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Thelodont phylogeny revisited, with inclusion of key scale-based taxa/ Telodontide fulogeneesiuuringud soomustepohiste taksonite kaasamisega.

INTRODUCTION

Our understanding of the Palaeozoic vertebrate subclass Thelodonti has improved greatly in recent years as a result of new discoveries (e.g., Wilson & Caldwell 1993, 1998; Mdrss 1999; Mdrss et al. 2002) as well as monographic revisions of articulated specimens and scale-based taxa (e.g., Mdrss & Ritchie 1998; Karatajute-Talimaa & Mdrss 2004; Mdrss et al. 2006, 2007). However, in the early years of study of thelodonts, they proved to be a difficult group for workers to deal with. Thelodont scales were first described by L. Agassiz (in Murchison 1838) but their status as a distinct group of jawless vertebrates evolved slowly over many decades (see historical review by, e.g., Turner 1991). Thelodonts preserved as articulated skeletons have been known since Powrie (1870) described 'Cephalopterus' pagei, the generic name of which was subsequently found to be preoccupied. Powrie believed his species to be an acanthodian. This error was corrected by Traquair (1896), who named the genus Turinia to contain Powrie's species and grouped it with other well-preserved Scottish thelodonts as jawless vertebrates (Agnatha). Thelodonti were formally recognized as a higher taxon within Agnatha but distinct from other jawless vertebrates by Kiaer (1932).

In recent decades new discoveries and monographic treatments of thelodonts have included a detailed study of scale-based species from the former Soviet Union and Spitsbergen (Karatajiito-Talimaa 1978), scale-based species of Estonia and Latvia (Marss 1986), Silurian species based on articulated specimens from Scotland (Marss & Ritchie 1998), Silurian and Devonian species of a new group called Furcacaudiformes by Wilson & Caldwell (1993, 1998), and Silurian and Devonian species based on scales and articulated squamations from Arctic Canada (Marss et al. 2006). Thelodont studies have also been significantly advanced by publication of a reference work on thelodonts from Russia and adjacent countries (Karatajiito-Talimaa & Mdrss 2004) and by the thelodont volume of the Handbook of Paleoichthyology (Marss et al. 2007).

However, the phylogenetic relationships within the group have remained problematic, and the question of monophyly of the Thelodonti has also been controversial (e.g., Turner 1991; Janvier 1996; Donoghue & Smith 2001; Wilson & Mdrss 2004).

The present contribution is our second attempt at resolving the within-group relationships of thelodonts. Our first attempt (Wilson & Mdrss 2004) was based almost entirely on articulated specimens (in reality, articulated squamations). In that paper 25 species of thelodonts were studied and a preliminary phylogenetic arrangement was proposed. For many of them, data were available for both scale histology and overall body form. For others, however, one of these key sets of features was absent due to imperfect preservation or lack of the needed analysis. The resulting phylogenetic tree (Wilson & Mdrss 2004, fig. 6; reproduced as Mdrss et al. 2007, fig. 34) suggested a basal split within Thelodonti between a group consisting of Archipelepis, Phlebolepis, and Erepsilepis and all other thelodonts. The latter group was further divided into one that included Turinia, Loganellia, and Phillipsilepis and a larger separate group of remaining species. This larger group was then divided between a clade consisting of Shielia spp. and Lanarkia spp., collectively sister to the fork-tailed thelodonts or Furcacaudiformes. The basic structure of that tree is reproduced here in Fig. IA for comparison with new findings.

However, the thelodont fossil record includes many very important species that are based solely on isolated scales. Isolated scales derived from acid dissolution of fossiliferous rocks can often be associated with considerable assurance into suites of scales representing different parts of the body of an individual species, using the clues given by intergradations of scale structure within the samples (e.g., Marss 1999). Not only are these scale-based species important for biostratigraphy, but they also often yield the most complete data concerning scale microstructure and histology. Such details tend to be best preserved in carbonate or carbonate-cemented rocks that are processed with acetic acid to yield scale-bearing residues.

[FIGURE 1 OMITTED]

The original study (Wilson & Marss 2004) began with data on 25 species and four outgroups scored for 53 characters, but one outgroup and one ingroup species were eliminated because of wildcard behaviour in the analyses (in multiple shortest trees, these species took radically different positions, causing a lack of resolution in the strict and majority-rule consensus trees). The final preferred phylogeny was thus based on 24 species of thelodonts and three outgroups.

In the present study we have augmented the original list of taxa from our earlier study by adding data on representative scale-based species. Some 14 scale-based species, each in a different genus, have been added for the present study, although a few of the new species are assigned to genera included in the earlier analysis. We have also revisited the list of characters and states, eliminating some and substituting others, and recoded the previous set of taxa. Our purpose is to produce a new phylogenetic analysis of 39 species of thelodonts that includes both scale-based and squamation-based species. We also compare the effect of updating the data matrix on an analysis of the original 24 species, and discuss the implications of the new phylogeny for thelodont evolution and classification.

