Redescription of Yinostius Major (Arthrodira: Heterostiidae) from the Lower Devonian of China, and the Interrelationships of Brachythoraci

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Zoological Journal of the Linnean Society, 2015. With 10 ﬁgures

Redescription of Yinostius major (Arthrodira: Heterostiidae) from the Lower Devonian of China, and the interrelationships of Brachythoraci

YOU-AN ZHU1,2, MIN ZHU1* and JUN-QING WANG1

1Key Laboratory of Vertebrate Evolution and Human Origins of Chinese Academy of Sciences, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing 100044, China 2University of Chinese Academy of Sciences, Beijing 100049, China

Received 29 December 2014; revised 21 August 2015; accepted for publication 23 August 2015

Yinosteus major is a heterostiid arthrodire (Placodermi) from the Lower Devonian Jiucheng Formation of Yunnan Province, south-western China. A detailed redescription of this taxon reveals the morphology of neurocranium and visceral side of skull roof. Yinosteus major shows typical heterostiid characters such as anterodorsally positioned small orbits and rod-like anterior lateral plates. Its neurocranium resembles those of advanced eubrachythoracids rather than basal brachythoracids, and provides new morphological aspects in heterostiids. Phylogenetic analysis based on parsimony was conducted using a revised and expanded data matrix. The analysis yields a novel scenario on the brachythoracid interrelationships, which assigns Heterostiidae (including Heterostius ingens and Yinosteus major) as the sister group of Dunkleosteus amblyodoratus. The resulting phylogenetic scenario suggests that eubrachythoracids underwent a rapid diversiﬁcation during the Emsian, representing the placoderm response to the Devonian Nekton Revolution. The instability of the relationships between major eubrachythoracid clades might have a connection to their longer ghost lineages than previous scenarios have implied.

ADDITIONAL KEYWORDS: Brachythoraci – Heterostiidae – morphology – phylogeny – Placodermi.

INTRODUCTION misidentified and given names such as Ichthyosauroides Kutorga, 1835, Asterolepis asmussi Agassiz, 1844–45 The Arthrodira Woodward, 1891 is the largest and most and Chelonichthys asmusii Agassiz, 1844–45. Asmuss diverse group within the Placodermi McCoy, 1848 (Carr, (1856) for the first time referred these Baltic speci- 1995; Young, 2010). The morphological disparity of mens to fish correctly, and named them Heterostius and arthrodires is perhaps best illustrated by the Homostius, respectively, under several specific names. Heterostiidae Jaekel, 1903, an enigmatic arthrodire Shortly thereafter, Pander (1857) gave a more de- taxon known for its large body size and extremely ex- tailed description of the Baltic species of Heterostius tended anterior lateral plates. The type genus of the including a reconstruction of part of the head and tho- family, Heterostius Asmuss, 1856, was among the first racic armour. group of early vertebrates to be described scientifical- Woodward (1891) redefined Chelonichthys asmusii ly. The highly visible, large bony plates from the soft as Heterosteus asmussi. Subsequently, the two names matrix found in the Baltic states had long been noted ‘Heterostius’ and ‘Heterosteus’ seemed to be used inter- by early palaeontologists. However, they were often changeably. To give an incomplete list of examples, the name ‘Heterosteus’ was applied in Heintz (1928), Denison (1978, 1984) and Janvier (1996), while ‘Heterostius’ was *Corresponding author. E-mail: [email protected] applied in Heintz (1930), Gross (1933), Stensiö (1963)

© 2015 The Linnean Society of London, Zoological Journal of the Linnean Society, 2015 1 2 Y.-A. ZHU ET AL. and Ørvig (1969). E. Mark-Kurik (pers. commu.) stated chapter on pachyosteomorphs. However, he stated that that the suffix ‘-ostius’ is derived from the adjective Heterostius ‘may turn out to be a coccosteomorph’, based latinized Greek word ‘ostinos’ (bony, having promi- on its elongated occipital region shared with Homostius, nent bones), while the suffix ‘-osteus’ is derived from which he assigned into Coccosteomorphi Stensiö 1944. the substantive ‘osteon’ (bone). Accordingly, the suffix Denison (1978) considered Heterostiidae as the sister ‘-ostius’ should not be corrected as ‘-osteus’ by reason group of all brachythoracids, although he acknowl- of an ‘inadvertent error’ (International Commission on edged that the thoracic armour of Heterostiidae ‘re- Zoological Nomenclature (ICZN), 1999: Art. 32.5.1). We sembles that of Pachyosteina’. He later moved the taxon accept this explanation and only use the names to a higher phylogenetic position by including it in ‘Heterostius’ and ‘Homostius’ in the following text. Brachythoraci Gross, 1932 (Denison, 1984), partly fol- Heintz (1928, 1930) described the Baltic specimens lowing Young (1981), who provided a revised cladogram of Heterostius in detail. Gross (1933) described a showing heterostiids among basal brachythoracids. heterostiid anterior lateral plate from Sötenich, Janvier (1996) described Heterostiidae as a Germany, and assigned it to Heterostius. Ørvig (1969) eubrachythoracid taxon, but beyond that is ‘of uncer- erected the second heterostiid genus, Herasmius, from tain phylogenetic position’. the Wood Bay Group (upper Lower Devonian or lower In the first published attempt to include any Middle Devonian) in Spitsbergen. The only species of heterostiid in a computerized analysis of brachythoracid the genus, Herasmius granulatus, is represented by phylogeny (Zhu & Zhu, 2013), Heterostius ingens is as- an incomplete skull roof. Herasmius granulatus Ørvig, signed to a much more crownward position. It is nested 1969 differs from Heterostius ingens Asmuss, 1856 in within Dunkleosteidae Stensiö, 1963, being the sister having a shorter and broader skull roof, broader and group of Dunkleosteus Lehman, 1956. However, the mor- longer central plates, thinner dermal bones, and much phological evidence that supports this scenario is mostly finer tubercular ornaments. The unidentified plate confined to the external aspects of the skull roof. (Ørvig, 1969: fig. 4C) should be the extended anteri- Here we provide a detailed redescription of the or lateral plate, which is integrated but not fused to holotype of Yinostius major, which yields new the anterior dorsolateral plate, and possibly belongs phylogenetically significant information, especially that to Herasmius granulatus.InHeterostius ingens the two of the neurocranium morphology. We then conduct an plates are fused. updated phylogenetic analysis, which for the first time Wang & Wang (1984) reported the third heterostiid includes basal brachythoracids in the ingroup. Also, genus Yinosteus from the South China block, which new characters are defined based on the comparative represents the first heterostiid outside Euramerica and anatomy of arthrodires, with particular emphasis on illustrates the wide distribution of the group. The fusion the visceral surface of the skull roof and neurocranium of the dermal plates and relatively extensive ossifica- morphology. With a revised data matrix, we hope to tion compared with most other brachythoracids suggest render a more convincing scenario that could lead to that the holotype of Yinosteus major Wang & Wang, a better understanding of not only the position of 1984 belongs to an adult individual. Yinosteus differs heterostiids, but also the brachythoracid phylogeny as from Heterostius and Herasmius in having a smaller a whole. body size, proportionately broader nuchal plate, larger nuchal gap and coarser tubercular ornaments. Part of GEOLOGICAL BACKGROUND the description in Wang & Wang (1984) needs to be properly illustrated. Also, characters that are The holotype material of Yinosteus major was collect- phylogenetically informative were not fully exploited. ed from black shale near Wuding in 1979 (Fig. 1). The The members of the Heterostiidae show similar- horizon was identified by Wang & Wang (1984) as the ities to the basal brachythoracid Homostiidae Jaekel, Black Shale Member of the Middle Devonian Haikou 1903, such as the large body size, anteriorly placed Formation. Shortly thereafter, Wang (1984) included orbits, elongated occipital region, anteriorly extended the horizon within the newly erected Jiucheng For- anterior lateral plate and reduction of ventral thorac- mation and maintained its Middle Devonian diagno- ic armour. However, heterostiids also resemble the ad- sis, which was supported by Liu (1994). The dating vanced eubrachythoracids in the position of the of the Jiucheng Formation was modified by Wang & posterolateral corner of the skull roof, and the highly Zhu (1995) to be late Emsian, Early Devonian, under developed posterior carinal process of the ventral keel the following arguments: first, the Jiucheng Forma- of the median dorsal plate (Stensiö, 1963; Denison, 1978; tion and the Pojiao Formation below it were continu- Young, 1981; Zhu & Zhu, 2013). ously deposited, and the latter is dated to be early This mosaic character complement of heterostiids has Emsian based on the invertebrate evidence; second, resulted in competing hypotheses of their phylogenetic the fish fauna from the Jiucheng Formation is com- assignment. Stensiö (1963) discussed Heterostius in the parable with European and Australian Emsian faunas.

Figure 1. Devonian sequence in the Wuding area (Yunnan, China), showing the stratigraphic position of Yinostius major. Complied after Liu & Wang (1973) and Zhao & Zhu (2010).

In addition to Yinosteus, the Jiucheng Formation yields of the neurocranium; d.end, endolymphatic duct; f.d.end, the antiarch Wudinolepis Chang, 1965, and arthrodires impression of the endolymphatic duct on the visceral Exutaspis Liu & Wang, 1981, Holonema Newberry, 1889, surface of the skull roof; f.dm, median subnuchal de- Jiuchengia Wang & Wang, 1983 and Xiangshuiosteus pression; f.laf, impression of the lateral articular fossa Wang, 1992. The Emsian dating for the Jiucheng For- for dermal neck joint; f.lcp, impression of the lateral mation was followed by the latest comprehensive review consolidated part of skull roof; fo, neurocranium fon- of Chinese Siluro-Devonian vertebrate biostratigraphy tanel; fo.pi, pineal fossa; fo.sg, subglenoid fossa; f.ppt, (Zhao & Zhu, 2010). impression of the pineal pit; f.pr.pop, impression of the posterior postorbital process of the neurocranium; f.pr.pto, impression of the postocular ventral process MATERIAL AND METHODS of the skull roof; f.pr.sv, impression of the supravagal ABBREVIATIONS process of the neurocranium; f.pro.dpr, impression of Institutional abbreviations the preorbital dermal process of the preorbital plate; IVPP, Institute of Vertebrate Paleontology and f.pt.u, impression of the nuchal paired pits on the Paleoanthropology, Chinese Academy of Sciences, Beijing, neurocranium; f.pto.dpr, impression of the postorbital China. dermal process of the postorbital plate; f.sov, impression of the supraorbital vault; f.th.n, impression of the Anatomiacal abbreviations posterior transverse nuchal thickening; f.th.pi, impres- ADL, anterior dorsolateral plate or its corresponding sion of the visceral thickening of the pineal plate; fr.ADL, portion of the anterior dorsolateral plate and anteri- fractured anterior dorsolateral plate; fr.MD, anterior or lateral plate complex; ADL-AL complex, anterior corner fractured and separated from the median dorsal dorsolateral plate and anterior lateral plate complex; plate; gc, glenoid condyle; g.Nu, nuchal gap; laf, lateral AL, anterior lateral portion of the anterior dorsolateral articular fossa for dermal neck joint; lcp, lateral con- plate and anterior lateral plate complex; btr.sh, solidated part of the skull roof; M, marginal plate; MD, basitrabecular shelf; C, central plate or its impres- median dorsal plate; MD.oa, overlap area of the median sion on the neurocranium; c.p, posterior corner of the dorsal plate; orb, orbit; Nu, nuchal plate or its im- skull roof; ch.pr.sv, channel for the supravagal process pression on the neurocranium; pca, posterior carinal

© 2015 The Linnean Society of London, Zoological Journal of the Linnean Society, 2015 4 Y.-A. ZHU ET AL. process of median dorsal keel; PDL, posterior YINOSTIUS WANG &WANG, 1984 dorsolateral plate; Pi, pineal plate; PL, posterior lateral TYPE AND ONLY SPECIES: YINOSTIUS MAJOR WANG & plate; PM, postmarginal plate or its impression; PNu, WANG, 1984 paranuchal plate or its impression on the neurocranium; Diagnosis: As for the type and only known species. ppt, pineal pit; pr.ant, antorbital process of the neurocranium; pr.ect, ectethmoid process; pr.gl,occipital glenoid process; pr.IX, neurocranium process that bears YINOSTIUS MAJOR WANG &WANG, 1984 the glossopharyngeus canal ventrally; pr.mp, posteri- Holotype: Near-complete head and thoracic armour, or median process of the nuchal plate or its slightly displaced but all plates occur on one slab (IVPP impression; Pro, preorbital plate; pr.opa, occipital para- V7142, Fig. 2). articular process; pr.poa, anterior postorbital process of the neurocranium; pr.pop, posterior postorbital Locality and horizon: Wuding, Yunnan Province, China; process of the neurocranium; pr.pto, postocular ventral Jiucheng Formation, Emsian, Lower Devonian. process of the skull roof; pr.sg, subglenoid process; pr.so, supraorbital process of the neurocranium; pr.sv, supravagal process of the neurocranium; pro.dpr, Emended diagnosis: Medium to moderately large preorbital dermal process of the preorbital plate; Psp, arthrodire, with the median dorsal plate having an es- parasphenoid; Pto, postorbital plate; pt.u, nuchal paired timated length of 16 cm. The skull roof shows typical pits on the neurocranium; pto.dpr, postorbital dermal heterostiid characters such as anteriorly tapered outline, process of the postorbital plate; R, rostral plate; r.sc, anterodorsally positioned small orbits and posteri- external ridge of the posterior semi-circular canal; Scl, orly positioned posterolateral corners. The neurocranium sclerotic plate; sov, supraorbital vault; th.pi, the vis- resembles that of eubrachythoracids in the posteri- ceral thickening of the pineal plate. orly positioned pineal foramen, long and narrow orbitotemporal region, laterally expanded supravagal process, and absence of subnasal shelf. The median Phylogenetic abbreviations dorsal plate is short and broad, with a length/breadth CI, consistency index; L, length of trees (in evolution- ratio of 0.52. The posterior carinal process of the median ary steps); n, number of trees; RI, retention index.

