The Mosasaur, 7: 19-34

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A Preliminary Paleoecological Investigation of Late Pennsylvanian Brachiopods from the LaSalle Limestone, LaSalle County, Illinois Stephen L. Brusatte* Department of Geophysical Sciences University of Chicago [email protected] 5734 S. Ellis Avenue, Chicago, IL 60637 and: 3 Shady Lane, Ottawa, IL 61350 (home) ABSTRACT - This paper describes the macroinvertebrate fauna of a new Upper Pennsylvanian (LaSalle Limestone, Bond Formation, McLeansboro Group, Missourian Series) outcrop exposed near LaSalle, Illinois. This fauna, which can be dated to 280-300 million years ago, consists of articulate brachiopods, crinoids, rugose corals, and bryozoans. An isolated tetrapod bone, two indeterminate shark teeth, and two pieces of petrified wood were also found. The brachiopod Linoproductus, the most common taxon at the site, has been found in a possible event concentration (mass-death layer). The brachiopod Composita, another common member of the fauna, exhibits extremely small sizes, a characteristic likely due to paedomorphic progenesis. Taken together, the fossil evidence found at the outcrop shows a continental sea that covered Illinois during the Pennsylvanian was gradually regressing, forcing its inhabitants to evolve.

Introduction During the Pennsylvanian Period, from 280-320 million years ago, most of the ancient continents had converged to form a supercontinent known as Pangea (Redfern, 2001). The collision of two smaller landmasses, known as Laurasia and Gondwana, produced this large continent. As a by-product of this collision, much of the land that now comprises North America was compressed, buckled, and uplifted, producing a mountain range that extended from what is now New England to Mexico (Baird, 1997). These mountains supplied large quantities of sediment to tropical river systems, which created large deltas as they emptied into shallow continental seas (Baird, 1997; Jennings, 1990). Furthermore, paleoclimatic studies suggest that the formation of the mountain system created conditions of atmospheric circulation that produced extensive amounts of rainfall over what is now North America (Phillips and Dimichele, 1981). Taken together, these factors created large coastal swamps and inland seas that filled lowland areas. During this time, Illinois was part of one such lowland area that extended for hundreds of miles (Jennings, 1990). As such, the land that now comprises much of Central Illinois was home to a continental sea, flanked by swamps and deltas at its margins. Two large delta systems, both flowing southwestward, emptied into the sea, periodically inundating the shorelines with vast quantities of mud, silt, and sand (Nelson et. al. 1997; Baird, 1997). Today, the remnants of such inundations are preserved as alternating layers of shale, limestone, and sandstone, many of which preserve exquisite fossils of the ani-

mals and plants that lived in and along the sea. Paleomagnetic studies conducted by Scotese et al. (1979) indicate that the Earth’s equator extended across what is now North America during much of the Pennsylvanian. According to their research, present-day Chicago was located almost directly along the equator during the Middle Pennsylvanian, producing a tropical-like climate. These tropical conditions, in association with an hypothesized increased level of atmospheric oxygen (Hannibal, personal communication), were two possible factors that resulted in diverse ecosystems of plants and animals. The best-studied Pennsylvanian fossils in Illinois belong to the Francis Creek Shale Member of the Lower Pennsylvanian. Commonly referred to as the “Mazon Creek Biota,” this assemblage of fossils is found throughout a belt of five northern Illinois counties. The Francis Creek Shale preserves a flourishing coal-swamp environment and is rich in plant fossils (especially lycopods, pteridophytes, and pteridosperms), along with those of crustaceans, bivalves, and other near-shore animals (Jennings, 1990). According to studies by Baird (1997) and Kuecher (1983), the Francis Creek Shale Member records the filling of a coastal estuary with deltaic sediment. Emergence of the coast and regression of the sea are results of such an environment. The Francis Creek Member, although never directly radiometrically dated, is likely over 300 million years old. Along with other Pennsylvanian coal-bearing deposits in Illinois, the Francis Creek Member has been well studied because of its famous fossil fauna and flora. However, younger Pennsylvanian rock units are not as well studied,

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Figure 1: A view of the Late Pennsylvanian Orlando Smith Road Outcrop looking southwest along Orlando Smith Road near Illinois Valley Community College in LaSalle County, Illinois. The site records an outcropping of the LaSalle Limestone, and preserves a unique fauna consisting of brachiopods, corals, crinoids, bryozoans, vertebrates, and plants.

despite the fact that many of these units can contribute valuable paleoecological data. One such unit is the LaSalle Limestone, a unit of intermittent limestone and shale that is between 280-300 million years old (Jacobson, personal communication). The LaSalle Limestone belongs to the Bond Formation (McLeansboro Group, Missourian Series) of the Upper Pennsylvanian. It was first named by Cady (1908) in a publication describing cement-making materials present in LaSalle County. This unit outcrops infrequently in LaSalle and Livingston Counties and is rarely preserved un-eroded north of LaSalle County. Since its original naming, the LaSalle Limestone has sometimes been correlated with the Millersville and Shoal Creek Limestone: two similar units also belonging to the Bond Formation. However, Russell Jacobson (1983) tentatively correlated the LaSalle and Millersville Limestones based on unpublished drill core data. Other than Jacobson’s study, there have been few other such geological examinations of the LaSalle Limestone. Additional works include a variety of abstracts (Tischler and Ruotsala, 1965; Tischler, 1964; Hughes and Morris, 1972) and an important contribution by Fraser (1991) that discussed the algal origin of the unit. Although it preserves a diverse and informative fossil assemblage, the LaSalle Limestone has also received scant mention in the paleontological literature, with most published works being restricted to abstracts. Hickey and Younker (1981) published the most detailed study of LaSalle Limestone fossils, focusing mainly on community structure and the pos-

sible life strategies of the most abundant fossil taxa. A distinct assemblage of crinoids, many of which proved to be new taxa, was discovered in Livingston County and described by Strimple and Moore (1971). Follow-up papers on this fauna include works by Strimple (1971), Strimple (1973), Lewis and Strimple (1990), and Ausich (1999). Additionally, a new species of polyplacophoran mollusk (Hoare and Maples, 1986) and a new species of asteroid (starfish) (Kesling and Strimple, 1966) have been described. An abstract by Merrill and Swanson (1980) briefly discussed conodonts found in the LaSalle Limestone, and antiquated publications by Newberry and Worthen (1866), Newberry and Worthen (1870), and Branson (1905) described three new shark teeth from what is likely the LaSalle Limestone. These three species, which may be invalid, are summarized in Stahl (1999). Several other teeth and shark tail fin taxa, many of which may also be invalid, were described by Newberry and Worthen (1866), Newberry and Worthen (1870), Meek and Worthen (1866), Meek and Worthen (1870), St. John and Worthen (1883), St. John and Worthen (1875), and Worthen and Meek (1875). It should be cautioned, however, that these teeth were described before the LaSalle Limestone was named, and locality data presented in the papers above likely represents LaSalle Limestone sites, but exact correlation is impossible. Notably absent has been published work on the abundant and diverse brachiopods of the unit, as only one major study (Grinnell and Andrews, 1964) has focused primarily on this phylum. This study, however, compared the presence of Composita in the LaSalle Limestone with four other limestone

