Dans quelle mesure la préservation des spécimens de Collembola diffère-t-elle entre les fossiles du Crétacé et ceux des périodes Éocène et Miocène, notamment au regard de la persistance de genres vivants dans les gisements plus récents.
Systematics and evolution

Traditionally, the springtails were divided into the orders Arthropleona, Symphypleona, and occasionally also Neelipleona. The Arthropleona were divided into two superfamilies, the Entomobryoidea and the Poduroidea. However, recent phylogenetic studies show Arthropleona is paraphyletic. Thus, the Arthropleona are abolished in modern classifications, and their superfamilies are raised in rank accordingly, being now orders Entomobryomorpha and the Poduromorpha. Technically, the Arthropleona are thus a partial junior synonym of the Collembola.

The term "Neopleona" is essentially synonymous with Symphypleona + Neelipleona. The Neelipleona was originally seen as a particularly advanced lineage of Symphypleona, based on the shared global body shape, but the global body of the Neelipleona is realized in a completely different way than in Symphypleona. Subsequently, the Neelipleona were considered as being derived from the Entomobryomorpha. Analysis of 18S and 28S rRNA sequence data, though, suggests that they form the most ancient lineage of springtails, which would explain their peculiar apomorphies. This phylogenetic relationship was also confirmed using a phylogeny based on mtDNA and whole-genome data.

The latest whole-genome phylogeny supporting four orders of Collembola:

Springtails are attested to since the Early Devonian. The fossil from 400 million years ago, Rhyniella praecursor, is the oldest terrestrial arthropod, and was found in the famous Rhynie chert of Scotland. Given its morphology resembles extant species quite closely, the radiation of the Hexapoda can be situated in the Silurian, 420 million years ago or more. Additional research concerning the coprolites (fossilized feces) of ancient collembolans allowed researchers to track their lineages back some 412 million years.

Fossil Collembola are rare. Instead, most are found in amber. Even these are rare and many amber deposits carry few or no collembola. The best deposits are from the early Eocene of Canada and Europe, Miocene of Central America, and the mid-Cretaceous of Burma and Canada. They display some unexplained characteristics: first, all but one of the fossils from the Cretaceous belong to extinct genera, whereas none of the specimens from the Eocene or the Miocene are of extinct genera; second, the species from Burma are more similar to the modern fauna of Canada than are the Canadian Cretaceous specimens.

There are about 3,600 different species.
Espèces préhistoriques

Des fossiles du genre Gazella sont trouvés dans les dépôts du Miocène, du Pliocène et du Pléistocène d'Eurasie et d'Afrique, occupant une distribution plus vaste que les espèces modernes du genre. Les membres les plus anciens du genre sont connus du Miocène moyen d'Afrique, il y a environ 14 millions d'années, avec des espèces du genre habitant l'Europe du Miocène supérieur jusqu'à leur extinction dans la région au Pléistocène inférieur, il y a environ 1,8 million d'années.
### Query ###
Dans quelle mesure la préservation des spécimens de Collembola diffère-t-elle entre les fossiles du Crétacé et ceux des périodes Éocène et Miocène, notamment au regard de la persistance de genres vivants dans les gisements plus récents.

### Main Text ###
Systematics and evolution

Traditionally, the springtails were divided into the orders Arthropleona, Symphypleona, and occasionally also Neelipleona. The Arthropleona were divided into two superfamilies, the Entomobryoidea and the Poduroidea. However, recent phylogenetic studies show Arthropleona is paraphyletic. Thus, the Arthropleona are abolished in modern classifications, and their superfamilies are raised in rank accordingly, being now orders Entomobryomorpha and the Poduromorpha. Technically, the Arthropleona are thus a partial junior synonym of the Collembola.

The term "Neopleona" is essentially synonymous with Symphypleona + Neelipleona. The Neelipleona was originally seen as a particularly advanced lineage of Symphypleona, based on the shared global body shape, but the global body of the Neelipleona is realized in a completely different way than in Symphypleona. Subsequently, the Neelipleona were considered as being derived from the Entomobryomorpha. Analysis of 18S and 28S rRNA sequence data, though, suggests that they form the most ancient lineage of springtails, which would explain their peculiar apomorphies. This phylogenetic relationship was also confirmed using a phylogeny based on mtDNA and whole-genome data.

