Aspidichthys ingens von Koenen, 1883

Dworczak, Patrycja G. & Szrek, Piotr, 2016, The Late Devonian placoderm Aspidichthys Newberry, 1873 from the Holy Cross Mountains, Poland, Fossil Record 20 (1), pp. 9-19 : 12-17

publication ID	https://doi.org/ 10.5194/fr-20-9-2016
DOI	https://doi.org/10.5281/zenodo.11047061
persistent identifier	https://treatment.plazi.org/id/290487AA-FFB9-FFDB-CD41-069188F08551
treatment provided by	Felipe
scientific name	Aspidichthys ingens von Koenen, 1883
status

Treatment

( Figs. 2–5 View Figure 2 View Figure 3 View Figure 4 View Figure 5 )

1933 Anomalichthys magnus n. sp., W. Gross, pp. 42– 44, Tab. 6, Fig. 4 View Figure 4 .

1933 Aspidichthys? ingens . – W. Gross, pp. 48–49, Tab. 6, Fig. 5 View Figure 5 .

1937 Aspidichthys ingens . – W. Gross, p. 40, Pl. 5, Fig. 4 View Figure 4 .

1956 Aspidichthys clavatus . – G. W. Sinclair & D. R. Walker, pp. 135–137, Figs. 1–3 View Figure 1 View Figure 2 View Figure 3 .

1957 Anomalichthys ingens . – J. Kulczycki, pp. 333–335, Figs. 1–3 View Figure 1 View Figure 2 View Figure 3 .

1973 Aspidichthys cf. ingens Koenen, H. -P. Schultze, pp. 69–75, Pl. 2A–D.

1976 Aspidichthys . – J. P. Lehman, pp. 21–22, Pl. 9, Figs. C–D.

1978 Aspidichthys ingens . – R. Denison, p. 103, Fig. 84.

Material: Four fragments of median dorsal plates: Muz. PGI-NRI 5.II.89 ( Kulczycki, 1957, Fig. 2 View Figure 2 ), MWG UW ZI/43/0045 ( Figs. 2–3 View Figure 2 View Figure 3 ), Muz. PIG 1809.II.17 ( Fig. 4 View Figure 4 ), and an incomplete median dorsal plate WNaZ/S/4/142 ( Fig. 5 View Figure 5 ). See Table 1 View Table 1 for detailed measurements and Table 2 for horizons .

Locality and age: Muz. PGI-NRI 5.II.89: middle Frasnian ( Palmatolepis punctata conodont zone) of Wietrznia Quarry in Kielce; WNaZ/S/4/142: upper Frasnian ( Palmatolepis rhenana conodont zone) of Kowala Quarry; Muz. PIG 1809.II.17, MWG UW ZI/43/0045: upper Frasnian ( Palmatolepis linguiformis conodont zone) of Płucki near Łagów.

Description: Specimen Muz. PGI-NRI 5.II.89 ( Kulczycki, 1957, Pl. 9, Fig. 2 View Figure 2 ) shows the anterior part of a median dorsal plate with clearly visible ornamentation. The median dorsal is broken and lacks its natural boundaries; the carinal process on the visceral side typical of brachythoracids is not visible. The ornamentation consists of smooth and rounded tubercles that are irregularly arranged. The diameter of tubercles varies between 2 and 4 mm, and the height varies between 1.8 and 3 mm. The number of tubercles on 25 cm 2 of the shield is approximately 101.

This specimen described above was taken into consideration by Kulczycki (1957) but not illustrated. Nevertheless, it served as the source of material from which conodonts were prepared. Specimens described below were collected very recently and have not been published before.

The specimen MWG UW ZI/43/0045 ( Figs. 2–3 View Figure 2 View Figure 3 ) shows partially preserved median dorsal plate and left posterior dorsolateral plate. The plate is strongly arched, enclosing at an angle of ca. 120 ◦ in the anterior half and rounded and flattened out in the posterior half. The external side of the plate is covered with large and rounded tubercles irregularly arranged. Tubercles are 5 mm in diameter at their largest and 1.4 mm in height. The number of tubercles on 25 cm 2 was not counted because a large part of them are eroded. The left posterior dorsolateral plate is preserved in the same block of rock and could belong to the same individual. This plate has the natural boundary along the lower, left, and upper margin, the last of which being an overlapping surface for the median dorsal plate ( Fig. 2 View Figure 2 ). The lateral line is well preserved, especially on left half of the plate, and is visible from the left anterior corner, close to the upper margin and border with median dorsal plate for about one-third of its length, and then turns and extends onto the right margin in approximately the middle of the plate. The posterior part of this plate is still covered by the matrix, and the most posterior margin lies under the anterior part of the median dorsal plate. The course of the lateral line is additionally marked with a longitudinal arrangement of tubercles.