SYSTEMATIC PALEONTOLOGY PLACODERMI MCCOY 1848 ARTHRODIRA WOODWARD, 1891 BRACHYTHORACI GROSS, 1932 FAMILY HETERODEIDAE JAEKEL 1903 Type genus: Heterostius Asmuss, 1856.

Diagnosis: Moderately to very large arthrodires with the cranial and trunk shields broad and dorsoventrally compressed. The skull roof narrows anteriorly, and the posterolateral corners of the skull roof are in line with the posterior margin. The orbits are small, anterodorsally positioned. The dermal plates on the posterior part of the skull roof are moderately long, while those on the anterior part are short. The con- dyles of the cranio-thoracic joint are strongly developed, but not transversely elongated. The lateral wall of the thoracic armour are much reduced, the anteri- or lateral plate is fused with the anterior dorsolateral plate. The anteroventral part of the anterior lateral plate develops into an elongated, rod-like process. The ventral thoracic armour is reduced to a single plate Figure 2. Yinostius major. Holotype IVPP V7142. Scale that extends far anteriorly under the head. bar = 5 cm.

© 2015 The Linnean Society of London, Zoological Journal of the Linnean Society, 2015 EARLY DEVONIAN ARTHRODIRE FROM CHINA 5 dorsal plate is highly developed. The rod-like anteri- corresponds to the subglenoid fossa on the visceral side or lateral and the anterior dorsolateral plates are com- of the ADL-AL complex (fo.sg, Fig. 6C–E) when ar- pletely fused to form a complex, with a spherical glenoid ticulated. We flatten the curving in the attempted re- condyle. The dermal ornament consists of coarse construction of the skull roof (Fig. 6D) for a better tubercles. display of the neck articulation. The reconstructed skull roof of Yinosteus major is nonetheless still longer and narrower than those of Heterostius ingens and MORPHOLOGICAL DESCRIPTION Herasmius granulatus. SKULL ROOF The orbit (orb, Figs 3B, 5) is small and anteriorly The skull roof is roughly isosceles trapezium in shape, placed, as in other heterostiids. The highly developed with its posterior margin about four times as broad preorbital (pro.dpr, Fig. 3B) and postorbital dermal pro- as its anterior margin. The posterolateral corner of the cesses (pto.dpr, Fig. 3B) comprise approximately two- skull roof corresponds to the lateral corner of the thirds of the orbital circle, indicating a dorsally placed postmarginal plate (PM; Figs 3B, 5, 6D, E). The corner orbit. The majority of brachythoracids have laterally is extremely posteriorly positioned to be behind the positioned orbits, with the exception of Homostius foremost point of the nuchal gap and the articular sulcatus Kutorga, 1837, in which the preorbital and fossa for the neck joint, as in some advanced postorbital dermal processes are butted together to en- pachyosteomorphs, such as Gorgonichthys clarki circle the dorsally positioned orbit entirely (Heintz, 1934: Claypole, 1892 (Stensiö, 1963: fig. 112B). In Heterostius fig. 1). However, this situation is not shared by other ingens (Heintz, 1930: fig. 2) and Dunkleosteus homostiids, such as Antineosteus lehmani Lelièvre, 1984. ‘intermedius’ (synonymized to D. terrelli Newberry, 1873, Dorsally positioned orbits might reflect an adaption see Denison, 1978) (Stensiö, 1963: fig. 112A) this corner to benthic living in parallel. is approximately level with the foremost point of the The left sclerotic ring is preserved in internal mould. nuchal gap. Posteriorly, the lateral parts of the skull The right sclerotic ring (Scl, Figs 5, 6D) is preserved roof are curved downward, and the posterolateral corner but its anterior part is embedded deep in the matrix.

Figure 3. Yinostius major. A, latex peel of the holotype; B, interpretation of the latex peel. The boundaries of fragmental parts are shown as dotted lines. ADL-AL complex, anterior dorsolateral plate and anterior lateral plate complex; f.pr.pop, impression of the posterior postorbital process of the neurocranium; f.pr.sv, impression of the supravagal process of the neurocranium; fr.ADL, fractured anterior dorsolateral plate; fr.MD, anterior corner fractured and separated from the median dorsal plate; laf, lateral articular fossa for dermal neck joint; lcp, lateral consolidated part of the skull roof; MD, median dorsal plate; MD.oa, overlap area of the median dorsal plate; pca, posterior carinal process of median dorsal keel; PDL?, possible posterior dorsolateral plate; PL?, possible posterior lateral plate; PM, postmarginal plate; pr.pto, postocular ventral process of the skull roof; pro.dpr, preorbital dermal process of the preorbital plate; pt.u, nuchal paired pits on the neurocranium; pto.dpr, postorbital dermal process of the postorbital plate; sov, supraorbital vault; th.pi, the visceral thickening of the pineal plate. Scale bar=5cm.

Figure 4. Yinostius major. Skull roof in internal mould and neurocranium, detailing the impression made by the visceral thickening of the pineal plate. f.ppt, impression of the pineal pit; f.th.pi, impression of the visceral thickening of the pineal plate. Scale bar=5cm.

The detail of the sclerotic ornaments is unknown, as processes of the skull roof (pr.pto, Fig. 3B; f.pr.pto, Fig. 5). only the visceral surface of the sclerotic plates is visible. Judging from the impressions, the postocular ventral A gap between the two preorbital dermal processes process is well developed, but not as prominent as that represents the rectangle-shaped rostral plate, which in taxa such as Dunkleosteus raveri Carr & Hlavin, is not preserved. It is unlikely that the rostral is pre- 2010. The mould of the skull roof in this region sug- served in V7142 as described by Wang & Wang (1984), gests that the triangular depression posterior to the given that the preserved neurocranium is lacking a supraorbital vault in taxa such as Dhanguura johnstoni rhinocapsule normally associated with the rostral plate. (Young, 2004: fig. 4) is missing in Yinosteus. The anterior-most impression along the midline (‘rostral’ Posterior to the postocular ventral processes are the in Wang & Wang, 1984) is here interpreted as left by paired lateral consolidated parts of the skull roof (lcp, visceral thickening of the pineal plate (th.pi, Fig. 3B; Fig. 3B; f.lcp, Fig. 5). They are represented by two elon- f.th.pi, Figs 4, 5) and the pineal pit (ppt, Fig. 3B; f.ppt, gated impressions along the lateral margin of the mould, Figs 4, 5). The fractured lateral margin of the impres- extending from the posterior wall of the supraorbital sion was produced when the pineal plate was peeled vault to the posterolateral corners of the skull roof. away from the neurocranium. The visceral thicken- The consolidated parts are simple thickenings, lacking ing of the pineal plate resembles those of most the lateral and mesial grooves along the lateral margin pachyosteomorphs (e.g. Dunkleosteus ‘intermedius’, of the skull roof (Young, 2004: fig. 4) in Dhanguura Stensiö, 1963: fig. 112A) in its narrow outline. In basal johnstoni. (e.g. Dhanguura johnstoni Young, 2004) and Judging from the mould of the skull roof, a well- coccosteomorph (e.g. Compagopiscis croucheri Gardiner developed transverse nuchal thickening (f.th.n, Fig. 5) & Miles, 1994) brachythoracids this thickening is mostly runs continuously along the entire posterior skull roof short and broad. border, reaching as far as the two posterolateral corners The supraorbital vault is preserved as an impres- of the skull roof. A pair of nuchal pits (pt.u, Fig. 3B; sion on the natural mould of the skull roof (sov, Fig. 3B; f.pt.u, Fig. 5) is present anterior to the middle portion f.sov, Fig. 5). It is moderately developed, wider of the nuchal thickening. The pits are represented by than that of the basal brachythoracids such as two circular concave regions that open ventrally and Holonema westolli Miles, 1971 and Buchanosteus are well separated by a median septum. This septum confertituberculatus Young, 1979, but is not as well de- does not extend continuously to the median posterior veloped as that of most eubrachythoracids in terms of nuchal process (pr.mp, Fig. 5) at the middle of the pos- both breadth and depth. terior nuchal border. The paired impressions immediately posterior to the The articular fossa (laf, Fig. 3B; f.laf, Fig. 5) for the supraorbital vaults were left by the postocular ventral neck articulation, similar to that of Heterostius ingens,

Only limited sutures of the plates are discernible from their impressions on the neurocranium, including the suture between the two central plates, the anterior boundary of the nuchal plate, the anterior boundary of the paranuchal plate, the suture between the nuchal and paranuchal plates, and the mesial boundary of the postmarginal plates. Note that these sutures are the visceral ones and cannot be readily used to infer the external geometry of the skull roof plates. For example, the visceral anterior margin of the nuchal plate is convex in most brachythoracids, while the external anterior margin of the nuchal plate can be convex, straight or concave. Even so, it is feasible to infer the nuchal or skull roof occipital elongation from the visceral suture between the nuchal and central plates. In Yinosteus major, the length ratio between the nuchal plate in visceral view and the skull roof is 0.54, approximately the same proportion as that of Heterostius ingens, in which the length ratio between the nuchal plate in external view and Figure 5. Yinostius major. Line drawing of the skull portion the skull roof is 0.50 (measured from Heintz, 1930: fig. of the holotype. The areas that do not belong to cranial struc- 2). The above two length ratios representing the extent tures are shown with slashes, and the depressed area on of the elongation of the heterostiid nuchal plates are the slab that does not belong to the specimen is shown with significantly smaller than that of Homostius sulcatus, horizontal lines. btr.sh, basitrabecular shelf; C, impres- in which the length ratio between the nuchal plate in sion of the central plate; f.d.end, impression of the visceral view and the skull roof is 0.67 (measured from endolymphatic duct on the visceral surface of the skull roof; Heintz, 1934: figs 1, 2). In comparison, in Coccosteus f.laf, impression of the lateral articular fossa for dermal cuspidatus Miller, 1841 the length ratio between the neck joint; f.lcp, impression of the lateral consolidated part nuchal plate and the skull roof is 0.39 and 0.46, in of skull roof; f.pr.pto, impression of the postocular ventral process of the skull roof; f.pro.dpr, impression of the preorbital external and visceral view, respectively (Miles & Westoll, dermal process of the preorbital plate; f.pt.u, impression 1968: fig. 2). In Dunkleosteus ‘intermedius’, the ratio of the nuchal paired pits on the neurocranium; f.pto.dpr, is 0.28 in external view and 0.32 in visceral view impression of the postorbital dermal process of the postorbital (Stensiö, 1963: figs 99A, 112A). plate; fr.ADL, fractured anterior dorsolateral plate; fr.MD, NEUROCRANIUM anterior corner fractured and separated from the median dorsal plate; f.sov, impression of the supraorbital vault; f.th.n, The neurocrania of brachythoracids are usually poorly impression of the posterior transverse nuchal thickening; ossified. Only a few complete or near-complete f.th.pi, impression of the visceral thickening of the pineal brachythoracid neurocrania (Stensiö, 1963, 1969; Young, plate; Nu, impression of the nuchal plate; PM, impression 1979) and several partly preserved ones (Dennis & of the postmarginal plate; PNu, impression of the paranuchal Miles, 1979b, 1981; Long, 1988a; Otto, 2005) are de- plate; pr.ant, antorbital process of the neurocranium; pr.mp, scribed. The most well-preserved neurocranium among impression of the posterior median process of the nuchal brachythoracids, that of Tapinosteus heintzi, lacks its plate; pr.so, supraorbital process of the neurocranium; pr.poa, occipital part. It is rare that the entire profile of the anterior postorbital process of the neurocranium; pr.pop, neurocranium is preserved as in Yinosteus major. posterior postorbital process of the neurocranium; pr.sv, Only the dorsal aspect of the neurocranium can be supravagal process of the neurocranium; Scl, sclerotic plate. observed in Yinosteus major. The neurocranium is flat Scale bar=5cm. and large. The endoskeletal rhinocapsule is lost along with the rostral plate. The M-shaped anterior margin of the neurocranium possibly outlines the area for the is extremely laterally positioned, closer to the paired olfactory tracts, olfactory bulbs and extracribrosal posterolateral corner of the skull roof than that of most regions of postnasal walls. The antorbital process of other arthrodires. The articular fossa is represented the neurocranium (pr.ant, Figs 5, 8C) is more devel- by a simple and relatively small facet, preserved as oped than that of most arthrodires with neurocrania an impression. The para-articular process is missing preserved, corresponding to the highly developed in Yinosteus major, or not developed enough to leave preorbital dermal process, which in turn reflects the any impression. mesial position of the eye capsule.

