New longirostrine crocodylomorph remains from the Blesa Formation (Barremian) in the Iberian Peninsula (Spain)
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Crocodylomorpha has been a highly morphologically and ecologically diverse clade over time. During the Mesozoic and Cenozoic, several crocodylomorph lineages colonized the marine environment; however, by the late Early Cretaceous the extinction of Thalattosuchia and the origination of new marine forms occur, and the “Middle” Cretaceous is a period of time where marine crocodylomorphs are poorly known. Here we describe two rostrum fragments (MPZ 2016/78 and MPZ 2016/79) collected in the upper part of the Blesa Formation (Barremian, Lower Cretaceous) in Teruel (Spain). The “Upper” Blesa Fm has been interpreted as a coastal–transitional depositional environment.
The specimens correspond to long-snouted crocodylomorphs. MPZ 2016/78 is the left half of a fragmentary rostrum with heterodonty in dentition size, M4? and M5? being the largest alveoli. This suggests that it belongs to a crocodylomorph with a generalist diet. By contrast, MPZ 2016/79 is a fragmentary right half of a more gracile and slender long rostrum. It is homodont in size, with several small teeth, common in animals specialized for ichthyophagy.
MPZ 2016/78 and MPZ 2016/79 have been assigned to Crocodylomorpha indet. This new crocodylomorph material, together with the fossil remains of marine vertebrates previously found in the same region (plesiosaurs, chelonians, osteichthyans, chondrichthyans and a new crocodylomorph), suggests that the “Upper” Blesa Formation was a coastal zone with a great wealth of fauna, making it an interesting area for the study of Barremian marine vertebrates.
KeywordsMarine crocodylomorph Early Cretaceous Blesa Formation Iberian Peninsula
Crocodylomorpha ha sido un clado muy diverso a lo largo del tiempo, tanto morfológica como ecológicamente. Durante el Mesozoico y el Cenozoico, varios linajes de cocodrilomorfos colonizaron el ambiente marino. A fines del Cretácico Inferior se produce la extinción de Thalattosuchia (principal clado de cocodrilomorfos marinos del Mesozoico) y el origen de nuevas formas marinas, de manera que el Cretácico "Medio" es un período de tiempo en el que los cocodrilomorfos marinos son poco conocidos. Aquí se describen dos fragmentos craneales de cocodrilomorfos (MPZ 2016/78 y MPZ 2016/79) recogidos en la parte superior de la Formación Blesa (Barremiense, Cretácico Inferior) en Teruel (España), interpretada como un ambiente sedimentario costero-transicional.
Los restos que se describen pertenecen a cocodrilomorfos de rostro alargado. MPZ 2016/78 corresponde con la mitad izquierda de un fragmento rostral, en el que se observa dentición heterodonta en tamaño, siendo M4? y M5? los alvéolos mayores. Esto sugiere que pertenece a un cocodrilomorfo con una dieta generalista. Por el contrario, MPZ 2016/79 es un fragmento de rostro, correspondiente a la mitad derecha de un rostro largo, más fino y grácil que el anterior. La dentición es homodonta en tamaño, con numerosos dientes pequeños, comunes en animales ictiófagos.
MPZ 2016/78 y MPZ 2016/79 son restos craneales fragmentarios que han sido asignados a Crocodylomorpha indet. Este nuevo material de cocodrilomorfo, junto con los restos fósiles de vertebrados marinos hallados anteriormente en la misma región (plesiosaurios, quelonios, osteictios, condrictios y un nuevo cocodrilomorfo), sugiere que la Formación Blesa “Superior” era una zona costera con una gran riqueza de fauna, lo que lo convierte en un área interesante para el estudio de los vertebrados marinos de Barremiense.
