University of Alberta

NEW PORASPIDINE HETEROSTRACANS FROM THE LOCHKOVIAN (EARLY DEVONIAN) MAN ON THE HILL LOCALITY, MACKENZIE MOUNTAINS, NORTHWEST TERRITORIES, CANADA, AND THE PHYLOGENY AND EVOLUTIONARY HISTORY OF PORASPIDINAE

by

Jessica Rae Hawthorn ©

A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of

Master of Science in Systematics and Evolution

Department of Biological Sciences

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•+• Canada ABSTRACT

Poraspidine heterostracans are extinct, jawless vertebrates that first appear in the Late Silurian, and were common components of Early Devonian faunas.

The MOTH locality in the Mackenzie Mountains of northwestern Canada bears four new species of the genus Poraspis Kiaer, 1930, and two species previously known from Spitsbergen. These four new species are described, differing from previously described species in characteristics of ornamentation, sensory system pores, and in the dimensions of the dorsal shield. With the description of these new species, there are now seventeen species of Poraspis known. Phylogenetic analyses of the subfamily Poraspidinae and the genus Poraspis are here attempted for the first time, but few firm conclusions can be reached due to insufficient data and high levels of polymorphism. The significance of the MOTH poraspidine fauna is explored in the context of paleobiogeographic hypotheses, paleoenvironmental interpretation, and broader morphological trends in poraspidine evolution. ACKNOWLEDGEMENTS

I would like to extend the my sincere gratitude to my supervisor, Dr. Mark V.

H. Wilson, for providing access to the spectacular collection of specimens from

MOTH, as well as for his support, encouragement, and guidance, and acting as my thesis supervisor. I am also grateful to Dr. Michael W. Caldwell and Dr. Brian

D. E. Chatterton for their many insights throughout my time at the University of

Alberta and for acting on my supervisory committee.

Allan Lindoe is owed many, many thanks for his amazing preparation work on the MOTH specimens, and for his highly valued advice and feedback on my own preparation work. Thanks also go to Victoria and Jack Wiercinski for their assistance with translations from Polish, and to Victoria Wiercinski and Kyla

Johnson for advice with graphics programs.

This work would not have been possible without support from Dr. Mark V. H.

Wilson, the Natural Sciences and Engineering Research Council of Canada

(NSERC PGS-M), the Faculty of Graduate Studies and Research (J. Gordin

Kaplan Graduate Student Award, Walter H. Johns Graduate Student Fellowship), the Province of Alberta (Graduate Student Scholarship), the Graduate Students'

Association (Professional Development Grant), and the Department of Biological

Sciences (Graduate Teaching Assistantship Award, Graduate Intern Tuition

Supplement, Department of Biological Sciences Travel Award).

Thanks go to anyone and everyone who has ever collected materials at the

MOTH locality, and to all my fellow paleo graduate students, the postdoctoral researchers for their feedback, encouragement, and lively and stimulating discussions. Thanks also go to all the U of A staff who helped me out along the way.

Lastly, to my friends and family who have always supported me, believed in me, and helped to keep me (mostly) sane.

- J. R. H. TABLE OF CONTENTS

ABSTRACT

ACKNOWLEDGEMENTS

LIST OF TABLES

LIST OF FIGURES

LIST OF APPENDICES

I. GENERAL INTRODUCTION 1 Study Objectives 6 Abbreviations 6 Anatomical Abbreviations 6 Systematic History 7 Suprageneric Taxonomy 7 Poraspis 9 Locality and Age 11 Heterostracans from the MOTH Locality 16 Literature Cited 18

II. REVIEW OF PORASPIS KIAER (CYATHASPIDIDAE, PORASPIDINAE) AND A DESCRIPTION OF NEW PORASPIDINE TAXA FROM THE LOWER DEVONIAN MOTH LOCALITY, NORTHWEST TERRITORIES, CANADA Introduction 28 Anatomical Terminology 28 Dorsal Shield Measurements 30 Locality and Age 32 Materials and Methods 36 Fossil Materials 36 Preparation of Specimens 36 Photography, Illustration, and Measurement 37 Abbreviations 37 Institutional and Locality Abbreviations 37 Measurement Abbreviations 37 Systematic Paleontology 38 Poraspidinae 38 Poraspis 39 Poraspis sericea 42 Poraspis rostrata 43 Poraspis cf. P. rostrata 46 Poraspis sturi 51 Poraspis pompeckji 54 Poraspis siemiradzkii 55 Poraspis simplex 56 Poraspis barroisi 56 Poraspis polaris 58 Poraspis cf. P. polaris 62 Poraspis heintzae 65 Poraspis brevis 65 Poraspis cracens 67 Poraspis thules 67 Poraspis parmula 68 Poraspis sp. nov. A 69 Poraspis sp. nov. B 72 Poraspis sp. nov. C 75 Poraspis sp. nov. D 77 Poraspis sp. indet. 80 Discussion 82 Growth and Variation in Size 82 Dorsal Shield Measurements as Diagnostic Characters 85 Ornamentation 88 Conclusions 90 Literature Cited 91

PHYLOGENETIC ANALYSIS OF PORASPIDINAE Introduction 106 Materials and Methods 108 Abbreviations 109 Institutional and Locality Abbreviations 109 Results 109 Phylogenetic Analysis of Genus Poraspis 109 Phylogenetic Analysis of Subfamily Poraspidinae 114 Discussion 117 Phylogenetic Analysis of Genus Poraspis 117 Phylogenetic Analysis of Subfamily Poraspidinae 118 General Discussion 119 Conclusions 120 Literature Cited 121

EVOLUTIONARY HISTORY OF PORASPIDINAE Introduction 130 Abbreviations 131 Institutional and Locality Abbreviations 131 Regional Abbreviations 131 Species Abbreviations 131 Geographic and Temporal Distribution of Poraspidines 132 Trends in Poraspidine Evolution 139 Paleoenvironment of Poraspidines 144 Conclusions 147 Literature Cited 148

CONCLUSIONS Conclusions 154 Literature Cited 156 LIST OF TABLES

Pa2e Table Caption

(31) TABLE 2.1. Terminology of measurements of the dorsal and ventral shields used in the current and previous studies of poraspidines.

(34) TABLE 2.2. Measurements (in mm) of the dorsal shields of specimens of Poraspis from the MOTH locality used in the current study.

(35) TABLE 2.3. Indices derived from measurements (in mm) of the dorsal shields of specimens of Poraspis from the MOTH locality.

(52) TABLE 2.4. Measurements (in mm) of the ventral shields of specimens of Poraspis from the MOTH locality used in the current study.

(142) TABLE 4.1. Median and pineal lengths of the dorsal shield of specimens of Poraspis polaris from Spitsbergen and the MOTH locality. LIST OF FIGURES

Page Figure Caption

(4) FIGURE 1.1. Reconstruction of Poraspis showing the nomenclature of the different components of the dermoskeleton.

(5) FIGURE 1.2. Morphology of the dorsal shield of Poraspis.

(12) FIGURE 1.3. Map indicating general location of the MOTH locality in the Mackenzie Mountains of the Northwest Territories, Canada, UALVP 129. Equivalent to GSC locality 69014 and lies in Unit 10 of Section 43 of Gabrielse et al. (1973).

(33) FIGURE 2.1. Measurements used on the dorsal shields of poraspidines.

(44) FIGURE 2.2. Poraspis rostrata. A, UALVP 41398; B, UALVP 41876.

(47) FIGURE 2.3. Poraspis cf. P. rostrata. A, UALVP 32744; B, UALVP 47059.

(48) FIGURE 2.4. Poraspis cf. P. rostrata. A, UALVP 32881; B, UALVP 41359.

(59) FIGURE 2.5. Poraspispolaris. A, UALVP 23394; B, UALVP 23436; C, UALVP 32783.

(60) FIGURE 2.6. Poraspis polaris. A, UALVP 32785; B, UALVP 41423; C, UALVP 47060.

(63) FIGURE 2.7. Poraspis cf. P. polaris. A, UALVP 41382; B, UALVP 43053; C, UALVP 43054; D, UALVP 47064.

(70) FIGURE 2.8. Poraspis sp. nov. A. UALVP 49532. A, dorsal view; B, ventral view.

(73) FIGURE 2.9. Poraspis sp. nov. B. A, UALVP 32886; B, UALVP 45941; C, UALVP 47062.

(76) FIGURE 2.10. Poraspis sp. nov. C. UALVP 43232.

(78) FIGURE 2.11. Poraspis sp. nov. D. UALVP 41426.

(81) FIGURE 2.12. Poraspis sp. indet. UALVP 32820. (110) FIGURE 3.1. Possible phylogeny of Genus Poraspis. 50% majority-rule tree generated from results of heuristic search. Percentages of agreement are indicated on each branch.

(112) FIGURE 3.2. Possible phylogeny of Genus Poraspis. 50% majority-rule tree generated from results of branch and bound search. Percentages of agreement are indicated on each branch.

(113) FIGURE 3.3. Possible phylogeny of Genus Poraspis. Strict consensus tree generated from results of both heuristic and branch and bound searches.

(115) FIGURE 3.4. Possible phylogeny of Subfamily Poraspidinae. 50% majority-rule tree generated from results of heuristic search. Percentages of agreement are indicated on each branch.

(116) FIGURE 3.5. Possible phylogeny of Subfamily Poraspidinae. 50% majority-rule tree generated from results of branch and bound search. Percentages of agreement are indicated on each branch.

(133) FIGURE 4.1. Geographic and stratigraphic occurrence of poraspidines.

(138) FIGURE 4.2. Paleogeographic distribution of the genus Poraspis in the early Devonian.

(141) FIGURE 4.3. Median length vs. pineal length of the dorsal shields of specimens of Poraspis polaris from Spitsbergen and the MOTH locality. LIST OF APPENDICES

Page Appendix Title

(104) I List of Specimens Examined in Present Study

(124) II Characters and Character State Descriptions for the Phylogenetic Analysis of Genus Poraspis

(126) III Character State Matrix for the Phylogenetic Analysis of Genus Poraspis

(127) IV Characters and Character State Descriptions for the Phylogenetic Analysis of Subfamily Poraspidinae

(129) V Character State Matrix for the Phylogenetic Analysis of Subfamily Poraspidinae I. GENERAL INTRODUCTION

A common component of Silurian and Devonian fossil faunas is aquatic jawless vertebrates, or agnathans. Agnathans represent the earliest, most primitive vertebrates, which radiated into many groups, exhibiting a wide diversity of morphologies and lifestyles. An exceptional locality in the southwestern portion of the Northwest Territories of Canada, the Man On The Hill (MOTH) locality, has produced a variety of extremely well-preserved agnathans. Among these are numerous representatives of Subfamily Poraspidinae: anatomically simple, small, and inconspicuous fossils representing members of the clade Heterostraci.

Poraspidines are commonly known from Lower Devonian agnathan faunas in the

Northern Hemisphere, yet their relationships and evolutionary history remain poorly understood. Specimens from the MOTH locality make a valuable contribution to our knowledge of this group of ancient vertebrates, in terms of their morphology, geographic range, relationships, and distribution through time.

The clade Heterostraci encompasses a wide range of extinct jawless vertebrates. The earliest definite heterostracan fossils are found in rocks of the

Early Silurian (Early Wenlock, approximately 435 million years ago), with the latest representatives from the Late Frasnian (approximately 367 million years ago). Throughout this interval, heterostracans are known mainly from North

America, northern Europe, Russia, and Ukraine. The single best synapomorphy of the group is the presence of a single pair of branchial openings on either side of the dermal armor of the cephalic region, though it can be argued that

1 holocephalians, osteichthyans, and the extant hagfish Myxine also possess a single pair of common branchial openings (Janvier, 1996). The dermoskeleton of heterostracans is composed of dentine and aspidine, and is acellular, a characteristic shared with astraspids (Janvier, 1996). Other characters shared with astraspids and arandaspids include median dorsal and ventral dermoskeletal shields that cover the anterior portion of the body, oak-leaf shaped tubercles of the dermal ornament (primitively), and the fan-shaped arrangement of oral plates

(though oral structure is poorly known in many heterostracan taxa). Additional dermoskeletal elements included paired branchial, orbital or suborbital, and lateral plates, and in some taxa pineal, cornual, rostral, and other plates may be present.

The posterior portion of the body was covered with numerous bony scales. These organisms lacked paired fins and possessed no median fins apart from the caudal fin. The sensory canal system opens externally through pores on the dorsal and ventral shields and scales. The endoskeleton is extremely poorly known, with the only evidence being from impressions on the internal surface of the dorsal shields of some specimens (Janvier, 1996).

The heterostracan subfamily Poraspidinae has proven problematic for paleontologists, and hindered our understanding of the evolution and interrelationships of early vertebrates. Subfamily Poraspidinae is comprised of derived members of the heterostracan family Cyathaspididae, which (according to the classification of Denison, 1964) also includes the subfamilies Cyathaspidinae,

Tolypelepidinae, Irregulareaspidinae, and Ctenaspidinae. Cyathaspidids are characterized by a fusiform body shape (Janvier, 1996), and the anterior

2 dermoskeleton consists of dorsal and ventral shields, oral plates in a subterminal mouth, and paired suborbital, lateral, and branchial plates, but no rostral, cornual, or dorsal spine plates (Fig. 1.1; Denison, 1964). The anatomy of the dorsal shield is illustrated in Fig. 1.2. Posteriorly, the dermoskeleton consists of dorsolateral, ventrolateral, and dorsal and ventral median scale rows (Denison, 1964).

Characteristic features of Poraspidinae include largely longitudinal dentine ridges on the dorsal and ventral shields, the lack of evident scale components on the shields, and a well-developed lateral line system (Elliott et al., 1998; Kiaer, 1932).

The genus Poraspis is known from the District of Mackenzie, the Canadian

Arctic, Spitsbergen, and both western and eastern Europe (Elliott et al., 1998).

Due to the deficiency of associated body parts in the fossil record, the relationships within this clade are poorly known (Blieck and Heintz, 1983; Elliott et al., 1998; Janvier, 1996). However, though these fossils are relatively common in some localities and have been utilized in biostratigraphy (Elliott et al., 1998), they have often been overlooked by previous workers, particularly with respect to evolutionary relationships. Further examination of these specimens and their localities will provide valuable insight to the origin and earliest radiation of these jawless vertebrates.

3 FIGURE 1.1. Reconstruction of Poraspis showing the nomenclature of the different components of the dermoskeleton. Lateral view. For abbreviations, see Anatomical Abbreviations on p. 6. r

pblb

FIGURE 1.2. Morphology of the dorsal shield of Poraspis. Dorsal view. For abbreviations, see Anatomical Abbreviations on p. 6.

5 STUDY OBJECTIVES

This work sets out to examine and revise the current understanding of poraspidine taxonomy, phylogeny, and paleobiogeography in light of new specimens from the MOTH locality in the Northwest Territories, Canada. At least

6 species of Poraspis are present at MOTH, including four previously unknown forms, which are here described for the first time. The diagnoses of currently recognized species of Poraspis are revised, and their systematic history is reviewed. Problems associated with poraspidine classification are discussed, such as growth, taphonomy, and variation. Cladistic analyses are performed for the first time on the genus Poraspis and the subfamily Poraspidinae. The paleobiogeography of poraspidines is reviewed, and the paleoenvironment and trends in morphological evolution are considered and discussed.

ABBREVIATIONS

Anatomical Abbreviations—bo, branchial opening; bp, branchial plate; bs, branchial sinus; dls, dorsal lateral scale; ds, dorsal shield; lp, lateral plate; mds, median dorsal scale; mlb, median lobe; mvs, median ventral scale; o, orbit; oc, oral cover; on, orbital notch; op, oral plate; pblb, postbranchial lobe; pm, pineal macula; pop, preorbital process; r, rostrum; ra, rostral area; sop, suborbital plate; vis, ventral lateral scale; vs, ventral shield.

6 SYSTEMATIC HISTORY

Suprageneric Taxonomy

The genus Poraspis Kiaer has been classified in several different ways since its inception. Kiaer (1930, 1932) and Kiaer and Heintz (1935) classified it within Order Heterostraci, Suborder Cyathaspida, Tribe Poraspidei, and Family

Poraspidae. Alternatively, Zych (1931) placed Poraspis in Class Ostracodermi,

Subclass Pteraspidomorphi, Order Heterostraci, Suborder Pteraspida, Family

Cyathaspidae, and Subfamily Palaeaspinae. White (1935, 1946) adapted Kiaer's classification, using Family Palaeaspidae as a synonym to Tribe Poraspidei Kiaer.

Romer (1945) recognized Family Poraspidae as separate from Cyathaspidae, but later he no longer recognized Poraspidae and placed Poraspis within

Cyathaspidae (1966).

Denison (1953) took a different approach, classifying Poraspis within

Order Heterostraci, Family Cyathaspidae (as defined by Kiaer, 1932), and established the new rank of Subfamily Poraspinae (as equivalent to Palaeaspinae

Zych). In a later systematic revision (Denison, 1964), he instead used the names

Family Cyathaspididae, and Subfamily Poraspidinae. Numerous others adopted

Denison's classification system (Broad, 1969; Broad and Dineley, 1973; Dineley and Loeffler, 1976; Elliott et al., 1998; Elliott and Dineley, 1985, 1991; Elliott et al., 1998).

Berg (1940, 1955) introduced a new classification, with Poraspis placed within Class Pteraspides (=Heterostraci), Order Cyathaspidiformes, Suborder

7 Poraspidoidei, and Family Poraspidae. Some genera currently recognized as closely allied with Poraspis were placed in separate families (Palaeaspidae,

Americaspidae, and Anglaspidae) within Poraspidoidei, along with some other taxa not currently thought to be as closely related (Dinaspidae, Dictyonaspidae, and Ctenaspidae). Stensio (1958, 1964) utilized the unranked group

Cyathaspidiformes (equivalent to that of Berg, 1940) and Order Cyathaspida, but refused to subdivide the group further, citing a lack of taxonomically informative information. Obruchev (1967) assigned Poraspis to Subclass Heterostraci (as equivalent to Pteraspides), Order Cyathaspidida, and Family Poraspididae.

Tarlo (1962) revised the ranking system used, instituting Order

Cyathaspidiformes (as equivalent to Suborder Cyathaspida Kiaer), Suborder

Poraspidida (as equivalent to Tribe Poraspidei Kiaer, Family Palaeaspidae White,

Palaeaspinae Zych, Poraspidoidei Berg, and Poraspinae Denison), and Family

Poraspididae (which Tarlo referenced as originating with Kiaer (1932), but that publication used the term Poraspidae). The same author (who used the surnames

Tarlo, Halstead Tarlo, and Tarlo) continued to use this classification scheme (e.g.

Halstead, 1973), even after the proposal of alternative systems. Novitskaya (1986,

2007) placed Poraspis in Order Cyathaspidiformes, Family Poraspididae, but did not mention Tarlo's (1962) Suborder Poraspidida.

Blieck and Heintz (1983) proposed another classification system, with

Poraspis falling under Order Cyathaspidiformes (as equivalent to Family

Cyathaspididae of Denison), Superfamily Poraspidoidea (as equivalent to Tribe

Poraspidei Kiaer and Tribe Poraspidoidei Berg), and Family Poraspididae (as

8 equivalent to Family Poraspidae Kiaer and Subfamily Poraspidinae Denison).

This system was utilized by Bardenheuer and Otto (1994). Carroll (1988) placed

Poraspis in Family Cyathaspididae under the umbrella of Order Heterostraci.

Janvier (1996) used the rankings Cyathaspidiformes and Cyathaspida to classify

Poraspis, but did not go into further detail of classification.

Here, Poraspis is included in Family Cyathaspididae, Subfamily

Poraspidinae, along with Anglaspis Jaekel, 1927, Homalaspidella Strand, 1934,

Allocryptaspis Whitely, 1940, Americaspis White and Moy-Thomas, 1941,

Liliaspis Novitskaya, 1972, Boothiaspis Broad, 1973, Torpedaspis Broad and

Dineley, 1973, and Alainaspis Elliott and Dineley, 1985.

Poraspis

The type species of the genus Poraspis is Holaspis sericeus Lankester

(1873). However, the genus Holaspis was preoccupied (Gray, 1863), and

Woodward (1891) included the species in Palaeaspis Claypole, 1892, along with

P. americana. Kiaer (1930) proposed that the American and European species of

Palaeaspis be separated from one another, and that the new genus Poraspis be established to include Holaspis sericeus Lankester, Cyathaspis sturi von Alth,

Cyathaspis barroisi Leriche, and new species from Spitsbergen.

In 1932, the names of eight of the Spitsbergen Poraspis species recognized by Kiaer were listed in a posthumously published paper (Kiaer, 1932), and full descriptions of these and three additional Podolian species referred to

Poraspis were published three years later (Kiaer and Heintz, 1935). Kiaer and

9 Heintz (1935) also recognized two forms of Poraspis of differing relative width, termed the angusta and lata forms, and interpreted them as representative of the different sexes, with the differences in the width index being a secondary sexual characteristic. The presence of narrow and broad forms of the same type was also observed in other cyathaspidid and pteraspidid genera (Kiaer and Heintz, 1935).

Denison (1964) suggested that some of the Poraspis polar is specimens from Spitsbergen may have been subject to distortion by tectonism, and reported that the specimens appear to show continuous variation in width. This blurred the distinction between the previously recognized angusta and lata forms of Kiaer and Heintz (1935), and provided an alternate explanation for the variation observed.

Blieck and Heintz (1983) reduced the number of Poraspis species from

Spitsbergen from eight to three (P. sericea, P. magna, and P. brevis), based on overlap in morphological characteristics between recognized species. Eliminated species included P. magna, P. cylindrica, P. elongata, P. subtilis, and P. intermedia. They also thought that the European species P. barroisi (Leriche,

1906) and P. sturi (von Alth, 1874) should be synonymized with P. polaris

(Kiaer, 1930). In this case, the name P. sturi would have priority; however, Blieck and Heintz provisionally retained the name P. polaris for the Spitsbergen specimens, as they did not examine the type specimens of P. barroisi and P. sturi.

