
Spassov, N. 1979. Sexual selection and the evolution of horn-like structures of Ceratopsian dinosaurs. — Palaeontology, Stratigraphy, litology, 11: 37—48.
Spassov N., Spiridonov, G. 1993. Vormela peregusna Gueld., 1770 — Tigeriltiss. In: Handbuch der Saugetiere Europas. Aula Verlag GmbH, Wiesbaden. Band 5/II (Carnivora).
Spassov, N., Lange-Badre, B. 1995. Asiavorator altidens gen et sp. nov., un mammifere carnivore nouveau de l’Oligocene superieur de Mongolie. — Annales de Paleontologie, 81 (3): 109—123.
Spassov, N., Raychev, D. 1997. Late Wurm Panthera pardus remains from Bulgaria: the European fossil leopards and the question of the probable species survival until the Holocene on the Balkans. — Historia naturalis bulgarica, 7: 109—113.
Spassov, N., Iliev, N. 1998. The late pleistocene and holocene horses of East Europe and the polyphylethic origin of the domestic horse. In: Stefanovich, M., Todorova, H., Hauptmann, H. (Eds). James H. Gaul in memoriam. The James Harvey Gaul Fondation, Sofia, 371—390.
Spassov, N. 2002. The Turolian Megafauna of West Bulgaria and the character of the Late Miocene ‘Pikermian biome’. — Bollettino della Societa Paleontologica Italiana, 41(1): 69—81.
Spassov, N. 2003. The Plio-Pleistocene vertebrate fauna in South-East ern Europe and the megafaunal migratory waves from the east to Europe. — Revue de Paleobiologie. Geneve, 22 (1): 197—229.
Koufos G., N. Spassov and D. Kovatchev. 2003. Study of Mesopithecus (Primates, Cercopithecoidea) from the Late Miocene of Bulgaria. — Palaeontographica, A, 269 (1—3): 39—91.
Spassov N. 2003. The Brown Bear in the southern Balkans. In: Krystufek, B., B. Flajsman, Huw Griffiths (Eds). Chapter 9. Living with Bears, A large European carnivore in a shrinking world. Ekoforum, Ljubljana, pp. 229—244.
Spassov, N., D. Geraads 2004. Tragoportax Pilgrim and Miotragocerus Stromer (Mammalia, Bovidae) from the Turolian of Hadjidimovo, Bulgaria , and a revision of the Late Miocene Mediterranean Boselaphini. — Geodiversitas, 26 (2): 339—370.
Spassov N., Tz. Tzankov, D. Geraads 2006. Late Neogene stratigraphy, biochronology, faunal diversity and environments of South-West Bulgaria (Struma river valley). — Geodiversitas, 28 (3): 477—498.
Spassov N., D. Geraads. 2007. Dolichopithecus balcanicus sp. nov., a new Colobinae (Primates, Cercopithecidae) from the Early Pliocene of South-eastern Europe, with a discussion on the taxonomy of the genus. — Journal of Human Evolution, 52: 434—442.
Geraads, D., N. Spassov. 2009. Rhinocerotidae (Mammalia) from the late Miocene of Bulgaria. — Palaeontographica, A, 287 (4—6): 99—122 [PDF].
Spassov N. 2009. The Southwesternmost Distribution of the Saiga in the Holocene of Europe: A Saiga Tatarica Find From an Archaeological Site in Bulgaria. In: Gatsov I. & J.-L. Guadelli (eds.) Saxa loquuntur. Volume in honour of the 65th anniversary of Nikolai Sirakov. Avalon publisher. Sofia, pp. 317—322 [PDF].
Kahlke, R.-D., N. Garcia, D. Kostopoulos, F. Lacombat, A. Lister, P. Mazza, N. Spassov, V. Titov (in press). Western Palaearctic palaeoenvironmental conditions during the Early and early Middle Pleistocene inferred from large mammal communities, and implications for hominin dispersal in Europe. In: J. Carrion, J. Rose and C. Stringer (eds.) — Ecological scenarios for human evolution during the Early and early Middle Pleistocene in the western Palaearctic. Special Issue of Quaternary Science Reviews, 2010 [PDF].