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Home , Axelrodichthys, Coelacanthidae, Latimeria, Mawsoniidae

The diet of the Early † araripensis Maisey, 1986 (Actinistia: )

by

François J. Meunier* (1), Camila Cupello (2), Yoshikata Yabumoto (3) & Paulo M. Brito (2)

Abstract. – The paleohistological study of a crushed specimen of the coelacanth †Axelrodichthys araripensis Maisey, 1986, coelacanthiform from the (Santana Formation) of the , North-East , reveals various fossilized bony elements corresponding to an actinopterygian . These scattered skel- etal elements are localized near, but outside, the calcified lung of †A. araripensis, in a preserved soft tissue patch with distinctive physical characteristics of the limestone matrix surrounding the specimen. Based on the position of these scattered bones and on the soft tissue patch that surrounds these structures, we infer that it corresponds, probably, to the dietary content found in situ of this articulated specimen of A. araripensis. Our contribution describes the dietary habits of this of coelacanth and infers some details regarding its paleoenvironmen- tal .

© SFI Received: 19 Dec. 2017 Résumé. – Sur le régime alimentaire d’un coelacanthe du Crétacé inférieur, †Axelrodichthys araripensis Maisey, Accepted: 1 Feb. 2018 1986 (Actinistia, Mawsoniidae). Editor: O. Otero L’étude paléohistologique d’un spécimen écrasé d’†Axelrodichthys araripensis Maisey, 1986, un coelacan- the du Crétacé inférieur du Bassin d’Araripe, Nord-Est du Brésil, montre la présence de divers éléments osseux fossilisés qui appartenaient à un poisson actinoptérygien. Ces éléments squelettiques épars sont localisés au voi- Key words sinage, mais à l’extérieur, du poumon calcifié d’†A. araripensis et ils sont enrobés dans une gangue particulière †Axelrodichthys dont les caractéristiques physiques et granulométriques sont différentes de celles de la gangue entourant le fos- Actinistia sile. La position de ces ossements épars, ainsi que leur préservation dans une gangue différente traduisant la Paleohistology présence de tissus mous, nous permettent d’affirmer qu’ils sont localisés dans le tube digestif, et leur anatomie Diet qu’ils appartenaient très probablement à un téléostéen, donc consommé par †Axelrodichthys. Cette contribution Bones décrit pour la première fois le régime alimentaire de cette espèce de coelacanthe, fournissant également de nou- Digestive tract veaux éléments sur son habitat. Early Cretaceous

Coelacanths are a group of sarcopterygians that, although Araripe Basin, Northeastern Brazil). The preservation of today represented by only two species ( chalum- material from the Araripe Basin Lagerstätten allows nae Smith, 1939 and Latimeria menadoensis Pouyaud et al., exceptional preservation of abdominal cavity soft tissue con- 1999), have a long evolutionary history dating back to the tents, such as muscles (Martill, 1988: pl. 2, figs 1-6), stom- Early (Zhu et al., 2012). During the Mesozoic, in ach contents (Martill, 1988: pl. 3, fig. 2), or lung collagenous the western part of , were represented wall in a very young fish (Britoet al., 2010: fig. 3). mainly by the family Mawsoniidae, a clade very common in Fossilized dietary contents are preserved only in favour- fresh and brackish water environments of Western Gondwa- able taphonomic conditions (e.g. Martill, 1988; Viohl, 1990; na during the split of this continent break up. During the Late Wilby and Martill, 1992; Cavin, 1999; Kriwet, 2001; Kriwet and Early Cretaceous, mawsoniids were represented et al., 2008). The dietary habits of †A. araripensis remain by four genera: †, †Axelrodichthys, †Lualabea largely unknown, although the presence of stomach contents and †Parnaibaia. in a specimen from the (Araripe Basin, †Axelrodichthys araripensis Maisey, 1986 is one of the Brazil) has been noted but without detailed description best-known coelacanths, mainly due to its abundance and (Yabumoto and Brito, 2013). Here we show the histological high quality of preservation found in the limestone nodules structure of the abdominal portion in a crushed specimen of of the Santana Formation, as well as, in the laminar lime- †A. araripensis and we describe, for the first time, the dietary stone of the slightly older Crato Formation (both from the content found in an articulated specimen of †A. araripensis

(1) uMR 7208 (CNRS-IRD-MNHN-UPMC), BOREA, Département Adaptations du Vivant, Muséum national d’Histoire naturelle, C.P. 026, 43 rue Cuvier, 75231 Paris c e d e x 05, . (2) Departamento de Zoologia, Universidade do Estado do Rio de Janeiro. Rua São Francisco Xavier 524, Maracanã, Rio de Janeiro, RJ, Cep 20550-900, Brazil. [[email protected]] [[email protected]] (3) Department of Natural History, Kitakyushu Museum of Natural History and Human History, 2-4-1 Higashida, Yahatahigashi-ku, Kitakyushu, Fukuoka, 805-0071, Japan. [[email protected]] * Corresponding author [[email protected]]

