones with a relatively complex suture; (ii) Cylicoceras, large, with strong ribbing which is projected forward on with stouter whorls and stronger ribbing; (iii) Staufenia, the venter. Coarse-ribbed forms tend to have stout similar to the latter but with a simplified suture. As con- quadrate whorl-sections, while smoother ones are siderable doubt still exists concerning the phylogeny of Platyconic. Specimens very similar to those from cen- this group a separate generic name is retained here for tral Europe occur in bed 3a but there are important it. Finally, (iv) Ludwigia appears in abundance. differences: in particular the _absence of very broad, The macroconchs within each group grade into one strongly-ribbed forms suggest that the Dorset fauna another and give the impression of being merely vari- may represent a slightly different horizon. ants of single biospecies. In the Leioceratinae, Leioceras - undulating clay parting - and Cylicoceras are distinct, recent collecting showing Obtusiformis Subzone this already to be the case back in the early Aalenian. It -3b: (Aa-S) Limestone, as below, softer, echinoder- confirms Rieber's (1963), Contini's (1969-70) and mal packstone with occasional buff ooliths; olive or Callomon and Chandler's (1994) findings that two khaki-grey but whitish and hard near top. Many entirely separate dimorphic groups exist side by side. large decalcified bivalves; ammonites rarer and pre- Ancolioceras has recently been found elsewhere in served as internal moulds. Bioturbated with voids, south Dorset (Chandler, unpublished field notes) asso- burrows and limonitic pockets. ".0·30 m ciated with a typical Leioceras comptum assemblage. It The appearance of large smooth discoidal Staufenia can be shown probably to have evolved from Leioceras sehndensis is cryptogenic in Dorset.The species is very (Cypholioceras) by strengthening of the ribbing and a shorr-ranging, so far only recorded from Aa-5. Exact decrease in the umbilical diameter. The earliest avail- matches are possible with material from central Europe able name would be Ancolioceras opalinoides (Mayer (Chandler 1982) and records of the species have now 1864) (LT Ammonitesmurchisonae acutus Quenstedt 1856, been confirmed elsewhere in Dorset (Chandler, unpub- pI. 46, figA, refigured 1886, pI. 59, fig.5; designated. lished field notes) associated with an otherwise identi- Rieber 1963, 41), for specimens like the lectotype also cal fauna. Murchisonae Subzone ed, with ooliths gathered into clouds or suspended in -3c: (Aa-7) Craterospongia Bed: Hard grey lime- patches of micrite. Divisible into five parts. stone with a few ooliths; many large bivalves, echin- Bradfordensis Zone, Gigantea Subzone oderm debris, large sponges (Craterospongia sp.) on -Sa: (Aa-ll) Limestone, very hard, heavily biotur- the upper surface. Heavily bioturbated with burrows bated, reddened in the lower part with small red filled by red limonitic marl. Ammonites preserved as ooliths, grading upwards into lighter red softer stone internal moulds, occasionally calcified. ...0·15 m with larger ooliths. The bed is divisible into two The Ludwigia fauna is divisible into two groups. In one, horizons of almost identical age. ...0·20 m the typical L. murchisonae, the ribbing abuts the keel at This level is known locally as the 'Dinner Plate Bed', almost 900- In the other, ancestral prosiradiate ribbing is after the abundant, perfectly preserved, large Brasilia maintained as in typical L. haugi. Intermed-iates do occur gigantea macroconchs which lie almost side by side in it. but the appearance of this morphological feature is an Most are fairly evolute, showing variability of inflation, important tool for the recognition oflate forms of the genus. ribbing and size. Very large intact Pleurotomaria sp. are Microconchs are relatively abundant compared with the not uncommon. preceding bed. The earliest available name is L. murchisonae (Sowerby 1827) whose holotype is at the centre of the range -Sb: (Aa-ll) A bed consisting of much broken shell debris, more coarsely oolitic than below. The of variability. First members of the genus Brasilia occur here ammonite fauna is identical to that of Sa. ....0·05 m and intergrade with Ludwigia: the delimitation of these two -mud seam- morphogenera is to a degree subjective. - undulating parting - -Sc: Fairly soft yellow bioturbated ironshot stone with abundant large brown ooliths. Divisible into Bradfordensis Zone, Bradfordensis Subzone two parts based on fossil content. Many of the fossils Bed 4: Limestones, hard, biodetrital, divisible into are coated by red limonite powder, which also occurs in three horizons. muddy pockets throughout the lower part of the bed. -4a: (Aa-8) Limestone, rather sandy, sparingly fer- -Sc(i): (Aa-12) The horizon is characterised by abun- ruginous, Craterospongia spp. at the base. Many dant very large Brasilia decipiens (up to diameter 0-40 ammonites, mainly as sandy body-chambers, the m). Brasilia and Graphoceras occur in roughly equal inner whorls replaced by limonite. ...0·30 m proportions. Brasilia [PaquieriaJ floccosa (Buckman The fauna contains Brasilia which is now dominant, 1904) occurs here with an unmistakable discoidal incorporating some morphotypes that have been morphology and fine falcoid ornament. A prominent ascribed to Ludwigia by some authors, e.g. Geczy (1967). level ofCtenostreon occurs in a rather soft, yellow rot- ted stone near the base. ...0·05 m This is the type horizon of Brasilia bradfordensis, although Ludwigia remains common. Concavum Zone & Subzone -Sc(ii): (Aa-13) Ironshot oolite as below, harder, con- -4b: (Aa-9) Limestone, hard, similar to that below, taining blue-centered micritic pockets. ...0·10 m sandy, grading upwards into pale grey densely oolitic limestone. ...0·15 m In the early forms of Graphoceras, the ancestral fal- Brasilia dominates and shows a marked size increase coid ribbing of Brasilia is retained but strengthened. All from the subadjacent horizon. Rare Ludwigia persists. have a compressed morphology, marked fastigate venter Microconchs have similar variability to those below. and a rather poorly differentiated keel. - mud p.arting- ·4c: (Aa-lO) Pale grey densely oolitic limestone, the buff ooliths non-limonitic Very well-preserved white -Sd: Limestones divisible into two horizons, both calcified ammonites with brown shells common near with abundant ammonites. the top, also an abundant bivalve and gastropod -Sd(i): (Aa-14) Coarse, hard, blue ironshot oolite, fauna. ...0·10-0· 20 m marly and rather yellow in the upper part .... 