AALENIAN TMETOCERAS (AMMONOIDEA) FROM IBERIA Taphonomy and Palaeobiogeography S. R. Femandez-L6pez, 1 M. H. Henriques,2 A. Linares,3 1. Sandovae and M. S. Ureta1 'Dept. y UEI de Paleontologia Facultad de Ciencias Geo16gicas (UCM) e Instituto de Geologia Econ6mica (CSIC-UCM) 28040-Madrid, Spain 2Dept. Ciencias da Terra Centro de Geociencias Universidade de Coimbra 3049-Coimbra Codex, Portugal 3Dept. de Estratigrafia y Paleontologia Facultad de Ciencias Universidad de Granada 18071 Granada, Spain Abstract From different areas of the Iberian Peninsula more than 600 specimens of Aalenian Tmeto­ ceras have been found. This taxonomic group represents less than 20% of the whole am­ monoids recorded in Opalinum, Murchisonae, Bradfordensis and Concavum biozones. Tmetoceras representatives, as well as Phylloceratina and Lytoceratina, were more fre­ quent in shelfal basins than in epicontinental platforms. Taphonomic data suggest a eudemic character of the representatives of T. scissum in shelfal basins or oceanic areas. Exceptional immigrants and drifted shells of this species arrived in shallow environments of neighbouring platforms. In contrast, representatives of T. regleyi inhabited preferen­ tially shallow environments of epicontinental platforms. T. scissum was a pandemic species, inhabiting oceanic or shelfal environments in the early Aalenian. However, some species of Tmetoceras, such as T. regleyi and T. flexicostatum, were geographically restricted in very distant areas. T. regleyi has been found only in Euro- pean areas of the West Tethyan Subrealm. A pattern of adaptive radiation may have taken place in the Western Tethys during the Opalinum-Murchisonae biochrons, giving rise to T. regleyi from T. scissum. Specialized forms of Tmetoceras (k-strategists such as the individuals of the species T. regleyi) are widespread in the epicontinental platforms around the Western Tethys during the Murchisonae and Bradfordensis biochrons. Epicontinental, specialized forms of T. regleyi suffered extinction in the latest Bradfordensis Biochron. Shelfal or oce­ anic, generalist forms of T. scissum disappeared in the Western Tethys or the Mediterranean Province in the latest Bradfordensis Biochron, but they survived in the East-Pacific Subrealm. 1. INTRODUCTION The subfamily Tmetoceratinae is a mono generic group, Tmetoceras (M+m), com­ prising several European forms distinguished at specific level on the basis of morphologi­ cal differences: T. scissum (Benecke, 1865), T. regleyi (Dumortier, 1874), T. difalense (Gemmellaro, 1886) and T. hollandae (Buckman, 1892). However, when fossils are abun­ dant, these species all appear to intergrade (cf. Callomon and Chandler, 1994). The main purpose of this paper is to show that the distribution of Tmetoceras shells around the margins of the Iberia during the Aalenian was influenced by biogeographical and taphonomic dispersal, related to changes in the relative depth of sea level. 2. TAPHONOMIC CHARACTERS AND DISTRIBUTION OF AALENIAN TMETOCERAS IN IBERIA More than 600 specimens of Aalenian Tmetoceras found in situ in different areas of the Iberian Peninsula have been studied (Figure 1). These specimens have been found in the following areas and outcrops: 1. N Lusitanian Basin (Cabo Mondego, Coimbra and Degracias; cf. Perrot, 1955; Mouterde et al., 1964, 1980; Rocha et al., 1981; Henriques, 1989, 1992, 1995). 2. Asturias (Santa Mera and El Puntal; cf. Suarez-Vega, 1974; Ferwindez-L6pez and Suarez-Vega, 1980). 3. Basque-Cantabrian Basin (Camino, Castillo Pedroso, Cillamayor, Rebolledo de la Torre and San Andres; cf. Fernandez-L6pez et al., 1988b; Goy et al., 1990; Canales et al., 1993). 4. NE Cameros (Prejano and Muro de Aguas; cf. Goy and Ureta, 1981; Ureta, 1985, 1988). 5. NW Iberian Basin (Canales de la Sierra, Castrovido, Hontoria, Rabanera, Talveila and Villavelayo; cf. Ureta, 1985; Ureta and Goy, 1986; Fernandez­ L6pez et al. , 1988a). 6. Aragonese Platform (Ob6n and Ricla; cf. Mouterde et al. , 1978; Fernandez­ L6pez and Aurell, 1988; Goy et al., 1988). 7. Tortosa Platform (Coll de Soms, Mas de Rojals, Vall Llarga and Vandell6s; cf. Fernandez-L6pez and Mouterde, 1985; Fernandez-L6pez et al., 1996). 8. NW Castilian Platform (Arcos de Ja16n and Fuentelsaz; cf. Goy and Ureta, 1987, 1991; Goy et al. , 1994). . 9. Central Castilian Platform (Barranco de la Hontanilla, Peracense and Rambla del Salto: cf. Fernandez-L6pez and G6mez, 1990a, b). Figure 1. Areas of Iberia mentioned in text: 1 ) N Lusitanian Basin, 2 ) Asturias, 3 ) Basque-Cantabrian Basin, 4 ) NE Cameros, 5 ) NW Iberian Basin, 6) Aragonese Platform, 7) Tortosa Platform, 8 ) NW Castilian Platform, 9 ) Central Castilian Platform, 10) SE Castilian Platform, l l) Maj orca, 12) External Subbetic Basin, 1 3 ) Oriental sector of Median Sub­ betic Basin, 14) Central sector with condensed sec­ tions of Median Subbetic Basin, and 1 5 ) Central sector with expanded sections of Median Subbetic Basin. 10. SE Castilian Platform (Ribarroja and Domefio; cf. Fernandez-L6pez, 1980, 1985). 11. Majorca (Cuber and Llodra; cf. Goy and Ureta, 1988; Alvaro et al. , 1989). 12. External Subbetic Basin (Cortijo Veteta and Sierr� de Gaena; cf. Sandoval, 1983). 13. Oriental sector of Median Subbetic Basin (Sierra de Ricote; cf. Seyfried, 1978; Linares and Sandoval, 1993; Garcia-G6mez et al., 1994). 