METHODS

Our starting point was the data from our earlier study (Wilson & Marss 2004); we updated the data by editing and recoding of states and by deleting characters that were found to be highly homoplasious in the earlier study (Wilson & Marss 2004) or were rendered uninformative after editing. We modified and reduced the number of states for several characters to simplify them and to attempt to capture the major features of character evolution rather than minor variations. We also reexamined the character coding of every species critically and made a number of changes based on our current understanding of body form and of scale morphology and histology. Finally, we added a small number of new characters to replace deleted characters, including one to reflect the new information available about ultrasculpture of the scale surface (Marss 2006a). The resulting list of 52 characters and states is given here as Appendix 1 and the resulting character-taxon matrix for 42 taxa (39 ingroup species and 3 outgroups) is given as Appendix 2. Key features of thelodont scale morphologies used as the basis for character definitions in Appendix 1 are shown in Fig. 2. Similarly, key features of scale histology used for character definitions are shown in Fig. 3. Thelodont bodies and articulated squamations were illustrated in our earlier paper (Wilson & Marss 2004) and also by Marss et al. (2007). We used the same three outgroups as in our earlier study, including 'Athenaegis Tolypelepis' which is a composite of two of the most primitive undoubted heterostracans so far known, Athenaegis being the main source of body-form character states and Tolypelepis being the main source of histological character states. A study such as this with only three representatives of the many species in outgroup taxa is not designed to test thelodont monophyly. A more rigorous test of monophyly would involve a much larger sampling from among other jawless vertebrates, and a much larger number of characters. In the present study we have assumed thelodont monophyly, using outgroups to root the resulting tree, thereby indicating the direction of evolutionary change within the group.

We prepared and edited the data matrix using MacClade Version 4.08 (Maddison & Maddison 2005) and analysed the matrix under the criterion of Maximum Parsimony using PAUP 4.0b10 (Swofford 2002). Using PAUP, we obtained the set of the shortest trees, the strict and majority-rule consensus trees based on those shortest trees, and we also generated random trees for the purpose of assessing the strength of the phylogenetic signal in the data matrix. Using MacClade again, we graphically displayed the strict and majority-rule consensus trees, mapped character changes onto them, and generated tree-fit and character-specific statistics.

In PAUP, we performed heuristic searches with mostly default options, except for obtaining starting trees by random addition with 100 replicates. Branch-Swapping was by TBR (Tree Bisection-Reconnection), with the steepest descent off, multrees in effect, swapping on the best trees only, and no topological constraints. Rooting was on the single composite outgroup (Athenaegis Tolypelepis), although data for two other outgroups (Rhyncholepis parvula and Tremataspis schmidti) were included in the analysis.

The character-taxon matrix contained 52 characters, all of them informative, all treated as unordered and of equal weight. The number of states per character ranged from 2 to 7, and the total number of apomorphic states was 80. Missing data per character ranged from zero to 83.3%, while inapplicable states per character ranged from zero to 85.7%.

We investigated whether the differences in the resulting phylogenies between our 2004 paper and the current study were caused mostly by changes in the characters and states or whether the difference in results was caused by addition of scale-based taxa. To examine this question, we re-analysed the same set of 24 taxa from the earlier study (Wilson & Marss 2004) but using the updated set of characters and states (Appendices 1 and 2). We then compared the resulting phylogeny with that produced by the earlier study.

[FIGURE 2 OMITTED]

We then added the 14 newly coded, scale-based taxa along with one ingroup species, Eestilepis prominens, that had been coded for our 2004 study but omitted because of wild-card behaviour. The complete data set was then analysed using the above-mentioned protocols. We also investigated the possibility of adding a fourth outgroup (Poracanthodes menneri) that we had attempted to include in 2004.

RESULTS

The analysis of the original 24 ingroup and three outgroup taxa using the original 53 characters (Wilson & Marss 2004, fig. 6) had given the preferred result illustrated here in Fig. IA (majority-rule consensus of the 31 shortest trees of length 153 steps). When analysed with the updated data set, the same 24 species yield the arrangement in Fig. 113 (majority-rule consensus of 212 trees at 156 steps). It is evident that the updated data matrix produces a different phylogenetic arrangement for several important taxa. Erepsilepis and Phlebolepis were grouped with Archipelepis near the base of the tree in the 2004 study (Fig. IA), but with the updated data they are grouped with Loganellia and Shielia (Fig. 1B). In addition, Shielia itself was grouped with Lanarkia in the 2004 study (Fig. IA), but is united with Loganellia, Erepsilepis, and Phlebolepis using the updated data (Fig. 1B). Turinia was united with Loganellia in 2004 but takes a much more primitive position using the revised data.

When the 14 scale-based taxa as well as Eestilepis prominens, known from a partially articulated squamation, were added to the analysis, the data matrix contained 39 thelodont species and three outgroup taxa, coded for 52 characters.

As with our previous study (Wilson & Marss 2004), our attempt to include the acanthodian outgroup Poracanthodes menneri was not successsfial. The primary character-state homologies of this species, relative to the characters designed for thelodont relationships, are difficult to determine because of the lack of comparability of its morphology and scales with the features of thelodonts. Moreover, when we included our tentative codings for Poracanthodes in the analysis, all structure of the phylogeny was destroyed and a large basal polytomy was generated. We therefore eliminated Poracanthodes as an outgroup and do not include it in our published data because we think it unwise to disseminate those preliminary but unreliable character-state codings.

In our 2004 paper we had preferred the phylogeny that omitted Eestilepis from consideration owing to its wild-card behaviour. Unlike our experience with Poracanthodes menneri, the new data matrix was much more successful in placing Eestilepis prominens with consistency, giving a similar relationship for this species in all shortest trees, despite its large proportion of missing data. Our preferred result, therefore, includes all 39 thelodonts for which we coded data.

