Video summary

Solving One of the Oldest Problems in Paleontology

Main summary

Key takeaways

Science and Nature

Scientific Concepts, Discoveries, and Nature Phenomena Mentioned

Dinosaur Evidence & Paleobiology

  • Egg-associated dinosaur fossils suggest that some dinosaurs:
    • were good parents
    • sometimes died while protecting young
  • Feathered dinosaurs (notably from China):
    • fossils preserve feather structures
    • electron microscopy is used to study feather microstructure
    • fossilized pigment cells can be used to infer color in some dinosaurs

Open Questions in Dinosaur Research

  • What dinosaurs sounded like (generally unknowable from fossils)
  • How dinosaur groups are related (phylogenetic placement uncertainties), including tensions involving:
    • megaraptorans
    • troodontids

The “Ontogeny Problem” in Paleontology

  • Ontogeny is defined as an organism’s development from embryonic stage through lifespan, not merely size growth.
  • Why it’s a problem:
    • Juveniles look different from adults, risking incorrect species assignments.
    • Future paleontologists may:
      • mistake different growth stages as separate species, or
      • lump distinct species together as “just juveniles/adults.”

Species Concept and Classification Stakes

  • A species is treated as a population with shared traits/behaviors, reproductive compatibility, and an independently evolving lineage.
  • Correct genus/species naming matters for evolutionary biology.

Historical Development of the Ontogeny Debate (Juvenile vs. Adult Species)

  • Early baby dinosaur discoveries highlighted that growth stages can resemble different “species.”
  • Over time, paleontologists increasingly suggested that many named dinosaurs were:
    • invalid species, actually representing growth stages of others.

Examples of Proposed Extreme Ontogenetic Changes

  • Crests/frills/horns changing through growth in duck-billed and horned dinosaurs
  • Triceratops vs. Torosaurus debates framed around ontogenetic variation (including “Torosaurus-type” claims)
  • Pachycephalosaurus dome and horn changes
  • T. rex tooth and skull feature changes proposed to be age-related

Counterpoint: Some scientists argued there was too much “splitting” (naming variants too readily), but disagreements were still intense.

Two Kinds of Classification Mistakes

  • False positives: treating specimens as different species when they are the same
  • False negatives: lumping specimens into one species when they are actually different

Example (False Positives)

  • C. Hart Merriam splitting North American brown bears into 86 species, later argued to be incorrect.

Methods for Testing Whether Fossils Belong to the Same Species (and Their Limitations)

1) Osteohistology

  • Method
    • Cut thin sections of fossil bone.
    • Use a microscope to examine bone microstructure.
    • Count cyclical growth markers (growth marks) to estimate:
      • growth rate
      • age at death
  • Key claim/limitation
    • Can often determine juvenile vs. adult
    • But generally cannot identify which species a juvenile belongs to.

Examples Mentioned

  • Dracorex and Stygimoloch argued as juvenile stages of Pachycephalosaurus (based on growth-rate differences).
  • Nanotyrannus (“Jane/Petey”) paper:
    • osteohistology interpreted as evidence they were still growing (juveniles of T. rex)
    • criticized as not disproving alternative juvenile identities.
  • Triceratops vs. Torosaurus:
    • osteohistology suggested differences consistent with age-related variation (or the reverse)
    • later discovery of Torosaurus juveniles used to challenge earlier conclusions.

2) Morphometrics (Shape Analysis)

  • Linear morphometrics
    • compares direct measurements between points on bones
    • example: Peter Dodson on Corythosaurus and Lambeosaurus (1970s)
  • Geometric morphometrics
    • places many landmarks on 3D shapes
    • uses multivariate statistics to compare shape variation

Workflow Elements Described

  • CT scan → digital skull models
  • landmark digitization (54 homologous landmarks)
  • Generalized Procrustes superimposition (align/scale/rotate)
  • compute variation with Principal Components Analysis (PCA)

Empirical Test Described

  • CT scanning 57 crocodilian skulls:
    • 43 American alligators
    • 13 Chinese alligators
    • 1 spectacled caiman
  • Result:
    • the two alligator species differ along a PCA axis
    • but species boundaries are not distinct enough for confident separation; overlap is large.

Conclusion / Limitation

  • Geometric morphometrics can show structured differences, but often does not cleanly separate species, especially with ontogenetic variation.

3) Cladistic Analysis of Ontogeny (“Cladistic Ontogeny” / “Ontograms”)

  • Core idea
    • Score which skeletal features appear in predictable order during growth.
    • Build a tree of growth stages (ontogenetic trajectory).
    • Originally intended for developmental staging.

Origin/Credit

  • Method attributed to Christopher Brochu (for crocodilian maturity staging).

