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e-description of a putative Early Cretaceous “teleosaurid” fromrance, with implications for the survival of metriorhynchids andeleosaurids across the Jurassic-Cretaceous Boundary
ouvelle description d’un « téléosauridé » hypothétique de France et implicationsur la survie des métriorhynchidés et des téléosauridés au passageurassique-Crétacé
ark T. Younga,∗,b, Marco Brandalise de Andradec, Jean-Jacques Cornéed, Lorna Steele,avide Foffa f
Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, The King’s Buildings, West Mains Road, Edinburgh, EH9 3JW,nited KingdomSchool of Ocean and Earth Science, National Oceanography Centre, University of Southampton, Southampton, SO14 3ZH, United KingdomDepartamento de Paleontologia e Estratigrafia, Instituto de Geociências, Universidade Federal do Rio Grande do Sul–UFRGS, avenue Bento Gonc alves 9500,1501-970, C. P. 15001 Porto Alegre (RS), BrazilUMR CNRS 5243, Géosciences Montpellier, Université Montpellier 2, CC 060, place Eugène-bataillon, 34095 Montpellier cedex 05, FranceDepartment of Earth Sciences, Natural History Museum, Cromwell Road, London, SW7 5BD, United KingdomSchool of Earth Sciences, Wills Memorial Building, University of Bristol, Bristol, BS8 1RJ, United Kingdom
a r t i c l e i n f o
rticle history:eceived 28 November 2012ccepted 8 January 2014vailable online xxx
eywords:retaceousranceetriorhynchidae
lesiosuchinaeleosauridaealanginian
a b s t r a c t
Thalattosuchia was a diverse clade of marine crocodylomorphs known from the Early Jurassic to theEarly Cretaceous. Recent studies have hypothesized that their extinction was two-phased: (1) habitatloss near/at the Jurassic-Cretaceous boundary heavily reduced their morphofunctional diversity, par-ticularly in Europe, while (2) climate change and a shift in marine fauna during the Early Cretaceous(either at the Valanginian-Hauterivian boundary or during the early Hauterivian) finished off the alreadystressed clade. Unfortunately, the Cretaceous fossil record of thalattosuchians is poor, with only oneputative “teleosaurid” specimen and approximately ten metriorhynchid specimens. Here we re-describethe youngest known teleosaurid from the Cretaceous (Valanginian of south-eastern France). Originallyconsidered to be a teleosaurid (possibly Steneosaurus), we demonstrate that it belongs to Metriorhynchi-dae, and a newly discovered subclade, Plesiosuchina. It differs from Plesiosuchus in the pattern of toothenamel ornamentation and the variation in dentary alveoli size. Referring this specimen to Metriorhynchi-dae means there are no definitive Cretaceous teleosaurid specimens. Furthermore, it suggests that bothdurophagous and piscivorous teleosaurids became extinct at the end of the Jurassic. Interestingly, this isthe fourth metriorhynchid lineage known to cross the Jurassic-Cretaceous boundary. As such, it wouldappear that the two thalattosuchian families responded very differently to the lowering sea levels atthe end of the Jurassic: teleosaurids possibly became extinct, while metriorhynchids were seeminglyunaffected.
Please cite this article in press as: Young, M.T., et al., Re-description of a putative Early Cretaceous “teleosaurid” from France, withimplications for the survival of metriorhynchids and teleosaurids across the Jurassic-Cretaceous Boundary. Annales de Paléontologie(2014), http://dx.doi.org/10.1016/j.annpal.2014.01.002
ots clés :rétacéranceetriorhynchidae
lesiosuchinaeleosauridaealanginien
Les Thalattosuchiens étaient un clade de crocodylomorphes connus du Jurassique inférieur au Crétacéinférieur. De récents travaux ont proposé que leur extinction se soit opérée en deux temps : (1) auxenvirons de la limite Jurassique-Crétacé leur habitat aurait disparu, ce qui aurait conduit à une importanteperte de leur diversité morphofonctionnelle, en particulier en Europe. (2) Au Crétacé inférieur (passageValanginien-Hauterivien ou Hauterivien inférieur), un changement climatique couplé à un changementfaunistique aurait conduit à l’extinction définitive du clade. Les Thalattosuchiens du Crétacé sont toutefoisrares. On ne connaît en effet qu’un seul exemplaire de « téléosauridé » et qu’une dizaine de spécimens
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de métriorhynchidés. Dans ce travail nous reprenons la description du plus jeune exemplaire de ce« téléosauridé » (Valanginien du SE de la France). Initialement considéré comme pouvant appartenir augenre Steneosaurus, il s’agit en fait d’un métriorhynchidé du subclade nouvellement découvert, Plesio-suchina. Il diffère de Plesiosuchus par l’ornementation de ses couronnes dentaires et les variations detaille des alvéoles dentaires. Il n’y a donc pas de spécimen de téléosauridé connu au Crétacé à l’heureactuelle. En conséquence, les téléosauridés durophages et piscivores pourraient avoir disparu à la findu Jurassique. Le fossile étudié appartient à un quatrième lignage de métriorhynchidé connu après lalimite Jurassique-Crétacé. Les deux familles de Thalattosuchiens auraient donc répondu différemment àl’abaissement du niveau marin à la fin du Jurassique : les téléosauridés auraient disparu tandis que lesmétriorhynchidés auraient perduré.
