Peabody Museum t of Natural History | Atal Se ae Yale University | LIBRARY New Haven, CT 068 eae AUG 29 1986 wt Pe ele) (Received 17 September 1987) Abstract The type species of the trilobite Hadrohybus Raymond 1925, H. dunbari from the Cow Head Group of western Newfoundland, is redescribed here. It has been regarded as a cheirurid, but analysis of its cranidial characters show that it is a bathyurid closely related to the well-known Early Ordovician genus Bolbocephalus, and it is considered to be a subgenus of that form. It is probably of early Middle Ordovician age. A second Hadrohybus species occurs in the late Early Ordovician of Vermont. Key Words Hadrohybus, Bolbocephalus, Bathyuridae, trilobite, Ordovician. Introduction Raymond (1925) described the type, and only named species of Hadrohybus, from the Ordovician, Cow Head Group of western Newfoundland. On the basis of these cranidia, Raymond considered that the genus was a cheirurid related to Nieszkowskia, and this © Copyright 1988 by the Peabody Museum of Natural History, Yale University. All rights reserved. No part of this publication, except brief quotations for scholarly purposes, may be reproduced without the written permission of the Director, Peabody Museum of Natural History. ISBN No. 0-912532-10-6 tory: en eT = 1 hora Marine Biological Laborataly’ ds Hole, Massthe ostilla ly 1988 Number 202 | th O rdovician Trilobite adrohybus Raymond 1925, and Its Family Relationships R. A. Fortey placement has remained, although Hadrohybus was only placed with question in Cheiruridae by Henningsmoen (in Moore, 1959) in the Treatise on Invertebrate Paleontology. Raymond's original illustrations were somewhat perfunctory, and a reconsideration of this peculiar trilobite is overdue. This paper reviews the family relationships of Hadrohybus. Age of Hadrohybus dunbari Occurrence The Cow Head Group of western Newfoundland consists of a series of conglomerates with interbedded shales and sandstone, which accumulated off the shelf- edge of the Laurentian continent during the Cambrian to Ordovician. The conglomerates were mostly derived from shallow water environments, and from one boulder of this type the specimens of Hadrohybus were recovered. James and Stevens (1986, fig. 40) record a succession on the type locality, Stearing Island, ranging through Early Ordovician to Early Whiterockian. Only two conglomerates yield pebbles large enough to have furnished the large Hadrohybus specimens. One of these is of Arenig age and is high in the Lower Ordovician. The other, of possible late Arenig age, may be the equivalent of the massive conglomerate bed of nearby Lower Head, and may be regarded as Whiterockian (Whittington 1963). On my visit to Stearing Island | was unable to find further specimens of Hadrohybus and direct evidence of its age is so far lacking. Raymond (1925) lists ‘‘Eoharpes fragilis, Homotelus catactus, lllaenus sp. and Pllomerops Peabody MUSCUIM greg et of Natural History [ Marine Biological ie Yale University | LIBRARY (Received 17 September 1987) Abstract The type species of the trilobite Hadrohybus Raymond 1925, H. dunbari from the Cow Head Group of western Newfoundland, is redescribed here. It has been regarded as a cheirurid, but analysis of its cranidial characters show that it is a bathyurid closely related to the well-known Early Ordovician genus Bolbocephalus, and it is considered to be a subgenus of that form. It is probably of early Middle Ordovician age. A second Hadrohybus species occurs in the late Early Ordovician of Vermont. Key Words Hadrohybus, Bolbocephalus, Bathyuridae, trilobite, Ordovician. Introduction Raymond (1925) described the type, and only named species of Hadrohybus, from the Ordovician, Cow Head Group of western Newfoundland. On the basis of these cranidia, Raymond considered that the genus was a cheirurid related to Nieszkowskia, and this © Copyright 1988 by the Peabody Museum of Natural History, Yale University. All rights reserved. No part of this publication, except brief quotations for scholarly purposes, may be reproduced without the written permission of the Director, Peabody Museum of Natural History. ISBN No. 0-912532-10-6 Laborat 4s Hole, MassThe 2ostilla Number 202 8 July 1988 Irdovician Trilobite hybus Raymond 1925, and Its Family Relationships R. A. Fortey placement has remained, although Hadrohybus was only placed with question in Cheiruridae by