At the level of the postorbital dermal process, the Between the posterior postorbital process and the neurocranium is poorly preserved with a large area supravagal process, a groove-like impression on the cracked and missing. There is no evidence of a subocular neurocranium extends posterolaterally (f.d.end, Fig. 5). process. If the subocular process is not protruding The impression is interpreted as left by the laterally, it is invisible in dorsal view as in our endolymphatic duct, which forms a bony tube bulging specimen. from the visceral surface of the skull roof. A similar At the right side where the missing area is smaller, situation with viscerally prominent endolymphatic duct the neurocranium shows a dorsolateral process. This is present in some arthrodires such as Dhanguura process is located posterior to the level of the postocular johnstoni (Young, 2004: fig. 4). Noteworthy is that the ventral process of the skull roof. We interpret this beginning of the endolymphatic duct where it pen- process as the supraorbital process sensu Stensiö, 1963 etrates out of the neurocranium, inferred by the im- (pr.so; Figs 5, 8C). The process is represented by a ves- pression, is far posterior to the anterior extremity of tigial swelling, similar to that of Tapinosteus heintzi the nuchal plate on the visceral surface of the skull Stensiö, 1963 and Dunkleosteus ‘intermedius’ (Stensiö, roof. This state is different from that in homostiids, 1963: figs 47A, 89A). in which the beginning of the endolymphatic duct is Posterior to the supraorbital process, the trabecular closer to the anterior extremity of the nuchal plate, structure of the neurocranium emerges laterally in and will be discussed below. dorsal view. Stensiö (1963) named the laterally pro- The highly developed supravagal process (pr.sv, Fig. 5) truding trabecular region of arthrodires as the left little space between it and the posterior postorbital basitrabecular shelf, a term borrowed from process for the cucullaris fossa, indicating an unusu- chondrichthyan cranial anatomy, while Dupret (2010) ally small cucullaris. The lobe shape of the supravagal named the similar structure in Kujdanowaspis Stensiö, process in Yinosteus major resembles the process im- 1942 to be the lateral bourrelete of the otic region mediately posterior to the posterior postorbital process (Dupret, 2010: fig. 5A). We adopt the former termi- and bearing the glossopharygeus canal ventrally in nology, but the basitrabecular shelves in arthrodires Tapinosteus heintzi and Trematosteus fontanellus (pr.IX, and chondrichthyans may not be homologous as in- Fig. 7D, E). However, in the latter two taxa, the process ferred by Stensiö (1963), as the common ancestor of bearing the glossopharygeus canal is anterior to the crown group gnathostomes possibly lacks this struc- beginning of the endolymphatic duct, while in Yinosteus ture (Zhu et al., 2013). The basitrabecular shelf of major the supravagal process is posterior to the be- Yinosteus major is well developed, to a similar extent ginning of the endolymphatic duct. Accordingly, it is to that of Trematosteus fontanellus Stensiö 1963. In unlikely that the supravagal process in Y. major is ho- contrast, the basitrabecular shelf of Tapinosteus hentzi mologous to the process bearing the glossopharygeus (Stensiö, 1963: fig. 47A) is under-developed and hardly canal in Tapinosteus heintzi and Trematosteus extended from the lateral wall of the neurocranium fontanellus. In V7142, the neurocranium posterior to in dorsal view. the posterior margin of the skull roof is not pre- The anterior postorbital process of Yinosteus major served, as with the glenoid process. (pr.poa; Figs 5, 8C) is present as a posterolaterally extended ridge on the basitrabecular shelf. This situation is different from that in Trematosteus fontanellus, THORACIC ARMOUR in which the process is defined by two notches on the Median dorsal plate (MD, Figs 3B, 6A, D) margin of the shelf (Stensiö, 1963: fig. 89B). We here This plate is preserved as a natural mould of its follow the terminology used by Young (1979) instead dorsal face. The left antero-lateral corner is missing, of that used by Stensiö (1963), in which the same struc- and the right antero-lateral corner is fractured and ture was named the basitrabecular process. located above the neurocranium (fr.MD, Figs 3B, 5). The posterior left part of the neurocranium is mostly The reconstructed shape (Fig. 6A) is considerably short concealed by the displaced ADL plate (ADL, Fig. 5). and board. The maximum breadth measures 31 cm. The The posterior right part of the neurocranium is also maximum length along the midline of the plate (not poorly preserved, as is the right posterior postorbital counting the protruding carinal process) measures 16 cm, process. Inferred from the current specimen, this process giving a length/breadth ratio of 0.52. In comparison, is unforked as in all other brachythoracids, and is the MD of Homostius sulcatus has a length/breadth vaguely slender in shape, corresponding to the ratio of 0.41 (measured from Heintz, 1934: fig. 32). dorsoventrally flattened skull in Yinosteus major.In The general shape of the plate resembles that of arthrodires with a laterally compressed skull such as Heterostius ingens and many pachyosteomorphs. The Tapinosteus heintzi (Stensiö, 1963: fig. 47A), the process plate is slightly arched. Its anterior margin is strong- is shorter and more robust for a better structural re- ly concave, corresponding to the large nuchal gap. The inforcement. lateral margin is also slightly concave, resulting in lat-

Figure 6. Yinostius major. A, median dorsal plate in dorsal view, with missing part slashed; B, right anterior dorsolateral plate and anterior lateral plate complex in lateral view, with missing anterior part restored in dashed lines, and the boundary of two fragmental parts in dotted lines; C, left anterior dorso-lateral plate and anterior lateral plate in medial view, with missing part restored in dashed lines; D, the ﬂattened reconstruction of the preserved skull roof and thoracic armour in visceral view, the non-preserved sutures are shown as dashed lines; E, neck joint in Yinosteus major; F, neck joint in Parabuchanosteus murrumbidgeensis, modiﬁed after White & Toombs (1972). ADL, anterior dorsolateral plate; ADL-AL complex, anterior dorsolateral plate and anterior lateral plate complex; AL, anterior lateral plate; C, central plate; ch.pr.sv, channel for the supravagal process of the neurocranium; fo.sg, subglenoid fossa; gc, glenoid condyle; g.Nu, nuchal gap; laf, lateral articular fossa for dermal neck joint; M, marginal plate; MD, median dorsal plate; MD.oa, overlap area of the median dorsal plate; Nu, nuchal plate; pca, posterior carinal process of median dorsal keel; Pi, pineal plate; PM, postmarginal plate; PNu, PNu, paranuchal plate; Pro, preorbital plate; pr.opa, occipital para-articular process; Pto, postorbital plate; R, rostral plate; rdg.ADL-AL, ridge that marks the visceral boundary between anterior dorsolateral and anterior lateral plate; Scl, sclerotic plate. Scale bar=5cm. erally extended antero-lateral corners. The posterior smooth and convex, not spatulate. No dorsal branch margin is roughly circular and without a posterior spine. of the main lateral line is visible. The dorsal surface of the plate is ornamented with coarse tubercles. The visceral aspect is unknown, except Anterior dorsolateral plate and anterior lateral plate the carinal process, which extends beyond the pos- complex (ADL-AL complex, Figs 3B, 6B–D) terior margin of the dorsal surface. This situation re- The ADL and AL plates of Yinosteus major are fused, sembles advanced pachyosteomorphs such as as in Heterostius ingens. Both sides of the ADL-AL Dunkleosteus terrelli and differs from that of Homostius complex are preserved as the moulds: the left side is sulcatus, in which the ventral keel is protruding an- near-complete, while the right is fractured, with its teriorly rather than posteriorly. The posteriorly pro- upper part displaced to overlap the lateral corner of truding part of the carinal process measures 7 cm in the skull roof (fr.ADL; Figs 3B, 5, 6B), and with an length. The posterior face of the carinal process is area overlapped by the right anterior lateral corner

© 2015 The Linnean Society of London, Zoological Journal of the Linnean Society, 2015 10 Y.-A. ZHU ET AL. of the MD (MD.oa; Figs 3B, 6B). The rest of the right finer than those on the median dorsal plate and the ADL-AL complex is located at the right side of the MD, posterior lateral plate. with most of the anterior rod-like extension missing (right ADL-AL complex, MD.oa; Fig. 3B). Posterior lateral plate (PL?; Fig. 3) The visceral surface of the left complex features a An indistinct triangular mould next to the PDL is in- fossa just below the glenoid condyle (fo.sg; Fig. 6C), terpreted as the posterior lateral plate. It is poorly pre- as well as a ridge (rdg.ADL-AL; Fig. 6C). In life the served and the current shape may not represent the fossa is so positioned that it could receive the actual outline of the plate. Coarse tubercles are visible. posterolaterally extended posterolateral corner of the skull roof, when the skull roof is raised and the posterolateral corner is depressed (Fig. 6D). In DISCUSSION Dunkleosteus terrelli, a similar subglenoid fossa is present, but in this case it is in the position to receive THE DIMENSION OF THE OCCIPITAL REGION OF the highly developed para-articular process on the NEUROCRANIUM IN ARTHRODIRES paranuchal plate (‘Dinichthys’ Newberry, 1868 in Heintz, In the gnathostome neurocrania, the occipital region 1932: fig. 73). is located posterior to the otic–occipital fissure (Jarvik, The ridge on the visceral surface of the left complex 1980). In those taxa that lack the otic–occipital fissure, probably represents the position where the ADL and the boundary between otic and occipital regions is AL are sutured. This is based on the observation that marked by the aperture of the vagus canal, as this ap- a similar ridge is present in many eubrachythoracids erture always corresponds to the otic–occipital fissure such as Eastmanosteus calliaspis Dennis-Bryan, 1987 whenever the latter is present (Schultze, 1993). However, and Dunkleosteus terrelli (Heintz, 1932: fig. 52) in which in Yinosteus major and many other arthrodires, the the area posterior to the ridge is the overlapped area otic–occipital fissure isnot discernible. In this case, the for the ADL. impression of the endolymphatic duct can be used to The ADL-AL complex of Yinosteus major resembles mark the otic–occipital boundary. that of Heterostius rhenanus Gross, 1933 in posses- In arthrodires, as in most other placoderms, the sing a highly developed glenoid condyle, a fossa ante- endolymphatic duct penetrates out of the neurocranium rior to the glenoid condyle and a ridge along the and extends posteriorly into the skull roof. The otic rod-like extension of the AL. These distinctive states region is often swelled to accommodate the laby- are possibly the synapomorphies of Heterostiidae. rinth, forming a posterior wall. This posterior wall is The dermal neck joints in arthrodires underwent con- deduced to be the posterior end of the otic region. When siderable evolutionary modifications and hold the endolymphatic duct penetrates this wall phylogenetic significance (Miles, 1969; Miles & Young, posterodorsally, the aperture marks the otic–occipital 1977). In many basal brachythoracids such as boundary. As the neurocranium is attached tightly to Parabuchanosteus murrumbidgeensis White, 1952, the the skull roof, the beginning of the endolymphatic duct movement of the neck articulation is confined by the in the skull roof is in approximately the same posi- presence of both a para-articular process and a tion with the aperture of the endolymphatic duct in subglenoid process (Jarvik, 1980: fig. 295). In most the neurocranium. As a result, when other land- eubrachythoracids such as Compagopiscis croucheri marks, namely the otic–occipital fissure or the aper- (Gardiner & Miles, 1994: fig. 6) and Dunkleosteus terrelli ture of the vagus canal are not available, the beginning (Heintz, 1932: fig. 68: pp. 70, 71), the condyle is di- of the endolymphatic duct on the visceral surface of rected inward to form a traverse cylinder, and is ar- the skull roof can be used to denote the otic–occipital ticulated to the matching rectangular articular facet, boundary in the neurocranium. allowing limited dimension of movement. In heterostiids, The elongated posterior part of the skull roof, es- the condyle is much more spherical without limiting pecially the long nuchal plate, was considered to be the para-articular process, the most kinetic structure a synapomorphy shared by heterostiids and homostiids among arthrodire neck joints, which might be linked (Denison, 1978; Young, 1981). As stated above, the to the peculiar feeding mechanism in Heterostiidae. nuchal plate in heterostiids is significantly shorter in proportion than that in most homostiids. Moreover, in homostiids such as Antineosteus lehmani (Fig. 8B), the Posterior dorsolateral plate (PDL?; Fig. 3) beginning of the endolymphatic duct on the visceral A mould of a triangular plate posterior to the mould surface of the skull roof is close to the anterior ex- of the MD is interpreted as the posterior dorsolateral tremity of the nuchal plate, implying that the occipi- plate. It is poorly preserved as a natural mould of its tal part of the neurocranium in homostiids is elongated, external surface, providing limited morphological in- as well as the nuchal plate. In most other formation. Tubercles are visible and are significantly brachythoracids such as Coccosteus cuspidatus, the be-