0·08 m An assemblage of dominant Brasilia with a high pro- This is the type horizon of Graphoceras concavum. portion of fine-ribbed or striate forms and very scarce Specimens are compressed, involute and ornamented Ludwigia. Microconchs are common and display rela- with sinuous ribs that curve strongly forward on the tively wide variability of ribbing and inflation. Many venter. The whorl-section is keeled and acute on the fine specimens occur with intact lappets. inner whorls, becoming fastigate on the bodychamber. The umbilicus is circular with a concave umbilical wall. This is the first horizon at which the sediment is pre- dominantly calcareous. Accordingly the preservation of Variants occur that are more evolute, have falcate ribbing, prominent keels and wider venters: they are the ammonites is now much better. The chambers of the ammonites are hollow and lined with coarse white spar. already suggestive of Hyperlioceras. -rather flat parting- Concavum Zone, Formosum Subzone Bed 5: The Horn Park Ironshot Bed (Parsons in -5d(ii): (Aa 15) Ironshot oolitic limestone, more Cope 1980): Brown to yellow ironshot oolite, in grey, reddened than below, the ooliths of soft limonite often ferruginous limestone matrix, the ooliths which weather out, leaving holes. ...0·06 m becoming larger towards the top. Stronglv bioturbat- -rather flat. ?n1:mecl Snrfllf:f'- -Se: Hard, reddened, coarsely oolitic limestone, Genus Leioceras Hyatt, 1867 [=Lioceras Bayle 1878, thinning eastwards, heavily bioturbated with fossils obj.] at all angles. The upper surface is planed off to pro- duce a spectacular erosion plane. Cypholioceras S.S.B., 1899 [M]: Medium sized, sub- oxyconic, moderately evolute, smooth or fine-ribbed Locally in parts of the quarry, an upward continua- macroconchs persisting unchanged from the Opalinum tion of the bed can be found (Fig.l). There is no marked Zone. stratigraphic break or change in lithology but this upper part sees the first appearence of a fauna containing rel- Ancolioceras S.S.B., 1899 [M] [Manselia S.S.B., atively common Hyperlioceras macroconchs. Thus the 1899]. This has stronger ribbing than Leioceras bed is here divided into two parts: (Cypholioceras) and is more involute. The whorl section is oxyconic. The entire group retains a suture-line close -Se(i): (Aa-I6) Reddened oolitic stone, heavily bioturbated and containing marly burrows at all angles. to that of the ancestral Leioceratids of Aa-l. In Bed 3a Ammonites common but difficult to identify the centre of variability for the population is at A. opali- because of heavy surface encrustations. ...0·10 m noides (sensu lato). Graphoceratid ammonites are generally rarer than As elsewhere in the Graphoceratidae, the retention in the beds below. The majority show a broadening of of the separate generic names for what are almost cer- the venter which has rather rounded shoulders. The tainly only successive stages of a single lineage is a mat- keel is now upright and more prominent. Ribbing is ter of historically-determined convention and nomen- fine to coarse, sometimes slightly bunched and strong- clatural convenience in labelling significantly differing ly falcate. There is a marked increase in the abundance morphologies. Similar remarks apply to the labelling of of sonninids (Euhoploceras acanthodes). dimorphs. The generic names could therefore be sub- sumed as subgeneric names within senior generic LOWER BAJOCIAN names with which they are coordinate, i.e. Leioceras (L. Discites Zone s.s.) [m], L. (Cypholioceras) [M] and L. (Ancolioceras) [M]. -Se(ii): (Bj-I) Heavily bioturbated, corroded, coarse, The last members of the Leioceratinae persists as reddened oolite with abundant fossils, but many indeter- Ancolioceras high into the Murchisonae Zone or even the minate and in poor condition. The upper centimetre is a lowest Bradfordensis Zone laminated irony crust with ammonites planed through by the erosion surface. In places this surface lies Leioceras Hyatt, 1867 [m]: Small finely ribbed forms below a thin mud seam ....0·10 m with lappets. These microconchs range unchanged from Here occur the first relatively common members of Aa-l into Aa-3. the genus Hyperlioceras. The earliest forms (Darellia Subfamily Staufeniinae, Maubeuge 1950 [M], Braunsina [m]) still bear a strong resemblence to Graphoceras into which they intergrade, but in the Genus Cylicoceras S.S.B.l899 [M] [Hyattina S.S.B., majority of cases they possess a characteristic high 1899; Geyerina S.S.B., 1913 = Geyeria S.S.B., 1899 (obj.) prominent keel. (non Buchecker 1880).]