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units in Kansas in an attempt to elucidate the taxonomy of this ubiquitous yet enigmatic genus. As compiled from field studies and a literature search, brachiopods, echinoderms (crinoids and asteroids), rugose corals, bryozoans, trilobites, ostracodes, gastropods, pelecypods, polyplacophoran mollusks, sponge spicules, foraminifera, phylloidal algae, petrified wood, conodonts, shark teeth and tail fins, and tetrapod bones have been noted in LaSalle Limestone sediments. Many of the better specimens come from a hitherto undescribed outcrop located along Orlando Smith Road near LaSalle and Jonesville, Illinois (Brusatte, 2001; Brusatte, 2002) The Orlando Smith Road outcrop (Figure 1) is comprised largely of limestone with several layers of intermittent red, black, and green shales. According to Fraser (1991) and Jacobson (personal communication), it was likely formed along the western flank of an algal reef, which was possibly located near the shore of a continental sea. Although no records of road construction were found, it is likely that the outcrop was created as a result of highway construction (Phillips, personal communication). According to Mike Phillips, the road was likely built sometime during the 1960’s, but it was only in the 1990’s that much of the dense vegetation was cleared from the site, exposing the outcrop (Jakupcak, personal communication). This is probably why the fossils found at the outcrop have hitherto remained unstudied. The outcrop is a favorite of local fossil collectors and is frequently visited by the geology classes at Ottawa Township High School and Illinois Valley Community College. Both programs have been collecting brachiopod and crinoid fossils at the site for over five years. Collections of these fossils can be found at both institutions. However, despite the popularity of the site, it was never properly described until Brusatte (2001) prepared a study of the outcrop as part of an independent study program at Ottawa Township High School. The results of that study are used in this paper to support several paleoecological hypotheses. Generally speaking, the Orlando Smith Road outcrop supports a marine fossil fauna that lived near the margins of an algal reef (Fraser, 1991). This fauna includes a diverse assemblage of brachiopods (Figures 4, 6), crinoids (Figure 3), and rugose corals (Figure 2). One tetrapod bone, two shark teeth, two pieces of petrified wood, and one bryozoan (Figure 5) were also found at the site. Examining these fossils can give insights into the paleoecology of the LaSalle County area during the Late Pennsylvanian.

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1). Fossils and rock samples collected at the site were then analyzed by the author at Ottawa Township High School, under the supervision of Joe Jakupcak. This analysis included the cleaning, measurement, and reconstruction of fossils, and the comparison of those fossils to similar forms found both in Illinois, including those from other LaSalle Limestone outcroppings, and throughout the Midwest.

Description The Orlando Smith Road Outcrop (Figure 1) is long and easy recognizable by passing motorists, measuring 200 meters in length and approximately 13 meters in height. The outcrop has an average dip of seven degrees to the southwest and preserves seven visible rock layers. Beginning from the top, the layers include: a massive fossiliferous ledge-forming limestone, a thin layer of red and black shale, a unit of massive fossilferous limestone, a layer of deeply eroded paper-thin shale, a unit of narrow limestone, a small layer of intermittent shale, and a narrow layer of smooth, gray limestone. The uppermost limestone layers (referred to hereafter as the second limestone horizon) preserve a diverse and abundant fossil fauna consisting primarily of articulate brachiopods.

Materials and Methods Research for this project was conducted between October 1999 and December 2001. Fieldwork, including fossil and rock collection, was conducted at the Orlando Smith Road Outcrop, located alongside Orlando Smith Road near Illinois Valley Community College in LaSalle County, Illinois (Figure

Figure 2: The rugose coral Lophophyllidium. This specimen is one of the three fossils of this genus found in the first limestone horizon at the Orlando Smith Road Outcrop. It is one of the rarer fossils found at the site.

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Figure 3: Isolated crinoid columnals. These fragmentary ossicles are found in the second limestone horizon at the Orlando Smith Road Outcrop. The LaSalle Limestone is known for its diverse crinoid fauna, but the majority of well-preserved crinoid fossils come from sites further south in Livingston County.

The most common taxa include Juresania, Linoproductus (Figure 4), Composita (Figure 6), Mucospirifer, Neospirifer, Antiquatonia, and Echinaria. Isolated crinoid columals, found preserved in several lenses (Figure 3); conodonts; bryozoans (Figure 5); two petrified wood samples; two indeterminate shark teeth; an isolated tetrapod bone fragment; and possible sponge spicules are also present. The most common brachiopod is Linoproductus, for which over 100 specimens have been identified (Figure 4). Linoproductus is a medium-sized geniculated brachiopod with ribbing on both valves and rugae appearing as broad wrinkles on the sides of the shell (Schwimmer and Sandy, 1997). Its shells range from plano-convex to slightly concavo-convex. The sizes of Linoproductus range from 11-27 millimeters in length and 12-30 millimeters in width. While articulated specimens are rare, fossils of the both the pedicle and brachial valve have been identified, generally in the same proportions. Specimens of Linoproductus have been found in a layer of concentrated fossil material, which may represent an event concentration (perhaps a “mass death” bed). Although only incomplete segments of this bed are known, the number of Linoproductus specimens per square foot may reach 50. The implications of this layer will be addressed in the discussion section of this paper. Also common is Juresania, of which over 50 specimens have been identified. Juresania is a medium-sized brachiopod with a subquadrate outline and geniculated valves

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(Schwimmer and Sandy, 1997). Both valves are ornamented with well-developed pustules (blisters) (Herbert et al., 1990). Although no such fossils have been found preserved at the Orlando Smith Road Outcrop, Juresania specimens are frequently found with attached spines, which likely functioned as anchors used to secure the animal into the substrate. The sizes of Juresania range from 14-27 millimeters in length and 17-28 millimeters in width. As with Linoproductus, articulated specimens are rare. This suggests that most specimens were likely transported or bioturbated after death, although few show signs of wear. Specimens of Composita are rarer, but well preserved when found (Figure 6). Composita is a medium-sized brachiopod with an elongate outline and biconvex valves (Schwimmer and Sandy, 1997). The brachial valve shows a pronounced fold and the pedicle valve a deep sulcus. Specimens of Composita range from 8 to 27 millimeters in length and 7 to 25 millimeters in width. Nearly every specimen is found with both valves articulated, meaning either that Composita specimens are hard to disarticulate, as shown by studies of brachiopod hinging mechanisms performed by Sheehan (1978), or that there was little transport after death. It is likely that both factors explain the pattern seen at the outcrop. The spiriferid brachiopods Neospirifer and Mucospirifer, although present, are rare, and are found only in certain zones of the outcrop, often above the possible event concentration bed of Linoproductus. Both Neospirifer and Mucospirifer are biconvex brachiopods with elliptical outlines, long hinge lines, mucronate cardinal extremities, and deep internal cavities, which held a large lophophore, the brachiopod feeding organ.