1
ltJidmMhfa
asia1vptamtmidds
2
ittt1dM
dameA(s1sn
. Introduction
Thalattosuchia was a highly successful clade of marine crocody-omorphs with a fossil record extending from the Early Jurassic tohe Early Cretaceous and attained a global distribution during theurassic (Hua and Buffetaut, 1997). Thalattosuchians are dividednto two families: Teleosauridae and Metriorhynchidae. Teleosauri-ae was a clade that lived in brackish/lagoonal//coastal environ-ents and were superficially similar to extant gavials, whereasetriorhynchidae was a clade of fully pelagic marine forms that
ad a hypocercal tail and hydrofoil-like forelimbs and are knownrom lagoonal/coastal/open-shelf environments (Fraas, 1902; Huand Buffetaut, 1997; Young et al., 2010; Young and Steel, in press).
One of the pressing questions regarding Thalattosuchia is whynd when they became extinct. However, the Early Cretaceous fos-il record for Thalattosuchia is very poor (Table 1). Currently theres only one putative teleosaurid from the Early Cretaceous, a partialnd poorly preserved left dentary (Figs. 1–7; Cornée and Buffetaut,979). This specimen is the only evidence that Teleosauridae sur-ived the regional marine regressions of the Tithonian and earliestart of the Early Cretaceous (see Hallam, 2001). Here we re-describehis specimen. We, however, find it to be a metriorhynchid and
member of a newly discovered subclade, Plesiosuchina. Thiseans not only did a taxon closely related to Plesiosuchus cross
he Jurassic-Cretaceous Boundary (JKB), but at least four lineages ofetriorhynchids survived into the Early Cretaceous. With this spec-
men being considered a metriorhynchid, there are currently noefinitive Cretaceous teleosaurids. We hypothesize that Teleosauri-ae became extinct at, or near, the JKB while metriorhynchids wereeemingly unaffected by the drop in regional sea levels.
. Historical overview of the Allauch mandible
The partial dentary (“Allauch mandible”; Figs. 1–7) was orig-nally described by Cornée and Buffetaut (1979). They referredhis specimen to Teleosauridae as Steneosaurus sp. This was dueo the incomplete nature of the specimen, and the similari-ies to “Steneosaurus” obtusidens (Cornée and Buffetaut, 1979:153). Subsequently, the Allauch mandible has been considered aurophagous teleosaurid, along with “Steneosaurus” obtusidens andachimosaurus (see Vignaud, 1995; Hua and Buffetaut, 1997).
The sister-group relationship between “Steneosaurus” obtusi-ens and Machimosaurus is supported by two recent phylogeneticnalyses (Young et al., 2012a; Martin and Vincent, 2013), and theirorphological similarities, especially in their dentition (see Hua
t al., 1994; Vignaud, 1995, 1997; Young et al., in press-a). Thellauch mandible was considered to share this dental morphology
tooth crowns with blunt apices and numerous apicobasal ridges,
Please cite this article in press as: Young, M.T., et al., Re-descriptionimplications for the survival of metriorhynchids and teleosaurids acr(2014), http://dx.doi.org/10.1016/j.annpal.2014.01.002
ee Cornée and Buffetaut, 1979; Vignaud, 1995; Hua and Buffetaut,997). However, here we show that the Allauch mandible does nothare the same dental morphologies as durophagous teleosaurids,or the mandibular apomorphies of Teleosauridae.
The Allauch mandible was collected in the massif d’Allauch nearMarseille, in Provence (south-eastern France). It was discovered atthe foot of the Pic du Taoumé hill, in the upper part of the Vallon desEscaouprès (n2b formation of Guyonnet-Benaize et al., 2010, Fig.4A). The fossil was found two metres above a regional hard-ground,in nodular, argillaceous limestones from an outer shelf depositionalenvironment (Cornée and Buffetaut, 1979). Preserved cephalopodsindicate an upper Valanginian age for these limestones (Masseet al., 1975). Shallow water limestones under the hard-ground datefrom the lower Valanginian (Masse, 1976; Guyonnet-Benaize et al.,2010). These deposits were formed on the northern margin of theTethys palaeo-ocean (Dercourt et al., 1993).
4. Institutional abbreviation
JJCC, Jean-Jacques Cornée personal collection, 15, rue Jules-Auvergne, Fontvieille, 13990, France; MDP, Musée de Paléontologiede Provence, Université d’Aix-Marseille 1, Marseille, France; MJML,Museum of Jurassic Marine Life, Kimmeridge, Dorset, United King-dom; NHMUK, Natural History Museum, London, United Kingdom.
Geological range: Late Kimmeridgian to late Valanginian (LateJurassic to Early Cretaceous). Geological range of approximately 20million years.
Geographical range: Europe (England, France, and Portugal).Diagnosis: Metriorhynchid crocodylomorphs with the follow-
ing unique combination of characters (autapomorphic charactersare indicated by an asterisk): large robust teeth, with moder-ate to strong mediolateral compression; carinae formed by a keeland true microscopic denticles (microziphodonty, dimensions donot exceed 300 �m); tooth enamel ornamentation is composed ofapicobasally aligned ridges; tooth crown mesial margins have a
of a putative Early Cretaceous “teleosaurid” from France, withoss the Jurassic-Cretaceous Boundary. Annales de Paléontologie
pronounced distal curvature*; mandibular symphysis is not short(> 6 pairs of dentary alveoli adjacent to the symphysis); dentaryalveoli size increases along the symphysis, with the posterior-mostsymphyseal alveoli being the largest dentary alveoli*; immediately
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Table 1Table of all published metriorhynchid specimens from the Cretaceous. Note that all the French Cretaceous metriorhynchids are from the Région Provence-Alpes-Côte d’Azur,and the German Cretaceous metriorhynchids are from Lower Saxony. Furthermore, the age of the Russian material is either latest Jurassic or earliest Cretaceous.Tableau de tous les spécimens publiés de métriorhynchidés du Crétacé. Notez que les tous les métriorhynchidés de France proviennent de la région Provence-Alpes-Côte d’Azur, ceuxd’Allemagne de Basse Saxe. L’âge des exemplaires russes est soit jurassique terminal soit crétacé basal.