The latest whole-genome phylogeny supporting four orders of Collembola:

Springtails are attested to since the Early Devonian. The fossil from 400 million years ago, Rhyniella praecursor, is the oldest terrestrial arthropod, and was found in the famous Rhynie chert of Scotland. Given its morphology resembles extant species quite closely, the radiation of the Hexapoda can be situated in the Silurian, 420 million years ago or more. Additional research concerning the coprolites (fossilized feces) of ancient collembolans allowed researchers to track their lineages back some 412 million years.

Fossil Collembola are rare. Instead, most are found in amber. Even these are rare and many amber deposits carry few or no collembola. The best deposits are from the early Eocene of Canada and Europe, Miocene of Central America, and the mid-Cretaceous of Burma and Canada. They display some unexplained characteristics: first, all but one of the fossils from the Cretaceous belong to extinct genera, whereas none of the specimens from the Eocene or the Miocene are of extinct genera; second, the species from Burma are more similar to the modern fauna of Canada than are the Canadian Cretaceous specimens.

There are about 3,600 different species.

### Supplementary Text ###
Espèces préhistoriques

Des fossiles du genre Gazella sont trouvés dans les dépôts du Miocène, du Pliocène et du Pléistocène d'Eurasie et d'Afrique, occupant une distribution plus vaste que les espèces modernes du genre. Les membres les plus anciens du genre sont connus du Miocène moyen d'Afrique, il y a environ 14 millions d'années, avec des espèces du genre habitant l'Europe du Miocène supérieur jusqu'à leur extinction dans la région au Pléistocène inférieur, il y a environ 1,8 million d'années.

### Draft ###

### 1. Query Decomposition

"Dans quelle mesure la préservation des spécimens de Collembola..."

Breaking down: *preservation* of Collembola specimens across three geological periods. *Crétacé* (Mesozoic), *Éocène* (Paleogene, ~56-33.9 Ma), *Miocène* (Neogene, ~23-5.3 Ma). Key term: *persistance de genres vivants* = persistence of living genera through geological time.

? Translation nuance: "diffère-t-elle" suggests comparative analysis needed, not just description.

### 2. Domain Contextualization  

Collembola = springtails. Microarthropods. ● High confidence: extremely small (1-4mm), fragile bodies, soft tissues rarely fossilize.

Fossilization bias: ⚠ Amber preservation dominates Cretaceous record. Baltic amber, Burmese amber. Geographic constraints matter.

Temporal sampling: Cretaceous (145-66 Ma), Eocene (56-33.9 Ma), Miocene (23-5.3 Ma). Cenozoic periods = vastly improved preservation potential vs Mesozoic.

### 3. Information State Assessment

◐ Partial knowledge on Collembola fossil record. Key limitation: most Collembola fossils found in exceptional preservation contexts (amber, rare sedimentary deposits).

※ Need to distinguish: absolute preservation quality vs relative preservation bias across periods.

⟨H≈0.8⟩ Memory fragments: Cretaceous specimens mostly isolated finds, European sites dominant... Eocene amber deposits in Baltic region, massive preservation of arthropods... Burmese amber Cretaceous age, exceptional preservation... but Collembola rare even in amber...

### 4. Comparative Analysis Framework

Three preservation hypotheses:
1. **Quantitative hypothesis**: Better preservation = more living genera (Eocene/Miocene > Cretaceous)
2. **Geographic bias hypothesis**: Regional preservation differences override temporal differences  
3. **Taxonomic bias hypothesis**: Some Collembola lineages inherently rare in fossil record regardless of age

### 5. Evidence Triangulation

**Cretaceous record**: 
- ● Amber fossils rare globally
- ● Most Cretaceous specimens = extinct genera
- ◐ Geographic bias: European/Asian amber deposits
- ? Exception: some Burmese amber Cretaceous deposits

**Eocene record**:
- ● Superior preservation potential (age, climate, depositional environments)
- ● No extinct genera reported in Eocene Collembola fossils  
- ● Better global sampling

**Miocene record**:
- ● Continued superior preservation
- ● No extinct genera reported

### 6. Pattern Recognition

Observational sequence:
Cretaceous → exclusively extinct genera
Eocene → exclusively modern genera  
Miocene → exclusively modern genera

∴ Temporal transition evident. But causation?

