POSTINGAN SELANJUTNYA: MENERAPKAN DIAGRAM TERNER AN-CPX-OPX UNTUK IDENTIFIKASI BATUAN BASA
EVOLUTION
Before diving into the explanation of evolution, it’s good to first get to know taxonomy.
A. TAXONOMY
a. Definition
Classification by giving names. The classification system starts from grouping general characteristics to specific ones.
b. History
Aristotle
Classified living beings into two major groups: animals and plants. Plants were further grouped into herbs, shrubs, and trees. Animals were divided into three groups: land, water, and air.
C. Linnaeus
Known as the father of taxonomy for systematizing taxonomy.
Developed the binomial nomenclature system:
Contains only genus and species. Species describe specific characteristics or where it was found.
Uses Latin, a dead language that no longer evolves.
Easier to use because it contains only two words (previously names could have up to seven words).
Example: Motacilla tragodytes L, 1758 means genus Motacilla, species tragodytes, named by Linnaeus in 1758 and already described.
Names like Motacilla tragodytes (L, 1758) do not explicitly indicate that Linnaeus described the species.
If only the genus is known (species not determined), add "sp" for animals (e.g., Felis sp.) and "spec" for plants (e.g., Magnifera spec.).
If multiple species are suspected but only genus is known, add "spp" (e.g., Felis spp.).
If the organism resembles a known species but is not exactly it, add "cf" (e.g., Magnifera cf. indica).
B. TAXONOMY IN FOSSILS
Many fossil names differ from their original names — is this a problem? It depends on which names are more widely used.
Morphotaxa are taxonomies based only on morphology and are widely used for plants and microfossils, especially pollen (fine to coarse powder made of pollen grains, the male microgametophyte of seed plants producing male gametes). This causes fossil names to differ from plant names. Example: Spinizonacoliptes.
Paleobotany: study of fossil plants, which differ depending on whether leaves, wood, or pollen are studied.
Phytoliths: silica from plants, especially in dry environments, with varying shapes used for naming.
C. EVOLUTION
a. Definition
Changes in inherited characteristics within a population.
b. Development of Evolutionary Theories
Anaximander
The cosmos formed from chaos.
Life arose from dead matter.
Higher organisms evolved from lower (simple to complex).
C. Linnaeus
Creation theory: all creatures created simultaneously by the Creator.
Current forms are the same as at creation.
Cuvier
Catastrophes wiped out all life at the end of each period.
New life appeared different from previous life after each catastrophe.
Buffon
Current life may have arisen from other life forms.
Eugene Darwin
Animals now may have come from stars.
Lamarck
Simple animals first appeared from non-living matter.
Progressed from simple to complex.
Organs frequently used grow and develop perfectly.
Charles Darwin
Current organisms evolved gradually from previous ones.
Struggle for existence requires competitive ability within or between organisms.
Evolution is influenced by three factors:
Genetics
Time
Natural selection: favors those who adapt to geology and climate.
c. Types of Evolution
Macroevolution:
Large scale, over a long time (more than one generation).
Seen in the fossil record.
Microevolution:
Small scale, over a short time.
d. Direction of Evolution
Retrogressive: from complex to simpler forms.
Progressive: from simple to more complex forms.
e. Evolution Pace
Very slow, e.g., brachiopods.
Moderate, e.g., horses.
Very fast, e.g., mammal development from Mesozoic to Cenozoic.
f. Final Result of Evolution
Divergent: one species evolves into many new species (e.g., mammals).
Convergent: similarity between two organs or organisms from different ancestors (e.g., shark and dolphin).
g. Selection
Morphological and physiological changes.
Occurs within a population.
Produces varied offspring.
Inherited genetics.
h. Effects of Evolution
Adaptation
Coevolution-Cooperation (joint evolution)
Speciation
Extinction
i. Evolution Symptoms
Shell growth.
Growth in specific parts (e.g., teeth).
Suture development (e.g., ammonites).
Direction of shell coiling.
Shapes of specific parts.