14. Central sector with condensed sections of Median Subbetic Basin (Cerro Men­ dez and Rio Fardes; cf. Linares, 1979; Hernandez-Molina et al., 1991; Linares and Sandoval, 1993; Garcia-G6mez et al., 1994). 15. Central sector with expanded sections of Median Subbetic Basin (Cerro Men­ dez, Montillana and Sierra de San Pedro; cf. Garcia-G6mez et al. , 1994; Li­ nares, 1979; Linares et al., 1988; Linares and Sandoval, 1992, 1993). These areas of the Iberian Peninsula comprise two separate habitats: epicontinental platforms and shelfal basins. Habitats of epicontinental platform were cratonic areas flooded by shallow marine waters. In contrast, habitats of shelfal basins were situated on the continental shelf showing open marine and oceanic environments. Two shelfal basins were located in Tethyan and Protoatlantic margins of the Iberian Plate throughout Aalenian time: the Betic and the Lusitariian basins (Figure 2). A set of very shallow epicontinental platforms, the so-called Iberian Basin, was situated between them. Depositional environments of these Aalenian basins varied from those of very sha­ llow outer platform to those of deep basin. Aalenian strata are fundamentally limestones which may attain 85 m thick (Henriques et al., 1996). Ammonoid assemblages of these en­ vironments varied from those with a predominance of Phy lloceratina and Lytoceratina to those that were mainly Ammonitina. For example, ammonoid assemblages in the Median Protoatlantic Iberia W Tethys Concavum Biochron Bradfordensis Biochron Figure 2. Frequency ofTmetocera- tinae and Phylloceratina plus Lyto- Murchisonae Biochron ceratina in different areas of the Opalinum Ejochron Iberia during the successive Aalenian biochrons. o 88OClMf)O � 0 G)m Tmetoceratina� Phylloceratinaaf]dLytoceratina Subbetic Basin are dominated by Phylloceratina and Lytoceratina during the Bradforden­ sis Biochron. In Lusitanian and Iberian basins, Ammonitina are the most frequent Aalenian ammonoids found, and Phylloceratina or Lytoceratina are very scarce. Fossils of Tmetoceras are also more abundant in the Betic Basin than in the Lusitanian or in the Ibe­ rian basins (Figure 3). The subfamily Tmetoceratinae represents less than 20% of the whole ammonoids recorded in Opalinuin, Murchisonae, Bradfordensis, and Concavum biozones. However, from a taphonomic and palaeoecological point of view, the distribu­ tion of Aalenian Tmetoceras shows conspicuous variations around the Iberian Plate at a zonal scale (Tables 1-4). Fragmentary, incomplete specimens are commonly represented among Aalenian am­ monoids of the Iberian Peninsula. No accumulated Tmetoceras have been identified among them. Fossil assemblages show high degrees of removal (i. e. , proportion of re sed i­ mented or reelaborate elements). The palaeontological material from Asturias, Basque­ Cantabrian and Iberian basins is composed of resedimented or reelaborate elements. They represent individuals with less than 50 mm in diameter. However, Betic and Lusitanian Tmetoceras are mostly composed of resedimented specimens showing diameter values be­ tween 13 and 78 mm. Two species of Tmetoceras have been recognized: T. scissum and T. regleyi (cf. Ferwindez-L6pez et al. , 1997). On the basis of morphological criteria, T. scissum comprise evolute shells having thin, acute, prominent and distant ribbing, and they have a moder­ ately complex suture line (Fig. 3A-D, F -G). In contrast, representatives of T. regleyi are more involute, showing thick, blunt and dense ribs, and their suture line is more simple (Figure 3E). Specimens of T. scissum are more abundant and they have higher strati graphical per­ sistence in the Betic and Lusitanian basins than in the epicontinental platforms of Iberia (Figure 4). In contrast, specimens of T. regleyi are practically restricted to areas of epicon­ tin ental platform, where they are the dominant species of the genus 'during the Mur­ chisonae and Bradfordensis biochrones. Nevertheless, very scarce adult specimens of T. regleyi have been found in the Murchisonae and Bradfordensis biozones from the Betic Basin. Shells of Tmetoceras recorded in Aalenian deposits of these areas compose taphonic populations of three types: TP 1, TP2 and TP3 (Figure 5). Taphonic populations of type 1 Figure 3. Aalenian Tmetoceras of the Iberian Peninsula. (A) Juvenile individuals of Tmetoceras scissum. Resedi­ mented elements with complete body chambers. CMB.19.1. Opalinum Biozone. Cerro Mendez (Central sector with expanded sections of Median Subbetic Basin). x2. (B) Post-juvenile individuals of Tmetoceras scissum. Re­ sedimented elements with incomplete body chambers. lRI 1.63.2. Opalinum Biozone. Sierra de Ricote (Oriental, sector of Median Subbetic Basin), xl. (C) Adult individual of Tmetoceras scissum. Reelaborated element with complete body showing a disarticulation surface (DS). CM.7.7S. Murchisonae Biozone. Cerro Mendez (Central sector with condensed sections of Median Subbetic Basin), xl. (D) Immature individual of Tmetoceras scissum. Reelaborated element with incomplete body chamber. CM.AS.20. Murchisonae Biozone. Cerro Mendez (Central sector with condensed sections of Median Subbetic Basin), xl. (E) Post-juvenile. individual of Tmetoceras regleyi. Reelaborated element with incomplete body chamber. SSSI26/14. Bradfordensis Biozone. Coli de Soms (Tortosa Platform), xl. (F) Post-juvenile individual of Tmetoceras scissum. Reelaborated element with incomplete body