New paroxyclaenid mammals from the early Eocene of the Paris Basin (France) shed light on the origin and evolution of these endemic European cimolestans

We present new species of an enigmatic family of mammals, which is endemic to Europe, the Paroxyclaenidae: Merialus bruneti sp. nov., Fratrodon tresvauxi gen. et sp. nov., Paraspaniella gunnelli gen. et sp. nov., and Sororodon tresvauxae gen. et sp. nov. The fossils described come from six localities of the Ypresian of the Paris Basin (France): Pourcy (MP7), Mutigny, Avenay, Condé-en-Brie (MP8 + 9), Grauves and Prémontré (MP10). They allow the description of three new genera and four new species belonging to the subfamilies Merialinae and Paroxyclaeninae. Two of these new species represent the earliest occurrence of each subfamily. Fossils from Mutigny, Avenay and Condé-en-Brie indicate that merialines were more abundant than paroxyclaenines during the Ypresian. Surprisingly, merialines disappeared from the fossil record at the end of the Ypresian – the youngest records are close to MP10 – while the paroxyclaenines were present in Europe until the end of the middle Eocene. Based on comparison with the data presently available for European mammals during the Ypresian, we suggest the existence of two periods of faunal turnover that must be more extensively studied in the future in order to be fully characterized: the ‘Intra-Ypresian Mammal Turnover’ and the ‘Ypresian–Lutetian Mammal Turnover’. Finally, because the oldest paroxyclaenids appear morphologically closer to cimolestids such as Procerberus than to pantolestans, it is suggested that similarities between paroxyclaenids and pantolestans could be due to convergence

Les lézards fossiles du Paléocène de Montchenot (Bassin de Paris, MP6)

Les faunes de lézards trouvées dans la localité de Montchenot (Paléocène supérieur, MP6, Est du Bassin de Paris) sont décrites. Ce matériel se répartit entre plusieurs groupes : Scincoidea, Lacertoidea (?Lacertidae), Amphisbaenia, Anguimorpha (?Anguidae et Shinisauridae). L’assemblage de Montchenot est dominé par des spécimens de petite taille, certainement le résultat d’un tri sélectif marqué. L’action de prédateurs peut produire de tels assemblages. Les taxons présents à Montchenot sont aussi présents, pour la plupart, dans deux gisements de même niveau (MP6) : ceux de Cernay-lès-Reims et de Rivecourt dans l’Est du Bassin de Paris. D’autre part, la faune de Montchenot diffère nettement (en composition et diversité) de celles reconnues dans les gisements de l’Éocène ancien (MP7) de la même zone géographique (Bassin parisien et belge). Ces diffèrences mettent en relief le fort impact de la transition Paléocène/Éocène sur les faunes de lézards.Here we describe the lizard fauna from the locality of Montchenot (Paris Basin, late Paleocene, MP6). This material can be allocated to five major clades: Scincoidea, Lacertoidea (?Lacertidae), Amphisbaenia, Anguimorpha (?Anguidae and Shinisauridae). The assemblage from Monchenot is dominated by small lizard specimens and appears as highly sorted. Predation could produce such biased assemblages. The composition of the lizard fauna from Monchenot is rather similar to those of Cernay-lès-Reims and Rivecourt, two coeval localities (MP6) in the Paris Basin. However, these faunas sharply contrast (in diversity and composition) with the lizard fauna found in the early Eocene of the same area (Paris Basin and Belgian Basin). These differences highlight the impact of the Paleocene/Eocene transition on the lizard fauna of Europe.</p