Back again with me, Kemal, the author of the blog "Catatan Belajarku" (My Learning Notes). So, how’s the spirit, bro? Still excited to talk about fossils? Hehehe. Alright, let’s keep going!
VERTEBRATE
A. Definition
Animals that have a backbone. Vertebrates first appeared during the Ordovician period and still exist today. They initially lived in the ocean as simple, worm-like organisms.
B. Characteristics
Possess segmented vertebrae that function as the axial support.
The brain is protected by a cranium (skull).
The skeleton is internal (endoskeleton), composed of hard bone, spongy bone, cartilage, and ligaments.
The body has bilateral symmetry.
C. Taxonomic Level
Subphylum: Vertebrate
D. Classifications
a. Chondrichthyes
Their body structure is made of cartilage. Key features:
Teeth are not fused with the jaw.
They lack a swim bladder.
They have spiral valves in their intestines.
b. Osteichthyes
Their body structure is made of true/hard bone. Key features:
Fusiform (spindle-shaped) body.
Swim bladder functions as lungs.
A single gill opening on each side of the body, covered by a bony flap called the operculum.
c. Myxini (Hagfish)
Their mouth has four pairs of tentacles at the tip.
The living pouch has a channel to the pharynx.
They have 5–15 pairs of gill pouches.
d. Cephalospidomorphi (Lampreys)
Possess a sucking mouth with horn-like teeth.
The living pouch is not connected to the mouth.
They have 7 pairs of gill pouches.
e. Amphibia
Can live in both water and on land.
Cold-blooded (body temperature follows the environment).
Breathe using lungs.
f. Reptilia
Crawling animals.
Warm-blooded.
Their bodies are covered with scales.
g. Aves (Birds)
Animals that can fly.
Their bodies are covered with feathers.
Limbs include legs and wings.
h. Mammalia (Mammals)
Females have mammary glands.
Warm-blooded.
Reproduce sexually.
E. Morphology
In general, vertebrate fossil identification focuses on two morphological aspects: bone morphology and tooth morphology.
a. Bone Morphology
Vertebrate bones are classified into two types: cranial bones and postcranial bones.
Cranial bones refer to the bones in the skull, primarily functioning to protect the brain. These bones are usually flat and plate-like in shape.
Postcranial bones include the supporting bones of the body and limbs. Limb bones are typically round and elongated, while supporting bones show more variation in shape.
The bones that make up each vertebrate class have distinct characteristics. For example, fish have bones shaped like spines, reptiles tend to have flat bones, and birds have lightweight, hollow bones.
b. Tooth Morphology
Teeth are very important in fossil identification, especially for classifying mammals down to the species level.
In non-mammalian animals, tooth structure tends to be simpler, with little variation in shape. The main difference is usually in tooth size, not form.
In contrast, mammalian teeth are more complex and can be clearly divided into different types:
Incisors – front teeth used for cutting
Canines – pointed teeth for tearing
Premolars – transitional teeth used for grinding and tearing
Molars– back teeth used for grinding food
Teeth of Vertebrates (Non-Mammals)
Teeth of Vertebrates (Mammals)
1. Morphology and Anatomy of Mammalian Teeth
Mammals have three fossilizable parts of their teeth:
Enamel: A hard layer or tissue that covers the crown of the tooth and contains calcium.
Dentin: A yellowish layer or tissue made of calcified material, located just beneath the enamel.
Cementum: A hard layer with a strong structure that covers the root of the tooth.
Parts of a tooth
2. Tooth Formula
Because mammalian teeth have distinctive shapes that differ from one another, mammal teeth can be represented using a tooth formula. Below is the tooth formula for mammals.
Let’s take the example of a rabbit, which has a tooth formula of 2033/1023. In this formula, the numerator (top number) is 2033, and the denominator (bottom number) is 1023.
The numerator represents the arrangement of teeth in the upper jaw, while the denominator shows the arrangement in the lower jaw. Both numbers represent half of the jaw (either the left or right side) because mammals have bilateral symmetry — meaning the left and right sides are mirror images. So, the upper left and upper right jaws both have 2-0-3-3 teeth, and the lower left and lower right jaws both have 1-0-2-3 teeth.