Palabras clavecocodrilomorfos marinos Cretácico Inferior Formación Blesa Península Ibérica
The evolutionary history of the crocodylomorphs includes several groups that have adapted to aquatic or semi-aquatic environments over time. However, not all of them have managed to live in the marine realm. During the Mesozoic, several independent marine radiations occurred, including Thalattosuchia, Dyrosauridae, and some taxa belonging to Pholidosauridae and Eusuchia (Mannion et al. 2015).
Marine crocodylomorph biodiversity increased until at least the Late Jurassic, with the radiation of Thalattosuchia, but there was an overall decline in biodiversity across the Jurassic/Cretaceous (J/K) boundary, with a loss of more than 75% of the genera, including theteleosaurid extinction in Europe (Mannion et al. 2015; Markwick 1998; Martin et al. 2014; Tennant et al. 2016; Young et al. 2014a). At least four metriorhynchoid genera (Young et al. 2014a) and one teleosaurid from Africa (Machimosaurus rex, Fanti et al. 2016) crossed the J–K boundary, but metriorhynchoids declined in biodiversity during the Early Cretaceous and were completely extinct by the Aptian (Chiarenza et al. 2015). After the J/K crash in diversity, the origination patterns of marine forms have very low rates in the Berriasian–Valanginian (Tennant et al. 2016), but a recovery in marine crocodylomorph biodiversity had started by the Late Cretaceous (Mannion et al. 2015; Markwick 1998; Martin et al. 2014). The oldest marine tethysuchian crocodyliform consists of a partial dentary from the Isle of Wight, most likely from the Upper Albian (Young et al. 2014b). Marine pholidosaurids are known in the Cenomanian–Turonian, and some dyrosaurids have been cited in the Cenomanian of Portugal (Buffetaut and Lauverjat 1978), the Santonian–Campanian of Egypt (Lamanna et al. 2004) and the Cenomanian of the Sudan (Buffetaut et al. 1990). However, Young et al. (2014b) conclude that there is insufficient evidence to be certain that any known Cenomanian specimen can be safely referred to Dyrosauridae (see also discussion in Young et al. 2016). The oldest marine gavialoid known, Eothoracosaurus, was found in the late Campanian of the Coon Creek Formation (Brochu 2004). Both Eusuchia and Dyrosauridae survived the K/Pg mass extinction (e.g. Barbosa et al. 2008; Brochu 2003; Brochu et al. 2002; Hastings et al. 2011; Hill et al. 2008; Mannion et al. 2015; Martin et al. 2014).
While Early Cretaceous marine deposits have yielded remains of marine reptiles (ichthyosaurs, plesiosaurs or mosasaurs) (Benson and Butler 2011), there is a general lack of marine crocodylomorphs in the Hauterivian–Barremian (Martin et al. 2014; Tennant et al. 2016), with the exception only of the Hauterivian Machimosaurus rex from Tunisia (Fanti et al. 2016).
The interval from Hauterivian to Campanian thus constitutes an interesting and poorly known period of time, where there is a replacement of the crocodylomorph fauna that inhabited the coastal and marine realm, with the extinction of Thalattosuchia and the first appearance of marine Pholidosauridae and posteriorly Dyrosauridae and Eusuchia, and with various temporal gaps in the marine crocodylomorph fossil record.