Figure 4: The brachiopod Linoproductus. This brachiopod is commonly found in the second limestone horizon, and a layer of concentrated fossil material of this genus may represent a mass death layer, possibly caused by a storm event.

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Figure 5: An indeterminate bryozoan. This specimen is the lone bryozoan specimen collected at the Orlando Smith Road Outcrop. It was found as float and cannot be correlated to either limestone horizon.

Specimens of these genera range from 18-37 millimeters in length and 37-62 millimeters in width. Both genera are most commonly found with both valves articulated. Equally rare are Echinaria and Antiquatonia. Echinaria is a large echinoconchid brachiopod, possessing a shallow sulcus, low fold, convex pedicle valve, and a large umbo (Herbert et al., 1990). Only four specimens have been positively identified from the Orlando Smith Road Outcrop, ranging from 8090 millimeters in length and 50-65 millimeters in width. Antiquatonia is a medium-sized strophomenid brachiopod with a concavo-convex profile, elongate outline, thick spine ridge, and a reticulated umbo. Like Juresania, both valves are nodose and show well-developed pustules. Ten specimens of Antiquatonia have been identified from the Orlando Smith Road Outcrop. Specimens of the brachiopods described above have all been found in the second limestone horizon, with the exception of Juresania, which has also been found in the bottom two limestone layers (here on referred to as the first limestone horizon). Three specimens of the rugose coral Lophophyllidium have also been recovered from the first limestone system (Figure 2). Lophophyllidium has been reconstructed as a solitary rugose coral (Babcock, 1997). Specimens of this genus are rare and range from 17-40 millimeters in length. Also found preserved in the second limestone horizon are isolated crinoid columnals, an unidentified tetrapod bone fragment, and two indeterminate shark teeth. The crinoid columnals, which are often found in lenses of rock but are generally rare along the outcrop, range in diameter from 0.5-20 millime-

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ters and show prominent ribbing (Figure 3). The tetrapod bone fragment, discovered dislodged from the outcrop and preserved on a block of loose limestone, has been correlated with the second limestone horizon. It measures 14 by 11 millimeters and is dark brown in color. The general shape of the specimen is cylindrical and seems to represent the diaphysis of a long bone, perhaps the femur or humerus. It will be discussed later. The two shark teeth were found by the author in the second limestone horizon during the 2002 field season and are currently under study. One specimen, which measures approximately two centimeters in length and one centimeter in width, is reddish-gray in color and has five denticles. It resembles a specimen discovered in the Lone Star Quarry (Oglesby, Illinois), another La Salle Limestone outcrop site, by W. Frankie (personal communication). The other tooth is white, approximately two by three centimeters, and is covered by fine serrations along its edge. Finally, two specimens of petrified wood have also been uncovered, both showing prominent venation. However, identification of both specimens proves difficult, although both likely originated from the coal swamps that flanked the intercontinental sea that covered the area. The fossils recovered from the Orlando Smith Road Outcrop represent a diverse, abundant, and rich fauna and flora, which contribute important paleoecological data for reconstructing the environment of Central Illinois during the Late Pennsylvanian.

Discussion The seven rock layers present at the Orlando Smith Road Outcrop seem to represent a fraction of an ideal cyclothem, defined by Willman and Payne (1942) as a sequence of rock units representing an ordered change from marine to nonmarine sediments. An ideal cyclothem consists of ten layers, many of which are often only a few centimeters thick, and includes layers of sandstone, shale, coal, and limestone. These cyclothems were caused by the rapid and frequent changes in depositional environments during the Pennsylvanian (Reinertsen and Smith, 1986). Geologists, including Klein and Kupperman (1992), have interpreted these frequent changes as evidence of sea level oscillation caused by cyclic expansion and contraction of the Gondwanan ice cap during a prolonged ice age which lasted from 260-320 million years ago (Redfern, 2001). The Orlando Smith Road Outcrop has been correlated with the LaSalle Limestone, which belongs to the LaSalle Cyclothem (Reinertsen and Smith, 1986). Judging by evidence collected at four LaSalle Limestone outcroppings, including the Orlando Smith Road Outcrop, one or two large limestone layers are common for this unit (Jacobson, personal communication; Brusatte, field observation). This layer is usually fossiliferous, but the abundance of fossils varies between all four sites with the Orlando Smith Road Outcrop preserving

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Figure 6: The brachiopod Composita. This brachiopod is common in the second limestone horizon at the Orlando Smith Road Outcrop, as well as other LaSalle Limestone outcroppings. The seven specimens to the left, designated by “OSR,” come from the Orlando Smith Road Outcrop, while the seven specimens to the right, designated by “LSQ,” were found at the Lone Star Cement Quarry in Oglesby, Illinois. Specimens from both sites are small compared to Composita fossils found in other areas, and suggest that paedomorphic progenesis, in response to environmental pressure, may have been a factor in the small size.

the most diverse and varied fauna. Two or three shale layers are also common, which range from green, black, and red to gray. The variation between the four studied LaSalle Limestone outcroppings, especially in regards to the thickness of the various limestone and shale layers, differs markedly from many other Pennsylvanian cyclothems in Illinois, which are often traceable and constant over large areas (although most are never “ideal”). What significance does this hold? It appears as if the LaSalle Limestone was deposited during a time of rapid deltaic progradation, when sediment loads in the delta system emptying into the continental sea were high. This was also coupled with the unique shoaling effects of a large algal reef complex (Fraser, 1991). Although all four LaSalle Limestone sites were deposited at the same time, the uneven distribution of sediment from the delta and the effects of the reef led to the formation of different rock layers at different locations, along with enabling certain sites to preserve fossils. This is commonly seen in other cyclothems deposited during times of progradation. However, post-Pennsylvanian exposure and erosion may have also been a factor (Jacobson, personal communication). Only further research and fieldwork will help clarify this. The Orlando Smith Road Outcrop appears to have been deposited near the margins of an algal reef, which in turn was located relatively close to the shores of a continental sea. Evidence supporting this assertion, including the presence of fossil algae and a variety of geological observations, are summarized by Fraser (1991). According to Fraser (1991) and