Cybium 2018, 42(1): 105-111. The diet of the Early Cretaceous coelacanth †Axelrodichthys araripensis Me u n i e r e t a l . from the Santana Formation. Our study adds to the knowl- Results edge of dietary habits and the environmental habitat of this species. Physical characteristics of the fossil matrix Although the abdominal cavity is partially crushed, the Material and Methods dietary contents are clearly distinct (Fig. 1). The area placed below the lumen of lung belongs to the digestive tract where The material has been previously prepared for a study the various bones are seen, and another area lies just against of the histological structure of the †A. araripensis calcified the bony plates. These isolated bones are arranged in groups lung (Brito et al., 2010; Cupello et al., 2015, 2017). Slices outside the lung (Fig. 2A, B). A comparison can be made of approximately 1 cm thickness were cut, and each slice with the position of the different organs in the abdominal was embedded in Stratyl (Chronolite 2060) and then cross cavity of the living coelacanth L. chalumnae (Fig. 1), in and horizontal sections were prepared with a saw (“Isomet” which the lung is completely surrounded by ossified plates or “Brot”), glued on a glass slide and ground to the suitable and is located near the gastrointestinal tract (Cupello et al., thickness. Thin sections were studied and photographed in 2015, 2017). transmitted natural and polarized light with a focus on the The fossil material is embedded in a limestone matrix lime stone matrix surrounding the lung plates. The material (Figs 3A, 4A) that contains fish bones and teeth (Fig. 3A-C), is housed at the Universidade do Estado do Rio de Janeiro, as well as some mineralized skeletal material of microcrus- collection number UERJ-PMB 143. tacae (Fig. 3D) and foraminifera (Fig. 3E). The scattered Additional material of †A. araripensis KMNH VP bony elements are localized in a specific soft tissue patch, 100,262 housed in the Kitakyushu Museum of Natural His- the granulometry of which is different from the fine-grained tory and Human History, Kitakyushu, Japan, and L. chalum- matrix and from the lumen of the lung (Figs 3A, B, 4A). nae CCC 22 (MNHN C20) deposited in the Collection of This peculiarity is clearly reinforced by the polarized light Comparative Anatomy of the Muséum national d’Histoire that reveals some polygonal organization of the soft tissue naturelle (France) were used for comparison. CCC 22 was patch (Figs 3C, 4B). Moreover, this specific soft tissue patch imaged by high-resolution computerized axial tomography and the scattered bones are limited by a dark pigmentation scanning (CAT scan) in a Parisian Hospital (France) using (Figs 3A, H, 4A) and lack of microcrustacae and foraminif- the voltage 120 kV, current 158 mA, voxel size 742 mm and era skeletons. Based on this evidence, we infer that these 1,807 views. specific areas represent the digestive tract.

Figure 1. – Abdominal cavity of extant and fossil coelacanths. A: Sections of a high-resolution computerized axial tomography scan of Latimeria chalum- nae (adult specimen, CCC 22), show- ing the position of the different organs in the abdominal cavity. B: Partially crushed specimen of †Axelrodichthys araripensis (adult specimen, UERJ- PMB 143). Arrows point to the lung plates; Dig T, digestive tract; L, lung and lumen of the lung; Oeso, oesopha- gus. Scale bars: A = 5 mm; B = 10 mm.

106 Cybium 2018, 42(1) Me u n i e r e t a l . The diet of the Early Cretaceous coelacanth †Axelrodichthys araripensis

the neural and hemal spines, which is turned forward and the second backward (Fig. 4A).