1.1 Marine crocodylomorphs from the Iberian Peninsula
The Iberian Peninsula is a highly interesting area of study for Mesozoic vertebrates, especially for crocodylomorphs from the Middle Jurassic to Late Cretaceous (e.g. Parrilla-Bel et al. 2013; Buscalioni et al. 2013; Puértolas-Pascual et al. 2013, 2015; Narváez et al. 2016). However, the record of marine crocodylomorphs mainly consists of poorly diagnostic remains, and few of them have been assigned to genus or species level. The presence of pholidosaurids has been cited in the Hauterivian–Barremian of Galve and the Wealden of Ortigosa de Cameros (Spain), as well as dyrosaurids in the Cenomanian of Nazaré (Portugal), but all of these citations need to be confirmed (Bardet et al. 2008). Thalattosuchians are better represented than pholidosaurids and dyrosaurids. There are some Middle Jurassic remains, including the holotype of Maledictosuchus riclaensis (Parrilla-Bel et al. 2013; Parrilla-Bel and Canudo 2015a), some indeterminate remains in Teruel and La Rioja (Spain), and Steneosaurus remains in Portugal (Buscalioni 1986; Bardet et al. 2008; Canudo 2011). However, most of the fossil record comes from Upper Jurassic outcrops: in Portugal (the Lisbon, Leiria, Faro and Coimbra regions) the presence of indeterminate Kimmeridgian and Tithonian teleosaurids, Machimosaurus and Steneosaurus (Bardet et al. 2008; Krebs 1967, 1968) has been cited; from the Kimmeridgian of Asturias (Spain) indeterminate thalattosuchian remains have been published (Ruiz-Omeñaca et al. 2004, 2007), as well as an indeterminate teleosaurid (Martínez et al. 1995), cf. Plesiosuchus (Young et al. 2012) and cf. Machimosaurus (Young et al. 2014c); a metriorhynchid from Griegos (Teruel, Spain) has been cited (Buscalioni 1986); Machimosaurus teeth (Young et al. 2014c) and a rostrum fragment from Teleosaurus (Boscá 1903) have been cited from Buñol (Valencia, Spain); and Machimosaurus remains have been cited in Extremadura (Spain) (Sauvage 1897–1898). The Early Cretaceous is a period that is singularly rich in vertebrate remains, mainly from continental and coastal environments (Kriwet et al. 2008; Buscalioni et al. 2008; Canudo et al. 2010). However, as occurs worldwide, Early Cretaceous marine crocodylomorphs are very scarce in the Iberian Peninsula. Bardet et al. (2008) cite three vertebrae and bone fragments from an indeterminate thalattosuchian from Alcalá de la Selva (Teruel, Spain), and a thalattosuchian specimen has been cited from the Berriasian of Jaen, Spain (Gea et al. 2001). Gasca et al. (2011) cite teeth belonging toaff. Machimosaurus from the Barremian of Allepuz (Teruel). These identifications about fragmentary material need to be reviewed.
In recent years, new marine vertebrate fossils have been recovered from the Blesa Formation (Barremian) in Teruel (Spain). These fossil remains correspond to isolated plesiosaurian vertebrae and teeth (Parrilla-Bel and Canudo 2015b), the braincase of a marine crocodylomorph (Parrilla-Bel et al. 2012, currently under review), and two rostrum fragments belonging to crocodylomorphs from Los Centenales and Fontanilla-2 sites respectively. The aim of this paper is the description of these two fossils.
1.2 Geographical and geological context
Geologically, both specimens were found in the Blesa Formation in the Olietesubbasin. The Iberian Basin of northeast Spain is an intracratonic basin that developed during the Mesozoic (Salas et al. 2001). An Early Cretaceous stage of rifting resulted in the formation of several subsident areas including the Olietesubbasin. The Olietesubbasin is located within the large Cretaceous Maestrazgo Basin (Soria et al. 1995; Salas et al. 2001). The Blesa Formation is divided into the “Lower” Blesa Formation and the “Upper” Blesa Formation. The lower part was deposited in a continental environment, and it is separated from the “Upper” Blesa by a distinct ferruginous transgression surface (Aurell et al. 2004). The “Upper” Blesa Formation was deposited in a coastal system. The sediments are mainly carbonate with more detrital levels towards the top of the formation. The vertebrate remains are from limestone levels in the lower part of the “Upper” Blesa Formation. The presence of oogonia attributed to Atopocharatrivolvis triquetra in the lower part of the Blesa Formation dates it to the early Barremian (Canudo et al. 2010; Riveline et al. 1996; see discussion in Canudo et al. 2012). At the moment, we consider the upper part of the Blesa Formation to be Barremian in age, waiting for this to be specified with greater precision.
