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Journal of Paleontology 92(3):373–387
early apical ontogeny) allows for testing of phylogenetic hypotheses on a limited geographic scale, broader phylogenetic analysis—and reliable assignment to supraspecific taxa—based solely on shell characters remains problematic (Allmon, 1996, 2011; Beu, 2010, p. 89). In this paper, we report four species assignable to the genus
Turritella sensu lato, from the Late Jurassic (Oxfordian) Chari Formation of Kutch, western India, and argue that these represent the oldest turritellid species known. The age of the Turritella- bearing horizons is well constrained by the coeval ammonites and belemnites. Two of these species of Turritella were previously described from these deposits (Mitra and Ghosh, 1979). Unfor- tunately, however, they went unnoticed by the paleontological community, and the specimens were lost. We therefore here re-describe them, based on new data obtained from numerous additional specimens and SEM analysis, and describe two more species as new. We compare the Indian species with diverse species acrossmany geological periods and continents to showthe extent of homeomorphism, but we explicitly note that nothing phylogenetic is intended by these comparisons.
Turritellidae versus Mathildoidea
Within gastropods, mathildoids are phylogenetically distant from turritellids. They are sometimes referred to as “lower hetero- gastropods,” more closely related to pulmonates and opistho- branchs than to
cerithioids.Yet the shells ofmanymathildoids are superficially similar to turritellids in being high-spired, with rela- tively small apertures. The group was also apparently more diverse in the Mesozoic, especially the Jurassic, than it is today (see Bandel, 1995; Bieler, 1995; Gründel and Nützel, 2013), posing an additional potential difficulty in distinguishing its spe- cies from early representatives of Turritellidae. The family Turritellidae is characterized by an elongate,
high-spired shell of many whorls, ending in an aperture that is relatively small, simple, and entire, lacking any elaboration of its margin (Marwick, 1957). The subfamily Turritellinae is characterized by external teleoconch sculpture of spiral threads, sometimes beaded, and curved growth lines; the aperture is rounded or quadrate and not large; the inner wall of the aperture is smooth and concave (Marwick, 1957; Bandel, 2006). Mathildoid species superficially resemble turritellids in shell shape and spiral ornamentation, but the former are usually
more slender (Bandel, 1995). Many species of mathildoids have strong carination similar to one of the species discussed here. Strong carination is also found in turritellids, such as Zaria angulata (Sowerby, 1840) from the Miocene of the Indian sub-continent (see Harzhauser et al., 2009, fig. 3a–d), and “Turritella” mortoni from the Paleocene of the U.S. Gulf and Atlantic coastal plains (Allmon, 1994, 1996). Shells of mathildoids, however, show a number of clear dif-
identification of them as turritellids is therefore based on other characters. For example, all our studied specimens lack axial sculpture and an apertural anterior canal, and all of our four species are relatively large (> 2 cm) compared to known Jur- assic mathildoids. A broader analysis of shell characters of our Jurassic species, compared to a number of Cretaceous turri- tellines and Mesozoic mathildioid species originally identified as Turritella (Tables 1–3), further supports our assignment by demonstrating that our species are more similar to Cretaceous turritellids than to Mesozoic mathildoids. Growth-line data are poorly known from fossil mathildoids, but extant species show mostly irregular and opysthocyrt growth lines (Bieler, 1995). The species considered here, however, have prosocline growth lines. Ecologically, the modern family Mathildidae is a mostly deep-water group (Bieler, 1995), with many Recent species inhabiting 550–600m depths within coral bank com- munities (Smriglio et al., 2007). The depositional environment of the Dhosa Oolite Member, from which the present species were obtained, in contrast, was an offshore setting below the fair-weather wave base (Singh, 1989; Fürsich et al., 1992), and no corals have been described from the Dhosa Oolite Member.
Geologic setting
Geologic time units.—During the Middle Jurassic (Bajocian– Bathonian), the Kutch Basin developed due to the fragmentation of Gondwana (Biswas, 1982, 1991). Mesozoic strata in Kutch
Table 1. Coded morphology of turritelline species described in this text (A–D), Cretaceous turritellines (E–I) and some mathildidoid species (J–N). The coded characters and their different states are given in Appendix 1.
Species Name
A Turritella jadavpuriensis B Turritella jhuraensis C Turritella amitava n. sp. D Turritella dhosaensis n. sp.
F J
Strat. Range Oxfordian
E Turritella encina Squires and Saul, 2006 (Squires and Saul, 2006)
Turritella iota Popenoe, 1937 (Squires and Saul, 2006) G Turritella hearni Merriam, 1941 (Squires and Saul, 2006) H Turritella petersoni Merriam, 1941 (Squires and Saul, 2006) I
N Mathilda cf. euglypha Laube (Hudleston, 1892)
K Promathilda decorta (Bandel, 1995) L Tofanella decussata (Bandel, 1995) M Cristalloella cassiana (Bandel, 1995)
Oxfordian Oxfordian Oxfordian Santonian
late Turonian Turonian
Turritella xylina Squires and Saul, 2006 (Squires and Saul, 2006) Cenomanian Mathilda bolina (Bandel, 1995)
Late Triassic Late Triassic Late Triassic Late Triassic Early Jurassic
1 2 345678 91011 0 3 112210 1 0 1
1 0-3 112120 1 0 1 1 1-4 121110 ? 0 1 1 5 ? 2 ? 1 2 0 1 0 1 1 0 ? 1 ? ? 1 0 ? 0 1
1 4 ? 1 ? ? 2 0 ? 0 1 1 1 ? 0 ? ? 2 0 ? 0 1
Cenomanian to early Turonian 1 0 ? 1 ? ? ? 0 ? 0 1 1 0 ? 1 ? ? 1 ? ? 0 1 2 3 ? 2 ? 1 1 1 1 1 0 2 3 112121 1 1 0 2 3 012211 1 1 0 2 3 002121 0 1 0 2 3 1 ? ? 0 1 1 ? 1 0
ferences compared to turritellids, most conspicuously their hetero- strophic (sinistral) protoconch, which shows an abrupt boundary with the dextral teleoconch. High-spired mathildoids are also smaller than most turritellids; their aperture frequently bears a short anterior canal; and their earliest teleoconch whorls almost always bear axial (vertical) ribs in addition to spiral sculpture. None of our specimens has preserved protoconchs; our
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