© 2015 The Linnean Society of London, Zoological Journal of the Linnean Society, 2015 EARLY DEVONIAN ARTHRODIRE FROM CHINA 11 ginning of the endolymphatic duct on the visceral surface cesses that can be seen in dorsal view (pr.ect, Fig. 7A, of the skull roof is also close to the anterior extrem- B), while in Yinosteus major, Tapinosteus heintzi and ity of the nuchal plate (Fig. 8C), implying that both Trematosteus fontanellus and all eubrachythoracids the occipital part of the neurocranium and the nuchal described to date the subnasal shelf is lost (Dennis plate are not elongated. In heterostiid Yinosteus major, & Miles, 1979b, 1981; Long, 1988a; Otto, 2005; the nuchal plate is considerably elongated, but the be- Stensiö, 1963). ginning of the endolymphatic duct on the visceral surface 2. The position of the pineal foramen. In Dicksonosteus of the skull roof is significantly posterior to the ante- arcticus and Parabuchanosteus murrumbidgeenis, rior extremity of the nuchal plate, indicating a normal- the pineal foramen is positioned between the ethmoid sized occipital part of the neurocranium (Fig. 8A). capsule and the anterior margin of the orbitotemporal Based on the above observation, the elongation of (fo.pi, Fig. 7A, B), while in Yinosteus major, the posterior part of the skull roofs in heterostiids and Tapinosteus heintzi and Trematosteus fontanellus, homostiids can be independently acquired, and whether the pineal foramen is positioned posteriorly in the it is a synapomorphy shared by the two groups needs middle section of the orbitotemporal region (fo.pi, to be tested by a parsimony analysis incorporating ad- Fig. 7C–E). ditional characters. The above observation also dem- 3. The length/breadth ratio of the orbitotemporal. In onstrates that among placoderms the visceral aspect Dicksonosteus arcticus and Parabuchanosteus of the skull roof can reveal important morphological murrumbidgeenis, the orbitotemporal is very short information regarding the neurocranium. compared with the otic, and is broad when compared both with the otic and with the supraorbital vault beside it (Fig. 7A, B), while in Yinosteus major, COMPARISON OF EXTERNAL ASPECTS OF THE Tapinosteus heintzi and Trematosteus fontanellus, NEUROCRANIA IN ARTHRODIRES the orbitotemporal is narrow and longitudinally com- prises a significantly larger portion of the The complexity of the vertebrate neurocrania yields neurocranium (in the latter two taxa the elonga- a considerable amount of morphological characters for tion of orbitotemporal may be linked to the large phylogenetic analyses (Stensiö, 1925, 1963; Young, 1979, orbit, but Yinosteus major possesses both a 1980; Maisey, 2005; Brazeau, 2009; Davis, Finarelli & small orbit and an elongated orbitotemporal, Coates, 2012). However, in brachythoracid arthrodires Fig. 7C–E). the neurocranial characters have received less atten- 4. The longitudinal proportion of the occipital. In tion phylogenetically. This is due to the fact that few Dicksonosteus arcticus (Fig. 7A), as well as other brachythoracids possess a well-preserved neurocranium, basal arthordires, the occipital is short, while in most and a lack of comparisons between available brachythoracids, such as Parabuchanosteus brachythoracid neurocrania. murrumbidgeenis, Yinosteus major and Tapinosteus The neurocranium of Yinosteus major is preserved heintzi, the occipitals are elongated (Fig. 7B–D). In with its dorsal outline. Comparison of the current speci- Trematosteus fontanellus and some aspinothoracids, men with other published information on arthrodire the occipital is shortened (Fig. 7E), presumably an neurocrania can shed light on the character evolu- autoapomorphy in Aspinothoracidi sensu Miles and tion of the brachythoracid neurocranium, contribut- Dennis (1979). ing to a better supported scenario of brachythoracid 5. Shape of the supravagal process outline. In phylogeny. Taxa used in the comparison include: Dicksonosteus arcticus the supravagal process is ap- ‘phlyctaeniid’ Dicksonosteus arcticus Goujet, 1975 as proximately right-angled (pr.sv, Fig. 7A), while in the outgroup of brachythoracids, Parabuchanosteus brachythoracids the supravagal processe is murrumbidgeenis as the most thoroughly studied basal more acute-angled. Among brachythoracids, brachythoracid, Yinosteus major, Tapinosteus heintzi Parabuchanosteus murrumbidgeenis possesses a rela- with neurocranium and brain cavity studied using serial tively blunt supravagal process (pr.sv, Fig. 7B), which grinding, and another eubrachythoracid taxon in Trematosteus fontanellus (pr.sv, Fig. 7E) is ex- Trematosteus fontanellus. tremely acute. The shape of the supravagal process The following characters that are potentially able is possibly linked to the shape of the nuchal plate. to contribute to a better-supported phylogenetic sce- 6. The presence or absence of a neurocranial fonta- nario can be identified from the comparison. nelle. In several aspinothoracids the neurocranium 1. The presence or absence of the subnasal shelf. In possesses one or more dorsal fontanels (fo, Fig. 7D, Dicksonosteus arcticus and Parabuchanosteus E). The lack of a fontanelle in basal brachythoracids murrumbidgeenis, the ventral wall of the such as Parabuchanosteus murrumbidgeenis and in orbitotemporal extends anteriorly to develop a basal arthrodires such as Dicksonosteus arcticus subnasal shelf, with a protruding ectethmoid pro- indicates that the fontanelle in advanced

Figure 7. Comparison of ﬁve arthrodire neurocraniua in dorsal view. A, Dicksonosteus arcticus, after Goujet (1984); B, Parabuchanosteus murrumbidgeenis, after Young (1979); C, Yinosteus major;D,Tapinosteus heintzi, after Stensiö (1963); E, Trematosteus fontanellus, after Stensiö (1963). The vertical bar shows the longitudinal proportions of the various regions of the neurocranium, with the black part corresponding to the occipital region, and the small circle representing the location of the pineal foramen. btr.sh, basitrabecular shelf; d.end, endolymphatic duct; f.dm, median subnuchal depression; fo, neurocranium fontanel; fo.pi, pineal fossa; pr.ant, antorbital process of the neurocranium; pr.ect, ectethmoid process; pr.gl, occipital glenoid process; pr.IX, neurocranium process that bears the glossopharyngeus canal ventrally; pr.poa, anterior postorbital process of the neurocranium; pr.pop, posterior postorbital process of the neurocranium; pr.so, supraorbital process of the neurocranium; pr.sv, supravagal process of the neurocranium; r.sc, external ridge of the posterior semi- circular canal. Not to scale.

eubrachythoracids is not homologous to the similar terior postorbital process and elongated occipital, as fontanelle in elasmobranchs, unless the well as basal arthrodire characters such as the pres- elasmobranchs originated from Eubrachythoraci, as ence of the subnasal shelf and the short and broad implied by Stensiö (1963, 1969). orbitotemperal. The neurocranium of Yinosteus major resembles those of the typical eubrachythoracids and Based on the above comparison, the neurocranium differs from those of basal brachythoracids in the of Parabuchanosteus murrumbidgeenis possesses typical absence of a subnasal shelf, long and narrow brachythoracid characters such as the non-forked pos- orbitotemperal and posteriorly positioned pineal foramen.

Figure 8. Comparison of skull roof and neurocranium among brachythoracids. A, Yinosteus major;B,Antineosteus lehmani, after Lelièvre (1984); C, Coccosteus cuspidatus, after Miles & Westoll (1968). The skull roof is shown in white, the neurocranium in grey, the occipital region dotted and the nuchal plate (visceral view) in horizontal lines; the outline of the hypotheti- cal neurocranium is shown with a dashed line. Not to scale.

PHYLOGENETIC ANALYSIS Elvaspis tuberculata Young, 2009, Dicksonosteus arcticus, Turrisaspis elektor Daeschler, Frumes & Mullison, 2003, The previous phylogenetic analyses of brachythoracids Groenlandaspis antarcticus Ritchie, 1975 and Holonema (Carr, 1991; Lelièvre, 1995; Trinajstic & Dennis-Bryan, westolli are assigned in a polychotomy with 2009; Carr & Hlavin, 2010; Zhu & Zhu, 2013) focused Brachythoraci. The assignment of the williamsaspid on eubrachythoracids and used basal brachythoracids Elvaspis tuberculata agrees with Denison (1978) who such as Buchanosteus confertituberculatus as outgroups. placed Williamsaspidae White, 1952, then including only Also, the characters in these analyses are mainly from one species Williamsaspis bedfordi White, 1952, in the skull roof and thoracic armour. We here perform a infraorder Phlyctaenii Miles, 1973, and disagrees with phylogenetic analysis based on an enlarged and revised Young (2009) who suggested that the williamsaspids data matrix, in which basal brachythoracids are in- belong to the Brachythoraci. Also, the exclusion of taxa cluded in the ingroup. The new matrix includes 60 taxa both from Groenlandaspididae Obruchev, 1964 and and 121 characters, in which 23 characters are new Holonematidae Obruchev, 1932 from Brachythoraci sup- and are listed in Appendix 2. ports the scenario proposed by Denison (1978) and is The new matrix was treated with MESQUITE v. 2.73 contrary to the other arguments that the Holonematidae (Maddison & Maddison, 2008). The analysis based on belongs to the Brachythoraci (Miles, 1971; Lelièvre, parsimony was performed with PAUP* v. 4.0b10 1995). (Swofford, 2003) using the heuristic algorithm. Under the current scenario, Antineosteus lehmani, Kujdanowiaspis podolica Brotzen, 1934 was designat- Homostius sulcatus, Buchanosteus confertituberculatus, ed the outgroup. We set 1000 random addition se- Goodradigbeeon australianum White, 1978, quence replicates, and ‘maxtrees’ to ‘automatically Parabuchanosteus murrumbidgeeni, Dhanguura increase’. The analysis gave 540 equally most parsi- johnstoni, Gemuendenaspis angusta Traquair, 1903 and monious trees of 496 steps each (CI = 0.2843; Xiangshuiosteus wui comprise the paraphyletic array RI = 0.6629). The strict consensus tree is presented in of basal brachythoracids. Antineosteus lehmani and Figure 9. The synapomorphies listed in Appendix 4 were Homostius sulcatus are included in a monophyletic group obtained under DELTRAN (delayed transformation) op- (Fig. 9, node 4, supported by four synapomorphies and timization. The Bremer decay indices were obtained a Bremer decay index of 1) comparable to the family using command files composed by TreeRot (Sorenson, Homostiidae, supporting the original assignment of 1999) in conjunction with the heuristic search algo- Antineosteus lehmani by Lelièvre (1984). The origi- rithm in PAUP*. nal identification of Dhanguura johnstoni as a homostiid Based on the analysis, 13 taxa are positioned between by Young (2004) is not supported by the current analy- the outgroup Kujdanowiaspis podolica and the ses, despite several shared characters between them, Eubrachythoraci Miles, 1971 (node 10, Fig. 9). We set such as the anteriorly pointed paranuchal plates. node 2 to define Phlyctaenioidei Miles, 1973, and node Buchanosteus confertituberculatus, Goodradigbeeon 3 (including Homostius sulcatus plus Antineosteus australianum and Parabuchanosteus murrumbidgeeni lehmani and all the taxa crownward of them) to define are placed in a monophyletic group (Fig. 9, node 6, sup- Brachythoraci (node 3, Fig. 9), as it is the best supported by one synapomorphy and a Bremer decay index ported node among the array (supported by nine of 4), which can be compared with the superfamily synapomorphies and a Bremer decay index of 3). Buchanosteoidea Denison, 1978.

Figure 9. Strict consensus tree of 540 most parsimonious trees using a revised data set of 121 characters and 60 taxa. Numerical values at the right side of the nodes denote Bremer decay indices. Named nodes: 2, Phlyctaenioidei; 3, Brachythoraci; 4, Homostiidae; 6, Buchanosteoidea; 10, Eubrachythoraci; 11, Coccosteomorphi; 12, Coccosteoidea; 13, Coccosteidae; 16, Panxiosteidae; 17, Incisoscutoidea; 21, Camuropiscidae; 27, Pachyosteomorphi; 29, Dunkleosteoidea; 37, Heterostiidae; 38, Aspinothoracidi; 45, Selenosteidae. CI, consistency index; L, length of trees (in evolutionary steps); n, number of trees; RI, retention index.

