Permian hypercarnivore suggests tooth complexity in early amniotes | Panda Anku

All vertebrates examined and histologically excised in this study (Supplementary Table 1) exhibit polyphyodontia and dentine growth lines (Figs. 2–4 and Supplementary Figs. 2–9) morphologically consistent with Ebner’s incremental lines of extant mammalian and crocodilian teeth: alternating opaque zones, lines running parallel to the pulp cavity and widths between 1 and 30 mm18. All of the functioning teeth were continuously replaced with the development of the replacement tooth lingual to the functioning tooth, resulting in resorption of its base and fallout.

Fig. 2: Incremental lines from Mesenosaurus efremovi.
figure 2

a ROMVP 85502, Lingual view of fragmented prosthesis with dashed red lines through plane of LL section of functional and replacement teeth. b General view of the LL section of the tooth family near the tip of the crown. c Detail view of functional tooth LL cross-section with incremental lines, white arrows. i.e Detailed view of the TR cross-section of the replacement tooth with incremental lines, white arrows.

Fig. 3: Incremental lines from Dimetrodon see. D.limbatus.
figure 3

a side view of Dimetrodon. b ROMVP 85510, maxillary tooth family, photographed in lingual view showing the plane of the LL section through the functional tooth and the replacement tooth. c General view of the LL longitudinal section near the tip of the crown of the functional and replacement tooth. i.e Detail view of functional tooth LL cross-section with incremental lines, white arrows. e Detailed view of the LL cross-section of the replacement tooth with incremental lines, white arrows. The skull drawing was modified by Reisz42 and Brink and Reisz43.

Fig. 4: Incremental lines from edaphosaurus sp.
figure 4

a side view of edaphosaurus. b USNM PAL 706602, maxillary tooth family, photographed in a lingual view showing the plane of the LL section through the functional tooth and replacement tooth. c General view of the LL longitudinal section near the tip of the crown of the functional and replacement tooth. i.e Detail view of functional tooth LL cross-section with incremental lines, white arrows. The skull drawing was modified by Romer and Price41 and Modesto44.

replacement pattern in Mesenosaurus efremovi

Substitute in the graceful predator Mesenosaurus efremovi from the Richards trace locality (Fig. 1) appears to occur as a wave in alternating tooth positions, replacing every other functional tooth in a sequence during one event. Gaps in the row of teeth represent stages in the replacement cycle when the old tooth has fallen out but the replacement tooth is not yet functional and has not ankylosed to the jawbone. Frequently these small replacement teeth are lost in fossilization, but in the case of dolese Mesenosaurus, preservation is so exquisite that these unattached replacement teeth are retained, often in place (Fig. 1e). We found numerous specimens of M.efremovi have tooth families containing a functional tooth and a single replacement tooth lingual to it, but in one maxilla (ROMVP 85456) a tooth family containing a functional tooth and two consecutive replacement teeth was observed (Fig. 1c).

The replacement rate found in a tooth family within one M.efremovi Dentures were 39 days (ROMVP 85502; Fig. 2) and 34 days for the left maxilla (ROMVP 85443; Supplementary Fig. 2). The replacement rates of three tooth families (mx10, mx12, and mx15) for ROMVP 85457 were estimated at 46, 36, and 35 days. Thus, the replacement rate for M.efremovi does not appear to vary significantly in a sample across tooth position, size, or ontogenetic age of the tooth.

Replacement patterns in other synapsids

Contrary to the availability of many Mesenosaurus Specimens for destructive sampling, other taxa are extremely rare and few specimens were available for destructive analysis. Thus only a single upper jaw of the apex predator Dimetrodon with a replacement tooth in place (Fig. 3). The functional tooth had a total of 459 incremental lines while the replacement tooth had a total of 354 lines, resulting in a replacement rate of 105 days. In contrast, the maxillary tooth for the basal sphenacodont haptodusa functional tooth lifetime was calculated to be approximately 152 days, and since there was neither a replacement tooth nor a resorption pit, the minimum replacement rate is 152 days.

Relatively little material was also available for the larger varanopid predator Watongia meieri known only from the holotype material, with a resorption pit on one of the two teeth (mx19) on a maxillary fragment, but both teeth lacked the apex of the crown; therefore only a minimum age could be determined from the incremental line counts. The tooth with the resorption pit was at least 81 days old, while the adjacent tooth that was not replaced was approximately 68 days old. A second maxillary tooth with a resorption pit at mx18 was determined to be 145 days old. In addition, a complete tooth without resorption pits was cut longitudinally LL and estimated at 108 days.

An upper jaw of the small, very rare herbivorous caseid Oromycter was available for destructive sampling (Supplementary Fig. 3). The tooth with a resorption pit at position mx07 had a total of 506 incremental lines, while the tooth without a resorption pit (mx09) had a total of 426 incremental lines. For the mx09 family of teeth, the missing replacement tooth was estimated at 115 incremental lines, resulting in an approximate replacement rate of 391 days.