DISCUSSION-Conclusion

Thanks to the exceptional preservation of the Santana , some authors have determined precisely the diet of various predatory of this formation (Wilby and Mar- till, 1992; Maisey, 1994). However, due to the methodology used in this study, based on thin sections previously used for a histological study of the calcified lung, it was not possi- ble to precisely identify the taxa represented by the bones. Meanwhile, our histological observations contributed to: i) demarcate the lumen of the digestive tract owing to the min- eral pigmentation and the specific granularity of the matrix; ii) describe sufficient morphological characteristics of the bones contained in the digestive tract to determine that these skeletal elements belong to a teleostean fish, particularly one with amphicoelous vertebrae, myorhabdos, endochondral ossification of the vertebral hemal arches.Here we infer that the various bones as a whole belonged at least to one entire Figure 2. – Calcified lung of the Cretaceous coelacanth †Axelrod- fish that was eaten by† A. araripensis. ichthys araripensis (UERJ-PMB 143). A-B: Two ground sections We consider that †A. araripensis swallowed its preys (transmitted natural light) of a partially crushed specimen. x, y, z through a suction mechanism probably without mastication. pointing the position of the scattered fossilized bones. Black arrows pointing to bony plates of the lung and black and white aster- Contrary to Maisey (1994), who was able to determine some isks to the normal gang of the fossil. (L = lumen of lung). Scale specimens in the stomach contents, we could not determine bar = 5 mm. the specific taxon of the prey, except that it corresponds to a teleostean fish. It was probably an elongate fish owing to the morphology of the caudal vertebra the length of which Description of the bones can be evaluate at least to 30-35 mm if the fish had about 50 Among the numerous bones that are seen in the three vertebrae. As the vertebrae were well ossified, we can infer areas of the thin sections (Figs 3A, 4A), we recognize two vertebrae, some neural and/or hemal spines, lepidotrichial that this fish was not a larva, but most probably a juvenile hemisegments, teeth, long and thin bones that are prob- fish or an adult of a small species. This elongated fish does ably myorhabdos (Fig. 3F-H), and a dentary (Fig. 4A). The not correspond to any of the species already described for lepidotrichial hemisegments are typically crescent-shaped the Lower Cretaceous Santana Formation, Araripe Basin, (Fig. 3G). The teeth are sharp and the thin pulp cavity is north-eastern of Brazil (Maisey, 1991; Brito and Yabumoto, visible in an exemplar (Fig. 3H). There are also many other 2011). We suggest that the fish found in the digestive tract undetermined bones (Fig. 4A). probably represents a new species of the paleoichthyofauna Two vertebrae have amphicoelous centrum. The first of the Santana Formation. one is a transversal section of an abdominal vertebra with The diet of other fossil coelacanths has been also two thin neural apophysis (Fig. 3A) and two more devel- described, such as: some scales and a paleostomatopod oped hemal arches with enchondral ossification (Fig. 3A, F). shrimp in the abdominal cavity of several specimens of The hemal cartilage has disappeared, but the irregular bony †Caridosuctor populosum Lund & Lund, 1984 (Lund and layer is characteristic of this ossification type (Fig. 3F) (e.g. Lund, 1984, 1985; see also Lund et al., 1985); a crushed and François, 1966, 1967; Meunier, 1979; Zylberberg and Meu- incomplete crustacean, a ganoid scale and some arthropod nier, 2008). A second amphicoelous centrum shows a paras- appendages in the stomach contents of †Swansea latime- agittal section of a caudal vertebra showing both neural and rae (Clément, 2005) (Clément, 2005, 2006); the stomach hemal arches (Fig. 3A). The length of the vertebra is equal contents of †A. araripensis have been pointed, although not to twice its diameter (diameter = 250 μm; length = 550 μm. identified and described (Yabumoto and Brito, 2013); and a Fig. 4A), and characterizes a certain elongate morphology conodont element from the gut contents of an undetermined for the fish. Another observation is the opposite direction of coelacanth (Zatoń et al., 2017).

Cybium 2018, 42(1) 107 The diet of the Early Cretaceous coelacanth †Axelrodichthys araripensis Me u n i e r e t a l .

Figure 3. – †Axelrodichthys araripensis stomach contents (UERJ-PMB 143). A: Close-up of the boxed area in x (Fig. 2A), (transmitted natural light) showing the various scattered fossilized bones. (1: precaudal vertebra; 2: rib?; 3: neural or hemal spine: 4: teeth; 5: lepidot- richial hemisegments; 6: myorhabdos; 7: perichondral ossification).B : Close-up of the boxed area in y (Fig. 2A) (transmitted natural light) showing the digestive tract area. White arrows pointing to microcrustacean skeletons (My = myorhabdos). C: Close-up of the left area of Fig. 2A (transmitted polarized light) to emphasize the different granulometries between the “digestive tract” contents (wide granulations) and the surrounding soft tissue patch (thin granulations). White asterisk pointing to the section of the vertebra in the upper left corner. D: Section of a small crustacean in the fossil soft tissue patch. E: Section of small foraminifera in the fossil soft tissue patch. F: Close-up of the right hemal arch of the vertebra 1 (Fig. 2A). Two white arrowheads point to the enchondral ossification of the hemal arch. (Ce = verte- bral centrum; My = myorhabdos). G: Hemisegments of lepidotrichia (5, Fig. 2A). H: Teeth (4, in Fig. 2A). The white arrowheads point to the black pigmentation that surround the digestive tract. Scale bars: A, B, C = 200 μm; D, E, F, G, H = 50 μm;

108 Cybium 2018, 42(1) Me u n i e r e t a l . The diet of the Early Cretaceous coelacanth †Axelrodichthys araripensis

Figure 4. – †Axelrodichthys araripensis stomach contents (UERJ-PMB 143). A: Close-up of the inset y (Fig. 2B), (transmitted natural light) showing the various scattered fossilized bones. White asterisk pointing to the longi- tudinal section of a vertebra, white arrow pointing to a lower jawbone. White arrowheads pointing to the black pigmentation that surrounds the digestive tract content. B: The same section (transmitted polarized light) in A revealing different granulometries between the “digestive tract” content (wide granulations) and the surround- ing soft tissue patch (thin granulations). Black asterisk and black arrow pointing respectively to the vertebra and lower jawbone. Scale bars: A, B = 200 μm).