Xiangshuiosteus wui is assigned as the sister group modiﬁcations. In the current analysis, the scenario of of Eubrachythoraci. This assignment differs from both eubrachythoracid phylogeny resembles the traditional the original coccosteid assignment of Xiangshuiosteus ones with both Coccosteomorphi (node 11, Fig. 9, sup- wui by Wang (1992) and the dunkleosteid assign- ported by nine synapomorphies and a Bremer decay ment by Zhu & Zhu (2013), and is better supported index of 1) and Pachyosteomorphi (node 27, Fig. 9, sup- by the addition of new characters regarding the ported by three synapomorphies and a Bremer decay distinction between basal brachythoracids and index of 1) being monophyletic. In the Pachyosteomorphi eubrachythoracids. all the taxa crownward of Rhachiosteus pterygiatus Gross, Eubrachythoraci is traditionally subdivided into 1938 are assigned to a monophyletic Dunkleosteoidea Coccosteomorphi and Pachyosteomorphi Stensiö, 1944, (node 29, Fig. 9, supported by nine synapomorphies and the latter being further subdivided into Dunkleosteoidea a Bremer decay index of 1) and Aspinothoracidi (node Vézina, 1990 and Aspinothoracidi sensu Miles & Dennis, 38, Fig. 9, supported by four synapomorphies and a 1979 (Carr, 1991; Gardiner & Miles, 1994; Trinajstic Bremer decay index of 1), respectively. & Dennis-Bryan, 2009; Carr & Hlavin, 2010). The With the addition of taxa in the current data matrix, previous analysis by Zhu & Zhu (2013) challenged the analysis yields a more detailed coccosteomorph phy- the monophly of Pachyosteomorphi in placing the logeny, subdividing Coccosteomorphi into two Coccosteomorphi, rather than Dunkleosteoidea, as the monophyletic groups that are comparable to the su- sister group of Aspinothoracidi. However, the low Bremer perfamily Coccosteoidea Denison, 1978 and decay index and subset analyses indicate that this sce- Incisoscutoidea Trinajstic & Dennis-Bryan, 2009, re- nario is weakly supported and could be subject to further spectively. The latter clade (node 17, Fig. 9, support-

© 2015 The Linnean Society of London, Zoological Journal of the Linnean Society, 2015 EARLY DEVONIAN ARTHRODIRE FROM CHINA 15 ed by five synapomorphies and a Bremer decay index & Miles, 1980 are placed in the basal position of of 1) is in turn composed almost exclusively of taxa Aspinothoracidi. The newly added Melanosteus occitanus from the Gogo Formation with the only exception being Lelièvre et al., 1987 is assigned as the sister group of Trematosteus fontanellus, and all coccosteomorphs from Rhinosteus parvulus Jaekel, 1911. Together with the Gogo Formation in the current analysis are in turn Brachyosteus dietrichi Gross, 1932, Stenosteus included in Incisoscutoidea. This scenario suggests the angustopectus Carr, 1996, Gymnotrachelus hydei Dunkle endemism of coccosteomorphs from the Gogo Forma- & Bungart, 1939, Pachyosteus bulla Jaekel, 1903 and tion, which make up the majority of arthrodires there. Heintzichthys gouldii Newberry, 1885 they compose a This argument also matches the general endemic nature monophyletic group comparable to the family of the Gogo vertebrate fauna (Long & Trinajstic, 2010; Selenosteidae Dean, 1901 (node 45, Fig. 9, supported Trinajstic et al., 2014). by seven synapomorphies and a Bremer decay index Coccosteoidea (node 12, Fig. 9, supported by five of 1). The inclusion of Heintzichthys gouldii into synapomorphies and a Bremer decay index of 1) is sub- Selenosteidae is in agreement with other analyses on divided into two monophyletic groups, one (node 13, the interrelationship of Aspinothoracidi (Carr & Hlavin, Fig. 9, supported by six synapomorphies and a Bremer 2010; Rücklin, Long & Trinajstic, 2015). Whether decay index of 1) of which includes Coccosteus cuspidatus Gorgonichthys clarki should be included in Selenosteidae and several taxa that are traditionally assigned to the can be left to future studies to answer. namesake Coccosteidae Traquair, 1888, namely The phylogeny of Dunkleosteoidea is better resolved Millerosteus minor Stensiö, 1959, Dickosteus threiplandi in the current analysis than in Zhu & Zhu (2013). Notable Miles & Westoll, 1963, Watsonosteus fletti Watson, 1932 differences between current and previous scenarios include and Protitanichthys rockportensis Eastman, 1907. the assignment of Westralichthys uwagedensis Long, Another monophyletic group (node 16, Fig. 9, support- 1987 within a more advanced position, being the sister ed by five synapomorphies and a Bremer decay index group of the clade (node 34, Fig. 9, supported by five of 1) is composed of Plourdosteus canadensis Woodward, synapomorphies and a Bremer decay index of 3) com- 1892, Janiosteus timanicus Ivanov, 1989 and Panxiosteus prising Dunkleosteus terrelli, D. raveri, D. amblyodoratus, oculus Wang, 1979, and can be compared with the family Heterostius ingens and Yinosteus major; and the as- Panxiosteidae Wang, 1979. When Wang (1979) erected signment of Eastmanoteus calliaspis Dennis-Bryan, 1987 this family, he considered it as ‘an intermediate between rather than Westralichthys uwagedensis, to the most the Pholidosteidae and the Dinichthyidae’. Members basal position of Dunkleosteoidea. of this family show a morphologically intermediate con- All members of Heterostiidae are Early or Middle dition between coccosteids and dunkleosteids. This situa- Devonian in age. The grouping of heterostiids in the tion is demonstrated by the phylogenetic shift that current scenario with Dunkleosteus, a Late Devonian Plourdosteus Ørvig, 1951 has undergone. It was ini- and phylogenetically crownward genus, considerably tially considered as a coccosteid with coccosteomorph extends the length of the ghost lineages in characters such as a posteriorly enclosed pectoral Dunkleosteoidea. In light of the current scenario, the fenestra (Stensiö, 1942; Ørvig, 1951; Miles & Westoll, timing of the brachythoracid evolution (Fig. 10) shows 1968). Vézina (1990) erected the family Plourdosteidae a rapid evolutionary phase during the Emsian, Early and placed it as the sister group of Dunkleosteidae. Devonian, when the major eubrachythoracid clades Gardiner & Miles (1994) and Long (1995) later as- emerged. The longer than previously conceived ghost signed Plourdosteidae to Coccosteomorphi rather than lineages of eubrachythoracid clades partly explain the Pachyosteomorphi. Carr & Hlavin (2010) proposed that instability of the relationship between major Plourdosteus could be referred to a better-established eubrachythoracid clades, which is demonstrated by the Panxiosteidae, and placed the family as the most basal low Bremer decay index support and the shifting sce- clade of Dunkleosteoidea. In the current senario, the narios between different analyses. phylogenetic position of Panxiosteidae is resolved as The eubrachythoracids possess distinctive features the sister group of Coccosteidae in Coccosteoidea, instead among placoderms such as laterally compressed body of being the most basal clade of Dunkleosteoidea. The and reduced dermal shield, both suitable for a free- phylogenetically unstable condition of Panxiosteidae swimming nektonic lifestyle (Denison, 1978; Carr, 1995; calls for further morphological description of Panxiosteus Janvier, 1996). The emergence of this type of body plan oculus and Plourdosteus canadensis. corresponds to the so-called Devonian Nekton Revo- Tapinosteus heintzi and a clade (node 40, Fig. 9, sup- lution, triggered possibly by saturated demersal niches ported by three synapomorphies and a Bremer decay and by the flourishing of microplankton supplied by index of 1) containing three durophagous taxa from nutrients from the newly evolved terrestrial biomass the Gogo Formation, namely Bruntonichthys multidens (Klug et al., 2010). Both these events would have oc- Dennis & Miles, 1980, Bullerichthys fascidens Dennis curred during the Early Devonian. The earlier diver- & Miles, 1980 and Kendrickichthys cavernosus Dennis sification of eubrachythoracid arthrodires indicates that

Figure 10. The timing of brachythoracid evolution in the Devonian period, based on the phylogeny in Figure 9. Sil, Si- lurian; Pri, Pridoli; Loc, Lochkovian; Pra, Pragian; Eif, Eifelian; Giv, Givetian; mya, million years. Monospeciﬁc genera are represented only by genus names. the placoderms, the dominant gnathostome group during morphology. The exoskeleton of Yinosteus major shows the Early to Middle Palaeozoic, responded to environ- typical heterostiid characters such as the anteriorly mental and ecological changes more rapidly than pre- tapered skull roof, the small and anteriorly placed orbits, vious scenarios suggest. and the rod-like anterior lateral plates. The neurocranium resembles the advanced eubrachythoracids rather than the basal brachythoracids in the absence CONCLUSIONS of the subnasal shelf, the posteriorly positioned pineal The holotype of Yinosteus major, an Emsian heterostiid foramen, the long and narrow orbitotemporal region arthrodire from Wuding, Yunnan, China, shows pre- of the neurocranium and short occipital region of the viously undescribed neurocranial and visceral skull roof neurocranium.

The occipital portion of the neurocranium in Yinosteus searchers to extract further morphological information major is relatively short. This contrasts with the situa- (Burrow, Jones & Young, 2005; Dupret et al., 2014; Gai tion in the corresponding dermal bone, the elongated & Zhu, 2014). The re-investigation of key taxa using nuchal plate, which was previously considered as a pos- these techniques is imperative for a better under- sible synapomorphy shared with the basal standing of the evolution of brachythoracids, arthrodires brachythoracid homostiids. and placoderms as a whole. The character evolution of the dorsal morphology in arthrodire neurocrania is summarized based on the com- ACKNOWLEDGEMENTS parison between five taxa including Yinosteus major. We recognize six new neurocranial characters that hold This work was supported by the Major State Basic Re- phylogenetic significance. With an expanded and revised search Projects (2012CB821902) of MST of China, the data matrix, the current phylogenetic analysis yields National Major Scientific Instrument and Equipment a new scenario regarding brachythoracid phylogeny, Development Project of China (2011YQ03012), and the in which Brachythoraci is composed of a paraphyletic National Natural Science Foundation of China array of basal taxa and a monophyletic Eubrachythoraci. (40930208). We are grateful to E. Mark-Kurik for pro- Among the basal taxa, Holonema westolli and Elvaspis viding insight regarding the nomination of Heterostius tuberculata were excluded from Brachythoraci. and Homostius, O. Matton and M. Arsenault for help Xiangshuiosteus wui is placed as the sister group of with the literature, Q. Cao for making latex peels, and Eubrachythoraci. Eubrachythoraci is divided into two Y.-H. Liu, W.-J. Zhao, Z.-K. Gai, J. Lu, T. Qiao, Q.-M. monophyletic groups, namely Coccosteomorphi and Qu and Z.-H. 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Wang J-Q. 1984. Geological and paleogeographical distribu- Zhu M, Yu X-B, Ahlberg PE, Choo B, Lu J, Qiao T, Qu tion of Devonian fishes in China. Vertebrata PalAsiatica 22: Q-M, Zhao W-J, Jia L-T, Blom H, Zhu Y-A. 2013. A Si- 219–229. lurian placoderm with osteichthyan-like marginal jaw bones. Wang J-Q. 1992. New discovery of early Middle Devonian Nature 502: 188–193. brachythoracid (placoderm fish) from Wuding Region of Zhu Y-A, Zhu M. 2013. A redescription of Kiangyousteus yohii Yunnan. Vertebrata PalAsiatica 30: 111–119. (Arthrodira: Eubrachythoraci) from the Middle Devonian of Wang J-Q, Wang N-Z. 1983. A new genus of Coccosteidae. China, with remarks on the systematics of the Vertebrata PalAsiatica 21: 1–8. Eubrachythoraci. Zoological Journal of the Linnean Society Wang J-Q, Wang N-Z. 1984. New material of arthrodira 169: 798–819. from the Wuding region, Yunnan. Vertebrata PalAsiatica 22: 1–7. Wang J-Q, Zhu M. 1995. Age of the Jiucheng Formation of APPENDIX 1 Wuding, Yunnan. Journal of Stratigraphy 19: 20–24. DATA MATRIX Watson DMS. 1932. On three new species of fish from the Old Red Sandstone of Orkney and Shetland. Summary of For characters 1–91 and characters 94–98, see Carr Progress of the Geological Survey 1931: 157–166. & Hlavin (2010); for characters 92 and 93, see Zhu White EI. 1952. Australian arthrodires. Bulletin of the British Y.-A. & Zhu M. (2013); for characters 99–121, see Ap- Museum (Natural History) (Geology) 1: 249–304. pendix 2. The codings that differ from Zhu Y.-A. & Zhu. White EI. 1978. The larger arthrodiran fishes from the area M (2013) are underlined. of Burrinjuck Dam, N. S. W. Transactions of the Zoological Society of London 34: 149–262. White EI, Toombs HA. 1972. The buchanosteid arthrodires ANTINEOSTEUS LEHMANI of Australia. Bulletin of the British Museum (Natural History) 10000 0-100 00012 ?1010 01110 0-011 01010 00??? ?0??? Geology 22: 379–419. ????? ?1001 0??11 00100 ????? ????0 01010 0000? ????1 Woodward AS. 1891. Catalogue of the fossil fishes in the British 12001 -00?0 00001 00000 ??000 00??1 1 Museum (Natural History). Part II. London: Taylor & Francis. Woodward AS. 1892. Further contributions to the Devonian fish-fauna of Canada. Geological Magazine 9: 481–485. BRACHYOSTEUS DIETRICHI Young GC. 1979. New information on the structure and relationships of Buchanosteus (Placodermi: Euarthrodira) from 11001 0-00(01) 21110 01100 10110 --201 11(01)1? 000?- the Early Devonian of New South Wales. Zoological Journal 10-00 -???- 01111 11?10 01100 10101 ????- -0100 00- of the Linnean Society 66: 309–352. 10 ???01 11201 -1110 11?11 01011 ??1?? 00100 ? Young GC. 1980. A new Early Devonian placoderm from New South Wales, Australia, with a discussion of placoderm phylogeny. Palaeontographica 167: 10–76. BRUNTONICHTHYS MULTIDENS Young GC. 1981. New Early Devonian brachythoracids ?0?00 0-??? ????? 11??? ???10 0-20? ??102 10??? ????? (placoderm fishes) from the Taemas – Wee Jasper region of ??0?? ?111? 1??11 ??101 00??1 301?1 ????? 01-?0 0-?01 New South Wales. Alcheringa 5: 245–271. 1???? ????? ??0?? ???00 10??1 ?0??? 1 Young GC. 1989. The Aztec fish fauna of southern Victoria Land – evolutionary and biogeographic significance. In: Crame JA, ed. Origins and evolution of the Antarctic biota. London: BUCHANOSTEUS CONFERTITUBERCULATUS Geological Survey of London Special Publication, 43–62. 1201? ???00 10012 ?0010 01110 ??011 1101? ??001 00001 Young GC. 2004. Large brachythoracid arthrodires (placoderm 1???1 21??1 00011 00??? ????? 1??00 01100 00011 0-??1 fishes) from the Early Devonian of Wee Jasper, New South 11001 -0-11 00001 1000? 0001? ?00-0 ? Wales, Australia, with a discussion of basal brachythoracid characters. Journal of Vertebrate Paleontology 24: 1–17. BULLERICHTHYS FASCIDENS Young GC. 2009. New arthrodires (Family Williamsaspididae) 11?01 0-?00 2??1? ????? 001?0 ?-101 1110? ???11 ????1 from Wee Jasper, New South Wales (Early Devonian), with 0100? ?11?? ????? ?0101 00101 11010 0???? ???11 0-?0? comments on placoderm morphology and palaeoecology. Acta 1??01 -01?? ?10?1 00000 10??? ????? 1 Zoologica 90: 69–82. Young GC. 2010. Placoderms (armored fish): dominant vertebrates of the Devonian period. Annual Review of Earth and CAMUROPISCIS LAIDLAWI Planetary Sciences 38: 523–550. Zhao W-J, Zhu M. 2010. Siluro-Devonian vertebrate 11110 10000 21111 1?11? 00010 11101 11002 101?0 0?011 biostratigraphy and biogeography of China. Palaeoworld 19: 1110? ?1110 11??0 01101 00101 ????1 01000 00110 ????1 4–26. 122-- 00??0 11-01 00000 ???10 000-0 0

