Tooth eruption in the Early Cretaceous British mammal Triconodon and description of a new species

Abstract

Triconodon mordax, from the lowest Cretaceous (Berriasian) part of the Purbeck Group, Dorset, is known by an ontogenetic series of specimens that document aspects of tooth eruption and replacement. Based on micro‐computed tomography of four specimens we refer one mandible to a new species, Triconodon averianovi, which differs from T. mordax in having a more slender, curved c; p4 notably low crowned with slender main cusp and smaller accessory cusps; and molars with weak cingula, m4 being notably smaller with weak cusps a and c. T. mordax is variable in the number of mental foramina and posterior jaw morphology. Scans reveal an earlier developmental stage (p3 in early eruption) than previously recognized for Triconodon, and demonstrate sequential, anteroposterior replacement of premolars; it remains unclear whether p1–2 were replaced. Scans also support an earlier hypothesis that m4 erupted late in life. Onset of m4 mineralization is likely to have coincided with eruption of p3, followed by replacement of dp4 by p4 and eruption of c. The m4 developed within the lingual side of the coronoid process, well above the tooth row. It remained in position and was subsequently accommodated in the active tooth row through unusually prolonged and localized growth of the posterior part of the mandible. This pattern is seen in some later triconodontids and appears to be unique to the family.

Molar occlusion and jaw roll in early crown mammals

“…Apart from this, the addition of molars at the posterior end of the molar series was possible without interference with the constrained occlusal system. In Triconodon m4 is formed within the coronoid above the functional tooth row 54 , 60 . This unusual placement could be linked to an increase in tooth count, as the Early Cretaceous Meiconodon and the Late Cretaceous Corviconodon have five lower molars 13 , 60 , 61 .…”

The origins of mammal growth patterns during the Jurassic mammalian radiation

“…All studied taxa are considered as diphyodont (undergoing a single replacement of teeth) on the basis of previous studies of representative dentulous specimens and/or phylogenetic bracketing (4,19,21,50,62). Although additional replacement of certain teeth is known in some eutriconodontan gobiconodontids (63)(64)(65), it has been shown that this is not a generalizable pattern within eutriconodontans (66). Our sample includes the "amphilestid" eutriconodontan Phascolotherium, but gobiconodontids were not represented in our sample.…”

Dental pathologies in lamniform and carcharhiniform sharks with comments on the classification and homology of double tooth pathologies in vertebrates

“…A wide array of dental pathologies have been reported across multiple vertebrate clades, in both extant ( Aalderink et al, 2015 ; Crossley et al, 1998 ; Jett et al, 2017 ; Jones & Franklin, 2006 ; Scarpetta & Bell, 2020 ; Shen et al, 2011 ; Winer et al, 2016b ; Winer, Liong & Verstraete, 2013 ) and extinct taxa ( Candeiro & Tanke, 2008 ; Jäger, Cifelli & Martin, 2020 ; Kirillova, 2009 ; Matthias, McWhinney & Carpenter, 2016 ; Reisz et al, 2011 ; Xing et al, 2013 ). In particular, a category of dental pathologies known as tooth doubling, or connate teeth, is well documented in extant mammalian clades, especially humans ( Agnihotri, Marwah & Goel, 2007 ; Camargo, Aritaa & Watanabe, 2016 ; Cetinbas et al, 2007 ; Ertaş et al, 2014 ; Guler et al, 2013 ; Hülsmann, Bahr & Grohmann, 1997 ; Hunasgi et al, 2017 ; Jain, Yeluri & Munshi, 2014 ; Kamura, 2019 ; Knežević et al, 2002 ; Mahendra et al, 2014 ; Sharma et al, 2015 ; Shokri, Baharvand & Mortazavi, 2013 ; Syed et al, 2016 ; Tasa, 1998 ; Tsesis et al, 2003 ).…”