Henningsmoen (in Moore, 1959) in the Treatise on Invertebrate Paleontology. Raymond's original illustrations were somewhat perfunctory, and a reconsideration of this peculiar trilobite is overdue. This paper reviews the family relationships of Hadrohybus. Age of Hadrohybus dunbari Occurrence The Cow Head Group of western Newfoundland consists of a series of conglomerates with interbedded shales and sandstone, which accumulated off the shelf- edge of the Laurentian continent during the Cambrian to Ordovician. The conglomerates were mostly derived from shallow water environments, and from one boulder of this type the specimens of Hadrohybus were recovered. James and Stevens (1986, fig. 40) record a succession on the type locality, Stearing Island, ranging through Early Ordovician to Early Whiterockian. Only two conglomerates yield pebbles large enough to have furnished the large Hadrohybus specimens. One of these is of Arenig age and is high in the Lower Ordovician. The other, of possible late Arenig age, may be the equivalent of the massive conglomerate bed of nearby Lower Head, and may be regarded as Whiterockian (Whittington 1963). On my visit to Stearing Island | was unable to find further specimens of Hadrohybus and direct evidence of its age is so far lacking. Raymond (1925) lists ‘‘Eoharpes fragilis, Homotelus catactus, Illaenus sp. and Pllomerops 2 Ordovician Trilobite Hadrohybus Postilla 202 * Fig. 1 Hadrohybus dunbari Raymond. a-c, holotype cranidium YPM 13031, x 1.5 in dorsal, anterior and lateral views; d, e, paratype, large incomplete cranidium, but showing postocular cheek, x1, YPM 13030, in anterior and dorsal views. Photographs of replicas supplied to the author by the Peabody Museum of Natural History (YPM), Yale University. 3 ‘Ordovician Trilobite Hadrohybus barrandei”’ as associated species with Hadrohybus. This assemblage appears most comparable with that described from the Lower Head boulder by Whittington (1963), and if this is the case it seems likely that the boulder yielding Hadrohybus is of Whiterockian age. Systematic Note Genus Bolbocephalus Whitfield, 1890 Subgenus Hadrohybus Raymond 1925 Type Species (Original designation) H. dunbari Raymond 1925 Bolbocephalus (Hadrohybus) dunbari Raymond 1925 (Fig. 1a-e) Hadrohybus dunbari sp. nov.: Raymond, 1925, p. 147-48, pl. 9, figs. 5, 6. Hadrohybus dunbari Raymond: Henningsmoen, 1959, in Moore 1959, p. 435. Type Material Holotype, cranidium, YPM 13031; paratype, cranidium, YPM 13030. Type Locality and Horizon Stearing Island, Cow Head, western Newfoundland, pebble in probably early Middle Ordovician conglomerates. Description Cranidium is large and highly convex (sagittal, transverse), with glabella highly vaulted and curving downward anteriorly, so that in dorsal view it overhangs cranidial margin. Maximum cranidial width at posterior margin; postocular cheek gently declined downwards. Glabella tapers forward initially, but expands in width at level of palpebral lobes to achieve maximum width at their anterior ends; anterior outline broadly rounded, but anterior view shows tendency toward an obtuse anteromedian acumination. Occipital ring not Postilla 202 seen on type material. Glabellar furrows effaced, but oval areas adjacent to the ~ shallow axial furrows opposite posterior parts of palpebral lobes presumably represent muscle insertion areas. At a point opposite the palpebral lobes the glabella is elevated into a prominent, slightly backward-turned knob, forming the conspicuous high point of the cranidium. Preglabellar area short, vertical to reclined, but cranidial anterior border apparently lacking. Palpebral lobes highly Curved, and approximately medially placed in dorsal view forming semicircles, anterior ends closer to glabella than posterior ends, and with clearly defined palpebral rims. Sutures do not diverge in front of palpebral lobes, thereby defining narrow (transverse), downsloping preocular cheeks. Area inside palpebral lobes gently inflated. Postocular suture describes a sigmoidal curve, in the midpart running more or less transversely, the postocular cheeks evidently wide (transverse) and showing at least the proximal part of a moderately defined posterior border furrow. The cranidium carries a distinctive surface sculpture best shown on the smaller example. Fine tubercles cover the glabella, and these are joined by raised lines on the glabellar flanks. The raised