COCCOSTEUS CUSPIDATUS EASTMANOSTEUS PUSTULOSUS 10002 0-00(02) 01120 11(02)01 01110 0-101 11012 11001 10?02 0-002 01220 ?1000 11110 ??00? 11012 00??? ????? 00011 11010 21100 01?11 00101 00111 00110 11101 ????? ????? ????? ?010? ??1?? ????? 001?1 ???11 ????1 11201 00111 0-001 12101 -0110 11001 00000 10010 000-0 1 -01?0 1?0?1 ??00? ??1?1 00??? ?

COMPAGOPISCIS CROUCHERI ELVASPIS TUBERCULATA 11112 0-000 21111 012-0 01000 0-201 11002 10011 00111 ????? ????? ????? ????? ????? ????? ????0 11011 00001 ?1?11 11110 21000 01111 00101 01101 11111 00000 00111 ????1 0???? ????? ????? ????? ????? ?1010 ????? ????0 1???? ????? 121-- 00100 11-01 00000 10110 000-0 0 ????? ??-?? ????0 100-1 1

DHANGUURA JOHNSTONI FALLOCOSTEUS TURNERI ??112 0-010 ??012 ?12-0 011?0 ??01? 0101? ????? ????? 11110 10002 01111 11110 00010 11101 11102 10110 ????? ????? ????? ????? ????? ????0 0???? ???0? ????? 1??01 00111 ?1111 21101 0???0 01100 00101 ????0 01000 00010 -?110 0100? ???0? ??0?? ????? ? ????1 121-- 0???0 1?-?1 ??000 ????0 000-0 0

DICKSONOSTEUS ARCTICUS GEMUENDENASPIS ANGUSTA 02000 0-101 00002 00010 11100 11000 11010 10001 ????? ????0 0?01? ????0 0111? ???01 110?0 10001 0?0?1 00001 11011 01000 0??10 00??? ????0 00000 01010 00001 ????? 11??? ????? ????? ????? ????? 0??00 0011? ????1 1??01 0-??0 12000 ---10 00000 1--0? 00000 000-1 1 -???? ????1 ??00? ????0 100-0 1

DICKOSTEUS THREIPLANDI GOLSHANICHTHYS ASIATICA ????2 0-012 0?220 ?12-1 01100 ??101 1101? 110?? ????? 1??0? ????2 01220 ?1??0 1?1?0 0-?01 1101? ????? ????? ????? ?11?0 ????1 00??? ????? ????0 1???1 01111 ????1 ????? ???1? ????? ?0100 2???? ????0 0???? ???11 ???11 11001 12001 -???0 1???1 ??00? ????0 000-0 ? -01?? ?1001 000?? ??1?? ????? ?

DINICHTHYS HERZERI GOODRADIGBEEON AUSTRALIANUM 1???? ????? ????? ????? ????? ????? ????? ????? ????? ????? ????0 0--?? ????? 1?0?? ????? 0-01? ????? ????? 0???1 ?101? ????? ????? ??101 11101 ????? ????? ????? ??1?? 1???? ?1??? ?1?1? 0???? 00100 0???0 ????? ????? 010?? ???0? 1???? ????1 ?1??1 ????? ?0??? ? ????1 0???? ????0 ????? ????? 1

DUNKLEOSTEUS AMBLYODORATUS GORGONICHTHYS CLARKI ????? ????? 21??? ????? ????? ????? ????? ????? ????? ????? 11001 0-101 01000 ?12-0 11000 ??101 11112 0000- 1?- ????? ????? ????? ????? ????? ????? ????? 10??1 1???? ?0??? ?0 -???- ????? ????? ?0100 1110? ????1 00??0 ???11 0-1?1 ????1 000?? ????? ?1??? ? 001-- 01100 11011 01001 ??11? ????? ?

DUNKLEOSTEUS RAVERI GROENLANDASPIS ANTARCTICUS ?0022 0-01? ????? ?12-1 ?1??0 0-00? ??11? ????? ????? ????0 0-111 1?112 ?10-0 00110 ??000 1101? ??0?1 ?0001 ????? ???1? ????? ?0??? ????? 0??00 ????? ???11 11??1 1???? ??0?? ????? ????? ????? ????? ????0 01010 ???1? ????0 12001 ??100 110?? ??00? 101?? ????? ? -???0 0?0?0 ??-0? ????0 100-1 1

DUNKLEOSTEUS TERRELLI GYMNOTRACHELUS HYDEI 10021 0-011 21000 112-1 11110 0-000 11012 00001 11- 10001 0-000 21000 -12-1 00010 -201 11101 0000- 11- 01 0101- 11010 11?11 00100 20111 01000 00??0 00111 00 -???- 01?1? 0??00 ?0111 000-0 3???2 00000 00010 11011 00001 -0100 11011 00001 10111 00100 0 0-001 011-- 11110 11-?1 01001 11111 00100 ?

EASTMANOSTEUS CALLIASPIS HADROSTEUS RAPAX 10102 0-012 01120 112-0 11100 0-101 11012 10001 11- ????2 0-101 2?010 ?12-0 10100 0-101 1110? 00??? 1???1 01 0111- 11010 11111 00101 (1 2)0111 11010 00010 00111 ????? ?1011 0???1 00100 11102 ????1 00??0 00-11 0-?01 0-0?1 12101 -0100 11001 00001 10111 00100 0 01211 -???0 1?-?1 ??001 ????? 00100 ?

HARRYTOOMBSIA ELEGANS KUJDANOWIASPIS PODOLICA 10112 0-000 01110 012-0 00000 0-101 10012 11011 0?111 02000 0-101 00002 ?0010 01000 11000 11000 10001 11010 21?10 011?1 00101 00101 01100 01000 00111 00001 11011 11000 ????0 00??? ????? 0???0 01010 00001 0-001 121-- 00100 11001 00000 10110 000-0 1 ????0 120-- 0--10 00-00 1--0? 00000 100-1 1

HEINTZICHTHYS GOULDII LATOCAMURUS COULTHARDI 11?01 0-001 21002 -12-2 10010 -200 11102 0000- 10- 11110 0-102 2111? 01100 00010 11100 11102 10011 0?011 10 -010- 11010 01111 10100 11101 01?01 00000 00011 ????1 21?01 011?0 01100 00101 31111 01000 00110 0-0?1 0-101 011-- 11110 11-?1 01001 101?1 00100 0 122-- 10100 11-01 00000 10110 000-0 0

HETEROSTIUS INGENS MCNAMARASPIS KAPRIOS 1001? ?-??1 2?002 ?12-0 01110 ??011 11011 00??? 1?- 10112 0-000 01100 012-0 00000 0-101 11012 10011 00111 00 ????? ?1001 0???? 00??? ????? ????0 01010 00111 ????1 11110 21010 01111 00101 00101 01101 01000 00111 10011 -???0 1?1?1 0010? ????1 01110 ? 0-001 121-- 00100 11001 00000 10110 000-0 0

HOLONEMA WESTOII MELANOSTEUS OCCITANUS 02002 0-011 10110 ?02-0 00000 ??100 11011 10011 00101 11002 0-00? 21??? ?1110 0011? 0-201 ?110? ????? 1?-?? 11010 10000 00010 000?? ?00?0 ????0 01(01)1(01) 10011 ????- ?1111 1???? ??100 ????0 11?12 ????? 001?? ????1 ????0 120-- 0-010 00001 0--0- ??000 100-0 0 0200? -1110 11?11 010?1 1111? 00100 ?

HOMOSTIUS SULCATUS MILLEROSTEUS MINOR 10000 0-100 00012 ?12-0 00110 0-010 01-10 00001 10- 1???2 0-102 01220 11011 01100 0-101 11011 11011 00011 ?1 01?1- ?1001 0???1 00100 ????? ????0 01010 01001 11011 21110 0???1 011?? ????? ????0 01101 00111 ???01 ????1 11011 -0010 001?1 00000 ??0?0 000-? 1 12200 -0??0 11001 00000 ????0 000-0 ?

INCISOSCUTUM RITCHIEI PACHYOSTEUS BULLA 11112 0-000 01110 01110 01000 10100 11012 10011 1???1 11001 0-001 21012 112-1 100?1 0-201 1110? ????- 1?- 1101- 01000 01111 00101 00101 10111 10001 00011 0-0?1 ?? ????- ?1?10 0???? 1?1?? ????? 1?002 0???? 0??11 0-??1 122-- 00100 11001 01000 10110 000-0 0 012-- 0?1?0 11-11 0100? 1011? ?0??? ?

INCISOSCUTUM SARAHAE PANXIOSTEUS OCULUS 11112 0-000 21110 01110 01000 10100 11012 1?011 1???1 11012 0-002 11220 ?12-0 10010 0-000 11012 ?1??? ????? 1101- 01000 01111 00101 00101 10111 10001 00011 ????1 ?101? ?10?? 1???? ?0??? ?0101 0??10 1???1 00111 0-0?1 111-- 00100 11001 0?000 1011? 000-0 0 111-- 201?0 11001 0000? 10110 00??? ?

JANIOSTEUS TIMANICUS PARABUCHANOSTEUS MURRUMBIDGEENIS ????? ??012 ??22? ????0 000?0 ???00 110?? ????? ????? 12010 0--00 00012 ?0010 01110 ??011 0101? 1100? ?0001 ????? ????? ????? ?0??? ????? ????0 1???? ???1? ????1 111-- ????? ????? ????? ????? ????? 1???0 01100 ????1 ????1 11001 2???0 1???1 ??00? ????? ????? ? -0-11 00001 1000? 0?010 000-0 ?

KENDRICKICHTHYS CAVERNOSUS PLOURDOSTEUS CANADENSIS 10?01 0-1?2 2?1?? ?12-1 ?0110 ??101 ?110? ??0?? 1???1 1?112 0-012 01220 ?12-1 10000 0-001 10012 11011 01111 0100? ?1?1? 1???1 ?0100 ????1 ????0 10??? 00010 ???01 11110 21011 1??11 00101 20101 ????0 11101 00111 0-001 11201 -0100 110?1 00000 ??1?? ?0100 1 111-- 20100 11001 00000 ?1100 000-0 1

KIANGYOUSTEUS YOHII PROTITANICHTHYS ROCKPORTENSIS ????? ????? ????? ????? ????? ????? ????? 10??? ?1??1 ?1?1? 11002 0-012 11220 112-1 11100 0-001 1101? 11??? ????? ????? ????? ????0 1??-1 0101? ??0?1 ????? 111?? 1???? ????? ??0?? ????? ????? ????? ????? ????0 1?11? ???1? ????1 11001 ????? ????? 101?? 00100 ? -?1101 10?1? ?00??? 0??0? 0-?1

RHACHIOSTEUS PTERYGIATUS WATSONOSTEUS FLETTI ????2 0-010 0??20 ?12-1 00110 ??201 11012 00??? 1???? ????2 0-012 ??220 ?12-2 01100 ??101 01011 100?1 00111 ????? ?1??? ????? ?01?? ????? ????0 01??1 ???1? ????1 02000 ????0 211?0 ????1 00100 ????? ????0 11101 01111 ???01 -???0 1???1 ??00? ????0 00100 ? 12001 -???0 1???1 ??000 ????0 000-0 ?

RHINOSTEUS PARVULUS WESTRALICHTHYS UWAGEDENSIS 1???2 0-001 2?012 ?1112 10111 0-201 1010? 0000- 1?- ?002? ????0 0122? ?1??0 0?100 ??001 1101? ????? ????? 00 -???- ?1?11 ????0 11111 ????2 ????2 00000 00111 ????1 ????? ???1? ????? 00??? ????? ????0 0???? ????1 ????1 00001 02101 -???0 1?-?1 ??001 ????? 00100 0 -01?? ?1001 000?? ??1?? ?0??? ?