The result for the inclusive analysis was 2558 shortest trees of length 204 steps. The strict consensus tree (Fig. 4A) has a high degree of resolution. The inclusive majority-rule tree (Figs 413, 5) is only slightly more resolved than the strict consensus tree (Fig. 4A). For the shortest trees, the Consistency Index (C.I.) was 0.39, the Retention Index (R.I.) was 0.72, and the Rescaled Consistency Index (RC.) was 0.28.

Comparing the inclusive tree for 39 thelodonts with that based on the original 24 species indicates that the inclusive majority-rule tree (Fig. 413) is about as well resolved as the tree based only on the original 24 species (Fig. 1B). The two trees differ in that furcacaudiforms are a distinct clade in the analysis of 24 taxa (Fig. 113) but they are united with Lanarkia, Phillipsilepis, and Nikolivia when the additional scale-based taxa are included (Fig. 4B).

Examination of the frequency distribution of 10 000 000 random trees generated from the inclusive data set (Appendix 2) showed a strong phylogenetic signal. The shortest tree found among the random trees was 346 steps (compared to the shortest overall trees of 204 steps). The random trees had a mean length of 436 steps, a standard deviation of 12.4, and a skewness of -0.30; the shortest trees found by the heuristic procedure (Fig. 4) are thus more than 18 standard deviations shorter than the average of the random trees and we conclude that the phylogenetic signal in the data is strong.

[FIGURE 3 OMITTED]

The character changes are mapped onto the majority-rule consensus tree in Fig. 5. Note that only unequivocal changes are shown; the lack of changes adjacent to polytomies (e.g., the clade Archipelepis spp. and Boothialepis; the polytomy among furcacaudid species; the polytomy among Shielia species) is a product of this restriction. Different, arbitrary resolutions of these polytomies would give different suggested synapomorphies at adjacent nodes. For example, when any one of the three constituent species of the clade Boothialepis + Archipelepis is placed as sister to the other two species, at least four synapomorphies are mapped unequivocally on the node: 11(1), 16(0), 17(3), and 22(2). These four synapomorphies are joined by state 4(2) if either of the two species of Archipelepis is placed as sister to the other two members of the clade. Characters evolving with the minimum number of possible steps overall (C.I. = 1.0) in the majority-rule tree are characters 3, 13, 14, 15, 25, 34, 35, 42, 43, 49, and 52. Characters evolving with the most homoplasy (C.I. [less than or equal to] 0.2) are characters 4, 11, 18, 24, and 46.

[FIGURE 4 OMITTED]

[FIGURE 5 OMITTED]

DISCUSSION

We consider that the present results represent a significant advance over our earlier attempt (Wilson & Marss 2004) both because of the improvements made in the data matrix and because of the more inclusive set of species in this new study.

Our analysis of the original 24 thelodont species using the updated data matrix shows that most of the changes in the relationships of these original species, compared with their relationships in the earlier study (Fig. IA vs Figs 113, 4), are caused by revisions to characters and states. Some other changes result from the addition of 15 mostly scale-based species to the analysis. The revised data matrix was able to place Eestilepis prominens with confidence; that species had acted as a wild-card and had been eliminated from the earlier analysis (Wilson & Marss 2004).

These results suggest to us that there is no fundamental barrier to the future analysis of additional, scale-based taxa despite their lack of data concerning body morphology. Similarly, the relationships of some of the articulated, squamation-based species for which ultrastructural data are currently lacking were not greatly changed by adding the scale-based taxa. This is good news for the future of thelodont phylogenetics.

Each of the three basic clades of thelodonts according to the present results has distinctive features indicated by the character-state changes mapped onto the phylogeny in Fig. 5, although the most basal clade (a trichotomy containing two species of Archipelepis and one of Boothialepis) has no unambiguous synapomorphies unless the trichotomy is arbitrarily resolved (see Results for details). This clade is distinguished from the other two clades by the following synapomorphies that the two larger clades share: scale base from wide to narrow (23:2-0), although the base configuration changes in some descendants to medium and/or wide, and pulp canals from absent to one (28:0-1), again with some subsequent changes to absent or more than one in certain descendants.

The large clade containing Nikolivia, Lanarkia, Phillipsilepis, and Furcacaudiformes (including Barlowodus and Apalolepis) is united by a rounded as opposed to a quadrangular scale base (21:2-0) except Furcacauda fredholmae and the clade consisting of all of these taxa except Nikolivia is united by a crown that overlaps posterior scales greatly (16:1-2), again with a few exceptions.

The largest clade, which includes Turinia, Thelodus, Loganellia, Phlebolepis, Shielia, and relatives is united by three synapomorphies. The first is that basal members of the clade share a moderately deep scale base (22:0-1), although according to our topology subsequent evolution leads to more variation in this character. The second is that most of the clade shares (homoplasiously with Lanarkia) a moderate to strong anterior process on the scale base (24:0-1). The third synapomorphy uniting the clade is a long, straight intestine (43:0-1), although only in a few species can probable gut endocasts be seen. In others, one can estimate gut proportions by the length of the post-branchnnl, pre-caudal trunk, which is rather long and slender in most species. However, based on a similar argument about body proportions, one would also expect a long, straight intestine in Lanarkia spp. based on their body proportions (Marss & Ritchie 1998), and if that were confirmed, the character might be optimized differently.