Specimen no. Muz. PGI-NRI 1809.II.17 ( Fig. 4 View Figure 4 ) is represented by a median dorsal plate. The plate is very fissured and curved. The angle between the left and right sides is 120 ◦ in the anterior half ( Fig. 4b View Figure 4 ); the posterior part is flattened secondarily. On the lateral part of the shield a natural boundary is preserved, but the keel is invisible. The shield is ornamented with irregularly arranged and not widely removed from each of the other tubercles ( Fig. 4d View Figure 4 ). The tubercles are rounded and are 2 to 2.5 mm in diameter. They are also more or less the same sizes on the entire surface of the shield. The height of tubercles was not measured because of the high abrasion of them. The number of tubercles on 25 m 2 of the shield is 72. The specimen additionally included a fragment of unidentified other plate, probably a part of one of the lateral plates of the trunk shield (breadth 3.65 cm, length 5.5 cm) with the same type of ornamentation. In the lateral and posterior regions of the median dorsal plate they are larger and sometimes also irregularly confluent.

The specimen (WNaZ/S/4/142, Fig. 5 View Figure 5 ) shows the anterior part of the median dorsal plate. The plate is thick (about 4.7 cm) and the visceral surface is not visible. The natural anterior margin is preserved. The ornamentation consists of round and smooth tubercles without regular arrangement. Tubercles are about 1 to 3 mm wide in diameter and 1.5 cm in height. The number of tubercles on 25 cm 2 have not been counted because a large part of them are eroded.

In the anterior part of those plates (MWG UW ZI/43/0045, Figs. 2–3 View Figure 2 View Figure 3 ; WNaZ/S/4/142, Fig. 5 View Figure 5 ), the small crest occurs. The crest is in the form of a median longitudinal thickening of steep sides, ascending gradually and reaching a height of about 25 mm in the anteriormost margin. The symmetry plane of this crest meets the plane of the shield at an angle of 30 ◦. The surface of this crest is covered with tubercles similar to the rest of the shield. The crest was originally present on specimen Muz. PGI-NRI 1809.II.17 but has been lost because of damage to this region of the shield ( Fig. 4a View Figure 4 ).

Counting of tubercles on the described specimens revealed that a younger specimen from Płucki (Muz. PGI-NRI 1809.II.17) has a lower number of tubercles than the older specimen from Wietrznia Quarry (Muz. PGI-NRI 5.II.89) (see Table 1 View Table 1 ).

Discussion: Already known species of the genus Aspidichthys are represented by A. ingens Koenen, 1883 and A. clavatus Newberry, 1873 (see the discussion by Denison, 1978, p. 103). The presented material is similar in shape and morphology to the specimens described by Kulczycki (1957) but is characterized by smaller tubercles. Tubercles in Kulczycki’s (1957) material reach up to 10 mm, while in the studied material they do not extend to even 5 mm in diameter. On specimen WNaZ/S/4/142, tubercles reach the smallest sizes even though this specimen represents the largest individual among all analysed specimens. The characters observed on studied specimens are very peculiar and correspond well to randomly distributed tubercules. Tubercules have stellate base of 5 mm in diameter at their largest. The plate is thick, arched and elongated. Those features have been observed and illustrated by previous authors ( Newberry, 1873, Pl. 35, Fig. 1 View Figure 1 ; Whiteaves, 1892, p. 355; Gross, 1933, Tab. 6, Fig. 4 View Figure 4 ; Sinclair and Walker, 1956, Fig. 1–3 View Figure 1 View Figure 2 View Figure 3 ; Kulczycki, 1957, Pl. 1–3; Schultze, 1973), as well as preliminary characterized material from the Holy Cross Mountains ( Szrek, 2009). All specimens described herein are different from those discussed by Schultze (1973, Pl. 2, Fig. a–b) by clearly larger distances between tubercles and thus are more reminiscent of those illustrated by Newberry (1873, Pl. 35, Fig. 1 View Figure 1 ), Gross (1933, Tab. 6, Figs. 4–5 View Figure 4 View Figure 5 ), Sinclair and Walker (1956, Fig. 1 View Figure 1 ), and Kulczycki (1957, Pl. 11, Figs. 2–3 View Figure 2 View Figure 3 ). Differences could lie in a local palaeogeographic morphological variations suggested by Kulczycki (1957) rather than sizes of particular individual and species differentiation.