Since mammals have four types of teeth, the numbers correspond to the order of tooth types: I C P M — Incisors, Canines, Premolars, and Molars.
So, 2033 means the rabbit’s upper jaw (left or right) has:
2 incisors
0 canines
3 premolars
3 molars
And 1023 means the rabbit’s lower jaw (left or right) has:
1 incisor
0 canines
2 premolars
3 molars
This means rabbits don’t have canines, which classifies them as herbivores.
How’s that? Pretty clear, right? Hehe. Below is an example of a tooth arrangement. Try to guess which species it is! (Scroll slowly so the answer doesn’t pop out right away).
Based on observation, this species has a tooth formula of 2123/2123, and the species is a monkey. However, humans also have the same tooth formula.
3. Types of Molars
Tribosphenic: The surface of the molar consists of 3 cusps (points). Found in species like the platypus and marsupials.
Quadrate: The surface of the molar consists of 4 cusps (points). Found in species like porcupines, raccoons, and some primates.
Bunodont: The cusps are rounded with blunt peaks. Found in hominids, bears (Ursidae), and sea lions (Otariidae).
Hypsodont: Teeth with high crowns and enamel that extends well past the gum line. Found in animals like cattle, deer, and horses.
Brachyodont: Teeth with short crowns, just slightly above the gum line, and having at least one root. Found in humans.
Lophodont: Characterized by long, numerous ridges (called lophids) on the tooth surface. Found in elephants, tapirs, and rodents.
Selenodont: The main cusps are elongated into crescent-shaped ridges. Found in deer (Cervidae), cattle (Bovidae), and horses (Equidae).
Secodont: Sharp, pointed cusps. Found in carnivores.
Differences between molars of carnivores, herbivores, and omnivores:
Carnivores: Upper and lower molars are large, sharp, and triangular, known as the carnassial type.
a. Cambrian Period
The first vertebrate fossils, known as ostracoderms, appeared during this time.
b. Early Silurian Period
The first jawed fish evolved.
c. Early Devonian Period
Four major groups of jawed fish emerged:
Acanthodians
Placoderms
Cartilaginous fish (e.g., sharks)
Bony fish (e.g., tuna)
d. Late Devonian Period
These jawed fish began to replace all primitive vertebrates.
e. Late Paleozoic Era Acanthodians and placoderms went extinct. However, cartilaginous and bony fish continued to evolve and exist today.
f. Carboniferous Period
Amphibians began to evolve, marked by the development of lungs and limbs. Vertebrates diverged into two major groups:
Animals living in cold and humid environments, which developed fur and internal pouches. These later evolved into mammal-like reptiles.
Animals living in hot and dry environments, which lacked fur and pouches. These evolved into reptiles, birds, mammals, and amphibians.
g. Late Paleozoic Era
Mammal-like reptiles became the dominant terrestrial vertebrates.
h. Mesozoic Era
Reptiles reached the peak of their evolutionary development.
i. Triassic Period
Marked the peak of vertebrate diversification and dominance.
j. Late Triassic Period
The first true mammals appeared.
k. Jurassic and Cretaceous Periods
Terrestrial animals dominated, and the first birds began to appear.
l. End of the Mesozoic Era
A mass extinction event occurred, wiping out many dominant reptilian species, including the dinosaurs.
G. Uses of Vertebrate Fossils
a. Biostratigraphic Purposes
In Indonesia, vertebrate fossils play a significant role in determining the age and depositional environments of terrestrial sediments. This is primarily because much of Indonesia’s geological record—particularly in regions such as Sumatra, Java, and Sulawesi—is dominated by Tertiary and Quaternary strata. During these periods, vertebrates were the dominant fauna, as dinosaurs had already gone extinct by the end of the Cretaceous.