chamber. PVI2/23. Bradfordensis Biozone. Ribarroja (SE Castilian Platform), xl. (G) Post-juvenile individual of Tmetoceras scissum. Resedimented element with incomplete phragmocone. SG. I07.1. Opalinum Biozone. S. Guiiio, Degracias (N Lusitanian Basin), xl. (H) Internal mould of a shell of ammonites (Brasilia) showing traces of open and lobulate fractures (F) likely produced by crustaceans. Bradfordensis Biozone. Domefto (SE Castilian Platform), xl. Table 1. Characters afthe Opalinum Tmetoceras in different areas afthe Iberia Opalinum Biozone SpecimensofTmetoceras Frequency Fossiliferouslevels ))34 »18 23 17 34 16 15 35 14 18 5 22 12 14 36 4 .1 4 o .1 3 «1 3 o 1 o 24 24 1 90 Degree of packing Degreeoftaphonomicheritage 0 Incompletephragmocones("/o) 60 Size-frequency distribution 20 7 61 o 98 o 69 64 o 36 22 0 0 0 80 37 100 100 100 100 37 uni- (U) or polymodal (P) asymmetric (A) or normal (N) negative (--) or positive (+) skew Shel/sofjuvenileindividuals absent (A) rare (R) predominant (P) Shel/sofadultindividuals u P u u A A R absent (A) rare (R) predominant (P) R u A Proportion of elements/species ,,34 ,,1 8 23 14 11 4 Diversityofthe genus 1 2 P 3 U A 20 3 3 o o 33 3 6 13 1 83 85 o R P 6 37 15 5 86 o o u 37 ISO 21 46 69 A Typeoftaphonicpopulation TPl -2 TPI-2 TPI-2 TPI-2 TPI-2 TP3 TP3 TP3 TP3 TPl TPI-2 TP2 TPI-2 TPI-2 13 Frequencyof Phyl/oceratina FrequencyofLytoceratina o «1 o «1 o o o o o o .1 o o o o o o o o o »10 14 4 Table 2. Characters afthe Murc hisan ae Tmetoceras in different areas afthe Iberia Murchisonae Biozone Specimens of Tmetoceras Frequency Fossiliferouslevels Degreeof packing Degreeoftaphonomicheritage Incompletephragmocones("/o) Size-frequen�ydistribution uni- (U) or polymodal (P) asymmetric (A) or normal (N) negative (--) or positive (+) skew Shel/sofjuvenileindividuals absent (A) rare (R) predominant (P) Shel/sofadultindividuals absent (A) rare (R) predominant (P) Proportion of elements/species Diversityofthegenus Typeoftaphonicpopulation Frequencyof Phyl/oceratina FrequencyofLytoceratina 5 9 3 40 o 60 5 TP2 o 5 «1 o o 100 TP3 o o 13 78 2 18 14 3 23 o 77 70 o 100 0 0 0 0 U A 13 39 2 TP3 TP2 TPl 12 30 12 .6 9 3 Table 3. Characters afthe Bradf ordensis Tmetoceras in different areas afthe Iberia Bradfordensis Biozone SpecimensofTmetoceras -30 Frequency 17 Fossiliferouslevels 15 Degree of packing _ 50 Degree oftaphonomic heritage 20 Incompletephragmocones("/o) 80 Size-frequencydistribution uni· (U) or polymodal (P) asymmetric (A) or normal (N) negative H or positive (+) skew Shells of juvenile individuals absent (A) rare (R) predominant (P) Shells of adultindividuals absent (A) rare (R) predominant (P) Proportionofelements/species -30 Diversityofthe genus 1 Typeoftaphonicpopulation TP1-2 FrequencyofPhylloceratina 0 FrequencyofLytoceratina 3 o 2 2 50 o 100 2 . TP1-2 o 0 o 0 o 34 3 2 25 3 .1 ,,1 17 3 2 2 97 33 0 96 o 0 50 100 42 100 100 20 U A P U A + 34 2 25 TP1 TP3 TP3 TP1 ,,1 0 0 0 0 0 0 0 0 2 10 o 0 o 100 o 0 75 10 29 61 U A 37 2 TP3 TP3 TP1 8 60 17 4 20 8 Table 4. Characters afthe Can c avum Tmetoceras ill different areas afthe Iberia Concavum Biozone Specimens of Tmetoceras Frequency Fossiliferouslevels Degree of packing Degreeoftaphonomicheritage Incompletephragmocones("/o) Size-frequency distribution uni- (U) or polymodal (P) asymmetric (A) or normal (N) negative H or positive (+) skew Shellsofjuvenileindividuals absent (A) rare (R) predominant (P) Shellsofadultlndividuals absent (A) rare (R) predominant (P) Proportionofelementslspecies Diversityofthegenus Typeoftaphonicpopulation FrequencyofPhylloceratina FrequencyofLytoceratina o 2 o o o o o o o 2 2 o 100 100 P 2 TP3 o o o o 2 .1 2 o 100 50 2 TP3 o o o o o o o 10 o 30 3 2 Protoatlantic CD sin Concavum Bc. 0 0 I Bradfordensis Bc. 30 30 I Murchisonae Bc. 0 0 I Opalinum Bc. 34 34 I Iberia �®i:® E lcontlnental latfonn 4 0 4 I 0 63 0 27 I 36 6 0 0 I 6 112 0 110 I 2 Total number of Tmetoceras = 611 T. scissum = 558 I T. �gleyi = 53 W Tethys @ @@@ Shelfal basin 0 0 I 0 77 72 I 5 92 88 I 4 193 193 I 0 Figure 4. Total number of Aalenian Tmetoceras obtained from each basin, indicating the specific number of specimens of T. scissum and T. regleyi. (TP I) are composed of mono specific shells showing unimodal and asymmetric distribu­ tion of size-frequencies, with positive skew. These populations have a high proportion of microconchs and the shells of juvenile individuals are predominant, whilst shells of adult individuals are scarce. Taphonic populations of type 2 (TP2) are composed of mono- or polyspecific shells showing unimodal and normal distribution of size-frequencies, with high kurtosis. Populations of this second type have a low proportion of micro conchs and the shells of juvenile individuals are scarce, whilst the shells of adult individuals are com­ mon. Taphonic populations of type 3 (TP3) are composed of poly specific shells showing uni- or polymodal and asymmetric distribution of size-frequencies, with negative skew. Shells of juvenile individuals are absent, micro conchs are very scarce and shells of adult ind�viduals are predominant in taphonic populations of this last type. SEDIMENTARY --- . - PALAEOENVIRONMENTS PROXIMAL OUTl!R PLATFORM DI$TAL OUTI!R PLATFORM = 50 Km CONFINED ENVIRONMENTS � E+ I E- TYPE - 1 TYPES OF TAPHONIC TYPE- 2 POPULATIONS TYPE - 3 CHARACTERS DISTRIBUTION OF SIZE-FREQUENCIES TYPE-3 uni-orpo/ymoda/ asymmetric negative skew SHELLS OF JUVENILE INDIVIDUALS absent SHELLS OF ADULT INDIVIDUALS - - predominant PROPORTION NUMBER OF MICROCONCHS NUMBER OF MACROCONCHS -0 PROPORTION NUMBER OF PRESERVED ELEMENTS _ 1 NUMBER OF SPECIES DIVERSITY OF GENUS - - _ po/yspecific I THRESHOLD I E+ I TYPE -2 unimodal normal high kurlosis scarce common low variable mono-or polyspecific OUTER ENVIRONMENTS E+ I E- TYPE- 1 unimodal asymmetric positive skew predominant scarce high high monospecific Figure 5. Types of taphonic populations of ammonites developed in environments of shallow outer platform as observed on Middle Jurassic ammonites of the Iberian Basin (after Fermindez-L6pez, 1995). 