I 3 UNIVERSITY OF | ILLINOIS LIBRARY AT URBANA-CHAMPAIGN GEOLOGY The person charging this material is re- sponsible for its return to the library from which it was withdrawn on or before the Latest Date stamped below. Theft, mutilation, and underlining of bookf are reasons for disciplinary action and may result in dismissal from the University. To renew call Telephone Center, 333-840O UNIVERSITY OF ILLINOIS LIBRARY AT URBANACHAMPAIGN apr 29mt JUL oil 'Ml thtt 199? *4p L161— O-1096 ($frt& s^j- FIELDIANA Geology Published by Field Museum of Natural History Volume 20, No. 6 January 25, 1971 A Strange Arthropod from the Mazon Creek of Illinois and the Trans Permo-Triassic Merostomoidea (Trilobitoidea) Frederick R. Schram Department of Zoology, Eastern Illinois University Charleston, Illinois An arthropod from the ironstone concretions of the Middle Pennsylvanian Essex fauna of Illinois (Johnson and Richardson, 1966) appears to be closely related to two Mesozoic species, Euthy- carcinus kessleri Handlirsch, 1914, from the Lower Triassic of Germany, and Synaustrus brookvalensis Riek, 1964, from the Middle Triassic of Australia. Together these animals appear to constitute the latest known occurrence of trilobitoids in the fossil record. Specimens of various collections have been used in this study and are denoted by prefixes as follows: PE — Field Museum of Natural History H — Collection of Mr. Jerry Herdina, Berwyn, Illinois S — Collection of Mr. and Mrs. Levi Sherman, Des Plaines, Illinois T — Collection of Mr. Francis Tully, Lockport, Illinois HTP— Collection of Mr. and Mrs. Ted Piecko, Chicago, Illinois. DESCRIPTION Trilobitomorpha St0rmer, 1944 Trilobitoidea St0rmer, 1959 Merostomoidea St0rmer, 1944 Euthycarcinoidea Gall and Grauvogel, 1964 (emend. Schram, herein) Library of Congress Catalog Card Number: 78-11*3279 Publication 1119 85 MAY 1 5 1972 86 FIELDIANA: GEOLOGY, VOLUME 20 Fig. 1. Kottixerxes gloriosus. T3, note relationship of sternites to the large preabdominal plates and the outlines of the preabdominal appendages bearing setae. X 1.8. Merostomoidea with elongate body divided into three distinct body regions: a head with sessile eyes, a pre-abdomen with tergites fused in groups and with well-developed rod-like "ligaments," and a post-abdomen; a styloid telson; the appendages of the typical trilobitoid type. M. Penn. — M. Trias. Euthycarcinidae Handlirsch, 1914 Head consisting of acron plus four (?) segments; preabdomen of 11 or 12 segments ventrally, with tergites fused to form five elements dorsally; four or five postabdominal somites. Kottixerxes n. gen. Diagnosis. — Euthycarcinid of moderate size; preabdominal ter- gites fused into plates, with the numbers of segments associated in these plates being two, two, three, three, one respectively from anterior to posterior; eyes sessile, ovoid in shape; five segements in the postabdomen, each tapering posteriorly; a relatively short telson. Type species. — Kottixerxes gloriosus Schram, n. sp. SCHRAM: MAZON CREEK ARTHROPOD 87 Fig. 2. Kottixerxes gloriosus. H406. X 3.5. Kottixerxes glorious n. sp. Figures 1-9. Description. — The cephalon is bluntly rounded in outline anteri- orly, with slightly developed "genal" spines (T3, fig. 1). The entire surface texture of the head shield is rough and somewhat papillose (T3). The sessile ovoid eyes are located on the edge of the cephalon at the anterolateral corners, H406 (fig. 2), which displays these as very faint, ghostly outlines. H122 (fig. 3) has what appear to be segments in the cephalic area. Whether these segments belong to the cephalon or are actually sternites of the anterior preabdomen cannot be determined. The five dorsal plates of the preabdomen are formed by the fusion of the preabdominal tergites. The first two plates are com- Fig. 3. Kottixerxes gloriosus. H122, bottom picture is a closeup of the head region with the antennae? (an) and the visible segmental borders of the cephalon (sb) marked. Top, X 4; bottom, X 7. 88 Fig. 4. Kottixerxes gloriosus. H410. In the upper picture, the remnants of the cephalic appendages are outlined for ease in interpreting the lower picture. Note the multisegmented rami of the "first antennae," the basal segment of the "second antennae," and the basal segment of a left "circumoral appendage." X 9 . 