Jacobson (personal communication), this reef was positioned along the topographical high of the LaSalle Anticlinorium. The Orlando Smith Road Outcrop is located along the west flank of the Anticlinorium. The three shale layers represent depositional periods when the outcrop site was affected by shale-producing shoaling cycles, related to sediment load carried by the delta system, while the four limestone layers represent periods when algae blooms were high (Fraser, 1991). This explains the distribution of certain fossil taxa. None of the three shale layers at the Orlando Smith Road Outcrop preserve any macrofossils. However, the second limestone horizon, and to a smaller extent the first limestone horizon, contains a diverse and abundant array of fossil brachiopods, rugose corals, and crinoids, as described in this paper. The apparent paucity of fossil material in the first limestone system is likely due to the thinness of the layer, and its limited exposure. The most common brachiopod taxon found at the outcrop is Linoproductus (Figure 4). Over 100 specimens of this genus have been positively identified, many of which are found in a layer of concentrated fossil material. While this layer may be an artifact of preservation, the fact that so many specimens of a certain genus are found buried together in a pocket of the outcrop suggests that this layer is an event concentration (a layer of shell material in which the process of concentration is ecologically rapid and comparatively simple-terminology of Kidwell, 1991), and that a common cause led to the death of the animals.

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Shell accumulation and fossilization is dictated by a myriad of causes, although Kidwell (1991) has systematically summarized the four basic types of shell concentrations. These include event concentrations; composite or multiple event concentrations, which record the accretion of multiple generations of taxa or multiple event concentrations; hiatal or condensed concentrations, which are similar to composite concentrations but involve a slow net level of sedimentation; and lag concentrations, which are thin layers that include shells concentrated by selective forces of erosion and winnowing. Of these four basic groups, it appears as if the Linoproductus layer at the Orlando Smith Road Outcrop most closely matches an event concentration. The major data supporting this interpretation are taphonomic. The layer in question only contains shells of Linoproductus, with no other taxon being present in the sections that have been studied. Furthermore, although most of the specimens are disarticulated, there appears to be a fairly even number of brachial and pedicle valves present, few of which show noticeable abrasion and none of which show evidence of predation or encrusters. Additionally, the shells preserved in the layer are variable in size. The absence of shell abrasion makes hydraulic winnowing or other erosion-based transport, signatures of lag concentrations, doubtful. The variety of shell sizes and near even mixture of brachial and pedicle valves also argue against a selective transport force. Holland (1988) found that the ratio of pedicle valves: brachial valves in a layer increases with abrasion, lending further evidence against a lag concentration or similar selective transport. While it is clear that the Linoproductus layer likely does not represent a lag concentration, supporting the hypothesis that the layer is an event concentration, and hence accumulated rapidly, is more difficult. However, various studies have shown that unabraided shells without signs of encrusting are often buried rapidly (Westrop and Rudkin, 1999). Furthermore, in the absence of any signs of selective transport, it is strange to find one taxon dominating a thin layer of sediment, while that same taxon is only one component of the community in units above and below the layer. This is made more enigmatic by the fact that Linoproductus is the sole taxon known from the layer, and is known from a variety of sizes. This immediately suggests an event concentration intrinsic to local shell producers, due to a certain type of ecology or lifestyle (Kidwell, 1991). It should be cautioned, however, that the above data and hypotheses are only preliminary conclusions, which must be reinforced by further collection and analysis. Much remains to be explained. For example, most of the Linoproductus shells in the layer are disarticulated, which suggests a period of exposure before burial. Although previous studies of Carboniferous brachiopod event concentrations have found disarticulated shell layers in compliance with an event concentration interpretation (Faulkner, 1988; Kidwell, 1991), the pattern seen at

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the Orlando Smith Road Outcrop must be studied in greater detail. Also, a more rigorous statistical analysis of the pedicle: brachial valve ratio is needed. If the Linoproductus layer is an event concentration, which preliminary analysis indicates it to be, then, according to Kidwell (1991) and Kidwell and Bosence (1991) it offers a unique opportunity to provide high-resolution ecological and evolutionary phenomena. In searching for causes, it is often difficult to determine exactly what led to an event concentration. Redfern (2001) described two bolide impacts that may have affected brachiopod populations during the Late Pennsylvanian. However, such a grandiose cause is likely not what caused the mass death layers seen at the Orlando Smith Road Outcrop. The most parsimonious conclusion is that the death of many of the Linoproductus specimens was caused either by rapidly-occurring high sediment levels, possibly caused by storm events, or by low currents, which would have led to lower dissolved food counts. Both cases can be explained by the dual action of a delta, which would have emptied sediment, and a large algal reef, whose currents may have interrupted or increased the flow of that sediment. Evidence for this hypothesis is varied, but supports the above conclusion. Linoproductus has been reconstructed as a small-to-medium sized brachiopod with a plano-convex to slightly concavo-convex shell. Such a shell, according to McNamara (1997), would have been beneficial in calm, shallow water environments. The reason for this hypothesis lies in the fact that the relatively smaller shell of Linoproductus and other brachiopods would have possessed a relatively smaller lophophore, the brachiopod feeding organ. During periods of stable currents and low sediment levels, the smaller lophophore would have sufficed. However, during periods of either low currents or high sediment levels the smaller lophophore would have inhibited the survival chances of Linoproductus, as it would not be able to filter food from the water as efficiently as a larger lophophore may have. How may this hypothesis be tested in relation to the Orlando Smith Road Outcrop? If the above conclusion is indeed correct, we should expect to see brachiopods with relatively larger lophophores colonizing the area directly above the mass-death bed of Linoproductus. This is exactly what is seen, as spiriferid brachiopods (both Neospirifer and Mucospirifer) are found in this layer. Neospirifer and Mucospirifer both possess biconvex shells, which allowed for a large lophophore. However, the preservation of fossils at the outcrop prevents the determination of an encrusting, hardground attached fauna, which would be stronger evidence for this hypothesis. During periods of normal currents and low sediment levels, this larger lophophore would have been biologically expensive to maintain, meaning that the spiriferid brachiopods should be expected to be much rarer than Linoproductus during these “normal” periods. This is precisely the case, as Mucospirifer and Neospirifer are both rare and both found almost exclusively above the mass death layer of