6' 100 I e- 90 Q) 80 Ol 2 ·c 70 Q) ..c u 60 ·E 50 0 c 0 40 ..c 0.. 2 30 -0 Q) 20 Q) 0, Q) 0 10 20 30 40 50 60 70 80 90100 Degree of packing (PO) o Concavum Tmetoceras • Bradfordensis Tmetoceras o Murchisonae Tmetoceras • Opalinum Tmetoceras PO - Number of specimens - Number of fossiliferous levels X 100 - Number of specimens THO - Number of reelaborated elements X 100 - Number of specimens Figure 6. Chart showing the different values of packing degree (PD) and taphonomic heritage degree (THD) in the different areas, at a zonal scale, indicating their type of taphonic population (TP- l, TP-2, TP-3 ). Different types of taphonic populations of Tmetoceras show also distinctive degrees of packing (Figure 6). This index is directly proportional to the abundance of specimens and it takes higher values when the number of fossiliferous levels decreases. Taphonic populations of type I have high values of packing (up to 55%). Taphonic populations of type 3 have low values of packing (under 30%). Thus, the degree of packing is another criterion to determine the type of taphonic population. In contrast, the degree of ta­ phonomic heritage, i.e. the proportion of reelaborated elements, is not correlated with the type of taphonic population but with the degree of stratigraphical or sedimentary con den - sation. Taphonic populations of type I showing very high degrees of packing and ta­ phonomic heritage were formed in condensed sections from the Median Subbetic Basin during the Murchisonae Biochron, as well as in condensed associations from the External Subbetic Basin during the Opalinum Biochron and from SE Castilian Platform during the Opalinum and Bradfordensis biochrons. Taphonic populations of type 3 showing very high degrees of taphonomic heritage associated with very low degrees of packing were formed in condensed sections from the Median Subbetic Basin during the Bradfordensis Bio­ chron. Some taphonic populations of type 3 displaying very high degrees of taphonomic heritage occur also in condensed associations from Aragonese Platform during the Conca­ vum Biochron and from NW Castilian Platform during the Bradfordensis Biochron. Opalinum Tmetoceras are fairly common in Lusitanian, Iberian and Betic basins (Fig­ ure 7). Their frequencies are lower than I % in the Tortosa, Aragonese and Castilian Platforms. Taphonic populations developed in the Betic and Lusitanian basins, as well as in the deepest environments of the Iberian Basin, were of types I and 2. In contrast, taphonic populations were of type 3 in the shallower environments of the Iberian Basin. All the Opalinum Tmeto­ ceras found in the Betic and Lusitanian basins are T. scissum (Figure 8). However, a post-ju­ venile specimen of T. regleyi has been found in the upper portion of the Opalinum Biozone, associated with abundant specimens of T. scissum in the NW Iberian Basin. 6°%L 50 40 30 20 10 6°%L 50 40 30 20 10 13 26 39 52 65 78 mm 0 6°%k 13 26 39 52 65 78 mm 0 7°% L 60 50 40 30 20 10 13 26 39 52 65 78 mm 0 60%Lo:h: 50 40 30 20 10 13 26 39 52 65 78 mm 0 50 40 30 20 10 13 26 39 S2 65 78 mm 0 0c::J �C) �� �lrL 30 60%L1rL 20 50 10 40 30 13 26 39 52 65 78 mm 0 20 10 13 26 3952 657ammD � Proportion of incomplete phragmocones Tmetoceratina� Phylloceratinaand Lytoceratina Figure 7. Frequency ofTmetoceratinae and Phylloceratina plus Lytoceratina in different areas ofIberia, and some size- frequency distributions of Tmetoceras, from the Opalinum Biozone. In the Iberian Peninsula, Murchisonae rocks are thin compared with the Bradforden­ sis rocks above or with the Opalinum below. Murchisonae ammonites are also more scarce. Specimens of Tmetoceras scissum are frequent in some Betic outcrops only, and they correspond mainly to mono specific taphonic populations of type 1 (Figure 9). Tmeto­ ceras recorded in the Murchisonae Biozone of the Basque-Cantabrian Basin comprise lo­ cal poly specific assemblages (Figure 10). A few specimens of Tmetoceras scissum have been obtained from the Basque-Cantabrian Basin, associated with scarce juvenile and post-juvenile specimens of T. regleyi that represent probable demic individuals. Some specimens of T. scissum founded in the NW areas of the Castilian Platform are adult. A few adult specimens of Tmetoceras regleyi have been obtained also from the central sector of Median Subbetic Basin, associated with abundant specimens of T. scissum. No Mur­ chisonae Tmetoceras are known from the Lusitanian Basin. Tmetoceras freq Demic T. scissum Ademic T. scissum Protoatlantic CD Opalinum Tmetoceras Iberia �� Ademic T. reg/eyi ................................................ . W Tethys @@@;@ Figure 8. Frequency of Opalinum Tmetoceras, indicating the type of taphonic population of T. scissum or T. regleyi in each area. Murchisonae Biozone 60%kb: 50 40 30 20 10 13 263952 6578mmD Tmeloceralinae � Phylloceralina and Lyloceralina Figure 9. Frequency ofTmetoceratinae and Phylloceratina plus Lytoceratina in different areas of Iberia, and the size- frequency distribution of Tmetoceras specimens in the central sector with expanded sections of Median Sub­ betic Basin, from the Murchisonae Biozone. Ammonoids are more frequent and widespread in the Bradfordensis Biozone than in the Murchisonae Biozone of Iberia. Bradfordensis Tmetoceras are quite frequent in Me­ dian Subbetic Basin, Lusitanian Basin and SE Castilian Platform (Figure 11). Taphonic populations of Tscissum developed in the Betic and Lusitanian basins, as well as in the SE Castilian Platform, were of types 1 and 2 (Figure 12). In contrast, taphonic popula­ tions of T scissum were of type 3 in shallower areas of the Iberian Basin and Betic Basin. However, specimens of T regleyi become relatively frequent in some deep areas of the Iberian Basin, composing taphonic populations of type 1, whilst in the Betic Basin only very scarce adult specimens of this species have been found. Bradfordensis taphonic populations of T scissum in the SE Castilian Platform, as well as taphonic populations of T regleyi in the Tortosa Platform, show distinctive features (Fig­ ure 11). These populations are of type 1 and they display higher proportions of incomplete phragmocones among the largest specimens. These higher proportions of fragmentary shells among the largest specimens is indicative of fragmentation of the shells by predators or scavengers associated with low values of sedimentation rates. Under opposite conditions, with high values of sedimentation rates and showing no evidence of predators or s�aven­ gers, the mechanical fragmentation of shells by turbulence produced higher proportions of incomplete phragmocones among the smallest specimens (Femandez-L6pez and Mouterde, 1994: Femandez-L6pez, 1997). The common occurrence of open and lobulate fractures in ammonite shells of these two areas also confirm this interpretation (Figure 3H). Protoatlantic CD Murchisonae Tmetoceras Iberia �®E@l E Icontinental latfonn W Tethys @ @@@ Sheifal basin Tmetoceras frequency uumuuumm_mm_mmm.... � Demic T scissum � Ademic T scissum __ -_- - -_-_ -_---_-_-_ :- _:--_:-_: -•••••••••••••••••• Gl_ •••••••••••••••••••••••• � �::��c :� :;:::�mic T regleyi :: : ::: ::::::.: ::: :I::;:] Figure 10. Frequency ofMurchisonae Tmetoceras, indicating the type of taphonic population of T scissum or T regleyi in each area_ 60%�/ 50 40 30 20 10 13 26 39 52 65 78 mm D 60%� 50 40 30 20 10 13 26 3952 6578 mmO 6°%L 50 40 30 20 10 13 26 39 52 65 78 mm 0 7°% L 60 50 40 30 20 10 13 26 39 52 65 78 mm 0 � Proportion of incomplete phragmocones Tmetoceratina� Phylloceratina and Lytoceratina Figure 11. Frequency of Tmetoceratmae and Phylloceratma plus Lytoceratma m dJtterent areas of Iberia, and some size-frequency distributions of Tmetoceras, from the Bradfordensis Biozone. Several Tmetoceras have been obtained from condensed associations along the Ibe­ rian Cordillera in deposits of the upper Aalenian and of the lower Bajocian (Figures 13, 14). These specimens are the only Tmetoceras identified in the Iberian Plate in post-Brad­ fordensis sediments, but they are reelaborate fossils. No Concavum Tmetoceras are known from the Lusitanian or Betic basins. 3. PALAEOECOLOGICAL INTERPRETATIONS AND HABITATS Type of taphonic population, abundance and frequency of specimens, strati graphic persistence and degree of packing are distinctive criteria in interpreting the palaeoecology and palaeobiogeography of the recorded associations of ammonites. Biogeographi ' cal dis­ persal and necroplanktic drift of shells (a case of taphonomic dispersal) were the main de­ termining factors on the final distribution of the ammonite shells (Figure 15). Consequently, the present distribution of ammonite shells reflect both their original and post-mortem distribution. Tmetocerasfreq. Demic T. scissum Protoatlantic CD Shelfal basin Ademic or parademic T. scissum Bradfordensis Tmetoceras Iberia � ®E@ W Tethys @@@§> Demic T. reg/eyi ............................. � Ademic or parademic T. reg/eyi . . .............................. ......................... ............................. � Figure 12. Frequency of Bradford ens is Tmetoceras, indicating the type of taphonic population of T. scissum or T. regleyi in each area. Con cavum Biozone Tmetoceratinae � Phylloceratina and Lytoceratina Figure 13. Frequency ofTmetoceratinae and Phylloceratina plus Lytoceratina ofthe Concavum Biozone in differ­ ent areas of Iberia. In Lusitanian and Iberian basins, representatives of Ammonitina are dominant among the Aalenian ammonoids, and the scarce specimens of Phylloceratina or Lytocerati­ na represent ademic organisms. In Betic Basin, as an area of the West Tethys, Aalenian Phylloceratina and Lytoceratina were represented by demic organisms. Eudemic Tmetoceras are represented in the fossil record by taphonic populations of type 1, characterized by the relative abundance of juvenile elements and high values of ta­ phonomic packing. In contrast, ademic Tmetoceras are represented by taphonic popula­ tions of type 3, showing low values of taphonomic packing, and they are dominated by adult elements. The active and passive biodispersal led to the occurrence of immigrant and transported