89 90 FIELDIANA: GEOLOGY, VOLUME 20 Fig. 5. X 10. Kottixerxes gloriosus. H409, closeup of a preabdominal appendage. posed of two segments, the third and fourth plates of three segments, and the last plate of only one segment. These thoracic plates extend laterad and ventrad from the dorsal roof of the somite, enveloping the sides of the preabdomen. The five segments of the postabdomen are not fused together in any way. They bear no ornament and are successively reduced in width posteriorly. The postabdomen terminates in a relatively short telson, seen on only one of the specimens at hand (H406, fig. 2). (The telson is not typically preserved. It is frequently not included within the material of the concretion.) Two small pairs of processes have been observed (H122, fig. 3; H407). It is possible they are parts of the antennae; however, they are poorly preserved in the specimens at hand and cannot be identi- SCHRAM: MAZON CREEK ARTHROPOD 91 fied with any degree of certainty. There is only the vaguest sug- gestion of the hypostome (H122, H405, H407; fig. 3) as impressions from below on the dorsal surface of the cephalon. H410 is the only specimen examined to date, poor as it is, that reveals something concerning the structure of the cephalic appendages (fig. 4). The "first antennae" appear to be multi-segmented structures with only one ramus. Only the basalmost segments of a possible "second antenna" were observed laterad to the multi-segmented rami, so no idea as to the nature or length of the flagellum could be arrived at. On the left side of the better counterpart of H410 the basal segment of a "circumoral appendage" can be seen (lateral to the region where the mouth appears to be); possibly the vaguest sug- Fig. 6. Holotype of Kottixerxes gloriosus, PE11010. X 2. 92 FIELDIANA: GEOLOGY, VOLUME 20 Fig. 7. Kottixerxes gloriosus. Closeup of T3 with the preabdominal ap- pendages (pa), ligament (1), border of the sternites (s), and the border of the tergal plates (t) marked. X 6.5. gestion of a biramous structure in the rest of the appendage can be discerned if one examines the specimen closely. Each of the preabdominal segments has an appendage. Ap- pendages have been well preserved on H409 (fig. 5) . Pyritic residues can be detected under xylene on H405 and ghostly outlines of the preabdominal appendages with setae can be seen on PE11010 (fig. 6) and T3 (fig. 1). It appears that the preabdominal appendages of Kottixerxes resemble the types described by Gall and Grauvogel (1964) for Euthycarcinus, i.e., a single telopodite of 13 or 14 seg- ments, each bearing setae. Heavily chitinized rod-like structures, within the body of the preabdomen, have been clearly preserved on all the specimens at hand. These structures (termed "apodemes" by Gall and Grauvogel) take origin near the anterolateral corners of the sternites and are directed at an angle posteriad and mediad (H409, fig. 5; T3, fig. 7). A small foramen is located apparently on Fig. 8. Kottixerxes gloriosus. HTP5095, upper photo, with the ligament (1), and the accessory foramen (f). H410, lower photo. X 10. 93 94 FIELDIANA: GEOLOGY, VOLUME 20 Table 1. Measurements in centimeters of the well-preserved specimens of Kottixerxes gloriosus. Pre- Post- Body Cephalon Cephalon abdominal abdominal length width length length length (-telson) Telson PE11010 1.25 .57 1.67 PE12696 1.70 2.93 H122 .56 .30 1.35 H405 .70 1.83 H406 .85 .55 1.14 .68 2.40 .36 H407 1.46 .87 2.35 S1005 .60 1.79 T3 1.35 .92 2.02 1.15 4.16 T4 1.10 .75 1.98 each segment behind the base of the appendages for that segment (HTP5095, fig. 8) . There are no appendages on the postabdominal somites. Measurements of the better preserved, available specimens are given in Table 1. Holotype.— PE11010 (fig. 6), donated to Field Museum by A. W. Kott of Summit, Illinois. Remarks. — The gut on almost all the specimens examined was consistently filled with very fine clastic material. These fillings, combined with the general body plan, would seem to indicate that Kottixerxes was a bottom-dwelling, detritus-feeding organism. This agrees with the conclusions of Gall and Grauvogel. The rod-like structures, "apodemes," appear to have been mobile. Apodemes on opposite sides or succeeding apodemes on a side may be preserved at varying angles, which would seem to indicate that they could move. These "struts" cross segmental borders in pres- ervation due to flattening and compression of the animal during diagenesis, but probably in life the structures were intrasegmental. Just what the accessory foramina behind the appendages may be is a mystery. Perhaps they represent excretory pores or gonopores. They could be the openings into the telopodite; however, they ap- pear to be too small for that. The exoskeleton itself seems to have been only lightly sclerotized. All the specimens examined with the exception of H122 were dis- torted due to compression, but none were broken or cracked as would be expected if