Biostratigraphy of Java based on index fossils (Puspaningrum, 2016)
Biostratigraphy of Sulawesi based on index fossils (Puspaningrum, 2016)
Biostratigraphy of Flores based on index fossils (Puspaningrum, 2016)
b. For paleoclimatology interpretation
c. For paleobiogeography purposes
d. For paleoecology purposes
e. For evolutionary development purposes
f. For history and culture
That’s all from me. Thank you for visiting and reading my blog. Please leave a comment and don’t forget to share. Thank you!
After learning about various animal fossils, now it’s time for us to switch topics for a bit—but don’t worry, we’re not straying too far. In this discussion, we’re still dealing with animals, but this time, it’s not about their body parts. So… what part are we talking about then? Curious? Let’s check it out!
A. Definition
Ichnofossils can be defined as sedimentary structures that result from the life activities of animals—or in cooler terms, trace fossils.
B. Types
a. Burrow: A hole or tunnel dug into soft, unconsolidated substrate.
b. Bioerosion trace fossil / Boring: A hole created in hard, consolidated substrate.
c. Track: An animal footprint formed while walking, usually characterized by a discontinuous trail.
d. Trail: A trace left by an animal moving with its belly in contact with the ground, usually characterized by a continuous, connected path.
e. Coprolite: Fossilized droppings or feces from an organism.
f. Egg/Nest: Fossilized eggs or preserved nests.
C. Principles of Ichnology
a. Same species, different structures
The same animal species can produce different sedimentary structures depending on their behavioral patterns.
b. Same burrow, different substrates
Burrows with similar shapes may be preserved differently depending on the type of substrate. Factors such as average grain size, sediment stability, water content, and sediment chemistry all influence preservation.
c. Different tracemakers, identical structures
Similar-looking sedimentary structures can be produced by different species.
D. Bioturbation, Ichnofacies, and Ichnofabric
a. Definitions
Bioturbation: The process by which primary sedimentary structures and properties are modified by the activities of organisms living within the sediment, often resulting in sediment mixing.
Ichnofacies: An ecological assemblage of trace fossils produced by a particular group of organisms.
Ichnofabric: The total amount and nature of sediment disruption caused by burrowing organisms, typically given a score from 1 to 5 to represent the degree of bioturbation.
b. Similarity between Ichnofacies and Ichnofabric
Both reflect the interaction between depositional energy, sedimentation rate, and bottom-water oxygen levels.
c. Difference between Ichnofacies and Ichnofabric
Ichnofacies: Data collection is done qualitatively.
Ichnofossils can be classified based on four main aspects:
a. Taxonomic Classification
Based on the International Code of Zoological Nomenclature.
When referring to a fossil at the genus level, it is called an ichnogenus, abbreviated as igen. When referring to a fossil at the species level, it is called an ichnospecies, abbreviated as isp.
The abbreviation isp is written after the species name, and igen is written after the genus name.
For example, Skolithos isp:
Here, Skolithos represents the fossil’s taxonomic genus name, and isp indicates that the species has been identified based on trace fossil characteristics. If the species cannot be clearly identified due to lack of distinctive features, only the genus name is used, followed by the abbreviation igen to indicate it as an ichnogenus.
Skolithos isp
b. Preservation Model
Classified by Seilacher based on the position of the trace fossil relative to the sedimentary layer. There are three types of classification:
Semirelief: The trace fossil is located on the top surface of the sediment layer.
Hyporelief: The trace fossil is located on the bottom surface of the sediment layer.
Full relief: The trace fossil is found within the sediment layer, between semirelief and hyporelief.
In the image above, you can see positive (+) and negative (–) signs. The positive (+) sign indicates that the trace fossil is convex (raised), while the negative (–) sign indicates that the trace fossil is concave (depressed) relative to the rock layer.
c. Life Patterns / Ethological Classification
The behavior of an organism can be observed in sedimentary structures and is classified into several types of behavior. Seilacher grouped them as follows:
Cubichnia: Traces formed by an organism when resting, hiding, or positioning itself to ambush prey. Characteristics include:
In the image above, there are two examples of Repichnia: Cruziana and Gyrochorte. Cruziana has a concave (–) semirelief shape that reflects the underside of the organism. This contrasts with Gyrochorte, which has a convex (+) semirelief shape reflecting the upper side of the organism.
