Science - USA (2020-07-10)

differ in shape from the stellate odontodes on
thecheek (Fig. 3A). Both the odontodes and
teeth consist of pallial semidentine ( 5 , 22 ), and
the circumpulpal dentine that infills the pulp
cavity in mature teeth is an atubular dentinous
tissue with fewer cell spaces enclosed (figs.
S11 and S12). By contrast, the facial lamina of
Tlamaspisis mostly unornamented labially

(fig. S13), except for two or three rows of tu-

bercles that transition abruptly into a single

row of conical teeth, which are bordered lin-

gually by a toothless flange (Fig. 4). This is rem-

iniscent of the marginal jawbones of crown

osteichthyans, even though the teeth are not

shed or replaced. The tooth histology in this

case is unknown.

In our phylogenetic analysis, acanthothor-

acids are separated from the gnathostome

crown group node by four internodes (fig. S1).

Nevertheless, there are distinct similarities

between acanthothoracid and osteichthyan

dentitions. Notably, multiple short dermal

jawbones, similar to those ofKosoraspisand

Tlamaspis, are present in the stem osteichthyan

SCIENCEsciencemag.org 10 JULY 2020•VOL 369 ISSUE 6500 213

Fig. 2. Palatoquadrate complex and dentition ofRadotina tesselata.(Ato
C) Palatoquadrate in internal (A), external (B), and ventral (C) views. (D) Dentition in
mesoventral (top) and medial (bottom) views. (E) Detailed image of teeth in
ventral view, with the relationship to (C) indicated with gray lines. (F) Block model of
dentition in transverse view, showing the region indicated by the yellow box in
(E).Thescansshownin(A)to(D)haveavoxelsizeof13.49mm, and the scans

shown in (E) and (F) have a voxel size of 0.72mm. In (A) to (D), green denotes

external dermal bone, cream indicates natural mold of external dermal bone, blue

indicates endoskeleton, and yellow indicates teeth and/or tooth-bearing dermal

bone. In (E) and (F), red to purple tones denote different tooth rows, gold indicates

a replacement tooth, green indicates pulp cavities, and blue indicates vasculature.

Scale bars, 10 mm [(A) to (C)]; 1 mm (D); 0.1 mm [(E) and (F)].

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