lines are most prominent on the front of the glabella, as they are on the preglabellar area. The interocular fixed cheeks are rugose. Discussion Only the cranidium of H. dunbari is known and comparative remarks are accordingly limited. However, a second species which can be attributed to Hadrohybus was described by Whittington (1953) as Bolbocephalus? species indeterminate. This species is from the Fort Cassin Formation of Vermont, which is of late Early Ordovician age. Again, only the Cranidium is known, and this is clearly like that of H. dunbari, although much smaller than either of the types of this species. The glabellar boss is prominent on the Vermont form, but further forward on the glabella (Whittington 1953, pl. 66, fig. 15), and directed somewhat forward. The surface sculpture apparently consists of much finer, concentric 4 Ordovician Trilobite Hadrohybus Bolbocephalus Nieszkowskia Hadrohybus A Fig. 2. Competing hypotheses of relationships of Hadrohybus. A, Cheirurid relationships; B, Bathyurid relationships. A greater number of cranidial synapomorphic characters favor B, which is adopted in this paper. Characters are: 1, waisted glabella; 2, opisthoparian sutures; 3, glabellar effacement; 4, terrace ridges present; 5, glabellar boss. Under hypothesis B the glabellar boss is a parallelism. lines on the glabella. These differences are sufficient to indicate that the Vermont form is a separate species from H. dunbari. The single specimen of a cranidium, however, is not considered an adequate basis for formally naming it. Family Assignment of Hadrohybus Raymond (1925) compared the morphology of Haadrohybus with that of the cheirurid Nieszkowskia, a family into which it was placed with question by Henningsmoen (in Moore 1959). This assignment appears to rest mainly on the presence of the curious glabellar boss in both genera. This resemblance is misleading as far as family relationships are concerned (Fig. 2). Here it is considered that Hadrohybus is closely related Postilla 202 Nieszkowskia Bolbocephalus Hadrohybus to the bathyurid Bolbocephalus Whitfield 1890, a well-known genus from the early Ordovician of North America. Because of its previous assignment to Cheiruridae, Hadrohybus was not considered in the revision of Bathyuridae by Whittington (1953) or Fortey (1979). Certain characters shown on Hadrohybus are present on representatives of both bathyurids and cheirurids and hence are not relevant to deciding familial relationships. These include the presence of tuberculate surface sculpture, the deeply incised palpebral furrow and the anteriorly rounded glabella. However, the ridgelike sculpture of the anterior border is not present on any cheirurid of which we are aware. The type species of Bolbocephalus is B. seelyi (Whitfield 1886) from Vermont which was redescribed by Whittington (1953). Fortey (1979) recently redescribed B. convexus 5 Ordovician Trilobite Hadrohybus (Billings 1865) from the Catoche Formation of western Newfoundland; this species offers a particularly close comparison with Hadrohybus. Neglecting the glabellar boss, the outline and forward protrusion of the glabella in both cases is identical, as is the absence of defined glabellar furrows. So is the position and curved form of the palpebral lobe, and the long (transverse) postocular cheek. There is no evidence that the facial suture of Hadrohybus is proparian, which of course it would have to be were Hadrohybus a cheirurid; the preservation of the only type specimen which shows the postocular cheek is admittedly imperfect. Surface sculpture on Bolbocephalus species consists of terrace ridges, or it is smooth, but the related bathyurid Petigurus has very coarse tuberculation and the sculptural difference is probably not important. Additionally, the following cheirurid characters are absent on Hadrohybus: 1) Incised posterior glabellar furrow. Even on relatively effaced cheirurids the basal glabellar furrow is well defined and backward curved, and there is no sign of this furrow on Hadrohybus. 2) Anterior cranidial border. A narrow (sagittal) anterior cranidial border which does not continue the downward slope of the frontal glabellar lobe is typical of cheirurids. When the border is encroached upon by the glabella, as in sohaerexochinids, it becomes almost obsolete, but in no cheirurid is there the flat, downsloping preglabellar area shown on Hadrohybus. 