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And Cryptotis Magna (Merriam, 1895) from Mexico – in Comparison to the Schmelzmuster in Other Shrews

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And Cryptotis Magna (Merriam, 1895) from Mexico – in Comparison to the Schmelzmuster in Other Shrews FOSSIL IMPRINT • vol. 75 • 2019 • no. 3–4 • pp. 299–306 (formerly ACTA MUSEI NATIONALIS PRAGAE, Series B – Historia Naturalis) TOOTH ENAMEL MICROSTRUCTURE IN MEGASOREX GIGAS (MERRIAM, 1897) AND CRYPTOTIS MAGNA (MERRIAM, 1895) FROM MEXICO – IN COMPARISON TO THE SCHMELZMUSTER IN OTHER SHREWS WIGHART V. KOENIGSWALD Institut für Geowissenschaften, Abteilung Paläontologie, Rheinische Friedrich-Wilhelms-Universität Bonn, Nussallee 8, D-53115 Bonn, Germany; e-mail: [email protected]. Koenigswald, W. v. (2019): Tooth enamel microstructure in Megasorex gigas (MERRIAM, 1897) and Cryptotis magna (MERRIAM, 1895) from Mexico – in comparison to the schmelzmuster in other shrews. – Fossil Imprint, 75(3-4): 299–306, Praha. ISSN 2533-4050 (print), ISSN 2533-4069 (on-line). Abstract: The enamel microstructure of molars in Mexican soricines Megasorex and Cryptotis is described and compared to the six types of schmelzmuster found in fossil and recent Soricidae. These types of schmelzmuster show a high correlation to the current systematics of Soricidae. In Megasorex, the relatively simple schmelzmuster is dominated by radial enamel. However, a very thin innermost layer of differentiated enamel indicates the beginning of a two-layered schmelzmuster. This corresponds to the Notiosorex-schmelzmuster. The teeth of Megasorex lack pigmentation, which is not reflected in its schmelzmuster. Similarities to the white-toothed Crocidura-schmelzmuster are superficial. Cryptotis has the typical two-layered enamel of derived Soricinae. The specific enamel type of the inner layer and the strong lateral inclination of its prisms represent a new modification of the highly derivedBlarina -schmelzmuster. Zusammenfassung: Die Mikrostruktur des Zahnschmelzes in den Molaren der Mexikanischen Spitzmäuse, Megasorex und Cryptotis, wird beschrieben und mit den sechs Schmelzmuster-Typen verglichen, die von den fossilen und rezenten Soriciden bekannt sind. Die unterschiedenen Schmelzmuster-Typen weisen eine sehr hohe Übereinstimmung mit der derzeitigen systematischen Gliederung der Soriciden auf. Das Schmelzmuster von Megasorex ist relativ einfach und wird von radialem Schmelz dominiert. Aber eine sehr dünne Innenschicht weist auf eine beginnende Zweischichtigkeit hin, wie sie im Notiosorex- Schmelzmuster zu beobachten ist. Den Zähnen von Megasorex fehlt die Pigmentierung, die sich aber nicht auf das Schmelzmuster auswirkt. Eine gewisse Ähnlichkeit zum dem Schmelzmuster der weißzähnigen Crocidura ist nur oberflächlich. Cryptotis hat das für evoluierte Soricinae typische zwei-schichtige Schmelzmuster. Der besondere Schmelztyp der Innenschicht und die starke seitliche Neigung der Prismen belegen eine Zugehörigkeit zum hoch abgeleiteten Blarina-Schmelzmuster, wobei Cryptotis eine neue Modifikation belegt. Key words: enamel microstructure, schmelzmuster, Soricidae, Mexico Received: April 12, 2019 | Accepted: August 20, 2019 | Issued: December 30, 2019 Introduction recognized and named after typical genera: Soriciella-, Anourosorex-, Crocidura-, Notiosorex-, Sorex- and the The enamel microstructure in molars of Megasorex Blarina-schmelzmuster. These types of schmelzmuster are gigas and Cryptotis magna shall be compared with the closely related to the actual systematic order of Soricidae variability of the enamel in soricid molars. The different (Reumer 1996, 1998, Gunnell et al. 2008, Rzebik-Kowalska tribes within Soricidae differ in their enamel microstructure 2009). This broad study provides the background for the (Koenigswald and Reumer 2020). The enamel in a single comparisons in this paper. species is not uniform, but rather is composed of different Megasorex gigas was not included in the former survey. enamel types. The three dimensional arrangement of the Its unpigmented teeth, as well as those of the Chinese enamel types within a tooth is described as “schmelzmuster”. Nectogale, are unique among soricines. In addition, the The variability of the molar schmelzmuster in Soricidae impressive name Megasorex gigas causes one to question was recently studied by Koenigswald and Reumer whether the schmelzmuster might be special, because of (2020). Six types of schmelzmuster in lower molars are the promised size change. The name, however, refers to the 300 DOI 10.2478/if-2019-0019 size differences within Notiosoricini. Notiosorex crawfordi from Colorado is distinctly smaller, but in comparison to other soricines, such as the sympatric Cryptotis magna and a Blarina brevicauda, the size of Megasorex magna is not exceptional (Text-fig. 1). The different types of schmelzmuster correlate with the various soricid groups. The soricid tribe