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Linoproductus. However, during times of higher sediment or low current levels, these larger lophophores were necessary for survival, as biologically expensive as they may be. The above evidence lends support to the hypothesis that the brachiopods preserved at the Orlando Smith Road Outcrop were populating in response to the changing sediment or low current levels caused by rapid influxes in sediment load carried by the delta system and the additional shoaling effect provided by the reef. Further evidence for this hypothesis is manifested by the brachiopod genus Composita, one of the best-known, best-studied, and most diverse Pennsylvanian brachiopods (Weller, 1914; Grinnell and Andrews, 1966). Girty (1915, quoted in Herbert et al., 1990) stated, “there is scarcely any Carboniferous genus which is so abundant in individuals, so free in variation, and at the same time so difficult to subdivide into species as the genus Composita.” Jakupcak (personal communication) traces this variation to the fact that Composita favored marginal marine environments and was forced to constantly change its morphology due to the changing nature of these environments. Such a hypothesis is supported by specimens gathered at the Orlando Smith Road Outcrop. Before examining how the morphology of Composita specimens found in the LaSalle Limestone is related to environmental pressures, it is necessary to briefly comment on the status of this widespread, but poorly understood, genus. Composita was first named in an 1838 paper by Shepard, and since this original publication, a variety of authors have assigned an excess of new species to the genus. A seminal 1964 paper by Grinnell and Andrews, which attempted to clear up the taxonomy of the genus, examined 42 named species, several of which they dismissed as doubtful. The authors then concluded, based partly on specimens from the LaSalle Limestone, that most named Composita species did not represent true neontological species, but rather were geometric gradations of a common form. They briefly discussed possibly sinking all species into Composita subtilita, but stopped short, saying that the numerous species have “usefulness as a typological species” (Grinnell and Andrews, 1966, p.227). Grinnell and Andrews (1966) noted the presence of the species C. subtilita and C. argentea in the LaSalle Limestone, but because of the aforementioned confusion, this paper will only examine Composita as a genus. Revising this genus is beyond the scope of this paper, and it is hoped that future researchers will take up the issue, perhaps utilizing cladistic methods. Thirty specimens of Composita have been collected from the Orlando Smith Road Outcrop, all of which show remarkable variation in morphology (Figure 6). Unlike many other Pennsylvanian sites in Illinois, Ohio, and Texas, however, the Orlando Smith Road Outcrop tends to preserve relatively small specimens of Composita (Schwimmer and Sandy, 1997; Herbert et al., 1990). The specimens collected, based on growth line data, also appear to be adults, so ontogeny does not appear to be a factor. Based on evidence presented by

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McNamara (1997), this small size may be due to the fact that Composita was forced to rapidly change by its unstable environment. In describing small size seen in other, similar brachiopods, McNamara discussed a major evolutionary mechanism: heterochrony, the relationship between organisms’ growth and evolutionary history. First introduced by biologist Ernst Haeckel, heterochrony measures how an organism can adjust its rates of growth due to both intrinsic and extrinsic (such as environmental) factors. The result of heterochrony often manifests itself in either peramorphic or paedomorphic organisms (animals that develop beyond their ancestors or animals that retain juvenile characteristics and develop less than their ancestors). Heterochrony is covered in detail in works by Gould (1977) and McNamara (1997). In the case of the Orlando Smith Road Outcrop, the principle of heterochrony may relate directly to the sizes of Composita. Often, organisms can adjust their rates of growth to better adapt themselves to environmental pressures (McNamara, 1997; Gould, 1977). This adjustment often comes in the form of progenesis, when organisms attain sexual maturity at a much earlier age. Progenesis can be beneficial, as it allows organisms more time to reproduce, and hence a better opportunity to pass on their genes. However, along with an earlier attainment of sexual maturity comes a smaller animal with retained juvenile characteristics. Smaller Composita specimens are seen at the Orlando Smith Road Outcrop. Is the size of these specimens due to progenesis? Such a hypothesis can often be difficult to prove. However, the number of growth lines on each Composita found at the Orlando Smith Road Outcrop shows that nearly every specimen collected is an adult, meaning that the smaller size is not simply due to the fact that the organisms are juveniles. The growth of brachiopods, and more specifically the nature and identification of true growth lines, has received much attention in recent years. Generally speaking, brachiopods possess a shell composed of three layers: the periostracum, primary layer, and secondary layer (Clarkson, 1998; Williams, 1968; Rudwick, 1959). The mantle, which secretes the shell, is infolded into a groove under the shell edge, where cells that eventually compose all three layers are secreted (Clarkson, 1998). As a new cell is formed, it moves towards the end of the shell in a “conveyer-belt” fashion, producing the layers and eventually growing calcite rhombs that give the shell its strength (Williams, 1968). Shell growth is rapid in the living brachiopod Terebratulina, which resembles Composita in form and is likely closely related (Curry, 1982; Kaesler, 1997). Growth lines, often neglected by authors as minor ornamentation unrelated to growth or unimportant in understanding ontogeny (Vogel, 1959; Surlyk, 1972), have been restudied, based in part on the new understanding of brachiopod growth discussed above (Hiller, 1988; Kaesler, 1997). Hiller (1988) found three types of growth lines: very fine diurnal lines

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formed by calcite increments at the shell margin, seasonal lines formed by abrupt regression of the mantle edge and marked by concentric steps on the shell surface, and disturbance lines irregularly formed by abrupt regression of the mantle edge due to sudden environmental factors. As the last two categories of growth lines are both marked by abrupt mantle regression, they are often very difficult to tell apart. Detailed microscopic examination can help differentiate them, but a general rule of thumb is that seasonal lines are somewhat regular in succession, while disturbance lines are irregularly placed on the shell (Hiller, 1988). Additionally, Rudwick (1962) has found that the more prominent, seasonal growth lines in some living brachiopods are darker and regularly spaced. The Composita specimens from the Orlando Smith Road Outcrop, and other specimens found in nearby LaSalle Limestone outcrops, show prominent growth lines despite their small sizes. This is significant, because as noted in living Terebratulina, juvenile growth is very rapid, and adult size is reached quickly (Curry, 1982). Therefore, it is unlikely that such small shells are juveniles, because larger specimens of the same genus (from sites in Texas and Ohio, and rare larger specimens from the LaSalle Limestone) show the same general number of prominent growth lines. These growth lines are not the diurnal lines of Hiller (1988), because these lines are difficult to demarcate on fossils and near impossible to see with the naked eye (Kaesler, 1997). They are also not likely disturbance lines, because they are regularly spaced, not irregularly spaced like known disturbance lines on fossil and living brachiopods (Rudwick, 1962; Curry, 1982). Their regular spacing leaves an identification of seasonal growth lines as the most parsimonious conclusion. Curry (1982) found that living Terebratulina deposit two seasonal growth lines per year, corresponding to two rapid spurts of growth and two periods of near dormancy, marked by a great slowing of growth in the winter. This cycle is well-timed by water temperature changes (Curry, 1982). It is possible that similar growth strategies were employed by Composita, but this is hard to support using the fossil record. The small shell sizes of the adult Composita found at the Orlando Smith Road Outcrop immediately suggest padeomorphosis as a mechanism. While, like specific growth strategies, this is hard to conclusively prove using the fossil record, previous work on fossil and living brachiopods lends support to this hypothesis. Williams and Wright (1961) hypothesized that terebratuloids evolved padeomorphically from spiferoids. They supported this assertion by noting the potential for sexual maturation at very early stages in living terebratuloid brachiopods, which several studies show are closely related and perhaps a sister group to athyridids (including Composita). Specifically, they reported that living Terebratulina septentrionalis can become mature at 1/4 of normal adult size (Williams and Wright, 1961). Additionally, Rudwick (1960) noted paedomorphosis in brachiopod lophophore evolution, and McNamara (1997) found that over 60 million years of evolution, the brachiopods Tegulorhynchia and Notosaria have