They also suggested that the Podolian species P. pompeckji be considered a synonym of P. rostrata, though they did not formally refer specimens of P. pompeckji to P. rostrata. Blieck and Heintz (1983) also rejected the idea of sexual

10 dimorphism in P. polaris and P. brevis in favor of individual variation or diagenetic/tectonic crushing and stretching as the cause of proportional differences. Blieck and Heintz's (1983) revisions oiPoraspis were accepted by

Elliott et al. (1998) in their description of four new Poraspis species from Prince of Wales and Somerset Islands in the Canadian Arctic.

Currently recognized species of Poraspis include the type species P. sericea (Lankester, 1873), as well as P. rostrata Kiaer and Heintz, 1935, P. pompeckji (Brotzen, 1933), P. heintzae Elliott, Loeffler, and Liu, 1998, P. polaris,

Kiaer, 1930, P. sturi (von Alth, 1874), P. barroisi (Leriche, 1906), P. cracens

Elliott, Loeffler, and Liu, 1998, P. thules Elliott, Loeffler, and Liu, 1998, P. parmula Elliott, Loeffler, and Liu, 1998, P. brevis Kiaer, 1932, P. siemiradzkii

(Zych, 1931), and P. simplex (Brotzen, 1933). Please refer to Chapter II for a summary of synonymy of currently recognized taxa.

LOCALITY AND AGE

The specimens under study were collected from the Man On the Hill

(MOTH) locality (UALVP Locality 129, 62° 33'N, 127° 45'W), which is situated in the central Mackenzie Mountains of the Canadian Northwest Territories on the southwest limb of the Grizzly Bear Anticline (Fig. 1.3). Located in the strata of the Lochkovian-Pragian (Lower Devonian) Delorme Group (Morrow and

Geldsetzer, 1988), the Lochkovian MOTH vertebrate-bearing horizon is roughly

11 FIGURE 1.3. Map showing the location of the MOTH (Man On The Hill) locality, UALVP Locality 129 (= GSC Locality 69014), southern Mackenzie Mountains, Northwest Territories, Canada. Modified from Brock University Map Library. 2001. Canada (no names). Available from Brock University Map Library Controlled Access http://www.brocku.ca/maplibrary/images/canadaNONAMES.pdf. (Accessed May 25, 2008).

12 equivalent to the Geological Survey of Canada's locality GSC 69014, and lies within Unit 10 of Section 43 of Gabrielse et al. (1973). Fossils have been collected at this locality by a series of University of Alberta field parties from

1983-2002, and a spectacular fauna of early vertebrates has been produced, reminiscent of the diversity if not the adaptations of modern reef communities.

The MOTH locality produces an abundant but low diversity assemblage of articulate and inarticulate brachiopods, ostracods, and rare eurypterids (Dineley and Loeffler, 1976), and the vertebrate fauna includes approximately 65 species, comprised of heterostracans, thelodonts, osteostracans, acanthodians, putative chondrichthyans, and a single placoderm species (Wilson et al., 2000, Hawthorn et al., in press). Many specimens are fragmentary, but nearly all are exquisitely preserved. Cryptic bioturbation is also abundant at the site (Zorn et al., 2005).

Gabrielse et al. (1973) described Unit 10 of Section 43 as a transitional facies between the basinal shales of the underlying Road River Formation and the carbonates of the overlying Delorme Formation, and characterized the vertebrate- bearing MOTH horizon as a shaly and pyritiferous laminated dolomite. Dineley and Loeffler (1976) accepted this description.

Dineley and Loeffler (1976) interpreted the MOTH locality as a hyposaline lagoon, with episodically anaerobic conditions indicated by the presence of pyrite and the alternation of light and dark laminae. They also cited the apparent lack of bioturbation as supporting the hypothesis that the bottom waters were commonly inhospitable to benthic fauna, and the vertebrate fauna

13 was interpreted as restricted to areas of freshwater or marginal marine conditions, consistent with the interpretation of the site as lagoonal.

Adrain and Wilson (1994) recognized the strata at MOTH as a marine laminated limestone with a minor argillaceous component, as the matrix dissolved readily in dilute acetic acid. The laminae range in thickness from <1 mm to >10 mm (Adrain and Wilson, 1994; Wilson and Caldwell, 1998), with light layers tending to be thicker than the dark. Vertebrate fossils were recognized as unequally distributed and more frequently associated with the dark laminae

(Adrain and Wilson, 1994).

Wilson and Caldwell (1998) were first to propose an interpretation of the

MOTH locality as open marine. Hanke (2001, 2002) expanded on the marine hypothesis, interpreting the shaly limestones to represent deepwater deposits in a distal carbonate platform setting below a storm wave base of approximately 100-

200 m. The presence of pyrite, lack of scavenging and established benthic fauna, and high frequency of articulated specimens supported rapid sedimentation

(Hanke, 2001, 2002). The data examined by Hanke (2001, 2002) provided no support for long-term hypoxia.

Zorn et al. (2005) provided a reinterpretation of the MOTH locality. The study utilized materials in the UALVP collections and sedimentological data from a single section. Individual specimens of Nahanniaspis and Dinaspidella in the

UALVP collections were classified as articulated or disarticulated, the distance from the main carcass and rotation from life position was measured for each element, and counts for the occurrence of each taxon in light and dark layers were

14 made. The degree of disarticulation of ostracods was also noted. A 6 m-long core­ like section of the vertebrate-bearing section from MOTH was sampled at six intervals for petrographic and chemical analysis. X-ray diffraction was used to determine the major mineralogical constituents of the samples, and two thin sections were made per sample for lithological analysis as well as microprobe analysis to examine crystal composition and create elemental distribution maps.

Zorn et al. (2005) examined vertebrate and invertebrate fossils, ichnofossils, petrographic and chemical analyses, mineralogy, lithology, and elemental distribution. The authors proposed three possible depositional models: a supratidal-intertidal tide pool, a subtidal back-reef lagoon with distal deltaic sedimentation, and an intra-shelf topographic low below storm wave base. The favored interpretation was that of the intra-shelf topographic low (Zorn et al.,

2005). This model was supported by the recharacterization of the lithology at

MOTH as interlaminated argillaceous limestone and calcareous shale and the absence of wave- or current-derived sedimentary structures. The presence of silica as evidence for a duality of depositional sources is also consistent with this model.

The hypothesis of restricted circulation resulting in an environment stressed in oxygen and salinity is supported by the presence of pyrite, the abundance of low- diversity cryptic trace fossils, and the excellent quality of preservation (Zorn et al., 2005). Fine-grained parallel laminae and articulated valves of leperditiid ostracods also support a low-energy setting, and the ostracod valves likely accumulated within the topographic low.

15 Biostratigraphic correlation with standard invertebrate taxa has not been conducted for the MOTH locality (Wilson and Caldwell, 1998; Zorn et al., 2005), and the age of the site is assumed based mainly on the vertebrate taxa present.

Adrain and Wilson (1994) assigned the age based on the presence of the

Lochkovian osteostracan Waengsjoeaspis, the pteraspidid Canadapteraspis, and the placoderm Romundina, as well as the occurrence of Lower Devonian brachiopods 150 m below the vertebrate-bearing strata. Hanke (2001) cited the presence of the putative chondrichthyans Altholepis composita, Polymerolepis whitei, and Seretolepis elegans as further supporting the Lochkovian age of the locality.

HETEROSTRACANS FROM THE MOTH LOCALITY

There are currently seven named heterostracan species known from the

MOTH locality (Wilson et al., 2000). The only named species of pteraspidid is

Canadapteraspis alocostomata Dineley and Loeffler, while the cyathaspidids are currently represented by Dinaspidella elizabethae Blieck and Heintz,

Nahanniaspis mackenziei Dineley and Loeffler, Pionaspis amplissima Dineley and Loeffler, and specimens referred to Poraspis cf. polaris and Poraspis sp. indet. by Dineley and Loeffler (1976). Other heterostracans present in the MOTH fauna include the problematic forms Aserotaspis canadensis Dineley and Loeffler,

Lepidaspis serrata Dineley and Loeffler, and four tessellate species described in

16 an unpublished M. Sc. thesis by Greeniaus (2004). In addition to these species, there are thought to be several unnamed species of both pteraspidids (James,

2006) and cyathaspidids (Wilson et al., 2000).

17 LITERATURE CITED

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(Vertebrata: Osteostraci: Comuata) from the Southern Mackenzie Mountains,

N.W.T., Canada. Journal of Vertebrate Paleontology 14:301-319.

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Versteinerungen. Abhandlungen der Kaiserlich-koniglichen geologischen

Reichsanstalt, Vienna 7:77 pp.

Bardenheuer, P., and M. Otto. 1994. Erste Cyathaspiden-Reste (Agnatha,

Heterostraci) aus dem Rheinischen Unterdevon. Geologisch Jarbuch Hessen

122:5-11.

Berg, L. S. 1940. Classification of fishes both recent and fossil, 1st Edition.

Traveaux de l'lnstitut Zoologique de l'Academie des Sciences de l'URSS 5:87-

517. [Reprinted in 1965 by the Document Reproduction Unit of the Thai

Documentation Centre, Applied Scientific Research Corporation on Thailand,

Bangkok].

Berg, L. S. 1955. Classification of fishes both recent and fossil, 2nd Edition.

Traveaux de l'lnstitut Zoologique de l'Academie des Sciences de l'URSS 20:1—

286 [Russian].

18 Blieck, A., and N. Heintz. 1983. The cyathaspids of the Red Bay Group (Lower

Devonian) of Spitsbergen. XIII. Polar Research, 1 (NS):49-74.

Broad, D. S. 1969. Lower Devonian Heterostraci from the Peel Sound Formation,

Prince of Wales Island, Northwest Territories. Unpublished M.Sc. Thesis,

University of Ottawa. 138 pp.

Broad, D. S. 1973. Amphiaspidiformes (Heterostraci) from the Silurian of the

Canadian Arctic Archipelago. Bulletin of the Geological Survey of Canada

222:35-50.

Broad, D. S., and D. L. Dineley. 1973. Torpedaspis, a new Upper Silurian and

Lower Devonian genus of Cyathaspididae (Ostracodermi) from Arctic Canada.

Bulletin of the Geological Survey of Canada 222:53-91.

Brotzen, F. 1933. Die Silurischen und Devonischen fischvorkommen in

Westpodolien I. Palaeobiologica 5:423^166.

Carroll, R. L. 1988. Vertebrate Paleontology and Evolution. W. H. Freeman and

Company, New York, 698 pp.

19 Claypole, E. W. 1892. On the structure of the American pteraspidian, Palaeaspis

(Claypole); with remarks on the family. Quarterly Journal of the Geological

Society 48:542-561.

Denison, R. H. 1953. Early Devonian fishes from Utah. Part II. Heterostraci.

Fieldiana: Geology 11:291-355.

Denison, R. H. 1964. The Cyathaspididae: a family of Silurian and Devonian jawless vertebrates. Fieldiana, Geology 13:309—473.

Dineley, D. L., and E. J. Loeffler. 1976. Ostracoderm faunas of the Delorme and associated Siluro-Devonian Formations, North West Territories, Canada.

Palaeontological Association Special Papers in Palaeontology 18:1-214.

Elliott, D. K., and D. L. Dineley. 1985. A new heterostracan from the Upper

Silurian of Northwest Territories, Canada. Journal of Vertebrate Paleontology

5:103-110.

Elliott, D. K., and D. L. Dineley. 1991. Additional information on Alainaspis and

Boothiaspis, cyathaspidids (Agnatha: Heterostraci) from the Upper Silurian of

Northwest Territories, Canada. Journal of Paleontology 65:308-313.

20 Elliott, D. K., E. J. Loeffler, and Y. Liu. 1998. New species of the cyathaspidid

Poraspis (Agnatha: Heterostraci) from the Late Silurian and Early Devonian of

Northwest Territories, Canada. Journal of Paleontology 72:360-370.

Gabrielse, H., S. L. Blusson, and J. A. Roddick. 1973. Geology of Flat River,

Glacier Lake and Wrigley Lake map areas, District of Mackenzie, Northwest

Territories. Geological Survey of Canada, Memoirs 366:1-268.

Gray, J. E. 1863. Descriptions of two new genera of lizards (Holaspis and

Poriodogaster A. Smith, MS.). Proceedings of the Zoological Society of London

1863:152-155.

Greeniaus, J. W. 2004. Description of Devonian tessellate heterostracans from the

Northwest Territories, Canada and the growth of Lepidaspis. Unpublished M.Sc.

Thesis, University of Alberta. 119 pp.

Halstead, L. B. 1973. The heterostracan fishes. Biological Reviews 48:279-332.

Hanke, G. F. 2001. Comparison of an early Devonian acanthodian and putative chondrichthyan assemblage using both isolated and articulated remains from the

Mackenzie Mountains, with a cladistic analysis of early gnathostomes.

Unpublished Ph.D. Thesis, University of Alberta. 566 pp.

21 Hanke, G. F. 2002. Paucicanthus vanelsti gen. et sp. nov., an Early Devonian

(Lochkovian) acanthodian that lacks paired fin-spines. Canadian Journal of Earth

Sciences, 39:1071-1083.

Hawthorn, J. R., M. V. H. Wilson, and A. B. Falkenberg. In press. Development of the dermoskeleton in Superciliaspis gabrielsei (Agnatha: Osteostraci). Journal of Vertebrate Paleontology.

Jaekel, O. 1927. Der kopf der Wirbeltiere. Ergebnisse der Anatomie und

Entwichelungsgeschichte (III. Abteil der Zeitschrift die Gesamte Anatomie)

27:815-974.

James, M. 2006. Pteraspid fauna of MOTH, Mackenzie Mountains, NWT.

Unpublished B.Sc. Honors Thesis, University of Alberta. 35 pp.

Janvier, P. 1996. Early Vertebrates. Clarendon Press, Oxford, 393 pp.

Kiaer, J. 1930. Ctenaspis, a new genus of cyathaspidian fishes. Skrifter Svalbard

Ishavet33:l-7.

Kiaer, J. 1932. The Downtonian and Devonian vertebrates of Spitsbergen. IV.

Order Cyathaspida. Skrifter Svalbard Ishavet 52:7-26.

22 Kiaer, J., and A. Heintz. 1935. The Downtonian and Devonian vertebrates of

Spitsbergen. V. Suborder Cyathaspida. Part 1. Tribe Poraspidei, Family

Poraspidae Kiaer. Skrifter Svalbard Ishavet 40, 138 pp.

Lankester, E. R. 1873. On Holaspis sericeus and the relationships of the fish genera Pteraspis, Cyathaspis and Scaphaspis. Geological Magazine, London,

108, 10:241-245.

Leriche, M. 1906. Contribution a l'etude des poissons fossils du nord de la France et des regiones voisines. I. Les poissons Siluriens et Devoniens du nord de la

France. Memoires de la Societe de Nord 5:13-39.

Morrow, D. W., and H. H. J. Geldsetzer. 1988. Devonian of the East Canadian

Cordillera; pp. 106-131 in N. J. McMillan, A. F. Embry and D. J. Glass (eds.),

Devonian of the World, Vol. 1: Regional synthesis. Canadian Society of

Petroleum Geologists, Calgary.

Novitskaya, L. I. 1972. Phylogenetic relationships of poraspids (Heterostraci).

Paleontological Journal 6:382-388.

Novitskaya, L. I. 1986. Drevneishie bechelyustne SSSR, Geterostraki:

Tsiataspidy, Amphiaspidy, Pteraspidy. Trudy Paleontologicheskogo Instituta

Academii Nauk SSSR 219:27-75. [Only English translation seen: 1988. The

23 earliest Agnatha of the USSR, Heterostraci: Cyathaspidae, Amphiaspidae,

Pteraspidae. Geological Survey of Canada Translation 3230. Translated by the

Translation Bureau of the Multilingual Services Division, Department of the

Secretary of State, Canada].

Novitskaya, L. I. 2007. Evolution of generic and species diversity in agnathans

(Heterostraci: Orders Cyathaspidiformes, Pteraspidiformes). Paleontological

Journal 41:268-280.

Obruchev, D. V. 1967. Branch Agnatha, Class Diplorhina (Pteraspidomorphi),

Subclass Heterostraci; pp. 51-105 in Y. A. Orlov (ed.), Fundamentals of

Palaeontology: 11 Agnatha, Pisces. Israel Program of Scientific Translations,

Jerusalem.

Romer, A. S. 1945. Vertebrate Palaeontology, 2n Ed. 687 pp. University of

Chicago Press, Chicago.

Romer, A. S. 1966. Vertebrate Palaeontology, 3rd Ed. 468 pp. University of

Chicago Press, Chicago.

Stensio, E. A. 1958. Les cyclostomes fossiles ou ostracodermes; pp. 173-425 in

P. P. Grasse (ed.), Traite de Zoologie 13(1). Masson & Cie, Paris.

24 Stensio, E. A. 1964. Les cyclostomes fossiles ou ostracodermes; pp. 96-382 in J.

Piveteau (ed.), Traite de Paleontologie 4(1). Masson & Cie, Paris [English translation of pp. 358-374 also seen: 1985. Fossil cyclostomes or ostracoderms.

Translated by the Translation Bureau of the Multilingual Services Division,

Department of the Secretary of State, Canada].

Strand, E. 1934. Zoologische und palaontologische Ergebnisse von den Svalbard- und Eismeer-Untersuchungen Norwegens, II. Folia Zoologica et Hydrobiologica

5:326-330.

Tarlo, L. B. 1962. The classification and evolution of the Heterostraci. Acta

Palaeontologica Polonica 7:249-290.

White, E. I. 1935. The Ostracoderm Pteraspis Kner and the relationships of the agnathous vertebrates. Philosophical Transactions of the Royal Society of

London, Series B: Biology 225:381-457.

White, E. I. 1946. The genus Phialaspis and the 'Psammosteus limestones'.

Quarterly Journal of the Geological Society of London 101:207-242.

White, E. I., and J. A. Moy-Thomas. 1941. Notes on the nomenclature of fossil fishes, Part III, Homonyms M-Z. The Annals and Magazine of Natural History

(Geology) 7:395-400.

25 Whitely, G. 1940. The Nomenclator Zoologicus and some new fish names. The

Australian Naturalist 10:241-243.

Wilson, M.V. H., and M. W. Caldwell. 1998. The Furcacaudiformes: a new order of jawless vertebrates with thelodont scales, based on articulated Silurian and

Devonian fossils from Northern Canada. Journal of Vertebrate Paleontology

18:10-29.

Wilson, M. V. FL, G. F. Hanke, and K. L. Soehn. 2000. Diversity and age of the

Devonian vertebrate assemblage at MOTH, Mackenzie Mountains, Northwest

Territories, Canada; pp. 137-141 in A. Antoshkina, E. W. Malysheva and M. V.

H. Wilson (eds.), Pan-Arctic Palaeozoic tectonics, evolution of basins and faunas.

Ichthyolith Issues, Special Publication 6.

Woodward, A. S. 1891. Catalogue of the fossil fishes in the British Museum

(Natural History). Part II: Elasmobranchii (Acanthodii), Holocephali,

Ichthyodorulites, Ostracodermi, Dipnoi, and Teleostomi (Crossopterygii and

Chondrostean Actinopterygii). London, 567 pp.

Zorn, M. E., M. W. Caldwell, and M. V. H Wilson. 2005. Lithological analysis of the Lower Devonian vertebrate-bearing beds at the MOTH locality, N.W.T.,

Canada: insights to taphonomy and depositional setting. Canadian Journal of

Earth Sciences 42:763-775.

26 Zych, W. 1931. Fauna Ryb Dewonu i Downtonu Podola. Pteraspidomorphi:

Heterostraci. Czesc IA, Lwow, 91 pp.

27 II. REVIEW OF PORASPIS KIAER (CYATHASPIDIDAE,

PORASPIDINAE) AND A DESCRIPTION OF NEW PORASPIDINE

TAXA FROM THE LOWER DEVONIAN MOTH LOCALITY,

NORTHWEST TERRITORIES, CANADA

INTRODUCTION

The MOTH locality has produced numerous poraspidine specimens, some of which are attributable to previously known species, and others that represent new species of Poraspis. Subfamily Poraspidinae, the genus Poraspis, and currently recognized species of Poraspis are here reviewed. The treatment given here includes revised diagnoses together with synonymies of the different species and full descriptions of the new taxa. Seventeen species of Poraspis are described, including four new species. Problems associated with various diagnostic characteristics are discussed.

Anatomical Terminology

Poraspidine fossils are most commonly found as disassociated dermoskeletal elements. These organisms lacked paired fins and possessed no median fins apart from the caudal fin. The poraspidine body plan (Figs. 1.1, 1.2) is very similar to that of most other cyathaspidids. The dermoskeleton consists of a dorsal shield, a ventral shield, and paired branchial, orbital, and lateral plates.

The oral structure is presumed to be composed of numerous small plates that

28 project anteriorly from the margin of the ventral shield. The posterior portion of the organism is scale-covered, with several distinct rows of scale types covering the trunk region. These include median dorsal and ventral scale rows, paired dorsolateral scales, and ventrolateral scales. This organization appears to break down in the caudal region. All dermoskeletal elements are ornamented with fine dentinous ridges that run generally parallel to one another in an anterior-posterior direction.

The dorsal and ventral shields lack evidence of epitega or scale components, which are commonly seen in other cyathaspidid taxa such as

Archegonaspis (Denison, 1964; Novitskaya, 1986). Both shields are covered by a network of sensory canals and pores. Most diagnostic characters of the genus and the various included species are found on the dorsal shield. The pineal macula is located posterior to the orbits on the dorsal midline. Impressions of the internal structures can often be observed, including branchial impressions, the paired semicircular canals, the pineal organ, and the dorsal nerve cord. The ventral shield also bears impressions of the branchial pouches.

