Bite Marks on Tests of the Echinoid Genus Echinocorys LESKE, 1778 from the Maastrichtian

Bite marks on tests of the echinoid genus Echinocorys Leske, 1778 from the Maastrichtian of Hemmoor (NW-Germany)[*]

Detlev Thies

Institute of Geology and Paleontology of the University Hanover

Callinstra

DFe 30, D-3000 Hanover 1

translated by Richard Forrest

Abstract

Feeding traces caused by fish are found on echinoid tests of the genus Echinocorys from the Maastrichtian of Hemmoor (NW-Deutschland). These traces were first described by Gripp (1929) and interpreted as the bite-marks of ray. A re-examination of the traces is undertaken on the basis of 28 marked tests, which have been collected more recently in Hemmoor. The ray theory is refuted, and it is demonstrated that the marks were more probably made by a bony fish of the genus Enchodus or Cimolichthys (Family Enchodontidae).

I. Introduction

Echinoids are attacked by a wide range of predators, especially fish and crustaceans, and have developed a number of different strategies (for example spines, endobenthonic lifestyle, etc) to avoid them (Smith 1984). The attacks of predators are not always successful. In cases of failure, traces of the predatory attack can remain on the surface of the echinoid test ("Traces of predation", Bishop 1975). In the living echinoids, such traces are known on the sand dollar (genera Encope and Leodia) (Kier & Grant 1965). Feeding traces on fossil echinoids were described by Gripp some time ago (1929) on test of Echinocorys from the Campanian of Lägerdorf and the Maastrichtian of Hemmoor (NW Germany). At that time Gripp observed two different types of traces on the echinoid test. While the tests from the Campanian of Lägerdorf show many short, irregular notches at the edge between oral surface and flank, tests from the Maastrichtian of Hemmoor show a different pattern of injuries. This characteristic pattern is of partly punctuated and partly continuous tracks, found on the sides of the test near the apex. Extensive new collections of Echinocorys tests from the Maastrichtian of Hemmoor (collection F. Schmid, Niedesächsishes Landesampt für Bodenforschung in Hanover) confirms Gripp’s observations respecting the characteristic feeding traces on Echinocorys from Hemmoor. However, Gripp’s interpretation of these tracks can as injuries sustained by repeated bites of a ray – a view on which Abel (1935) had already declared doubts – is no longer adequate. A new interpretation of the finding needs to be sought.

II. Material

28 tests of Echinocorys were used for the study of feeding traces. All the specimens come from the non-operational quarry of Hemmoor Zement AG (TK25 2220 Cadenberg and 2320 Lamstedt). The section profile of Schulz & Schmid (1983) shows a sequence from the sumensis zone (Lower Maastrichtian) to the baltica/danica zone (Upper Maastrichtian). The tests bearing feeding traces were distributed throughout the sequence, the majority of finds being from the argentea/junior zone (24 examples from the sections F 915 to F 938 of the sequence of Schulz & Schmid 1983).

All specimens described here are the in the collection of F. Schmid (NLfB, Hanover). This collection contains approximately 930 coronae of Echinocorys from Hemmoor. The proportion of injured tests is about 3%.

III. Description of the Marks

A very detailed description of the traces is found in Gripp (1929). Briefly, these are in part furrows and in part individual punctures on the surface of the echinoid test, located around the apex. (Plate 1, Fig. 1, 2, 4, 5; Plate 2, Fig. 1). Both the furrows and the punctures are normally found in groups of three (more rarely to two-or four).

Furrows

The furrows have a width of approximately 1 mm. They are found generally in groups of three, parallel to each other, and spaced at about 2-3 mm.

Punctures

The punctures are spindle-shaped in profile with a longitudinal diameter of approximately 1 mm, and found in groups of three spaced about 2-3 mm apart.

Gripp noted that the channels and punctures have an average spacing of 3.5 mm. I do not consider this difference to be significant. Presupposing that the same predator on Echinocorys is represented in all cases, the different sizes of the feeding traces can be explained by different ages and sizes of the predator.

Without exception, each group of three impressions is matched by a second group. If one looks from apically at the corona, it is some centimeters separated on the opposite side (Plate 1, Fig. 5; Plate 2, Fig. 1; A-A, B-B). It can itself be two groups of furrows (Plate 1, Fig. 4) or two groups of punctures (Plate 2, Fig. 1; also Plate 1, Fig. 1) or a single group of furrows or punctures (Plate 1, Fig. 5). A standard unit therefore always consists of two groups of three symmetrically arranged, and of the same type. The furrows are vertically, while the punctures are aligned parallel to the axis. In the present material, the maximum spacing between the two groups is approximately 5.5 cm (Plate 1, Fig. 4). Several standard units always overlap on the echinoid corona (seen especially on Plate 1, Fig. 1).