Specimen Age Locality Reference
1 Cricosaurus macrospondylusholotype
Late Valanginian Landkreis Hamelin-Pyrmont,Germany
Karl et al., 2006
2 Cricosaurus macrospondylusreferred specimen
Early Valanginian Département desHautes-Alpes, France
Hua et al., 2000
3 Cricosaurus schroederi holotype Early Valanginian Landkreis Schaumburg,Germany
Karl et al., 2006
4 cf. Cricosaurus Late Valanginian Colombia Larsson et al., 20125 Dakosaurus andiniensis referred
specimen(Early?) Berriasian Yesera del Tromen-Pampa Tril
area, Neuquén Province,Argentina
Pol and Gasparini, 2009
6 Geosaurus lapparenti holotype Late Valanginian Département du Var, France Debelmas and Strannoloubsky, 19567 Geosaurus lapparenti referred
specimenEarly Hauterivian Département du Var, France Debelmas, 1952
8 cf. Geosaurus lapparenti Early Valanginian Département du Vaucluse,France
Debelmas, 1958
9 Metriorhynchidae indeterminate Late Valanginian or earlyHauterivian
Département du Vaucluse,France
Debelmas and Demains D’Archimaud, 1956
10 Metriorhynchidae indeterminate Late Tithonian or early Berriasian Khoroshevskii Island, VolgaRegion, Russia
Ochev, 1981
11 Metriorhynchidae indeterminate Early Barremian Josa, Teruel, Spain Parrilla-Bel et al., 201212 Neustosaurus gigondarum holotype Early Valanginian Département du Vaucluse,
FranceRaspail, 1842
13 Plesiosuchina indeterminate (waspreviously considered to be ateleosaurid)
Late Valanginian Département desBouches-du-Rhône, France
Herein; Cornée and Buffetaut, 1979
Fig. 1. Plesiosuchina indeterminate JJCC 1. Partial dentary in lateral view, A. photograph, and B. line drawing. Abbreviations, for: foramen; den: dentary; D1: dentaryaP . dessfl
psat
Pm
ii
lveolus/tooth 1; mvmd: mandibular ventral margin deflection.lesiosuchina indéterminé JJCC 1. Dentaire partiel en vue latérale : A. photographie, et Bexion margino-ventrale mandibulaire.
osterior to the mandibular symphysis, the mandible rises dorsallyharply, such that the ventral margin of the dentary (along withngular) is dorsally deflected, this results in a distinct “kink” alonghe mandibular ventral margin*.
Note that all the autapomorphic non-dentary characteristics oflesiosuchus (see Young et al., 2012a) are unknown for the Allauchandible, and thus, are not listed here.
Plesiosuchina indeterminate
Please cite this article in press as: Young, M.T., et al., Re-descriptionimplications for the survival of metriorhynchids and teleosaurids acr(2014), http://dx.doi.org/10.1016/j.annpal.2014.01.002
Specimen: JJCC 1–left (and incomplete) dentary. The specimens in the personal collection of JJC (JJCC). The specimen can be exam-ned by contacting JJC via e-mail.
in. Abréviations : for : foramen ; den : dentaire ; D1 : alvéole dentaire/dent 1 ; mvmd :
Specimen agreement: There is an agreement in place tobequeath the specimen to the Natural History Museum, London.
Cast of specimen: MDP 12.514.Locality and horizon: Escaouprès valley, in the massif
d’Allauch, département des Bouches-du-Rhône, France. NeocomianTrilogy, n2b Formation.
Age: Late Valanginian, Early Cretaceous.Differential diagnosis: This specimen can be distinguished
from Plesiosuchus manselii by the following four characteristics:
of a putative Early Cretaceous “teleosaurid” from France, withoss the Jurassic-Cretaceous Boundary. Annales de Paléontologie
• the labial surface of the tooth crowns have numerous apicobasallyaligned ridges which are of high relief and readily identifiable.The tooth crown labial surfaces in P. manselii are almost entirelysmooth;
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F graph,tP dessin
•
•
FrvcPaf
ig. 2. Plesiosuchina indeterminate JJCC 1. Partial dentary in medial view, A. photoc: tooth crown.lesiosuchina indéterminé JJCC 1. Dentaire partiel en vue médiane : A. photographie, et B.
the lingual surface of the tooth crowns have numerous apicobasalenamel ridges that are of high relief and are readily identifiable(very similar to the morphology of the labial surface). The tooth
Please cite this article in press as: Young, M.T., et al., Re-descriptionimplications for the survival of metriorhynchids and teleosaurids acr(2014), http://dx.doi.org/10.1016/j.annpal.2014.01.002
crown lingual surfaces in P. manselii have apicobasal ridges, butthey of low relief and can be hard to observe without optical aids;the mandibular “kink” (strong dorsal deflection of the mandible,creating a “kink”-like morphology along the ventral margin)
ig. 3. Plesiosuchina indeterminate JJCC 1. Partial dentary, close-up on the anterioregion of the mandible in lateral view, A. photograph, and B. line drawing. Abbre-iations, for: foramen; den: dentary; D1: dentary alveolus/tooth 1. Scale bar is inentimetres.lesiosuchina indéterminé JJCC 1. Dentaire partiel, agrandissement de la régionntérieure de la mandibule en vue latérale : A. photographie, et B. dessin. Abréviations :or : foramen ; den : dentaire, D1 : alvéole dentaire/dent 1. Échelle en centimètres.