Domichnia: Traces representing the dwelling or living place of an organism. Characteristics include:
Orientation can be horizontal (parallel to sediment layers) or vertical (perpendicular to sediment layers).
Usually shaped like cylindrical tubes (straight or U-shaped) or more complex branching forms.
May show evidence of scratches, cemented walls, or striations.
Thalassinodes: feeding/dwelling traces showing three-way burrow intersections (one vertical and two horizontal).
d. Past Environment / Depositional Setting
Trace fossils are grouped into 5 ichnofacies. The formation of these ichnofacies is controlled by salinity, bathymetry, substrate surface, and rock type. The five ichnofacies are:
Scoyenia ichnofacies
Formed in terrestrial or freshwater environments. Examples of genera: Scoyenia, Planolites, and Isopodichnus.
Skolithos ichnofacies
Formed in intertidal zones with sandy substrates and high water fluctuations. Organisms in this environment build deep burrows to:
Protect themselves against drying out or unfavorable temperatures.
Adapt to changes in seawater salinity.
Protect themselves from sediment surface shifts due to tides or waves.
The fossils are dominated by U-shaped, vertical, and some horizontal burrows. Examples of genera: Skolithos, Diplocraterion, Thalassinodes, and Ophiomorpha.
Cruziana ichnofacies
Formed in shallow marine environments with lower tides and deeper water than Skolithos ichnofacies. Generally, the burrows are vertical or horizontal. Examples of genera: Rusophycus, Cruziana, and Rhizocorallium.
Zoophycos ichnofacies
Formed in bathyal marine zones. Due to the deep water, wave influence is minimal, the water is calm, oxygen levels are relatively low, and the seabed is muddy. Dominated by horizontal burrow forms such as Zoophycos.
Nereites ichnofacies
Formed in abyssal marine zones with clay substrates. Trace fossil abundance is low, but diversity of trace types is high. Examples of genera: Nereites and Scalarituba.
Psilonichus ichnofacies
Formed in non-marine and very shallow environments. Burrows are Y or U shaped, with vertical shafts and horizontal tunnels. An example is Track.
e. Burrow Taxonomy
Here, I’m using burrow taxonomy as an example because in our recent paleontology lab, the main focus was on burrows. The parameters used as the basis for naming burrows are as follows:
Orientation relative to bedding planes (Orientation)
There are two types of orientation relative to bedding planes:
Subhorizontal: when the burrow runs parallel to the bedding planes.
Subvertical: when the burrow runs perpendicular to or cuts across the bedding planes.
Presence or absence of branching (Branching)
Branched: The burrow has branches. Branching is further classified into three types:
Tunnel: horizontal branches
Shaft: vertical branches
Boxwork: combination of tunnel and shaft
Unbranched: No branches present.
General morphology (Shape)
The general shapes vary and include:
U-shaped
Cylindrical
Wall-shaped
J-shaped
Winding/meandering
Lobate
Radial
Tunnel with shaft
Club-shaped
Helicoidal
Prismatic
Funnel-shaped
Plug-shaped
Bifurcated
Burrow filling (Filling)
The burrow cavity is filled with other minerals. Filling is classified based on the origin of the minerals:
Active filling: minerals deposited by the organism itself, characterized by curved and perpendicular septa (walls) within the burrow, showing the organism’s digging effort.
Passive filling: minerals deposited by non-biological processes such as gravity or water currents.
Burrow lining (Burrow lining)
The lining of the burrow is produced by the organism, typically from excreted minerals, and is usually smoother than the surrounding sediment minerals. There are two types:
Burrow lining present
No burrow lining present
Note: Filling and burrow lining are often difficult to distinguish clearly.
Taxonomi burrow
An example of the taxonomy:
For instance, if we find a burrow fossil that looks like this:
The identification steps are as follows:
Check the orientation
In the image, the orientation isn’t directly visible. Let’s hypothesize that the image was taken looking down from above the rock layer. Therefore, we can determine that the trace fossil shape is a positive semirelief with a subhorizontal orientation because it runs parallel to the bedding plane.