Gripp’s description can be supplemented with following observations:

It is noticeable that a group of three punctures (even taking into account the curvature of the echinoid test) never lies completely in a level. If one connects the two opposite puncture groups, the middle-line is displaced towards the apex (Plate 2, Fig. 3) or to the oral side of the corona (Plate 1, Fig. 2). In groups of furrows the middle furrow is much longer than the outside ones (Plate 1, Fig. 6). The newly collected reveals from Hemmoor show that is the characteristic feeding traces are found not only on the apical but also on the oral surfaces of some tests (Plate 2, Fig. 2).

As Gripp determined, the tracks have healed almost without exception. This is shown by necrotic growths on the surface of the damaged calcareous plates (Plate 1, Fig. 3). The predator has not been able to penetrate or break the echinoid test. Either the aggressor broke off the attack, or the echinoid found some alternative means of escape, so that it survived the attack with a largely undamaged test. In an example from the Hemmoor material it can be seen that the echinoid had a chance of survival even if the test was largely destroyed. Plate 2, Fig. 2 shows a specimen shows furrowed feeding-traces that stop suddenly at an edge on the oral surface on both sides of a pit. The test area between the traces was obviously broken away. However it regenerated, though not to the level of the surface of the test, leaving a clear scar.

Feeding traces on the Echinocorys test that demonstrate a successful attack are almost unknown in the Hemmoor material. This can be explained in that a successful attack of this predator on Echinocorys was likely to lead to the total destruction of the test. (In this respect states the predominance of healed tests tells us nothing about the success rate of the predator. Only in exceptional cases can a more or less completely test destroyed can give information only on the cause of death of the echinoid). An example from the material present here (Plate 2, Fig. 4) has a part of the apical surface of the test is indented. The tracks on the preserved sides of the corona order are arranged around the depressed area and healed. They consist of single groups of punctures and furrows – their respective counterparts would be to on the destroyed part of the test. The broken rim of the test is overgrown with ephisites (bryozoans) (Plate 2, Fig. 5). It is significant that the growth of ephisites on the edge of the break has damaged the test before the entombment in the sediment. The unhealed tracks show that this echinoid was the victim of an attack it did not survive.

Finally, it must be noted that the traces described above appear only the on test of the genus Echinocorys. The genera Cardiaster Forbes, 1850 and Galerites Lamarck, 1801, which are also to be found in the Maastrichtian of Hemmoor, do not show these injuries.

IV. Interpretation of the Marks

Where traces consist of two opposite parts they can be interpreted easily as bite marks of a fish, with which the two injuries are the tooth rows of upper and lower jaw. While the punctures are the consequence of the penetration of teeth into the echinoid test, the furrows are caused by a bite slipping off the test.

Some characteristics of the biting fish can be derived directly from the type of the injuries:

1) The spindle-shaped outline of the punctures shows that the teeth that penetrated into the shell were shaped lance-shaped.

2) The longitudinal diameter of the punctures of approximately 1 mm show that the teeth were of considerable size.

3) Because of the similarity of the damage, the upper and lower jaws must have had similar dentitions.

4) Since itself the impressions (punctures) of the tooth row of upper and lower jaws on the echinoid test in rows are parallel to the axis of the bite, these teeth must have been in the most anterior part of a rounded, not a sharp or beak shaped jaw.

5) The notable spacing up to approximately 5.5 cm between the marks of upper and lower jaws shows a wide gape, on big jaws and with it on a relatively big animal.