The entire clade apart from Turinia shares sinuous or branching dentine tubules, as opposed to straight ones, in the mid-crown of scales (31:0-1), although this feature is also seen in furcacaudiforms. All members of the clade except Turinia and Thelodus share two unreversed synapomorphies: presence of a pulp depression in the scale base (25:0-1), and absence of a pulp cavity in the scale (26:1-0).

The new phylogeny makes interesting predictions about unseen features of both scale-based and squamation-based taxa. For example, the scale-based Thelodus laevis might be expected to have a body form something like those of Turinia and Loganellia. Stroinolepis maenniki is predicted to have a Loganellia-like body form. Longodus and Helenolepis are predicted to share additional features with Phlebolepis and Shielia. Trimerolepis, Valiukia, and Paralogania are predicted to share features with Shielia. Valiukia and Paralogania had already been united with Shielia in Shieliidae (Marss et al. 2006, 2007), but the inclusion of Trimerolepis is a novel result, the genus previously being classified in Katoporodidae (Marss et al. 2007). Similarly, Barlowodus and Apalolepis are predicted to share body-form features with Furcacaudiformes rather than with the Thelodontiformes. Barlowodus had been included in the Furcacaudiformes by Marss et al. (2002, 2006) but it, along with Apalolepis, was not classified with Furcacaudiformes by Marss et al. (2007). Similarly, Boothialepis is expected to share morphological features with Archipelepis. When articulated specimens of these taxa are discovered, their morphologies will test the predictions of the phylogeny presented here.

Predictions concerning squamation-based taxa are focused mainly on those species for which limited data are currently available concerning histological or other ultrastructural features. Eestilepis prominens for example, known from a partial squamation that does not allow coding of most morphological features (Marss et al. 2002, 2006), is predicted to share histological features with Paralogania and Shielia, and morphological features with Shielia.

The phylogeny indicates that some aspects of thelodont classification are in need of revision. A strict interpretation of these results indicates that the Thelodontiformes, as previously conceived (e.g., Marss et al. 2007), contained relatives of what were then classified as Loganelliiformes (e.g., Stroinolepis), Furcacaudiformes (e.g., Barlowodus, Apalolepis), and Shielfformes (Eestilepis), as well as members of a basal clade of thelodonts (Archipelepis and Boothialepis) and basal branches from the two most diverse clades (e.g., Nikolivia as a basal branch of one clade and Turinia and Thelodus as successive basal branches of the other). A revised classification of thelodonts will allocate the various constituents of that paraphyletic assemblage to their various rightful groups. We here suggest a framework for that revised classification, using the 'sequencing convention' to indicate successive sister-group relationships, as follows:
Subclass Thelodonti Jaekel, 1911
  Order Archipelepidiformes, nov.
    Archipelepididae Marss (in Soehn et al. 2001)
      Archipelepis Marss (in Soehn et al. 2001)
  Boothialepididae Marss, 1999
      Boothialepis Marss, 1999

Order Furcacaudiformes Wilson & Caldwell, 1998
  Family Nikoliviidae Karatajiite-Talimaa, 1978
    Nikolivia Karatajiite-Talimaa, 1978

  Family Lanarkiidae Obruchev, 1949
    Lanarkia Traquair, 1898
    Phillipsilepis Marss et al., 2002
  Family Pezopallichthyidae Wilson & Caldwell, 1998
    Pezopallichthys Wilson & Caldwell, 1998
  Family Drepanolepididae, nov.
    Drepanolepis Wilson & Caldwell, 1998
Family Barlowodidae Marss et al., 2002
    Barlowodus Marss et al., 2002
Family Apalolepididae Turner, 1976
    Apalolepis Karatajiite-Talimaa, 1968
Family Furcacaudidae Wilson & Caldwell, 1998
    Canonia Vieth, 1980
    Furcacauda Wilson & Caldwell, 1998
    Cometicercus Wilson & Caldwell, 1998
    Sphenonectris Wilson & Caldwell, 1998
Order Thelodontiformes Kiaer, 1932
  Family Turiniidae Obruchev, 1964
    Turinia Traquair, 1896
Family Coelolepidae Pander, 1856
  Thelodus Agassiz (in Murchison 1838)
Family Loganelliidae Marss et al., 2002
  Stroinolepis Marss & Karatajiite-Talimaa, 2002
  Loganellia Fredholm, 1990
Family Longodidae Marss, 2006b
  Longodus Marss, 2006b
Family Helenolepididae, nov.
  Helenolepis Karatajiite-Talimaa, 1978
Family Phlebolepididae Berg, 1940
  Phlebolepis Pander, 1856
  Erepsilepis Marss et al., 2002
Family Shieliidae Marss et al., 2002
  Trimerolepis Obruchev & Karatajiit&Talimaa, 1967
  Eestilepis Marss et al., 2002
  Valiukia Karatajiit&Talimaa & Marss, 2002
  Paralogania Karatajiite-Talimaa, 1997
  Shielia Marss (in Marss & Ritchie 1998)


doi: 10.3176/earth 2009.4.08

Appendix 1. List of characters and states for phylogenetic analysis of 39 species of thelodonts and three outgroup taxa. Illustrations of important character states are found in the cited references and/or in Figs 2 and 3. Important summaries of the features of thelodonts can be found in Karatajiite-Talimaa (1978), Marss (1986), Turner (1991), Wilson & Caldwell (1993, 1998), Marss & Ritchie (1998), and Marss et al. (2002, 2006, 2007).

