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Home , Athyris, Rhynchonella, Rhynchonellata, Rhynchonelliformea, Spirifer, Terebratellidae

EXPERIMENT 1

MORPHOLOGICAL CHARACTERS, SYSTEMATIC POSITION AND AGE OF FOSSIL GENERA PERTAINING TO

Outline of Experiment______1.1 Introduction 1.5 Precautions To Be Taken Before Studying Fossil Specimens Expected Learning Skills 1.6 Laboratory Exercises 1.2 Requirements 1.7 Results and Discussion 1.3 Brachiopods: Systematics, General Morphology and Age Range 1.8 References 1.4 Common Genera 1.9 Further Suggested Readings

1.1 INTRODUCTION

You have studied the general morphology, systematic position and geological history of brachiopods in Unit 13 of Block 4 of BGYCT-137. You have learnt that the brachiopods form a major fossil group of . Their fossils first appeared in rocks of early age and the distant descendants of these ancient forms are still living in the oceans and seas. Brachiopods are entirely marine animals; occur in all oceans at depths ranging from the intertidal to 5000 m and till date no has been found in the fresh water environment. All brachiopods are sessile (non-mobile), benthic and solitary marine animals having a shell made of two unequal valves and live on the sea floor usually in clusters. Many of them remain fixed to the sea floor while others just lie on the sea-bed. In this experiment, we intend to provide you with some practical experience in studying some common fossil genera of brachiopods. It is important to note that brachiopods have around 4500 known genera, out of which merely 100 genera are surviving in today’s ocean.

9 Stratigraphy and Palaeontology: Laboratory BGYCL………………………………………………………………………………………………….…...... ….…...... -138 The morphological study of various genera of brachiopods or any fossil group is important to accurately identify the genera and to differentiate one form from another. It also helps us to establish the evolutionary sequence of a group with respect to its geological age range, which in turn, provides data to know the diversity, palaeobiogeography, palaeoecology and geological significance of any group or its genera. Expected Learning Skills______After performing this experiment, you should be able to:  list the systematic positions of some common genera of brachiopods;  identify and describe their morphological characters;  prepare their line drawing with labeling of morphological features; and

 write their stratigraphic/geological age and palaeoecology 1.2 REQUIREMENTS

To perform this experiment successfully, following are the requirements:  Pen, pencil, eraser, sharpener, scale, stencil and hand lens  Practical note-book  Fossil specimens of brachiopods Instructions: You are required to study Unit 13 of BGYCT-137 course (Stratigraphy and Palaeontology) before performing this experiment. Bring this practical manual along with Block 4 of BGYCT-137 course while attending the Practical Counselling session. 1.3 BRACHIOPODS: SYSTEMATICS, GENERAL MORPHOLOGY AND AGE RANGE 1.3.1 Systematic Palaeontology/Taxonomic Hierarchy Kingdom Animalia Subkingdom Metazoa Phylum Brachiopoda Subphyla Linguliformea Craniiformea 1.3.2 General Morphology The shell of a brachiopod consists of two-valves, which are held together either by teeth and socket (e.g., rhynchonelliformeans or articulates) or by muscles (e.g., linguliformeans and craniiformeans or inarticluates). The two valves of brachiopods are morphologically quite different, each valve is bilaterally symmetrical and one valve is always larger than the other. The larger valve is commonly known as pedicle or ventral valve. It contains an opening known as pedicle opening or foramen at the beak. The smaller valve is known as brachial or dorsal valve (Fig. 1.1). Each valve has a 10 Morphological Characters, Systematic Position and Experiment……………………….…………………………………………………………………………….…...... …... 1 Age of Fossil Genera Pertaining to Brachiopods pointed end which is known as beak. It represents an initial point of growth of a valve. In brachiopod shells, the shell growth mostly occurs in the form of concentric lines, radial ribs or corrugations on the exterior surface of the valves. The arched part of the valve near the beak is called umbo. The beak is considered the posterior end of the valve whereas the rounded margin located opposite to the beak is the anterior end as shown in Fig. 1.1. Commissure is the line where the two valves meet (Fig. 1.1b). It may be straight or zig-zag.