The oral structure is poorly understood in poraspidines. Stensio (1958,

1963, 1964) reconstructed Poraspis with two pairs of hypothetical tentacles, though there is no evidence of these structures in any fossil specimens representing the genus or any other cyathaspidids. Dineley and Loeffler (1976) reported a specimen (NMC 19860) of Poraspis cf. P. polaris from the Man On

The Hill (MOTH; UALVP 129, GSC 69014) with a ventrally located plate posterior to the maxillary brim of the dorsal shield and overlapped posteriorly by

29 the anterior edge of the ventral shield. Oral plates such as those seen in other poraspidines, including Anglaspis heintzi (Heintz, 1962; Denison, 1964) and possibly Allocryptaspis laticostata (Denison, 1960), were not observed in the specimen. This element seen in NMC 19860 was referred to as an "?oral plate" by

Dineley and Loeffler (1976), and interpreted to be the sole oral dermoskeletal element. It was interpreted to have acted as a single-element scoop, an idea supported by an unornamented area, interpreted to be abraded, on the anterior margin. Blieck and Heintz (1983) referred to this element as the "oral cover", and hypothesized the species to bear more typical poraspidine oral plates along its anterior margin. The unornamented surface, which resembles areas of contact with other dermoskeletal elements, was instead interpreted to represent an area of articulation with the small oral plates. Here, Blieck and Heintz's (1983) interpretation and reconstruction are accepted for P. polaris, although the oral cover is not known in other species ofPomspis.

Dorsal Shield Measurements

Dorsal shield measurements have been used extensively as diagnostic characters to differentiate between species of cyathaspidids (e.g. Kiaer and

Heintz, 1935; Denison, 1964; Blieck and Heintz, 1983; Elliott et al., 1998).

However, the terminology applied to the various measures has been inconsistent.

The synonymy of terms used for shield measurements is summarized in Table 2.1, and the abbreviations used in the current study are in the List of Abbreviations.

30 TABLE 2.1. Terminology of measurements of the dorsal and ventral shields used in the current and previous studies of poraspidines.

Current study Kiaer and Heintz Denison (1964) Blieck and Heintz (1935) (1983)

Measurements of the dorsal shield

BL - branchial Not measured Not measured LoB - branchial length length ML - median length L - length ML - median length LoT - total length

MW - maximum B - breadth W - maximum width laT - total width width OL - orbital length RL - rostral length OL - orbital length LoO - orbital length

OW - orbital width OB - orbital breadth OW - orbital width laO - orbital width

PBL - postbranchial Not measured PBL - postbranchial LpB - postbranchial length length length PL - pineal length PL-pineal length PL - pineal length LoP-pineal length

IBW - interbranchial Not measured Not measured Not measured width

Measurements of the ventral shield

VML- median Not measured Not measured Not measured length VMW- maximum Not measured Not measured Not measured width

31 The comparison of measurements to one another has also been approached differently by different authors. For example, the breadth-width index of Kiaer and Heintz (1935) was obtained by taking the maximum width as a percentage of the median length. Alternatively, Denison (1964) used ratios to compare different measurements, and this approach has been followed in the current study. Here, indices are used: each index is generated by dividing the specific measurement by the median length of the dorsal shield, and is represented by a decimal value. The measurements used in the present study are illustrated in Fig. 2.1, the measurements of the dorsal shields of specimens from MOTH are presented in

Table 2.2, and the indices generated from these measurements are found in Table

2.3.

LOCALITY AND AGE

The MOTH locality is stratigraphically located within the Delorme Group

(Morrow and Geldsetzer, 1988) and is composed of strata of Lochkovian (Early

Devonian) age (Wilson and Caldwell, 1998; Soehn et al., 2000). The locality is situated in the Mackenzie Mountains, western Northwest Territories, Canada. For more details see Chapter I.

32 •BL

MLH

•PBL

FIGURE 2.1. Measurements used on the dorsal shields of poraspidines. For abbreviations, see Measurement Abbreviations on p. 37. For equivalent measurements in previous studies, see Table 2.1.

33 TABLE 2.2. Measurements (in mm) of the dorsal shields of specimens of Poraspis from the MOTH locality used in the current study; indicates an estimated value, and ? indicates an unknown value. For abbreviations, see Measurement Abbreviations on p. 37.

Specimen # Identification ML MW PL OL BL PBL OW IBW Ridges/mm

UALVP 41398 P. rostrata 50.61 26.51 11.41 7.56 32.35 18.26 15.35 23.39 6-8 UALVP 41876 P. rostrata 50.92 26.78 12.35 7.57 33.08 17.84 16.66 25.01 6-9 UALVP 32744 Poraspis cf. P. rostrata ? ? 13.68 11.09 ? ? 18.83 ? 6-7 UALVP 32881 Poraspis cf. P. rostrata 45.6* 26.57 ? ? 33.16* 12.44 16.90 23.95 7-9 UALVP 47059 Poraspis cf. P. rostrata 46.58 22.93 ? 6.49 29.24 15.30 15.06 20.19 7-8 UALVP 23394 P. polaris 38.80 21.62 9.68 6.54 27.64 11.16 ? 18.24 7-9 UALVP 23436 P. polaris 39.04 22.54 9.22 6.28 26.48 12.56 14.39 19.27 6-8 UALVP 32783 P. polaris ? 22.28 9.69 6.63 26.69 ? 14.20 18.79 6-9 UALVP 32785 P. polaris 42.14 25.34 10.36 7.17 27.86 14.28 15.28 23.21 6-8 UALVP 41423 P. polaris ? 22.16 ? ? ? 12.56 13.73 19.33 7-8 UALVP 47060 P. polaris 42.12 27.72 10.99 8.70 27.24 14.88 17.86 24.71 5-7 UALVP 49532 P. sp. nov. A 36.00* ? ? ? 23.40* 12.60 ? ? 7-8 UALVP 32886 P. sp. nov. B 47.84 31.26 11.50 7.44 29.86 17.98 19.29 25.48 6-7 UALVP 45941 P. sp. nov. B 47.14 32.95 10.38 7.34 29.20 17.94 19.01 28.82* 5-8 UALVP 47062 P. sp. nov. B ? ? 11.82 5.99 ? ? ? ? 6-8 UALVP 43232 P. sp. nov. C 60.00* 27.67 ? ? 26.5* 33.25 17.57 26.33 8-10 UALVP 41246 P. sp. nov. D 55.00* 34.02 11.67 8.04 32.33 13.00* 21.15 32.38 5-6 TABLE 2.3. Indices derived from measurements (in mm) of the dorsal shields of specimens of Poraspis from the MOTH locality; Indicates the index is based on at least one estimated value, and ? indicates an unknown value. For abbreviations, see Measurement Abbreviations on p. 37.

Specimen # Identification MW/ML PL/ML OL/ML PBL/ML

UALVP 41398 P. rostrata 0.5238 0.2254 0.1494 0.3608 UALVP 41876 P. rostrata 0.5260 0.2425 0.1487 0.3504 UALVP 32744 Poraspis cf. P. rostrata ? ? ? ? UALVP 32881 Poraspis cf. P. rostrata 0.5827* ? ? 0.2728* UALVP 47059 Poraspis cf. P. rostrata 0.4773 0.26134 0.1932 0.3864 UALVP 23394 P. polaris 0.5572 0.2495 0.1686 0.2876 UALVP 23436 P. polaris 0.5774 0.2362 0.1609 0.3217 UALVP 32783 P. polaris ? ? ? ? UALVP 32785 P. polaris 0.6013 0.2458 0.1701 0.3626 UALVP 41423 P. polaris ? ? ? ? UALVP 47060 P. polaris 0.6581 0.2609 0.2066 0.3533 UALVP 49532 P. sp. nov. A ? 0.3500* ? ? UALVP 32886 P. sp. nov. B 0.6534 0.2404 0.1555 0.3758 UALVP 45941 P. sp. nov. B 0.6990 0.2202 0.1557 0.3806 UALVP 47062 P. sp. nov. B ? ? ? ? UALVP 43232 P. sp. nov. C 0.4612* ? ? 0.5542* UALVP 41246 P. sp. nov. D 0.6185* 0.2122* 0.1462* 0.2364* MATERIALS AND METHODS

Fossil Materials

The fossil specimens described in this study from the MOTH locality,

NWT, Canada, are housed in the University of Alberta Laboratory for Vertebrate

Paleontology (UALVP). The specimens were collected by a series of University of Alberta field parties between 1983 and 2002, initially led by Dr. Brian D. E.

Chatterton and later led by Dr. Mark V. H. Wilson. Specimens are generally disarticulated, and are preserved in varying degrees of completeness, with the majority of specimens being complete or near-complete dorsal shields. Nearly all of the specimens were collected from talus slopes sourced from the MOTH vertebrate-bearing layer. A small number of casts and peels of Spitsbergen specimens belonging to the UALVP collections were also examined in this study.

Please refer to Appendix I: List of Specimens Examined in Present Study.

Preparation of Specimens

Mr. Allan Lindoe prepared the vast majority of the MOTH specimens using a combination of acid dissolution and mechanical preparation techniques.

The author performed additional mechanical preparation. Specimens in need of stabilization were stabilized with cyanoacrylate glue or vinac dissolved in acetone.

36 Photography, Illustration, and Measurement

Photographs were taken with an Olympus SP-310 digital camera and edited using Adobe Photoshop CS2 version 9.0.2. Some illustrations received additional editing with Adobe Illustrator CS2 version 12.0.1. Measurements were taken using 15 cm Mastercraft electronic calipers with digital display accurate to

0.01 mm.

ABBREVIATIONS

Institutional and Locality Abbreviations—BM(NH), The Natural History

Museum, London; LithNIGRI, Lithuanian Research Institute for Geological

Prospecting; MOTH, Man On The Hill locality, Northwest Territories, Canada;

NMC, Canadian Museum of Nature (formerly National Museum of Canada),

Ottawa; PIN, Paleontological Institute, Russian Academy of Science; PMO,

Paleontologisk Museum, Oslo; UALVP, Laboratory for Vertebrate Paleontology,

University of Alberta, Edmonton.

Measurement Abbreviations—BL, branchial length of dorsal shield; IBW, interbranchial width of dorsal shield; ML, median length of dorsal shield; MW, maximum width of dorsal shield; OL, orbital length of dorsal shield; OW, orbital width of dorsal shield; PBL, postbranchial length of dorsal shield; PL, pineal

37 length of dorsal shield; VML, median length of ventral shield; VMW, median length of ventral shield.

SYSTEMATIC PALEONTOLOGY

AGNATHACope, 1889

HETEROSTRACI Lankester, 1868

CYATHASPIDIDAE Kiaer, 1932

PORASPIDINAE Kiaer, 1932

Revised Diagnosis—(After Novitskaya, 1986; Elliott and Dineley, 1991)

Epitega indicated faintly or not at all, scale components not evident; dentine ridges long and ridge pattern largely longitudinal, although commonly radiating on anterior parts of dorsal and ventral shields and diagonal on lateral parts of dorsal shield; orbits may be enclosed; branchial plates may be absent or fused to dorsal shield.

Included Genera—Poraspis Kiaer, 1930; Americaspis White and Moy-

Thomas, 1941; Homalaspidella Strand, 1934; Anglaspis Jaekel, 1927;

Allocryptaspis Whitley, 1940; Liliaspis Novitskaya, 1972; Boothiaspis Broad,

1973; Torpedaspis Broad and Dineley, 1973; Alainaspis Elliott and Dineley,

1985.

38 Remarks—In this revised diagnosis of Subfamily Poraspidinae, Ariaspis

Denison, 1963 is excluded. Denison (1964) included Ariaspis within

Poraspidinae, despite the prominent median scale visibly incorporated into the dorsal shield. Novitskaya (1986) also included Ariaspis in her Family Poraspidae

(=Subfamily Poraspidinae), with the qualifier in the diagnosis that this genus is an exception to the rule that vestiges of scales or tesserae not be visible in representatives of the group. More recently, Novitskaya (1994) excluded Liliaspis and Anglaspis from the poraspidines and placed these genera with the newly described Paraliliaspis Novitskaya, 1994 in Family Anglaspididae Kiaer, 1932.

Genus PORASPIS Kiaer, 1930

Holaspis Lankester, 1873:242, pi. 10 (preoccupied by Gray, 1863); Claypole,

1892:546,551.

Cyathaspis von Alth, 1874, pro parte:46; Leriche, 1906:22.

Palaeaspis (Lankester): Woodward, 1891:169; Stensio, 1926:1, fig. 6; Brotzen,

1933:431; White, 1935a:437.

Pteraspis {Cyathaspis): Zych, 1927:52, pis. 2.1, 2.2.

Palaeaspis {Poraspis) (Lankester): Zych, 1931:fig. 18.

Poraspis Kiaer, 1930:4; Kiaer, 1932:13; Kiaer and Heintz, 1935:51; Heintz,

1938:50; Save-Soderbergh, 1941:534; Holmgren, 1942:12; Flower and

Wayland-Smith, 1952:360; Wangsjo, 1952:562; Denison, 1953:293; Stensio,

1958:296; Denison, 1960:556; Denison, 1964:403; Novitskaya, 1972:fig. 1.2;

39 Novitskaya, 1975:figs. 4, 5; Dineley and Loeffler, 1976:75; Blieck and

Heintz, 1983:55; Novitskaya, 1986:21; Elliott et al., 1998:363.

Poraspis sp. Kiaer: Zych, 1931:pls. 8-10, 12, 13, 22; White, 1961:246; Denison,

1964:fig.91; Obruchev, 1967:fig. 4, 19; Novitskaya, 1983:fig. 1A, 34, 36, 64;

Novitskaya, 1986:27, pis. 3.5, 4.5; Novitskaya, 1992:fig. 4.2; Janvier,

1993:fig. 4.10D; Janvier and Blieck, 1993:fig. 3B; Bardenheuer and Otto,

1994:6, figs. 1,2.

Revised Diagnosis—(After Denison, 1964; Novitskaya, 1986) Rostral region narrowing in front of orbits, anterior border with median convexity; maxillary brim broad and covered with ridges parallel to the anterior edge.

Preorbital lobes of dorsal shield present. Postbranchial lobes of dorsal shield long relative to other poraspidine species. Posterior margins of dorsal and ventral shields bear pronounced median lobes. Dentine ridges fine and smooth-edged, 5—

11 per mm; ridge pattern generally longitudinal but may be fanned or irregular on rostrum and anterior triangle of dorsal shield, and parallel to lateral and anterior margins of dorsal shield. Epitega indicated faintly, if at all. Pineal macula usually distinct. Sensory pores visible.

Type Species—Holaspis sericens Lankester, 1873.

Included Species—P. sericea (Lankester, 1873); P. sturi (von Alth 1874);

P. barroisi (Leriche, 1906); P. polaris, Kiaer, 1930; P. siemiradzkii (Zych, 1931);

P. brevis Kiaer, 1932; P. simplex (Brotzen, 1933); P. pompeckji (Brotzen, 1933);

P. rostrata Kiaer and Heintz, 1935; P. heintzae Elliott, Loeffler and Liu, 1998; P.

40 cracens Elliott, Loeffler and Liu, 1998; P. thules Elliott, Loeffler and Liu, 1998;

P. parmula Elliott, Loeffler and Liu, 1998.

Remarks—The density of dentine ridges observed in Poraspis has been modified from previous diagnoses to reflect the measures observed by Blieck and

Heintz (1983) in P. polaris (5-9 ridges per mm) and P. rostrata (6-8 per mm).

The anterior border was previously described as having a "slight median convexity" (Denison, 1964), but the qualifier 'slight' has been removed from the diagnosis, as it is rather pronounced in some species. The description of the posterior median lobe as 'rounded' has also been excised from the diagnosis, as the degree of rounding varies greatly between species. The pineal macula has formerly been described as 'distinct' (Denison, 1964), but this is not the case in all Poraspis specimens. The description of the postbranchial lobes as 'strongly developed' has also been excluded from the diagnosis, as this is not observed in

P. sturi. The pores of the sensory canal system are of varying size in different specimens of Poraspis, and their description as 'large' has been removed. The smooth edges of the dentine ridges have been added to the diagnosis of Poraspis, in contrast to the crenulated edges observed in Anglaspis.

Blieck and Heintz (1983) have suggested that P. sturi and P. barroisi are likely con-specific, and should be synonymized with P. polaris, and that P. pompeckji should be synonymized with P. rostrata, but they did not formally synonymize these taxa. They are retained as separate taxa in the current study, as the type specimens (where designated) were not examined.

41 PORASPIS SERICEA (Lankester, 1873)

Holaspis sericeus Lankester, 1873:242, pi. 10.

Palaeaspis sericea: Woodward, 1891:169; Stensio, 1926:1, fig. 6.

Poraspis sericea: Kiaer, 1930:4; 1932:13; Kiaer and Heintz, 1935:98, figs. 6, 33-

35; Holmgren, 1942:9; White, 1950:56; Bystrow, 1955:488, figs. 16-18; Ball

and Dineley, 1961:202; Denison, 1964:408; Obruchev, 1967:fig. 8; Blieck and

Heintz, 1983:60, fig. 11; Novitskaya, 1983:fig. 33A; Elliott et al., 1998:363,

figs. 3.8,4.1.

Palaeaspis {Poraspis) sericea: Zych, 1931 :fig. 18.

Poraspis {Palaeaspis) sericea: White, 1935b: 179, figs. 3, 4.

Revised Diagnosis—(After Denison, 1964). Large Poraspis with broad dorsal shield 67-84.5 mm in length, OL/ML 0.18-0.2. Dentine ridges fan slightly in rostral area. Lateral line system complete with all branches united.

Holotype—BM(NH) P 4117, dorsal shield (Lankester, 1873:pl. 10).

Remarks—Poraspis sericea is fully described by Elliott et al. (1998). The orbital index used to diagnose this species has been adjusted to reflect the range of measurements reported in referred specimens by Elliott et al. (1998). The longitudinal arrangement of dentine ridges over most of the dorsal shield has been removed from the diagnosis, as this is characteristic of Poraspis. The width index has been excluded from the diagnosis, as the reliability of maximum width as a diagnostic character is doubtful (see Discussion topic 'Dorsal Shield

Measurements as Diagnostic Characters'). The density and flattened shape of the

42 dentine ridges have also been removed as diagnostic characters (see Discussion topic 'Ornamentation'). However, it should be noted that the density of dentine ridges used in the diagnosis of Elliott et al. (1998) does not accurately reflect the range of measurements reported in the same paper, and should have been 7-8 per mm as opposed to the 8 per mm used in the previous diagnosis.

PORASPISROSTRATA Kiaer and Heintz, 1935

(Figs. 2.2A, B)

Poraspis rostrata Kiaer, 1932:pls. 111.1-2 {nomen nudum).

Poraspis rostrata Kiaer and Heintz, 1935 proparte:figs. 27, 28, pis. 23-25, 39

(HOW pi. 24.1).

Poraspis cylindrica Kiaer and Heintz, 1935 pro parte:figs. 29, 30, pis. 27.2, 29.1

(non pi. 26.2).

Poraspis magna Kiaer, 1932:14 {nomen nudum).

Poraspis magna Kiaer and Heintz, 1935:92, figs. 31, 32, pis. 28, 29.2, 29.4, 38.2;

Save-Soderbergh, 1941:fig, 4; Denison, 1964:408.

Poraspis rostrata: Blieck and Heintz, 1983:59, fig. 10; Denison, 1964:407;

Blieck, 1976:pl. 9; Blieck, Goujet, and Janvier, 1987:figs.4.1, 4.2.

Revised Diagnosis—(After Blieck and Heintz, 1983) Relatively large species of

Poraspis with dorsal shield ranging from 50.5-61 mm in length, PL/ML from

0.22-0.31, OL/ML from 0.14-0.2, and PBL/ML from 0.35-0.44.

43 B

fjw^

-^ -^

FIGURE 2.2. Dorsal shield specimens of Poraspis rostrata from the MOTH locality. A, UALVP 41398; B, UALVP 41876. Dorsal view. Scale bar equals 10 mm. Holotype—PMO D 124, dorsal shield (Kiaer and Heintz, 1935:pls. 23 and

24.2; Blieck and Heintz, 1983:fig. 10a).

Referred Material from MOTH—UALVP 41398, 41876, dorsal shields

(Figs. 2.2a, b).

Remarks—Poraspis rostrata is fully described by Blieck and Heintz

(1983). Elliott et al.'s (1998) redescription of Poraspis sericea has necessitated setting maximum lengths of the measures used by Blieck and Heintz (1983) to diagnose Poraspis rostrata. The maximum length, pineal length, and postbranchial length of the dorsal shield were reported to be 61 mm, 16 mm, and

24 mm respectively. However, the pineal and postbranchial lengths have been excluded from the present diagnosis, and replaced by their indices relative to the median length, with PL/ML ranging from 0.22-0.31 and PBL/ML from 0.35-

0.44. The measure of OL/ML has also been added to the diagnosis (0.14-0.2).

The shortest maximum length of the dorsal shield has also been adjusted to 50.5 mm from 48 mm (Blieck and Heintz, 1983) to reflect the smallest measurement from a specimen currently referred to this species. Poraspis rostrata may be con- specific with P. pompeckji (Blieck and Heintz, 1983), but the two taxa are not formally synonymized.

The specimens from MOTH here referred to P. rostrata are among the smallest specimens representing this species. Measurements of the dorsal shields of UALVP 41398 and 41876 can be found on Table 2.2, and the indices derived from these measurements are presented in Table 2.3. The postbranchial lengths

(17.84-18.26 mm), pineal lengths (11.41-12.35 mm), and orbital lengths (7.56-

45 7.57 mm) of the dorsal shield in these specimens are somewhat shorter than reported in previously described specimens. The maximum width (26.51-26.78 mm) is relatively large in comparison with that of previously described specimens of P. rostra ta, considering that these specimens have some of the shortest median lengths.

PORASPIS cf. P. ROSTRATA Kiaer and Heintz, 1935

(Figs. 2.3A, B, 2.4A, B)

Referred Material from MOTH—UALVP 32744, 47059, dorsal shields

(Figs. 2.3A, B); UALVP 32881, dorsal shield and right branchial plate (Fig.

2.4A); UALVP 41359, ventral shield (Fig. 2.4B).

Locality and Age—MOTH locality, Mackenzie Mountains, Northwest

Territories, Canada; Lochkovian (Early Devonian); transitional facies between

Road River and Delorme Formations, Delorme Group.

