Structural pattern in the tusks of the Miocene mammutid Zygolophodon turicensis and its utility in the taxonomy of elephantimorph proboscideans

ABSTRACT

The cross sections of tusks of all elephantimorph proboscideans show well-developed intersecting lines that form a conspicuous net-like structure termed the Schreger pattern. This trait is usually used to discriminate the tusks of recent elephants from those of mammoths. In Neogene elephantimorphs, however, the pattern remains largely unstudied and its utility unexplored. This study provides the first detailed assessment of the Schreger pattern in a Neogene elephantimorph. We have obtained thin sections from the basal half of the upper tusks of Zygolophodon turicensis, a mammutid from the middle Miocene of the Czech Republic, provide the full description of Schreger pattern and assess its utility in elephantimorph taxonomy. The arrangement of Schreger lines more closely resembles that of Anancus arvernensis and mammoths rather than that of Mammut americanum, a mammutid closely related to Z. turicensis. We further found that the visibility of the Schreger pattern can be affected by mineralisation as well as by the natural formation of dentin. Our results indicate that the appearance of the inner structure of elephantimorph tusks is not associated with their shape and is probably not reflective of phylogenetic affinities. Still, the appearance of the Schreger pattern remains useful for species identification.

KEYWORDS:

• Schreger pattern
• tusk
• Zygolophodon
• Mammutidae
• Proboscidea
• Miocene

Acknowledgments

We are indebted to Martina Roblíčková (MZM) for the possibility to obtain tusk samples for our analyses and Mihály Gasparik (Hungarian Natural History Museum, Department of Palaeontology and Geology) for providing us with photographs of Schreger pattern in Anancus arvernensis and access to specimens under his care. We would also want to express our gratitude to Martina Moravcová (State Geological Institute of Dionýz Štúr, Bratislava, Slovakia) and Ursula B. Göhlich (Natural History Museum, Vienna, Austria) for their constructive reviews that improved our manuscript. This study was funded through the institutional support of long-term conceptual development of research institutions provided by the Ministry of Culture of the Czech Republic (ref. MK000094862) and the Specific research project at the Faculty of Science at Masaryk University, Brno (MUNI/A/0944/2019).

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary material

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Additional information

Funding

This work was supported by the Ministry of Culture of the Czech Republic [ref. MK000094862]; Faculty of Science at Masaryk University, Brno [MUNI/A/0944/2019].