the animal were heavily armored (such as the crusta- cean Belotelson magister from this same fauna). The typically poor preservation of the preabdominal appendages indicates that even SCHRAM: MAZON CREEK ARTHROPOD 95 Fig. 9. Reconstruction of Kottixerxes gloriosus, scales 1 cm. these structures were only lightly sclerotized. Thus we might speculate again that this animal slowly swam through the flock zone (the upper few centimeters of organically rich soup overlying the more consolidated mud) or skimmed over the surface of the sediment, feeding as it progressed. DISCUSSION The segmental pattern of this arthropod and the Mesozoic forms is very interesting. The preabdominal tergites are fused in groups to form preabdominal dorsal plates. In comparing the three species of euthycarcinids, (see Table 2) no pattern in the number of fused tergites per preabdominal plate emerged. Indeed, in instances where similar phenomena can be observed in the recent fauna (primarily in the "myriapod" groups) they have proven to be quite variable. All the euthycarcinids, however, have 11 (or 12) segments in the preabdomen which have fused dorsally in varying patterns into fewer plates. The postabdomen in Euthycarcinus has four or five segments; Kottixerxes has five segments, while in Synaustrus there are only four. The deficiency of a postabdominal segment 96 FIELDIANA: GEOLOGY, VOLUME 20 in Synaustrus may be due to either a fusion of any two postabdominal segments, a fusion of the last segment with the telson, or a failure of the telson to bud off a fifth segment in this genus. Table 2. Comparison of the three species of Euthycarcinidae in regard to certain aspects of their morphology. ( ) indicates conclusions of Riek (1968) Pre- Post abdominal abdominal Telson Cephalon Tergites pattern somites long blunted decorated Euthycarcinus kessleri 1,3,3,3,1(2) 5 + + + Synaustrus brookvalensis 1(2),2, 3,3,2 4 + — — Kottixerxes gloriosus 2,2,3,3,1 5 — + — The presence of rod-like "apodemes" associated with the pre- abdominal appendages seems to be the most puzzling and contro- versial aspect of euthycarcinid anatomy. Riek (1964), in his original description of Synaustrus, considered these structures to be artifacts due to preservation. He claims to be able to reproduce these by flattening any reasonably sclerotized siphlonurine mayfly nymph (personal communication). The abdomen of these nymphs is bi- convex in section. The rod-like struts, in his experiments, represent the anterior margin of a tergite that is overlapped by the hind margin of a preceding tergite. These structures are well developed, however, on almost all specimens of Kottixerxes. I am inclined to agree in part with the interpretation of Gall and Grauvogel, who termed these structures "apodemes." But apodemes in modern arthropods are typically plate-like infoldings of the exoskeleton. They function as places of muscle attachment around the appendage base. These rod-like structures are very peculiar and would appear to be more like ligaments or tendons associated with the appendicular musculature or the exoskeleton. Just why these structures are de- veloped the way they are is not clear. Why would a group of poorly sclerotized, bottom-dwelling, detritus-feeders require such special- ized, apparently well-sclerotized, rod-like "ligaments" or "struts"? There is considerable debate as to the taxonomic affinities of this group. Gall and Grauvogel, having considered the similarities of Euthycarcinus to the trilobitoids in passing, insisted that the euthycarcinids were true Crustacea and erected a new subclass to accommodate them. This position would seem to be unlikely when their criteria are examined. First, body regionalization is known throughout the Arthropoda and the segmentation of the regions in the euthycarcinids bears little resemblance to that in any known crustacean group. Second, two sets of antennae are not restricted I Fig. 10. A. Eulhycarcinus kessleri (redrawn from Gall and Grauvogel, 1964); B. Synaustrus brookvalensis (redrawn from Riek, 1968); C. Emeraldella brooki (redrawn from St0rmer 1959); D. Oxyuropoda ligioides (redrawn from Carpenter and Swain, 1908). Scales 1 cm. 97 98 FIELDIANA: GEOLOGY, VOLUME 20 to the Crustacea, but occur also in some of the trilobitoids, and as such can be considered only convergent to the crustacean condition. Finally, the nature of the "mandibles" and postoral appendages is extremely obscure in all three species of euthycarcinids and cannot be safely used at this time as indicators of phyletic relationship. Furthermore, the work of Manton (1964) indicates that "mandibles" arose more than