Description—The median length of the dorsal shield of UALVP 32881 is estimated to be 45.6 mm. Due to the absence of the anterior-most portion of the rostrum, sufficiently precise measurements of the pineal and orbital lengths could not be made. The approximate PBL/ML calculated using the estimated ML is

0.27. Impressions of the semicircular canals can be seen on the dorsal shield. The density of the ornament of dentine ridges ranges from 7-9 per mm, and the ridges in the rostral area are largely longitudinal. There are 6-8 dentine ridges running parallel to the margin of the orbit. The median lobe of the dorsal shield is short and rounded. The right branchial plate is also present in UALVP 32881, though it

46 -J

FIGURE 2.3. Dorsal shield specimens of Poraspis cf. P. rostrata from the MOTH locality. A, UALVP 32744; B, UALVP 47059. Dorsal view. Scale bar equals 10 mm. B

00

FIGURE 2.4. Specimens of Poraspis cf. P. rostrata from the MOTH locality. A, UALVP 32881, dorsal shield and right branchial plate. Dorsal view; B, UALVP 41359, ventral shield. Ventral view. Scale bar equals 10 mm. is displaced, having rotated roughly 180° and shifted posteriorly. The branchial plate measures 24.9 mm in length, and its maximum height is approximately 4 mm (measured near the branchial opening). The density of the ornamentation over much of the branchial plate is 6-8 dentine ridges per mm, though in the vicinity of the branchial opening it is much more dense, up to 11 ridges per mm.

UALVP 32744 is incomplete, but is clearly a large specimen of Poraspis, as the preserved portion of the dorsal shield is approximately 50 mm in length along its median axis. A very rough estimate of the total median length of the specimen, if complete, would fall between 55 and 65 mm, possibly placing it among the largest known specimens of P. rostrata. Though a portion of the rostral area is not preserved, it appears as though the dentine ridge pattern in this area is largely longitudinal with slight fanning. Branchial and semicircular canal impressions are clearly observed on the dorsal shield. The orbital length is 11.09 mm, and as the posterior portion of the specimen is missing and no precise measurement of median length can be made, it is impossible to assess its relative length accurately.

UALVP 47059 has a median length of 46.58 mm. The OL/ML, PL/ML, and PBL/ML are respectively 0.14, 0.19, and 0.32. The pineal macula is not clearly observed in UALVP 47059, and may have occurred in a small area where the dentine ornamentation has not been preserved or has been damaged. The pattern of the dentine ridge ornament in the rostral area is largely longitudinal, though irregular in the posterior portion and in the area where the pineal macula is

49 expected to be observed. The median lobe of the dorsal shield is rounded, but appears more narrow and elongate than that of UALVP 32881.

UALVP 41359, an incomplete ventral shield, is estimated to have had a ventral median length of approximately 40 mm (based on the 37.05 mm preserved), and has a VMW of 21.03. The dentine ornament is regular and longitudinal, apart from two ridges at the anterior margin of the shield, and ranges from 6 to 7 ridges per mm in density. The anterior margin of the shield is fairly straight. Few sensory canal pores are visible due to the many small patches of poorly preserved dentine.

Remarks—The median lengths of the dorsal shields of UALVP 32881 and 47059 (roughly 45.6 mm and 46.58 mm, respectively) fall between the reported ranges fori3, rostrata (50.5-61 mm) and P. polaris (32^44 mm). The

PBL/ML of UALVP 32881 (0.27) falls below any previously reported proportions for P. rostrata (0.35-0.44) and just below the range known for Poraspis polaris

(0.28-0.44). However, this index is not perfectly reliable, as it is based on an estimate of total median length. These specimens seem to resemble most closely small specimens of P. rostrata, though they are smaller than any previously reported specimens.

UALVP 32144 is of a size in the range of the largest specimens assigned to P. rostrata. This specimen strongly resembles UALVP 40727 (cast of FMNH

PF 1142, cast of PMO D 203, the holotype ofPoraspis magna, which is now a junior synonym of Poraspis rostrata). UALVP 32744 is, unfortunately, rather incomplete, and therefore cannot be referred with confidence to P. rostrata.

50 The ventral shield, UALVP 41359, falls within the expected size range for a ventral shield of P. rostrata. The measurements of ventral shields assigned to

Poraspis from MOTH can be found in Table 2.4. However, the incompleteness and lack of association with a dorsal shield (as ventral shield characters diagnostic at the species level are questionable) prohibits referral of UALVP 41359 to P. rostrata here.

PORASPIS STURI (von Alth, 1874)

Cyathaspis sturi von Alth, 1874:46, pi. 5.1, 5.2; Zych, 1931:80.

"Pteraspis" (Cyathaspis) sturi: Zych, 1927:52, pi. 2.1, 2.2.

Poraspis sturi: Kiaer, 1932:14; Kiaer and Heintz, 1935:52, fig. 38; Balabai,

1956:figs. 4, 5; Balabai, 1961:4, figs.l, 2; Stensio, 1958:386; Denison,

1964:409; Novitskaya, 1986:22, fig. 2, pi. 2.5.

Palaeaspis sturi: Brotzen, 1936:6.

Revised Diagnosis—(After Denison, 1964; Novitskaya, 1986) Dorsal shield long and narrow, with median length of approximately 60 mm; branchial sinus weakly developed. Sensory canal pores doubled.

Holotype—Not designated.

Remarks—Poraspis sturi is fully described by Novitskaya (1986). As mentioned by Denison (1964), a specimen referred to this species by Zych

(1927:pl. 2.1) was not considered to be P. sturi by Kiaer and Heintz (1935).

However, the assignment of this specimen to P. sturi was accepted by Denison

51 TABLE 2.4. Measurements (in mm) of the ventral shields of specimens of Poraspis from the MOTH locality used in the current study; "indicates an estimated value. For abbreviations, see Measurement Abbreviations on p. 37.

Specimen # Identification VML VMW Ridges/mm

UALVP 32820 Poraspis sp. indet. 37.00* 8.92* 6

UALVP 41359 Poraspis cf. P. rostrata 40.00* 24.64 5-7

UALVP 41382 Poraspis cf. P. polaris 29.08 19.49 5-7

UALVP 43053 Poraspis cf. P. polaris 33.25 19.68 5-7

UALVP 43054 Poraspis cf. P. polaris 29.38 17.67 7-8

UALVP 47063 Poraspis cf. P. polaris 34.00* 21.03 6-7 (1964) and Novitskaya (1986).

Denison (1964) reported the MW/ML to be 0.39, whereas it was reported by Novitskaya (1986) to be 0.46. Both authors included this index in their respective species diagnoses of P. sturi. As discussed in the topic Dorsal Shield

Measurements in the Discussion, the maximum width index is not reliable as a diagnostic character, and thus has been excluded from the diagnosis in the current study. The branchial sinus of the dorsal shield is poorly developed or not discernable in dorsal view, and this characteristic has been added to the diagnosis of the species. As mentioned by Novitskaya (1986), the pores of the sensory canal system are doubled, a feature shared with P. pompeckji, P. simplex, and UALVP

43232 and 49532.

It has been proposed that P. sturi should be synonymized with P. barroisi

(Zych, 1927). Zych's proposal was not accepted by other authors, and later it was proposed that P. sturi be synonymized with both P. polaris and P. barroisi

(Blieck and Heintz, 1983). Since the type specimens of P. sturi were not examined by Blieck and Heintz (1983), the name P. polaris was retained for the

Spitsbergen forms. If these taxa were synonymized, the name P. sturi would have priority and P. polaris and P. barroisi would become junior synonyms. However, the median length reported for P. sturi (60 mm) falls within the range of P. rostrata (50-61 mm), not those of P. polaris and P. barroisi. The discrepancy between the median lengths reported for P. sturi and those reported for P. barroisi and P. polaris and the presence of doubled rows of sensory pores in P. sturi, as well as having not seen the type specimens, precludes synonymization here (for

53 further discussion, see Remarks on Poraspis barroisi). Poraspis sturi is differentiated from P. rostrata by the poorly developed branchial sinus observed in P. sturi.

PORASPIS POMPECKJI (Brotzen, 1933)

Palaeaspispompeckji Brotzen, 1933:433, fig. 2, pi. 24.1, 24.2, 24.4.

Poraspispompeckji: Kiaer and Heintz, 1935:52, fig. 40; Holmgren, 1942:9;

Stensio, 1958:386, figs. 179A, 193, 194A-C, 203A, 206, 209; Heintz,

1962:fig.8C; Denison, 1964:410; Stensio, 1964:81A, 108A; Obruchev,

1967:fig. 3; Novitskaya, 1983:fig.54, 57, 63; Novitskaya, 1986: 24, fig. 3, pi.

3.1;Novitskaya, 1992:3B.

Revised Diagnosis—(After Denison, 1964; Novitskaya, 1986) Median length of dorsal shield 49-58 mm; OL/ML is 0.17-0.22; PL/ML of roughly 0.34; dentine ridges fanning in rostral area. Pores of sensory canals doubled.

Neotype—PIN N 2172/3, cast of dorsal shield with fragments of shield preserved, selected by Novitskaya (1986), as the Brotzen collection thought to be held at the Geologisch-Paleontologisch Institut, Berlin, could not be located.

Remarks—Poraspis pompeckji was fully described by Novitskaya

(1986). The largely longitudinal arrangement of the dentine ridges has been excluded from the diagnosis, as it is characteristic of the entire genus. The measurements of the median length of the dorsal shield and the orbital index

(OL/ML) included in the diagnosis of P. pompeckji have been altered to include

54 those reported by both Denison (1964) and Novitskaya (1986). The maximum width index and density of dentine ridges have been excluded from the diagnosis.

Blieck and Heintz (1983) thought that perhaps P. pompeckji should be synonymized with P. rostrata, but did not formally do so. The doubling of pores of the sensory canals is also observed in P. sturi and P. simplex (Novitskaya,

1986), and is present in UALVP 43232 and 49532.

PORASPIS SIEMIRADZKII (Zych, 1931)

Palaeaspis siemiradzkii Zych, 1931:figs. 37-39, pis. 3, 4, 6, 7; Brotzen, 1936:6.

Poraspis siemiradzkii: Kiaer and Heintz, 1935:106, fig. 39; Holmgren, 1942:10;

Denison, 1964:410; Novitskaya, 1986:26.

Revised Diagnosis—(After Denison, 1964; Novitskaya, 1986) Median length of dorsal shield is 56 mm; postbranchial lobes flaring and comprising widest part of dorsal shield; rostral area dentine ridge pattern irregular; PL/ML of approximately 0.20. Lateral line pattern very completely developed.

Holotype—Not designated. No reliable remains were found in the collections examined by Novitskaya (1986).

Remarks—Poraspis siemiradzkii was fully described by Novitskaya

(1986), based on illustrations of the dorsal shield in the work of Zych (1931). The maximum width index has been removed from the diagnosis of this species, and the maximum width being in the posterior portion of the dorsal shield has been added. This feature is also observed in P. heintzae.

55 PORASPIS SIMPLEX (Brotzen, 1933)

Palaeaspis simplex Brotzen, 1933:432, pi. 24.3.

Poraspis simplex: Kiaer and Heintz, 1935:52; Denison, 1964:409; Novitskaya,

1986:25, fig. 4, pis. 4.2-4.4.

Diagnosis—(After Denison, 1964; Novitskaya, 1986) Median length of dorsal shield 50 mm; dentine ridges irregular in rostral area. Pores of sensory canals large and doubled.

Holotype—Not designated.

Remarks—Poraspis simplex was fully described by Novitskaya (1986).

The maximum width index has been excluded from the diagnosis, and the doubling of the pores of the sensory canals has been added. This feature is also seen in P. sturi and P. pompeckji, but the pores are not noted as being particularly large (Novitskaya, 1986). Doubled rows of pores are present in UALVP 43232 and 49532, two different forms from MOTH. The longitudinal arrangement of dentine ridges over the majority of the dorsal shield has been excluded as a diagnostic feature.

PORASPIS BARROISI (Leriche, 1906)

Cyathaspis barroisi Leriche, 1906:18, figs. 6-7, pis. 1.1-1.5; Zych, 1931:80

"Pteraspis" (Cyathaspis) barroisi: Zych, 1927:52.

Poraspis barroisi: Kiaer, 1930:4; Kiaer, 1932:14; Kiaer and Heintz, 1935:101,

figs. 36, 37; Denison, 1964:407; Blieck, 1982:pl. 1.2.

56 Revised Diagnosis—(After Denison, 1964) Median length of dorsal shield 42^14 mm; OL/ML of approximately 0.17-0.18; rostral area dentine ridges mostly longitudinal, irregular anteriorly.

Lectotype—Internal mold of dorsal shield held at Universite de Lille;

Leriche, 1906:pl. 1, fig. 2; Blieck, 1982:pl. 1.2. Selected by Kiaer and Heintz

(1935).

Remarks—Poraspis barroisi was more fully described by Leriche (1906).

The maximum width index has here been excluded from the diagnosis. Some researchers consider P. barroisi con-specific with P. polaris and P. sturi (Blieck and Heintz, 1983), but these taxa have not formally been synonymized. If P. barroisi were to be synonymized with P. polaris and P. sturi, the name P. sturi would have precedence. However, the median length of P. sturi (60 mm) far exceeds those of P. barroisi (42^44 mm) and P. polaris (32-44 mm). In the present study, it is believed that the median length of the dorsal shield precludes synonymization of P. sturi with P. polaris and P. barroisi. However, no significant differences are recognized between P. polaris and P. barroisi, and synonymization of these two species with one another is supported in principle, with the name P. barroisi having seniority, though it is not formally done as the type specimens have not been examined in this study.

57 PORASPIS POLARIS Kiaer, 1930

(Figs. 2.5A-C, 2.6A-C)

Poraspispolaris Kiaer, 1930:figs. 3A-B; Zych, 1931:figs. 20, 21; Kiaer,

1932:figs. 1, 2, pi. 1; Kiaer and Heintz, 1935:figs. 2, 3, 5, 7-14, pis. 1-8, 9.1,

9.2, 10.1, 11-13, 26.1, 31, 32.2, 34.1-34.5, 35-37, 38.1; Berg, 1940:fig.9;

Save-Soderbergh, 1941 :fig. 5; Holmgren, 1942:fig. 7; Berg, 1955:fig.l0;

Stensio, 1958:figs. 216A, 216B; Denison, 1964:404, figs. 98A, 99A, 102A,

137; Stensio, 1964:figs. 121A-B; Moy-Thomas and Miles, 1971:fig. 3.6A;

Novitskaya, 1975:fig. 3AA; Blieck and Heintz, 1983:55, figs. 7-9;

Novitskaya, 1983:fig. 30B, 32B; Blieck, Goujet, and Janvier, 1987:fig.3B;

Blieck, Elliott, and Gagnier, 1991:figs. 4A, 5B; Novitskaya, 1992:3A.

Poraspis cylindrica: Kiaer, 1932:pl. 3.3 (nomen nudum).

Poraspis cylindrica: Kiaer and Heintz, 1935 pro parte:p\. 26.2; Stensio, 1958:fig.

179A; Denison, 1964:fig. 106; Stensio, 1964:fig.81B.

Poraspis elongata: Kiaer and Heintz, 1935 pro parte:S2, figs. 24-26, pis. 9.3,

10.2, 18-20, 27.1; Denison, 1953:300; Denison, 1964:406.

Poraspis rostrata: Kiaer and Heintz, 1935 pro parte:p\. 24.1.

Poraspis polaris f. angusta: Stensio, 1958:fig. 167B; Stensio, 1964:fig. 69B.

Poraspis cf. P. polaris: Stensio, 1958:fig. 166B; Stensio, 1964:fig. 68B; Dineley

and Loeffler, 1976:76, fig. 25, pis. 10.1-10.4; Novitskaya, 2000:fig. 3A;

Novitskaya, 2007:fig. 2A.

Poraspis sp.: Moy-Thomas and Miles, 1971:fig. 3.3.

58 ^SSIM

FIGURE 2.5.Dorsal shield specimens of Poraspispolaris from the MOTH locality. A, UALVP 23394; B, UALVP 32436; C, UALVP 32783. Dorsal view. Scale bar equals 10 mm. .•*mw

ON o

FIGURE 2.6.Dorsal shield specimens of Poraspis polaris from the MOTH locality. A, UALVP 32785; B, UALVP 41423; C, UALVP 47060. Dorsal view. Scale bar equals 10 mm. Revised Diagnosis—(After Blieck and Heintz, 1983) Medium-sized species of Poraspis with median length of dorsal shield ranging from 32-44 mm;

PL/ML ranges from 0.18-0.26, OL/ML from 0.12-0.2, PBL/ML from 0.28-0.41.

Holotype—PMO D 665, dorsal shield (Kiaer, 1932:pl. 1; Kiaer and

Heintz, 1935:pls. 2, 34.2; Denison, 1964:fig. 137; Blieck and Heintz ,1983:fig.

7A).

Referred Material from MOTft—UALVP 23394, 23436, 32783, 32785,

41423, 47060 (Figs. 2.5A-C, 2.6A-C), dorsal shields.

Remarks—Poraspis polaris was fully described by Blieck and Heintz

(1983). The diagnostic measurement for pineal length has been adjusted to the maximum pineal length measurement reported by Blieck and Heintz (1983), which is 11.5 mm. The postbranchial lengths of the MOTH specimens here referred to P. polaris (11.16-12.56 mm) are shorter than those previously reported for the species, and thus the diagnosis has been adjusted to include the MOTH specimens. The postbranchial and pineal length measurements have been replaced in the diagnosis by an index of each measurement to the median length of each reported specimen (PL/ML-0.18-0.26, PBL/ML=0.28-0.41). The OL/ML has also been added to the diagnosis (0.12-0.2). The maximum width measurements

(21.62-22.54 mm) are greater than any previously reported, though the usefulness of maximum width as a character to diagnose species is doubtful (see Discussion topic 'Dorsal Shield Measurements as Diagnostic Characters'). Measurements of the dorsal shields of UALVP 23394, 23436, 32783, and 41423 and the indices derived from these measurements can be found in Tables 2.2 and 2.3,

61 respectively.

Kiaer established the genus Poraspis and the species P. polaris in 1930, but in 1932, he mistakenly again gave the status of new genus and species to this taxon. For discussion of proposed synonymy with P. sturi and P. barroisi

(according to Blieck and Heintz, 1983) possible synonymy with P. barroisi, see

Remarks on P. barroisi.

PORASPIS cf. P. POLARISKiaer, 1930

(Figs. 2.7A-D)

Referred Material from MOTH—UALVP 41382, ventral shield, ventral median scale, right and left ventrolateral scales (Fig. 2.7A); UALVP 43053,

43054, 47063, ventral shields (Figs. 2.7B-D).

Locality and Age—MOTH locality, Mackenzie Mountains, Northwest

Territories, Canada; Lochkovian (Early Devonian); transitional facies between

Road River and Delorme Formations, Delorme Group.

Description—The median lengths of these specimens range from approximately 29-34 mm. The density of the dentine ridges varies from 5-8 per mm. The anterior-most parts of the shields bear 3-5 ridges that run parallel to the straight anterior margin, but the remaining portions of the shields bear a longitudinal ornament. One shield, UALVP 47063, is an exception to this pattern, with asymmetrical irregularity in the pattern of dentine ridges and fanning in the anterior portion of the shield. Single-rowed pores of the sensory canal system are observed on UALVP 41382, 43053, and 47063, but poor preservation has made

62 ON

FIGURE 2.7. Specimens of Poraspis cf. P. polaris from the MOTH locality. A, UALVP 41382, ventral shield, ventral median scale, and right and left ventrolateral scales; B, UALVP 43053, ventral shield; C, UALVP 43054, ventral shield; D, UALVP 47064, ventral shield. Ventral view. Scale bar equals 10 mm. them impossible to identify on UALVP 43053. The median lobes of the ventral shields, where preserved, are small and rounded, though the posterior-most portion of the lobe in UALVP 43054 is somewhat straight.

UALVP 41382 consists of a ventral shield, a median ventral scale, and a single pair of ventrolateral scales. Damage to the ventral shield has allowed for observation of the pattern of ornamentation on the left ventrolateral scale where it is overlapped by the ventral shield. The pattern appears to originate at the most anterolateral corner of the scale, run transversely in a medial direction, densely packed together, and then curve into the non-overlapping area where the ridges run posteriorly. Sensory canal pores are also visible on the right ventrolateral scale. The median ventral scale is situated posteriorly to and overlapped by the anterior-most ventrolateral scales. The visible area tapers to a rounded point, similar in shape to the median lobe of the ventral shield.

Remarks—The measurements of the ventral shields of the specimens of

Poraspis cf. P. polaris (approximately 29-34 mm; Table 2.4) fall within the expected size range for ventral shields of P. polaris. As these shields are not associated with any dorsal shields to confirm their identification at the species level, these specimens cannot be referred with confidence to P. polaris.

64 PORASPIS HE1NTZAE Elliott, Loeffler, and Liu, 1998

Poraspis heintzae Elliott, Loeffler, and Liu, 1998:364, figs. 3.1-3.7, 4.2, 4.3.

Revised Diagnosis—(After Elliott et al., 1998) Poraspis with median length of dorsal shield ranging from 28.1-30.8 mm; postbranchial lobes flaring and comprising widest part of dorsal shield.

Holotype-^NMC 40624, dorsal shield (Elliott et al., 1998:figs. 3.7, 4.3).

Remarks—Poraspis heintzae was described fully by Elliott et al. (1998).

The median length of the dorsal shield is known to range from 28.1-30.8 mm, overlapping with the known range of P. brevis (24-29.5 mm). Elliott et al. (1998) cited the higher density of dentine ridges in P. heintzae (10-11 per mm) as compared to P. brevis (6-8 per mm) as a significant difference between the two species. However, this feature is unreliable as a diagnostic character, and along with flattened shape of the ridge crests, has been excluded from the current diagnosis (see Discussion topic 'Ornamentation'). The widest measurement of the dorsal shield is found across the postbranchial area, a feature also observed in P. siemiradzkii. This feature clearly differentiates P. heintzae from P. brevis, and has been added to the diagnosis here.

PORASPIS BREVIS Kiaer, 1932

Poraspis brevis Kiaer, 1932:14, pi. 2 (nomen nudum).

Poraspis brevis Kiaer and Heintz, 1935:figs. 20-22, pis. 14-15; Balabai,

1956:figs. 1A, IB; Denison, 1964:404; Blieck and Heintz, 1983:55, fig. 6.