. The entire group has rather inflated whorls and is Classification of the Graphoceratidae often more evolute than Ancolioceras. Its members have A suggested generic organisation of the relatively complex suture lines and strong ribbing Graphoceratidae is presented below. Generic names which projects forward on the'venter. They stand apart placed in square brackets are nominal genera mostly from the other Leioceratids and clearly evolve from an created by Buckman and regarded here as junior syn- earlier stock, possibly C. undatum of the Upper onyms. The aim is to couple these nominal genera on Toarcian. Hyattina of the lower Murchisonae Zone has the basis of their assumed dimorphic associations, [M] strong similarities and appears to represent last mem- = macroconch, [m] = microconch. bers of the genus Cylicoceras. Canavarella S.s.B., 1904 [m] [Rhaeboceras S.S.B, Family Graphoceratidae, Buckman 1905 1889, non Meek 1876; Costiceras Contini 1969]. Small Subfamily Leioceratinae, Spath 1936 coarsely-ribbed oxycones with lappets. The type of the Collecting here and elsewhere (Callomon and genus Canavarella is C. belophora Buckman 1904, found Chandler 1994; Chandler (unpublished)) supports associated with Cylicoceras macroconchs in the Scissum Rieber's (1963) and Contini's findings (1969-70) that Bed of Bridport; therefore a dimorphic coupling of the Leioceratinae comprise at least two distinct groups, Cylicoceras [M] and Canavarella [m] is used here. both dimorphic and established well before the start of Genus Staufenia Pompeckj 1906. At present the the Murchisonae Zone. The division can be traced back same name is used for both macro- and micro conch as into the Opalinium Zone below, as illustrated by no suitable alternative is available. Buckman from his opaliniforme hemera, and probably lower into the Toarcian. In bed 3a (Aa-4) three separate lineages are evident: Leioceras, Cylicoceras and Staufenia. Externally S. sinon resembles Cylicoceras and proba- S.S.B., 1899; Paineia S.S.B., 1904; Planifastigites S.S.B., bly evolved from it. One consistent feature that sets it 1925]. Fastigate pIa tycones, mostly rather evolute apart is a much simplified suture line. The genus ammonites with medium to strong ribbing. The keel is evolved into species that are large discoid oxycones with often weak and ill-defined from the sloping shoulders of tiny umbilicus and a razor-sharp venter, S. staufensis the venter. from the Bradfordensis Zone of central Europe. This Apedogyria S.S.E., 1899 pars [m]: At present no suit- species has not been recorded from Britain but S. sehn- able separate name is available for the microconchs of densis is reported from the Obtusiformis Subzone of Brasilia. Some have been figured by Buckman as Horn Park (Chandler 1982) and other localities nearby. Ludwigella, but this name is in common usage for the Members of the genus are extremely rare in Britain. microconchs of Graphoceras. Brasilia (Apedogyria) subcor- Staufenia Pompeckj 1906 pars [m]. Small, strongly nuta is a typical microconch of Brasilia. Apedogyria is ribbed oxycones inseparable from Canavarella other used here although the type of Buckman's genus is a than by their simplified sutures. macroconch. This case typifies a common nomenclatur- al dilemma in dimorphic lineages that have been arbi- Subfamily Graphoceratinae, Buckman 1905 trarily segmented on purely morphological grounds but The subfamily Graphoceratinae has its roots in the in which separate generic taxa are maintained for the lower Aalenian. Specimens very close to Ludwigia are dimorphs: the morphological changes in the macro- already present as extreme rarities in faunal horizon Aa-3 conchs rarely coincide with those - if any - in the of the Scissum Zone (RBC, unpublished), as in microconchs. Germany (L. praecursor Rieber, 1963). By the start of the Murchisonae Zone Ludwigia is fully differentiated from Genus Graphoceras S.S.B. 1898 Cylicoceras, the probable ancestor. A trend towards an increasingly oxyconic morphology continues with the change of Brasilia into Genus Ludwigia Bayle 1878 Graphoceras in the upper Gigantea Subzone. Evolution Ludwigia Bayle 1878 S.s. [M] [Cosmogyria S.S.E. 1899; proceeds by a gradual shift of morphology evident in the Welschia S.S.B, 1899; Crickia S.S.E., 1899; Hyattia S.S.B., entire population. Rather than speak of, for example, 1899; Kiliania S.S.B., 1899.] Graphoceras concavum, we would do better to speak of Platycones with square to fastigate whorl-sections. 'the Graphoceras concavum morphology' at, say , the Early members of the group retain on the venter strong Graphoceras limitatum assemblage level, i.e. Aa-16. Such prosiradiate ribbing, which persists to the keel. Two dis- statements are equally true for the entire family tinct faunas, both dimorphic, begin to differentiate soon Graphoceratidae. after the appearance of the genus: the early L. haugi and, Graphoceras S.S.B. 1898 [M] [Lucya S.S.B., 1902; slightly later, the L. murchisonae group with closer Deparoceras S.S.B., 1904; Platygraphoceras S.S.E., 1904]. strong ribs that fade on the venter. Ribbing in the L. Compressed oxycones, involute to moderately evolute murchisonae group abuts the keel at a high angle. coiling with fastigate or acute whorl sections. Ribbing is Pseudographoceras S.S.B., 1899 [m] [Ludwigina sinuous to falcate and variable in strength. S.S.B., 1899; Strophogyria S.S.B., 1899]. Large micro- Ludwigella S.S.B. 1901 [m]. Mostly rather evolute conchs with lappets and strong ribbing. Shells are oxycones. The type of the genus was stated to be rather evo1ute and carry a distinct low keel bordered by Ludwigella arcitenens by Buckman in 1902; its type spec- square shoulders. imen is a microconch with lappets. The name Genus Brasilia S.S.E., 1898 Ludwigella was however predated by Buckman, 1901 and was applied to a macro conch: Ludwigella concava Q. In the latest Murchisonae Zone members of the Sowerby) (Proc. Cotteswold Club, vo1.l3, p.226). Ludwigia murchisonae group appear with compressed Ludwigella has been widely used for the microconchs of shells and finer ribbing, giving rise to Brasilia. The tran- Graphoceras by many authors and it is so used here. sition from