ROLFOSTEUS CANNINGENSIS XIANGSHUIOSTEUS WUI 11110 11000 01101 01110 00000 11101 11002 10110 ????0 0-110 0?122 ?12-0 01100 ??001 1101? ????? ????? 0-111 11??0 21101 011?0 0110? ?0101 ????1 01101 00010 ????? ????? ????? ????? ????? ????0 0???? ???1? ????1 12001 0-0?1 121-- 00100 11-01 00000 ??110 000-0 0 -???0 0?0?1 ??00? ????? ????? ?

STENOSTEUS ANGUSTOPECTUS YINOSTEUS MAJOR 11001 0-001 21002 -12-0 101?? -201 11101 0000- 10- 10010 ??0?? 21??? ?1??? 1???? ??01? ???11 00??? 1?-?? 10 -???- 01?1? 01?00 10111 ????0 ????2 ?0000 00-1? 0-?01 ????? ????? ????? ????? ????? ????? ?1??0 ????? ????1 1???? 01111 -?1?0 11-?1 ??001 ?1111 00100 ? ?010? ?1101 0010? ?0111 01110 ?

TAPINOSTEUS HEINTZI APPENDIX 2 11??2 0-000 21110 112-0 00000 0-201 1111? 00??? 1???? NEW CHARACTERS ????? ?1010 ?11?? ?0??? 1010? ????0 ????? ?01?? 0--?1 1??-- 10??0 11001 0000? ?11?? 00??? ? SKULL ROOF TOROSTEUS TUBERCULATUS 99. Development of the crista supraethmoidalis at the 11112 0-000 01200 012-0 00000 0-101 1101? 11011 00?11 visceral surface of the skull roof: underdevel- 1101? 21010 01??1 00101 00101 01111 01011 00111 0-001 oped, absent or present but not convergent in the 121-- 00100 11001 00000 10110 000-0 1 midline (0); developed, horizontally across the visceral surface of the skull roof (1). The developed crista supraethmoidalis is present TOROSTEUS PULCHELLUS in basal arthrodires such as Dicksonosteus arcticus 11112 0-000 01201 01000 00000 10101 1101? 1?011 and in basal brachythoracids such as 00?11 1101? 210?0 01111 00101 1010? 01111 01010 00111 Parabuchanosteus murrumbidgeenis and 0-001 121-- 00100 11001 00000 10110 000-0 1 Dhanguura johnstoni. The similar structure is also present in Aspinothoracidi such as Enseosteus TREMATOSTEUS FONTANELLUS jaekeli. In Aspinothoracidi the crista supraethmoidalis is positioned anterior to the ?0?12 0-000 21111 ?12-0 00100 ??201 1110? ????? ????? pineal pit, while in basal arthordires and basal ????? ?1??? ????? ????? ??1?? 1110? 00??? ???1? 0-??1 1??00 brachythoracids the crista supraethmoidalis is pos- -?1?0 11-11 0?01? 1111? ?0??? ? terior to the pineal pit. 100. Rostral and pineal plates fused into one plate: TUBONASUS LENNARDENSIS absent (0); present (1). 11??0 11002 21111 01110 000?0 11101 11102 ??110 0?111 101. Shape of the pineal plate on the external surface 11?10 21?01 ????0 0110? ?0101 ?00?1 01000 00010 -???1 of the skull roof: short and broad (0); long and 121-- 00100 11-01 00000 ??110 000-0 0 narrow (1). This character may be linked to the elongation and narrowing of the orbitotemporal region of the TURRISASPIS ELEKTOR neurocranium. 02000 0-101 10012 ?12-0 00100 0-000 11010 1?0?? ?0?01 102. Lateral development of the supraorbital vault com- ????? ????? ????? ????? 00??? 1??00 01010 ???1? 0-0?0 pared with the breadth of the skull roof at the 12101 --0?0 000?0 ?--0? 00000 100-1 1 level immediately behind the supraorbital vault.

This definition of the skull roof breadth is to make deeper (0); occlusal portion deeper, or nearly equal this character independent to character 113: under- between these two parts of the infragnathal plate developed, indicated by the ratio of the breadth (1). of both sides of the lateral expansion of the Anderson (2008) identified two distinct supraorbital vaults/the breadth of the skull roof morphotypes in eubrachythoracids indicating dif- at the level immediately behind the supraorbital ferent feeding niches. The deep blade and narrow vault less than 0.3 (0); developed, indicated by dental portion in most coccosteomorphs implies the ratio of the breadth of the lateral expansion a scissor-like occlusion, while the narrow blade of the supraorbital vaults/the breadth of the skull and deep dental portion in most pachyosteomorphs roof larger than 0.3 (1). implies a vice-like occlusion. 103. Development of the postorbital process of the 111. Parasphenoid thickened around the postorbital plate: moderately developed (0); highly buccohypophysial foramen: absent (0); present (1). developed, defined as the postorbital process com- Parasphenoid thickened around the posing one-quarter of the orbit (1). buccohypophysial foramen is to date the 104. Position of the anterior end of the endolymphatic synapomorphy of Eubrachythoraci. In basal duct on the visceral suface of the skull roof, in- arthrodires such as Turrisaspis elector and basal dicating the neurocranial aperture of the brachythoracids such as Parabuchanosteus endolymphatic duct: anteriorly positioned, defined murrumbidgeensis and Antineosteus lehmani, the as positioned anterior to the nuchal thickening parasphenoid is thinner and not thickend around (0); posteriorly positioned, on the nuchal the buccohypophysial foramen. thickening. 112. Stem-like prehypophysial region of the 105. Posterior lateral shape of the nuchal plate: nuchal parasphenoid: absent (0); present (1). straight, not expanded laterally (0); nuchal trap- The stem-like prehypophysial region of the ezoid, expanded laterally (1). parasphenoid is present in several aspinothoracids Modified after Gardiner & Miles (1990: charac- such as Gymnotrachelus hydei (Carr, 1994: fig. ter 22.36). This character not being included in 9). Trematosteus fontanellus is coded as posses- several previous analyses (Carr, 1991; Carr & sing stem-like prehypophysial region of the Hlavin, 2010; Zhu & Zhu, 2013) was due to all parasphenoid because it is significantly narrow- eubrachythoracids to date possessing er than the postohypophysial region, although its posterolaterally expanded nuchal plates, render- prehypophysial region is very unusual in being ing this character uninformative if only considerably elongated and anteriorly broad- eubrachythoracids are included as the ingroup. ened into a sword-shape. 106. Median ridge on the visceral surface of the nuchal plate, corresponding to the median depression on NEUROCRANIUM the occipital region of the neurocranium: absent (0); present (1). 113. Breadth of the orbitotemporal neurocranium, in- 107. Position of the paired nuchal pits: anteriorly po- dicated by the breadth between the two inner sitioned, defined by position anterior to or on the margins of the supraorbital vaults: wide, defined transverse nuchal thickening (0); posteriorly po- by the ratio of the breadth of the obitotemporal sitioned, defined by position posterior to the trans- neurocranium/the breadth of the skull roof at the verse nuchal thickening (1). level immediately behind the supraorbital vault Nuchal pits positioned posterior to the trans- larger than 0.4 (0); narrow, defined by the ratio verse nuchal thickening is present in several of the breadth of the obitotemporal neurocranium/ aspinothoracids such as Dinichthys herzeri (Carr the breadth of the skull roof less than 0.4 (1). & Hlavin, 2010: fig. 1). 114. Shape of the supravagal process of the 108. Position of the skull roof and thoracic armour ar- neurocranium, indicated by the impression of the ticulation: not close to posterolateral corner of the channel left by the supravagal process on the vis- skull roof (0); close to posterolateral corner of the ceral surface of the skull roof when the skull roof (1). neurocranium is not preserved: near right- 109. Skull roof fenestra: absent (0); present (1). angled (0); developed laterally to form an acute angle (1). This character may be linked to the posterolateral GNATHAL PLATES AND PARASPHENOID expansion of the dermal nuchal plate (character 110. Shape of the infragnathal plate, defined by the 104). The right-angled supravagal process is pri- depth of the occlusal portion and posterior blade marily present in basal arthrodires such as portion, respectively: blade portion significantly Kujdanowiaspis podolica, Dicksonosteus arcticus

and Holonema westolli. Several basal 120. External surface of the anterior lateral plate brachythoracids such as Antineosteus lehmani quadrated by four ridges radiating from the os- also possess a near right-angled supravagal sification centre of the plate: absent (0); present process. (1). 121. Anteroventral groove on the ventral surface of the interolateral plate: absent (0); present (1). THORACIC ARMOUR Miles (1965) considered that the anteroventral 115. Posterior development of the posterior carinal groove accommodated the neuromasts. This groove process of the keel on the visceral surface of the is present in most basal arthrodires and lost in median dorsal plate: posteriorly developed, beyond most eubrachythoracids, retained only in the posterior margin of the median dorsal plate Coccosteus cuspidatus. in dorsal view (0); not posteriorly developed, not beyond the posterior margin of the median dorsal plate in dorsal view (1). APPENDIX 3 This character definition is different from Carr TAXA LIST AND SOURCE REFERENCES & Hlavin (2010: cha. 35) in that the latter only Name: Antineosteus lehmani Lelièvre, 1984 discriminated the presence and absence of pos- Locality and horizon: Akka-N-Arrouch, Morocco. Late terior carinal process, but did not indicate its Emsian, Early Devonian. extent of development. The posterior carinal Source reference: Lelièvre, 1984, 1988. process beyond the posterior margin of the median Name: Brachyosteus dietrichi Gross, 1932 dorsal plate is the result of both the develop- Locality and horizon: Bad Wildungen, Germany. Late ment of itself and the shortening of thoracic Frasnian, Late Devonian. armour. Source reference: Stensiö, 1963. 116. Median dorsal plate elevated dorsally into a Name: Bruntonichthys multidens Dennis & Miles, median crest: (0) absent; present (1). 1980 The median dorsal crest is only present in basal Locality and horizon: Kimberley, Australia. Early arthordires, including holonematids and Frasnian, Late Devonian. groenlandaspids, as well as the basal Source reference: Dennis & Miles, 1980. brachythoracid Gemuendenaspis angusta. Name: Buchanosteus confertituberculatus Young, 1979 117. Anterior dorsolateral plate and anterior lateral Locality and horizon: Buchan, Australia. Emsian, plate fused into one complex: not fused (0); fused Early Devonian. (1). Source reference: Long, Mark-Kurik & Young, 2014; 118. Anterior ventral corner or anterior ventral wing White & Toombs, 1972; Young, 1979. (sensu Carr, 1996) of the anterior lateral plate Name: Bullerichthys fascidens Dennis & Miles, 1980 extends anterolaterally: not extending Locality and horizon: Kimberley, Australia. Early anterolaterally, the lateral profile of the anteri- Frasnian, Late Devonian. or lateral plate is sub-triangular or rhomboid (0); Source reference: Dennis & Miles, 1980. extending anterolaterally, making the lateral profile Name: Camuropiscis laidlawi Dennis & Miles, 1979a of the anterior lateral plate ‘boomerang’-shaped Locality and horizon: Kimberley, Australia. Early (1). Frasnian, Late Devonian. Homosteids such as Homostius sulcatus and Source reference: Dennis & Miles, 1979a; Trinajstic Antineosteus lehmani also possess an elongated & Dennis-Bryan, 2009. anterior lateral plate. However, in homosteids the Name: Coccosteus cuspidatus Miller, 1841 elongation in most part applies to the upper Locality and horizon: Lower Caithness Flagstone lamina rather than the anterior ventral corner Group, Scotland. Eifelian, Middle Devonian. of the anterior lateral plate and does not fit the Source reference: Miles & Westoll, 1968. above definition. Therefore, in the current data Name: Compagopiscis croucheri Gardiner & Miles, matrix Homostius sulcatus and Antineosteus 1994 lehmani are coded as ‘0’ in character 116. Locality and horizon: Kimberley, Australia. Early 119. In those taxa that possess an anterolaterally ex- Frasnian, Late Devonian. tended anterior lateral plate, the extent of the Source reference: Gardiner & Miles, 1994; Trinajstic extension: extended normally (0); extended into & Dennis-Bryan, 2009. a rod-like structure (1). In those taxa that do Name: Dhanguura johnstoni Young, 2004 not possess an anterolaterally extended anteri- Locality and horizon: New South Wales, Australia. or lateral plate, this character is scored as ‘not Source reference: Young, 2004. applicable’. Name: Dicksonosteus arcticus Goujet, 1975