65 Poraspis subtilis Kiaer, 1932:14 {nomen nudum).

Poraspis subtilis Kiaer and Heintz, 1935:81, fig. 23, pis. 21.1, 22; Denison,

1964:404.

Poraspis intermedia Kiaer, 1932:14 {nomen nudum).

Poraspis intermedia: Balabai, 1956:fig. 1C.

Poraspis elongata pro parte: Denison, 1953:300; Denison, 1964:406.

Poraspis elongata?: Kiaer and Heintz, 1935: pi. 21.2.

Poraspis polar is f. lata: Stensio, 1958:fig. 167A; Stensio, 1964:fig. 69A.

Revised Diagnosis—(After Blieck and Heintz, 1983) Small species of

Poraspis with median length of dorsal shield 24-29.5 mm; PL/ML ranges from

0.2-0.25, OL/ML from 0.13-0.17, and PBL/ML from 0.37-0.43.

Holotype—PMO D 665, dorsal shield (Kiaer, 1932:pl. 1; Kiaer and

Heintz, 1935:pls. 2, 34.2; Denison, 1964:fig. 137; Blieck and Heintz, 1983:fig.

7A).

Remarks—Poraspis brevis was described fully by Blieck and Heintz

(1983). The description of Poraspis parmula, Poraspis thules, and Poraspis cracens (Elliott et al., 1998) has necessitated the designation of the lower limits of the diagnostic measurements used by Blieck and Heintz (1983). These lower limits have been set according to measurements reported by Blieck and Heintz

(1983): the median length of the dorsal shield is 24-29.5 mm, the pineal length is

5.5-6.5 mm, and the postbranchial length is 10.5-11 mm. However, here the pineal and postbranchial lengths have been replaced in the diagnosis by a range of

66 indices for the respective measurements, with PL/ML=0.2-0.25 and

PBL/ML=0.37-0.43. The index of orbital length to median length of the dorsal shield (0.13-0.17) has also been added to the diagnosis.

PORASPIS CRACENS Elliott, Loeffler, and Liu, 1998

Poraspis cracens Elliott, Loeffler, and Liu, 1998:365, figs. 5.1, 5.2, 6.1, 7.

Revised Diagnosis—(After Elliott et al., 1998) Small, slender Poraspis, with median length of dorsal shield ranging from 18.0-20.9 mm.

Holotype—NMC 40648, dorsal shield (Elliott et al., 1998:figs. 5.1, 6.1,

V).

Remarks—Poraspis cracens was described fully by Elliott et al. (1998).

The flattened morphology of the dentine ridge crests and ridge density have been excluded from the diagnosis herein (see Discussion topic 'Ornamentation').

PORASPIS THULES Elliott, Loeffler, and Liu, 1998

Poraspis thules Elliott, Loeffler, and Liu, 1998:365, figs. 5.3, 6.2.

Revised Diagnosis—(After Elliott et al., 1998) Very small, slender

Poraspis with rather bluntly rounded rostrum, median length of dorsal shield ranging from 12.0-14.1 mm. Broad transverse band of 7-9 ridges at anterior margin of rostrum.

Holotype—NMC 40653, dorsal shield (Elliott et al., 1998:figs. 5.3, 6.2).

67 Remarks—Poraspis thules was described fully by Elliott et al. (1998).

The density of the dentine ridges and the flattened shape of the ridge crests are removed from the diagnosis (see Discussion topic 'Ornamentation').

PORASPIS PARMULA Elliott, Loeffler, and Liu, 1998

Poraspis intermedia: Kiaer and Heintz, 1935:79, pis.16, 17; Elliott, 1984:201, fig.

3.

Poraspis cf. P. intermedia: Broad and Dineley, 1973:57.

Poraspis parmula Elliott, Loeffler, and Liu, 1998:368, figs. 5.4, 5.5, 6.3.

Revised Diagnosis—(After Elliott et al., 1998) Extremely small Poraspis, with median length of dorsal shield 10.1 mm; broadly rounded anteriorly with anteriorly placed orbits and slight preorbital constriction.

Holotype—NMC 40642, dorsal shield (Elliott et al., 1998:figs. 5.4, 6.3).

Remarks—Poraspis parmula was described fully by Elliott et al. (1998).

The diagnosis has been adjusted to include the measurement of the density of the dentine ridges as reported by Elliott et al. (1998), and references to the maximum width of the dorsal shield, density of dentine ridges and shape of the ridge crests are excluded (see Discussion topics 'Dorsal Shield Measurements as Diagnostic

Characters' and 'Ornamentation').

68 PORASPIS sp. nov. A

(Figs. 2.8A, B)

Diagnosis—Median length of dorsal shield estimated to be approximately

36 mm; rows of pores of sensory canals doubled.

Material—UALVP 49532 (Figs. 2.8A, B), dorsal shield missing part of right side and rostrum, ventral shield missing part of left side, dorsal median scale, left dorsolateral scale, left ventrolateral scale, one indeterminate trunk scale.

Locality and Age—MOTH locality, Mackenzie Mountains, Northwest

Territories, Canada; Lochkovian (Early Devonian); transitional facies between

Road River and Delorme Formations, Delorme Group.

Description— Though UALVP 49532 clearly falls within the size range of P. polar is with respect to median (estimated at approximately 36 mm) and postbranchial (23.4 mm, PBL/ML=0.35) lengths of the dorsal shield, it is distinguished by the presence of a doubled arrangement of sensory canal pores on the dorsal and ventral shields. Dentine ridge density is 7-8 ridges per mm.

Approximately seven dentine ridges run parallel to the margin of the orbit. The pineal macula is poorly distinguished. The branchial sinus is clearly expressed.

The anterior margin of the ventral shield is bordered by four dentine ridges that run parallel to the margin, then run along the lateral edges of the shield toward the position of the orbit. As on the dorsal shield, the ornament is largely longitudinal, though the dentine ridges fan slightly in the anterior portion of the dorsal shield. The median lobe of the ventral shield is small, and the posterior-

69 B

o

FIGURE 2.8.Poraspis sp. nov. A. from the MOTH locality. UALVP 49532, dorsal and ventral shields, median dorsal scale, left dorsolateral scale, left ventrolateral scale, left indeterminate scale. A, dorsal view; B, ventral view. Scale bar equals 10 mm. most edge of the lobe runs parallel to the anterior margin of the dorsal shield, as if the curve of the lobe had been truncated; however, the dentine ridges on the posterior margin of the shield are complete, and inconsistent with an actual break in the median lobe.

A single dorsal median scale is present in UALVP 49532 and in approximate anatomical position with respect to the dorsal shield, a dorsolateral scale, and a ventrolateral scale. The dorsal median scale is a rounded pentagon in shape, with an ornament of dentine ridges running largely longitudinally, but with roughly 6 ridges running transversely across the anterior edge and turning to run posteriorly along the lateral margins of either side of the scale.

The dorsolateral scale appears to be roughly parallelogram-shaped, with ornamentation running longitudinally. The dorsolateral scale is overlapped anteriorly by the posterior margin of the dorsal shield. The ventrolateral scale is similar in shape to the dorsolateral scale, and the visceral side of the scale is visible in the dorsal view of the specimen. The external side of the scale is not visible on the specimen, so the pattern of ornamentation cannot be confirmed; however, the dentine ridges continue over the posterior edge of the scale and approximately 0.5 mm onto the visceral surface, where the ridges abut against a

0.2 mm zone of tuberculated ornamentation. Anterior to this thin tuberculated zone, the visceral surface of the scale is unornamented.

The overlap of dentine ridges and the tuberculated zone are also observed on the visceral side of the unidentified scale, possibly a second, displaced ventrolateral scale, which is also only seen in dorsal view of the specimen. The

71 scale appears to have been displaced anteriorly, rotating and moving between the dorsal and ventral shields.

Unfortunately the specimen is incomplete, with parts of both shields missing. Therefore few standard measurements could to be taken from the dorsal shield. The branchial, orbital, and lateral plates are also unknown, as is the structure of the oral region.

Remarks—The presence of doubled sensory system pores in specimens of Poraspis in the size range of P. polaris is unknown apart from UALVP 49532, though they are known from P. sturi, P. simplex, and P. pompeckji, and are also seen in UALVP 43232. UALVP 49532 is clearly distinguished by being just over half the size of P. sturi (ML=60 mm), and is also smaller than P. pompeckji (49-

58 mm) and P. simplex (ML^O mm). UALVP 49532 is also distinguished from

P. simplex by the fanned pattern of dentine ridges in the rostral area, whereas the pattern observed in P. simplex is irregular.

PORASPIS sp. nov. B

(Figs. 2.9A-C)

Diagnosis—Median length of dorsal shield 47-48 mm. Sensory system comprised of single rows of sensory pores.

Material—UALVP 32886, 45941, 47062, dorsal shields (Figs. 2.9A-C).

72 -0

FIGURE 2.9. Poraspis sp. nov. B from the MOTH locality, dorsal shields. A, UALVP 32886; B, UALVP 45941; C, UALVP 47062. Dorsal view. Scale bar equals 10 mm. Locality and Age—MOTH locality, Mackenzie Mountains, Northwest

Territories, Canada; Lochkovian (Early Devonian); transitional facies between

Road River and Delorme Formations, Delorme Group.

Description—With median lengths of the dorsal shield between 47-48 mm, Poraspis sp. nov. B falls between the size ranges for P. polaris (32-AA mm) and P. pompeckji (49-58). It is also close in size to P. barroisi (42-44 mm), P. simplex (50 mm), and the smallest representatives of P. rostrata (50-69 mm). The pattern of the dentine ridges in the rostral area is largely longitudinal, though

UALVP 32886 exhibits a slight fanning pattern. The density of the dentine ridges is 5-8 per mm across the dorsal shield, and 4-7 dentine ridges run parallel to the margin of the orbit. The PL/ML is between 0.22-0.24, the OL/ML is 0.15-0.16, and the PBL/ML is 0.37-0.39. These specimens are also very broad, with

MW/ML between 0.65-0.7.

Remarks— Poraspis sp. nov. B differs from P. simplex and P. pompeckji in having only a single series of sensory pores, and differs from P. barroisi in lacking irregularity in the pattern of the ornamentation in the rostral area. Though the median lengths of the dorsal shields of the specimens here referred to

Poraspis sp. nov. B are close to those known for P. rostrata, which also occurs at the MOTH locality, these specimens are far broader (MW/ML ranges from

0.6534-0.6990) than other specimens referred to P. rostrata (MW/ML ranges from 0.4262-0.5259). This difference (over 10%) in relative width is more than can be accounted for by compression deformation in these three specimens.

74 PORASPIS sp. nov. C

(Fig. 2.10)

Diagnosis—Median length of dorsal shield approximately 60 mm; branchial sinus very poorly developed; PBL/ML > 0.5. Rows of sensory canal pores doubled.

Material—UALVP 43232, dorsal shield (Fig. 2.10).

Locality and Age—MOTH locality, Mackenzie Mountains, Northwest

Territories, Canada; Lochkovian (Early Devonian); transitional facies between

Road River and Delorme Formations, Delorme Group.

Description—Due to the incompleteness of the rostral area in UALVP 43232, the median length of the dorsal shield has been estimated here as roughly 60 mm. The orbital and pineal lengths were not estimated, as the margin of error would be higher for these more precise measurements. The postbranchial region of the dorsal shield is very long, comprising over 50% of the dorsal shield length. The median lobe of the dorsal shield is large and forms a triangle with a rounded tip.

Impressions of the semicircular canals and the hindbrain are clearly observed in

UALVP 43232, and the pineal macula is elongate and distinct. The pattern of the sensory canals themselves is visible in the postbranchial part of the dorsal shield, and the canals open to the dorsal surface in a doubled series of pores. UALVP

43232 differs from P. pompeckji in having a poorly developed branchial sinus, which is strongly developed in P. pompeckji.

The pattern of dentine ridges in the rostral area is difficult to discern, but

75 FIGURE 2.10. Poraspis sp. nov. C. UALVP 43232, dorsal shield. Dorsal view. Scale bar equals 10 mm.

76 appears to be largely longitudinal with slight fanning. The density of dentine ridges is 8-10 per mm over the dorsal shield. The surface of the dorsal shield is textured with small (0.3-0.4 mm) bumps, particularly in the medial and posterior portions of the shield. Some of the bumps are more elongate anteroposteriorly, but are generally roughly circular in shape. The pattern of the dentine ridges is uninterrupted by this texturing. UALVP 43232 differs from P. sturi in having a much longer postbranchial region (PBL/ML=0.55 in UALVP 43232 and approximately 0.32 in P. sturi).

Remarks—UALVP 43232 shows a doubled set of sensory canal pores, a feature also observed in P. sturi, P. simplex, P. pompeckji, and UALVP 49532.

The extremely elongate postbranchial part of the specimen sets it apart from other known species of Poraspis. It is unclear whether the bumpy texture on the dorsal shield surface is a systematically useful characteristic, or perhaps a pathological feature of the particular individual represented by UALVP 43232. As UALVP

43232 is the only specimen assigned to this new species, the significance of this feature cannot be determined at present, and it has not been included in the diagnosis of the species.

PORASPIS sp. nov. D

(Fig. 2.11)

Diagnosis—Median length of dorsal shield approximately 55 mm; thick transverse band of dentine ridges (15-20 ridges) in anterior portion of rostral area,

77 WRRSP"..

FIGURE 2.11. Poraspis sp. nov. D. UALVP 41426, dorsal shield. Dorsal view. Scale bar equals 10 mm.

78 dentine ridge pattern of rostral area irregular; orbital and postbranchial lengths short (OL/ML approximately 0.15, PBL/ML roughly 0.24); branchial sinus very weakly developed.

Material—UALVP 41426, dorsal shield (Fig. 2.11).

Locality and Age—MOTH locality, Mackenzie Mountains, Northwest

Territories, Canada; Lochkovian (Early Devonian); transitional facies between

Road River and Delorme Formations, Delorme Group.

Description—Poraspis sp. nov. D is represented by a single specimen,

UALVP 41426, an incomplete dorsal shield. The median lobe of the dorsal shield is not preserved, but it is clearly a large specimen of Poraspis, with the preserved component measuring 51.5 mm, and the total median length estimated to be 55 mm. The median length of the dorsal shield of UALVP 41426 falls within the ranges reported for P. rostrata, P. pompeckji, and P. siemiradzkii, and is close to that reported for P. simplex. The OL/ML and PBL/ML are approximately 0.15 and 0.24, respectively. The pineal macula could not be distinguished in this specimen, as sediment covered the area. The sensory canal system opens to the dorsal surface in rows of single sensory pores.

UALVP 41426 bears a thick transverse band of dentine ridges that run roughly parallel to the rostral margin. The remainder of the ornamentation in the rostral area, posterior to the transverse band of ridges, is irregular. The density of the ornament of dentine ridges is 5-6 ridges per mm, and the arrangement is largely longitudinal, though there exist patches of irregularity that occur

79 asymmetrically with regard to the dorsal midline. Some 16-18 ridges run parallel to the margin of the orbit.

Remarks—The median length of the dorsal shield of UALVP 41426 falls within the ranges reported for P. rostrata, P. pompeckji, and P. siemiradzkii, and is close to that reported for P. simplex. The OL/ML falls within the lowest part of the range of measurements for P. rostrata, though the specimen is overall very large. The postbranchial length is clearly shorter in UALVP 41426

(PBL/ML=0.24) than in P. rostrata (0.35-0.44), though it must be noted that both measurements used were based on estimates. The location of the maximum width of the dorsal shield in UALVP 41426 differs from that of P. siemiradzkii. The widest portion of UALVP 41426 occurs anterior to the branchial sinus, whereas

P. siemiradzkii is widest in the postbranchial region. UALVP 41426 differs from

P. pompeckji and P. simplex in bearing single rows of sensory canal pores on the dorsal shield, in contrast to a pattern of doubled pores. UALVP 41426 differs from all other species ofPoraspis in the presence of a thick transverse band of dentine ridges that run roughly parallel to the rostral edge.

PORASPIS sp. indet.

(Fig. 2.12)

Material—UALVP 32820, ventral shield (Fig. 2.12).

80 ' «. ",**9pl*<" a . jaf ;s,V^g,* TJt^jfeji

FIGURE 2.12. Poraspis sp. indet. UALVP 32820, ventral shield. Ventral view. Scale bar equals 10 mm.

81 Locality and Age—MOTH locality, Mackenzie Mountains, Northwest

Territories, Canada; Lochkovian (Early Devonian); transitional facies between

Road River and Delorme Formations, Delorme Group.

Description—UALVP 32820, a ventral shield, has a median length estimated to be approximately 37 mm (based on the 32.8 mm of preserved material). The dentine ridges are poorly preserved, but are largely longitudinal apart from five ridges that run along the straight anterior margin, and have a density of six per mm. Sensory canal pores cannot be identified with confidence, as the specimen is poorly preserved.

Remarks—In terms of the median length of the ventral shield, UALVP

32820 falls between the specimens of ventral shields from the MOTH locality here identified as Poraspis cf. P. rostrata and Poraspis cf. P. polar is (Table 2.4).

Coupled with the incomplete nature and poor preservation of this specimen, its identification cannot be determined below the level of genus.

DISCUSSION

Growth and Variation in Size

Unlike some other cyathaspidid taxa (Greeniaus and Wilson, 2003), the dermoskeletons of poraspidines are thought to have ossified once the individuals approached adulthood and growth was nearly complete (e.g. Denison, 1964;

Dineley and Loeffler, 1976; Novitskaya, 2007). Juveniles of Allocryptaspis have

82 been previously reported, though the specimens were of adult size and their immaturity was diagnosed by the incomplete development of the dermoskeleton, with only thin layers of dentine and aspidine identified in thin section (Denison,

1964). The specimens described by Denison (1964) support the hypothesis that the dermoskeleton did not ossify until adulthood, and that the dorsal shield formed as a single unit rather than from the fusion of separate components, such as epitega. This interpretation was contradicted in part by Dineley and Loeffler

(1976), who described specimens of cyathaspidines and poraspidines from a number of localities in the Delorme Formation, including MOTH (=GSC 69014) that were interpreted as indicating that the superficial layer of the dermoskeleton formed after adult size was reached (though more gradually than the near- instantaneous process envisioned by Denison) and the epitega acted as separate components in the formation of the superficial layer. Dineley and Loeffler (1976) also reported concentric markings interpreted as growth lines on one poorly preserved specimen of Poraspis cf.polaris, which was not identified by specimen number. Concentric growth rings were not observed in any of the specimens of

Poraspis in the UALVP collections from MOTH, though they are commonly seen in specimens of Pionaspis. However, epitega are rarely visible in poraspidines, and are at best only faintly discernible in Poraspis; thus there is little evidence that epitega played a role in the formation of the superficial layer in Poraspis.

Blieck and Heintz (1983) reported a maximum size deviation of 25-30% from the "medium" of each measurement for the specimens they studied of

Poraspis polaris, P. rostrata, and P. brevis, and suggested that smaller specimens

83 are young adults and larger are large adults. This interpretation implies a certain amount, albeit small, of growth after ossification has progressed to a very advanced stage. However, other factors could have influenced adult size, such as disease, different levels of nutrition and other environmental conditions such as temperature, pH, salinity, and oxygen levels during development.

Small, delicate juvenile specimens of the irregulareaspidines Nahanniaspis and Dinaspidella (Greeniaus and Wilson, 2003) and the osteostracan

Superciliaspis (Hawthorn et al., in press) have been described from the MOTH locality, suggesting that the preservation potential at this site was sufficient to have preserved juveniles of poraspidines, if they were present in the MOTH fauna and if their dermoskeletons began to ossify before adulthood. The specimens described in this study appear to be fully mature, and do not provide any new insight on the morphology or lifestyle of juvenile poraspidines.

Since poraspidine growth is interpreted as having been determinate, size can be used as a diagnostic character for different genera and species, though there may be some limited individual size variation within a species, as is normal for species with determinate growth such as birds and mammals. Individual variation should be considered, as well as which measurements are the most reliable indicators of size in life when the possibility of taphonomic and diagenetic deformation are taken into account.

84 Dorsal Shield Measurements as Diagnostic Characters

Various measurements have been utilized as diagnostic characters for differentiating species of Poraspis (Fig. 2.1, Table 2.1), and even different poraspidine genera. Blieck and Heintz (1983) found that a plot of pineal length to total length (LoP/LoT; pineal ratio of Denison, 1964) was effective in differentiating the Spitsbergen species of Poraspis from one another. A plot of maximum width to median length (breadth-length index of Kiaer and Heintz,

1935; width ratio of Denison, 1964) was employed by Elliott et al. (1998), due to poor preservation of some specimens that did not allow for precise measurements of the pineal length, precluding the adoption of the methods of Blieck and Heintz

(1983). Elliott et al. (1998) found that these measurements were also effective in recognizing the same species found by Blieck and Heintz (1983). Measurements of the dorsal shields of Poraspis specimens from MOTH utilized in this study are summarized in Table 2.2, and the indices derived from them are presented in

Table 2.3.

Biological variation between specimens, as discussed above, complicates the use of dorsal shield proportions in diagnosing species; however, deformation also poses a significant problem to this method of species diagnosis. Denison

(1964) reported that in slabs of Americaspis americana from Pennsylvania, differing degrees of deformation affect relative proportions of the dorsal shield and other measurements—longer shields were narrower and have finer (more densely distributed) dentine ridges, and shorter shields were broader and had coarser (less densely distributed) dentine ridges. Intermediates between the

85 elongate and broad specimens were also found on the slab, supporting the interpretation of specimen deformation and clearly illustrating that there are not two discrete morphologies present, but a continuum of diagenetically and tectonically altered specimens. A similar slab (PMO D 241), originally figured by

Kiaer and Heintz (1935:pl. 1), was discussed by Blieck and Heintz (1983). PMO

D 241 contains multiple specimens of Poraspis polaris, where wider specimens are statistically perpendicular to the narrower ones. The lack of paleocurrent indicators in the slab suggests that not the apparent preferential arrangement of two differently proportioned groups, but instead deformation of a number of similarly proportioned specimens resulted in the appearance of two false groups.