The specimens where the anterior margin of the median dorsal plate is preserved (MWG UW ZI/43/0045, Figs. 2–3 View Figure 2 View Figure 3 ; WNaZ/S/4/142, Fig. 5a–c View Figure 5 ) show a more rounded margin in the part where it turns posteriorly than on the specimen illustrated by Sinclair and Walker (1956, Figs. 1–2 View Figure 1 View Figure 2 ), on which this part turns at almost a right angle. This region is visible only in the specimens MWG UW ZI/43/0045 and WNaZ/S/4/142 and those of Sinclair and Walker (1956, Figs. 1–2 View Figure 1 View Figure 2 ). Moreover, the carinal process mentioned by Kulczycki (1957) and Schultze (1973) is not accessible for investigation because it is not visible in the new material from the Holy Cross Mountains, making a detailed comparison difficult. However, other morphological features of the external side of the median dorsal plates (overall shape longer than wide, ornamentation composed of large tubercles, thickness of bones that are arched and which enclose at an angle of 120 ◦ of the median dorsal plate) correspond to other described specimens ( Sinclair and Walker, 1956; Kulczycki, 1957) and confirm identification of Aspidichthys ingens Koenen, 1895 .

The median dorsal plate of species Aspidichthys ingens represented by specimen no. WNaZ/S/4/142 is not complete, but species-related features are preserved (e.g. large, rounded irregularly arranged tubercles and relatively thick shield; Denison, 1978) which are commonly observed on the plates and suggest that the plate belongs to this species. The studied specimen has smaller tubercles (1–3 mm in diameter) than the specimens described by Kulczycki (1957), which have tubercles of even 10 mm in diameter. This specimen can be compared with Aspidichthys described by Schultze (1978, Pl. 3), where the ornamentation contains tubercles about 4 mm in diameter; however, the studied specimen shows a large keel. In the material described by Schultze (1978), an inconsiderable bump occurs on the anterior part of the shield. This bump is clearly visible on almost all specimens studied.

The studied remains occur in the pelagic facies, suggesting that Aspidichthys lived in a deep-water environment ( Ivanov and Ginter, 1997; Szrek, 2006) as active predators would have had a demersal lifestyle ( Janiszewska et al., 2007; Szrek, 2007). The conodont analysis shows that placoderms from Wietrznia Quarry lived in slightly shallower water than those from Kowala Quarry. In the sample from the punctata zone (Wietrznia Quarry), Icriodus is more numerous than in the sample from the early rhenana zone (Kowala Quarry), where Icriodus elements are in the minority, which suggests a deeper environment. In the sample from Wietrznia Quarry ( punctata conodont zone) there were 10 Icriodus elements and 19 Palmatolepis elements. In the sample from Kowala Quarry ( rhenana conodont zone) there were 25 elements of Icriodus and 326 elements of Palmatolepis . Sample form Płucki revealed 33 Icriodus and 44 Palmatolepis elements. For details, one can refer to Table 2, which indicates a progressive and stepwise deepening of the environment and is correlated with the synsedimentary block tectonics and permanent growth of the sea level in the studied area during the Frasnian suggested by previous authors (e.g. Szulczewski, 1995). Analyses of the Płucki section ( Racki et al., 2002; Woroncowa-Marcinowska, 2006; see Table 2) demonstrated a deep-sea environment in the linguiformis conodont zone. Moreover, the regression at the Frasnian–Famennian boundary has been suggested based on the percentage share of Palmatolepis and Icriodus elements ( Janiszewska et al., 2007), which could be correlated with global changes in sea level (McGhee Jr., 2013). The conjunction of the regression and environmental changes during the reef fauna crisis could have led to the disappearance of Aspidichthys during the Frasnian to Famennian transition.

The analysis of the placoderm fauna from the Upper Kellwasserkalk of Płucki shows similarities to the contemporary fauna from Bad Wildungen. For 14 genera ascertained in Płucki (Szrek, 2008, 2009), 9, including Aspidichthys , are common to Bad Wildungen. This is most likely directly related to the short palaeogeographic distance between both localities. Exhaustive analysis of palaeobiogeographic distribution of different placoderm taxa also from Morocco, France, Iran, and Australia suggests vicinities between all of these areas without a significant barrier ( Rücklin, 2010) for bottom-dwelling fishes (e.g. deep ocean).