The “Lower” Blesa Formation has provided a highly diverse assemblage of continental tetrapods: amphibians, squamates, chelonians, mammals, pterosaurs, crocodylomorphs and dinosaurs (Badiola et al. 2008; Canudo et al. 2010; Puértolas et al. 2015; Alonso and Canudo 2016). However, in the “Upper” Blesa Formation vertebrates are scarcer. There are isolated remains of osteichthyans, chondrichthyans, chelonian plates, teeth and cranial and postcranial elements of crocodylomorphs (Parrilla-Bel et al. 2012), cranial remains of pterosaur (Ulloa-Rivas and Canudo 2014), as well as teeth and vertebral centra belonging to plesiosaurs (Parrilla-Bel and Canudo 2015a).
The material described in this paper consists of two rostrum fragments, MPZ 2016/78 from Fontanilla-2 and MPZ 2016/79 from Los Centenales. Both specimens are housed at the Museo de Ciencias Naturales de la Universidad de Zaragoza (MPZ).
Specimens MPZ 2016/78 and 79 are fragmentary and poorly diagnostic, but the ornamentation of the external surface of the rostra, the thecodont tooth implantation (each tooth being situated apart from its neighbours in an individual alveolus) and the tooth replacement (a replacement tooth below the functional tooth) allow us to rule out plesiosaur or ichthyosaur affinities (Rieppel 2001; Sassoon et al. 2015) and to assign the rostra to Crocodylomorpha. The two rostrum fragments (MPZ 2016/78 and 79) correspond to long-snouted crocodylomorphs, but the morphology and size of the two specimens are different and they belong to two different taxa.
Long-snouted species are found in all clades of marine crocodylomorphs (Thalattosuchia, Dyrosauridae, Pholidosauridae, Gavialoidea and Tomistominae), but also in other, non-marine taxa, such as freshwater pholidosaurids or gavialoids such as the extant Gavialis gangeticus. In addition, several species of Crocodylus have long and slender rostra, though not as narrow or elongated as those of Gavialis or Tomistoma so they are not commonly included in the longirostrine condition (Pol and Gasparini 2009). Similar crocodilian skull morphologies have been considered to be an example of convergent evolution, arising as a response to similar ecological/functional constraints linked to the diet (e.g. Piras et al. 2014).
As noted above, the Barremian was a period of the Early Cretaceous in which there was an absence of marine crocodylomorphs (Tennant et al. 2016). The most common crocodylomorphs that inhabited Europe in this age were bernissartids, atoposaurids, goniopholidids and hylaeochampsids, the same associations that have also been found in the Iberian Peninsula (Schwarz-Wings et al. 2009; Buscalioni et al. 2008; Puértolas-Pascual et al. 2015). Atoposaurids are small crocodyliforms with a broad head and a short, pointed snout. Hylaeochampsids are small eusuchians with short and broad skulls, as found in bernissartids, small-sized crocodiles with a brevirostrine skull (Romer 1956; Sweetman et al. 2015). Some goniopholidids such as Vectisuchus (usually considered a goniopholidid but with an unclear phylogenetic position) have a long slender snout (Buffetaut and Hutt 1980), but the snout of Goniopholididae is usually broad and hardly elongated (a platyrostral snout) (e.g. Pritchard et al. 2013). All these taxa are continental crocodylomorphs and lack the longirostrine condition (with the exception of Vectisuchus). None of them shares morphological similarities with MPZ 2016/78 or 79. In addition, the fossil remains MPZ 2016/78 and 79, found in marine facies, although are broken they lack evidences of having suffered long transportation. In this context we assume that they correspond with marine forms.
