Zoological Journal of the Linnean Society, 2008, 154, 278–290. With 3 figures A new Early Cretaceous lamniform shark (Chondrichthyes, Neoselachii) JÜRGEN KRIWET1*, STEFANIE KLUG2, JOSÉ I. CANUDO3 and GLORIA CUENCA-BESCOS3 Downloaded from https://academic.oup.com/zoolinnean/article/154/2/278/2614020 by guest on 25 March 2021 1Museum of Natural History, Department of Collection, Humboldt-University Berlin, Invalidenstr. 43, 10115 Berlin, Germany 2Museum of Natural History, Department of Research, Humboldt-University Berlin, Invalidenstr. 43, 10115 Berlin, Germany 3Grupo Aragosaurus, Universidad de Zaragoza, Facultad de Ciencias, c. Pedro Cerbuna 12, 50009 Zaragoza, Spain Received 6 September 2007; accepted for publication 17 September 2007 Eoptolamna eccentrolopha gen. et sp. nov. (Chondrichthyes, Lamniformes) from the near coastal upper Barremian Artoles Formation (Early Cretaceous) of Castellote (northwestern Spain) is described on the basis of about 50 isolated teeth. This taxon represents one of the earliest lamniform sharks known to date. We hypothesize that most pre-Aptian lamniforms belong to an ancient group characterized, amongst others, by a very weak gradient monognathic heterodont dental pattern, and by tearing-type dentition. There is a nutritive groove in the lingual root protuberance in juveniles of Eoptolamna, which persists in adults. A single pair of symphysial and a pair of upper intermediate teeth might have been present. Consequently, a new family, Eoptolamnidae, is introduced to include the new form, as well as Protolamna and probably Leptostyrax. The Eoptolamnidae represent an ancient family within Lamniformes. The origin of lamniform sharks remains, however, ambiguous despite recent advances. The new Spanish taxon is widespread in the Barremian of north-eastern Spain, and occurs in a wide range of facies from near-coastal to lake deposits. This lamniform also occurs in the Lower Cretaceous of northern Africa. © 2008 The Linnean Society of London, Zoological Journal of the Linnean Society, 2008, 154, 278–290. ADDITIONAL KEYWORDS: Eoptolamna – Eoptolamnidae – Leptostyrax – morphology – plesiomorphic condition – Protolamna. INTRODUCTION Early Cretaceous, neoselachians seem to have diver- sified rapidly, and in the late Early Cretaceous, shark Neoselachian sharks are a highly diversified group of faunas of modern appearance, including open pelagic marine vertebrates occupying the top levels in food and deep-water forms, appeared (Kriwet & Klug, webs, with almost all major clades being known as 2008). However, the fossil record of neoselachians fossils in the Late Jurassic, with the exception of from the uppermost Jurassic and Early Cretaceous Squaliformes and Lamniformes (e.g. Saint-Seine, continues to be relatively incomplete, and interpret- 1949; Thiollière, 1854; Beaumont, 1960; Schweizer, ing Early Cretaceous lamniform diversity is still 1964; Cappetta, 1987; Thies, 1992; Duffin & Ward, ambiguous (e.g. Rees, 2005; Kriwet & Klug, 2008). 1993; Cavin, Cappetta & Seret, 1995; Brito & Seret, Early Cretaceous neoselachian sharks have been 1996; Leidner & Thies, 1999; Kriwet & Klug, 2004; less intensively studied compared with those from the Underwood, 2006). During the Late Jurassic and Late Cretaceous (e.g. Cappetta, 1975; Biddle & Lan- demaine, 1988; Batchelor & Ward, 1990; Biddle, 1993; *Corresponding author. Underwood & Mitchell, 1999; Underwood, Mitchell & E-mail: [email protected] Veltkamp, 1999; Underwood, 2004; Rees, 2005). This 278 © 2008 The Linnean Society of London, Zoological Journal of the Linnean Society, 2008, 154, 278–290 A NEW EARLY CRETACEOUS SHARK 279 is especially evident for those from the Iberian Pen- were dissolved in buffered acetic acid for a maximum insular. The knowledge of Early Cretaceous Iberian of 24 h. The residues were screen washed with a neoselachians, although it has improved in recent 500-mm sieve, and the vertebrate remains were sorted years, is based mainly on small assemblages compris- under a stereoscopic microscope. ing only a few taxa from near-coastal to brackish, The Maestrat sub-basin is one of four Early and even freshwater, deposits in the province of Cretaceous sub-basins (Maestrat, Cameros, Colum- Teruel (Estes & Sanchiz, 1982; Canudo, Cuenca- bres, and South Iberian) in the Iberian Basin, and Bescós & Ruiz-Omenaca, 1996a; Kriwet & Kussius, forms the easternmost Iberian Range. The Iberian 1996; Kriwet, 1999). Basin is a wide intracratonic Mesozoic basin located This paper provides the description of one of the in the north-east of Iberia (Aurell, Bosence & oldest fossil lamniform species. The new species from Waltham, 1995; Canudo et al., 1996b; Salas & Downloaded from https://academic.oup.com/zoolinnean/article/154/2/278/2614020 by guest on 