Locality and horizon: Dickson land, Spitsberg. Pragian Source reference: Carr & Hlavin, 2010; Lelièvre, to Emsian, Early Devonian. Janvier & Goujet, 1981. Source reference: Carr & Hlavin, 2010; Goujet, 1975, Name: Goodradigbeeon australianum White, 1984. 1978 Name: Dickosteus threiplandi Miles & Westoll, Locality and horizon: Murrumbidgee, Australia, 1963 Emsian, Early Devonian. Locality and horizon: Orkneys and Caithness, Source reference: White, 1978. Scotland. Late Eifelian to Early Givetian, Middle Name: Gorgonichthys clarki Claypole, 1892 Devonian. Locality and horizon: Ohio, USA. Famennian, Late Source reference: Miles & Westoll, 1963. Devonian. Name: Dinichthys herzeri Newberry, 1868 Source reference: Carr & Hlavin, 2010; Dunkle & Locality and horizon: Delaware County, Ohio, USA. Bungart, 1940; Denison, 1978; Stensiö, 1963. Famennian, Late Devonian. Name: Groenlandaspis antarcticus Ritchie 1975 Source reference: Carr & Hlavin, 2010. Locality and horizon: Aztec siltstone, Victorian Land, Name: Dunkleosteus amblyodoratus Carr & Hlavin, Antarctica. Givetian according to Young (1989), origi- 2010 nally identiﬁed by Ritchie (1975) as Late Devonian. Locality and horizon: Ontario, Canada. Frasnian or Source reference: Ritchie, 1975; Young, 1989. Famennian, Late Devonian. Name: Gymnotrachelus hydei Dunkle & Bungart, 1939 Source reference: Carr & Hlavin, 2010. Locality and horizon: Ohio, USA. Famennian, Late Name: Dunkleosteus raveri Carr & Hlavin, 2010 Devonian. Locality and horizon: Erie County, Ohio, USA. Early Source reference: Carr, 1994; Carr & Hlavin, 2010; Famennian, Late Devonian. Dunkle & Bungart, 1939. Source reference: Carr & Hlavin, 2010. Name: Hadrosteus rapax Gross, 1932 Name: Dunkleosteus terrelli Newberry, 1873 Locality and horizon: Bad Wildungen, Germany. Late Locality and horizon: Ohio, Tennessee, Pennsylva- Frasnian, Late Devonian. nia and California, USA. Late Frasnian to Famennian, Source reference: Carr & Hlavin, 2010; Stensiö, 1963. Late Devonian. Name: Harrytoombsia elegans Miles & Dennis, 1979 Source reference: Carr & Hlavin, 2010; Heintz, 1932. Locality and horizon: Kimberley, Australia. Early Name: Eastmanosteus calliaspis Dennis-Bryan, 1987 Frasnian, Late Devonian. Locality and horizon: Kimberley, Australia. Early Source reference: Miles & Dennis, 1979; Trinajstic Frasnian, Late Devonian. & Dennis-Bryan, 2009. Source reference: Carr & Hlavin, 2010; Dennis-Bryan, Name: Heintzichthys gouldii Newberry, 1885 1987. Locality and horizon: Ohio, USA. Famennian, Late Name: Eastmanosteus pustulosus Eastman, 1897 Devonian. Locality and horizon: Wisconsin, New York, and Iowa, Source reference: Carr, 1991; Carr & Hlavin, 2010. USA, and Holy Cross Moutain, Poland. Givetian, Middle Name: Heterostius ingens Asmuss, 1856 Devonian to Early Famennian, Late Devonian. Locality and horizon: Aruküla beds, Estonia. Eifelian, Source reference: Carr, 1991; Carr & Hlavin, 2010; Middle Devonian. Denison, 1978. Source reference: Heintz, 1928, 1930. Name: Elvaspis tuberculata Young 2009 Name: Holonema westoii Miles, 1971 Locality and horizon: New South Wales, Australia. Locality and horizon: Kimberley, Australia. Early Emsian, Early Devonian. Frasnian, Late Devonian. Source reference: Young, 2009. Source reference: Carr & Hlavin, 2010; Miles, 1971. Name: Fallocosteus turneri Long, 1990 Name: Homostius sulcatus Kutorga, 1837 Locality and horizon: Kimberley, Australia. Early Locality and horizon: Aruküla beds, Estonia. Eifelian, Frasnian, Late Devonian. Middle Devonian. Source reference: Long, 1990; Trinajstic & Source reference: Carr & Hlavin, 2010; Heintz, 1934, Dennis-Bryan, 2009. 1968. Name: Gemuendenaspis angusta Traquair, 1903 Name: Incisoscutum ritchiei Dennis & Miles, 1981 Locality and horizon: Hunsrückschiefer, Germany, Locality and horizon: Kimberley, Australia. Early Early Emsian, Early Devonian. Frasnian, Late Devonian. Source reference: Miles, 1962. Source reference: Dennis & Miles, 1981; Trinajstic Name: Golshanichthys asiatica Lelièvre, Janvier & & Dennis-Bryan, 2009. Goujet, 1981 Name: Incisoscutum sarahae Long, 1994 Locality and horizon: Kerman, Iran. Early Frasnian, Locality and horizon: Kimberley, Australia. Early Late Devonian. Frasnian, Late Devonian.

Source reference: Long, 1994; Trinajstic & Source reference: Carr & Hlavin, 2010; Miles, 1966b; Dennis-Bryan, 2009. Schultze & Cloutier, 1996; Vézina, 1988; 1990. Name: Janiosteus timanicus Ivanov, 1989 Name: Protitanichthys rockportensis Eastman, 1907 Locality and horizon: Timan, Russia. Late Givetian, Locality and horizon: Michigan, USA. Early Givetian, Middle Devonian. Middle Devonian. Source reference: Carr& Hlavin, 2010; Ivanov, Source reference: Carr & Hlavin, 2010; Case, 1931; 1989. Miles, 1966b. Name: Kendrickichthys cavernosus Dennis & Miles, Name: Rhachiosteus pterygiatus Gross, 1938 1980 Locality and horizon: Bergisch-Gladbach, Germany. Locality and horizon: Kimberley, Australia. Early Late Givetian, Middle Devonian to Early Frasnian, Late Frasnian, Late Devonian. Devonian. Source reference: Dennis & Miles, 1980. Source reference: Gross, 1938; Miles, 1966a. Name: Kiangyousteus yohii Liu, 1955 Name: Rhinosteus parvulus Jaekel, 1911 Locality and horizon: Sichuan, China. Givetian, Middle Locality and horizon: Bad Wildungen, Germany. Late Devonian. Frasnian, Late Devonian. Source reference: Liu, 1955; Zhu & Zhu, 2013. Source reference: Carr & Hlavin, 2010; Stensiö, 1963. Name: Kujdanowiaspis podolica Brotzen, 1934 Name: Rolfosteus canningensis Dennis & Miles, 1979b Locality and horizon: Podolica, Ukraine. Lochkovian, Locality and horizon: Kimberley, Australia. Early Early Devonian. Frasnian, Late Devonian. Source reference: Dupret, 2010; Stensiö, 1944, 1963. Source reference: Dennis & Miles, 1979b; Trinajstic Name: Latocamurus coulthardi Long, 1988a & Dennis-Bryan, 2009. Locality and horizon: Kimberley, Australia. Early Name: Stenosteus angustopectus Carr, 1996 Frasnian, Late Devonian. Locality and horizon: Ohio, USA. Famennian, Late Source reference: Long, 1988a; Trinajstic & Devonian. Dennis-Bryan, 2009. Source reference: Carr, 1996; Carr & Hlavin, 2010. Name: Mcnamaraspis kaprios Long, 1995 Name: Tapinosteus heintzi Stensiö, 1963 Locality and horizon: Kimberley, Australia. Early Locality and horizon: Bad Wildungen, Germany. Late Frasnian, Late Devonian. Frasnian, Late Devonian. Source reference: Long, 1995; Trinajstic & Source reference: Stensiö, 1963. Dennis-Bryan, 2009. Name: Torosteus tuberculatus Gardiner & Miles, 1990 Name: Melanosteus occitanus Lelièvre et al., 1987 Locality and horizon: Kimberley, Australia. Early Locality and horizon: Montagne Noire, France. Late Frasnian, Late Devonian. Frasnian, Late Devonian. Source reference: Gardiner & Miles, 1990. Source reference: Lelièvre et al., 1987. Name: Torosteus pulchellus Gardiner & Miles, 1990 Name: Millerosteus minor Stensiö, 1959 Locality and horizon: Kimberley, Australia. Early Locality and horizon: Orkneys and Caithness, Scot- Frasnian, Late Devonian. land. Early Givetian, Middle Devonian. Source reference: Gardiner & Miles, 1990. Source reference: Desmond, 1974; Stensiö, 1959, 1963. Name: Trematosteus fontanellus Gross, 1932 Name: Pachyosteus bulla Jaekel, 1903 Locality and horizon: Bad Wildungen, Germany. Late Locality and horizon: Bad Wildungen, Germany. Late Frasnian, Late Devonian. Frasnian, Late Devonian. Source reference: Gross, 1932; Stensiö, 1963. Source reference: Carr & Hlavin, 2010; Stensiö, 1963. Name: Tubonasus lennardensis Dennis & Miles, 1979b Name: Panxiosteus oculus Wang, 1979 Kimberley, Australia. Early Frasnian, Late Locality and horizon: Yunnan, China. Givetian, Middle Devonian. Devonian. Source reference: Dennis & Miles, 1979b; Long, 1988b; Source reference: Carr & Hlavin, 2010; our obser- Trinajstic & Dennis-Bryan, 2009. vations; Wang, 1979. Name: Turrisaspis elektor Daeschler, Frumes & Name: Parabuchanosteus murrumbidgeenis White, Mullison, 2003 1952 Locality and horizon: Pennsylvania, USA. Famennian, Locality and horizon: Murrumbidgee, Australia, Late Devonian. Emsian, Early Devonian. Source reference: Daeschler, Frumes & Mullison, 2003. Source reference: Long, Mark-Kurik & Young, 2014; Name: Watsonosteus ﬂetti Watson, 1932 White, 1978. Locality and horizon: Orkney Isles, Scotland, UK. Name: Plourdosteus canadensis Woodward, 1892 Late Givetian, Middle Devonian. Locality and horizon: Quebec, Canada. Early Frasnian, Source reference: Miles & Westoll, 1963. Late Devonian. Name: Westralichthys uwagedensis Long, 1987

Locality and horizon: Western Australia, Australia. Node 15: 82, 93 (0) Middle Famennian, Late Devonian. Node 16: 23 (0)*, 28 (0), 56, 92, 96 (2) Source reference: Carr & Hlavin, 2010; Long, 1987. Node 17: 3, 9 (0), 16 (0), 23 (0)*, 72* Name: Xiangshuiosteus wui Wang, 1992 Node 18: 13 (2)*, 14 (0)*, 75*, 79 Locality and horizon: Yunnan, China. Emsian, Early Node 19: 37 (0), 48, 75*, 121 (0) Devonian. Node 20: 2, 54 (0)*, 74 Source reference: Oour observations; Wang, 1992. Node 21: 18, 26, 83 (0) Name: Yinosteus marjor Wang & Wang, 1984 Node 22: 15 (0), 22*, 27 (0)*, 30 (0), 34, 41, 48 (0), Locality and horizon: Yunnan, China. Emsian, Early 51 (0), 72 (0)*, 76, 80* Devonian. Node 23: 5 (0), 6, 38, 40 (0), 53, 55, 60 (0), 62, 77, Source reference: Current paper; Wang & Wang, 1984. 85 (0) Node 24: 10 (2), 33 Node 25: 7 (0), 24*, 50 APPENDIX 4 Node 26: 43 (0), 83, 93 (2) LIST OF SYNAPOMORPHIES THAT DEFINE THE CLADES Node 27: 36 (0), 41, 118 SHOWN IN FIGURE 9 Node 28: 4 (0)*, 46 (0)*, 66*, 72*, 77 (0), 115 Asterisks indicate ambiguous character states re- Node 29: 2 (0), 10 (2), 21, 22, 42, 69, 79, 110*, 121 solved using DELTRAN (delayed transformation) op- (0)* timization. Character state is ‘1’ unless marked Node 30: 13 (2), 28 (0), 65 (0), 71 (0), 86, 92* otherwise. Node 31: 80 Node 2: 34, 14, 17, 26 (0), 71, 95*, 106 (0) Node 32: 66 (2), 89* Node 3: 1, 10 (0), 24, 29, 60, 63+, 90, 105, 116 (0)* Node 33: 4 (2), 92 (0) Node 4: 2 (0), 31 (0)*, 36 (0), 55* Node 34: 10*, 11 (2), 13 (0), 14 (0), 24* Node 5: 4, 16*, 30*, 54, 79 (0), 114, 120 (0) Node 35: 20, 74 (0)* Node 6: 100 Node 36: 117 Node 7: 9, 18 (2)*, 98*, 102 Node 37: 4*, 29*, 35*, 77*, 103*, 108, 119* Node 8: 29 (0), 83*, 84* Node 38: 9 (0), 11 (2), 14, 33 Node 9: 13, 14 (0), 24 (0) Node 39: 8, 34 (0), 49 (0)*, 83 (0), 92*, 93 (2)* Node 10: 2*, 5*, 8 (0)*, 12*, 15 (0), 22, 28, 35 (2)*, Node 40: 5*, 53, 66 (0) 57*, 58*, 65*, 68*, 70*, 74*, 99 (0)*, 101, 111*, 113* Node 41: 2 (0), 24*, 56*, 85 (0) Node 11: 37, 39, 43*, 44, 50 (0)*, 51 (2), 71 (0), 73, Node 42: 67, 88*, 97, 107, 110* 93 Node 43: 10*, 13 (0)*, 21*, 65 (0), 75*, 91 (0) Node 12: 10, 13 (2)*, 76, 78, 80 Node 44: 5*, 23 (0), 45 (0), 93, 104* Node 13: 4 (0), 20*, 22, 53, 99, 113 (0) Node 45: 8 (0), 15 (2), 24, 28 (2), 61*, 99, 121 (0)* Node 14: 9 (0), 43 (0) Node 46: 5 (2), 83*, 92 (2)