The fish-fauna of the northwest German Upper Chalk consists of sharks, rays and bony fish. To which of these three groups can the fish which produced the bite marks be assigned? The fact that no more than 3-4 teeth of a jaw have never penetrated simultaneously into the curved echinoid test and that the upper and lower jaws were several centimeters wide led Gripp (1929) to the assumption that only big and laterally oriented jaws could have produced the tracks. He thought that the bearers of such jaws must be certain ray-like fishes. However, this assumption can no longer be upheld for several reasons. Admittedly, rays (= Superorder Batoidea) possess jaws of a certain size orientated laterally; however more detailed investigation shows the symphyseal region of the upper jaws is incurved, while the lower jaw at this position is curved outwards (Stehmann 1978). Jaws of this structure would not leave uniform traces as found here. Furthermore, most rays possess exclusively blunt crushing teeth. Where pointed teeth are found, these have a pointed, conical crown, which would not have left a spindle-shaped impression (Bigelow & Schröder 1953, Cappetta 1972). Study of selachian teeth from the Maastrichtian of Hemmoor by Herman (1982) has shown moreover that the Batoidea here are extremely rare and represented only by the family Rhinobatidae (banjo fish, up to now only a single tooth). The banjo fish have crushing teeth with a small indented crown and prefer small fish, crabs and mollusks as food (Bigelow & Schröder 1953). This precludes rays as originators of the bite marks. More significantly, it is already a candidate for the originator of the marks in the sharks. Superficially, a predator/prey relationship between a shark and Echinocorys is possibly, especially since Herman (1982) identified the teeth of 17 shark-genera with more or less lance-shaped teeth in the chalk of Hemmoor. In the majority of cases, the morphology of these teeth (several cusps per tooth with Notidanus, diagonally-orientation of the cusps and diagnostic heterodont with the Squaliforms) does not match the marks on the echinoid tests. In other forms (Parasquatina, Scyliorhinus) it is known that living representatives of these taxa do not feed on echinoids (Bigelow & Schröder 1948, Cadenat & Blache 1981). Paraginglymostoma and Hemiscylliums from Hemmoor can be eliminated on the basis of their small size alone. Heterodontus is the only serious candidate as possible predator on Echinocorys. Heterodontid sharks, as durophageous feeders typically prey on shelled molluscs and crustaceans as well as echinoids (Ripe 1976, Whitley 1940). The extreme rarity of Heterodontus in the Maastrichtian of Hemmoor (up to now only 2 teeth have been found, Herman 1982) clearly refutes this assumption.

Consequently, only the bony fish remain as conjectural originators of the bite marks. Observations of living bony fish show that these animals regularly prey on echinoids; in some genera they even form the main component of the food (Fricke 1971, Edge-All 1967). A particular study of the bony fish fauna of the Maastrichtian of Hemmoor is not yet available. Herman (1982) mentions however numerous enchodontid teeth (Fam. Enchodontidae) from this locality. The actinopterygian remains from the Campanian and Maastrichtian of the adjoining Westphalian and Dutch-Belgian area have however been studied in detail (Albers & Weiler 1964; Marck 1858, 1863, 1876,1885; Siegfried 1954). Woodward (1902-1911) covered the bony fish of the English Upper Chalk. Outside Europe, rich bony fish faunas are known from the Maastrichtian of North-Africa and the Congo (Arambourg 1952, Dartevelle & Casier 1943-1959). For a closer approach to the question, a list of characteristic of the fish is considered. A combination of the characteristics 1, 2, 4 and 5, big fish with wide gape and big, lance-shaped teeth in the most anterior of the jaw is found among the bony fish of the Upper Chalk in the family Enchodontidae, and I assume therefore that the originator of the bite marks belongs to this family. (Characteristic 3 – corresponding dental structure in upper- and lower jaws – is often lost through incomplete conservation of fossil fish.) The family Enchodontidae is represented in the Campanian and Maastrichtian of northwest Europe by the genera Enchodus, Palaeolycus, Cimolichthys and Apateodus (Albers & Weiler 1964, Siegfried 1954). Palaeolycus, with its pointed muzzle, is characteristically an ambush predator. By analogy to living ambush predators, for example the gar-pikes (Fam. Belonidae), its food will have consisted predominantly of smaller fish and nektonic invertebrates (Nikol’skii 1961). With Apateodus, only small, inconspicuous teeth are fond in the anterior part of the jaw; larger teeth are found only in the posterior part (Kruizinga 1923, Woodward, 1902-1911). I consider it therefore likely that the producer of the marks is belongs either to the genus Cimolichthys or the genus Enchodus. In contrast to Apateodus, the most anterior parts of the jaws contain large, dagger-like teeth in these two genera (Siegfried 1954, Woodward 1902-1911). An unambiguous generic identification appears impossible at the moment. It needs detailed knowledge of the dental morphology of the individual Enchodus and Cimolichthys types, which cannot be learned from the predominantly fragmentarily preserved fossil remains.

V. Acknowledgements

Professor Dr. F. Schmid (NLfB Hanover) inspired the work on bite marks. The photographs were taken by H. Axmann (NLfB Hanover). D. J. Ward (Orpington, England) has corrected the English legends.

VI. References

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