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Unusual Gut Contents in a Cretaceous Ichthyosaur B deposits of Lyme Regis and Whitby in England and Holtz- maden in Germany. One of the earliest accounts (Buckland 1836) described coprolitic masses containing fish scales, within the body cavities of several ichthyosaurs from Lyme Regis. Later re-examination showed that the Unusual gut contents in a fish remains to belong to the Liassic holostean Pholido- phorus, and identified numerous dibranchiate cephalopod Cretaceous ichthyosaur hooklets (Pollard 1968). Large vertebrate remains includ- ing fish and small ichthyosaurs have been recorded as gut Benjamin P. Kear1,2*, Walter E. Boles2,3 contents in some Jurassic ichthyosaur specimens and Elizabeth T. Smith2 (McGowan 1974). Cephalopods, however, represent the 1South Australian Museum, North Terrace, Adelaide 5000, Australia dominant component of most ichthyosaur gastric residues 2Vertebrate Palaeontology Laboratory, School of Biological, Earth and from Lyme Regis and Holtzmaden (see Pollard 1968; Environmental Science, University of New South Wales, Sydney 2052, Keller 1976; Massare 1987; Bo¨ttcher 1989). Australia 3Australian Museum, 6 College Street, Sydney 2010, Australia The partial ichthyosaur skeleton (QM F16811, Queens- * Author and address for correspondence: South Australian Museum, land Museum, Brisbane, Queensland, Australia) discussed North Terrace, Adelaide 5000, Australia ([email protected]). here is assigned to Platypterygius longmani, a large (ca.7m in total length) ichthyosaur known primarily from the Recd 03.04.03; Accptd 21.05.03; Online 21.07.03 Upper Albian (Lower Cretaceous) of Queensland, Aus- Despite ichthyosaurs being one of the most exten- tralia (Wade 1990). An exceptionally preserved foetal skull sively studied Mesozoic marine reptile groups, there and fragmentary skeleton are preserved within the body is little documented direct evidence of dietary habits cavity. Foetal remains are rare in Cretaceous ichthyosaurs in most taxa. Here, we report the discovery of and are best known in taxa of Triassic and Jurassic age hatchling-sized marine protostegid turtle remains (Deeming et al. 1993; Brinkman 1996). Gut contents were and an enantiornithine bird (in association with extracted during preparation with acetic acid and included actinopterygian fish and phosphatic nodules) within actinopterygian fish remains, phosphatic nodules, disar- the body cavity of a gravid female ichthyosaur ticulated small turtle bones and the proximal tibiotarsus (Platypterygius longmani ) from the Lower Cre- of a bird (figure 1). The turtle fossils represent one or taceous of Australia; this is the first evidence, to our several hatchling-sized protostegids, an extinct family of knowledge, of feeding by ichthyosaurs upon both marine turtles classified with the Chelonioidea (Gaffney & turtles and birds. The exceptionally preserved gut Meylan 1988; Hirayama 1998). The bird bone is assigned contents show little evidence of digestion, suggesting to Enantiornithes, a basal subclass of Cretaceous birds consumption shortly before the ichthyosaur’s death. with a widespread Gondwanan distribution (Chiappe Poor swimming ability may have made hatchling 2002). turtles easy prey that could have been either swal- lowed whole or processed by shake feeding. Inges- tion of bird remains probably occurred through 2. DESCRIPTION AND REMARKS scavenging. Opportunistic feeding on vertebrates is The presence of an advanced foetus within the body at odds with existing interpretations of dietary hab- cavity of QM F16811 indicates that this individual was a its in Cretaceous ichthyosaurs, which favour gravid female close to parturition at the time of death. The predation primarily upon cephalopods. Such spe- large size (skull length of ca. 400 mm) and the articulated cialization is considered a contributing factor in the state of the foetus suggest that it was not ingested as prey. group’s ultimate extinction. However, the evidence Its anterior (craniad) placement and positioning with the here that at least some forms were able to use a wide head towards the anterior end of the adult ichthyosaur’s range of available food types suggests that the body cavity is also consistent with the condition observed decline of ichthyosaurs in the mid-Cretaceous may in other gravid ichthyosaur specimens (Bo¨ttcher 1990). be linked to other factors such as competition with The remains interpreted as gut contents are entirely dis- ecologically analogous pursuit predators. articulated and occur as a disaggregated mass throughout the anterior portion of the rib cage of the adult ichthyo- Keywords: ichthyosaurs; gut contents; hatchling turtles; saur. There is no evidence of gastroliths. The most com- enantiornithine bird; Cretaceous; Australia mon bony fossils are the teeth, cranial