3) Genal sculpture. The usual sculptural type on the genal areas of cheirurids included a honeycomblike arrangement of pits as well as tuberculation, which is not present on Haadrohybus. In summary, very little evidence supports Postilla 202 the hypothesis that Hadrohybus is a cheirurid, and many facts suggest that it is not. It is closely comparable to a known bathyurid of similar age and provenance. The discovery of the free cheek and pygidium of Hadrohybus can be expected to confirm this family assignment. The resemblance between the glabellar boss of Hadrohybus and the cheirurid Nieszkowskia is regarded as the result of probable convergence. Position of Hadrohybus within the Bathyuridae The close comparison between Hadrohybus and Bolbocephalus has been discussed above. There remains the question of whether Hadrohybus should be accorded separate generic status or subgeneric status within an enlarged concept of Bolbocephalus. Petigurus is the most closely related bathyurid to Bolbocephalus (Fortey 1979) and is the sister group to Bolbocephalus and Hadrohybus. Figure 3 shows the distribution of characters of the cranidia of these genera, together with Bathyurus as the typical bathyurine. This shows there are really no characters which can be regarded as autapomorphic for Hadrohybus cranidia apart from the glabellar boss, whereas Bolbocephalus and Hadrohybus have several additional autapomorphies, about the same number as Petigurus. All these taxa form a compact subgroup within Bathyurinae. The best recourse for the moment is to regard Hadrohybus as a subgenus of Bolbocephalus, based on the glabellar boss, because there are two species showing this distinctive character. Discovery of the free cheek and pygidium of Hadrohybus may add additional characters. Ordovician Trilobite Hadrohybus Bathyurellinae Bathyurus Fig. 3. Cladogram of relationships of Hadrohybus within Bathyuridae, based on cranidial characters. Bathyurus, shown as the sister group of Petigurus + Bolbocephalus, does not have cranidial autapomorphies and its recognition depends on the pygidium. Derived characters are: 1, glabellar boss; 2, sculpture of terrace ridges; 3, waisted glabella; 4, loss of typical bathyurid tuberculation; 5, exceptionally thick cuticle; 6, very coarse glabellar tuberculation; 7, large size; 8, glabella protrudes over cranidial margin; 9, deep palpebral furrows; 10, loss of horizontal anterior cranidial border; 11, rounded and tumid frontal glabellar lobe; 12, tuberculate sculpture. Postilla 202 Petigurus Bolbocephalus (Bolbocephalus) Boibocephalus (Hadrohybus) 7 Ordovician Trilobite Hadrohybus Postilla 202 Literature Cited Billings, E. 1865. Palaeozoic Fossils. Vol. 1. Containing descriptions and figures of new or little known species of organic remains from the Silurian rocks. 1861-1865. Montreal, Geol. Surv. Canada. Fortey, R. A. 1979. Early Ordovician trilobites from the Catoche Formation (St. George Group), western Newfoundland. Bull. Geol. Surv. Canada 321:61-114. Henningsmoen, G. 1959. Cheiruridae, p. 431-38. in R. C. Moore (ed.), Treatise on Invertebrate Paleontology. Part O. New York City, Geol. Soc. Am. and Univ. Kansas Press. James, N. P. and R. K. Stevens. 1986. Stratigraphy and correlation of the Cambro-Ordovician Cow Head Group, western Newfoundland. Bull. Geol. Surv. Canada 366:1-143. Moore, R. C. (ed.) 1959. Treatise on Invertebrate Paleontology. Part O. Trilobita. New York City, Geol. Soc. Am. and Univ. Kansas Press. 560 p. Raymond, P. E. 1925. Some trilobites of the Lower Middle Ordovician of Eastern North America. Bull. Mus. Comp. Zool., Harvard Univ. 67(1):1-180, 10 pls. Whitfield, R. P. 1886. Notice of geological investigations along the eastern shore of Lake Champlain, conducted by Prof. H. M. Seely and Prest. Ezra Brainerd, of Middlebury College, with descriptions of the new fossils discovered. Bull. Am. Mus. Nat. Hist. 1:293-345, pls. 24-34. 1890. Observations on the fauna of the rocks at Fort Cassin, Vermont, with descriptions of a few new species. Bull. Am. Mus. Nat. Hist. 3:25-39, pls. 1-3. Whittington, H. B. 1953. North American Bathyuridae and Leiostegiidae (Trilobita). J. Paleont. 27:647-78. 1963. Middle Ordovician trilobites from Lower Head, western Newfoundland. Bull. Mus. Comp. Zool., Harvard Univ. 129(1):1-118, 36 pls. The Author R. A. Fortey. Department of Paleontology, British Museum (Natural History), Cromwell Road, London SW7 5BD, England.