Here we compare the feeding behaviour of †Axelrodich- of prey are found in the posterior part of the digestive tract thys to that of Latimeria, as it is the only living actinistian practically undamaged (Herbin et al., unpubl. obs.). (Cloutier, 1991; Clément, 2005; Yabumoto, 2008). †A. arar- †Axelrodichthys araripensis is a species present in both ipensis had few minute teeth on its jaws (Maisey, 1994), and the Crato and Santana formations of the Araripe Basin (Brito has been considered as an edentulous fish (Maisey, 1994; and Yabumoto, 2011). The fact that †Axelrodichthys, as well Forey, 1998) that probably captured and swallowed its prey as the other Cretaceous mawsoniids, were mainly freshwa- using suction rather than mastication; and thus the prey skel- ter form species may be an explanation for the fact that the eton is more or less undamaged within the digestive tract, material found in the digestive tract is a new species, per- haps endemic to freshwater. Apart from a few species such having been swallowed whole. The living coelacanth, L. cha- as the Obaichthyidae, †Obaichthys decoratus and †Denti- lumnae, is a predatory and selective carnivore (Forey, 1998). lolepisosteus laevis, most of the fish found in the Santana It is a slow-swimming solitary feeder adapted to drifting in Formation nodules are marine forms, known in other sedi- a vertical head-stand position just above the deep sea floor mentary basins associated with marine invertebrates (Brito (Fricke et al., 1991). It is a predominantly nocturnal bottom and Yabumoto, 2011). For the ichthyofauna from the slightly or near bottom drift feeder that eats essentially benthic fishes older Crato Formation, †Dastilbe is the unique taxon not yet but also occasionally cephalopods (McCosker, 1979; Uyeno found in the Santana Formation (Brito and Amaral, 2008). and Tsutsumi, 1991). Its mouth probably opens quickly, the All other species appear to be the same as the Santana For- prey is grasped and then is sucked in whole (Uyeno, 1991; mation. This fact led to the hypothesis that there was an Uyeno and Tsutsumi, 1991). Coelacanths are probably suc- interchange between the “Crato ” and the marine envi- tion feeders, as Millot et al. (1978) have previously pointed ronment. Therefore, we can hypothesize that the specimen of out, swallowing prey with surrounding water (Yabumoto et A. araripensis described here had probably fed in freshwater al., 2012). Even if †Axelrodichthys lived in shallower waters, and that it was able to enter brackish or even coastal waters we can easily suppose that its feeding behaviour resembled of the epicontinental sea, which cut western Gondwana dur- that of the living coelacanth, at least for prey capture. Con- ing the Mid-Cretaceous. trary to †Axelrodichthys, even if Latimeria has some rela- tively well-developed caniniform teeth (Millot and Anthony, Acknowledgments. – We wish to thank Marie-Madeleine Loth (FRE CNRS MNHN 2696 Univ. Paris 6) for her technical assist- 1958; Castanet et al., 1975; Meunier et al., 2015), it also ance during this project. Special thanks to David Martill for Eng- swallows its prey without crushing it and the skeletal parts lish editing this manuscript and valuable scientific comments.

Cybium 2018, 42(1) 109 The diet of the Early Cretaceous coelacanth †Axelrodichthys araripensis Me u n i e r e t a l .

P.M.B.’s research has been partially supported by grants from the Kriwet J., 2001. - Feeding mechanisms and ecology of pycno- CNPq (304082/2013-9), FAPERJ (E-26/103.128/2011), Prociên- dont fishes (, pycnodontiformes).Mitt. Mus. Nat. cia UERJ/FAPERJ (Brazil) and by a fellowship from the Dépar- kd. Berl. Geowiss. Reihe., 4: 139-165. tement des Milieux et Peuplements Aquatiques, Muséum national Kriwet J., Witzmann F., Kling S. & Heidke U.H., 2008. - d’Histoire naturelle, Paris. C. Cupello research has been partially First direct evidence of a three level trophic chain in supported by CNPq (142252/2011-5) and Capes fellowships (BEX the fossil record. Proc. R. Soc., Lond., B: Biol. Sci., 275: 181- 0346/13-6 and PNPD/Capes). We thank the referees for their valu- 186. able scientific advice to improve our manuscript. Lund R. & Lund W., 1984. - New genera and species of coela- canths from the Bear Gulch Limestone (Lower ) of Montana (USA). Geobios, 17(2): 237-244. 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