and B. line drawing. Abbreviations, mvmd: mandibular ventral margin deflection;
occurs immediately posterior to D7. In P. manselii it occurs imme-diately posterior to D9. In P. manselii this marks the end of themandibular symphysis, as such, the symphysis of the Allauchmandible is slightly foreshortened;
• dentary alveoli D1-D5 are subequal, D6 is enlarged, D7 further
of a putative Early Cretaceous “teleosaurid” from France, withoss the Jurassic-Cretaceous Boundary. Annales de Paléontologie
enlarged, while D8 is intermediate in size between the D6-D7.In P. manselii dentary alveoli D1-D3 are approximately subequalin diameter, D4-D9 are larger than the anterior-most alveoli
Fig. 4. Plesiosuchina indeterminate JJCC 1. Partial dentary, close-up on the dentaryalveoli in lateral view, A. photograph, and B. line drawing. Abbreviations, D1: dentaryalveolus/tooth 1. Scale bar is in centimetres.Plesiosuchina indéterminé JJCC 1. Dentaire partiel, agrandissement de l’alvéole dentaireen vue latérale : A. photographie, et B. dessin. Abréviations : D1 : alvéole dentaire/dent1. Échelle en centimètres.
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Fig. 5. Plesiosuchina indeterminate JJCC 1. Close-up on dentary tooth 7 in lingual-distal view, A. photograph, and B. line drawing. Grey shading represents matrix.Pl
6
Brtmtcc
FvPg
Fig. 7. Plesiosuchina indeterminate JJCC 1. Close-up on the anterior region of thedentary tooth in medial view, A. photograph, and B. line drawing. Abbreviations, tc:tooth crown.Plesiosuchina indéterminé JJCC 1. Agrandissement de la région antérieure de la dent
lesiosuchina indéterminé JJCC 1. Agrandissement de la dent 7 du dentaire en vueinguale-distale : A. photographie, et B. dessin. Le grisé représente la gangue.
and are approximately equal in diameter, D10-D13 progressivelydecrease in diameter.
. Description
Which part of the symphysis is preserved?: Cornée anduffetaut (1979) considered the Allauch mandible to be a posterioregion of the left dentary. However, this identification was based onhe specimen being a teleosaurid and on there being a suture on the
edial surface for the splenial. While the state of preservation of
Please cite this article in press as: Young, M.T., et al., Re-descriptionimplications for the survival of metriorhynchids and teleosaurids acr(2014), http://dx.doi.org/10.1016/j.annpal.2014.01.002
he medial surface (Fig. 2) makes identifying sutures difficult, whenompared to a well-preserved P. manselii mandible (Figs. 8–10) it islear that region where a splenial-dentary contact would be is not
ig. 6. Plesiosuchina indeterminate JJCC 1. Close-up on dentary tooth 7 in lingualiew, A. photograph, and B. line drawing. Grey shading represents matrix.lesiosuchina indéterminé JJCC 1. Agrandissement de la dent 7 du dentaire en vue lin-uale : A. photographie, et B. dessin. Le grisé représente la gangue.
du dentaire en vue médiane : A. photographie, et B. dessin. Abréviations : tc : couronnedentaire.
preserved. Moreover, there are two further reasons for consideringthat this specimen is the anterior-most region of the symphysis:
• the medial and lateral surfaces of the dentary converge anteriorto the first preserved alveolus and there is no evidence for furtheranterior alveoli (Figs. 2 and 7);
• the dentary that is preserved immediately anterior to thefirst dentary alveolus has a slightly convex external surface(Figs. 1 and 3). This matches the shape of the anterior dentary inother metriorhynchids (e.g., see Lepage et al., 2008; Young et al.,2012a).
Dentary: Only the symphyseal portion of the left dentary ispreserved (Figs. 1–7). It is approximately 28 cm in length. Over-all, the preservation is poor. It has been subjected to post-mortemmediolateral compression and some shearing. As such, the spec-imen no longer retains its natural shape. The external surfaceof the dentary’s posterior region is poorly preserved, meaningthat the surangulodentary (= lateral mandibular) groove cannot beobserved. Due to the incomplete nature of the specimen, the suturesbetween the dentary, the surangular and angular are not preserved.Furthermore, we cannot observe any part of the splenial. The exter-nal (= lateral) surface of the dentary is gently convex, and hasnumerous small, sub-circular foramina (Fig. 1). The external surfaceornamentation is composed of anteroposteriorly aligned ridges andgrooves (Figs. 1 and 3). The ornamentation pattern shifts around thefirst dentary alveolus (D1; see Fig. 3). Around the D1 (anterior to theD1, the interalveolar septum, and immediately medial and lateral
of a putative Early Cretaceous “teleosaurid” from France, withoss the Jurassic-Cretaceous Boundary. Annales de Paléontologie
to the D1) the ornamentation becomes much more pronounced,being composed of very prominent and closely packed anteropos-teriorly aligned ridges. Along the posterior-margin of D1 the ridges
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Fig. 8. Plesiosuchus manselii MJML K434. Partial dentary in lateral view, A. photograph, and B. line drawing. Abbreviations, for: foramen; den: dentary; mvmd: mandibularvP et B. dm
cp
bDAaovl(bM
emvdaut
FdPs
entral margin deflection; sp: splenial.lesiosuchus manselii MJML K434. Dentaire partiel en vue latérale : A. photographie,andibulaire ; sp : splénial.
onverge, creating some sub-circular ornamentation. No receptionits are present on the lateral margin of the dentary.