(a) (b) Fig. 1.1: Shells of brachiopods showing external morphology: a) dorsal view; and b) side view.

Fig. 1.2: Dorsal view of a brachiopod shell showing internal morphology of the pedicle valve. (Source: simplified after Clarkson, 1979) The pedicle valve has a deep medial depressed area described as the sulcus that receives medial elevated portion termed as fold of the brachial valve. Teeth are knob-like projections that are present on the posterior end of the pedicle valve and fit into the small depressions known as sockets of the brachial valve. The contact point where teeth and sockets of the two valves rotate to open and close forms the hinge and the portion of the posterior end

11 Stratigraphy and Palaeontology: Laboratory BGYCL………………………………………………………………………………………………….…...... ….…...... -138 where both valves meet is known as hinge line (Fig. 1.2). A straight hinge line is described as strophic, while a curved one is named as astrophic. Brachiopod valves come in a variety of shapes like convex, concave or flat and some forms show interesting external ornamentation of costae and plicae. Costae are very fine radial ridges on the external surface of the valve originating from the beak and plicae are radial ridges present on external as well as internal surfaces of the valve. In a few forms, the valves are covered with spines. 1.3.3 Stratigraphic Range Brachiopods have a very long geological history. They first appeared near the beginning of the Cambrian period and some of the forms are still alive today on the floor of the modern oceans. 1.4 COMMON GENERA

1.4.1 Linoproductus Systematic Palaeontology Kingdom Animalia Phylum Brachiopoda Subphylum Rhynchonelliformea Class Order Productida Family Linoproductidae Linoproductus Morphological Description: It is a medium to large sized genus of brachiopods. It has concavo-convex valves. Shell is of medium to large size and its outline is elongated to subcircular. The ventral profile inflated posteriorly and brachial valve gently concave. The pedicle valve convex, brachial valve starts from flat, but becomes concave. The margins of the two valves are often turned ninety degrees from the hinge and become very elongated. Surface of both valves are marked with fine striations that are slightly wavy. Hinge commonly occurs in the widest part of shell and tends to be distorted at spine bases, which are widely scattered ventrally. The cardinal process is sessile and supported by lateral ridges. Adductor scars and brachial ridges are weakly marked. The genus is also known for having some of the largest shells. Spines are occasionally present. The genus Linoproductus is distinguished by its strongly convex pedicle valve and its slightly concave brachial valve (Fig. 1.3). Stratigraphic Range: to . Palaeoecology: The genus Linoproductus (known originally as Productus) was a marine that commonly lived as sessile, low-level epifaunal suspension feeder.

12 Morphological Characters, Systematic Position and Experiment……………………….…………………………………………………………………………….…...... …... 1 Age of Fossil Genera Pertaining to Brachiopods

(a) (b) Fig. 1.3: Linoproductus: a) Photograph; and b) Line drawing of the external views of the valves of Linoproductus showing the shape and growth lines. 1.4.2 Systematic Palaeontology Kingdom Animalia Subkingdom Metazoa Phylum Brachiopoda Subphylum Rhynchonelliformea Class Rhynchonellata Order Family Spiriferidae Genus Spirifer Morphological Description: This genus is triangular in shape and characterised by having a long and straight (strophic) hinge line. It has a biconvex shell, prominent umbo and well-developed interarea of the pedicle valve, large delthyrium and triangular brachial valve. The external surface of the shell is marked by strong radial ribs, sulcus and plica (Fig. 1.4).

(a) (b) (c)

Fig. 1.4: Spirifer: a) Line drawing of the side view; b) Line drawing of the dorsal view of Spirifer (Source: modified after Nield, 1987); and c) Photograph showing external view. (Courtesy: Mr. A. A. Quarshi, Srinagar) Stratigraphic Range: to . Palaeoecology: The genus Spirifer was a marine animal, lived as sessile and epifaunal suspension feeder. 13 Stratigraphy and Palaeontology: Laboratory BGYCL………………………………………………………………………………………………….…...... ….…...... -138 1.4.3 Systematic Palaeontology Kingdom Animalia Subkingdom Metazoa Phylum Brachiopoda Subphylum Rhynchonelliformea Class Rhynchonellata Order Family Athyrididae Genus Athyris Morphological Description: It usually has a biconvex transverse shell. The hinge line is curved. The both valves of the shell are almost equally convex. The umbo ventrally, round foramen, small deltidial plates and teeth are prominent on the dental plates. Long and thin dental plates are present on the pedicle valve whereas the brachial valve contains cardinal plates. The concentric growth lines occur on the external surface of the shell (Fig. 1.5).