Check the branching
The next identification step follows the burrow taxonomy flowchart, which is to identify whether branching exists or not. In the image, there is no branching (unbranched).
Check the shape
Next, we identify the shape. The form is cylindrical because it looks like an elongated tube.
Check the filling
The next step is to identify the type of filling. Since there are no visible septa (partitions) inside the tube, we conclude that the filling is passive filling.
Check the burrow lining
At the final step, we examine the burrow edges to see if there is any burrow lining. Burrow lining can be recognized by a noticeable difference in color between the burrow edge and the burrow itself. It can also be seen in the grain size uniformity (coarse or fine). The image shows that the color and grain size between the burrow edge and the burrow are not uniform, so we conclude that there is burrow lining.
In summary, the information we have gathered is:
Subhorizontal – unbranched – cylindrical – passive filling – lining
When we compare this information with the burrow taxonomy chart, we identify that the fossil is called Palaeophycus.
That’s all from me. Thanks for reading my blog! I appreciate any feedback or suggestions :)
Still talking about animal fossils—this time, we’re diving into one of SpongeBob’s friends. Can you guess who it is? That’s right! One of our main topics today is Patrick, who is actually an example of an echinoderm. In addition to echinoderms, I’ll also be covering the arthropod group. Let’s check them out one by one!
ECHINODERMATA
A. Characteristics
Their bodies are spiny.
Triploblastic.
Exoskeleton made of calcium carbonate (CaCO₃).
High regenerative ability.
Bilateral symmetry in the larval stage.
Pentaradial symmetry in adulthood.
B. Taxonomix Level
Phylum: Echinodermata
C. Classification
a. Asteroidea (sea stars)
Star-shaped with ambulacral grooves.
Have five arms/tentacles.
Fossils are rarely found.
Aboral surface
Oral surface
b. Ophiuroidea (brittle stars)
Do not have ambulacral grooves.
Have long, slender, and highly flexible arms.
Star-shaped body.
Rarely found as fossils because their skeletons disintegrate quickly after death. When fossils are found, they are often well-preserved due to rapid burial and fossilization.
Aboral surface
Oral surface
c. Echinoidea (sea urchins)
Shaped like an egg, heart, or globular form.
Have many plates on their body.
Ambulacral grooves are perforated with pores.
Commonly found as fossils.
There are two types of echinoidea:
Regular: clearly displays pentameral symmetry.
Irregular: pentameral symmetry is not clearly visible.
Oral (bottom) and aboral (top) surfaces of sand dollars
Irregular echinoidea
Regular echinoidea
d. Holothuroidea (sea cucumbers)
Have soft, fine spines.
Move flexibly but slowly.
Mouth located at the anterior end and anus on the aboral side.
e. Crinoidea (sea lilies)
Arms are segmented.
Body shaped like a cup.
Mouth and anus are located on the upper surface.
f. Blastoidea (extinct)
Similar to crinoidea, but differs in the theca.
The body has 5 prominent radiating grooves.
There are 5 V-shaped plates.
g. Eocrinoidea (extinct)
Similar to crinoidea, but differs in the theca.
h. Edrioasteroidea (extinct)
Small fossils grow on top of edrioasteroids.
Resembles a starfish.
The organism is round with 5 tentacles.
The tentacles grow in a curved, spiral, or near-spiral pattern.
i. Helicoplacoidea (extinct)
Does not have pentameral vascular symmetry.
The skin is covered with overlapping spiral ossicles that function like armor.
Actually, trilobites have their own subphylum called Trilobitomorpha. However, I intentionally separated the class Trilobita as a main discussion topic because trilobites have very diverse shapes, making them useful as indicators of certain regions and specific ages. Additionally, there are already maps showing the distribution of trilobite habitats, commonly known as trilobite provinces.
These different forms are due to:
Evolution progressing from simple to more complex shapes.