Exoskeleton

1. Head plates: absent = 0; many small = 1; few large = 2

2. Dermal skeleton of trunk: monodontodia = 0; polyodontodia = 1; other = 2

General scale arrangement

3. Longitudinal rows of larger scales among smaller ones: absent = 0; present = 1

4. Scale distribution on trunk: irregular or in longitudinal rows = 1; in diagonal rows = 2 Scale regions

5. Specialized scales immediately anterior to or surrounding orbits: low-crowned as head scales = 0; high-crowned, with one point = 1; multipointed = 2; enlarged scales/small platelet(s) = 3

6. Distinct mid-dorsal and mid-ventral body scales: absent = 0; present = 1

7. Distinct scales of leading edges of fins: absent = 0; present = 1

Trunk scales

Size of scales

8. Size of scales (length): very small (0.1-0.5 mm) = 0; small (0.5-1.0 mm) = 1; medium (1-2 mm) = 2; large (2-4 mm) = 3

9. Scales of very different sizes: absent = 0; present = 1 Crown shape

10. Configuration: irregular = 0; water drop-like = 1; diamond = 2; elongate oval = 3; cuneiform = 4; flammate = 5; slender and high = 6 (Fig. 2P, Q; Fig. 2H; Fig. 213, F, G; Fig. 2E; Fig. 2D, K, L; Fig. 2M, N, O; state 6 not illustrated)

11. Crown surface: flattened = 0; moderately raised (<45 deg.) = 1; strongly raised (>45 deg.) = 2 (Fig. 2G, R; Fig. 2A; Fig. 2D, E)

12. Crown posterior structures: one point = 0; three or more points = 1; fine serration = 2 (Fig. 2A, B, D, G, K; Fig. 2C, M-0; Fig. 2J).

13. Postero-lateral spines on crown: absent = 0; present = 1 (Fig. 2A-L, P-R; Fig. 2M-0)

14. Postero-lateral spines attached: horizontally = 0; vertically = 1 (Marss et al. 2007, figs 60-02; Marss 2003, pl. 2, fig. 11)

15. High crests on body scales: none = 0; one central = 1 (Fig. 2G; Fig. 2E)

16. Crown overlaps base posteriorly: no = 0; slightly or moderately (<1/2 of crown length) = 1; greatly (>1/2 of crown length) = 2 (Fig. 2P, Q; Fig. 2A, B, G, H; Fig. 2D, K, L, O, R) Crown sculpture

17. Crown upper side ornamented with: simple longitudinal ridges = 0; relatively wide smooth medial plate = 1; narrow median plate or double median ridge plus side longitudinal ridge(s) = 2; radiating bifurcating ridges = 3 (Fig. 2D-G; Fig. 2H, I, M, N; Fig. 2A-0, K, L, O; Fig. 2Q)

18. Crown posterior lower side: smooth = 0; sculptured = 1 (Fig. 2A, B2, D2, H2; Fig. 2E, Q2) Crown ultrasculpture

19. None = 0; fine longitudinal striation = 1; wavy transeverse lamellae and irregular polygons = 2; (Marss 2006a, fig. I IA; Marss 2006a, figs 1C, O, 2D, F, I ID; Marss 2006a, figs 2I-Q, 11 G) Neck

20. Absent or as narrow groove = 1; high and distinct = 2 (Fig. 2A, D1, Q2; Fig. 2G2) Base

21. Configuration: rounded = 0; oval =1; quadrangular = 2; elongate rhombic = 3 (Fig. 2132, D2, H2; Fig. 2132; Fig. 2M-P, Q2; not illustrated)

22. Depth: shallow = 0; moderate = 1; very deep = 2 (Fig. 2D1, E; Fig. 2G2; Fig. 2Q2, R)

23. Width: narrow = 0, moderate = 1; wide = 2 (Fig. 2132, H2; Fig. 2D, F, M-0; Fig. 2P, Q)

24. Anterior process: absent = 0; moderate = 1; long to very long = 2 (Fig. 2A, C, E, H, I, J, Q; Fig. 213, G2, M, N; Fig. 2D, K, O, R)

Microstructure of adult scales

25. Pulp depression: absent = 0; present = 1 (Fig. 3A, B, F; Fig. 3C, D)

26. Pulp cavity: absent = 0; present = 1 (Fig. 3C, D; Fig. 3A, B, F)

27. Pulp cavity 'pockets': absent = 0; present = 1 (Fig. 3A, F; Fig. 313)

28. Pulp canals: absent = 0; single = 1; multiple = 2 (Fig. 3A; Fig. 313, F; Fig. 3C)

29. Length of (main) pulp canal: short = 0; medium = 1 (< 1/2 length of crown); long = 2 (> 1/2 length of crown) (Marss 1986, pl. 3, fig. 2; Marss et al. 2006, fig. 8D; Marss et al. 2007, fig. 23)

30. Dentine canals in mid crown: absent = 0; present = 1 (Fig. 3A, B, F; Fig. 3C, D)

31. Dentine tubules in mid crown: straight= 0; sinuous/ branching = 1 (Fig. 3A, B; Fig. 3D, F)

32. Sharpey fibre tubules: fine = 0; medium = 1; long & strong = 2 (Karataji t&Talimaa & Marss 2002, fig. 6A, B; Marss et al. 2006, text-fig. I ID; Marss et al. 2006, text-fig. 63A)