Animalia

&lt;p&gt;Pan-Shinisaurus indet.&lt;/p&gt; &lt;p&gt;MATERIAL EXAMINED. &mdash; MNHN. F.MTC240-MTC242, MTC243, nearly fifty osteoderms, a few complete, most more or less severely damaged by digestive processes or post-burial damages (Fig. 9).&lt;/p&gt; &lt;p&gt;DESCRIPTION&lt;/p&gt; &lt;p&gt;Measures (mm): maximum width (w) of osteoderms ranges between 1.1 and 3.9 mm. The osteoderms, when complete, are oval, suboval or subrectangular elements with more or less irregular margins. Gliding surfaces are absent. All bear a prominent medial keel that extends the full length of the osteoderm. A slight concavity on the underside of some osteoderms reflects the form of the keel. From the keel a pattern of deep pits or grooves and marked ridges radiates. The dorsal surface of most osteoderms is flat but a few have a rather strongly vaulted shape which certainly reflect different positions on the body.&lt;/p&gt; &lt;p&gt;COMPARISONS AND DISCUSSION&lt;/p&gt; &lt;p&gt; Some characters are traditionally used to separate anguimorph taxa (and more specifically anguid genera) by their osteoderms (Hoffstetter 1962a; Meszoely 1970; Bochaton &lt;i&gt;et al.&lt;/i&gt; 2015, 2016), including the presence of a gliding surface and of a keel. For example, Gauthier (1982) considered keeled body osteoderms to be the plesiomorphic state for Anguimorpha. Referral of the osteoderms from Montchenot to Pan &lt;i&gt;-&lt;/i&gt; &lt;i&gt;Shinisaurus&lt;/i&gt; (&lt;i&gt;sensu&lt;/i&gt; Smith &amp; Gauthier 2013) follows from the combination of the features described above. These osteoderms are similar in shape to those of other fossil pan-shinisaurs, particularly &lt;i&gt;Provaranosaurus fatuus&lt;/i&gt; Smith &amp; Gauthier, 2013 (Smith &amp; Gauthier 2013, early Eocene of the Wasatch Formation, Wyoming, United States), &lt;i&gt;Merkurosaurus ornatus&lt;/i&gt; Klembara, 2008 (Klembara 2008, early Miocene, Orleanian, MN3, Bohemia) and an indeterminate pan-shinisaur from Messel (Smith 2017, middle Eocene, Germany). Crocodile-tailed lizards (Chinese crocodile lizard) or shinisaurs are represented by a single living species, &lt;i&gt;Shinisaurus crocodilurus&lt;/i&gt; Ahl, 1930. It is worth noting that similar osteoderms have already been reported in the European Paleocene and early Eocene, in particular in the localities of Cernay (MP6, Hoffstetter 1943), Dormaal and Le Quesnoy (early Eocene, MP7, Hecht &amp; Hoffstetter 1962; Aug&eacute; 1990) and perhaps at Rivecourt- Petit P&acirc;tis (Smith &lt;i&gt;et al.