On the dorsal surface of the dentary, eight complete alveoli cane discerned and the anterior section of the ninth (Fig. 1). Other than1, the medial margins of the dentary alveoli are not preserved.ll of the preserved alveoli are very large, closely set together andppear as though they would be circular/sub-circular in shape. Allf the interalveolar spaces are approximately equal in length andery narrow in comparison to the neighboring alveoli (always beingess than half the width of the proceeding or preceding alveolus)Figs 1, 3 and 4). Furthermore, the typical thalattosuchian diastemaetween D4-D5 (Andrews, 1913; Hua, 1999; Young et al., 2012a;artin and Vincent, 2013) is absent.The wide, flat surface medial to the alveolar row (see Young
t al., 2012a, Figure 21) would be exposed in dorsal view had theandible not been distorted. However, this surface is now only
isible in medial view. In medial view, it is the flat, smooth surfaceorsal to the symphyseal suture (Figs. 2 and 7). It is very large, wide
Please cite this article in press as: Young, M.T., et al., Re-descriptionimplications for the survival of metriorhynchids and teleosaurids acr(2014), http://dx.doi.org/10.1016/j.annpal.2014.01.002
nd slightly concave just like in P. manselii (Young et al., 2012a, Fig-re 21; Figure 9). In the durophagous teleosaurid Machimosaurus,his surface is slightly convex (see Hua, 1999, Plate 2, Figure 1;
ig. 9. Plesiosuchus manselii MJML K434. Partial dentary in medial view, A. photograph, aneflection; sp: splenial; ss: dentary symphyseal sutural surface.lesiosuchus manselii MJML K434. Dentaire partiel en vue médiane : A. photographie, et B.
p : splénial ; ss : surface de la suture symphysaire du dentaire.
essin. Abréviations : for : foramen ; den : dentaire ; mvmd : flexion margino-ventrale
Martin and Vincent, 2013, Figure 5). Overall, in medial view, thedentary is poorly preserved.
Based on how closely the Allauch mandible resembles those ofP. manselii, we can determine where the symphysis would have ter-minated. This is due to the distinct ventral “kink” which occursimmediately posterior to the mandibular symphysis (Fig. 1). InP. manselii, this “kink” occurs immediately posterior to the D9 andthe symphyseal suture (MJML K434, Fig. 8). The only P. manseliispecimen to have an articulated mandibular symphysis has 9 adja-cent pairs of alveoli (NHMUK PV R1089; Young et al., 2012a). In theAllauch mandible the “kink” occurs immediately posterior to theD7. As such, the mandibular symphysis was shorter in this taxonthan in P. manselii.
Dental morphology: The five anterior alveoli have teeth in situand a sixth tooth crown is preserved medial to the seventh alveolus(Fig. 1). The most complete crowns are the third and fourth den-tary teeth and the crown preserved medial to the seventh alveolus(Figs 1, 4–6). The teeth show a caniniform morphology, as they are
of a putative Early Cretaceous “teleosaurid” from France, withoss the Jurassic-Cretaceous Boundary. Annales de Paléontologie
single cusped, mediolaterally compressed and curved lingually. Thethree best-preserved crowns all curve slightly distally (posteriorly),with the D3 showing this morphology best (see Figs. 1, 3 and 4). No
d B. line drawing. Abbreviations, den: dentary; mvmd: mandibular ventral margin
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Fig. 10. Plesiosuchus manselii MJML K434. Partial dentary in dorsal view, close-up on the anterior-most alveoli, A. photograph, and B. line drawing. Abbreviations, den :dP alvéolf
cttse2
o(biaeCeaobadvA2
lmgmiY((o
idw(og
1982; Hua et al., 1993; Hua, 1999; Martin and Vincent, 2013)and “Steneosaurus” obtusidens (NHMUK PV R3168; Andrews, 1913)clearly shows it does not belong to a durophagous/macrophagousteleosaurid or any other teleosaurid. Teleosaurids possess an
onstriction is present at the crown-root junction. The basal sec-ions are wider mediolaterally, creating an ovoid cross-section. Theeeth lack the distinctive apicobasal faceting observed on the labialurface of Geosaurus species (Young and Andrade, 2009; Andradet al., 2010). The teeth are robust and large (preserved teeth up to.5 cm in apicobasal length).
The enamel surface ornamentation is composed of numer-us apicobasally aligned ridges that are parallel to sub-parallelFigs. 1, 3–6). They vary from being fairly well-packed toeing widely spaced. Due to preservation, we cannot determine
f this difference is related to variation between the lingualnd the labial surfaces or due to differences between newlyrupted crowns and more fully erupted crowns. However, contraornée and Buffetaut (1979) the ornamentation differs consid-rably from the densely packed ridges observed in Torvoneustesnd the durophagous/macrophagous teleosaurids “Steneosaurus”btusidens, and Machimosaurus (Hua, 1999; Young et al., 2013a,, in press-a; Martin and Vincent, 2013). It also lacks thenastomosed apical region of Torvoneustes, “Steneosaurus” obtusi-ens and Machimosaurus, in which the enamel ridges becomeery short and are arranged in an anastomosed pattern (seendrade et al., 2010; Young and Steel, in press; Young et al.,013a, in press-a).
