@inproceedings{8637613,
  abstract     = {{Heterochrony, a change in developmental rate and timing [1], is one of the mechanisms proposed to explain alterations of meristic characters, such as loss and gain of skeletal elements [2]. As an attempt to verify the possible role of heterochrony in the evolutionary transformation of the cyprinid pharyngeal tooth formula the development of pharygeal teeth in zebrafish (Dano rerio) was studied under the influence of decreased thyroid hormone levels. Thiourea was used to decrease thyroid hormone, a treatment known to causes retardation of several developmental processes including skeletal development and tooth formation [3].
Retarded development resulted in a high degree of variability and fluctuating asymmetry (left right asymmetry) in the dentition. Additional teeth developed. These were added to an existing tooth row anterior to the first tooth in the row. Additional teeth were also added lateral to an existing tooth row, either ventrally or dorsally with respect to regular position of the tooth row. The latter feature resembled the start of formation of an accessory tooth rows. Older individuals, compared to younger individuals, showed a higher rate of morphological alterations and also a higher number of additional teeth. They regularly displayed both, an extra tooth in a row and an extra tooth row. 
References:
[1] Gould, S.J. (1977):. Ontogeny and Phylogeny - Harvard University Press 
[2] Kapitanova, D. & Shkil, F. (2014) Heterochronies in teleost caudal fin evolution: Experimental evidence. - Conference: The Fifth meeting of the European Society for Evolutionary Developmental Biology (EED) 
[3] Shkil et al. (2012): Thyroid hormone in skeletal development of cyprinids: effects and morphological consequences - Journal of Applied Ichthyology 28:398-405}},
  author       = {{Woltmann, Iris and Shkil, Fedor and De Clercq, Adelbert and Huysseune, Ann and Witten, Eckhard}},
  booktitle    = {{Interdisciplinary Approaches in Fish Skeletal Biology, 4th Meeting, Abstracts}},
  language     = {{eng}},
  location     = {{Tavira, Portugal}},
  title        = {{Extra teeth in the pharyngeal dentition of slow developing zebrafish}},
  year         = {{2015}},
}