&lt;/i&gt; 2014). Hecht &amp; Hoffstetter (1962) and Aug&eacute; (2005) suggested that these osteoderms could be attributed to the genus &lt;i&gt;Necrosaurus&lt;/i&gt; as they are also similar to those of &lt;i&gt;Palaeovaranus cayluxi&lt;/i&gt; (Ex &lt;i&gt;Necrosaurus&lt;/i&gt;), see figs. in Rage 1978; Estes 1983; Aug&eacute; &amp; Smith 2009; Klembara &amp; Green 2010. However, the taxonomic status and phylogenetic affinities of these lizards are a complex matter. Georgalis (2017) pointed out that the name &lt;i&gt;Necrosaurus&lt;/i&gt;, as established by Filhol (1876) is a nomina nuda and that Zittel (1887 -1890) was the first author to make the name &lt;i&gt;Palaeovaranus cayluxi&lt;/i&gt; available. The phylogenetic affinities of &lt;i&gt;Palaeovaranus&lt;/i&gt; are a moot point: briefly, McDowell &amp; Bogert (1954) noted significant morphological differences between &lt;i&gt;Palaeovaranus&lt;/i&gt; and members of the Platynota (&lt;i&gt;sensu&lt;/i&gt; Pregill &lt;i&gt;et al.&lt;/i&gt; 1986) and they referred it to xenosaurid lizards, an option first adopted by Hoffstetter (1954). Later this author returned &lt;i&gt;Palaeovaranus&lt;/i&gt; to the Platynota (Hoffstetter 1962b). Lee (1997) rejected this taxon as paraphyletic. The phylogenetic position of &lt;i&gt;Palaeovaranus&lt;/i&gt; is still a matter of discussion, although several derived characters suggest Platynotan relationships (see discussion in Smith 2017). In contrast, the attribution of &lt;i&gt;Provaranosaurus fatuus&lt;/i&gt; and specimen SMF ME 11403 (an autotomized tail) from Messel to pan-shinisaur is a settled matter as they show no Platynotan derived characters (Smith &amp; Gauthier 2013; Smith 2017). The fossils from Dormaal (osteoderms, vertebrae and an undescribed dentary) previously attributed to &lt;i&gt;Necrosaurus&lt;/i&gt; (&lt;i&gt;Palaeovaranus&lt;/i&gt;) show no Platynotan features and are nearly identical to the material of &lt;i&gt;Provaranosaurus fatuus&lt;/i&gt; described by Smith &amp; Gauthier 2013. In particular, &lt;i&gt;Provaranosaurus&lt;/i&gt; has both rectangular and oval osteoderms, as in the material from Monchenot, while &lt;i&gt;Palaeovaranus&lt;/i&gt; bears only ovoid osteoderms. On the basis of these resemblances, the osteoderms from Monchenot may be referred to pan- &lt;i&gt;Shinisaurus&lt;/i&gt; and the presence of rectangular osteoderms seems to exclude an attribution to &lt;i&gt;Palaeovaranus&lt;/i&gt;.&lt;/p&gt;Published as part of &lt;i&gt;Augé, Marc Louis, Dion, Michaël &amp; Phélizon, Alain, 2021, The lizard (Reptilia, Squamata) assemblage from the Paleocene of Montchenot (Paris Basin, MP 6), pp. 645-661 in Geodiversitas 43 (17)&lt;/i&gt; on pages 655-657, DOI: 10.5252/geodiversitas2021v43a17, &lt;a href="http://zenodo.org/record/5628435"&gt;http://zenodo.org/record/5628435&lt;/a&gt

