Development of the dentition in Alligator mississippiensis: Upper jaw dental and craniofacial development in embryos, hatchlings, and young juveniles, with a comparison to lower jaw development

Abstract

Development of the upper dentition in Alligator mississippiensis was investigated using a close series of accurately staged and aged embryos, hatchlings, and young juveniles up to 11 days posthatching, as well as some young and old adult specimens. Studies from scanning electron microscopy, light microscopy, acetate and computer reconstructions, radiography and macroscopy were combined to elucidate the details of embryonic dental development, tooth initiation pattern, dentitional growth, and erupted functional dentition. The results were compared with those from the lower jaw and related to the development of other craniofacial structures. Approximately 17 early teeth in each jaw half develop as surface teeth, of which 13 project for 1 to 12 days before sinking into the mesenchyme. The first three teeth initiate directly from the oral epithelium at Ferguson stages 14-15 (days 15-19 after egg laying), before there is any local trace of dental lamina formation. All other teeth develop from a dental prolamina or lamina; and with progressive lamina development, submerged teeth initiate from the aboral end leading to the formation of replacement teeth. All teeth form dentin matrix, but 12 early teeth do not form enamel. Approximately 20 embryonic teeth are resorbed, 6 are transitional, and 42 function for longer periods after hatching. The embryonic tooth initiation pattern (illustrated by defining a tooth position formula) does not support the previous models of Odontostichi, Zahnreihen, and Tooth Families, each of which postulates perfect regularity. Up to three interstitial tooth positions develop between sites of primary tooth initiation, and families with up to five generations at hatching are at first arbitrarily defined.

Development of the dermal skeleton in Alligator mississippiensis (Archosauria, Crocodylia) with comments on the homology of osteoderms

“…Matching the dentigerous elements of the upper jaw, and correlating with the previous development of the dentition (FS 15;Westergaard and Ferguson, 1990), the dentary also develops early during embryogenesis (at FS 17). The sequence of onset for the mandibular series is: angular, dentary, and coronoid (FS 17) ?…”

“…nasal (FS 21), is the same as that recorded by Rieppel (1993b ; Table 3), although he consistently observed each element one Ferguson developmental stage later. Early formation of the maxilla (at early FS 18) and premaxilla (at mid FS 18) was also noted by Westergaard and Ferguson (1990). The earliest detection of the nasal bone comes from the work of Klembara (1991) at FS 20.…”

“…Dried skeletal materials, representing multiple suba- The postpareital is excluded as it was not observed. The results from this study as well as the work of Westergaard and Ferguson (1990) were obtained from serial histology; data from Klembara (1991) and Rieppel (1993b) were obtained from whole-mount preparations. See text for details.…”

A large archosauriform tooth with multiple supernumerary carinae from the Upper Triassic of New Mexico (USA), with comments on carina development and anomalies in the Archosauria

“…Erickson (1995) also suggested aberrant tooth replacement as a possible cause. Tooth replacement in alligators, and presumably other archosaurs, is a complex succession of fully and partially developed teeth, including some teeth that never fully form (Edmund 1960(Edmund , 1962Westergaard and Ferguson 1990). It is difficult to imagine how tooth replacement could cause a supernumerary carina, as tooth crown enamel development starts from an enamel knot at its tip and gradually follows toward its base, much like that seen in mammals (Kassai et al 2005) and squamates (Delgado et al 2005).…”

The Molecular Circuit Regulating Tooth Development in Crocodilians

“…Each tooth position contains a complex tooth family unit that includes a functional tooth (ft), a replacement tooth (RT) and a dental lamina (dl) (Westergaard and Ferguson 1990;Wu et al 2013). Each adult alligator ft lasts for about 1 y (Edmund 1962) and is then replaced by an RT.…”