(a) (b) (c) Fig. 1.5: Line drawing of Athyris: a) External; b) Side; and c) Dorsal views. Stratigraphic Range: to Triassic. Palaeoecology: The genus Athyris was a marine animal that commonly lived as sessile, low-level epifaunal suspension feeder. 1.4.4 Systematic Palaeontology Kingdom Animalia Subkingdom Metazoa Phylum Brachiopoda Subphylum Rhynchonelliformea Class Rhynchonellata Order Family Rhynchonellidae Genus Rhynchonella Morphological Description: This genus includes small to medium sized forms of brachiopods. It has a triangular-shaped shell with curved hinge line. It

14 Morphological Characters, Systematic Position and Experiment……………………….…………………………………………………………………………….…...... …... 1 Age of Fossil Genera Pertaining to Brachiopods has large teeth and short dental plates. Pedicle valve is slightly curved and contains small umbo and deep sulcus. Brachial valve yields a small cardinal process. Brachidium composed of small curved crura (Fig. 1.6).

(a) (b) (c) Fig. 1.5: Line drawing of Rhynchonella: a) External; b) Anterior; and c) Side views. (Source: modified after Nield, 1987)

Stratigraphic Range: Jurassic. Palaeoecology: The genus Rhynchonella was a marine animal, lived as sessile, epifaunal suspension feeder. 1.4.5 Systematic Palaeontology Kingdom Animalia Subkingdom Metazoa Phylum Brachiopoda Subphylum Rhynchonelliformea Class Rhynchonellata Order Family Genus Terebratula Morphological Description: The genus has a range of shell shapes, from biconvex, elongate to oval or round (Fig. 1.6). The outer surface of the shell contains poorly developed concentric growth lines. Anterior margin contains two folds with corresponding ridges and sulci. Pedicle foramen is round. It has a curved hinge line and dental plates are absent. Brachial valve has strong adductor impressions and an indentation bounded by two folds situated on the frontal margin of the valve. The pedicle opening is present.

(a) (b) (c) Fig. 1.6: Line drawing of Terebratula: a) Side view; b) Dorsal view; and c) Anterior view. (Source: redrawn after Nield, 1987)

15 Stratigraphy and Palaeontology: Laboratory BGYCL………………………………………………………………………………………………….…...... ….…...... -138 Stratigraphic Age: Triassic to . Palaeoecology: The genus Terebratula was a marine animal, lived as a stationary, epifaunal suspension feeder. 1.4.6 Terebratella Systematic Palaeontology Kingdom Animalia Phylum Brachiopoda Subphylum Rhynchonelliformea Class Rhynchonellata Order Terebratellida Family Genus Terebratella Morphological Description: The shell is oval in shape. The pedicle valve is strongly convex and brachial is less convex to more or less flattened (Fig. 1.7). Hinge line is straight to slightly curved. Umbo contains a large foramen. It has a prominent beak. The external surface of the shell is marked by the radiating ribs. Deltidial plates are long and narrow. Shell contains small and dense punctae.