Ludwigia to Brasilia is gradual and arbitrary (see note under Leioceras above) This genus retains a Genus Hyperlioceras S.S.B., 1889 wide diversity of form and size throughout its range. At By a broadening and flattening of the venter, the two levels at Horn Park (Aa-ll and 12) it attains large transients of Graphoceras in Aa-15/16 evolve into the size and typifies in each case a prominent and easily first Hyperlioceras. They still fully intergrade with recognisable horizon. One of them, B. decipiens, has also Graphoceras; initially, the macroconchs exactly match- been recognised as a good guide fossil in central Europe ing Buckman's genus Darellia, and its corresponding (H. Rieber, pers. comm.). micro conch Braunsina. Only the earliest Discites Zone The area of Beaminster, in which Horn Park lies, is faunas are recorded from Horn Park. the only one with a relatively complete succession of the Bradfordensis Zone in southern Britain. outer whorls. The low keel varies from absent to strong- clear that much is missing by erosion or non-deposition, ly developed and may be bisulcate. the contents of individual faunal horizons contain sam- ples of evolving biospecies buried over durations which Braunsina S.S.B., 1902 [m] [Reynesella S.S.B., 1902, in geological terms are insignificant: they are snapshots Lopadoceras S.S.B., 1904.]. The microconchs completely in the history of developing lineages. intergrade with Ludwigella. They are evolute, have round whorl-sections and simple lappets. The preservation of much of the plentiful material is perfect, making comparisons with Buckman's speci- The graphoceratid composition of faunal mens effortless. Furthermore, the complete adult nature horizon Aa-6 of the material permits ontogenic interpretation and the dimorphic status of the specimens to be assessed easily. So far, faunal horizon Aa-6 has not been proved at Table 1 and the accompanying plates are an important Horn Park. To complete the tally of Buckman's nominal source of reference; they act as a guide to the composi- species (in the range Aa-3 to Aa-16), a list is given of tion of what are probably in all but one or two cases Graphoceratidae re-collected from bed 4 of Quarry Hill monobiospecific assemblages within each faunal horizon. (Quarr Hill), Chideock (SY 434931). Here Aa-6 is well Buckman never finished his work on the represented and from it Buckman obtained a number of Graphoceratidae and considered that the space avail- his type specimens, some of which are types of genera. able in his monograph (1887-1907) could not do it jus- Important nominal species of other authors are also tice. By the publication of the Treatise (Arkell 1957), included. Buckman's genera amounting to almost fifty were Leioceratinae Spath, 1936 reduced to seventeen included in two subfamilies, [M]: Leioceras (Ancolioceras) * substriatum Buckman, Graphoceratinae and Leioceratinae. 1899, L. (A.) subfalcatum (Buckman 1899), L. (A.) costa- Evolution within the graphoceratids is gradualistic, tum Buckman 1888. the division between genera being arbitrary and the [m]: Leioceras striatum Buckman 1899, L. gracile intergradation between them complete. With such large Buckman 1899. amounts of material it is clear that the overlap between successive faunas is considerable. The generic taxa cho- Staufeniinae Maubeuge, 1950 sen to be retained have been selected on the basis of con- [M]: Cylicoceras [Hyattia] wilsonum (Buckman 1899) vention and convenience. The line of decent for the TTs., C. aff. uncinatum (Buckman 1899)., Staufenia sehn- Graphoceratinae is Ludwigia, Brasilia, Graphoceras and densis (Hoffman 1913). Hyperlioceras. Ludwigia and Brasilia have no more claim to separate existences than, say, Brasilia and Graphoceras [m]: Cylicoceras (Canavarella) af! subcostosum or Graphoceras and Hyperlioceras. In these cases the (Buckman 1899). generic names are well known and entrenched in the lit- Graphoceratinae Buckman, 1905 erature, they provide convenient labels for morphotypes within the evolving graphoceratid lineage. In the The species of Ludwigia have a very characteristic Leioceratinae, Leioceras (Cypholioceras) to Leioceras acute edge to the umbilicus (Ancolioceras) constitutes one series of transients or [M]: Ludwigia [Apedogyria] [*] patellaria (Buckman chronospecies with Cylicoceras and Staufenia evolving 1899) TTs., L. [Cosmogyria] subtabulata (Buckman 1898) side by side with it, probably ilS entirely separate popu- TTs., L. [U:7elschia][*] obtusiformis (Buckman 1899) TTs., lations. Throughout the entire Aalenian-Lower L. [Hyattia][*] pustulifera (Buckman 1899) TTs., L Bajocian and probably elsewhere, the macroconch pop- [Kiliania] [*] lacinosa (Buckman 1904) TTs., L [Kiliania] ulations are the best time-discriminators. Microconchs armipotens (Buckman 1904) TTs., L. [Kiliania] depilata show repetitive morphology and have restricted ranges (Buckman 1925) TTs., L. gradata Buckman 1904, L. of variability in each faunal horizon. The sexual tuberata Buckman 1904, L. * murchisonae (J de C dimorphs constitute breeding pairs in evolving popula- Sowerby 1827). tions. For this reason the microconchs are regarded as subgenera of the retained macroconch genera. [m]: Ludwigia (Pseudographoceras)umbilicata (Buckman 1899), L. (P.)patula (Buckman 1899)., L. (P.) tuberculata In every case the extreme fine and coarse elements of Buckman, 1899, L. (P.)subtuberculata Rieber 1963. each assemblage constitute the rarities. Buckman noticed these as unusual and figured a number of them. The plates in his work therefore give a biased impression of the relative abundances of what is to be found. As it is the primary purpose of this work to establish the horizons of types of nominal species, variants of 'hori- zontal' biospecies, probably monospecific have not be subjected here to reclassification or placed in exhaus- / tive synonymies, which would be beyond the scope of the nresent work. Table 1 The range, abundance (rare (R), occurs (0), common (C)) and probable type horizon (+) of the nominal species collected from faunal horizons at Horn Park