Tmetoceras, which respectively are miodemic and parademic organisms. Bio­ dispersed Tmetoceras are represented in the fossil record by taphonic populations of type 2 or 3 showing median values of taphonomic packing. Taphonomic data suggest a eudemic character to the T. scissum representatives recorded in shelfal basins of the Iberian Plate (Figure 16). Aalenian T. scissum are widely distributed in the Betic and Lusitanian basins, where they occur in rich but nearly mono specific associa­ tions. Eudemic T. scissum inhabited basin areas, characterized by the occurrence of juvenile specimens and taphonic populations of type 1. In contrast, many allochthonous elements of T. scissum from the Iberian Basin are interpreted as having arrived at their present locations by necroplanktic drift. The taphonomic dispersal produced the concentration of adult shells of T. scissum in shallow neritic environments, representing ademic organisms. They did not breed or ontogenetically develop in the Castilian and Aragonese platforms. In the Castilian Plat­ form, there is evidence of shell transport from the north (Femandez-L6pez and G6mez, 1990a). Northwestwards from Castilian and Aragonese platforms, the NW Iberian Basin, NE Cameros, Basque-Cantabrian Basin and Asturias were the depositional sites ofautochthonbus and allochthonous shells of T. scissum throughout the Aalenian time. . Concavum Tmetoceras Protoatlantic Iberia W Tethys G) �� @@@@ Shelfal baBln Shelfal baBln Tmetoceras frequency ........... .................. . Ademic T. scissum ..n .. n I • T �-3 • [.n Figure 14. Frequency of Con cavum Tmetoceras. indicating the type of taphonic population of T. scissum in each area. Inferred OUTofthe living area without breeding PARADEMIC MIODEMIC with breeding EUDEMIC Inferred IN the living area Figure 15. Summary of the palaeobio­ geographical categories mentioned in this work. The palaeobiological entities, in particular am­ monites, are demic when their remains are found in their living area. Conversely, they are ademic organisms or taxa when they are in­ ferred outside of their living area. Demic spe­ cies may be inferred in their breeding area (eudemic), in an area normally occupied but where they do not breed (miodemic), or in a living area occasionally reached by passive bio­ dispersal (parademic; after Fernandez-L6pez, 1990, 1991 and Fernandez-L6pez and Melen­ dez, 1995). ADEMIC DEMiC Some Opalinwn specimens exhibiting morphological characters of T. regleyi have been found in the NW Iberian Basin, but they are interpreted as post-juvenile, ademic organisms (Figure 17). The active and passive biodispersal led to the occurrence of immigrant and trans­ ported T. regleyi in the Iberia, which respectively represent miodemic and parademic organ­ isms. The active biodispersal led to the occurrence in outer platforms of immigrant T. regleyi, which represent miodemic organisms, during the Murchisonae Biochron. Taphonic popula­ tions of T. regleyi dominated by juvenile individuals were produced by eudemic organisms in the Iberian Basin during the Bradfordensis Biochron. Scarce adult specimens of T. regleyi confined to isolated horizons in the Betic Basin are interpreted as evidence of parade mic or­ ganisms dispersed during the Murchisonae and Bradfordensis biochrons. In conclusion, shells of Aalenian Tmetoceras have been accumulated in widely dis­ tributed areas throughout the Iberian Plate during the Opalinum Biochron. However, the taphonomic and biogeographical dispersal of Tmetoceras through the Iberian Basin was hindered during the Murchisonae Biochron, as a consequence of the relative fall of sea level. A new relative rise of sea level during the Bradfordensis Biochron favoured the im­ migration of juvenile Tmetoceras in the deepest areas of the epicontinental platforms. S e - Concavum Biochron Bradfordensis Biochron Murchisonae Biochron Opalinum Biochron Protoatlantic Iberia o eeoeoo C,M)G) _ Eudemic or miodemic T. scissum � Ademic or parademic T. scissum W Tethys 0 e� Figure 16. Zonal chart of the palaeobiogeographical distribution of Tmetoceras scissum representatives in the Iberia. Concavum Biochron Bradfordensis Biochron Murchisonae Biochron Opalinum Biochron Protoatlantic Iberia o f)f)OOOG � _ Eudemic or miodemic T. reg/eyi � Ademic or parademic T. reg/eyi W Tethys o 4D�� • • • . . . • • • . . • • • • Figure 17. Zonal chart of the palaeobiogeographical distribution of Tmetoceras regleyi representatives in the Iberia. veral specimens of Tmetoceras have been found in the rocks of the Concavum Biozone, but they are reelaborate elements derived from older sediments. The Iberian Basin was not ac­ tive as an epicontinental migration route for Aalenian Tmetoceras. T. scissum inhabited environments of shelfal basins. T. regleyi inhabited environments of epicontinental plat­ forms. However, T. scissum occurs together with T. regleyi in beds of the Iberian and Betic basins. These two species appear to intergrade, but they were ecological and bio­ geographically differentiated. Several lines of taphonomic evidences (such as type of ta­ phonic population, abundance, frequency, strati graphic persistence, degree of packing, and degree of taphonomic heritage) support the concept that the environments of outer epicon­ tinental platform were the sites inhabited by T. regleyi. 