and postcranial 1. INTRODUCTION elements of fish. These include mainly vertebrae (ca.2– Ichthyosaurs, a highly successful group of Mesozoic mar- 8 mm in total length), although numerous well-preserved ine amniotes, have been considered the dominant high- skull bones (neurocranials, operculars and a small speed pursuit predators of the Mesozoic seas. The group ceratohyal) are present. Several fragmentary spine-like is traditionally characterized by a superficially ‘fish-like’ elements might represent ribs and fin rays. The small size body shape with a triangular stabilizing dorsal fin and ver- and morphology (including a prominent central foramen tically oriented lunate caudal fin. These features are best in the ceratohyal) of the fish remains suggest that they illustrated in taxa of Jurassic and Cretaceous age (Sander belong to teleosts. This group is common in the Toolebuc 2000). Current knowledge of ichthyosaur dietary habits Formation of Queensland and includes some smaller- is derived from preserved gastric residues (Pollard 1968), bodied taxa (e.g. Dugaldia) to which the material might coprolites (Buckland 1829) and dental morphology be attributed. Three teeth (of 5–7 mm in height) and a (Massare 1987). Surprisingly, however, most documented jaw fragment also suggest the presence of larger fish in the direct evidence (i.e. gastric contents) is based on a handful gastric mass, possibly the clupeomorphs Cooyoo or of specimens from the famous Liassic (Lower Jurassic) Pachyrhizodus. Proc. R. Soc. Lond. B (Suppl.) 270, S206–S208 (2003) S206 2003 The Royal Society DOI 10.1098/rsbl.2003.0050 Unusual gut contents in a Cretaceous ichthyosaur B. P. Kear and others S207 Numerous light grey irregular phosphatic nodules occur well as the surrounding clayey mudstone, also lacked any in conjunction with the fossil remains in the adult ichthyo- distinct sedimentary structures to suggest concentration saur’s rib cage. These are uniform and almost featureless through current action. in internal structure but do occasionally contain small All of the turtle remains studied are poorly ossified (a inclusions, possibly representing digested bone fragments. feature consistent with their early developmental stage) Pollard (1968) reported ‘buff coprolotic clay’ masses and exhibit a fibrous surface texturing. This differs from within the body cavities of Lower Jurassic ichthyosaurs the surface-pitting characteristic of bones modified by from Lyme Regis. Buckland (1835) identified similar digestion, which commonly also possess corroded articular material as phosphatic in composition and showed it to ends, thinning of long-bone shafts and edge rounding be derived from the digestion of fish and reptile bones. along breaks (Andrews 1990). The absence of such fea- The turtle remains recovered from the gastric residue tures from both the turtle and bird elements at hand may are disarticulated but were found within the same area of indicate that they were ingested shortly before the adult the body cavity: anteriorly in the vicinity of the pectoral ichthyosaur’s death. girdle. All of the remains are poorly ossified, being com- Poor swimming ability may have made hatchling protos- posed of cancellous endochondral bone, and appear to tegid turtles easy prey for ichthyosaurs. Their small size derive from one or more hatchling-sized (ca. 100–120 mm would have enabled them to be swallowed whole, in total length) individuals. The cranial elements are well- although, the characteristically robust teeth of P. longmani preserved and include a complete left frontal, left opis- were certainly suitable for dismembering larger individ- thotic, right prootic, supraoccipital and left quadrate. uals, perhaps by shake feeding (Kear 2002). Postcranial remains include a thoracic vertebral centrum, Predation upon hatchling turtles is consistent with the two anterior costals, a well-preserved left femur, two elongate skull and mandible of P. longmani, which suggest proximal carpal or tarsal elements and a damaged ilium. a preference for small-bodied prey. Indeed, this may have The thoracic centrum shows no evidence of fusion with prompted ingestion of the enantiornithine bird, whose the neural arch, although paired elongate dorsal facets floating carcass could have been scavenged from the wat- suggest the presence of cartilage. Similarly, the limb bones er’s surface. Direct capture of birds by ichthyosaurs is lack ossified articular ends and the ilium does not appear unlikely because most enantiornithines are thought to to have a fully formed acetabular extremity. This mor- have been volant and non-aquatic, their remains occurring phology is consistent with the early developmental stage in marine deposits probably as a result of post-mortem of the individual(s). fluviatile transport
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