Body shape

33. Body shape: depressed =0; fusiform=1; compressed =2

34. Distinct anal notch: absent = 0; present = 1

35. Caudal peduncle and tail: long and slender = 0; short and very deep = 1

Cephalopectoral area

36. Cephalopectoral area: short = 0; moderately long to very long = 1

37. Orbit location: lateral or behind anterolateral corners of head = 0; at anterolateral corners of head = 1

38. Orbits: small = 0; large = 1

39. Mouth shape: subterminal, transverse, broad = 0; terminal, nearly circular = 1

40. Head: broad, rectangular = 0; conical, tapered = 1; bluntly rounded = 2

Gut

41. Branchial row (where known): more or less horizontal = 0; strongly oblique = 1

42. 'Stomach' chamber: funnel-shaped = 0; barrel-shaped =1

43. Intestine: long and slender = 0; short and wide = 1

Fins

Paired fins

44. Pectoral/suprabranchial fins: absent = 0; present = 1 (see Wilson et al. 2007)

45. Pectoral fins: 'rays' of subparallel scale rows = 0; fleshy base of scale covered skin = 1 (see Wilson et al. 2007)

46. Pelvic/ventral fins: absent = 0; present = 1 (see Wilson et al. 2007) Dorsal and anal fins

47. Dorsal fin(s): absent = 0; one or two = 1

48. Anal fin: absent = 0; present = 1 Caudal fin

49. Caudal fin length as proportion of total body: less than 30% = 0; more than 40% = 1

50. Caudal fin main lobes: dorsal and ventral lobes differ greatly in size or shape = 0; d and v lobes similar in size and shape = 1

51. Caudal fin web supported by many, slender, ray-like scale rows = 0; supported by few, large lobes = 1; without obvious lobes or rays = 2

Lateral line system

52. Arrangement of lateral line system on body: longitudinal lines = 0; short segments forming rightangled network = 1
Appendix 2. Character-taxon matrix for 39 species of thelodonts
and three outgroups scored for 52 characters. Missing data
= '?'; inapplicable state = '-'.

                  1   5    1    1    2    2    3     3     4    4   5
                           0    5    0    5    0     5     0    5   0
Stroinolepis
  maenniki        00?????012100-0120?121001000-01?????????????????????
Loganellia
  scotica         0002101102000-012001110110011110000010000?010011000?
Loganellia
  sulcata         0001101004000-0121011101100111110?00?000???1????000?
Loganellia
  prolata         0001?01104000-0220011102100111110?00?000???1????000?
Shielia taiti     000120100501100221?120111002211010010000?0?10110002?
Shielia parca     0001201005011002211120121002????1?01?00????1????0???
Shielia gibba     0001?0110501100221?1211210022?????01?00????1????0???
Shielia
  multispinata    00???010050110022111201210022110????????????????????
Paralogania
  martinssoni     00???011050111011111211110022110????????????????????
Valiukia
  flabellata      00???0?00511110111?120111002211?????????????????????
Phlebolepis
  elegans         0002300202100-01001120211001011010010000?00100110101
Erepsilepis
  margaritifera   000????202100-0100?12021100?????0????0?????1????0???
Helenolepis
  obruchevi       00???0?102000-0220?1222210010110????????????????????
Trimerolepis
  lithuanica      00???0?102110-0101?1202210021110????????????????????
Thelodus laevis   000??01102000-01001221010100-010????????????????????
Eestilepis
  prominens       0002?01105120-011??2?110????????0??1????????????????
Lanarkia
  horrida         0011111114200-0200?100120101200?000010000??11000000?
Lanarkia
  spinulosa       0011??1115210-0200?100120???????0?0?10000??1??1?0???
Lanarkia
  lanceolata      0001?01114200-0200?10011???12???0000?0000??1?100000?
Phillipsilepis
  crassa          0001?01313200-1201?10010010110000?0??000????????000?
Phillipsilepis
  cornuta         0001?0?313200-1201?100100101100?????????????????????
Phillipsilepis
  pusilla         0001?0?113200-1101?1001001??????0?0?????????????0???
Archipelepis
  bifurcata       0002?0?200100-0031?122200100-0010?0????0????????0???
Archipelepis
  turbinata       000200?100100-003??1222001??????0?0??000???1-???000?
Boothialepis
  thorsteinssoni  000??0?200100-00301122210110-000????????????????????
Turinia pagei     0001001202000-0110?12111011110000001100000011???0?2?
Turinia
  australiensis   00?????202100-010011211101?11000????????????????????
Barlowodus
  excelsus        00?????005210-012012001001011002????????????????????
Nikolivia
  gutta           00???0?101000-0110?1000001011001????????????????????
Apalolepis
  angelica        00?????205210-0100?2000001?2001?????????????????????
Pezopallichthys
  ritchiei        0001000004100-0220?1000101??????201000111110-000010?
Furcacauda
  heintzae        0002211005010-0221?2000001??????211001111110-1101110
Furcacauda
  fredholmae      0002111002010-0211?2200001??????211001111110-1101110
Sphenonectris
  turnerae        0002211002010-0221?2000001??????211001110110-0001110
Drepanolepis
  maerssae        0002000004110-022??2000001??????211001111110-1101110
Cometicercus
  talimaaae       0002?11002010-022??2000001??????211?0?????10-1101110
Canonia
  costulata       00?????002000-020122000001?10012????????????????????
Canonia
  grossi          00?????005010-02002200000110-01?????????????????????
Longodus
  acicularis      00?????114000-010021100110010010????????????????????
Athenaegis
  Tolypelepis     21013112060-0-010-?130200112000-000100000?10-0000111
Tremataspis
  schmidti        2201-1-2060-0-01--?130200000-00-0001-1021??11000002?
Rhyncholepis
  parvula         120131-2060-0-01--0130200------0100000121??0-101000?