4. GLOBAL DISTRIBUTION OF TMETOCERAS Tmetoceras can be considered a pandemic genus of ammonites abundantly repre­ sented in the northern margins of the West Tethyan Subrealm, from north Africa and west­ ern Europe eastwards to southeast Asia and beyond, and around the Pacific Ocean, including the East-Pacific Subrealm (Figure 18). Although no abundant Aalenian Tmeto­ ceras are known from the Arctic Province, some species have been found in Alaska (Westermann, 1964, 1981, 1992). Aalenian Tmetoceras occur in the following two prov­ inces of the Boreal Realm: the Bering Province (North Pacific margin and northwestern North America; cf. Imlay, 1955, 1962, 1964; Poulton, 1982; Poulton and Tipper, 1991; Poulton et al. , 1991) and the Sub-Boreal Province (Scotland, northern France, northern Germany, Poland; Morton, 1965; Bielecka et al., 1970; Morton and Hudson, 1995). Specimens of T. scissum have been found in the following three provinces of the West Tethyan Subrealm: 1. Northwest European Province (northwestern areas of the Iberian Basin, Britain, northern France, Germany, Rumanian Carpathians; cf. Buckman, 1892, 1907; Arkell, 1933; Patrulius and Popa, 1971; Dietl, 1977; Dietl and Etzold, 1977; Callomon and Chandler, 1990, 1994; Callomon, 1995). Figure 18. Palaeogeographical distribution of Tmetoceras representatives. 2. Sub-Mediterranean Province (epicontinenta1 seas of North Africa, northern Lu­ sitanian Basin, southeastern areas of the Iberian Basin, southern and central France, southern Germany, Switzerland, Iran, Caucasus; cf. F1amand, 1911; Fischer, 1915; Kakhadze, 1942; Co10, 1961, 1964; Rieber, 1963; E1mi, 1967; Seyed-Emami, 1967; Contini, 1970; Braun and Jordan, 1976; E1mi and Ca1oo, 1985; Benshili, 1989; Rostovtsev, 1991; Westermann, 1992; E1mi and Rulleau, 1994; Rulleau, 1995). 3. Mediterranean (or West Tethyan) Province (she1fa1 or oceanic areas of North Af­ rica, southern Spain, Italy, Austria, Hungary, Bulgaria; cf. Benecke, 1865; Vacek, 1886; Gregorio, 1886; Gemmellaro, 1886; Ramaccioni, 1934; Maubeuge, 1955; Dubar, 1960; Geczy, 1967; Fischer, 1970; Venturi, 1985; Kalin and Ureta, 1987; Mouterde and E1mi, 1991; Sadki, 1996; Callomonetal., 1995; Cresta, 1996). T. scissum has been recognized in southern Asia (cf. Sato, 1954; Sato in Koma1arjun and Sato, 1964; Braun and Jordan, 1976) and in the West Pacific Province (Japan and far eastern of the former USSR; cf. Sato, 1954). Specimens of T. scissum have been found also in the following three provinces of the East-Pacific Subrea1m: 1. Andean Province (western South America, Chile, Peru, Argentina; cf. Burckhardt, 1903; Westermann and Riccardi, 1972; Bogdanic et ai., 1985; Hi1le­ brandt and Westermann, 1985; Hillebrandt et al., 1986; Groschke et al., 1988; Riccardi et al., 1990, 1992; Westermann, 1992). 2 . . Athabascan Province (western North America; Frebo1d, 1951, 1964; Frebo1d et ai., 1969; Im1ay, 1982; Poulton et ai., 1991; Poulton and Tipper, 1991; Poulton et ai., 1992). 3. Shoshonean Province (Western Interior of the United States; Im1ay, 1973). In conclusion, T. scissum was a pandemic species, inhabiting oceanic or she1fa1 envi­ ronments in early Aa1enian. However, some species of Tmetoceras, such as T. regleyi and T. flexicostatum, were geographically restricted in very distant areas. T. regleyi has been found only in European areas of the West Tethyan Subrealm. Representatives of T. regleyi were distributed mainly in the Sub-Mediterranean and Northwest European provinces, in­ habiting shallow environments of epic on tin ental platforms (cf. Dumortier, 1874; Gemme­ Haro, 1886; Roman and Boyer, 1923; Buckman, 1892; Schlegelmich, 1985; Rulleau, 1995). It is suggested here that a pattern of adaptive radiation may have taken place in the Western Tethys during the Opalinum-Murchisonae biochrons, giving rise to T. regleyi from T. scissum. Specialized forms of Tmetoceras (k-strategists such as the individuals of the species T. regleyi) are widespread in the epicontinental platforms around the Western Tethys during the Murchisonae and Bradfordensis biochrons. Epicontinental, specialized forms of T. regleyi suffered extinction in the latest Bradfordensis Biochron. Shelfal or oce­ anic, generalist forms of T. scissum disappeared in the Western Tethys or the Mediterra­ nean Province in the latest Bradfordensis Biochron (Ferwindez-L6pez et ai., 1997), but they survived in the East-Pacific Subrealm. In latest Bradfordensis Biochron or in earliest Concavum Biochron, T. scissum gave rise to T. kirki (Westermann), a species restricted to the East-Pacific Subrealm (Westermann, 1964, 1992; Westermann and Riccardi, 1972; Bogdanic et al., 1985; Hillebrandt and Westermann, 1985; Poulton and Tipper, 1991). From a palaeobiogeographical point of view, distinctive sedimentary basins of Iberia belonged to three adjacent bioprovinces throughout Aalenian time: Mediterranean, Sub­ Mediterranean and Northwest European provinces (Figure 19). The relative orientation of the Iberian Peninsula has been accomplished on the basis of the palaeogeographical data published by Ziegler (1990) and Dercourt et al. (1993) . . The Mediterranean Province included the Betic Basin and it occupied regions open to oceanic influence, showing characteristically high abundance of Phyllo- and Lytoceratina, where Hammatoceratidae plus Tmetoceratinae were more frequent than Graphoceratidae. The Sub-Mediterranean Province essentially occupied the epicontinental seas bor­ dering the northern