Body size, dental pathology and maternal genetic diversity of ancient horses in the eastern Baltic Sea region and western Russia

This study investigates the body size, dental pathology, and maternal genetic diversity of ancient horses in the eastern Baltic and western Russia, revealing that wild populations were pony-sized, the earliest domestic horses in Lithuania date to 799–570 cal BCE with confirmed bit wear, and high mitochondrial DNA diversity indicates multiple maternal lineages.

The Gist

Imagine a massive, global family reunion for horses, but instead of gathering in a park, the family members are scattered across time and space—from the wild steppes of ancient Russia to the forests of Lithuania and Finland. This paper is like a detective story where scientists act as time-traveling investigators, piecing together the lives of these ancient horses using three main clues: how big they were, what was wrong with their teeth, and their family DNA.

Here is the story of what they found, told in simple terms:

1. The "Goldilocks" Size of Ancient Horses

Scientists wanted to know: How big were these horses, and could they carry a human rider?

• The Wild Giants: They looked at wild horses from a site in Russia called Ivanovskaya, dating back about 8,000 years. Think of these horses as the "grandparents" of the modern domestic horse. They were surprisingly sturdy, standing about 141 cm (4'7") tall at the shoulder and weighing around 410 kg (900 lbs). They were like the "large SUVs" of the ancient world—big enough to provide plenty of meat for hunters.
• The Tiny Wild Horse: Then, they found one lone wild horse in Lithuania. This one was much smaller, weighing only about 270 kg (600 lbs). It was like finding a miniature pony in a herd of full-sized horses. This suggests that even wild horses varied greatly in size depending on where they lived.
• The "Pony" Era: When they looked at the horses that humans actually started riding in Lithuania (from about 1,000 BCE to 1,400 CE), they discovered something surprising: they were tiny. Most were pony-sized, averaging about 125 cm (4'1") tall.
  • The Analogy: Imagine trying to ride a horse that is the size of a large dog or a very small pony. Despite their small stature, the scientists calculated that these "ponies" were strong enough to carry an average adult man (about 75–80 kg) along with their gear. They were the "compact cars" of the medieval world: small, efficient, but definitely capable of doing the job.

2. Dental Detectives: Teeth Tell Tales

Teeth are like the "black boxes" of a horse's life. They show us how the animal was treated and what it suffered.

• The "Bit" Evidence: One tooth from a Lithuanian horse (dated to around 800–500 BCE) had a specific type of wear on it. It looked like a vertical strip of wear on the side of the tooth. This is the "smoking gun" of a bit. Just as a human's teeth might show wear from grinding or a specific habit, this horse's tooth showed it had a metal or leather bit in its mouth for a long time. This confirmed that this was a domesticated horse being ridden or driven, making it the oldest known domestic horse in Lithuania.
• The "Toothache" Case: Another horse had a very painful condition called EOTRH. Imagine a tooth that is constantly being eaten away by the body while simultaneously growing too much bone around it. It's like a toothache that never goes away and gets worse over time. This horse was likely old and suffering, showing us that ancient vets (or at least ancient horse owners) had to deal with dental pain just like we do today.

3. The Genetic Family Tree

Finally, the scientists looked at the horses' mitochondrial DNA (mtDNA). Think of mtDNA as the maternal family name passed down from mother to daughter, unchanged for thousands of years.

• A Diverse Crowd: They expected to find that all domestic horses came from one specific "mother" lineage. Instead, they found a huge mix. The ancient horses belonged to many different genetic families (haplogroups).
• The "Common Thread": While most families were unique, one specific genetic family (Haplogroup B) appeared in wild horses in Russia, ancient horses in Lithuania, and horses in Finland. It was like finding the same last name in three different countries, suggesting that this specific maternal line was very widespread and successful across Europe long before horses were fully domesticated.
• The Mystery: They couldn't find DNA in the oldest Lithuanian wild horses (perhaps they were too old or the DNA was destroyed), but the ones they did get DNA from showed that nature had a lot of variety before humans started breeding them for specific traits.

The Big Picture

This paper tells us that the history of horses in Northern Europe wasn't a straight line from "wild giant" to "domestic giant."

1. Wild horses were big and varied.
2. When humans first started using horses in this region, they were small ponies, not the massive warhorses of later medieval legends.
3. These small ponies were tough enough to carry riders and were already being "bridled" (given bits) by 800 BCE.
4. The genetic diversity was high, meaning humans didn't just pick one type of horse to tame; they likely tamed many different local families of horses.