Moreover, the tooth crowns Allauch mandible differs from theight microscopice anastomosed pattern observed in Dakosaurus
aximus and Geosaurus giganteus (see the scanning electron micro-raphs in Andrade et al., 2010). The enamel ornamentation patternore closely matches P. manselii. Both P. manselii and Plesiosuchina
ndet. have numerous apicobasal ridges on the lingual surface (seeoung et al., 2012a and Figs. 6 and 11), but they differ in relief“height”). The labial surface of P. manselii teeth are largely smoothFig. 11A), whereas in Plesiosuchina indet. this surface is as heavilyrnamented as the lingual surface.
The carinae of all teeth are well defined and prominent, extend-ng from the base to the apex of the crown on both the mesial andistal margins. As all preserved teeth are attached to the specimen
Please cite this article in press as: Young, M.T., et al., Re-descriptionimplications for the survival of metriorhynchids and teleosaurids acr(2014), http://dx.doi.org/10.1016/j.annpal.2014.01.002
e could not examine any under scanning electron microscopySEM). Recent studies have found that SEM is required to properlybserve and describe the denticle morphology of metriorhynchidenera (Andrade et al., 2010; Young et al., 2013a).
es de l’extrémité antérieure : A. photographie, et B. dessin. Abréviations : den : dentaire ;
The third and fourth dentary teeth lack any spalling of theenamel (Figs. 3 and 4), or the characteristic carinal wear ofD. maximus (Young et al., 2012a, b). The tooth adjacent to the sev-enth alveolus has a broken tooth crown (Figs. 5 and 6). However,the break lacks distinct facets and much of the crown’s enamel hasbroken off post-mortem. As such, the apical damage may be theresult of taphonomy, rather than tooth-food abrasion.
7. Discussion
7.1. Comparisons
Comparing the partial left dentary of Plesiosuchina indet.(Figs. 1–7) to the mandibles of Machimosaurus hugii (Buffetaut,
of a putative Early Cretaceous “teleosaurid” from France, withoss the Jurassic-Cretaceous Boundary. Annales de Paléontologie
Fig. 11. Plesiosuchus manselii MJML K181. Isolated tooth crown, A. photograph inlabial view, and B. close-up on the carina in lingual-distal view.Plesiosuchus manselii MJML K434. Couronne dentaire isolée : A. photographie en vuelabiale, et B. agrandissement de la carène en vue linguale-distale.
nterior transverse expansion of the mandibular symphysis (anpomorphy of the family; Andrews, 1913), whereas this speci-en lacks this feature. In addition, the interalveolar spaces of
he dentary are very small, far smaller than in Machimosaurusand most thalattosuchians). In teleosaurids (Hua et al., 1993; Hua,999; Lepage et al., 2008; Martin and Vincent, 2013), metriorhyn-hine metriorhynchids (Andrews, 1913; Gasparini and Dellapé,976; Lepage et al., 2008) and basal geosaurine metriorhynchidsAndrews, 1913; Young et al., 2013a), the anterior interalveolarpaces are variable in size, ranging from being larger than the adja-ent alveoli to being half the size. The extreme reduction in anteriornteralveolar distance observed in this specimen (always being lesshan a quarter of the length of the immediate alveoli) is characteris-ic of Geosaurini metriorhynchids (e.g. P. manselii and D. maximus:oung et al., 2012a; Torvoneustes carpenteri: Wilkinson et al., 2008).oreover, teleosaurids have a particular arrangement of the ante-
ior dentary alveoli. The D3-D4 are very closely set, while theres a diastema between D4-D5 (Andrews, 1913; Hua, 1999; Youngt al., 2012a; Martin and Vincent, 2013). This D4-D5 diastema isypical of most thalattosuchians. This specimen however lacks the4-D5 diastema, and all interalveolar spaces are approximately the
ame length. Young et al. (2012a) noted these two characteristicsnly co-occur among thalattosuchians in Geosaurini. As such, wean conclusively refer this partial mandible to Geosaurini and byxtension remove it from Teleosauridae.
Although we can refer the partial left dentary to Geosaurini, cane refer it to any of the four Late Jurassic genera? We can exclude
ur specimen from Torvoneustes as:
the tooth crown apices are not blunt and rounded;the enamel ornamentation of apicobasally aligned ridges are notas numerous and as tightly packed as that of in Torvoneustes;the enamel ornamentation does not contact the carinae (althoughthis is only known to occur in T. carpenteri);there is no anastomosed apical enamel ornamentation, i.e. theridges do not become very short, and become anastomosed ratherthan apicobasally aligned (Andrade et al., 2010; Young et al.,2013a, b).
Interestingly, this suite of dental characteristics is also presentn Machimosaurus and “Steneosaurus” obtusidens (see Andrews,913; Buffetaut, 1982; Hua et al., 1993, 1994; Hua, 1999; Vignaud,995, 1997; Lepage et al., 2008; Ruiz-Omenaca et al., 2010; Martinnd Vincent, 2013; Young and Steel, in press; Young et al., inress-a), further strengthening our removal of the dentary fromurophagous/macrophagous teleosaurids.
We can also exclude this specimen from Geosaurus as:
the tooth crowns are not laminar (strongly mediolateral com-pressed);crowns have apicobasally aligned ridges (typically absent inGeosaurus, although an early Kimmeridgian tooth from Englandhas apicobasal ridges on the lingual surface; Young et al., in press-b);the teeth lack the three apicobasal labial facets typical of thisgenus (i.e. “tri-facetted” labial surface);no reception pits are present on the lateral margin of the dentary(which in Geosaurus is caused by a maxillary overbite) (Youngand Andrade, 2009; Andrade et al., 2010; Young et al., 2013a).
