SPECIES : definition and types

INTRODUCTION :

In both paleontology and biology, a species is considered a fundamental unit of classification that represents a group of organisms,  which are capable of interbreeding and producing fertile offspring. However, defining what constitutes a species can be challenging, and various approaches and criteria have been proposed over time.

In paleontology, identifying species is especially challenging since extinct organisms can't be directly observed and their DNA is rarely preserved. Paleontologists mainly depend on fossilized morphological features such as shape, size and structure to distinguish and define species from the past.

SPECIES CONCEPT IN PALEONTOLOGY :

It is the fundamental unit of taxonomic classification which represent a basic category of organisms. The concept of species is crucial in understanding the diversity and relationships among different organisms.

Taxonomic classification proceeds beyond the species level to include higher ranks such as genus, family, order, class, phylum, kingdom and domain, each representing broader categories encompassing a greater number of related species.

IDENTIFICATION OF SPECIES :

In paleontology, defining species can be challenging due to the limitations of studying extinct organisms.

The main method for identifying species in paleontology is called the Morphological Species Concept (MSC).

MSC classifies species based on their physical characteristics ,which preserved in the fossil record. Paleontologists carefully examine the morphology, or the form and structure, of fossilized remains to identify and differentiate species.

The morphological method for identifying species :

1. Fossil Collection : Paleontologists gather fossil specimens from various locations to ensure a diverse representation of organisms from different time periods and environments.
2. Morphological Analysis : The collected fossils are then studied in detail to identify distinctive morphological features. Paleontologists examine the external structures, such as skeletal elements, shells, teeth, or other hard parts, as well as internal structures like bone microstructure or organ impressions.
3. Comparisons and Classification : Paleontologists compare the morphological features of the collected fossils with known species from the fossil record and living organisms. They look for similarities and differences in key characteristics, such as size, shape, ornamentation, surface texture, and other anatomical features.
4. Creation of Taxonomic Keys : Paleontologists often create taxonomic keys or identification guides based on the observed morphological variations. These keys provide a systematic way to identify and classify fossils based on specific characteristics and their variations.
5. Expert Judgement : Species identification in paleontology requires expertise and experience. Paleontologists rely on their knowledge of anatomy, paleoecology, evolutionary patterns and comparative analysis to make informed judgments about species distinctions.

TYPE SPECIMEN :

When a new species is described, a type specimen is designated to represent that species. It serves as the basis for future comparisons and ensuring consistency in scientific naming and descriptions.

Types of type specimens :

depending on the taxonomic group:

A. Primary 

B. Secondary

A. Primary type :

Type specimens are selected or described by the researcher who first identified and named the species.

1. Holotype : A holotype is a single specimen designated as the primary reference for a species, possessing the diagnostic features that define it.
2. Paratype : Paratypes are additional specimens that are designated alongside the holotype. They are also used as reference specimens to demonstrate the variability of the species. Paratypes may exhibit some differences from the holotype but should still fall within the range of characteristics described for the species.
3. Syntype : In cases where the original description is based on multiple specimens, but no single specimen is designated as the holotype, those specimens are referred to as syntypes. Syntypes collectively represent the original description of the species.
4. Lectotype : A lectotype is designated from the syntypes when a holotype was not originally designated. It is a single specimen selected retrospectively to serve as the primary reference for the species.
5. Neotype : In situations where all original specimens (holotype, paratypes, and syntypes) are lost or destroyed, a neotype can be designated. A neotype is a new specimen chosen to act as the primary reference for the species.

B. Secondary types :

Type specimen are select or described by the another researcher .

1. Topo type: A topotype is a specimen collected from the same locality as the holotype or the original type series. It is used to confirm the geographic distribution and maintain consistency with the original description.
2. Plesio type: A specimen upon which a subsequent or additional description or figure is based; any specimen identified with a described or named species by a person other than the describer. Secondary types: Hypotype - a described, figured, or listed specimen.
3. Plasto type: It identified on the basis of an artificial specimen cast or molded.

Summary :

Species names are written in binomial nomenclature, a system established by Carl Linnaeus. Each species has unique two part of scientific name consisting of a genus name (capitalized) followed by a specific epithet (in lowercase), such as Homo sapiens (human) or Canis lupus (gray wolf). This naming system helps scientists communicate and reference specific organisms consistently across different languages and regions.