Specimen MPZ 2016/79 is a fragment of a long rostrum with a constant width and height, most probably of a slender-snouted longirostrine form. The variation in the alveolar size is small, it being considered homodont. Also the interalveolar space is constant. Thalattosuchians, gavialoids and dyrosaurids have a “regular” rostrum (constant width and height along the maxilla), homodonty in dentition size and a constant interalveolar space. Gavialoids have a festooned alveolar border because of the alignment of the maxillary and dentary tooth rows (e.g. Argochampsa, Hua and Jouve 2004). Dyrosaurids have occlusal sulci between the alveoli, but not deep enough dorsally to be seen from above; the lateral margin of the maxillais linear and the tooth row is not festooned in dorsal view (Jouve 2005). MPZ 2016/79 has a linear lateral margin of the maxilla, and lacks occlusal sulci. Instead, it has reception pits on the maxilla, medial to the maxillary alveoli (the dentary teeth occlude lingually to their maxillary counterparts, resulting in an alligator-like overbite; Brochu 2003). Occlusal pits are described in other long-snouted crocodylomorphs, such as Maledictosuchus riclaensis (Parrilla-Bel et al. 2013) or Machimosaurus hugii, which bears reception pits between the posterior maxillary alveoli, close to the level of the lingual alveolar margin (Martin and Vincent 2013). MPZ 2016/79 has a longitudinal groove along the lateral side of the maxilla dorsal to the dental margin of the alveoli. Ventral to this groove the ornamentation is reduced. A similar maxillary groove has been described in Terminonaris robusta and Terminonaris browni (Wu et al. 2001), but in these species the groove is continuous along the maxilla. Goniopholidids and other pholidosaurids bear a maxillary depression, but this is located in the posterior region, in contact with the jugal (Martin and Buffetaut 2012; Martin et al. 2016).
The presence of at least two marine crocodylomorph taxa in the Upper Blesa Formation has ecological implications. The Blesa Formation (Barremian, Lower Cretaceous) has been described as a coastal–transitional environment, where marine vertebrate fossils as plesiosaurs have been found (Parrilla-Bel and Canudo 2015b). The presence of plesiosaurs and various crocodylomorphs implies the coexistence of several active, medium-sized predators in this environment. This could only have been maintained by the existence of great amounts of lower organisms to feed on, with niche partitioning or temporal or spatial differentiation. A detailed geological and paleontological study of this formation, currently being undertaken, will provide interesting data on this rich ecosystem and increase our knowledge of marine reptiles, which are globally scarce in the Barremian.
We describe two marine crocodylomorph remains from the Barremian of Spain. Both specimens, MPZ 2016/78 and MPZ 2016/79, are fragmentary and lack clear diagnostic characters, so we assign them to Crocodylomorpha indet. Both specimens (MPZ 2016/78 and MPZ 2016/79) are longirostrine forms, but they show different morphologies. MPZ 2016/79 is long-snouted and with several small teeth, common in animals specialized for ichthyophagy. By contrast, MPZ 2016/78 corresponds to a more robust, long-snouted taxon. The alveoli are larger than in MPZ 2016/79 and the tooth row is heterodont in size, which could correspond to a crocodylomorph with a more generalist diet. Accordingly, we can recognize two crocodylomorphs with different lifestyles in the “Upper” Blesa Formation. The new crocodylomorph material, together with the fossil remains of marine vertebrates (such as small-medium-sized plesiosaurs, chelonians, osteichthyans, and a new crocodylomorph) previously found in the same region, suggest that the “Upper” Blesa Formation was a coastal zone with a great wealth of fauna. A deeper study of this Barremian vertebrate association in the Blesa Formation, with the presence of taxa poorly known worldwide during the Lower Cretaceous will provide interesting data of the coastal biota of the Barremian of the Iberian Peninsula.
This paper forms part of project CGL2014-53548 and is subsidized by the Spanish Ministry of Economy and Competitiveness, the European Regional Development Fund and the Government of Aragón (‘Grupos Consolidados’ and ‘Dirección General de Patrimonio Cultural’). We thank Javier Andreu and Fernando Gracia, who provided the material described. We also thank S. Jouve, the anonymous reviewers and the editors for their comments, which helped to improve the article, and Rupert Glasgow, who revised the English grammar.
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