Anguidae Gray 1825

Anguidae indet. MATERIAL EXAMINED. — MNHN.F.MTC241 (Fig. 8). The incomplete left dentary represents the middle and posterior parts of the bone and its ventral margin is broken. DESCRIPTION This small dentary (L: 2.9 mm) carries eight rather widely spaced tooth positions, but only one tooth is preserved. In medial view, the subdental shelf and the dental row are slightly concave. The subdental shelf forms a narrow, rounded surface overhanging the sulcus Meckeli. This fossa is rather narrow and faces mostly ventrally, mainly towards the anterior end of the bone. The dentition is subpleurodont (sensu Camp 1923; Hoffstetter 1954), that is the teeth tend to be attached to a single plane and the subdental table, as defined byRage & Augé (2010) becomes an inclined surface. Hence tooth bases are attached to a moderately inclined or concave surface. Moreover, this type of implantation is often associated with a poor development or absence of the sulcus dentalis and subdental shelf; effectively the dentary from Montchenot has no sulcus dentalis and a poorly developed, rounded subdental shelf. The lateral surface is gently convex, smooth and preserves only two labial (mental) foramina. The base of the single preserved tooth is not covered by cementum, except for two small anterior and posterior deposits. It is somewhat expanded, so that the mesial side of the tooth base comes near the dorsal margin of the subdental shelf. The tooth shaft slightly bends posteriorly and it steadily tapers dorsally towards the crown. The apex is rather rounded, with an incipient central bulb and two slight lateral shoulders. The tooth base is excavated by a central replacement pit. The tooth projects about onehalf of its height above the parapet of the dentary. There are no striae on the apex of the tooth but they could have been obliterated by weathering. COMPARISONS AND DISCUSSION Dentary MNHN.F.MTC241 is referred to an anguimorph lizard because it shows the following combination of characters: 1) Sulcus Meckeli faces ventrally in anterior portion of dentary (Estes et al. 1988); 2) narrow and rounded subdental shelf; 3) teeth subpleurodont; 4) absence of sulcus dentalis; 5) crescentis or boat shaped tooth row (Estes 1964); and 6) teeth unicuspid, without lateral cups, not closely spaced (Camp 1923). Some of these characters are regarded as anguimorphan synapomorphies (e.g. character 1, Estes et al. 1988), however several of them are not clear synapomorphies as they are subject to important variability among anguimorph taxa and often they are not unique to anguimorphs (Evans 2008). For example, the narrowness and reduction of the subdental shelf are very different among anguimorph lizards: from a well developed subdental shelf in Xenosaurus to a near absence in Varanus (see other examples in Bochaton et al. 2016). Conflicting characters that are often cited as anguimorphan synapomorphies are clearly absent in the dentary from Montchenot: tooth apex pointed and tooth replacement alternate or distally displaced replacement pit on tooth bases (McDowell & Bogert (1954). Pointed, canine like teeth indicative of predaceous habits are common in anguimorph lizards but rounded tooth apex occasionally provided with a cutting edge (Estes 1964) has sometimes been regarded as an anguid synapomorphy (Estes et al 1988). Alternate tooth replacement is a clear feature of some extant and fossil anguimorph taxa, e.g. Varanus, Lanthanotus, Heloderma, Saniwa, Palaeovaranus (Ex Necrosaurus). Otherwise, tooth replacement shows important intra-individual and intraspecific variability among anguid taxa. In some anguids the variability appears along the tooth row: in the genera Gerrhonotus and Diploglossus, the first tooth bases have a central replacement pit while the others bear a distally displaced replacement pit. The same variability is also evident in the genus Pseudopus (Anguinae, see figures in Klembara 2012; Klembara et al. 2010, 2014). The presence of these two characters (rounded apex and tooth replacement) may be indicative of anguid affinities but the evidence is at best feeble and further comparisons with more complete material should be carried out. Many purported terrestrial Anguimorpha have been described from the Mesozoic fossil record in Europe, Asia and North America (e.g. Hoffstetter 1967; Alifanov 2000; Evans 1994; Evans et al. 2006; Fernandez et al. 2015). In particular, the Cretaceous record includes fossils that bear some resemblances to extant terrestrial anguimorphan families (e.g.? Xenosauridae, Pérez-García et al 2015; Anguidae, Blain et al. 2010; Helodermatidae, Nydam 2000, 2013; Platynotan, Norell et al. 2007; Mo et al. 2012; Varanoidea, Houssaye et al. 2013). In contrast, fossils attributed to anguimorphan lizards in the early European Paleocene are far more scanty. Lizard extinctions across the K/T boundary may explain this poor record (Longrich et al. 2012) but it may also reflect the paucity of fossil lizards described so far in the European Paleocene (table 1). Among them, the incomplete dentary referred to Anguimorpha indet. found in the late Paleocene of Rivecourt (Smith et al. 2014, fig. 7) bears some resemblances with the dentary from Montchenot: teeth subpleurodont, rounded subdental shelf, teeth apparently with a central replacement pit but all these features are plesiomorphic within Anguimorpha. Another possibility could be an attribution to another anguimorphan lizard, a pan-shinisaur whose osteoderms are present in the locality. However, except for its anguimorphan relationships, nothing in the morphology of this dentary (particularly its size) is consistent with such an attribution.Published as part of Augé, Marc Louis, Dion, Michaël & Phélizon, Alain, 2021, The lizard (Reptilia, Squamata) assemblage from the Paleocene of Montchenot (Paris Basin, MP 6), pp. 645-661 in Geodiversitas 43 (17) on pages 653-655, DOI: 10.5252/geodiversitas2021v43a17, http://zenodo.org/record/562843