Fig.1.7: Photograph of Terebratella. (Courtesy: Prof. R. Nagendra, Anna University, Chennai) Stratigraphic Range: Triassic to Recent. Palaeoecology: The genus Terebratella is a marine animal, living as a stationary epifaunal suspension feeder. 1.4.7 Lingulella Systematic Palaeontology Kingdom Animalia Subkingdom Metazoa Phylum Brachiopoda Subphylum Linguliformea Class Lingulata Order Lingulida Family Lingulidae Genus Lingulella 16 Morphological Characters, Systematic Position and Experiment……………………….…………………………………………………………………………….…...... …... 1 Age of Fossil Genera Pertaining to Brachiopods Morphological Description: The shell is elongate, oval or subtriangular (Fig. 1.8). The anterolateral margin is slightly rounded, length of the shell greater than width. It has triangular pedicle groove and visceral areas of both valves weakly impressed. The dorsal visceral area has low median ridge, extending anterior to mid valve. Anterior lateral and central muscle scars closely spaced. Beak is pointed and surface of the valve is gently convex marked by strong concentric ribs. In some specimens faint radial striae are observed. The genus is weakly bi-convex, tapering towards the umbones. The pedicle valve has a distinct hinge line and is larger than that of the brachial valve. Shell contains a distinct and subtriangular pedicle groove. Its external surface is ornamented with fine and dense concentric growth lines.

(a) (b) Fig. 1.8: Genus Lingulella: a) Photograph; and b) Line drawing of the external view showing the shape of the shell and growth lines. Stratigraphic Range: Cambrian to . Palaeoecology: The genus Lingulella was a marine animal and lived as mobile infaunal suspension feeder. 1.4.8 Lingula Systematic Palaeontology Kingdom Animalia Subkingdom Metazoa Phylum Brachiopoda Subphylum Linguliformea Class Lingulata Order Lingulida Family Lingulidae Genus Lingula Morphological Description: Shell is elongate, oval to subrectangular in outline. Its lateral margins are sub-parallel and anterior margin is broadly rounded to straight. Pedicle valve has a wide triangular pedicle groove and lateral vestigial prop-areas. The dorsal interior has a visceral area extending somewhat anterior to the mid valve. The dorsal central and anterior lateral muscle scars are closely spaced and bisected by weak median septum. 17 Stratigraphy and Palaeontology: Laboratory BGYCL………………………………………………………………………………………………….…...... ….…...... -138 The posterior margin is rounded, with a median beak. Vascular media is absent. The dorsal visceral area is extending somewhat anterior to the mid valve shell with concentric growth lines, showing a low median ridge in the brachial valve. Lingulid brachiopod is recognised by its growth lines on its shell and it has symmetrical valves. The shell is small in size and is distinguishingly biconvex (Fig. 1.9).

(a) (b) Fig. 1.9: Genus Lingula: a) Photograph; and b) Line drawing of the external view showing the shape of the shell with concentric growth lines. Stratigraphic Range: Orodovician to Recent. Paleoecology: It is a marine infaunal and suspension feeder brachiopod. It lives commonly in compact and stable sediments under the influence of moderate, near-bottom currents. 1.4.9 Dalmanella Systematic Palaeontology Kingdom Animalia Phylum Brachiopoda Class Rhynchonellata Order Family Dalmanellidae Genus Dalmanella Morphological Description: Shell is subcircular to subquadrate in outline, with variably biconvex valves with a shallow median longitudinal depression (Fig. 1.10). The surface of the valves is covered by strong, radial, sub-angular and sub-equal composite ribs. The total number of ribs is varying from thirty eight to forty including primary ribs. The primary ribs are further divided into two to four secondary ribs. Lateral ribs curve back distinctly to the cardinal angles. Cardinal angles are rounded. The interspaces between the ribs are concave, usually occupied by the finer secondary ribs. The posterior margin of the shell is slightly curved. The beak is minute, pointed, curved and rising slightly beyond the hinge line. The hinge line is straight, but less than the width of the shell. Hinge area is slightly triangular. The width of the shell is greater than the length, maximum width of the shell above the middle line of the shell. The grooves between the 18 Morphological Characters, Systematic Position and Experiment……………………….…………………………………………………………………………….…...... …... 1 Age of Fossil Genera Pertaining to Brachiopods costal ribs are formed by the subdivisions of the primary ribs. The primary ribs usually are stronger, deeper than those between the branches. The brachial valve is sub-orbicular to convex with weak median depression.