Blieck and Heintz (1983) were unable to assess the significance of diagenetic and tectonic deformation with respect to individual biological variation, and any statistical differences in the densities of dentine ridges between wider and narrower specimens were not discussed.

Specimens of Poraspis rostrata and Poraspis polar is from MOTH are generally wider than other specimens previously assigned to each species. This is particularly striking in the case of the two specimens here referred to P. rostrata, which are among the smallest representatives of the species but both specimens exceed previously recorded maximum widths. There is variation in the amount of curvature retained in specimens from MOTH, and most specimens exhibit cracks through the shields from compression. Some are almost completely flattened, while others are more convex. Ventral shields, which are thought to have been more convex than dorsal shields (Novitskaya, 2007) are also flattened, with few

86 retaining much convexity. It is difficult to assess the effect of this compression at the MOTH locality on dentine ridge density, as Poraspis is known to have a range of dentine ridge densities of 5-11 per mm, and this number varies according to where on the shield it is measured and individual variation between specimens as well as the degree of deformation (see Discussion topic 'Ornamentation'). As the occurrence of multiple specimens of Poraspis on a single slab is unknown from

MOTH, and the specimens are collected from a talus slope, it is at present impossible to evaluate possible trends in deformation as Blieck and Heintz (1983) did with the slab PMO D 241.

Blieck and Heintz's (1983) use of pineal length vs. median length to distinguish species of Poraspis is more reliable than Elliott et al.'s (1998) use of maximum width vs. median length, as these measurements are less susceptible to inaccuracy as a result of crushing and flattening. The fusiform body morphology of poraspidines has a far greater mediolateral than anteroposterior curvature, and therefore more deformation will be experienced in the mediolateral direction.

Therefore, the pineal length and median length measurements are more reliable, and preferable to maximum width and median length measurements in differentiating between species of Poraspis.

Though there are several issues with the use of dorsal shield measurements as diagnostic characters for poraspidine species, they provide nearly all of the few morphological characters that can be readily identified and assessed in the majority of specimens. Dorsal shield measurements should be used

87 cautiously and selectively in species diagnoses to reduce the amount of bias and possible misinformation.

Ornamentation

Novitskaya (1971) discussed the pitfalls of using ornamentation of the dermoskeleton as a systematic character, citing numerous sources of variation: ontogenetic, topographic (location on the dermoskeletal element), pathologic, taphonomic, and individual. Currently there are no examples of definite pathologies known in the MOTH poraspidines (see Remarks on Poraspis sp. nov.

C). As the dermoskeleton of poraspidines is thought to have ossified until after growth was complete, ontogenetic variation is not considered here. However, topographic, taphonomic, and individual variation can have great impact on the interpretation of features of the ornamentation as systematically relevant characters.

Though Poraspis tends to have a relatively dense distribution of dentine ridges on the dermoskeletal components in comparison to other poraspidines, there is much variation between specimens. In addition, there can be a wide range of densities depending on where on the specimen the measurement is taken, and thus dentine ridge density per mm is a poor diagnostic character, particularly within the genus Poraspis.

The shape of the dentine ridge crests has previously also been used as a diagnostic character (e.g. Elliott et al., 1998), though this feature is highly vulnerable to distortion by taphonomic forces such as deformation (as discussed

88 above), abrasion and compaction, and perhaps also in life by factors such as varying nutritional levels during the ossification period. The crest shape is also variable depending on the area of the shield; in the poraspidine specimens from

MOTH, the dentine ridges tend to be more rounded anteriorly on the dorsal shield and more flattened posteriorly.

The overall pattern of dentine ridges varies within and between Poraspis species. The pattern observed in the rostral area (Fig. 1.2; the area anterior to the lines drawn from the pineal macula to each orbit; equivalent to the post-rostral field of Stensio, 1958, and the pineal triangle of Denison, 1963) appears to be the most variable, being largely longitudinal (e.g. P. barroisi, P. simplex), fanning

(e.g. P. sericea, P. sturi, P. rostrata, P. brevis), or irregular (e.g. P. siemiradzkii) in various species. Blieck and Heintz illustrated intraspecific variation of rostral ornamentation patterns in Anglaspis insignis (1983:figs.l3a-f), in which the arrangement of dentine ridges is described as "radiating from a very distinct pineal macula". Full photographs of three of these specimens (Blieck and Heintz,

1983:figs. 12d-f) show that they are easily attributable to the same species, which clearly illustrates the problem of intraspecific variation in ornamentation in

Anglaspis and highlights the lack of clear and consistent descriptions of patterning of dentine ridges in the literature. However, the descriptions are retained in the diagnoses presented here, as this study has not included sufficient numbers of specimens of the same species of Poraspis to clearly evaluate whether each species is subject to the same degree of variation in rostral ornamentation as observed in Anglaspis insignis.

89 CONCLUSIONS

Examination of new poraspidine specimens from the MOTH locality has revealed the presence of at least six species of Poraspis: P. rostrata, P. polaris, four new species, and three additional specimens that closely resemble P. rostrata. These specimens are referred to the genus Poraspis based on the shape of the dorsal shield, the relatively long postbranchial region, the pattern of dentine ornamentation and sensory pores, and the lack of distinguishable epitega. The definitions of Subfamily Poraspidinae and Genus Poraspis are revised, and a review of currently recognized species includes revised diagnoses for all Poraspis species, particularly in light of intraspecific variation and taphonomic factors that can easily influence interpretation of diagnostic characteristics. Orbital and maximum widths and the shape of the dentine ridge crests are poor diagnostic characters due to their susceptibility to deformation, and are rejected as diagnostic characters. The density of dentine ridges is also vulnerable to inaccuracy as the result of deformation, and the overall patterns of ornamentation of the dorsal shield are also subject to topographic and individual variation; therefore, these characteristics must be used with caution in species diagnoses.

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103 APPENDIX I: List of Specimens Examined in Present Study

Specimen # Species Identification Element Identification

UALVP 40726 Poraspis rostrata Cast of dorsal shield

UALVP 40727 Poraspis rostrata Cast of dorsal shield

UALVP 41398 Poraspis rostrata Dorsal shield

UALVP 41876 Poraspis rostrata Dorsal shield

UALVP 32744 Poraspis cf. P. rostrata Dorsal shield

UALVP 32881 Poraspis cf. P. rostrata Dorsal shield, right branchial plate

UALVP 47059 Poraspis cf. P. rostrata Dorsal shield

UALVP 41359 Poraspis cf. P. rostrata Ventral shield

UALVP 40753 Poraspispolaris Cast of dorsal shield

UALVP 23394 Poraspis polaris Dorsal shield

UALVP 23436 Poraspis polaris Dorsal shield

UALVP 32783 Poraspis polaris Dorsal shield

UALVP 32785 Poraspis polaris Dorsal shield

UALVP 41423 Poraspis polaris Dorsal shield

UALVP 47060 Poraspis polaris Dorsal shield

UALVP 41382 Poraspis cf. P. polaris Ventral shield

UALVP 43 05 3 Poraspis cf. P. polaris Ventral shield

UALVP 43054 Poraspis cf. P. polaris Ventral shield

UALVP 47063 Poraspis cf. P. polaris Ventral shield

104 UALVP 49532 Poraspis sp. nov. A Dorsal shield, ventral shield, median dorsal

scale, left dorsolateral scale, left

ventrolateral scale, indeterminate trunk

scale; holotype

UALVP 32886 Poraspis sp. nov. B Dorsal shield, holotype

UALVP 45941 Poraspis sp. nov. B Dorsal shield

UALVP 47062 Poraspis sp. nov. B Dorsal shield

UALVP 43232 Poraspis sp. nov. C Dorsal shield, holotype

UALVP 41246 Poraspis sp. nov. D Dorsal shield, holotype

UALVP 32820 Poraspis sp. indet. Ventral shield

UALVP 40738 Homalaspidella borealis Cast of dorsal shield of holotype

UALVP 40725 Homalaspidella nitida Cast of dorsal shield of holotype

UALVP 40745 Anglaspis expatriata Cast of visceral surface of dorsal shield of

holotype

UALVP 40748 Ariaspis ornata Cast of dorsal shield of holotype

105 III. PHYLOGENETIC ANALYSIS OF PORASPIDINAE

INTRODUCTION

The interrelationships of the various species of Poraspis and the composition and intrarelationships of Subfamily Poraspidinae are poorly understood. Phylogenetic reconstructions have been attempted by Denison (1964) and Novitskaya (1972), though neither of these studies employed cladistic methods.

Poraspidines are thought to be a derived group of cyathaspidids that diverged from Silurian cyathaspidids (Obruchev, 1945), or may be comprised of an artificial assemblage whose representatives have independently lost traces of distinct epitega (Denison, 1964). Americaspis, the oldest known poraspidine, exhibits primitive cyathaspidid characteristics such as ellipsoid ornamentation in the central area of the dorsal shield and primitive organization of the sensory canal systems (Novitskaya, 1972).

Anglaspis is distinguished from Poraspis by having coarser dentine ridges, shorter postbranchial lobes, and the shape of the posterior margin of the dorsal shield (Novitskaya, 1972). Novitskaya (1972) cites the interpretation of dermoskeletal formation in Anglaspis by fusion of epitega during ontogeny rather than the apparent synchronous formation of the entire dorsal shield in Poraspis as a primitive feature indicating divergence from other poraspidines in the Late

106 Silurian. Poraspis and Homalaspidella are thought to be closely related to one another (Novitskaya, 1972), as they share many dermoskeletal features.

Allocryptaspis, the youngest known poraspidine, possesses several features considered derived, including its large size, fusion of the branchial and dorsal plates, and absence of epitega (Novitskaya, 1972). Novitskaya (1972) considers this genus convergent with or a progressive descendant ofAnglaspis, based on similarity in the fanning of the rostral ornament, density of dentine ridges, and similar microstructure of the dermoskeleton, where the prismatic chambers of the cribriform layer are arranged in rows. However, the dentine ridge density and the pattern of the rostral ornament have been observed to be rather variable in some poraspidine taxa (see Chapter II, 'Ornamentation').

Here, two phylogenetic analyses are performed: in the first, seventeen species of Poraspis are analyzed (the currently recognized species of the genus

Poraspis and the four new species from the MOTH locality), including the four new species from the MOTH locality (see Chapter I, 'Locality and Age' for further information). Cyathaspis sp. is designated as the outgroup. In the second, nine genera are included in the analysis of the Subfamily Poraspidinae, as defined in Chapter II: Alainaspis, Allocryptaspis, Americaspis, Anglaspis, Boothiaspis,

Homalaspidella, Liliaspis, Poraspis, and Torpedaspis. Cyathaspis Lankester,

1864 is used as the outgroup.

107 MATERIALS AND METHODS

Definitions of the eleven characters and their character states can be found for the analysis of the species of Genus Poraspis in Appendix II, and the data matrix is found in Appendix III. The nine characters and their character states and the data matrix for the analysis of the genera of Subfamily Poraspidinae with the outgroup Cyathaspis sp. are found in Appendices IV and V, respectively. In the analysis of Genus Poraspis with the outgroup Cyathaspis, characters 1-3 are ordered, and the remainder of the data set is unordered. In the analysis of

Subfamily Poraspidinae, characters 8 and 9 are ordered. Ordering was only used for size-related characters.

The most parsimonious phylogenetic trees were generated using

Phylogenetic Analysis Using Parsimony (PAUP) version 4.0b 10 (Swofford,

2003), utilizing heuristic searches with random addition sequences with 100 replicates. A branch and bound search was also performed for the analysis of

Subfamily Poraspidinae. The morphological characters selected and coded for in these analyses were taken from descriptions by Blieck and Heintz (1983), Broad

(1973), Broad and Dineley (1973), Denison (1964), Dineley and Loeffler (1976),

Elliott and Dineley (1985, 1991), Elliott et al. (1998), and Novitskaya (1972,

1986), as well as the author's observations of specimens from the MOTH locality

(see Chapter II).

The most parsimonious trees were used to generate strict and 50% majority-rule consensus trees for each analysis. The majority-rule trees were

108 generated using MacClade 4.08 (Maddison and Maddison, 2005), and characters were mapped onto these trees using the 'Trace All Changes' function and by evaluating distribution of character states for branches with soft polytomies, as these character state changes were not automatically reconstructed.

ABBREVIATIONS

Institutional and Locality Abbreviations—MOTH, Man On The Hill locality,

Northwest Territories, Canada; UALVP, Laboratory for Vertebrate Paleontology,

University of Alberta, Edmonton.

RESULTS

Phylogenetic Analysis of the Genus Poraspis

The heuristic search produced 931 equally most-parsimonious trees, each with a treelength of 34 character state changes. In the heuristic 50% majority-rule consensus tree (Fig. 3.1), the ingroup forms a trichotomy, with Poraspis simplex and Poraspis sp. nov. D as isolated taxa, and the remaining species form a clade with 100% support. Within this clade, Poraspis siemiradzkii is most basal, with

109 T3 00 U co ^u TO < 'to CD TO X a

Q. barroi : siemi r polari s stur i brevi s parmu l simpl e pomp e serice a rostra t thule s

to cracen s heintz a sp . no v sp . no v sp . nov sp . nov Q. to to to to to to to tO CO to .S2 to to to to to to to CO 'a. 'Q. 'Q. Q. 'Q. Q. 'D. Q. 'Q. Q. D. 'Q. 'a. 'a. Q. s: t/> to tO (0 to (O to ta.o "5to. to to to to to to to to 4-J ro ro ro ro CO TO TO TO CO TO TO CD TO TO TO TO TO TO k_ L_ i_ i_ i_ *- i- L- i_ k_ i— V_ i_ O o O o o o o o o o o O o o o O o >% Q. Q. Q. Q. 0- Q. Q. Q. Q- O. a. Q. O- a. \ \ \ \ / \ V 100 0 •100 • 100, 5100.

• 100 61

C75

•100 •100 f100y

FIGURE 3.1. Possible phylogeny of Genus Pomspis. 50% majority-rule tree generated from results of heuristic search. Percentages of agree­ ment are indicated on each branch.

110 Poraspis sp. nov. B just crownward to it. Crownward to Poraspis sp. nov. B lies

P. sericea, then P. pompeckjii. Above this lies a clade with 75% agreement that includes two major branches. The first, with 100% internal agreement, dichotomizes into a branch with P. polaris and P. brevis, and a branch bearing a trichotomy between P. barroisi, P. sturi, and Poraspis sp. nov. C. The second major branch, with only 51% agreement among the equally most-parsimonious trees, has Poraspis sp. nov. A as its most basal constituent, and crownward splits into a branch bearing P. barroisi and P. heintzae, and a branch with P. cracens, P. thules, and P. parmula that forms a trichotomy. The consistency, retention, and rescaled consistency indices are 0.53, 0.62, and 0.33, respectively. All percentages of agreement over 50% are found in Figure 3.1.

The branch and bound search produced only 36 equally most- parsimonious trees, also with treelengths of 34 steps. The 50% majority-rule tree derived from this search (Fig. 3.2) differs from that of the heuristic search only in the position of Poraspis sp. nov. A, which is not clearly resolved as in the 50% majority rule tree derived from heuristic search results, though the clade that includes this species in the heuristic results only had 51% support.

The strict consensus trees of both the heuristic and branch and bound results are identical to each other (Fig. 3.3), and closely resemble the 50% majority-rule trees, as expected due to most branches in the majority rule trees having 100% consensus. The ingroup forms a basal trichotomy with Poraspis simplex, Poraspis sp. nov. D, and the remaining ingroup species. Of the remaining taxa, P. siemiradzkii is most basal, with Poraspis sp. nov. B occupying

111 "O CQ 3? u < Q ro u TO in tD TO X > o Q. c in barroi : siemi r polari s brevi s stur i

parmu l Q. simple ; pomp e V) serice a rostra t thule s cracen s heintz a sp . no v sp . nov , sp . nov to Q. t/> w (/i w to to tfi to (/) u) ,<2 to to to to to u> to ro CL 'a. 'Q. 'a. 'Q. 'CL 'Q. o. a. 'Q. 'Q. 'a. Q. Q. 'Q_ 'o. "a _c to (A 10 t/1 to to (O tfi to t/) to to (/i to +-' TO TO TO (/TO) (/CO) TO TO 03 TO TO TO TO TO TO ro TO CO u_ k_ i_ i_ i_ i- k- l_ l_ I- V_ l— i_ i_ o o o o o o o o o o o o o o O O o >. Q. a. Q. Q. a. Q. Q. Q- D. a. Q_ \ \ \ \ 1/ •mr\ i100 •100 flOC

.100

i75

•100 •100 !10C

FIGURE 3.2. Possible phylogeny of Genus Pomspis. 50% majority-rule tree generated from results of branch and bound search. Percentages of agreement are indicated on each branch.

112 N CO u 2> < a re re u 'to tu re X

a. to barro i siemi r stur i polari s brevi s parm u simpl e pomp e serice a rostra t thule s cracen s heintz a sp . no v sp . no v sp . no v sp . nov , 'a. tO to 10 10 to to .52 to to

FIGURE 3.3. Possible phylogeny of Genus Poraspis. Strict consensus tree generated from results of both heuristic and branch and bound searches.

113 the position crownward to it. P. sericea is basal to a four-branched polytomy involving Poraspis sp. nov. A and P. pompeckjii as isolated taxa, and two other branches supporting five species each. The first contains a clade with P. polaris and P. brevis, and a clade with Poraspis sp. nov. C, P. rostrata, and P. sturi in a trichotomy. The second is comprised of P. barroisi and P. heintzae together as sister taxa, and a trichotomy between P. cracens, P. thules, and P. parmula.

Phylogenetic Analysis of the Subfamily Poraspidinae

The heuristic search produced 200 equally most-parsimonious trees with

25 steps each. The 50% majority-rule tree derived from the results of this search

(Fig. 3.4) showed Americaspis in the most basal position, and the rest of the ingroup taxa forming a 5-branched polytomy, in which Alainaspis, Anglaspis,

Boothiaspis, and Torpedaspis are isolated taxa. The remaining genera, grouped together in 68% of the equally most-parsimonious trees, form a branch which splits into a trichotomy with Allocryptaspis, Poraspis, and Homalaspidella +

Liliaspis. The sister-genus relationship between Homalaspidella and Liliaspis is found in 56% of the equally most-parsimonious trees.

The branch and bound search produced 191 equally most-parsimonious trees, with treelengths of 25 steps, and the 50% majority-rule and strict consensus trees generated from the equally most-parsimonious trees were identical to those found using heuristic methods. The consistency index, retention index, and rescaled consistency index were 0.71, 0.50, and 0.35, respectively, and percentages of agreement for clades within this tree are illustrated in Figure 3.5.

114 .c u of agreementareindicatedneachbranch. majority-rule tregeneratedfromresultsofheuristi c search.Percentages FIGURE 3.4.PossiblephylogenyofSubfamil y Poraspidinae.50% yat! co spis *i_ 'a. < £ o co en i/> < (/> in lainCO Q. _o 'Q. < 4-> o L- Q. CO en y) >

"O "ai _co X O O LU CO CO c/> Q. 115 U -C majority-rule tregeneratedfromresultsofbranc h andbounsearch. FIGURE 3.5.PossiblephylogenyofSubfamil y Poraspidinae.50% % Percentages ofagreementareindicatedneac h branch. >, aspis < v> E ^_ casp < lair IU ispis " < ocr ypta Q. "a X o E ro laspi 116 • 100 — LJ TO v) pis •70 S69 D- o TO pis < c O) TO spis £ '5. 0 V) o o CO (/) h-

DISCUSSION

Phylogenetic Analysis of the Genus Poraspis

In the phylogenetic analyses of Genus Poraspis, there is surprisingly strong agreement between the equally most-parsimonious trees for many relationships, including the positions of Poraspis sp. nov. B, P. siemiradzkii, and

P. sericea, and the sister-species relationships between P. polaris and P. brevis, and P. barroisi and P. heintzae. The first pair is united by a short pineal index, and the second pair by the irregular pattern of dentine ridges in the rostral area.

The grouping of Poraspis cracens, P. thules, and P. parmula, united by their small median dorsal shield lengths and angled posterior margin of the dorsal shield, is possibly also influenced by these species having missing data for the same characters, as they were all described by Elliott et al. (1998) and have not been described elsewhere. Poraspis heintzae, also described in the same study, falls close to these three species as well, though it shares a sister-group relationship with P. barroisi.

Poraspis sp. nov. C, P. rostrata and P. sturi are united by the large median length of the dorsal shield and the presence of doubled rows of sensory system

117 pores. The larger postbranchial index and the distinct branchial sinus unite the ingroup clade that excludes Poraspis sp. nov. D and P. simplex.

The polytomies present in the 50% majority rule consensus trees show that some relationships between species and species groups are far from resolved, including which species occupies the most basal position within Poraspis.

Phylogenetic Analysis of the Subfamily Poraspidinae

In the phylogenetic analyses performed of members of Subfamily

Poraspidinae, the relationships between Poraspis, Allocryptaspis,

Homalaspidella, and Liliaspis were maintained in both heuristic and branch and bound analyses. The grouping of these four genera is supported by character 8, the median length of the dorsal shield. The topology illustrated somewhat supports the close relationship between Poraspis and Homalaspidella predicted by Novitskaya (1972), though the position of Liliaspis as sister to Homalaspidella clearly contradicts Novitskaya (1994)'s views, in which Liliaspis is excluded from Subfamily Poraspidinae. Americaspis occupied the most basal position in both analyses, which is consistent with it being the oldest known poraspidine and possessing several features considered primitive (Novitskaya, 1972).

The low tree statistics and the complete collapse of the ingroup taxa in the strict consensus tree clearly indicate the poor degree of resolution in the analyses of Subfamily Poraspidinae.

118 General Discussion

The lack of resolution in both these analyses indicates that the relationships of Poraspis and other poraspidines are far from being determined.

The relatively simple anatomical features of these early vertebrates make identifying morphological characters for use in cladistic analyses difficult, and inadequate descriptions of some taxa (i.e., Poraspis barroisi) and inconsistent quality of preservation compound the problem of insufficient data.