Finally we can exclude our specimen from Dakosaurus as:
Please cite this article in press as: Young, M.T., et al., Re-descriptionimplications for the survival of metriorhynchids and teleosaurids acr(2014), http://dx.doi.org/10.1016/j.annpal.2014.01.002
crowns have apicobasally aligned ridges (which are absent inDakosaurus);the teeth serrations are not macroziphodont;
PRESSntologie xxx (2014) xxx–xxx
• tooth crowns lack occlusal wear facets along the carinae;• no reception pits are present on the dentary between the alveoli
(which in Dakosaurus is caused by the tightly fitting tooth-toothocclusion);
• mandibular symphysis is not short, i.e. more than five alveoli areadjacent;
• the anterior dentary lacks the sharp dorsal inclination of the ven-tral margin (Pol and Gasparini, 2009; Young and Andrade, 2009;Andrade et al., 2010; Young et al., 2012a, b.
This leaves the Geosaurini genus Plesiosuchus. The Allauchmandible shares with Plesiosuchus: the distinct “kink” along themandibular ventral margin, the progressive increase in dentarysymphyseal alveoli size, and the pronounced distal curvature ofthe tooth crowns mesial margin (Young et al., 2012a; see Figures1, 8). However, tooth crowns of D. maximus also have this strongdistal curvature (Young et al., in press-c). As such, this characteris-tic is an apomorphy of a larger clade than previously thought. Theother dental apomorphy of P. manselii, the presence of microscopicrectangular-shaped denticles cannot be confirmed without futureSEM work. As such, we refer to this specimen as Plesiosuchinaindeterminate. It differs from P. manselii in the development of theenamel apicobasal ridges, mandibular symphysis length, and vari-ation in the sizes of the dentary alveoli. However, until future, morecomplete, specimens are discovered we refrain from describing anew taxon.
7.2. Implication for Thalattosuchia and the Jurassic-CretaceousBoundary
Based on our re-description of Plesiosuchina indet., there are nodefinitive teleosaurid specimens from the Cretaceous. Currently,the youngest confirmed instances of longirostrine/piscivorous(Steneosaurus) and brevirostrine/durophagous (Machimosaurus)teleosaurids is from the early Tithonian of Western Europe (Billon-Bruyat et al., 2005; Ruiz-Omenaca et al., 2010). Therefore, it appearsthat all teleosaurids went extinct either during the Tithonian or atthe Jurassic-Cretaceous Boundary (JKB). During the Tithonian, andcontinuing into the Early Cretaceous, sea levels fell (Hallam, 2001).In particular the Sub-Boreal province of north-west Europe, whilethe Boreal province of northern Europe has a sea level low at thebase of the Cretaceous (see Hallam, 2001 and references therein).However, in the southern Andes of Argentina and Chile, there isno difference in sea level across the JKB (see Hallam, 2001 and ref-erences therein). Interestingly, teleosaurids are not found in theUpper Jurassic of the southern Andes of Argentina and Chile, whileat least three metriorhynchid genera are: Cricosaurus, Dakosaurusand Purranisaurus (Spalletti et al., 1999; Pol and Gasparini, 2007).This may suggest that teleosaurids became extinct due to habitatloss (i.e. the regression of shallow epeiric seas). However, as thelate Tithonian and Early Cretaceous marine fauna is still poorlyknown we cannot discount the possibility that Early Cretaceousteleosaurids may be discovered in the future.
This is in stark contrast with the fossil record of metri-orhynchids. Of the seven known metriorhynchid genera foundin Tithonian deposits, four are found in the Early Cretaceous:Cricosaurus, Dakosaurus, Geosaurus (Young et al., 2010) and nowPlesiosuchina indetetminate. Only Purranisaurus (the holotype ofwhich is currently being re-described), Rhacheosaurus and Tor-voneustes have not been discovered in the Cretaceous (Young et al.,2010, 2013b).
Based on current knowledge, two metriorhynchid genera went
of a putative Early Cretaceous “teleosaurid” from France, withoss the Jurassic-Cretaceous Boundary. Annales de Paléontologie
extinct during the Kimmeridgian or at the Kimmeridgian-Tithonianboundary (Metriorhynchus and Gracilineustes: Wilkinson et al.,2008; Young et al., 2010). During the Oxfordian, three furthergenera/clades disappear: “Metriorhynchus” brachyrhynchus, the
outh American “Metriorhynchus” casamiquelai + “M.” westermannilade (until the holotype of Purranisaurus potens is re-described weannot be sure that Purranisaurus is a member of this clade) andyrannoneustes lythrodectikos (Young et al., 2010, 2012a, 2013a). Asuch, even if there is an extinction event at the JKB, metriorhynchidsid not experience a greater extinction rate than at any other stageoundary event during the Late Jurassic. Therefore, based on oururrent understanding of the fossil record, metriorhynchids did notxperience a notable decline in generic diversity at the JKB.