Their habitat, such as the availability of food sources, which can affect the size of the trilobite.
Trilobites lived around the Cambrian to Permian periods. They became extinct during the Permian period due to extreme drying of the Earth's climate. Generally, trilobites can be divided into three body parts that are key for identification:
Cephalon
Thorax
Pygidium
Morphology of trilobites
A. Trilobites can be distinguished based on:
a. The size ratio between the cephalon and the pygidium
Micropygous: cephalon size is much larger than the pygidium. Example: Redlichia.
Subisopygous: cephalon and pygidium sizes are nearly equal. Example: Bathyurus.
Isopygous: cephalon and pygidium are the same size. Example: Ogygiocaris.
Macropygous: pygidium size is larger than the cephalon. Example: Scutellum.
b. Suture
Types of sutures
Examples of classifications based on suture types
c. Hypostome
The hypostome is a ventral (underside) structure of the trilobite’s cephalon (head). Generally, based on the hypostome, trilobites can be classified into three types:
1. Natant: The hypostome (H) is not attached to the anterior doublure / it is free and aligned with the edge of the anterior glabella (G). In the illustration, the dotted line shows the front (anterior glabella) aligned with the front part of the hypostome.
2. Conterminant: The hypostome (H) is attached to the anterior doublure / positioned intersecting and aligned with the edge of the anterior glabella (G). In the illustration, the dotted line shows the front (anterior glabella) aligned with the front part of the hypostome.
3. Impendent: The hypostome (H) is attached to the anterior doublure / positioned intersecting but not aligned with the edge of the anterior glabella (G). In the illustration, the dotted line shows the front (anterior glabella) is far ahead of the hypostome, so they do not align.
Below is an illustration of the hypostome viewed from various angles:
B. Trilobite Evolution
The general evolution of trilobites can be seen in the image below:
It can be concluded that trilobite morphology evolved starting from an elongated form. In the early stages, their morphology was very complex. Over time, the segments in the thorax began to reduce and their eyes started to disappear. Then spines began to appear while other parts continued to diminish. This reduction process continued until trilobites became extinct in the Permian period.
In fact, there are several processes that accompany trilobite evolution, including:
1. Effacement
Some trilobite orders, especially Agnostida, Corynexochida, and Asaphida, experienced reduction or simplification in parts of the cephalon, thorax, and pygidium. This is related to the trilobites’ adaptation to a burrowing lifestyle. The effacement can be seen in the image below:
2. Spinocity
Spinocity can be defined as the growth of spines on trilobites, which can arise from almost any part of the exoskeleton, especially along the margins. For example, the extension of the pleura (segments on the thorax). The growth of these spines is a defensive adaptation to protect themselves from predators, indicating that life during the Paleozoic era was very dangerous for trilobites.
3. Miniaturization
Miniaturization is the reduction in size of trilobites, usually caused by a decreasing food supply. This can happen for two reasons: the trilobite population increases, leading to higher competition for food, or the food itself becomes scarce. The purpose of reducing their body size is so that trilobites require less food to survive, helping to maintain the available food resources.
C. Some Trilobite Morphologies
1. Atheloptic Morphology
Trilobites living in deep marine environments are characterized by absent or reduced eyes, as an adaptation to their deep, low-light, aphotic habitat.
2. Pelagic Morphology
They have large eyes and an elongated, slender body shape as adaptations to enable trilobites to swim well and disperse across the entire ocean (long-distance travel).
3. Olenimorph
The exoskeleton is thin, the number of thorax segments increases, and the body shape is flat and wide as an adaptation to low oxygen levels and high sulfur concentrations. The various transversal thorax pleurae cover the gills and extend laterally, allowing for maximum oxygen absorption and providing a large surface area for symbiotic bacteria (sulfur-eating bacteria as a feeding strategy) to live.
4. Pitted Fringe
The expansion of the cephalon into a concave space is an adaptation for filter feeding (helping to stabilize the trilobite during filtration).
D. Habitat
E. Types of Trilobites based on Geological Time Scale
