SONINNIIDAE Buckman, 1892

Sandoval, José, 2022, Sonniniidae Ammonitina, Middle Jurassic from Southern Spain: taxonomic, biostratigraphical and palaeobiogeographical analysis, Geodiversitas 44 (27), pp. 801-851 : 807-808

Family SONINNIIDAE Buckman, 1892 in Buckman (1887 -1907)

DESCRIPTION

Howarth (2013, in Treatise), describes Sonniniidae as follows: “Typical forms are stout planulates with strong hollow keel, ribs, and midlateral tubercles at least early in growth. Other forms show great variety, from evolute planulates to sphaerocones and oxycones, but almost all have Sonninia like innermost whorls, and ribs, tubercles or spines at some stage. Several genera are dimorphic”.

REMARKS

In the latest version of the Treatise ( Howarth 2013), the family Sonniniidae is divided into two subfamilies: Sonniniinae Buckman, 1892 and Witchelliinae Callomon & Chandler, 2006 in Chandler et al. (2006). In Sonniniinae , Howarth included the following genera: Sonninia [with the subgenera S. ( Sonninia ) Douvillé, 1879; S. (Euhoploceras) Buckman, 1913; S. ( Papilliceras ) Buckman, 1920; and S. (Alaskinia) Westermann, 1978]; Sonninites Buckman, 1923 ; Shirbuirnia Buckman, 1910 ; Pseudoshirbuirnia Dietze et al., 2005 ; and Dorsetensia Buckman, 1892 . In Witchelliinae , Howarth (2013) included the genera: Witchellia Buckman, 1889 ; Asthenoceras Buckman, 1899 ; Fontannesia Buckman, 1902 ; Newmarracarroceras Hall, 1989 ; and Guhsania McLearn, 1926 .

Almost simultaneously to the publication of the Treatise by Howarth, a study bySandoval et al. (2012) concerning the latest Grammoceratinae , and later a follow-up study by Sandoval & O’Dogherty(2018) characterized Asthenoceras as typical of Grammoceratinae with close phylogenetic relationships with the Late Toarcian-Middle Aalenian genus Vacekia . Thus, the latest forms of Vacekia and earliest forms of Asthenoceras are morphologically very similar, with a simple septal suture and a hollow, notably high keel. The genus Fontannesia , which has been classified as possibly belonging to Grammoceratinae ( Linares & Sandoval 1988) or Witchelliinae ( Chandler et al. 2006), has a simple septal suture, but not as simplified as among contemporaneous Grammoceratinae , and keel is not as high. The genus Newmarracarroceras (type, Dorsetensia clarkei Crick, 1894 [ Crick 1894: 388]; OD), from Western Australia, New Guinea, and eastern Indonesia, is remarkably similar to Fontannesia in the type of coiling, cross-section, ribbing, keel, and septal suture. It has only minor differences with respect to Fontannesia , i.e. a more compressed whorl section and weaker ribbing, which disappears before the end of the PH. In view of these small dissimilarities in addition to the remote geographical areas they occupied, Fontannesia and Newmarracarroceras could be classified as two separate genera but certainly with close phylogenetic relationships.

The genus Latiwitchellia Imlay, 1973 (type species Witchellia (Latiwitchellia) evoluta Imlay, 1973 [ Imlay 1973: 70, pls 31-33; HT, OD, the specimen of the pl. 31: figs 1, 2, 5, 6]), from Oregon ( United States), which was originally included byImlay (1973: 70) as a subgenus of Witchellia , occurs in some sections of the Subbetic (Betic Cordillera, Spain). This genus, which is not mentioned by Howarth (2013, in the Treatise), shows similarities with Asthenoceras and, particularly, with Linaresites Sandoval, 2012 (type species, Fontannesia montillanensis Linares & Sandoval, 1988 [ Linares & Sandoval 1988: 8, HT in pl. 1: figs 12, 13]), which is not mentioned either in the new Treatise. According to Sandoval et al. (2012), Latiwitchellia, which occurs in the Discites and Ovale zones of the Subbetic, appears to be the latest representative of the subfamily Grammoceratinae , rather than a primitive Witchelliinae .

The genus Guhsania McLearn, 1926 ( McLearn 1926: 98) from Middle Jurassic (Lower Bajocian, Laeviuscula Zone) of British Columbia ( Canada) shows similarities with Witchellia but is less involute and the ribs become large and widely spaced on the outer whorl.

Lastly, the genus Dorsetensia , with a relatively simple septal suture, and closely similar to Witchellia in general morphology, ornamentation, size, and type of dimorphism, should be included in Witchelliinae rather than in Sonniniinae .

In short, the genus Asthenoceras is excluded from Sonniniidae ; Dorsetensia is transferred from Sonniniinae to Witchelliinae , while certain doubts remain concerning the taxonomic status of Fontannesia , Newmarracarroceras , and Latiwitchellia, which appear to be the last representatives of Grammoceratinae .

DIMORPHISM

Dimorphism is remarkably common and usually quite pronounced in the sonniniids. Macroconchs [M] are relatively large in size and have a simple peristome. Although several Subbetic shells are incomplete and lack an intact peristome, making it difficult to discriminate from the inner whorls of larger forms, some genera have two distinct types of dimorphism: Type 1) Several specimens, well preserved, complete with mouth borders and signs of maturity such as crowding of sutures, eccentric coiling of the last whorl, modification of the ribbing on the last third of the BC, and constriction of the peristome, have plain mouth borders and have no lappets. Westermann (1966: 309) proposed that such specimens likely represented dimorphous of Euhoploceras. This idea was supported by Sandoval & Chandler (2000: see pl. 9, figs 1-5), after analyzing the genus Euhoploceras of southwest England and southern Spain. According to the Treatise ( Howarth 2013), this type of dimorphism is common in the subfamily Sonniniinae . Chandler (2019: 782) supposed that these forms are small adult macroconchs, which he named as mesoconchs. Type 2) More common are small specimens (<40 mm in diameter) that have lateral lappets, which are long and spatulate in some forms. In certain cases, these microconchs have modified coiling of the last whorl. These ‘ Pelekodites -style’ ammonites vary from rare spinose forms to more common ribbed-only shells and are slightly more evolute than their corresponding macroconchs. According to Howarth (2013, in the Treatise) this type of dimorphism with clearly differentiated [M] and [m] is common in the subfamily Witchelliinae . Here, it is assumed that this latter dimorphism, more characteristic than the former type, occurs in both Sonniniinae and Witchelliinae .

Although dimorphism is common and readily apparent in sonniniids, it is almost always difficult to assign macroconchs and microconchs to the same taxon, particularly at species level. Therefore, in species descriptions, [M] is used for the “macro” forms and [m] for “micro”, but macro- and microconchs are often not assigned to the same species and sometimes not even to the same genus.

DISTRIBUTION

Sonniniids extend from the Upper Aalenian (Concavum Zone) to the Lower Bajocian (Humphriesianum Zone) worldwide, except in the Boreal Realm. This stratigraphic range is occupied in the Subbetic domain. The sampled sections in this domain have provided specimens belonging to the genera Sonninia (subgenera Euhoploceras, Sonninia , and Papilliceras ), Sonninites , Witchellia and Dorsetensia . Sandoval & Chandler (2000) made a detailed study of the upper Aalenian-lowermost Bajocian S. (Euhoploceras), and therefore, this subgenus will be analysed only briefly here. TheFigure 6 shows the approximate stratigraphic range of the sonniniid “species” recorded in the Subbetic domain.