Cretaceous Research 93 (2019) 129e142 Contents lists available at ScienceDirect Cretaceous Research journal homepage: www.elsevier.com/locate/CretRes Juvenile spinosaurs (Theropoda: Spinosauridae) from the middle Cretaceous of Morocco and implications for spinosaur ecology * Rebecca J. Lakin , Nicholas R. Longrich Department of Biology and Biochemistry, Milner Centre for Evolution, University of Bath, Bath, BA2 7AY, UK article info abstract Article history: The Spinosauridae is a specialised clade of theropod dinosaurs known from the Berriasian to the Cen- Received 29 May 2018 omanian of Africa, South America, Europe and Asia. Spinosaurs were unusual among non-avian di- Received in revised form nosaurs in exploiting a piscivorous niche within riverine and estuarine habitats, and they include the 24 August 2018 largest known theropod. Although fossils of giant spinosaurs are increasingly well-represented in the Accepted in revised form 18 September fossil record, little juvenile material has been described. Here, we describe new examples of juvenile 2018 Available online 19 September 2018 spinosaurines from the middle Cretaceous (Cenomanian) Kem Kem beds of Morocco. The fossils include material from a range of sizes and are relatively common within the Kem Kem deposits, suggesting that Keywords: juveniles exploited the same semiaquatic niche as the adults throughout ontogeny. This implies that the Dinosauria Cenomanian delta habitats supported an age-inclusive population of spinosaurs that was neither Spinosauridae geographically or environmentally separated, though some ecological separation between juveniles and Juvenile adults is likely based on the large variation in size. Bones or teeth of very small (<2 m) spinosaurs have Ontogeny not been found, however. This could represent a taphonomic bias, or potentially an ecological signal that Cretaceous the earliest ontogenetic stages inhabited distinct environments. Skeletal remains include individuals referable to Sigilmassasaurus brevicollis and a second spinosaurine taxon. Consistent with this, we also identify two distinct cranial morphs of Spinosauridae present within the Kem Kem, supporting previous recognition of distinct taxa in the assemblage. © 2018 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). 1. Introduction cervical vertebrae (Evers et al., 2015), but also recently from por- tions of the skull (Hendrickx et al., 2016). These are Sigilmassasaurus The Spinosauridae is a diverse family of theropod dinosaurs brevicollis (¼Spinosaurus maroccanus; Evers et al., 2015) and a including ten described genera (Taquet & Russell, 1998; Buffetaut & second spinosaurid taxon, possibly Spinosaurus (Hendrickx et al., Ouaja, 2002; Kellner et al., 2011; Allain et al., 2012; Buffetaut, 2012; 2016) or a relative (Evers et al., 2015). Malafaia et al., 2013; Evers et al., 2015) found across five continents Spinosaurs are thought to have been piscivorous on the basis of (Ruiz-Omenaca~ et al., 2005; Keller et al., 2011; Barrett et al., 2011; their elongated, crocodile-like skulls and their conical, spearing Buffetaut, 2012; Allain et al., 2012; Candeiro et al. 2017; Gasca teeth (Sues et al., 2002; Buffetaut, 2007; Hasegawa et al., 2010; et al., 2018). Spinosaurs are known from the Berriasian (Sales Richter et al., 2013). Furthermore, an intricate series of canals et al., 2017) to the Cenomanian (Buffetaut & Ouaja, 2002), and are across the distal parts of the upper and lower jaws, interpreted as a particularly common in the middle Cretaceous (Cenomanian) aged system of pressure receptors, have been cited as an adaptation for deposits of North Africa, including Egypt (Stromer, 1915), Algeria hunting aquatic prey (Ibrahim et al., 2014b; Vullo et al., 2016; Arden (Taquet & Russell, 1998; Benyoucef et al., 2015), and Morocco et al., 2018), though this is disputed (Leich & Catania, 2012; Barker (Buffetaut, 1989; Ibrahim et al., 2014a, 2014b). Within the Kem Kem et al., 2017; Henderson, 2018). The skeletal morphology of spino- region are two distinct morphologies, originally assigned only from saurines suggest a semiaquatic lifestyle, similar to extant croco- dilians (Amiot et al., 2010; Ibrahim et al., 2014b; Goedert et al., 2016; Aureliano et al., 2018). Adaptations for aquatic locomotion include retracted nares (Dal Sasso et al., 2005), a reduced pelvis and * Corresponding author. E-mail addresses: [email protected] (R.J. Lakin), [email protected] hindlimbs, and pachyostotic long bones (Ibrahim et al., 2014b; (N.R. Longrich). Aureliano et al., 2018). https://doi.org/10.1016/j.cretres.2018.09.012 0195-6671/© 2018 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). 