Debeerius ellefseni
Debeerius is a euchondrocephalan most closely related to Heteropetalus
elegantulus, but it is considerably larger. It ranges in length to
about 30 cm.
Link to
animation.
A few specialized scales line the anterior cranial lateral line canals, a few others outline the first dorsal fin rays; otherwise scales are absent. The delicate chimaerid-like pectoral fins are propulsive in structure and position. The dorsal fin is elongate and composed of separately supported elements for undulatory motion, but the caudal peduncle and fin indicate that Debeerius could also swim with significant caudal undulatory propulsion. The dorsal fin spine is barbed and could be raised, and lowered into a groove along the back. As similar as they are to those of modern chimaerids, these fins too were probably distally translucent to transparent. The dark barred color pattern of the skin has been excellently preserved; it is as illustrated above. Only the black pattern is preserved, however.
All complete specimens are males; we have not found any females so
far.
Teeth of Debeerius ellefseni. Scale is in
mm. La, labial view; Li, lingual view.
Tiny but heterodont teeth far forward on the jaws are for plucking and comminuting. Many specimens have gut contents, that are a mixture of broken calcareous shells (bivalves?) and algal material. D. ellefseni appears to have been a sediment feeder as well as a feeder on the algae and small invertebrates on the sediment.
Special Scientific Significance:
The autodiastylic suspensorium upon a chimaeroid-like braincase, gill basket, and pectoral fins indicate several points: 1, this type of suspensorium is primitive for the Class Chondrichthyes; 2, the autodiastylic suspensorium, as originally theorized by Sir Gavin DeBeer, is probably primitive for the gnathostomes; and 3, that chimaeroid-like gill baskets and pectoral fins are far more widespread within the subclass Euchondrocephali than merely within the Holocephali.
References:
- Grogan,
E. D., R.
- Grogan, E.D., & R. Lund. 2000. "Debeerius ellefseni
(Fam. Nov., Gen. Nov., Spec. Nov.), an autodiastylic chondrichthyan
from the Mississippian Bear Gulch Limestone of Montana (USA), the
relationships of the Chondrichthyes, and comments on gnathostome
evolution." Journal of Morphology 243:219-245.
- Lund, R. and E.D. Grogan, 1997. "Relationships of the Chimaeriformes and the basal radiation of the Chondrichthyes." Reviews of Fish Biology and Fisheries 7:1-59.