Notiosoricini contains two extant genera, Notiosorex and Megasorex, and occurs in the southern US, Mexico and the northern part of South America. In the survey by Koenigswald and Reumer (2020), only Notiosorex crawfordi from Colorado could be b investigated. Here, the investigation of Megasorex shall clarify whether it shows a similar or the same schmelzmuster as Notiosorex. Notiosoricini are characterized by a reduced c dental formula and the specific articular process of the mandible (Reumer 1984, 1998, Harris 1998, Hutterer 2005). Within the Soricinae, the tribes Notiosoricini and Nectogalini (= Neomyini) are sister groups (Dubey et al. 2007), but several authors do not separate the two tribes (e.g. Gunnell et al. 2008). In addition to the two extant genera Notiosorex and Megasorex, the tribe Notiosoricini contains two fossil genera, Beckiasorex and Hesperosorex. They are known from several fossil species since the Miocene (Carraway d 5 mm 2010), and occur in the southern US and Mexico. Megasorex HIBBARD, 1950 is monospecific. The species Megasorex gigas (MERRIAM, 1897) was initially assigned to the closely related genus Notiosorex, but separated by Hibbard (1950), because of the size difference, a heavy rostrum, and the white teeth in Megasorex. In contrast, Notiosorex has pigmented tooth tips (Text-fig. 1). Their coloring may be weak, but is generally present. Text-fig. 1. Comparison of mandibles of Soricidae. a) Megasorex Cryptotis magna was included in this study as a gigas, right dentary, Mexico (UNAM 43090, KOE 4222). counterpart to Megasorex that most probably shows a b) Notiosorex crawfordi, right dentary, Colorado (UCM different schmelzmuster. Cryptotis belongs to the soricine 20281). c) Cryptotis magna left dentary (inverse), Mexico tribe Blarini and has pigmented tooth cusps, like most (UNAM 29439, KOE 4220). d) Blarina carolinensis, right dentary (UTCM 526, KOE 4203). For the better comparison in soricines (Text-fig. 1). size, all are to the same scale. Photos (a), (c) and (d) by Georg Oleschinki, (b) by Nicole Neu-Yagle. Material and methods In addition to a great number of soricids that were dentition level (Koenigswald and Clemens 1992). Špoutil studied for another survey (Koenigswald and Reumer 2020), et al. (2010) investigated the enamel of some Eulipotyphla the following materials were investigated especially for this at the level of prism. For the actual question, the level of study: schmelzmuster in lower molars is adequate. According to Megasorex gigas (MERRIAM, 1895) Mexico, (UNAM initial observations, the schmelzmuster of upper molars is 43090) (KOE 4222); differentiated as well, but sections for comparisons are more Cryptotis magna (MERRIAM, 1895) Mexico, Colima: difficult to obtain. The enlarged incisors definitely show Rancho La Mora (UNAM 29439) (KOE 4220); a schmelzmuster different from that in the molars. Such Blarina carolinensis, Tennessee (UTCM 526); differences are related to the dentition level. Notiosorex crawfordi, Colorado (KOE 2114 and UCM The molar morphology of soricid molars is very complex. 20281). A transverse section of the trigonid of the lower molars just The material of Megasorex and Cryptotis was collected below the paralophid notch was selected for the comparison of soricid schmelzmuster. The arrangement of different in Mexico, Colima, Rancho La Mora at an elevation of enamel types within the trigonid can clearly be analyzed, and 1,322 m (Cervantes et al. 2008), and was made available for this section can be reproduced easily. Comparative studies this study by Fernando Cervantes-Reza from the “Colección of many soricids confirmed that the arrangement of enamel Nacional de Mamíferos (CNMA)” of the “Instituto de types in the paralophid is repeated in the protolophid and the Biologia, Mexico”. hypolophid. Thus, the observations in transverse sections of Investigations of enamel microstructure and comparison a tooth row can be summarized in order to characterize the between taxa may occur at various levels, according to enamel of a species. the applied techniques and magnifications: at the level of From Megasorex gigas as well as from Cryptotis crystallites, prisms, enamel types, schmelzmuster, and at the magna, a part of the mandibles containing lower molars was 300 embedded into an artifi cial resin (epoxy). For embedding, the specimen was oriented in such a way that the intended plane of investigation is parallel to one of the sidewalls of paralophid the box. The preferred section plane can then be reached by paraconid sectioning or grinding parallel to this side. After hardening of the resin, the block was cut with a saw in the intended protoconid plane, but slightly outside of the teeth, to avoid cracking of the enamel. Grinding was done fi rst on a wheel, then on fi ne talonid metaconid grinding paper with water, and fi nally with grinding powder Megasorex gigas (1,000 mesh = 5µ), until
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