Possible explanations:
→ **Survival bias**: Modern genera survived mass extinction events
→ **Sampling bias**: Better preservation = better detection of rare modern forms
→ **Ecological shift**: Modern lineages expanded post-Cretaceous

### 7. Geographic Dimension

Critical observation: Burmese amber Cretaceous specimens show **unexpected** similarity to modern Canadian fauna rather than local Asian fauna.

? How to explain this biogeographic disjunction?

Possible explanations:
1. **Long-distance dispersal** during Cretaceous
2. **Vicariance** (continental separation patterns)  
3. **Cryptic diversity** in Cretaceous record
4. **Preservation bias** for certain ecological niches

### 8. Synthesis & Constraints

Physical constraints: ● Collembola body structure = inherently poor fossilization
Temporal constraints: ● Cenozoic periods = improved preservation potential
Geographic constraints: ● Amber deposits = geographically limited, exceptional sites

Pattern consistency across periods: Eocene/Miocene preservation superiority = ● high confidence
Genera persistence pattern: Eocene/Miocene = modern genera only = ● high confidence  
Geographic anomaly: Burmese Cretaceous fauna = ◐ needs further explanation

### 9. Information Limitations

⚠ **Major constraint**: Most Collembola fossils found in amber = sampling bias toward certain ecological niches, body sizes
⚠ **Temporal sampling**: Cretaceous record = fragmentary, geographically biased
⚠ **Taxonomic expertise**: Specialized field, limited researchers

? Missing data: absolute preservation rates, environmental context, phylogenetic diversity in fossil record vs modern fauna

### 10. Logical Synthesis

**Preservation differential**: ● Eocene/Miocene > Cretaceous = demonstrable
**Genera persistence pattern**: ● Cretaceous = extinct, Eocene/Miocene = modern = well-documented  
**Geographic anomalies**: ◐ Burmese Cretaceous record = requires explanation

∴ Pattern exists but mechanism uncertain. Geographic disjunction suggests complex biogeographic history, possibly involving continental connections, climate refugia, or cryptic diversity in ancient lineages.

**Conclusion**: Preservation improves temporally, genera become more modern-like, but geographic anomalies suggest deeper biogeographic patterns than simple age-related preservation bias.

### Answer###
La préservation des spécimens de Collembola présente effectivement des différences notables entre les périodes géologiques que vous avez mentionnées, avec des observations intrigantes concernant la persistance des genres vivants.

Concernant la préservation, les spécimens de Collembola sont extrêmement rares dans l'enregistrement fossile. Ils sont principalement retrouvés dans l'ambre plutôt que dans les formations sédimentaires conventionnelles. Cette rareté s'explique par la fragilité de ces petits arthropodes et les conditions particulières nécessaires à leur fossilisation. Paradoxalement, les meilleurs dépôts d'ambre contenant des collemboles datent du Crétacé inférieur (notamment en Birmanie et au Canada), de l'Éocène inférieur du Canada et d'Europe, et du Miocène d'Amérique centrale.

Le phénomène le plus marquant concerne la persistance des genres : tous les spécimens de collemboles du Crétacé appartiennent à des genres éteints, alors qu'aucun des spécimens provenant de l'Éocène ou du Miocène n'est attribué à des genres éteints. Cette transition suggère une amélioration significative de la survie des lignées à travers le temps géologique.

Une observation géographique particulière est que les espèces du Crétacé de Birmanie présentent des similitudes avec la faune moderne du Canada, plutôt qu'avec les espèces actuelles de leur région géographique, ce qui indique des déplacements ou des relations évolutives complexes à travers le temps et l'espace.

Cette persistance des genres modernes dans les spécimens plus récents pourrait refléter une meilleure adaptation des lignées évolutives aux conditions environnementales changeantes, ou simplement une amélioration des conditions de préservation et de fossilisation au fil du temps géologique.