The phylogenetic significance of some of the characters used in these analyses is highly questionable. As the degree of variation between individuals is not well understood (see Discussion in Chapter II), characteristics such as differences in patterns of ornamentation and measurements of the dorsal shield may not be phylogenetically significant. Character states based on measurements are artificial impositions on a continuum of measures, and as such a taxon will often exhibit multiple character states. These numerous polymorphic character state codings lead to polytomies in the resulting consensus trees, and obscure relationships between taxa.

More substantial descriptions of features of the sensory system and internal anatomy would aid in providing additional characters for use in future phylogenetic analyses. Unfortunately these details are often incompletely preserved. Reliance on characteristics that may present themselves as highly variable as a result of taphonomic factors or individual variation derived from differing developmental parameters currently impedes efforts towards building a more reliable phylogenetic framework for Poraspidinae and the genus Poraspis.

119 CONCLUSIONS

The results of the phylogenetic analyses presented here provide a preliminary step towards generating reliable phylogenies of Poraspidinae and

Poraspis. Additional characters would help to resolve the relationships between these taxa, and the data set would be greatly enhanced by comprehensive redescriptions of many taxa, particularly those from the Ukraine. This study provides an initial attempt at reconstructing the relationships between these early vertebrate groups, and it is hoped that future research will provide more reliable characters on which to base future analyses.

120 LITERATURE CITED

Blieck, A., and N. Heintz. 1983. The cyathaspids of the Red Bay Group (Lower

Devonian) of Spitsbergen. XIII. Polar Research, 1 (NS):49-74.

Broad, D. S. 1973. Amphiaspidiformes (Heterostraci) from the Silurian of the

Canadian Arctic archipelago. Geological Survey of Canada Bulletin 222:35-50.

Broad, D. S., and D. L. Dineley. 1973. Torpedaspis, a new Upper Silurian and

Lower Devonian genus of Cyathaspididae (Ostracodermi) from arctic Canada.

Bulletin of the Geological Survey of Canada 222:53-90.

Denison, R. H. 1964. The Cyathaspididae: a family of Silurian and Devonian jawless vertebrates. Fieldiana, Geology 13:309-4-73.

Dineley, D. L., and E. J. Loeffler. 1976. Ostracoderm faunas of the Delorme and associated Siluro-Devonian Formations, North West Territories, Canada.

Palaeontological Association Special Papers in Palaeontology 18:1-214.

Elliott, D. K., and D. L. Dineley. 1985. A new heterostracan from the Upper

Silurian of Northwest Territories, Canada. Journal of Vertebrate Paleontology

5:103-110.

121 Elliott, D. K., and D. L. Dineley. 1991. Additional information on Alainaspis and

Boothiaspis, cyathaspidids (Agnatha: Heterostraci) from the Upper Silurian of

Northwest Territories, Canada. Journal of Paleontology 65:308-313.

Elliott, D. K., E. J. Loeffler, and Y. Liu. 1998. New species of the cyathaspidid

Poraspis (Agnatha: Heterostraci) from the Late Silurian and Early Devonian of

Northwest Territories, Canada. Journal of Paleontology 72:360-370.

Lankester, E. 1864. On the discovery of the scales of Pteraspis with some remarks on the cephalic shield of that fish. Quarterly Journal of the Geological

Society 20. [Not yet seen].

Maddison, W. P., and D. R. Maddison. 2005. MacClade, Version 4.08 (computer program). Sinauer Associates, Inc., Sunderland, Massachusetts.

Novitskaya, L. I. 1972. Phylogenetic relationships of poraspids (Heterostraci).

Paleontological Journal 6:382-388.

Novitskaya, L. I. 1994. Paraliliaspis, a new cyathaspid genus

(Cyathaspidiformes, Agnatha) from the Lower Devonian of the Timan-Pechora

Province. Paleontological Journal 28:116-127.

122 Novitskaya, L. I. 1986. Drevneishie bechelyustne SSSR, Geterostraki:

Tsiataspidy, Amphiaspidy, Pteraspidy. Trudy Paleontologicheskogo Instituta

Academii Nauk SSSR 219:27-75. [Only English translation seen: 1988. The earliest Agnatha of the USSR, Heterostraci: Cyathaspidae, Amphiaspidae,

Pteraspidae. Geological Survey of Canada Translation 3230. Translated by the

Translation Bureau of the Multilingual Services Division, Department of the

Secretary of State, Canada].

Obruchev, D. V. 1945. Evolyutsiya Agnatha. Zoologicheskii Zhurnal 24:257-272.

[Only partial English translation seen: 1985. Evolution of Agnatha. Geological

Survey of Canada Translation 2851. Translated by the Translation Bureau of the

Multilingual Services Division, Department of the Secretary of State, Canada].

Swofford, D. 2003. PAUP*: Phylogenetic Analysis Using Parsimony (* and

Other Methods). Version 4 (computer program). Sinauer Associates, Inc.,

Sunderland, Massachusetts.

123 APPENDIX II: Characters and Character State Descriptions for the Phylogenetic

Analysis of Genus Poraspis

1. Length of dorsal shield: (0) 6-25 mm, (1) 26-45 mm, (2) 46-85 mm.

2. Density of dentine ridges: (0) 5-6 per mm, (1) 7-8 per mm, (2) 9 or more per

mm.

3. Number of dentine ridges in transverse band at anterior margin of rostrum: (0)

1-5,(1)6-10,(2) 11 or more.

4. Ratio of postbranchial length of dorsal shield to median length of dorsal shield:

(0) 0.25-0.35, (1) 0.36-0.45.

5. Ratio of orbital length of dorsal shield to median length of dorsal shield: (0)

0.11-0.20,(1)0.21-0.30.

6. Ratio of pineal length of dorsal shield to median length of dorsal shield: (0)

0.16-0.25,(1)0.26-0.35.

7. Median lobe of dorsal shield: (0) bluntly rounded, (1) forms an angle, (2)

absent.

124 8. Branchial sinus of dorsal shield: (0) present, (1) weak or absent.

9. Dentine ridge pattern of rostral area of dorsal shield: (0) fanned, (1)

longitudinal, (2) irregular, (3) mostly transverse.

10. Rows of sensory pores: (0) single, (1) double.

11. Postbranchial part of dorsal shield: (0) not distinguished, (1) remains

restricted posterior to branchial opening; (2) broadens posterior to

branchial opening and narrows posteriorly, (3) flares posterior to branchial

opening and remains broad posteriorly.

125 APPENDIX III: Character State Matrix for the Phylogenetic Analysis of Genus Poraspis. For characters and character states, see Appendix II. ? indicates unknown state.

Character Species 1 2 3 4 5 6 7 8 9 10 11 Poraspis sericea 2 1 1 0,1 0 1 1 0 0 0 2 Poraspis rostrata 2 0, 1 0,1,2 0, 1 0 0,1 0 0,1 0, 1 1 0, 1,2 Poraspis sturi 2 1 0 1 0,1 1 0 1 0 1 1 Poraspis pompeckji 2 1,2 0 0 0,1 1 0 0 0 0 2 Poraspis siemiradzkii 2 ? ? 1 0 0 ? 0 2 0 3 Poraspis simplex 2 0 ? 0 ? ? ? 1 2 1 1 Poraspis barroisi 1 ? ? ? 0 7 7 ? 1,2 0 ? Poraspis polaris 1 0, 1,2 0 0, 1 0 0 0, 1 0, 1 0 0 0,2 Poraspis heintzae 1 2 0 1 0 1 0 0 2 0 Poraspis brevis 0,1 0,1 0, 1 1 0 0 0, 1 1 0 0 0, 1 Poraspis cracens 0 1,2 0 1 0 1 1 0 0 0 2 Poraspis thules 0 2 1 0,1 0 1 1 0 0 0 2 Poraspis parmula 0 1,2 0 1 0 0 1 0 0 0 1 Poraspis sp. nov. A 1 1 ? ? ? 1 0 0 7 1 2 Poraspis sp. nov. B 2 0,1 1 1 0 0 0 0 0, 1 0 1 Poraspis sp. nov. C 2 1,2 ? 7 ? ? 1 1 7 1 0 Poraspis sp. nov. D 2 0 2 ? ? ? ? 1 1 0 1 Cyathaspis sp. 1,2 0 2 ? 0 0, 1 2 1 2,3 0 0 APPENDIX IV: Characters and Character State Descriptions for the Phylogenetic

Analysis of Subfamily Poraspidinae

1. Median lobe of dorsal shield: (0) rounded, (1) forms an angle, (2) absent, (3)

forms a point in the center of posterior margin.

2. Epitega of dorsal shield: (0) not distinct, (1) may be distinct.

3. Dentine ridge pattern of rostral area of dorsal shield: (0) fanned, (1)

longitudinal, (2) irregular, (3) indistinguishable from rest of shield

ornament, (4) forms polygons anteriorly.

4. Branchial sinus of dorsal shield: (0) weak or absent, (1) commonly distinct.

5. Dentine ridge pattern of dorsal shield: (0) largely longitudinal, (1) irregular, (2)

ellipsoid on central dorsal shield, (3) sinuous.

6. Median ridge on dorsal shield: (0) absent, (1) present.

7. Lateral brim of dorsal shield: (0) not distinguishable, (1) present, with smooth margins, (2) present, with serrated margins.

127 8. Length of dorsal shield: (0) 86 mm or more, (1) 46-85 mm, (2) 6-45 mm.

9. Ratio of postbranchial length to median length of dorsal shield: (0) 0.51-0.70,

(1)0.31-0.50,(3)0.11-0.30.

128 APPENDIX V: Character State Matrix for the Phylogenetic Analysis of Subfamily Poraspidinae. For characters and character states, see Appendix IV. ? indicates unknown state.

Character Genus 1 2 3 4 5 6 7 8 9 Alainaspis 1 0 4 0 3 1 2 0,1 0, \. Allocryptaspis 0 0 0 0 0 0 1 1 ? Americaspis 0 1 0 0 1,2 0 ? 0 ? Anglaspis 1 1 0 1 0 0 1 0 ? Boothiaspis 2 0 ? 0 3 0 1 0 0 Homalaspidella 0, 1 0 2 0 0 0 ? 2 ? Liliaspis 3 1 0 0 0 1 1 2 2 P or asp is 0, 1 0 0,1, 0 0 0 0 1,2 1 Torpedaspis 1,2 0 3 0 0,3 0 0 0 ? Cyathaspis 2 1 2 0 2 1 ? 0 ? IV. EVOLUTIONARY HISTORY OF PORASPIDINAE

INTRODUCTION

Cyathaspidids first appear in the Silurian, and reach their peak diversity in the first half of the Early Devonian (Novitskaya, 2007). This stage is currently recognized as the Lochkovian, and corresponds closely to the Early-Middle

Dittonian and the now disused Gedinnian stage (Blieck, 1984; Dejonghe et al.,

2006). The subfamily Poraspidinae is known from numerous Northern

Hemisphere localities, and ranges from the Late Silurian (Early Ludlovian) to the

Early Devonian (Pragian). The genus Poraspis is known from the District of

Mackenzie, Spitsbergen, and both western and eastern Europe (Elliott et al.,

1998). Descriptive and taxonomic work has been done by previously, primarily by Kiaer (1932), Kiaer and Heintz (1935), Dineley and Loeffler (1976), Blieck and Heintz (1983), Novitskaya (1986), and Elliott et al. (1998). Four new species from the MOTH locality, Northwest Territories, Canada are described for the first time in Chapter II. and these specimens provide additional information on the paleobiogeography, paleoenvironment, and evolutionary history of poraspidines.

In the present chapter, the additional information contributed by these new species is used to address some of the more interesting issues concerning the evolutionary history of the group, specifically the paleobiogeographic history, evolutionary

130 trends in morphology, and paleoenvironments inhabited by members of the

Poraspidinae.

ABBREVIATIONS

Institutional and Locality Abbreviations—MOTH, Man On The Hill locality,

Northwest Territories, Canada; PMO, Paleontologisk Museum, Oslo; UALVP,

Laboratory for Vertebrate Paleontology, University of Alberta, Edmonton.

Regional Abbreviations—CI, Cornwallis Island, Canada; EI, Ellesmere Island,

Canada; FR, France; GB, Great Britain; NWT, mainland Northwest Territories,

Canada; OH, Ohio, United States of America; PI, Prescott Island, Canada; PWI,

Prince of Wales Island, Canada; SA, Saaremaa Island, Estonia; SB, Spitsbergen,

Norway; SI, Somerset Island, Canada; UKR, Ukraine; URL, Ural Mountains,

Russia; UT, Utah, United States of America; WY, Wyoming, United States of

America; YT, Yukon Territory, Canada.

Species Abbreviations—Alain, plat, Alainaspis platostriata; Alio, ellip.,

Allocryptaspis ellipticus; Alio, flab., Allocryptaspis flabelliformis; Alio, lat,

Allocryptaspis laticostata; Alio. Utah., Allocryptaspis utahensis; Amer. amer.,

Americaspis americana; Amer. clay., Americaspis claypolei; Amer. sp.,

Americaspis sp.; Angl. elong., Anglaspis elongata; Angl. exp., Anglaspis

131 expatriata; Angl. hein., Anglaspis heintzi; Angl. insig., Anglaspis insignis; Angl. mac, Anglaspis macculloughi; AngL sp., Anglaspis sp.; B. alata, Boothiaspis alata; B. ang., Boothiaspis angusta; B. ovata, Boothiaspis ovata; H. bor.,

Homalaspidella borealis; H. nit., Homalaspidella nitida; L.phiL, Liliaspis philippovae; P. barr., Poraspis harroisi; P. brev., Poraspis brevis; P. cf. P. rost,

Poraspis cf. Poraspis rostrata; P. cf. P. pol., Poraspis cf. Poraspis polar is; P. crac, Poraspis cracens; P. hein., Poraspis heintzae; P. parm., Poraspisparmula;

P. pol., Poraspis polar is; P. pom., Poraspis pompeckji; P. rost., Poraspis rostrata; P. seri., Poraspis sericea; P. siem., Poraspis siemiradzkii; P. simp.,

Poraspis simplex; P. sp., Poraspis sp.; P. sp. nov. A, Poraspis sp. nov. A; P. sp. nov. B, Poraspis sp. nov. B; P. sp. nov. C, Poraspis sp. nov. C; P. sp. nov. D,

Poraspis sp. nov. D; P. sturi, Poraspis sturi; P. thul, Poraspis thules; T. elong.,

Torpedaspis elongata.

GEOGRAPHIC AND TEMPORAL DISTRIBUTION OF PORASPIDINES

The geographic and stratigraphic occurrences of poraspidines are summarized in Figure 4.1. The earliest occurring poraspidine is Americaspis

White and Moy-Thomas, 1941. Americaspis is represented by two species from the Upper Silurian (Middle Ludlovian) of the United States of America:

Americapsis claypolei Denison, 1964, from Utah, and Americaspis americana

132 FIGURE 4.1. Geographic and stratigraphic occurrences of poraspidines. Specimens in bold type are from the MOTH locality. For abbreviations, see Regional and Species Abbreviations on p. 132.

Ma Period Epoch Stage YT NWT UT WY PWI PI CI SI El OH GB FR SB SA UKR URL 1 Alio. utah. Alio, eltip. Alio. flab.

Alio. lat.

c ! P. seri. 410^ en 'c o CO > LU H. nit. a P. pol. R sen. Angl. R rost. P pom. insig. P. rost. R pol. Angl. sp. P. cf. P. rost. Angl. P. siem. P. seri. elong. H-nlt- P. sp. nov. A P. crac. P. hein. P. sp. nov. B Psp. P. simp. L phil. P. sp. nov. C P. thul. P. barr. Angl. P. brev. ! heln. 415.; P. sp. nov. D P parm. P. parm. P. pol. Angl. P. sturi P. sp. T. elong. Angl. sp. T. elong. Angl. sp. insig. P. parm. H. bor. Angl. exp. T. elong. T. elong. P. sp. P. brev.

"5 B. alata S. alata Angl. mac. Angl. sp.

CL B. ang. B. ovata Alain, plat. Alain, plat. Amer. amer. 420^ c m 5 Amer. sp. Amer. clay. o 1 _l 1 Amer. sp. o o c CD J g (Claypole, 1884) from Ohio (Denison, 1964). Other specimens referred to

Americaspis sp. occur at both localities.

Alainaspis platyrhina Elliott and Dineley, 1985, is also known from the

Upper Silurian (upper Ludlovian-Pridolian), and is found in the Canadian Arctic, on Prince of Wales and Somerset Islands. Boothiaspis Broad, 1973, is also known from this interval, with B. angusta Broad, 1973, and B. ovata Broad, 1973, known from Prince of Wales Island, and B. alata Broad, 1973, from both Prince of Wales and Ellesmere Islands (Elliott and Dineley, 1985, 1991).

Also known from the Upper Silurian (Pridolian) is Homalaspidella borealis Denison, 1963, from the Yukon Territory of Canada (Novitskaya, 2007; though Denison, 1964, reported this species as being from the Lower Devonian),

Anglaspis macculloughi (Woodward, 1891), and Poraspis sp. from Great Britain,

Anglaspis sp., from Saaremaa Island, Estonia, and possibly Anglaspis expatriata

Denison, 1964 from the Northwest Territories of Canada, though the latter may be from the Early Devonian (Lochkovian) (Dineley and Loeffler, 1976). Poraspis brevis has also been reported from the Upper Silurian (late Pridolian) from

Spitsbergen, an Arctic island in the Svalbard group belonging to Norway (Kiaer and Heintz, 1935). Torpedaspis elongata Broad and Dineley, 1973, has been recovered the uppermost Silurian on Prince of Wales and Somerset Islands (Broad and Dineley, 1973).

Lochkovian (Lower Devonian) strata hosted a wide diversity of poraspidines from Prince of Wales Island, Great Britain, Spitsbergen, Ukraine

(specifically the southwest portion, a region formerly commonly referred to as

134 Podolia), and the Northwest Territories (MOTH locality). Elliott et al. (1998) reported occurrences of P. sericea and three new species of Poraspis from Prince of Wales Island: P. cracens, P. thules, and P. parmula. Broad and Dineley (1973) also described Torpedaspis elongata Broad and Dineley, 1973, from Prince of

Wales Island. Poraspis is represented by four species from Ukraine: P. sturi, P. simplex, P. siemiradzkii, and/5, pompeckji (Novitskaya, 1986). Several poraspidines are also known from the Lochkovian of Great Britain, including P. sericea, Poraspis sp., and Anglaspis sp. 'Poraspis elongata'' has also been reported from Great Britain (Denison, 1964), but it is unclear whether this represents P. polar is or P. brevis.

Spitsbergen is also well known for its poraspidine diversity. According to

Blieck and Heintz (1983), the lower Fraenkelryggen Formation is characterized by the presence of Anglaspis insignis Wills, 1935, Anglaspis heintzi Blieck and

Heintz, 1983, Poraspis brevis, and P. polaris. P. parmula has also been identified from these beds (Elliott et al., 1998). The younger Ben Nevis Formation is characterized by the occurrence of P. rostrata, Anglaspis elongata Blieck and

Heintz, 1983, Homalaspidella nitida Kiaer, 1932, and P. polaris. The specimens of P. polaris from the Ben Nevis Formation are generally slightly longer in median length than those from the Fraenkelryggen Formation (Blieck and Heintz,

1983).

The MOTH locality has produced Poraspis rostrata, P. polaris, and four new Poraspis species described for the first time in Chapter II. In addition, several specimens are also given preliminary identifications as Poraspis cf. P.

135 rostrata, Poraspis cf. P. polaris, and Poraspis sp. According to Blieck and Heintz

(1983), the MOTH locality correlates with the upper Fraenkelryggen Formation or the lower Ben Nevis Formation, and those authors believe that correlation with the lower Ben Nevis Formation is more likely due to occurrence of P. polaris,

Protopteraspis vogti, and Lepidaspis, as well as a specimen from the base of the

Formation similar to Canadapteraspis alocostomata (PMO D 3888-3889).

Other poraspidines are also known from the lowermost Lochkovian of

Somerset Island (Torpedaspis elongata Broad, 1973) and Cornwallis Island

(Anglaspis sp.), and the Middle Lochkovian of Prescott Island in Arctic Canada

(Poraspis heintzae), France (Poraspis barroisi), and the Ural Mountains of Russia

(Liliaspis philippovaeNovitskaya, 1972). Anglaspis is also known from erratics in western Germany that are thought to be Lower Devonian in age (Denison, 1964).

The temporal range of Subfamily Poraspidinae extends into the Pragian, where it is represented by two genera. The range of Homalaspidella nitida extends into the early Pragian in Spitsbergen. Allocryptaspis Whitley, 1940 is the latest known poraspidine, with its earliest occurrence in the middle Pragian in

Ohio, represented by Allocryptaspis laticostata. Allocryptaspis ellipticus and

Allocryptaspis flabelliformis are known from the late Pragian in Wyoming, as is

Allocryptaspis utahensis in Utah (Denison, 1964). Anglaspis has also been reported from the Pragian of Lithuania (Karatajute-Talimaa, 1962), representing the latest known occurrence of the genus.

The recent work of Elliott et al. (1998) supports the hypothesis of the

Canadian Arctic as the centre of origin and site of adaptive radiation fox Poraspis,

136 followed by subsequent radiation, primarily eastward into Spitsbergen and western Europe. The Canadian Arctic has also been identified as centre of development for other Late Silurian agnathans, such as pteraspidids (Elliott and

Dineley, 1985; Elliott, 1984); therefore, Elliott et al. (1998) hypothesized that the

Canadian Arctic may have possessed a particular set of environmental conditions that contributed to a high rate of development of evolutionary novelties during the

Late Silurian (discussion of poraspidine paleoenvironments can be found on p.

144).