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become more paedomorphic over time. These studies show that paedomorphosis has been a major factor in brachiopod evolution, including in groups close to Composita, and lends support to this form of heterochrony as being the driving factors of the small size of this genus seen in the LaSalle Limestone. If indeed the smaller size of these specimens is related to paedomorphosis, and specifically progenesis, the question remains concerning what pressures were causing this evolution of smaller sizes to occur. According to McNamara (1997), there are two basic common pressures that have, in the past, caused fossil organisms to attain maturity at an earlier age: predation and changing environments. No specimens of Composita, or any other brachiopod preserved at the Orlando Smith Road Outcrop, show evidence of predation. In addition, Peck (1993) has shown that up to 97.5% of dry mass in living articulate brachiopods is inorganic, and constitutes little value to predators. While this absence of evidence and information from modern species does not completely rule out predation, it seems unlikely that a large scale pressure caused by predation, if even environmentally likely, would show no outward signs. Therefore, a likely and testable explanation for such progenesis is environmental pressure. The aforementioned distribution of the taxa Linoproductus, Neospirifer, and Mucospirifer seem to manifest an environment subject either to infrequent and isolated high sediment rates or low currents. Could such events have also promoted the earlier onset of maturity and hence the evolution of smaller shells in Composita? The likely answer is twofold: the high sediment/low current rates were causing Composita to develop quicker, as was the rapidly shifting environment due to deltaic progradation. Both factors made it necessary for Composita to attain maturity earlier in order to have a better chance of propagating its genes. Evidence for this assumption is found in the previous study of Hickey and Younker (1981). This study examined the LaSalle Limestone and its fossils as a community, and examined both environmental changes and r and K-strategists. The authors found that the environment represented by the LaSalle Limestone was frequently under stress caused by the transgression of the continental sea, and this resulted in the evolution of its fauna. A detailed stratigraphic study found four basic environmental stages, with the unstable stages marked by a low-diversity fauna composed primarily of r-strategists and attributed to “catastrophic or environmental changes” (Hickey and Younker, 1981 p.2). Composita was included in this study, but it is apparent that the authors were unaware of the vast abundance of this genus in some layers of the LaSalle Limestone. Therefore, their model might be somewhat simplistic, but the pattern of correlating times of environmental stress with low-diversity r-strategists holds. The Composita specimens seen at the Orlando Smith Road Outcrop, and at additional sites, manifest many characteristics of r-strategists as outlined by Hickey and Younker (1981) and Pianka (1970), including highly variable population densities, high productiv-

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ity, and, based on the data presented in this paper, rapid development and early sexual maturity. Furthermore, Composita can be identified as an opportunistic, extreme r-strategist, based on criteria set forth by Hickey and Younker (1981) and Levinton (1970), including unusual abundance in atypical facies and overwhelming numerical dominance of an assemblage. As a result, Composita should be added to the list of rstrategists known from the LaSalle Limestone. Additional Composita specimens collected by the author at the Lone Star Cement Quarry in Oglesby, Illinois, also seem to manifest padeomorphic characteristics (Figure 6). These specimens are even smaller in size than those found at the Orlando Smith Road Outcrop, with none of over 75 collected specimens showing sizes larger than two centimeters by two centimeters. Also, like those known from Orlando Smith Road, these specimens appear to be adults based on growth line data presented above. The Lone Star Quarry would have been positioned nearly directly on the reef during much of the Pennsylvanian, meaning that the genus Composita, which is the most common brachiopod found in the Quarry, was perhaps well adapted to the reef and its periodic high sediment/low food cycles. Additional Composita specimens collected at several different LaSalle Limestone sites in 2002, along with further study, currently in progress by the author, will hopefully clarify this possibility. Using the aforementioned specimens as a guide, it appears as if rapid sediment or low food levels were not only present, but also intense drivers of evolution in the brachiopods seen at the Orlando Smith Road Outcrop. If high sediment loads were the culprit, what may have caused these infrequent periods? The fact that a delta may have been relatively near the reef, and hence the Orlando Smith Road Outcrop, provides a plausible mechanism for the transfer of sediment. Because the delta system emptied water derived from as far north as present-day Michigan, any number of localized storm events along the lengths of the rivers emptying into the delta may have been enough to increase the sediment load. However, a more plausible mechanism was suggested by Miller and West (1993). In a paper describing PennsylvanianPermian cyclothems in Kansas, they suggested that monsoon events might have caused similar high sediment deposits. In fact, Horne (1978) and Fraser (1991) noted that by the Late Pennsylvanian, the Illinois Basin had been largely filled by sediment, resulting in the shallowing of the continental sea. The extreme shallowing of the sea restricted strong currents to those generated by major storm events, possibly including monsoons (Fraser, 1991). It is possible that repeated or major monsoon events, or any major or repeated storm events, may have been enough to regularly cause strong currents, which might have increased the sediment levels at the Orlando Smith Road Outcrop and forced the inhabiting brachiopods to evolve over time. Or, perhaps, the same storm events, or possibly a reef-caused shoaling effect unrelated to storms, may have also led to low or interrupted currents, which would have prevented enough nutrient cycling and may have resulted in an environmental pressure over geologic time. In both events, which