KEY: Aa-: Aalenian, Bj-: Bajocian. A reference and type status (if any) is given for each morphospecies. For species or subspecies founded by authors other than Buckman, the plate and figure references relate to the works by the author as listed in the bibliography. Morphospecies are grouped under macro- and microconchs separately. Dimorphs are given separate morphosubgeneric names.

MACROCONCHS Aa- Aa- Aa- Aa- Aa- Aa- Aa- Aa- Aa- Aa- Aa- Aa- Aa- Aa- Bj- REFERENCE AND TYPE STATUS 2 3 4 5 7 8 9 10 11 12 13 14 15 16 1

Leioceras (Cypholioceras) lineatum Buckman, 1899 C+ Supp.pl. 8, figs.I-3, HT (mon.). Leioceras (Cypholioceras) comptum (Reinecke, 1818) C+ 0 Reinecke, 1818, pI. 1, figs.5-6, HT L.eioceras (Cypholioceras) bijidalum Buckman, 1899 0 C+ Supp. p1.7, figs. 1-3, ST Leioceras (Cypholioceras) capillare (Buckman, 1928) 0 C+ C+ TA. 786, HT; TTs. Leioceras (Cypholioceras) opalinoides horni (Geczy, 1967) 0 C Geczy, 1967, pI. 40, fig.l, HT Leioceras (Ancolioceras) * substriatum Buckman, 1899 R R C+ 0 R R Supp. pI. 6, figs.l4-16, HT(mon); CTs. Leioceras (Ancolioceras) costatum Buckman, 1888 R R C+ C 0 R Mon. pl.7, fig. 7, ST Leioceras (Ancolioceras) subfalcalum (Buckman, 1899) 0 C R . Supp. pI. 11, figs. 25-27, ST Leioceras (Ancolioceras) subacutum (Buckman, 1899) 0 0 Supp.pl. 13, figs. 4-6, ST Cylicoceras [Geyerina] evertum (Buckman, 1899) R R R+ Supp. pl.ll, figs. 10-12, HT(mon.); CT Cylicoceras [Geyerina] [*Jfasciatum (Buckman, 1899) R R R+ Supp. pl.6, figs.l7-19, HT (mon). Cylicoceras [Hyattina] [*] brasilum (Buckman, 1899) C C+ Supp. pl.l3, figs. 7-9a, ST Cylicoceras * undatum Buckman, 1899 0+ 0 R R Supp. pl.5, figs. 5-6, HT Cylicoceras uncinatum (Buckman, 1899) 0 0 R Supp. pl.5, figs.7-11, ST Staufenia aff. sinon (Bayle, 1878) R+ R Bayle, 1878, pl.83, fig.l, LT Staufenia sinon citaae (Geczy, 1967) R Geczy, 1967, pI. 39, fig. 1, HT Staufenia sehndensis (Hoffman, 1913) R+ Hoffman, 1913, pI. 4, fig. 3, LT Ludwigia [welschia] [*] obtusiformis (Buckman, 1899) C C+ C 0 R R Supp. pl.l2, figs. 1-3a , HT . Ludwigia haugi Douville', 1885 C C+ 0 R Quenst., 1846, pl.7, fig. 12 =L1; designated Rieber 1963 (as 'HT). Ludwigia [Hyattia] [*]puslulifera (Buckman, 1899) 0 C+ R Supp.pl. 13, figs 1-3a, ST Ludwigia crassa Horn, 1909 R R R Horn, 1909, pl.l3, figs.2, LT Ludwigia [Kiliania][*] lacinosa (Buckman, 1904) 0 C+ R Supp. pl.l5, figs. 4-6, ST Ludwigia [FSiliania] armipotens (Buckman, 1904) 0 0 0 Supp. p.65 , fig. 23 (in text), ST Ludwigia [Kiliania] depilata (Buckman, 1925) R 0 0+ TA. pI. 610, figs. 1-2, HT Ludwigia fueloepi Geczy, 1967 R Geczy, 1967, pI. 45, fig.6, HT Ludwigia laevigata Buckman, 1904 0 C+ Supp. Pl.ll, figs. 13-15, ?=HT (mon); CTS. Ludwigia murchisonae perrotae Geczy, 1967 C Geczy, 1967, pI. 45, fig. 3, HT Ludwigia murchisonae enayi Geczy, 1967 R Geczy, 1967, pI. 44, fig.5, HT Ludwigia * murchisonae a de C Sow, 1827) R C+ C 0 0 R Mon. pI. 2, fig. 1-2, HT refigured. Ludwigia tuberata Buckman, 1904 R R Supp. pI. 15, figs. 1-3, HT(mon). Ludwigia gradata Buckman, 1904 0 C+ 0 0 R R Supp.p.70, fig. 27 (in text), ST Ludwigia [Apedogyria] [*] palellaria (Buckman, 1899) 0 0 Supp.pl. 14, figs. 3-5, ST Ludwigia [Crickia] [*] reflua (Buckman, 1899) 0 C+ 0 0 0 Supp.pl. 11, figs. 16-18, ST; CTs. Ludwigia vaceki Geczy, 1967 0 Geczy, 1967, pI. 46, fig.5, HT Ludwigia obtusiformis buckmani Geczy, 1967 C Geczy,1967, p1.43, fig.l, HT Brasilia *bradfordensis (Buckman, 1881) R C C+ C 0 Mon ..pl.4, figs.5-6, LT designated Rieber 1963 Brasilia [Brasilina] baylii (Buckman, 1887) C C+ R Mon. p1.3, figs.6-7, ST MACROCONCHS Aa- Aa- Aa- Aa- Aa- Aa- Aa- Aa- Aa- Aa- Aa- Aa- Aa- Aa- Bj- REFERENCE AND TYPE STATUS 2 3 4 5 7 8 9 10 ~1 12 13 14 15 16 1 "-

Brasilia bradfordensis falcatiformis (Geczy, 1967) C C Geczy,1967, pI. 51, fig.l, HT Brasilia bradfordensis elmii (Geczy, 1967) R Geczy,1967, pI. 51, figA, HT Brasilia [Apedogyria] platychora (Buckman, 1899) C C C+ C R Mon.pI.5, figs. 1-2, ST, CT Brasilia [?Manselia] austera (Buckman, 1923) 0 C+ C 0 T.A. p!. 409, figs.1-2, HT Brasilia [Brasilina] baylii (Buckman, 1887) C+ C R Mon. p1.3, figs.6-7, ST Brasilia efJricata Buckman, 1902 R C+ C C Mon. p!.7,figs. 3-4, ST Brasilia [Pseudographoceras] deleta (Buckman, 1899) 0 C+ C Supp. pUl, figs. 22-24, ST Brasilia [Pseudographoceras] limatum (Buckman, 1904) 0 C+ 0 Supp. p. 92, fig. 54 (in text), HT (man.). Brasilia ambigua (Buckman, 1888) C C+ 0 Mon. p!. 7, figs.1-2, HT Brasilia similis (Buckman, 1889) C+ C C R Mon. pI. 15, figs. 1-2, ST Brasilia similis maubeugei Contini, 1969 0 C 0 Maubeugei, 1965, p.78, fig. in text p.79, HT Brasilia [Brasilina] [*] tutcheri (Buckman, 1904) C C C+ 0 Supp.p. 83, fig. 44-45 (in text), ST Brasilia [Hyattia] subcava (Buckman, 1899) 0+ C 0 Supp.p.56, fig.13a-d, HT (man.). Brasilia [Cosmogyria] maggsi (Buckman, 1899) R C+ R Supp. pLlO, fig.23-25, HT Brasilia [Brasilina] crinalis (Buckman, 1899) R C+ 0 Supp. pLlO, figs.29-31, ST Brasilia decipiens (Buckman, 1888) C C+ 0 0 Mon. pU2, fig. 8-9, HT Brasilia [Planifastigites] platys (Buckman, 1925) 0 C+ R T.A. pI.579, fig.1-2, HT Brasilia [Wiltshireia] [*] gigantea (Buckman, 1888) C+ 0 Mon. pLll, fig.l & PU2, fig. 4, HT; CT . Brasilia [Strophogyria] pinax (Buckman, 1899) C+ R Supp. p.63, fig.21, ST; CT Brasilia [Paineia] [*] nitens (Buckman, 1904) 0 0+ 0 Supp. p.77, fig. 33, ST Brasilia [Paquieria] jloccosa (Buckman, 1899) 0 C+ 0 Supp.pLlO, figs. 20-22, HT (man.). Brasilia pinguis Buckman, 1888 C+ C Mon,pLl2, figs.l-3, HT(mon.). Graphoceras pulchrum (Buckman, 1902) 0 C C+ Mon.p!. 10, figs.3-4, HT (man.). Graphoceras concavum (Sowerby, 1815) R 0 C+ 0 R Mon. p1.2, figs. 6-7, HT, refigured. Graphoceras decorum Buckman, 1902 R 0 C C+ C Mon. p!.8, fig. 3-4, HT (man.). Graphoceras [Lucya] cavatum (Buckman,1902) C+ C Mon.p!. 9, figs. 1-4, HT (man.). Graphoceras [Platygraphoceras] [*] apertum (Buckman, 1888) 0 C+ C R Mon. pI. 10, figs. 10-11, HT Graphoceras stigmosum Buckman, 1902 R 0 C C+ C Mon. pI.9, figs. 5-6, ST GraphocerG:!. *v-scriptum Buckman, 1888 R C+ 0 0 0 Mon. pLlO, figs. 5-6, ST Graphoceras [Lucya] marginatum (Buckman, 1904) C+ C C 0 Supp. p.75, fig.31 (in text), ST Graphoceras [Lucya] magnum (Buckman, 1902) C+ C Mon.p!. 6, figs.l-2, HT (man). Graphoceras limitatum Buckman, 1902 R C C+ C Supp.pI. 10, fig. 7, HT Graphoceras [Deparoceras] hamatum (B uckman, 1904) R 0 C+ C Supp.p.79, fig.37 (in text), ST Graphoceras robustum Buckman, 1904 R R C C+ C Supp. pLl5, figs. 9-11, HT (man.). Graphoceras Deparoceras] [*]fallax (Buckman, 1888) R+ R R R Mon. p!. 14, figs.l 0-11 , HT Graphoceras [Lucya] [*] caduceiferum (Buckman, 1902) R+ R R R Mon.p!. 21, figs.l 0-11 , HT(mon.). Graphoceras [Deparoceras] formosum (Buckman, 1888) 0 C+ C 0 Mon. pI. 10, figs. 1-2 ,HT (man.). Graphoceras inclusum Buckman, 1904 R 0 C+ C Supp. p!. 15, figs. 15-17, ST Hyperlioceras [BraunseIla] lenum (Buckman, 1902) R R Mon. p!. 7, figs.5-6, ST Hyperlioceras [Braunsina] [*] contortum (Buckman, 1904) R C+ C Supp.p!. 17, figs.l6-18, HT (man.) Hypherlioceras [BraunseIla] [*] semilenum (Buckman, 1904) 0 Supp.p!. 17, figs.l9-21, HT (man.). Hyperlioceras [Dare Ilia] politum (Buckman, 1898) 0 C+ Mon.p!. 16, figs. 3-4, HT Hyperlioceras [Reynesia] lepidum (Buckman, 1902) C+ Mon.p!. 11, figs.4-5, HT (man.). "-ACROCONCHS Aa- Aa- Aa- Aa- Aa- Aa- Aa- Aa- Aa- Aa- Aa- Aa- Aa- Aa- Bj- REFERENCE AND TYPE STATUS 2 3 4 5 7 8 9 10 11 12 13 14 15 16 1

iyperlioceras [Reynesia] [*] intermedium (Buckman, 1888) R C+ Mon.pl. II, figs. 2-3, HT iyperlioceras [Reynesia] coelum (Buckman, 1902) 0 C+ Mon. pI. 16, figs.IO-II, ST iyperlioceras [Toxolioceras] incisum (Buckman, 1904) C+ C Supp.pI.21, figs. 31-33, ST iyperlioceras [Toxolioceras] mundum (Buckman, 1904) R 0+ Supp.pl.l8, figs. 4-6, HT (man.) . iyperlioceras afL rudidiscites Buckman, 1902 R Mon. pI. 18, figs. 1-2, HT. "-ICROCONCHS •• ~eioceras opalinum (Reinecke, 1818) 0 0 R Reinecke, 1818, pl.l, figs. 1-2. SD: Buckman, 1887. ~eioceras striatum Buckman, 1899 0+ R R R Mon. pI. 13, fig.l2, LT, designated Rieber, 1963 (as 'HT'). ,eioceras partitum Buckman, 1899 0 0 R R Mon. pI. 13, fig. II ?=HT (man). ~eioceras gracile Buckman, 1899 0 0 R R Supp. pI. 6, figs. 11-13, HT (man). -;Ylicoceras (Canavarella) subcostosum (Buckman, 1889) 0 0 Supp. pI. 20, figs. 10-12, LT. -;Ylicoceras (Canavarella) cariniferum (Buckman, 1899 ) 0+ Supp. pI. II, figs. 7-9, HT (man). -;Ylicoceras (Canavarella) paucicostatum (Rieber, 1963) R Rieber, 1963, pI. 2, figs. 4-5, HT. ~udwigia (Pseudographoceras) cosmia (Buckman, 1899) C C+ Supp.p.63, fig.20 (in text), ST. ,udwigia (Pseudographoceras) agria (Buckman, 1899) 0 C+ Supp.p.62, fig.19 (in text), ?=HT (man.). ~udwigia (Pseudographoceras) bullifera (B uckman, 1899) R R+ Supp. pl.l4, figs.l-2, ST. ,udwigia (Pseudographoceras) umbilicata (Buckman, 1899) R C+ 0 0 Supp. p. 61, fig.18 (in text), ST. ,udwigia (Pseudographoceras) * literata Buckman, 1899 0+ Supp. pI. lI,figs.19-21, HT. ,udwigia (Pseudographoceras) patula (Buckman,1899) C+ Mon. pI. 3, fig.3, ST. ~udwigia (Pseudographoceras) tuberculata Buckman, 1904 C+ 0 0 R Supp.pI.3, figs. 4-5, LT.designated Horn, 1909. ,udwigia (Pseudographoceras) subtuberculata Rieber, 1963 0+ R Rieber, 1963, pI. 5, figs. 12-13, HT. ~rasilia (Apedogyria) subcornuta Buckman, 1899 C+ C C 0 Supp. pI. 14, figs. 13-15, ST; CTs. hasilia (Apedogyria) glevensis (Buckman, 1904) C C C Supp. pI. 20, figs.25-27, HT (man.) . ~rasilia (Apedogyria) carinata (Buckman, 1904) 0+ 0 0 0 Supp. pI. 19, figs.40-42,?=ST; CTs. ~rasilia (Apedogyria) rugosa (Buckman, 1904) 0 C+ 0 0 0 Supp. pI. 20, figs. 34-36, HT (man), CT. "Jraphoceras (Ludwigella) tenue Buckman, 1904 R R 0 0 C C+ Supp.pl. 20, figs.37-39, ST. haphoceras (Ludwigella) arcitenens Buckman, 1902 0 0 0 C+ C Mon. pI. 4, figs.I-2, ST. "Jraphoceras (Ludwigella) altenuatum Buckman, 1904 R C 0 C+ 0 Supp.pl. 19, figs. 10-12, ST "Jraphoceras tLudwigella) altractum Buckman, 1904 C+ C C C 0 Supp. pI. 19, figs. 31-33, HT(mon), haphoceras (Ludwigella) impolitum Buckman, 1904 R R C C C C 0+ Supp. pI. 19 ,figs. 25-27, ST. haphoceras (Ludwigella) rudis Buckman, 1889 R R R 0 C 0 0 Mon. pI. 15, figs. 11-12, HT. haphoceras (Ludwigella) cornu Buckman, 1881 C C+ 0 0 Supp.p. 86, figs. 49-50 (in text), HT. haphoceras (Ludwigella) castum Buckman,1904 0 C C C C+ Supp.pl. 20, figs. 31-33, ST. "Jraphoceras scriptitatum Buckman, 1923 C+ 0 0 0 TA. pI. 388, figs. 1-2, HT. "Jraphoceras debile Buckman, 1904 R 0 0 0 Supp.pl. 20, figs. 22-24, HT (man.). haphoceras (Ludwigella) micrum Buckman, 1904 C C+ C Supp.pl. 19, figs. 7-9, ST . "Jraphoceras (Ludwigella) vibratum Buckman, 1904 0 C+ C Supp.pl. 19, figs. 13-15, ST. haphoceras (Ludwigella) subrudis Buckman, 1902 0 C+ 0 Mon.pl.l5, figs. 14-15, ST. haphoceras (Ludwigella) latum (Buckman, 1904) 0 C C 0 Supp. pI. 20, figs. 19-21, ST. iyperlioceras (Braunsina) fastigatum Buckman, 1904 C C+ Supp. pI. 20, figs. 1-3, ST. iyperlioceras (Braunsina) cornigerum Buckman, 1904 0 C+ C Supp. pI. 20, figs. 4-6, HT (man.). iyperlioceras (Braunsina) asperum Buckman, 1904 0 C+ Supp. pI. 17, figs. 13-15, HT (man.). iyperlioceras (Braunsina) rotabilis (Buckman, 1904) 0 C+ Supp.pl. 17, figs. 7-9, HT (man.). Acknowledgements stratigraphique'. Ann. Sci. Univ. Besancon, 3 ser., Geologie 11,204 pp. Cope, lC.W, 1980 'A correlation of Jurassic rocks in the British