Acknowledgements. We thank the reviewers H. Blom, G. Hanke, and H.-P. Schultze for helpful comments leading to improvement of this paper. This research was supported by Natural Sciences and Engineering Research Council of Canada Discovery Grant A9180 to MVHW and by Estonian Science Foundation Grant 7334 to TM.

Received 6 August 2009, accepted 23 September 2009

REFERENCES

Berg, L. S. 1940. Classification of fishes, both recent and fossil. Trudy Zoologicheskogo Instituta Akademii Nauk SSSR, 5,1-517 [in Russian].

Donoghue, P. C. J. & Smith, M. P. 2001. The anatomy of Turinia pagei (Powrie) and the status of the Thelodonti. Transactions of the Royal Society of Edinburgh: Earth Sciences, 92, 15-37.

Fredholm, D. 1990. Agnathan vertebrates from the Lower Silurian of Gotland, Sweden. Geologiska Foreningens Stockholm Forhandlingar, 112, 61-84.

Gross, W. 1947. Die Agnathen and Acanthodier des obersilurischen Beyrichienkalks. Palaeontographica Abt. A, 83,1-60.

Gross, W. 1967. Ober Thelodontier-Schuppen. Palaeontographica Abt. A, 127, 1-67.

Jaekel, O. 1911. Die Wirbeltiere. Eine Ubersicht iiber die fossilen and lebenden Formen. Gebrdder Borntraeger, Berlin, 252 pp.

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

Karatajute-Talimaa, V. N. 1968. New thelodonts, heterostracans and arthrodires from the Chortkov Horizon of Podolia. In Ocherki po filogenii i sistematiki iskopaemykh ryb i beschelyustnykh [Sketches on the phylogeny and taxonomy of fossil fishes and Agnatha], pp. 33-42. Nauka, Moscow [in Russian].

Karatajute-Talimaa, V. N. 1970. Downtonian ichthyofauna of Lithuania, Estonia and North Timan. In Paleontologiya i stratigrafrya Pribaltiki i Belorusii. Sbornik II [Paleontology and stratigraphy of East Baltic and Belarus'. Volume 11] (Grigelis, A., ed.), pp. 33-66. Mintis, Vilnius [in Russian, with English summary].

Karatajute-Talimaa, V. N. 1978. Telodonty silura i devona SSSR i Shpitsbergena [Silurian and Devonian thelodonts of the USSR and Spitsbergen]. Mokslas, Vilnius, 344 pp. [in Russian].

Karatajute-Talimaa, V. N. 1997. Taxonomy of loganiid thelodonts. Modern Geology, 21, 1-15.

Karatajute-Talimaa, V. N. & Marss, T. 2002. Upper Silurian thelodonts of Severnaya Zemlya Archipelago. Geodiversitas, 24, 405-443.

Karatajute-Talimaa, V. N. & Marss, T. 2004. Subclass Thelodonti. In Fossil Vertebrates of Russia and Adjacent Countries. Agnathans and Early Fishes (Novitskaya, L. I. & Afanassieva, O. B., eds), pp. 12-68. GEOS, Moscow [in Russian].

Kiaer, J. 1932. New coelolepids from the Upper Silurian on Oesel (Esthonia). Eesti LoodusteaduseArhiiv, Seeria 1, 10,167-176.

Maddison, D. R. & Maddison, W. P. 2005. MacClade Version 4, Release 4.08. Sinauer Associates, Inc., Sunderland, Massachusetts, USA.

Marss, T. 1986. Silurian vertebrates of Estonia and West Latvia. Fossilia Baltica, 1, 1-104 [in Russian, with English summary].

Marss, T. 1999. A new Late Silurian or Early Devonian thelodont from the Boothia Peninsula, Arctic Canada. Palaeontology, 42, 1079-1099.

Marss, T. 2003. Paralogania from the Rootsikdla (Wenlock) and Paadla (Ludlow) stages of Estonia. Proceedings of the Estonian Academy of Sciences, Geology, 52, 98-112.

Marss, T. 2006a. Exoskeleton ultrasculpture of early agnathans and fishes. Journal of Vertebrate Paleontology, 26, 235-252.

Marss, T. 2006b. Thelodonts (Agnatha) from the basal beds of the Kuressaare Stage, Ludlow, Upper Silurian of Estonia. Proceedings of the Estonian Academy of Sciences, Geology, 55, 43-66.

Marss, T. & Karatajute-Talimaa, V. N. 2002. Ordovician and Lower Silurian thelodonts of Severnaya Zemlya Archipelago. Geodiversitas, 24, 381-404.

Marss, T. & Ritchie, A. 1998. Silurian thelodonts (Agnatha) of Scotland. Transactions of the Royal Society of Edinburgh: Earth Sciences, 88, 143-195.

Marss, T., Wilson, M. V. H. & Thorsteinsson, R. 2002. New thelodont (Agnatha) and possible chondrichthyan (Gnathostomata) taxa established in the Silurian and Lower Devonian of the Canadian Arctic Archipelago. Proceedings of the Estonian Academy of Sciences, Geology, 51, 88-120.