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are not necessarily mutually exclusive, storms or monsoons would have played a major role in the ecology, lifestyle, and evolutionary history of the brachiopods of the region. Along with periods of high sediment or low currents, the Orlando Smith Road Outcrop also shows evidence of another environmental factor: deltaic progradation, which led to the gradual emergence of land and regression of the continental sea. Three fossils found at the outcrop lend evidence to this hypothesis. One of the fossils, an isolated bone found preserved in the first limestone horizion likely belongs to a tetrapod (either an early “amphibian” or amniote). The size of the bone suggests that it derived from the diaphysis of a long bone (possibly the femur or humerus) belonging to a tetrapod one meter or more in length. Such bones are rare in the LaSalle Limestone, but a similar specimen found in the Lone Star Quarry, near the Orlando Smith Road Outcrop, was reconstructed by John Bolt (personal communication) as belonging to either a small reptile or “labyrinthodont” amphibian. Both animals would have inhabited the swamps that occupied the margins of the continental sea. The fact that the bone is dark brown and smooth suggests that it was buried relatively quickly (Martill and Naish, 2001), meaning that the tetrapod likely lived very close to the spot at which it was buried. This evidence, along with stratigraphic evidence, supports the fact that the continental sea was gradually regressing southwestward due to deltaic progradation. The LaSalle Limestone is not present in the Chicago and Morris quadrangles (Willman, 1971; Culver, 1922), meaning that at the time the layer was deposited the sea may have already advanced past those areas, which were perhaps covered completely by land. Livingston County, located south of the Orlando Smith Road Outcrop site, contains a greater number of LaSalle Limestone outcrops (Strimple and Moore, 1971) than LaSalle County. This may mean that at the time the LaSalle Limestone was deposited, part of LaSalle County was home to the boundary between water and land, while Livingston County was still mostly open water. While these patterns may be a result of post-Pennsylvanian erosion, the ordered distribution of outcroppings lends evidence to the above hypothesis. However, once again, only further study will help clarify this point. If the above hypotheses are correct, the stratigraphic layers and fossil fauna and flora of the Orlando Smith Road Outcrop show two general environmental trends: rapid sedimentation and/or low current levels caused by high deltaic sediment load, the shoaling effects of an algal reef, and storms; and gradual regression of the sea and emergence of the land caused by deltaic progradation. In both instances the fossil fauna of the outcrop was forced to evolve to cope with the changing environment, which has produced the rich abundance and diversity of specimens found at the outcrop and other LaSalle Limestone sites. Further research at other Pennsylvanian fossil sites in Illinois, including a more rigorous study of Composita currently underway by the author, should only add to our understanding of this dynamic time.

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Acknowledgements I thank R. Jacobson and an anonymous reviewer for critical reviews of this paper. J. Jakupcak, M. Phillips, and W. Sheridan gave comments on an earlier version of this paper. Much of the work presented herein stemmed from an Ottawa Township High School independent study program instructed by J. Jakupcak, who was instrumental in helping with the fieldwork necessary for this study and the completion of the paper. Other acknowledgements are due to T. Daeschler for help with the figures; M. Pillion, B. Leonard, B. Olsen, J. Personette, B. Sriraman, C. Myers, and D. Husted (Ottawa Township High School); S. Kidwell (University of Chicago); B. Popp, L. Martin, T. Cesario, W. Frankie, and members of the online Dinosaur Mailing List. I would also like to thank the State of Illinois and LaSalle County for access to the Orlando Smith Road outcrop, and Ottawa Township High School for the use of facilities and funds. Lastly, I would like to thank my family for their continued support, including my brothers Michael and Christopher, who both carried out fieldwork crucial to this study.

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APPENDIX TABLE 1-FAUNAL/FLORAL LIST OF THE OUTCROP Genus ................................................Higher Taxon ..............................Location ....................................Abundance Linoproductus ....................................Brachiopoda................................Second Horizon ........................100+ specimens Juresania............................................Brachiopoda................................First, Second Horizon ..............50+ specimens Composita ..........................................Brachiopoda................................Second Horizon ........................30 specimens Mucospirifer ......................................Brachiopoda................................Second Horizon ........................2 specimens Neospirifer ........................................Brachiopoda................................Second Horizon ........................12 specimens Echinaria ..........................................Brachiopoda................................Second Horizon ........................4 specimens Antiquatonia ......................................Brachiopoda................................Second Horizon ........................10 specimens Articulata indet. ................................Brachiopoda................................Second Horizon? ......................2 specimens Crinoidea indet. ................................Echinodermata ............................First, Second Horizon ..............50+ specimens Lophophyllidium ................................Cnidaria ......................................First Horizon ............................3 specimens Bryozoa indet.....................................Bryozoa ......................................?? Float? ..................................1 specimen Plantae indet. ....................................Indet. ..........................................?? Float? ..................................2 specimens Vertebrata indet. ................................Chordata ....................................Second Horizon ........................1 specimen Chondrichthyes indet. ........................Chordata ....................................Second Horizon ........................2 specimens

APPENDIX TABLE 2-FAUNAL/FLORAL LIST OF THE LASALLE LIMESTONE (Compiled from field work and literature sources; including all known named taxa without comments on their validity) Genus ..................................Higher Taxon ..........................Source Linoproductus ......................Brachiopoda ............................Field Observation; Brusatte, 2001; Brusatte, 2002 Composita ............................Brachiopoda ............................Field Observation; Hickey and Younker, 1981; Grinnell ..............................................................................................and Andrews, 1964; Brusatte, 2001; Brusatte, 2002 Juresania..............................Brachiopoda ............................Field Observation; Brusatte, 2001 Mucospirifer ........................Brachiopoda ............................Field Observation; Brusatte, 2001 Neospirifer ..........................Brachiopoda ............................Field Observation; Hickey and Younker, 1981; Brusatte, 2001 Echinaria ............................Brachiopoda ............................Field Observation; Brusatte, 2001 Antiquatonia ........................Brachiopoda ............................Field Observation; Brusatte, 2001 Derbyia ................................Brachiopoda ............................Field Observation; Hickey and Younker, 1981; Brusatte, 2001 Crurithyris ..........................Brachiopoda ............................Hickey and Younker, 1981 Orbiculoidea........................Brachiopoda ............................Hickey and Younker, 1981 Leiorhynchus ......................Brachiopoda ............................Hickey and Younker, 1981 Rhipidomella ......................Brachiopoda ............................Hickey and Younker, 1981 Lingula ................................Brachiopoda ............................Hickey and Younker, 1981 Chonetinella ........................Brachiopoda ............................Hickey and Younker, 1981 Phricodothyris ....................Brachiopoda ............................Hickey and Younker, 1981 Punctospirifer......................Brachiopoda ............................Hickey and Younker, 1981 Hustedia ..............................Brachiopoda ............................Hickey and Younker, 1981 Hystriculina ........................Brachiopoda ............................Hickey and Younker, 1981 Beecheria ............................Brachiopoda ............................Hickey and Younker, 1981 Tegulifernia..........................Brachiopoda ............................Hickey and Younker, 1981 Meekella ..............................Brachiopoda ............................Hickey and Younker, 1981 Delocrinus ..........................Crinoidea ................................Hickey and Younker, 1981 Sciadiocrinus ......................Crinoidea ................................Strimple and Moore, 1971; Lewis and Strimple, 1990 Elibatocrinus ......................Crinoidea ................................Strimple and Moore, 1971 Erisocrinus ..........................Crinoidea ................................Strimple and Moore, 1971; Ausich 1999 Apographiocrinus ................Crinoidea ................................Strimple and Moore, 1971; Ausich, 1999 Contocrinus ........................Crinoidea ................................Strimple and Moore, 1971 Endelocrinus........................Crinoidea ................................Strimple and Moore, 1971; Ausich, 1999 Exoriocrinus ........................Crinoidea ................................Strimple and Moore, 1971