margins of Tethys (cf. Page, 1996); in particular, eastern areas of the Iberian Basin (SE Castilian Platform, Tortosa Platform and Aragonese Platform, at least), but also some regions open to oceanic influence such as the North Lusitanian Basin. In the f­ Z W o « 0:: C) --l « Z Sub-Mediterranean (5 Province ::J f- � 250 km I-l Leioceratinae + Graphoceratinae Tmetoceratinae + Hammatoceratidae Phylloceratina + Lytoceratina Figure 19. Areas of the Iberian Peninsula occupied by three separate ammonite bioprovinces throughout Aalenian time. NW and Central areas of the Castilian platform were not inhabited by Tmetoceras, although some shells ar­ rived to these shallow, epicontinental, outer platforms by nekroplanktic drift. The diversity of ammonoid faunas decrease towards the northern areas, from the Mediterranean Province to the Northwest European Province. This biogeographic gradient was latitudinally limited by environmental factors, including temperature, showing no evi­ dences of a bathymetric control. Sub-Mediterranean Province, demic Phyllo- and Lytoceratina were generally absent; ademic Phyllo- and Lytoceratina were not important elements of the preserved associa­ tions; ammonoid diversity was relatively high; and Graphoceratidae were more frequent than Hammatoceratidae plus Tmetoceratinae. No demic Tmetoceras are known from the NW and Central areas of the Castilian Platform. The Northwest European Province encompassed northwestern areas of the Iberian Basin (Asturias, Basque-Cantabrian Basin and NE Cameras). In this province even ademic Phyllo- and Lytoceratina were generally absent; ammonoid diversity was relatively low; and Graphoceratidae representatives were predominant elements (up to 90%). The distribution of the Sub-Mediterranean Province in the Iberian Plate (Figure 19), from areas open to oceanic influence of the Lusitanian Basin to areas occupied by shallow epicontinental seas of the Iberian Basin, allows us to exclude a bathymetric control of this bioprovince. The ammonoid provincialism through the Aalenian in these areas may have been latitudinally limited by environmental factors, including temperature rather than depth, since the diversity of ammonoid faunas decrease towards the northern areas. 5. CONCLUSIONS Tmetoceras scissum and T. regleyi appear to intergrade, but they were ecological and biogeographically differentiated. In Iberia at least, populations of T. sqissum and T. regleyi were not coexistent. However, by necroplanktic drift, the shells of these species may be associated in the same sites and beds. Taphonomic data suggest a eudemic character in shelfal basins or oceanic areas to the representatives of 7! scissum. Nevertheless, exceptional immigrants and drifted shells of this species arrived in shallow environments of neighbouring platforms. In contrast, _ representatives of T. regleyi inhabited preferentially shallow environments of epic on tin en­ tal platforms. Several taphonomic criteria (type of taphonic population, abundance, frequency, strati graphic persistence, degree of packing, and degree of taphonomic heritage) support the concept that epicontinental platforms were the sites of adaptive radiation of T. regleyi. ,The biogeographical dispersal of T. scissum and T. regleyi, and the arrival of immi­ grants in the epicontinental platforms of Iberia, were favoured by the relative sea-level rise during the Opalinum and Bradfordensis biochrons. The relative sea-level fall during the Murchisonae and Concavum biochrons decreased the accessibility of Tmetoceras shells from shelfal basins to epicontinental platforms. The Iberian Basin was not active as an epicontinental migration route for Aalenian Tmetoceras. The ammonoid provincialism throughout the Aalenian in Iberia may have been lati­ tudinally limited by environmental factors, including temperature, since the diversity of ammonoid faunas decrease towards the northern areas. The taphonomic interpretation of successive transients is very important in explaining the palaeobiogeographical distribution of species and the diversity of genera. The general conclusion is that taphonomic analysis of successive transients, as in this case, are relevant in interpreting the biogeographical distribution and the taxonomic diversity of ammonites. ACKNOWLEDGMENTS The authors wish to express their acknowledgement to Doctor E. Cariou (Univ. Poi­ tiers) for the critical reading of the manuscript and suggestions made. The authors are grateful to Uly Martin for the preparation of the photographs. This work was financed by the projects PB9 l -0383 (DGICYT), PB92-00l l (DGICYT -CSIC), PB94-0786 (DGICYT) and PB96-0838 (DGES-CSIC), and by two Luso Hispanic Integrated Actions (E9-95 and HP94-043). REFERENCES Alvaro, M., Barnolas, A. , Cabra, P., Comas-Rengifo, M.l, Del Olmo, P., Fernandez-L6pez, S. , Goy, A. , R ami rez del Pozo, 1, Simo, A. , and U reta, M. S. , 1989, El Jurasico de Mallorca (Islas Baleares), Cuad. Geol. Iberica 13: 67- 1 20. Arkell, W.l, 1933, The Jurassic System in GreatBritain. Clarenton Press, Oxford, pp. 1 - 6 8 1 . Benecke, E. W., 1 865, U ber Trias und Jura in den Sii dalpen, Geognostiche-palaont. Beitr. 1 : 1-204. Benshili, K., 1989, Li as- Dogger du Moyen Atlas plisse (Maroc), sedimentologie, biostratigraphie et evolution paleogeogr aphique, Doc. Geol. Fac. Sci. Lyon 106: 1 1-283. 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