130 R.J. Lakin, N.R. Longrich / Cretaceous Research 93 (2019) 129e142 Spinosaurs are the largest known theropod dinosaurs (Dal Sasso 3. Materials & methods et al., 2005; Therrien & Henderson, 2007; Gimsa et al., 2016). The largest specimen currently known is MSNM V4047 referred to The material presented here consists of three cervical vertebrae Spinosaurus aegyptiacus (Dal Sasso et al., 2005), which has an (FSAC-KK-7280, FSAC-KK-18119, FSAC-KK-18122), two dorsal verte- estimated skull length of 175 cm and an estimated body length of brae (FSAC-KK-18118, FSAC-KK-18121), a right premaxilla (FSAC-KK- 12e15 m (Therrien & Henderson, 2007). Other specimens, 7281) and a right quadrate (FSAC-KK-18120). We describe our including the holotype of S. aegyptiacus, have estimated total body vertebrae using the laminar nomenclature laid out in Wilson (1999). lengths of 10e14 m (Therrien & Henderson, 2007; Ibrahim et al., Specimens were acquired from commercial sources in the region of 2014b). Like all dinosaurs, however, giant spinosaurs would have Erfoud and Begaa (Fig. 1C) between October 2017 and March 2018 hatched from relatively small eggs before ultimately growing to (Fig.1B) Of the numerous Kem Kem outcrops in the region (Fig.1C), it adult size. Fossils of juvenile dinosaurs are generally very rare is difficult to know from which locality any of our isolated specimens (Lockley, 1994; Hone & Rauhut, 2010), and juvenile spinosaurs have originated, and given that the material is likely to have been only recently been described for the first time (Maganuco & Dal reworked, it is also difficult to know where in the environment these Sasso, 2018). However, little is still known about the growth and specimens may have originally been deposited post-mortem. How- life histories of giant spinosaurs. Small spinosaurine teeth are ever, the horizon can be verified from the taphonomic differences common from Kem Kem deposits (Richter et al., 2013), however, between the Ifezouane and Aoufous Formations. In the Ifezouane these cannot be reliably used for size or age estimations because of Formation, preservation is generally good, with bones preserved as the variation in spinosaur teeth within regions of the jaw (Monfroy, white, red fossils, or dark colored fossils in sandy matrix, often with 2017), and the polyphyodonts nature of all theropods (Erickson, bright red clays (Krassilov & Bacchia, 2013). In the Aoufous Forma- 1996; Therrien et al., 2005). tion, preservation is generally poorer, with specimens preserved in Here, we describe new material of juvenile spinosaurs. These more powdery yellow to tan coloured matrix (Krassilov & Bacchia, include a quadrate, cervical and dorsal vertebrae, and a premaxilla, 2013). These differences provide an independent means of veri- all found in the Kem Kem beds of eastern Morocco near the towns fying provenance and mean that fossils can typically be assigned to of Begaa and Erfoud. one of the two Kem Kem subunits with some confidence. We estimated body length by isometrically scaling from the proportions of the spinosaur reconstruction published in Ibrahim 2. Geological & palaeoecological setting et al. (2014b). Due to the controversial nature of this reconstruc- tion at the time of publication (Scott & Currie, 2017), and ongoing The Kem Kem beds represent the upper part of the informally- research into the locomotory and lifestyle adaptations of Spinosau- named ‘Continental Intercalaire’ (Rodriguez et al., 2011; rus, we also reconstruct body length estimations from the bipedal Benyoucef et al., 2015). The Kem Kem beds were originally reconstruction by Dal Sasso et al. (2005). This was done by cali- thought to be early Cretaceous in age, but the current consensus is brating the length, width and height of our juvenile specimens that this geological unit is Cenomanian in age based on both the (Table 1) with the corresponding known adult specimens from the shark fauna and faunal similarities with the Cenomanian aged literature (Stromer,1915; Dal Sasso et al., 2005; Ibrahim et al., 2014b) Bahariya Formation of Egypt (Sereno et al., 1996; Cavin et al., 2010). and scaling up by dividing the length, width and height of a juvenile The Kem Kem beds sit unconformably on marine strata of specimen with those of its corresponding adult specimen to calcu- Cambrian-Devonian age (Cavin et al., 2010; Ibrahim et al., 2014a). late a multiplication factor, then multiplying the estimated length of Above, they are overlain by cliff-forming Cenomanian-Turonian the adult model with the multiplicative inverse of the multiplication marine limestones (Martill et al., 2011), reflecting the pattern of factor. Measurements for all specimens are given in Table