Lophosteus(fig. S14), which has acanthothoracid-
like dermal ornament ( 25 ). The cheek pattern
ofKosoraspis(fig. S10B) also closely approaches
that of primitive crown osteichthyans ( 26 ). The
possibility that the gnathostome crown is rooted
close to acanthothoracids, with arthrodires
and certain other so-called placoderm groups
forming a divergent clade rather than a para-
phyletic segment of the gnathostome stem,
should be given serious consideration.
The newly described acanthothoracid denti-
tions exhibit a combination of shared charac-teristics and remarkable diversity. The diver-
sity of the dentitions has functional and archi-
tectural aspects. Functionally, the dentition
of CPW.9 appears to be adapted for crush-
ing, that ofRadotinaadapted for cutting, and
those ofKosoraspisandTlamaspisadapted214 10 JULY 2020•VOL 369 ISSUE 6500 sciencemag.org SCIENCE
Fig. 3. Palatoquadrate complex, ethmoid, and dentition ofKosoraspis
peckai.(AandB)Národní Muzeum (NM) specimen Lc 552 palatoquadrate
complex in external (A) and internal (B) views, with associated tooth-bearing
elements. Lowercase letters refer to detailed views of dental elements, as
specified. (C) Dental element (a) in external (top), internal (bottom), and oblique
anteroventrolateral (left) views. (D) Dental element (b) in occlusal (left) and
basal (right) views. (E) NM Lc 16 ethmoid-trabecular region in ventral view with
articulated premedian plate, two articulated supragnathals, and disarticulated
dental elements. (F) Dental element (c) (supragnathals) in occlusal (top) and
basal (bottom) views. (G) Dental element (d) in occlusal (left) and oblique (right)
views. See fig. S9 for further details. Voxel size of (A) to (D) is 24.59mm and
that of (E) to (G) is 11.35mm. The color coding used for (A) to (F) is the same as
that in Fig. 2, A to D. Scale bars, 10 mm [(A), (B), and (E)]; 1 mm [(C), (D),
(F), and (G)].RESEARCH | REPORTS