May 2004

LATE PENNSYLVANIAN BRACHIOPODS — BRUSATTE

APPENDIX TABLE 2 (continued) Plummericrinus ..................Crinoidea ................................Strimple and Moore, 1971; Microcaracrinus ..................Crinoidea ................................Strimple and Moore, 1971; Ausich, 1999 Galateacrinus ......................Crinoidea ................................Strimple and Moore, 1971 Polygonocrinus ....................Crinoidea ................................Strimple and Moore, 1971 Laudoncrinus ......................Crinoidea ................................Strimple and Moore, 1971 Stenopecrinus ......................Crinoidea ................................Strimple and Moore, 1971 Anobasicrinus......................Crinoidea ................................Strimple and Moore, 1971 Haeretocrinus ......................Crinoidea ................................Strimple and Moore, 1971; Ausich, 1999 Terpnocrinus........................Crinoidea ................................Strimple and Moore, 1971 Ulocrinus ............................Crinoidea ................................Strimple and Moore, 1971 Probletocrinus ....................Crinoidea ................................Strimple and Moore, 1971 Parulocrinus ........................Crinoidea ................................Strimple and Moore, 1971; Ausich, 1999 Allosocrinus ........................Crinoidea ................................Strimple and Moore, 1971 Moundocrinus......................Crinoidea ................................Strimple and Moore, 1971 Polusocrinus ........................Crinoidea ................................Strimple and Moore, 1971 Chilidonocrinus ..................Crinoidea ................................Strimple and Moore, 1971 Halogetocrinus ....................Crinoidea ................................Strimple and Moore, 1971 Stellarocrinus ......................Crinoidea ................................Strimple and Moore, 1971; Strimple, 1973 Celonocrinus ......................Crinoidea ................................Strimple and Moore, 1971 Brabeocrinus ......................Crinoidea ................................Strimple and Moore, 1971; Strimple, 1973; Ausich, 1999 Exocrinus ............................Crinoidea ................................Strimple and Moore, 1971; Ausich, 1999 Clathrocrinus ......................Crinoidea ................................Strimple and Moore, 1971; Strimple, 1973; Ausich, 1999 Isoallagecrinus ....................Crinoidea ................................Strimple and Moore, 1971 Dichocrinus ........................Crinoidea ................................Strimple and Moore, 1971 Paramphicrinus ..................Crinoidea ................................Strimple and Moore, 1971 Euonychocrinus ..................Crinoidea ................................Strimple and Moore, 1971 Kallimorphocrinus ..............Crinoidea ................................Ausich, 1999 Dunbarella ..........................Pelecypoda ..............................Hickey and Younker, 1981 Streblopteria ........................Pelecypoda ..............................Hickey and Younker, 1981 Edmondia ............................Pelecypoda ..............................Hickey and Younker, 1981 Lima ....................................Pelecypoda ..............................Hickey and Younker, 1981 Orthomyalina ......................Pelecypoda ..............................Hickey and Younker, 1981 Astartella ............................Pelecypoda ..............................Hickey and Younker, 1981 Annulichoncha ....................Pelecypoda ..............................Hickey and Younker, 1981 Acanthopecten ....................Pelecypoda ..............................Hickey and Younker, 1981 Straparollus ........................Gastropoda ..............................Hickey and Younker, 1981 Platyceras ............................Gastropoda ..............................Hickey and Younker, 1981 Ditomopyge ........................Trilobita ..................................Hickey and Younker, 1981 Lophophyllidium..................Cnidaria ..................................Field Observation; Hickey and Younker, 1981; Brusatte, 2001 Calliasterella ......................Asteroidea................................Kesling and Strimple, 1966 Glaphurochiton....................Mollusca ..................................Hoare and Mapes, 1986 Archeolithophyllum ............Algae ......................................Fraser, 1991

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APPENDIX TABLE 3-INDETERMINATE OR PROBABLE FAUNA/FLORAL LIST OF THE LASALLE LIMESTONE (includes all known named taxa in the literature, without comments on their validity) Genus ....................................Higher Taxon ..........................Source Cuneiphycus ..........................Algae ......................................Fraser, 1991 Aviculopecten ........................Pelecypoda ..............................Meek and Worthen, 1866 Edmondia ..............................Pelecypoda ..............................Meek and Worthen, 1870 Myalina ................................Pelecypoda ..............................Meek and Worthen, 1866 Pleurotomaria ......................Gastropoda ..............................Meek and Worthen, 1866 Naticopsis..............................Gastropoda ..............................Meek and Worthen, 1870 Nautilus ................................Cephalopoda............................Meek and Worthen, 1870 Scaphiocrinus........................Crinoidea ................................Meek and Worthen, 1870 Poteriocrinus ........................Crinoidea ................................Worthen and Meek, 1875 Productus ..............................Brachiopoda ............................Meek and Worthen, 1870 Hemipronites ........................Brachiopoda ............................Meek and Worthen, 1870 Orthis ....................................Brachiopoda ............................Meek and Worthen, 1870 Petalodus ..............................Chondrichthyes ......................Cesario, Personal Communication; Newberry and Worthen, ................................................................................................1866 Psephodus ............................Chondrichthyes ......................Branson, 1905; Stahl, 1999 Deltodus ................................Chondrichthyes ......................Newberry and Worthen, 1866; Stahl, 1999 Chomatodus ..........................Chondrichthyes ......................Newberry and Worthen, 1866 Vaticinodus ............................Chondrichthyes ......................St. John and Worthen, 1883 Acondylacanthus ..................Chondrichthyes ......................St. John and Worthen, 1883 Lophodus (=Agassizodus) ....Chondrichthyes ......................St. John and Worthen, 1875 Helodus ................................Chondrichthyes ......................Newberry and Worthen, 1866 Sandalodus ............................Chondrichthyes ......................Newberry and Worthen, 1866 Lophodus ..............................Chondrichthyes ......................Newberry and Worthen, 1870 Cymatodus ............................Chondrichthyes ......................Newberry and Worthen, 1870; Stahl, 1999 Crinoidea indet. ....................Crinoidea ................................Field Observation; Brusatte, 2001 Bryozoa indet. ......................Bryozoa ..................................Field Observation; Jacobson, Field Observation; Brusatte, 2001 Vertebrata indet. ....................Chordata ..................................Field Observation; Bolt, Jacobson, Phillips, and Cesario, ................................................................................................Personal Communications; Brusatte, 2001 Chondrichthyes indet. ..........Chondrichthyes ......................Field Observation; Frankie, Personal Communication Osteichthyes indet.................Osteichthyes ............................Field Observation Plantae indet. ........................Plantae ....................................Field Observation; Brusatte, 2001 Sponge Spicules ....................Porifera....................................Field Observation; Fraser, 1991 Articulata indet. ....................Brachiopoda ............................Field Observation Ostracoda indet. ....................Ostracoda ................................Fraser, 1991 Foraminifera indet.................Foraminifera............................Fraser, 1991