While the decline in metriorhynchid species diversity start-ng in the late Tithonian and continued into the Early CretaceousPierce et al., 2009; Young et al., 2010), geological megabiases canxplain almost all of the observed species diversity patterns inetriorhynchidae (Young, 2009). The decline in specific diversity
cross the JKB correlates with the decline in the number of knownormations that have metriorhynchids, which itself is caused by the
arine regression in Europe (Young, 2009).Some recent studies on marine reptile taxic and phylogeneti-
ally interpolated diversity have suggested there was an extinctionvent at the JKB (Pierce et al., 2009; Young et al., 2010; Bensonnd Butler, 2011). However, ichthyosaur Cretaceous taxic diversityurve (Fischer et al., in press) and ichthyosaur Late Jurassic-arly Cretaceous survival/extinction rates across stage boundariesFischer et al., 2012) show that in-depth re-descriptive studiesnd a re-appraisal of alpha taxonomy is needed prior to undertak-ng macroevolutionary studies on marine reptiles. When coupled
ith the large geological megabiases, quantifying trends in marinealaeobiodiversity and identifying extinction events is more diffi-ult than previously realized.
The survival of four metriorhynchid genera across the JKB isnteresting in the light of new research on ichthyosaurs. Recenttudies found no evidence that the JKB impacted on ichthyosauriversity, with potentially as many as nine ophthalmosaurid
chthyosaur lineages crossing the JKB (Fischer et al., 2012) andne basal thunnosaurian lineage (Fischer et al., 2013). As such,here is no evidence that ophthalmosaurid, and possibly moreasal, ichthyosaurs and metriorhynchid crocodylomorphs were
mpacted by the regional marine regressions during the latest Juras-ic and earliest Cretaceous. As both clades were unaffected byhe JKB and had numerous convergent adaptations to a pelagicifestyle (e.g., hypocercal tail, hydrofoil-like forelimbs, osteoporoticightening of the skeleton) they, therefore, were not restricted toear-shore/coastal environments and did not suffer a restriction invailable habitat.
By the early Valanginian, possibly mesopelagic metriorhynchidsre discovered. A specimen referred to Cricosaurus macrospondylusas divided external nares which are significantly posterodorsallyetracted (Hua et al., 2000), the holotype of Cricosaurus schroederias very large orbits that were filled by large and robust scle-otic rings (Karl et al., 2006), while the holotype of Neustosaurusigondarum has the largest tail fluke of any known metriorhynchid,ith almost half of the total number of caudal vertebrae con-
ributing to the fluke (Raspail, 1842). These adaptations suggesthat metriorhynchids (in particular the genus Cricosaurus) hadecome sustained, and possibly mesopelagic, swimmers (Youngt al., 2010). Therefore, Plesiosuchina indet. was part of a diverseauna of marine reptiles (including the metriorhynchids Cricosaurusnd Geosaurus; see Table 1 and the ophthalmosaurid ichthyosauregirosaurus; Fischer et al., 2011) that lived along the northernargin of the Tethys Ocean during the Valanginian.
Please cite this article in press as: Young, M.T., et al., Re-descriptionimplications for the survival of metriorhynchids and teleosaurids acr(2014), http://dx.doi.org/10.1016/j.annpal.2014.01.002
isclosure of interest
The authors declare that they have no conflicts of interest con-erning this article.
PRESSntologie xxx (2014) xxx–xxx 9
Acknowledgements
We would like to thank Yves Lepage (Le Havre, France) for read-ing over an earlier version of this manuscript and improving itsquality, Suzanne Jiquel (Montpellier, France) for photography of theAllauch mandible, B. Martin-Garin (Marseille, France) for providinginformation on the cast in the Museum of Paleontology of Provence,Steve Etches (MJML) for access to his collection, and ValentinFischer (Liège, Belgium) for PDF copies of the Debelmas papersand his “in press” manuscript. We would also like to thank JeremyMartin and Zulma Gasparini for their reviews, which improved thequality of this manuscript. MBA receives a post-doctoral researchgrant from CNPq (proc. 500899/2011-8).
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Young, M.T., Andrade, M.B., Brusatte, S.L., Sakamoto, M., Liston, J., 2013a. The oldestknown metriorhynchid super-predator: a new genus and species from the Mid-dle Jurassic of England, with implications for serration and mandibular evolutionin predacious clades. Journal of Systematic Palaeontology 11, 475– 513.
Young, M.T., Andrade, M.B., Etches, S., Beatty, B.L., 2013b. A new metriorhynchidcrocodylomorph from the Lower Kimmeridge Clay Formation (Late Jurassic)of England, with implications for the evolution of dermatocranium orna-mentation in Geosaurini. Zoological Journal of the Linnean Society 169,820– 848.
Young, M.T., Beatty, B.L., Brusatte, S.L., Steel, L., 2014. First evidence of denticu-lated dentition in teleosaurid crocodylomorphs. Acta Palaeontologica Polonica,http://dx.doi.org/10.4202/app.00002.2013 (E-published 28/October/2013).
Young, M.T., Steel, L., Middleton, H., 2014. Evidence of the metriorhynchidcrocodylomorph genus Geosaurus in the Lower Kimmeridge Clay Forma-tion (Late Jurassic) of England. Historical Biology, http://dx.doi.org/10.1080/08912963.2013.801468 (E-published 1/July/2013).
of a putative Early Cretaceous “teleosaurid” from France, withoss the Jurassic-Cretaceous Boundary. Annales de Paléontologie
Young M.T., Steel L., Rigby M., Howlett E., Humphrey S. (In review). Largest knownspecimen of the genus Dakosaurus (Metriorhynchidae: Geosaurini) from theKimmeridge Clay Formation (Late Jurassic) of England, and an overview ofDakosaurus specimens discovered from this formation (including reworkedspecimens from the Woburn Sands Formation). Historical Biology.