(a) (b) (c) Fig. 1.10: Genus Dalmanella: a) Photograph; b) Line drawing of the external view; and c) Line drawing of the dorsal view of the valve showing the shape and growth lines. Stratigraphic Range: Ordovician to Silurian. Palaeoecology: The genus was a marine stationary low-level epifaunal suspension feeder that usually attached to substrata. 1.4.10 Syringothyris Systematic Palaeontology Kingdom Animalia Phylum Brachiopoda Subphylum Rhynchonelliformea Class Rhynchonellata Order Spiriferinida Family Syringothyrididae Genus Syringothyris Morphological Description: The shell of genus Syringothyris is strongly transverse. The lateral profile is weakly convex and sulcus rapidly extends anteriorly with borders subtend 30 to 35 degree angle. The sulcus has a flat bottom and is dorsally elongated into a very short tongue. Ventral interarea is distinctly flat or slightly concave apically with large open delthyrium. The delthyrium is marked by a narrow deep groove known as syrinx that gives name to this genus. The dorsal valve is transversely subpentagonal in outline and gently convex in mid sector having flattened flanks in transverse profile and maximum convexity umbonally in lateral profile. Interarea is low and weakly concave. Ornamentation is weak and costae are flat, increasing in size toward front margin and laterally rapidly diminishing in size. The growth lines are finely concentric and are more prominent. The surface of interarea bears distinct growth lines. Stratigraphic Range: Carboniferous. Palaeoecology: The genus Syringothyris was a marine animal, lived as an immobile low-level epifaunal suspension feeder. 19 Stratigraphy and Palaeontology: Laboratory BGYCL………………………………………………………………………………………………….…...... ….…...... -138

(a) (b) Fig. 1.11: Genus Syringothyris: a) Photograph; and b) Line drawing of the external view. 1.5 PRECAUTIONS TO BE TAKEN BEFORE STUDING FOSSIL SPECIMENS

It should be noted that fossil specimens are non-renewable valuable scientific resource. Therefore, you are advised to handle them very carefully during their study. It is to be kept in mind that no damage will occur, in any case, to the fossil specimens provided to you for study at the laboratory. No marking either with pen or pencil or any other means will be allowed in any specimens. Before leaving the laboratory, all specimens will be handed over to the counselor or laboratory incharge. 1.6 LABORATORY EXERCISES

The fossil specimens of brachiopod, belonging to the genera described in Section 1.4, will be provided to you for study at your study centre. You will have to perform the following activities: I. Draw the sketch of the specimen on your practical note-book. II. Label its various morphological features (refer Figs. 1.1 and 1.2 for labeling various morphological features). III. Write its systematic position or palaeontology. IV. Briefly, describe the morphology of the shell. V. Write the stratigraphic range and palaeoecology of the genus under study. Format for Studying Fossil Specimens Fossil No.: …………….. Date: ……………… Systematic Palaeontology Kingdom Subkingdom Phylum Subphylum Class Order Family Genus 20 Morphological Characters, Systematic Position and Experiment……………………….…………………………………………………………………………….…...... …... 1 Age of Fossil Genera Pertaining to Brachiopods Systematic Palaeontology: It includes taxonomic hierarchy of the genus. Morphological Description: It includes sketches of the specimen as well as labeling and description of its morphological features. Stratigraphic Age: It includes the age range of the genus. 1.7 RESULTS AND DISCUSSION

Based on the morphological study, the given fossil specimens have been identified as Linoproductus, Spirifer, Athyris, Rhynchonella, Terebratula, Terebratella, Lingulella, Lingula, Dalmanella and Syringothyris. 1.8 REFERENCES

 Clarkson, E.N.K. (1979) Invertebrate Palaeontology and Evolution, Blackwell Science Ltd., USA.  Nield, E.W. and Tucker, V.C.T. (1985) Palaeontology – An Introduction, Pergamon Press, Oxford. 1.9 FURTHER SUGGESTED READINGS

 Shah, S.K. (2013) Elements of Palaeontology, Geological Society of India, Bangalore.  Woods, H. (2004) Palaeontology Invertebrate, CBS Publishers and Distributors Pvt. Ltd., New Delhi.  https://paleobiodb.org/classic

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