once within the living arthropods. It is possible that they also arose independently in the Euthycarcinoidea. Riek (1968) has re-examined Synaustrus and reinterpreted Euthycarcinus. He has come to agree with Gall and Grauvogel and places the Euthycarcinoidea in the Branchiopoda as a separate subclass. His reinterpretation of the cephalon would be a strong argument for this assignment, but again, the evidence is very incon- clusive. Riek's new observations are attractive, however, and per- haps should not be rejected until all specimens of all three species can be examined. Riek (1964) originally believed Synaustrus to be a merostomoidean. I tend to concur with this judgment. Not only is the general body plan of the euthycarcinids merestomoid, but what is known of the preabdominal appendages of all three species would indicate that this group should probably be placed in the trilobitoids. The preabdominal appendages are single- branched telopodites with 13 or 14 setiferous segments. This is more reminiscent of the condition found in some of the trilobitoids than in the Crustacea. The primitive crustacean limb, as exempli- fied by the cephalocarids, branchiopods, and leptostracans, ap- parently was a foliaceous appendage with exopods, endopods, and well-developed epipodites. The only crustacean limb that even closely approximates that found in the three euthycarcinid species is the specialized type possessed by the eumalocostraca, but even this retains the basic biramous plan. Thus I would choose to place the Euthycarcinoidea in the Merostomoidea for the present. It is also possible that the euthycarcinoids are Merostomata. Such a designation would be more attractive than placing them in the Crustacea. Positive evidence on the nature and arrangement of the cephalic appendages would settle the question, but such is lacking. No chelicerae are indicated on any of the euthycarcinids but this is negative evidence. The possibility of assignment to the Merostomata should remain open. Of all the Merostomoidea, the Euthycarcinoidea appear to be near the order Emeraldellida (Emeraldella brocki and Molaria spinifera Walcott, 1912). In comparing the merostomoidean orders SCHRAM: MAZON CREEK ARTHROPOD 99 Table 3. Summary classification of the Merostomoidea with emphasis on the Euthycarcinoidea. Subclass: Merostomoidea, St0rmer, 1944 Order: Limulavida, Walcott, 1911 Order: Nectaspida, Walcott, 1912 Order: Leanchoiliida, St0rmer, 1944 Order: Emeraldellida, St0rmer, 1944 Order: Euthycarcinoidea, Gall and Grauvogel, 1964 (emend. Schram, herein). Family: Euthycarcinidae, Handlirsch, 1914 Euthycarcinus kessleri, Handlirsch, 1914 Synaustrus brookvalensis, Riek, 1964 Kottixerxes gloriosus, nov. ?Family: Oxyuropodidae, Carpenter and Swain, 1908 Oxyuropoda ligioides, Carpenter and Swain, 1908 with each other it appears that the differences between the euthy- carcinids and the other groups merit an ordinal distinction within the framework of our current understanding of the Trilobitoidea. It is possible that a problematic arthropod from the Devonian should be included in the Euthycarcinoidea. Oxyuropoda ligioides Carpenter and Swain, 1908, shares a number of features with the euthycarcinid species. Oxyuropoda has three body regions: a ceph- alon, a preabdomen with five (or six) dorsal plates and the possi- bility of many more ventral segments, and a postabdomen of five segments with a telson bearing two rami. What Carpenter and Swain refer to as a chelate first thoracic appendage could possibly be a development of one of the antennae. From their reconstruction and description, it appears that at least their first, and possibly their second thoracic segment is actually part of the cephalon. A re-examination of the original material of Oxyuropoda ligioides is necessary before any definitive judgment can be made; however, it would appear that this problematic fossil might be included within the Euthycarcinoidea as a separate family. Rolfe (1969) prefers to retain Oxyuropoda in the Tanaidacea for the time being. The Euthycarcinoidea would have a geologic range (Middle Pennsylvanian to Middle Triassic) long after the trilobitoids were thought to be extinct. The Merostomoidea were previously known only from the Middle Cambrian in the Burgess Shale of British Columbia. The latest reported supposed trilobitoid previous to Riek's observations was the Early Devonian Cheloniellon calmani Broili, 1933. It would appear that the trilobitoids had a very long history and underwent a rather extensive radiation, though most of their career took place in environments where they were mot 100 FIELDIANA: GEOLOGY, VOLUME 20 preserved. The Euthycarcinoidea also cross over the Permo- Triassic boundary in which some massive extinctions of Paleozoic creatures took place. The order Euthycarcinoidea thus becomes another on a growing list of groups which cross the Permo-Triassic boundary unaffected. The study of the Essex fauna continues to reveal that the Paleozoic radiation did not suddenly come to an end, but was part of a continuum leading into the Mesozoic. SUMMARY A new merostomoidean trilobitoid, Kottixerxes gloriosus, is de- scribed. It is found to have definite affinities with two Triassic forms which together with it are placed as an order within the Merostomoidea. The presence of this order in the Late Paleozoic and Early Mesozoic indicates a long and divergent history for the trilobitoids. The known distribution of the order embraces North America, Europe, and Australia. ACKNOWLEDGMENTS The author wishes to acknowledge the generous co-operation he received from Messrs. Herdina, Sherman, and Tully, and Mrs. Helen Piecko. Deep thanks are extended to Mr. Kott for donating the holotype. The stimulating discussion and constructive criticism of the manuscript by Dr. E. S. Richardson, Jr. of Field Museum was, as always, perceptive and helpful, and deeply appreciated. The debate with Edgar Riek, when he was in Chicago in 1969, over interpretations of euthycarcinoidean anatomy was most stimulating. Henry Dybas of Field Museum provided discussion and analysis of modern arthropod anatomy. Thanks are also expressed to Drs. H. B. Whittington and W. D. I. Rolfe for reviewing the manuscript and suggesting modifications. However, this does not imply agree- ment with the author's ideas, nor in any way mitigate any defects of presentation. REFERENCES Carpenter, G. H. and I. Swain 1908. A new isopod from Kiltocan County, Kilkenny. Proc. Roy. Irish Acad., 27, pp. 61-67. Gall, J. C. and Grauvogel, L. 1964. Un Arthropode peu connu: le genre Euthycarcinus Handlirsch. Ann. Paleontol., 50, pp. 1-18. SCHRAM: MAZON CREEK ARTHROPOD 101 Handlirsch, A. 1914. Eine interessante Crustaceenform aus der Trias der Vogesen. Verhandl. K. K. zool.-bot. Ges., 64, pp. 1-8. Johnson, R. G. and E. S. Richardson, Jr. 1966. A remarkable Pennsylvanian fauna from the Mazon Creek Area, Illinois. Jour. Geol., 74, no. 5, pp. 626-631. Manton, S. 1964. Manidbular mechanisms and the evolution of arthropods. Phil. Trans. Roy. Soc, London, (B), 247; 737, pp. 1-183. Riek, E. F. 1964. Merostomoidea (Arthropoda, Trilobitomorpha) from the Australian Middle Triassic. Rec. Aust. Mus., 26, no. 13, pp. 327-332. 1968. Re-examination of two arthropod species from the Triassic of Brookvale. New South Wales. Rec. Aust. Mus., 27, no. 17, pp. 313-321. Rolfe, W. D. I. 1969. In R. C. Moore, ed., Treatise on Invertebrate Paleontology, Part R, Arthropoda U, pp. R621-R622. SlMONETTA, A. M. 1964. Osservazioni sugli arthropodi non trilobiti della "Burgess Shale" (Cam- brio Medio). Ill Contribute I Generi Molaria, Habellia, Emeraldella, Parahabelia (nov.), Emeraldoides (nov.). Monitore Zool. Italiano, 72, pp. 213-231. ST0RMER, L. 1944. On the relationships and phylogeny of fossil and recent Arachnomorpha. Norske Videnskaps-Akad., 1944, no. 5, 158 pp. 1959. Trilobitoidea. In Moore, R. C, ed., Arthropoda: Treatise on Inverte- brate Paleontology, Part 0, pp. 23-37. Walcott, C. D. 1912. Middle Cambrian branchiopoda, malacostraca, trilobita, and mero- stomata. Smithson. Misc. Coll., 57, no. 6, pp. 145-228. ADDENDUM Since this paper went to press, another specimen of Kottixerxes gloriosus has come to the author's attention; W654 (fig. 11) from the collection of Mr. and Mrs. Fran Wolff of Park Forest, Illinois. The specimen is 14 mm. long and is composed of a cephalon, a preabdomen of 11 segments, and a postabdomen with the three proximalmost segments preserved. No appendages are detectable. The preabdomen of this individual is distinctive. The specimen clearly displays the 11 sternites of the body trunk and the lateral extensions of 11 tergites. The tergites are not fused as they are in the adults. This specimen would seem to represent a juvenile. This small individual with unfused tergites would be from a stage in the life history of the species prior to a molt or molts which led to the fused tergal condition in the mature forms. 102 FIELDIANA: GEOLOGY, VOLUME 20 Fig. 11. Kottixerxes gloriosus, W654. Supposed juvenile form with unfused preabdominal tergites. X 8. The existence of this juvenile stage of Kottixerxes tends to strengthen the relationship of the Euthycarcinoidea to the Cambrian merostomoideans, such as Emeradella, which it resembles.