Biogeography and Mass Extinction: Extirpation and re-invasion of <i>Normalograptus</i> species (Graptolithina) in the Late Ordovician Palaeotropics
Bibliographic record
Abstract
SUMMARY Normalograptids constitute a distinctive but not easily identified group of derived axonophorans. A new study of Normalograptus morphology indicates that many Late Ordovician taxa previously identified as Normalograptus are actually referable to Styracograptus and related climacograptoids. These re-identifications have led to the recognition of a complex biogeographic history among normalograptids and their descendants, including an interesting pattern that had previously been overlooked – a late Katian disappearance of Normalograptus from the palaeotropics. Normalograptid palaeogeographic distribution in the Ordovician appears to comprise 5 main phases: (1) evolutionary origin probably in relatively high palaeolatitudes in the early to mid Darriwilian; (2) spread to global distribution in later Darriwilian time; (3) retreat from most low palaeolatitude regions during the early Katian, with perhaps a slightly delayed retreat from Laurentia; (4) a complete extirpation from the low palaeolatitudes by the mid Katian (Ea4); (5) reinvasion of the low palaeolatitudes that accompanies the remarkable ecological and evolutionary replacement of the Diplograptina by species of Normalograptus and their descendants during the latest Katian–early Hirnantian. We propose two sets of hypotheses to explain Late Ordovician Normalograptus distribution. First, given the low species diversity of Normalograptus , we suggest as a null hypothesis that the disappearance of normalograptids from low palaeolatitudes during the late Sandbian and early Katian as simply a stochastic outcome – a small clade simply went extinct by chance alone. The alternative is that the loss of Normalograptus species reflects some form of extinction for cause, either: (1) competitive exclusion; or (2) an inability to adapt to changing environmental conditions. In the case of the competitive exclusion hypothesis, the most likely competitors are species of the Diplograptina.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".