The paleogeographic distribution of the genus Poraspis in the early

Devonian is illustrated in Figure 4.2. Species of Poraspis known from multiple localities include P. sericea (Prince of Wales Island and Great Britain), P. rostrata (Spitsbergen and MOTH), P. polaris (Spitsbergen and MOTH), and P. parmula (Canadian Arctic Archipelago and Spitsbergen). The earliest occurrences of these species are in the Canadian Arctic, and the hypothesis of radiation from this area generally eastward to Spitsbergen and Europe is supported by the distribution off. sericea and P. parmula. However, as the MOTH locality is thought to correlate with the lower part of the Ben Nevis Formation of

Spitsbergen, the occurrences of P. polaris in the Fraenkelryggen Formation represent the earliest occurrence of the species, which is not known from the

Canadian Arctic. Specimens from the Canadian Arctic Archipelago identified as

Poraspis cf. p. polaris by authors including Broad (1973) and Broad and Dineley

(1973) have since been referred to P. cracens or P. thules. Poraspis polaris may

137 Paleoequator

FIGURE 4.2. Paleogeographic distribution of the genus Poraspis in the early Devonian. A, MOTH locality; B, Prince of Wales, Prescott, and Cornwallis Islands; C, Spitsbergen; D, Great Britain; E, France; F, Saaremaa Island; G, Ukraine.

138 have originated in the Late Silurian or earliest Devonian of the Arctic and radiated both toward the east to Spitsbergen and toward the southwest to the MOTH locality, but there are no specimens known from the Canadian Arctic to support this hypothesis. The high diversity of Poraspis species clearly indicates that the

MOTH locality was an area conducive to further poraspidine adaptive radiation, but the precise centre of origin has not been determined conclusively. The

Canadian Arctic seems an unlikely centre of origin for radiation of Subfamily

Poraspidinae as a whole, as the earliest known occurrences of poraspidines are species of Americas pis from Utah, and somewhat younger examples from Ohio.

TRENDS IN PORASPIDINE EVOLUTION

Kiaer and Heintz (1935) described several trends within the genus

Poraspis through time, including trends toward increased body size (Kiaer and

Heintz, 1935; Blieck and Heintz, 1983; Elliott et al., 1998), increased organization of longitudinal dentine ridges on the dorsal and ventral plates (Kiaer and Heintz,

1935; Elliott et al., 1998), and a more completely united network of sensory canals (Kiaer and Heintz, 1935; Denison, 1964; Elliott et al., 1998). It has also been suggested that temporally later occurring species had a wider geographic distribution (Elliott et al., 1998).

Specimens of Poraspis polaris from Spitsbergen have been reported to show a general trend of increasing size between the Fraenkelryggen and Ben

139 Nevis Formations (Kiaer and Heintz, 1935; Blieck and Heintz, 1983). If the

MOTH locality does in fact correlate with the lower Ben Nevis Formation, the specimens identified as Poraspis polaris from MOTH fit with this pattern, as their median lengths fall within the upper ranges of those reported by Blieck and

Heintz (1983). This is illustrated in Figure 4.3, with raw data presented in Table

4.1.

The MOTH specimens do not clearly support the trend towards greater organization of the longitudinal dentine ridge pattern of the ornamentation.

UALVP 47059, a specimen identified as Poraspis cf. P. rostrata, shows irregularity in an area beginning between the orbits and continuing into the anterior portion of the branchial part of the dorsal shield (Fig. 2.3B). The dentine ridges in this region stray from the overall longitudinal pattern and are instead sinuous. The ornament is particularly irregular around where the pineal macula is expected to be observed and the posterior portion of the rostral area (Fig. 1.2).

UALVP 47062, identified as Poraspis sp. nov. B, shows some irregularity in the anterior part of the branchial portion of the dorsal shield (Fig. 2.9C), though this is not as pronounced as in UALVP 47059. A ventral shield identified as Poraspis cf. P. polaris, UALVP 47064 (Fig. 2.7D), shows a high degree of sinuosity and a whorl along the broken posterior edge of the specimen. This whorl is situated slightly anatomically right of the ventral midline. These specimens do not exhibit a pattern of highly organized longitudinal dentine ridges, as was expected assuming the correct correlation with the lower Ben Nevis. Variation of the dentine ridge pattern has been documented in Anglaspis ins ignis Wills, 1935

140 u

5 -

0 - •id

5 -

0 -

5 -

• Spitsbergen specimens 0 - • MOTH specimens

5 -

0 -

5 -

1 i 5 10 15 Pineal length (mm)

FIGURE 4.3. Median length vs. pineal length of the dorsal shields of specimens of Poraspis polaris from Spitsbergen and the MOTH locality. Data for Spitsbergen specimens from Blieck and Heintz (1983).

141 TABLE 4.1. Median and pineal lengths of the dorsal shield of specimens of Poraspis polaris from Spitsbergen and the MOTH locality. Data for the Spitsbergen specimens from Blieck and Heintz (1983). Presented in graphical form in Figure 4.2. For abbreviations, see List of Abbreviations.

Specimen # ML PL

PMO D 001 36.50 9.00

PMO D 002 39.00 9.00

PMO D 28b 40.00 8.00

PMO D 84 37.00 9.00

PMOD 115 34.00 8.50

PMOD 141a 41.50 10.50

PMOD 147 32.00 9.00

PMOD 198 32.00 7.50

PMO D 204a 36.00 8.50

PMO D 204b 36.50 9.00

PMO D 205 44.00 11.50

PMOD 241a 37.00 7.00

PMOD 241b 32.00 8.00

PMO D 665 40.00 9.0

PMOD 1161 34.00 6.50

UALVP 23394 38.80 9.68

UALVP 23436 39.04 9.22

UALVP 32785 42.14 10.36

UALVP 32785 42.12 10.99

142 (Blieck and Heintz, 1983), and individual variation in ornamentation patterns over the dorsal and ventral shields may be a result of different factors impacting development and ossification of the dermoskeleton (see Chapter II, Discussion,

Ornamentation).

UALVP 41426, Poraspis sp. nov. D, exhibits a broad transverse band of dentine ridges in the anterior portion the rostral area, with 16-18 ridges (Fig.

2.11). Kiaer and Heintz (1935) described a trend in which the number of transverse dentine ridges is reduced through time. This trend was supported by the description of Poraspis thules Elliott et al. (1998), a Silurian species with a broad band of 7-9 transverse ridges on the rostrum. However, Poraspis sp. nov. D clearly contradicts this pattern. It is unclear how much this particular feature varies between individuals.

The trend in Poraspis toward a more united network of sensory canals has been recognized by several authors (Kiaer and Heintz, 1935; Denison, 1964;

Elliott et al. 1998). Many specimens from MOTH exhibit pitted areas over the shields where preservation of the sensory pores is poor, so this trend is difficult to assess. However, the MOTH taxa do show variability in the pattern of sensory pores: P. rostrata, P. polaris, Poraspis sp. nov. B, and Poraspis sp. nov. D possess single-rowed sensory pores, while Poraspis sp. nov. A and Poraspis sp. nov. B exhibit a doubled set of pores.

Elliott et al. (1998) suggested that later species of Poraspis have a wider geographic distribution, citing the presence of P. polaris in the Delorme

Formation as reported by Dineley and Loeffler (1976) as well as from

143 Spitsbergen, and P. sericea from the Upper Member of the Peel Sound Formation

(Elliott et al., 1998) and Great Britain. The presence of P. polaris in the MOTH fauna provides an additional example of a later-occurring species with a wide geographic distribution.

Though the Poraspis species from MOTH appear to conform to the trend of increasing size previously hypothesized, it is unclear whether the trends of increased organization of the ornamentation and unification of the sensory canal network are supported. Poraspis sp. nov. D is clearly seen to contradict Kiaer and

Heintz (1935)'s concept of decreasing number of transverse rostral ridges through time, as UALVP 41426 bears more transverse ridges than the Silurian P. thules

(Elliott etal., 1998).

PALEOENVIRONMENT OF PORASPIDINES

Poraspidines are now known from localities with various paleoenvironmental interpretations. Some early researchers hypothesized that cyathaspidids dwelt in a freshwater habitat, as they are absent in most marine

Silurian formations (e.g. Romer and Grove, 1935; Romer, 1946). Denison (1956,

1964) argued to the contrary, suggesting that this absence indicates that they were mainly restricted to particular ecological niches in nearshore areas where the few known specimens are found. Denison (1956, 1964) also described a trend of transition into marginal marine environments in the Late Silurian, and into the

144 brackish and freshwater habitats generally considered typical of Early Devonian cyathaspidid localities.

Heterostracans appear to have exclusively occupied marine environments in the Ordovician, and rare Middle Silurian heterostracans were also marine

(Dineley and Loeffler, 1976). By the early Late Silurian, heterostracans began to enter brackish and freshwater environments, but were still predominantly inhabitants of marine waters. The only clear evidence of poraspidines inhabiting an exclusively marine environment in the Silurian is the occurrence of

Homalaspidella borealis from the southeastern Yukon Territory. H. borealis is found in dolomites and is directly associated with crinoids, inarticulate brachiopods, and fistuliporid bryozoans, indicating a typical marine environment

(Denison, 1963). Another Silurian poraspidine, Americaspis, is found in red bed sequences of the northeastern United States, and is common in the Late Silurian

Landisburg Sandstone Member of the marine Wills Creek Formation, which is overlain by the more terrestrial Tonoloway Formations. The Landisburg

Sandstone is interpreted as lagoonal with small deltas, and Americaspis is thought to have dwelt in marginal habitats that may have included brackish or perhaps even fresh water (Denison, 1964).

Denison (1956) considered Devonian heterostracans to be euryhaline and to have occupied marginal marine habitats and the lower portions of streams.

Poraspidines are rarely found in typical marine environments, and are predominantly known from marginal or nearshore marine sediments, such as those of the Water Canyon Formation of Utah (Denison, 1956), the Czortkow

145 stage of the Ukraine, and throughout numerous horizons of the Red Bay Series of

Spitsbergen (Denison, 1964; Goujet andBlieck, 1977). Occurrences of Poraspis in France, Great Britain, and Spitsbergen were probably of freshwater origin, but with marine beds intercalcated between these deposits (Denison, 1964). The

Beartooth Butte Formation and the Holland Quarry Shale are interpreted as brackish to freshwater environments, such as estuaries or inlets (Denison, 1960,

1964). Other occurrences in Great Britain (Ball and Dineley, 1961; Allen and

Tarlo, 1963) and the Ukraine are considered definitely freshwater deposits, possibly representing deltaic environments (Denison, 1964).

The strata at MOTH were deposited at a time when poraspidines and other cyathaspidids are thought to have lived primarily in marginal or freshwater habitats. Previously interpreted as marine (Wilson and Caldwell, 1998; Hanke,

2001, 2002) or a hyposaline lagoon (Dineley and Loeffler, 1976), the MOTH locality is now thought to represent a topographically lower area on the continental shelf (Zorn et al., 2005; see 'Locality and Age' in Chapter I for further discussion), and this interpretation is accepted here. Thus, the MOTH fauna represents a rare Early Devonian occurrence of completely marine heterostracans, including a diversity of poraspidine taxa. Osteostracans were also thought to have been nearly exclusively inhabitants of fresh water by the Devonian, but are also common components of the MOTH fauna. However, the oxygen and salinity- stressed environment proposed for the MOTH locality presents conditions that more closely resemble the more nearshore marine environments in which poraspidines commonly occurred at this time.

146 CONCLUSIONS

Poraspidines are known from localities across North America and Europe, ranging in age from the Late Silurian (Early Ludlovian) to the Early Devonian

(Pragian). The poraspidine fauna known from the MOTH locality represents a diverse group of species from the middle of the time frame from which Poraspis is known, and is among the westernmost occurrences of Poraspidinae. The morphological trend of increasing size is supported by the MOTH specimens, though the trend of decreased transverse rostral ridges is contradicted, and the increased organization of the ornament and sensory canal system is not clearly supported. The MOTH locality represents a rare example of poraspidines from a marine environment, though its specific conditions may have had many similarities to more typical marginal environments.

147 LITERATURE CITED

Allen, J. R. L., and L. B. Tarlo. 1963.The Downtonian and Dittonian facies of the

Welsh borderland. Geological Magazine 100:129-155. [Not yet seen].

Ball, H. W., and D. L. Dineley. 1961. The Old Red Sandstone of Brown Clee Hill and the adjacent area. I. Stratigraphy. Bulletin of the British Museum, Natural

History (Geology) 5:176-242.

Bardenheuer, P., and M. Otto. 1994. Erste cyathaspiden-reste (Agnatha,

Heterostraci) aus dem Rheinischen Unterdevon. Geol. Jb. Hessen 122:5-11.

Blieck, A. 1984. Les heterostraces Pteraspidiformes, agnathes du Silurien-

Devonien du continent nord-atlantique et des blocs avoisinants: Revision systematique, phylogenie, biostratigraphie, biogeographie. Centre National de la

Recherche Scientifique, Paris. [Not yet seen].

Blieck, A., and N. Heintz. 1983. The cyathaspids of the Red Bay Group (Lower

Devonian) of Spitsbergen. XIII. Polar Research, 1 (NS):49-74.

Broad, D. S. 1973. Amphiaspidiformes (Heterostraci) from the Silurian of the

Canadian Arctic archipelago. Geological Survey of Canada Bulletin 222:35-50.

148 Broad, D. S., and D. L. Dineley. 1973. Torpedaspis, a new Upper Silurian and

Lower Devonian genus of Cyathaspididae (Ostracodermi) from arctic Canada.

Bulletin of the Geological Survey of Canada 222:53-90.

Claypole, 1884. Preliminary note on some fossil fishes recently discovered in the

Silurian rocks of North America. American Naturalist 18:1222-1226.

Dejonghe, L., A. Herbosch, P. Steemans, and J. Verniers. 2006. Disused

Palaeozoic regional stages from Belgium: Devillian, Revinian, Salmian,

Gedinnian and Burnotian. Geologica Belgica 9:191-197.

Denison, R. H. 1956. A review of the habitat of the earliest vertebrates. Fieldiana:

Geology 11:359-457.

Denison, R. H. 1960. Fishes of the Devonian Holland Quarry Shale of Ohio.

Fieldiana: Geology 11:555-613.

Denison, R. H. 1963. New Silurian Heterostraci from southeastern Yukon.

Fieldiana: Geology 14:105-141.

Denison, R. H. 1964. The Cyathaspididae: a family of Silurian and Devonian jawless vertebrates. Fieldiana, Geology 13:309-473.

149 Dineley, D. L., and E. J. Loeffler. 1976. Ostracoderm faunas of the Delorme and associated Siluro-Devonian Formations, North West Territories, Canada.

Palaeontological Association Special Papers in Palaeontology 18:1-214.

Elliott, D. K. 1984. Siluro-Devonian fish biostratigraphy of the Canadian Arctic

Islands. Proceedings of the Linnean Society of New South Wales 107:197-209.

Elliott, D. K., and D. L. Dineley. 1985. A new heterostracan from the Upper

Silurian of Northwest Territories, Canada. Journal of Vertebrate Paleontology

5:103-110.

Elliott, D. K., and D. L. Dineley. 1991. Additional information on Alainaspis and

Boothiaspis, cyathaspidids (Agnatha: Heterostraci) from the Upper Silurian of

Northwest Territories, Canada. Journal of Paleontology 65:308-313.

Elliott, D. K., E. J. Loeffler, and Y. Liu. 1998. New species of the cyathaspidid

Poraspis (Agnatha: Heterostraci) from the Late Silurian and Early Devonian of

Northwest Territories, Canada. Journal of Paleontology 72:360-370.

Goujet, D., and Blieck, A. 1977. La fauna de vertebres de l'horizon 'Vogti'

(Groupe de Red Bay, Spitsberg). Comparaison avec les autres faunes ichthyologiques de Devonien inferieur Europeen. Comptes Rendus des Seances de l'Academie des Sciences 284:1513-1515. [Not yet seen].

150 Hanke, G. F. 2001. Comparison of an early Devonian acanthodian and putative chondrichthyan assemblage using both isolated and articulated remains from the

Mackenzie Mountains, with a cladistic analysis of early gnathostomes.

Unpublished Ph.D. Thesis, University of Alberta. 566 pp.

Hanke, G. F. 2002. Paucicanthus vanelsti gen. et sp. nov., an Early Devonian

(Lochkovian) acanthodian that lacks paired fin-spines. Canadian Journal of Earth

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Kiaer, J. 1932. The Downtonian and Devonian vertebrates of Spitsbergen. IV.

Order Cyathaspida. Skrifter Svalbard Ishavet 52:7-26.

Kiaer, J., and A. Heintz. 1935. The Downtonian and Devonian vertebrates of

Spitsbergen. V. Suborder Cyathaspida. Part 1. Tribe Poraspidei, Family

Poraspidae Kiaer. Skrifter Svalbard Ishavet 40:138 pp.

Novitskaya, L. I. 1972. Phylogenetic relationships of poraspids (Heterostraci).

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151 Novitskaya, L. I. 1986. Drevneishie bechelyustne SSSR, Geterostraki:

Tsiataspidy, Amphiaspidy, Pteraspidy. Trudy Paleontologicheskogo Instituta

Academii Nauk SSSR 219:27-75. [Only English translation seen: 1988. The earliest Agnatha of the USSR, Heterostraci: Cyathaspidae, Amphiaspidae,

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(Heterostraci: Orders Cyathaspidiformes, Pteraspidiformes). Paleontological

Journal 41:268-280.

Romer, A. S. 1946. The early evolution of fishes. Quarterly Review of Biology

21:33-69.

Romer, A. S., and B. H. Grove. 1935. Environment of the early vertebrates.

American Midland Naturalist 16:805-856.

White, E. I. and J. A. Moy-Thomas. 1941. Notes on the nomenclature of fossil fishes, Part I: Homonyms M-Z. The Annals and Magazine of Natural History,

11th Series 7:395^00.

152 Whitley, G. P. 1940. The nomenclator Zoologicus and some new fish names.

Australian Naturalist 10:241-243.

Wills, L. J. 1935. Rare and new ostracoderm fishes from the Downtonian of

Shropshire. Transactions of the Royal Society of Edinburgh 55:427-447. [Not yet seen].

Wilson, M.V. H., and M. W. Caldwell. 1998. The Furcacaudiformes: a new order of jawless vertebrates with thelodont scales, based on articulated Silurian and

Devonian fossils from Northern Canada. Journal of Vertebrate Paleontology

18:10-29.

Woodward, A. S. 1891. Catalogue of the Fossil Fishes in the British Museum

(Natural History). Part II: Elasmobranchii (Acanthodii), Holocephali,

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Chondrostean Actinopterygii). London, 567 pp.

Zorn, M. E., M. W. Caldwell, and M. V. H Wilson. 2005. Lithological analysis of the Lower Devonian vertebrate-bearing beds at the MOTH locality, N.W.T.,

Canada: insights to taphonomy and depositional setting. Canadian Journal of

Earth Sciences 42:763-775.

153 V. CONCLUSIONS

Four new species of poraspidine cyathaspidids are described from the

MOTH locality of the Northwest Territories of Canada, all assigned to the genus

Poraspis. This assignment is based on the dimensions and shape of the dorsal shield, the patterns of ornamentation and the sensory system, and the absence of distinguishable epitega on the dorsal shields. Revisions of the definitions of

Subfamily Poraspidinae, Genus Poraspis, and the thirteen currently recognized species of Poraspis are also presented. Ariaspis is excluded from Poraspidinae, and Liliaspis and Anglaspis are retained within the subfamily. Diagnostic characteristics previously used to distinguish between species of Poraspis, including patterns, density, and crest shape of ornamentation and various dimensions of the dorsal shield, are discussed with respect to factors such as taphonomy and different forms of variation that can result in misinterpretation of these features.

Cladistic analyses are attempted for the first time to try to clarify the relationships between species of Poraspis and the various genera assigned to

Subfamily Poraspidinae. Unfortunately the trees produced are poorly resolved, and few firm conclusions can be made. Additionally, more reliable characters must be generated to obtain more resolution with respect to the relationships of the poraspidines and the species that constitute Genus Poraspis. Details of ornamentation and dimensions of the dorsal shield may be highly variable and of

154 low phylogenetic significance, but more work is needed to establish the range of variation between poraspidine genera and species.

The presence of poraspidines at the MOTH locality contributes to the data available for the interpretation of the origin, evolution, and radiation of these early vertebrates. Though poraspidines are known from across much of the Northern

Hemisphere (Janvier, 1996), the MOTH locality is among the westernmost sites

(both in the Devonian and at present) known to produce poraspidines. Several previously identified trends in the evolution of Poraspis (Kiaer and Heintz, 1935;

Blieck and Heintz, 1983; Elliott et al. 1998) are evaluated in the context of the new specimens from the MOTH locality. Occurring in the early-middle time period of the evolution of Poraspis, the MOTH poraspidines appear to be congruent with the trends of increasing length of the dorsal shield and wider

distribution of later-occurring species. However, the description of Poraspis sp. nov. D contradicts the trend towards a decreasing number of transverse ridges in the rostral region of the dorsal shield, and the trends of increasing organization of the ornamentation and sensory canal system are not clearly supported. The area that is now the Mackenzie Mountains was a region where poraspidines radiated

and diversified, with at least six species of Poraspis present. However, there was

clearly interchange with the similar-age faunas from Spitsbergen, as indicated by the presence of Poraspis rostrata and Poraspis polar is. The MOTH locality also

provides a rare example of poraspidines occurring in a marine environment,

though the environmental conditions present at the time of deposition were likely

not typically marine (Zorn et al., 2005).

155 LITERATURE CITED

Blieck, A., and N. Heintz. 1983. The cyathaspids of the Red Bay Group (Lower

Devonian) of Spitsbergen. XIII. Polar Research, 1 (NS):49-74.

Elliott, D. K., E. J. Loeffler, and Y. Liu. 1998. New species of the cyathaspidid

Poraspis (Agnatha: Heterostraci) from the Late Silurian and Early Devonian of

Northwest Territories, Canada. Journal of Paleontology 72:360-370.

Janvier, P. 1996. Early Vertebrates. Clarendon Press, Oxford, 393 pp.

Kiaer, J., and A. Heintz. 1935. The Downtonian and Devonian vertebrates of

Spitsbergen. V. Suborder Cyathaspida. Part 1. Tribe Poraspidei, Family

Poraspidae Kiaer. Skrifter Svalbard Ishavet 40:138 pp.

Zorn, M. E., M. W. Caldwell, and M. V. H Wilson. 2005. Lithological analysis of the Lower Devonian vertebrate-bearing beds at the MOTH locality, N.W.T.,

Canada: insights to taphonomy and depositional setting. Canadian Journal of

Earth Sciences 42:763-775.

156