25 March 2021 the upper Barremian of Castellote (north-eastern Guimer, 1996; Martín-Chivelet et al., 2002). Its devo- Spain) is assigned to a new genus based on its tooth lopment is related to an anticlockwise rotation of the morphology. The suprageneric placement within lam- Iberian plate and crustal thinning during the Meso- niforms and the generalized and plesiomorphic dental zoic (Martín-Chivelet et al., 2002). This thinning was condition within Lamniformes are discussed. inverted in the Palaeogene, producing the present- day Iberian and Catalonian Coastal Ranges and parts of the surroundings of the Ebro, Duero, and Tajo MATERIAL AND GEOLOGICAL SETTING basins. Generally, two rifting phases are identified, This paper focuses on about 50 teeth recovered from spanning from the Late Permian to the Triassic and the fossil site of Vallipón in the north-western part of from the late Oxfordian to the Early Cretaceous the Maestrat sub-basin, near the city of Castellote, (Martín-Chivelet et al., 2002). c. 150 km southeast of Zaragoza (Fig. 1). Most teeth The development of the Maestrat, Cameros, Colum- are damaged, i.e. lacking parts of the root and/or bres, and South Iberian sub-basins is related to a crown. Sediment samples of c. 500 kg containing ver- prolonged phase of intracontinental rifting, and coin- tebrate bones and teeth were collected from the basal cided with the gradual opening of the North Atlantic part of the Artoles Formation in this sub-basin, and (e.g. Ziegler, 1988; Vergés & Garcia-Sanz, 2001). They Figure 1. Geographical and geological situation of the Vallipón site, upper Barremian, near Teruel in north-eastern Spain. © 2008 The Linnean Society of London, Zoological Journal of the Linnean Society, 2008, 154, 278–290 280 J. KRIWET ET AL. contain a sedimentary and structural record of three of parasymphyseals(?) present; mesiodistally com- main phases of tectonic subsidence (Salas et al., 2001) pressed teeth, with generally a single pair of lateral and 13 depositional sequences, which are character- cusplets; robust roots with short branches; lingual ized by massive successions of continental to shallow- protuberance more or less massive; with nutritive marine carbonates and clastics. groove, which might be secondarily closed. The Maestrat sub-basin is filled with Upper Jurassic–Lower Cretaceous palustrine and marine Genera included: Eoptolamna gen. nov., Leptostyrax, sediments. The Valanginian–Barremian sequence and Protolamna. (K1.1–K1.7) is up to 1500-m thick, and is character- ized by estuarine shallow-water carbonate platforms GENUS EOPTOLAMNA GEN. NOV. along the basin margins with important freshwater Downloaded from https://academic.oup.com/zoolinnean/article/154/2/278/2614020 by guest on 25 March 2021 discharges. Molluscs and calcareous algae dominated Derivation of name: From the Greek words: ‘eos’, the carbonate production. Three Early Cretaceous meaning ‘dawn, early’; ‘adruptos’, meaning ‘tearing’; formations are recognized in the Vallipón section and ‘Lamna’, meaning ‘modern lamniform shark’, in (from bottom to top): Mirambel (lower Barremian), allusion to the early occurrence and tearing-type Artoles (upper Barremian–lower Aptian) and Utrillas dentition of this lamniform. (Albian) formations. The Artoles Formation, mainly marls and limestones with abundant invertebrate Type species: Eoptolamna eccentrolopha gen. et sp. nov. remains, was formed on a shallow marine platform. There is a 30–50-cm thick layer at its base, consisting Generic diagnosis: Eoptolamnids with the following of sands and conglomerates of red and yellow colour characteristics: tooth crown faces with distinct verti- (e.g. Canudo et al., 1996b; Cuenca-Bescós & Canudo, cal median crest extending from cusp–root junction 2003). This represents a transgressive lag deposit almost to apex; few additional shorter and flexuous containing abundant isolated bones and teeth of ver- ridges present; well-developed lateral cusplets tebrates. The top of the Artoles Formation is dated on broadly united with main cusp, stronger inclined lin- the basis of the macroforaminifer Paleorbitolina len- gually than main cusp, and in front of labial cusp ticularis lenticularis (Blumenbach, 1805), confirming plane in profile view; lingual face of main cusp a late Barremian age for the fossiliferous layers strongly cambered; cutting edges well developed and (Canudo et al., 1996b). Up to now, 43 vertebrate taxa continuous; labial basal sledge smooth, delineating a representing a mixture of marine and continental short and narrow concavity; root high and coalescing forms have been identified (Ruiz-Omeñaca & Canudo, in upper parts, free in lower part; lingual protuber- 2001). Canudo et al. (1996b) proposed a coastal setting ance well developed,