Isles, This paper is completed to celebrate thirty years of part two: Middle and Upper Jurassic'. Geol. Soc. London Special Dorset geology by the Wessex Cephalopod Club and to Report 15, 109 pp. commemorate the work of my friend and teacher, the late Donovan, D.T, Callomon, lH. & Howarth, M.K., 1981 'Classification J. Hanson. I am indebted to the Curry Fund of the of the Jurassic Ammonitina'. In: M.R. House and J.R. Senior (eds). The Ammonoidea, Syst. Ass. Special. Vo1.18,101-55. Geologists' Association for their generous support towards Geczy, B., 1967 'Ammonoides jurassiques de Csernye, Montagne part of the production costs for the manuscript and plates. Bakony, Hongrie. Part II, excl. Hammatoceratidae'. Geol. I acknowledge with gratitude the assistance in the field of Hungarica 35, 413pp, 65 pis. the Wessex Cephalopod Club: Messrs J. H. Callomon, A. Henriques, M.H., 1992 Biostratigrafia e Paleontologia (Ammonoidea) do G. England, W J. E. Jones, D. Roberts and D. T C. Sole, Aaleniano em Portugal. Tesis doctoral, Centro de Geociencias da Universidade de Coimbra. also G. Davies and M.B. Thompson. John Callomon has Henriques, M.H., Gardin, S., Gomes, C.R., Soares, A.F., Rocha, R.B., been instrumental in providing constant encouragement Marques, IF., Lapa, M.R. & Montenegro, lD., 1994 'The and support as well as making numerous constructive Aalenian-Bajocian boundary at Cabo Mondego (Portugal)'. comments regarding the manuscript. Derek Peters assist- Miscellanea del Servizio Geologico Nazionale 5,63-77,2 pis. ed with the preparation of the text. David Sole has made Hoffmann, G., 1913Stratigraphie und Ammoniten-Fauna des unteren Doggers in Sehnde bei Hannover. Schweizerbart, Stuttgart, 202 pp., p1s.l8 pis. available a number of important specimens for study. Horn, E., 1909 Die Harpoceraten der Murchisonae Schiten des Donau The project would have been impossible without the co- Rhein zuges. Mitt. bad. geol.Landesanst, Heidelberg. 4, 251-323, 7 pis. operation of the sites owners over the years, Mr G. Pinney, Mr Linares, A. and Sandoval, J., 1990 'The lower boundary of the Bajocian in the Barranco de Agua Larga section (Subbetic A. N. Wells and Mr and Mrs T and J. Gibbs. A number of Domaine, Southern Spain)'. In: S. Cresta and G. Pavia (eds), Atti specimens were presented or prepared by R. and T Chiarini, del meeting sulla stratigrafia del Baiociano. Memorie descrittive B. Huber, H. Rieber and R. Ruegg (Zurich). Hans Rieber delia carta geologica d' Italia 40, 13-22. also contributed to the preparation of the manuscript. Maubeugei, P. L., 1965 'Catalogue des Ammonites du Jurassique inferieur et moyen (Hettangien a Bathonian) du Musee cantonal de Bale-Campagne'. Tatigkeitsbericht der Naturforschenden Gesellschaft Baselland 25, 43-130. Althoff, W., 1940 'Die Ammonitenzonen der oberen Ludwigien- Morton, N., 1990 'Bearreraig (Isle of Skye, N.W. Scotland) as bound- schichten von Bielefeld'. Palaeontographica A.92, 44 pp, 6 pis, Stuttgart. ary stratotype for the base of the Bajocian Stage'. In: S. Cresta and G. Pavia (eds), Atti del meeting sulla stratigrafia del Baiociano. Arkell, W L 1957 In: Treatise on Invertebrate Paleontology. Part L. Memorie descrittive delia carta geologica d' Italia 40, 23-48. Mollusca 4 Cephalopoda. Ammonoidea. (Ed. by R.C. Moore). 22 Morton, N., 1994 'Stratigraphical markers in the Aalenian-Bajocian + 490 pp. Kansas & New York. succession at Bearrerraig, Isle of Skye, Scotland'. Miscellanea del Bomford, G., 1948 'New sections in the Inferior Oolite'. Proc. Geol. Servizio Geologico Nazionale 5, 79-90, 6 figs. Assoc. 59, 148-50. Morton, N. and Chandler, R. B., 1994 'Ammonite biostratigraphy of Buckman, S.S., 1887-1907 A Monograph of the Ammonites of the Inferior the Aalenian-Bajocian boundary: comparison of faunal horizons Oolite Series. Pa1aeontographical Society, London: 456 +, 103 pp. in Dorset/Somerset and Isle of Skye'. Miscellanea del Servizio (1887-1894) and Supplement (1898-1907): 262 pp, 24 pis. Geologico Nazionale 5, 91-92. Buckman, S.S., 1893 'The Bajocian of the Sherborne district: its rela- Morton, N. and Hudson, l D., 1995 'Field guide to the Jurassic of the tion to subjacent and superjacent strata'. Quart. J. Geol. Soc. Isles of Raasay and Skye, Inner Hebrides, NW Scotland'. In: PD. London, 49, 479-522. Taylor (ed.), Field Geology of the British Jurassic, Geological Society, Buckman, S.S., 1909-1930 Type Ammonites. London, Wheldon and London, 209-80. Wesley.vols. 1-7,790 pis. Reprint (1972-1976), Historia Naturalis Parsons, C., 1980 'Aalenian and Bajocian Correlation Chart' In lC.W. Classica, 93: no. 1. Cramer Verlag and Wheldon and Wesley, Cope 1980, 3-21 Lehre and Codicote. Quenstedt, F. A., 1845-1849 Petrefactenkunde Deutschlands. Die Buckman, S.S., 1910 'Certain Jurassic (Lias-Oolite) strata of south Cephalopoden. Tubingen. 580 pp.-pls. 30-36 Dorset and their correlation'. Quart.J. Geol. Soc. London 66,52-89. Quenstedt, F. A., 1883-1888 Die Ammononiten des SchwabischenJura, Callomon, l H., 1995 'Time from fossils: S.S. Buckman and Jurassic II, Der Braune Jura; Schweizerbart, Stuttgart, Lief 10-15, high-resolution geochronology'. In: M. l Le Bas (ed.) 