The left dentition of the large herbivorous caseid Ennatosaurus, known from only five specimens, had two posterior teeth with resorption pits at positions d08 and d07 (Supplementary Fig. 4). Tooth position d08 had a visibly larger and more developed resorption pit, with the functional tooth having a total of 628 incremental lines, while d07 had a smaller resorption pit and a total of 567 incremental lines. The missing replacement teeth for d07 and d08 were estimated at 136 and 169 incremental lines, respectively, resulting in a replacement rate of approximately 431 and 459 days, respectively.

An upper jaw of the herbivorous edaphosaurid edaphosaurus had a resorption pit at tooth position mx09 (Fig. 4) and was estimated to have a total of 506 incremental lines. The adjacent tooth at position mx10 had no resorption pits and was found to have a total of 429 lines. For the mx09 family of teeth, the missing replacement tooth was estimated at 131 incremental lines, resulting in a replacement rate of 381 days.

Surrogate patterns in early and extant reptiles

For the insectivorous parareptile Delorhynchus The functional tooth had a total of 147 incremental lines while the replacement tooth had 43 lines (Supplementary Fig. 5), resulting in a replacement rate of 104 days. For the other parareptiles colobomecter The premaxillary functional tooth had a total of 157 incremental lines while the replacement tooth had a total of 59 lines, resulting in a replacement rate of 98 days (Supplementary Fig. 6). For the omnivore Eureptil Captorhinus, the functional tooth was 146 days and the replacement tooth was 69 days, resulting in a replacement rate of approximately 77 days. For the other Euptile, the highly specialized insectivore Opistodontosaurusthe maximum tooth ages for positions d04 to d07 were 151, 155, 206 and 258, respectively (Supplementary Fig. 7). Although no replacement teeth were available, it was possible to use the resorption pit heights to estimate the replacement rates at 182 and 193 days for d06 and d07, respectively. Although these prices differ from Captorhinus are not unexpected since this small, close relative of Captorhinus has a very strange, unusual set of teeth that specializes in feeding on harder-shelled invertebrates.

In addition to the above Paleozoic amniotes, two skulls were examined for the varanid lizards present, Varanus bengalensis and Varanus komodoensis, as well as cast teeth of the latter were also available for study and comparison. The maxillary bone of Varanus bengalensis Worn bit with six replacement events but only the mx04 tooth position was cut. Functional tooth 188 was determined to have incremental lines, and since a continuous trace for the incremental lines of the replacement tooth was not visible, the replacement rate was estimated based on its total dentin area divided by the mean line width of the functional tooth. The estimated replacement rate for V. bengalensis was about 110 days. not how M.efremovithe base of the teeth is marked by plicidentin and neither tooth interlocking (ziphodontia; Supplementary Fig. 8) nor resorption pits were observed V. bengalensis.

Similar to Mesenosaurus, Varanus komodoensis, an endangered varanid lizard, exhibits ziphodonty on both the mesial and distal tooth surfaces, providing a valuable comparison to the fossil taxon. Two isolated adult teeth, in the process of attachment but not yet ankylosed to the jawbone, were dissected. The first tooth was estimated to have 106 lines and the second tooth had approximately 135 lines. A third isolated tooth loss (from resorption from the replacement tooth or from food processing)29 provided by the Toronto Zoo was determined to have approximately 227 incremental lines. Thus, from the age of initial attachment to the age of falling out, a tooth appears to be functional for an average of 107 days. Also as in Mesenosaurusthe adult skull of V. komodoensis (ROM R7565) showed that each tooth position had multiple replacement teeth for both the tooth and the maxilla, which was also confirmed by Auffenberg’s data30.

Surrogate pattern in a parent amniote

For the representative carnivorous ancestral amniote Seymouria (Supplementary Fig. 9) The functional tooth was determined with a maximum of 171 incremental lines, while the missing replacement tooth was estimated at approximately 36 lines. Thus, the estimated replacement rate for Seymouria was calculated with 135 days.

replacement rate and body mass

There does not appear to be a significant relationship between replacement rate and body mass (kg) for the taxa studied (Supplementary Fig. 10). Although the largest full-sized taxon Ennatosaurus had the longest replacement rate, but the other large species had different rates, while the smallest taxa (Captorhinus, Delorhynchus, colobomecterand Opistodontosaurus) all have different replacement rates. Instead, replacement rates appear to be related to feeding behavior, as the herbivorous synapsids all exhibited long replacement rates and long tooth lifespans (Fig. 5).

Fig. 5: Denture rates and age in different taxa.
Figure 5

a Relationship between the total number of Ebner incremental lines (age) for the functional tooth and the replacement rate or duration (days) of the tooth families. The symbols indicate the type of feeding behavior, with circles representing carnivores, triangles representing herbivores, squares representing insectivores, and diamonds representing omnivores. b Pedigree of all taxa (n= 11) used in the analyzes showing age in millions of years (length of bars) and longevity of teeth (gradient in branch colors). c Pedigree of all taxa (n= 9) used in the analyzes showing age in millions of years (mya) (length of bars) and denture rate (slope in branch colors). Reconstructed using the ‘contMap’ function in the R package ‘phytools’. The tree was modified by Maddin, Evans and Reisz45 and Reisz and Sues12. Source data is provided as a source data file.

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