Use to Test Taxonomy

  • Claims: ontogenetic trees can indicate whether specimens fall into:
    • separate growth-series patterns (two species), or
    • a single growth series (one species)

Named Examples

  • Nick Longrich & Dan Field
    • Torosaurus scattered through Triceratops growth series → Torosaurus not just fully mature Triceratops
  • Amelia Zietlow (2020)
    • expectations for ontograms under multiple species or strong sexual dimorphism
    • discussion of patterns (splitting along the series vs. branch-specific derived traits)

Major Limitations Argued

  • Requires an outgroup/artificial embryo to polarize ancestral vs. derived character states.
  • For fossils, “immature state” is unknown; artificial embryo can become a composite of the smallest specimens, potentially belonging to different species, contaminating the ontogeny matrix.
  • Predictions may not uniquely test taxonomic hypotheses because multiple topologies may fit the same qualitative expectation.
  • If only one specimen exists of a third species, the method can’t form a recognizable group for it (the algorithm still must place every specimen somewhere).

Bottom line: the video argues cladistic ontogeny is not suitable for reliably testing taxonomic hypotheses.

The Proposed “General Solution” Using Ontogenetically Invariant Traits

Core Discovery / Argument

After comparing the methods, the presenter argues that:

  • reliable species ID may come from traits that do not change during ontogeny (ontogenetically invariant traits).

Key Observation (Modern Animals)

  • In American vs. Chinese alligators, many traits remain unchanged across growth stages and can identify species even in hatchlings.

Invariant Trait Categories (As Described)

  • Foramina (for nerves/blood vessels)
  • Head sinus system / pneumatic openings
  • Cranial bone articulation patterns
  • Tooth counts (with limited intra-species variability)

Example: Invariant Cranial Traits (Alligators)

The described invariant features include:

  • Subnarial foramen presence/absence position relative to skull bones
  • differences in maxillary sinus recesses and whether they communicate
  • neurovascular pathway placement (e.g., position of neurovascular foramen)
  • prefrontal bone geometry differences
  • direction and presence/location of specific foramina on skull bones
  • ectopterygoid extent/shape differences
  • foramen aerium and presence of additional foramina
  • palatine bone foramina presence
  • details of vomer shape/steps and internal sinuses

The video claims each invariant trait provides near-certain species identification.

Developmental Mechanism Proposed

The invariance is attributed to developmental timing:

  • these traits arise very early in embryogenesis
  • before skull bones form
  • later skull morphology develops “around” early-established vascular/nerve/sinus/tissue patterns

Broader implication:

  • because all amniotes share early developmental constraints, the approach may apply to:
    • mammals
    • reptiles
    • birds
    • and likely many vertebrates

Connection to Dinosaur Taxonomy (Nanotyrannus)

  • The presenter argues Nanotyrannus has characteristics matching traits predicted to be ontogenetically invariant.
  • Claimed support:
    • a specimen called “Dueling Dinosaurs” had independent evidence of maturity (i.e., not a juvenile T. rex), supporting the invariant-trait approach.

The presenter proposes a general framework to solve the ontogeny problem, rather than relying only on isolated case debates.

Named Researchers / Sources Featured (As Stated in the Subtitles)

  • Anatoly Rozhdestvensky (1965)
  • Peter Dodson (1975)
  • C. Hart Merriam (historical taxonomy example)
  • Steve Gatesy
  • Christine Janis
  • Jack Horner (Triceratops/Torosaurus discussion)
  • Jane and Petey (Nanotyrannus specimens; referenced by names)
  • Mark Norell
  • John Flynn
  • Manjin (listed; first name not fully specified in subtitles)
  • William Harcourt Smith
  • Melanie Hopkins
  • Alan Turner
  • Christopher Brochu
  • Nick Longrich
  • Dan Field
  • Amelia Zietlow (2020)
  • Woodward et al. (2020 paper referenced)
  • Carr (growth/ontogram analysis referenced; year not explicitly confirmed beyond “Carr’s 2020 study”)
  • Benjam[in] Seepser and additional “Skeleton Crew” patrons listed in closing credits:
    • Christopher Bellis Jones
    • Johnson
    • Aaron Anderson
    • Adam Ollis
    • Blacklight Virus
    • Black Spectral Pig
    • Brett Booth
    • Changyuraptor
    • Freaky Owl
    • Freddy Harper
    • Jimothy
    • Keenan Taylors
    • Kit Tales of Chimaer
    • Kevin Preem
    • King Zashu
    • Lincoln Rivenbark
    • Long Dunk
    • Matthew Miller
    • Nacho Raptor
    • Nicholas Afanasev
    • R Wesley Nipper
    • Raylan
    • Rusty HBK
    • Squat Pump
    • The Wigster
    • Torus
    • Youve
    • Zaku Meister

Original video