'Milestones 441-816, pis 55-90. in geology'. Geological Society, London, Memoirs 16, 127-150. Richardson, L., 1928 'The Inferior Oolite and contiguous deposits of Callomon, J. H. and Chandler, R.B., 1990 'A review of the ammonite the Burton Bradstock-Broadwindsor district, Dorset'. Proc. horizons of the Aalenian-Lower Bajocian stages in the Middle Cotteswold Nat. Field Club 23, 35-68, pis. 2-6. Jurassic of Southern England'. In: S. Cresta and G. Pavia (eds) Rieber, H., 1963 'Ammoniten und Stratigraphie des Braunjura j) der 'Atti del meeting sulla stratigrafia del Baiociano'. Memorie descrit- Schwabischen Alb'. Palaeontographica AI22, 89 pp., pls.1-8. tive delia carta geologica d' Italia 40, 85-111. Rocha, R.B., Henriques, M.H., Soares, A., Mouterde, R., Caloo B., Callomon, l H. and Chandler, R.B., 1994 'Some early Middle Jurassic Ruget, C. and Fernandez-Lopez, S., 1990 'The Cabo Mondego sec- ammonites of Tethyan affinities from the Aalenian of southern tion as a possible Bajocian Boundary stratotype'. Miscellanea del England'. Palaeopelagos Special Publication 1, 17-40,8 pis. Servizio Geologico Nazionale 5,63-77,7 figs., 2 pis. Callomon, lH. and Cope, J. C W., 1995 'The Jurassic Geology of Sadki, D., 1994 'I.; Aalenian superieur et Ie Bajocien inferieur du Dorset'. In PD. Taylor (ed.), Field Geology of the British Jurassic, Haut-Atlas marocain: revision biostratigraphique et correlations'. Geological Society London, pp.51-1 03 Miscellanea del Servizio Geologico Nazionale 5, 177-90, 7 figs. Chandler, R.B., 1982 'The first record of Staufenia (Staufenia) sehnden- Senior, lR., Parsons, C.F. and Torrens, H..S., 1970 'New sections in the sis (Hoffmann) in Britain'. Proc. Geol. Assoc. 93, 301-4. Inferior Oolite of South Dorset'. Proceedings of the Dorset Natural Chandler, R.B. and Sole, D.TC., 1995 'The Inferior Oolite at East Hill History and Archaeological Society 91, 114-19. Quarry, Bradford Abbas, Dorset'. Proceedings of the Dorset Natural Spiegler, W, 1966 'Graphoceratidae des Ober-Aalenium (Jura, N W History and Archaeological Society 117, 101-8. Deutschland)'. Mia. geol. Staatsinst. Hamburg 35,5-113, pls.l-9. Ann. Contini, D., 1969 'Les Graphoceratidae du Jura franc-comtois'. Ureta Gill, M.S., 1983 Bioestratigrafiay paleontologia (Ammonitina) del Scient. Univ. Besancon Geol. (3), 7,95 pp, 24 pis. Aaleniense en el sector noroccidental de la Cordillera Iberica. Tesis l:()ntini_ n 1Q70 'T' A~ lpnipn POt lp R~inripn r111 Tllr~ Pr~::mr_r()mtnl<: Ptlll1P nr\rtnr'Al l,\SVS;/:.c;; TTnl'U rnmnlllt i\Aar1riti u~;~ ~ Ll"? nn

Plate 2: Bed 3b, (Aa-5) [Mj. 1a & b. REG 173 Ludwigia aff. depilata (Buckman); 2a & If. REG 73 Ludwigia pustulifera (Buckman); 3a & b. REG 582 Ludwigia armipotens (Buckman); 4a & b. REG 15 Staufenia sehndensis (Hoffman); Sa & b. REG 160 Gylicoceras brasilum (Buckman); 6a & b. REG 120 Staufenia aff. sehndensis (Hoffman). Plate 3: Bed 3c, (Aa-7) [Mj. 1a & b. REG 79 Ludwigia depilata (Buckman); 2a & b. REG 150 Ludwigia murchisonae a. de C. Sowerby); 3a & b. REG 151 Ludwigia reflua (Buckman); 4a & b. REG ~83 Ludwigia cf crassa Horn; 5a & b. REG 167 Ludwigia laevigata Buckman; 6a & b. REG 270 Ludwigia murchisonae a. de C. Sowerby); 7a & b. REG 9 Ludwigiafuelopei Geczy; 8a & b. RBG 103 Ludwigia reflua (Buckman); 9a & b. REG 5 Ludwigia obtusiformis buckmanni Geczy; lOa & b. REG166 Ludwigia tuberata Buckman. Plate 4: Beds 4a-c, (Aa-8 to Aa-1O) [Mj. 1a & b. REG 112 Brasilia platychora. (Buckman) (4a); 2a & b. REG 164 Ludwigia vaceki Ceczy (4a); 3a & b. REG 28 Brasilia austera (Buckman) (4b); 4a & b. REG 22 Brasilia bradfordensis (Buckman) (4a); Fig. 5a & b. REG 63 Ludwigia aff murchisonae (J. de C. Sowerby) (4a); 6a & b. REf; 26 Brasilia austera (Buckman) (4a); 7a & b. RBG 61 Brasilia affbradfordensis (Buckman) (4a); 8a & b. RBG 305 Brasilia baylli (Buckman) (4c); 9a & b. REG 105 Brasilia effricata Buckman (4c); lOa & b. RBG 111 Brasilia platychora (Buckman)(4c); 11a & b. REG 46 Brasilia bradfordensis (Buckman) (4c); 12a & b. REG 300 Brasilia subcava (Buckman) (4c). Plate S: Beds 4c-Sa, (Aa-lO to Aa-ll) [MIla & b. REC 308 Brasilia gigantea (Buckman) (Sa); 2a & b. REC 309 Brasilia platychora (Buckman) (Sa); 3a & b. REC 8 Brasilia eftricata (Buckman) (Sa); 4a & b. REC 320 Brasilia bradfordensis (Buckman) (Sa); Sa & b. REC 314 Brasilia aft ambigua (Buckman) trans. similis (Buckman) (Sa); 6a & b. REC 104 Brasilia similis maubergei Contini (4c); 7a & b. REC 60 Ludwigia obtusiformis (Buckman) (4c); 8a & b. REC 281 Brasilia similis (Buckman) (4c); 9a & b. REC 47 Ludwigia gradata Buckman (4c); lOa & b. REC 107 Brasilia bradfordensis (Buckman) (4c); lla & b. REC Sl Brasilia tutcheri (Buckman) (4c). Plate 6: Beds Sa & Sc, (Aa-11 to Aa-13) [M]; 1a & b. REC 310 Brasilia decipiens (Buckman) (Sci); 2a & b. REC 312 Brasilia effricata Buckman (Sa); 3a & b. REC 16 Brasilia similis aff maubergei Contini (Sa); 4a & b. REC 86 Graphoceras cavatum (Buckman) (Scii); Sa & b. REC 222 Graphoceras decorum Buckman (Scii); 6a & b. REC 387 Brasilia tutcheri (Buckman) (Sci); 7a & b. REC 306 Brasilia nitens (Buckman) (Sa); 8a & b. REC 115 Brasilia subcava (Buckman) (Sa); 9a & b. REC 7 Brasilia crinalis (Buckman) (Sci). Plate 7: Beds Sa-c, (Aa-ll to Aa-13) [Mj. 1. REG 269 Brasilia decipiens (Buckman) (Sci); 2a & b. REG 41 Brasilia nitens (Buckman) (Sa); 3a & b. REG 92 Brasilia floccosa (Buckman) (Sci); 4a & b. REG 87 Graphoceras magnum (Buckman) (Scii); Sa & b. REG 384 Graphoceras concavum (Sowerby) (Scii); 6a & b. REG 93 Graphoceras v-scriptum Buckman (Scii); 7a & b. REG 89 Graphoceras magnum (Buckman) (Scii); 8a & b. REG 213 Graphoceras apertum (Buckman) (Scii); 9a & b. REG 219 Graphoceras decorum Buckman (Scii). Plate 8: Bed 5d, (Aa-14 to Aa-15) [Mj. 1a & b. REG 356 Graphoceras aff. cavatum (Buckman) (5di); 2a & b. REG 215 Graphoceras concavum (Sowerby) (5dii); 3a & b. REG 386 Graphoceras concavum (Sowerby) (5di); 4a & b. REG 360 Graphoceras aff. formosum (Buckman) (5dii); Sa & b. REG 88 Graphoceras fonnosum (Buckman) (5dii); 6a & b. REG 42 Graphoceras caduceiferum (Buckman) (5dii); 7a & b. REG 361 Graphoceras fallax (Buckman) (5di); 8a & b. REG 383 Graphoceras stigmosum Buckman (5dii); 9a & b. REG 202 Graphoceras concavum (Sowerby) (5dii); lOa & b. RBG 382 Graphoceras stigmosum Buckman trans. Hyperlioceras (5dii); lla & b. REG 218 Graphoceras aff, concavum (Sowerby) (5di); 12a & b. REG 220 Graphoceras limitatum Buckman (5dii).

I· 17b