Marss, T., Wilson, M. V. H. & Thorsteinsson, R. 2006. Silurian and Lower Devonian thelodonts and putative chondrichthyans from the Canadian Arctic Archipelago (Cornwallis, Baillie-Hamilton, Devon, and Prince of Wales islands). Special Papers in Palaeontology, 75, 1-140.

Marss, T., Turner, S. & Karatajute-Talimaa, V. N. 2007. Agnatha 11: Thelodonti. In Handbook of Paleoichthyolog; Volume IB (Schultze, H.-P., ed.), pp. 1-143. Verlag Dr. Friedrich Pfeil, Munich.

Murchison, R. I. 1838. On the fishes of the Ludlow rocks, or upper beds of the Silurian System. Report of the British Association for the Advancement of Science, Liverpool, 1837,1-91.

Murchison, R. I. 1839. The Silurian System. 1st edition. John Murray, London, 768 pp.

Obruchev, D. V. 1949. Type Vertebrata. In Atlas rukovodyashchikh form iskopaemykh faun SSSR. Tom 2. Silurijskaya sistema [Atlas of index fossils of the fossil faunas of the USSR. Vol. 2. Silurian System] (Luppov, N. P., ed.), pp. 316-328. Nauka, Moscow.

Obruchev, D. V. 1964. Subclass Thelodonti (Coelolepides). In Osnovy paleontologii. Beschelyustnye i drevnie ryby [Fundamentals of palaeontology. Agnathans, fishes] (Orlov, Y. O., ed.), pp. 39-44. Nauka, Moscow [in Russian].

Obruchev, D. V. & Karatajute-Talimaa, V. 1967. Vertebrate faunas and correlation of the Ludlovian Lower Devonian in eastern Europe. Journal of the Linnean Society (Zoology), 47,5-14.

Pander, C. H. 1856. Monographie der fossilen Fishee des silurischen Systems der russisch-baltischen Gouvernments. Buchdruckerei der Kaiserlichen Akademie der Wissenschaften, St. Petersburg, 91 pp.

Powrie, J. 1870. On the earliest vestiges of vertebrate life, being a description of the fish remains of the Old Red Sandstone rocks of Forfarshire. Transactions of the Edinburgh Geological Society, 1, 284-301.

Soehn, K. L., Marss, T., Caldwell, M. W. & Wilson, M. V. H. 2001. New and biostratigraphicatty useful thelodonts from the Silurian of the Mackenzie Mountains, Northwest Territories, Canada. Journal of Vertebrate Paleontology, 21,651-659.

Swofford, D. L. 2002. PAUP*. Phylogenetic Analysis Using Parsimony (* and Other Methods). Version 4. Sinauer Associates, Sunderland, Massachusetts, USA.

Traquair, R. H. 1896. The extinct vertebrate animals of the Moray Firth area. In A Vertebrate Fauna of the Moray Firth Basin, Vol. II (Harvie-Brown, J. A. & Buckley, T. E., eds), pp. 235-285. Harvie Brown and Buckley, Edinburgh.

Traquair, R. H. 1898. Report on fossil fishes. Summary of Progress of the Geological Survey of the United Kingdom, 1897,72-76.

Turner, S. 1976. Thelodonti (Agnatha). In Fossilium Catalogus I, Animalia, pars 122 (Westphal, F., ed.), pp. 1-35. Dr. W. Junk B. V., 's-Gravenhage.

Turner, S. 1991. Monophyly and interrelationships of the Thelodonti. In Early Vertebrates and Related Problems of Evolutionary Biology (Chang, M.-M., Liu, Y.-H. & Zhang, G.-R., eds), pp. 87-119. Science Press, Beijing.

Vieth, J. 1980. Thelodontier-, Acanthodier-, and Elasmobranchier-Schuppen aus dem Unter-Devon der kanadischen Arktis (Agnatha, Pisces). Gottinger Arbeiten zur Geologie and Palaontologie, 23, 1-69.

Wilson, M. V. H. & Caldwell, M. W. 1993. New Silurian and Devonian 'fork-tailed' thelodonts are jawless vertebrates with stomachs and deep bodies. Nature, 361, 442-444.

Wilson, M. V. H. & Caldwell, M. W. 1998. The Furcacaudi-formes, 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. H. & Marss, T. 2004. Toward a phylogeny of the thelodonts. In Recent Advances in the Origin and Early Radiation of the Vertebrates, Honoring Hans-Peter Schultze (Arratia, G., Wilson, M. V. H. & Cloutier, R., eds), pp. 95-108. Verlag Dr. Friedrich Pfeil, Munich.

Wilson, M. V. H., Marss, T. & Hanke, G. F. 2007. Paired fins of jawless vertebrates and their homologies across the agnathan-gnathostome transition. In Major Transitions in Vertebrate Evolution (Sues, H.-D. & Anderson, J., eds), pp. 95-108. Indiana University Press, Bloomington.

Mark V. H. Wilson (a) and Tiiu Marss (b)

(a) Department of Biological Sciences and Laboratory for Vertebrate Paleontology, University of Alberta, Edmonton, Alberta T6G2E9 Canada; mark.wilson@ualberta.ca

(b) Institute of Geology at Tallinn University of Technology, Ehitajate tee 5, 19086 Tallinn, Estonia; Tiiu.Marss@gi.ee
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