Youtube video link of this presentation: https://youtu.be/UyclPb-nBZc Hello there, in this presentation Nusrat Nahian Fatema points out Evolutionary trends in Trilobites ( Invertebrate Paleontology ). References: 1.https://www.trilobites.info/trends.htm#:~:text=An%20analysis%20of%20morphological%20diversity,decreased%20toward%20their%20extinction%20in 2. https://en.wikipedia.org/wiki/Trilobite 3. Fundamentals of Invertebrate Paleontology ( Sreepat Jain) Follow our Facebook Page: https://www.facebook.com/earthdetective Follow our Linkedin Page: https://www.linkedin.com/company/eart... Copyright Disclaimer Under Section 107 of the copyright act 1976, allowance is made for "fair use" for purposes such as criticism, comment, news, reporting, teaching, scholarship, and research. Non-profit, educational, or personal use tips the balance in favour of fair use. This presentation is only made for teaching and educational purposes. #trilobites #paleontology #evolution #geology #trend #invertebrate

1. EVOLUTIONARY TREND
IN TRILOBITES
Nusrat Nahian Fatema
This presentation as video is available on Youtube channel name “Earth Detective”. Link in the description.

2. Content
 INTRODUCTION
 ATHELOPTIC MORPHOLOGY : REDUCTION AND LOSS
OF EYES
 EFFACEMENT : THE LOSS OF SURFACE DETAILS
 MINIATURIZATION
 SPINOSITY
 PELAGIC MORPHOLOGY
 OLENIMORPH
 PITTED FRINGE

3. The principal
evolutionary trends
The principal evolutionary trends from
primitive morphologies include the origin of
several morphologies appeared independently
within different major taxa.
 Changes in cephalon and glabella.
 Reduction , variation in eyes and facial
sutures.
 Changes of thorax
 Pygidium increase
 Spinosity development
 Hypostome specialization.
 Effacement

4. The principal
evolutionary trends
Patterns of evolutionary changes due to
developmental heterochronies and
ontogenetic processes:
1.Paedomorphic tendencies(acquisition of a
proparian suture,development of forms with a
forward widened glabella)
2.Peramorphic trends(the acquisition of a
smooth glabella and the appearance of
swollen glabellae.

5. ATHELOPTIC MORPHOLOGY : Reduction And Loss
Of Eyes
 deep-water benthic habitats,
 blind or nearly-blind trilobites
 Example : Devonian trilobites that
started with ancestors bearing large,
functional eyes.

6. Effacement : The Loss Of Surface Details
 cephalic, pygidial, and thoracic
furrows effacement
 burrowing lifestyle adaptation
 pelagic streamlining
 loss of details
 no selection pressure

7. MINIATURIZATION
 size reduction.
 complex marine system microhabitats
 maturity and size correlated
 reduced thoracic segments(progenesis)

8. SPINOSITY
 defensive adaptation.
 originate from exoskeleton
 stabilization structures on loose silty
substrate
 flotation structures for slow-swimming
 consistent and diagnostic characters

9. PELAGIC MORPHOLOGY
 extremely large eyes
 streamlined body shape
 good swimming abilities

10. OLENIMORPH
 thin exoskeleton
 benthic habitats(low oxygen and high
Sulphur compound)
 widened, flat body
 thoracic segments increase

11. PITTED FRINGE
 expanded cephalon
 numerous fenestrations
 adaptation to filter-feeding.
 genal prolongations

12. References :
• https://www.trilobites.info/trends.htm#:~:text=An%20analysis%20of%20morphologi
cal%20diversity,decreased%20toward%20their%20extinction%20in
• https://en.wikipedia.org/wiki/Trilobite
• Fundamentals of Invertebrate Paleontology ( Sreepat Jain)

13. Thank You