In short, the ancient horses of the Baltic region were the underdogs of the horse world: small, diverse, and resilient, carrying the weight of history on their small, sturdy backs.

Technical Summary

1. Problem Statement

The evolutionary history of the modern domestic horse (Equus caballus, DOM2 lineage) is well-documented, originating in the Pontic-Caspian steppe (~2700 BCE). However, significant gaps remain regarding:

• The timeline and nature of horse introduction into Northern Europe (Fennoscandia and the Baltic states).
• The body size and weight of wild horse populations in the eastern Baltic and western Russia, and how they compare to early domestic horses.
• Differentiation between wild and domestic horses in archaeological contexts where morphological distinction is difficult.
• The utilization of horses (e.g., riding, burden carrying) and their health status in these regions prior to and during the early medieval periods.
• Maternal genetic diversity and lineage continuity in these specific geographic regions.

2. Methodology

The study employed a multidisciplinary approach combining osteometry, veterinary pathology, and ancient DNA (aDNA) analysis on 59 archaeological samples (bones and teeth) from Lithuania, Finland, Russia, and Estonia.

• Body Size Estimation:

  • Samples: 25 wild horses from the Ivanovskaya site (Russia, 5900–3800 BCE), 2 phalanges from a Late Bronze Age Lithuanian site (Mineikiškės), and 43 domestic horse metapodials from Lithuania spanning the Pre-Viking Iron Age, Viking Age, and Medieval periods.
  • Technique: The authors used updated regression equations to estimate withers height, croup height, and body mass. Unlike previous studies using May (1985), they applied equations that account for limb segment proportions.
  • Rider Weight: Maximum rider weights (including gear) were estimated for Lithuanian domestic horses and compared to contemporaneous human skeletal data.
  • Comparative Analysis: Ivanovskaya wild horse sizes were compared against Eneolithic horses from Deriivka (Ukraine), Botai, and Tersek (Kazakhstan).

• Pathological Analysis:

  • Dental remains were examined by equine veterinarians to identify signs of bridling (bit wear) and disease.
  • Specific focus was placed on identifying Equine Odontoclastic Tooth Resorption and Hypercementosis (EOTRH).

• Ancient DNA (aDNA) Analysis:

  • Extraction: DNA was extracted from 59 samples in a dedicated clean-room facility.
  • Amplification: A 572–573 bp fragment of the mitochondrial control region was amplified using overlapping primer sets.
  • Sequencing & Analysis: Sequences were aligned with modern and ancient reference datasets (Achilli et al., 2012). Haplotype networks (median-joining and temporal statistical parsimony) and maximum likelihood phylogenetic trees were constructed to assess maternal lineages and diversity.
  • Genetic Diversity Metrics: Haplotype diversity ($h$) and nucleotide diversity ($\pi$) were calculated for Lithuania, Finland, and the Middle Volga region.

3. Key Contributions

• Updated Morphometric Data: Provided the first body size estimates for wild horses from the Ivanovskaya site (Pontic-Caspian steppe) and re-evaluated Lithuanian horse sizes using modern, more accurate equations.
• Confirmation of Domestication: Identified the oldest confirmed domestic horse in Lithuania (and the eastern Baltic) based on definitive bit wear, dating to 799–570 cal BCE.
• Pathological Discovery: Reported the first ancient case of EOTRH in a horse from the region, indicating advanced age and specific dental health issues.
• Genetic Baseline: Established a baseline of maternal genetic diversity for ancient horses in the eastern Baltic and western Russia, identifying 11 distinct haplogroups.

4. Key Results

A. Body Size and Weight

• Ivanovskaya Wild Horses: Averaged 141.3–141.5 cm at the withers and 410.3 kg in body mass. They were intermediate in size between earlier and later Eurasian steppe horses.
• Lithuanian Wild Horse: A single specimen (Šventoji 43, 4000 BCE) weighed only **265 kg**, significantly smaller than the Russian wild horses, suggesting regional size variation or population decline.
• Lithuanian Domestic Horses: Consistently pony-sized.
  • Pre-Viking (100–700 CE): ~127.4 cm withers, ~306 kg.
  • Viking (800–1100 CE): ~124.5 cm withers, ~276 kg.
  • Medieval (1200–1400 CE): ~125.0 cm withers, ~270 kg.
  • Rider Capacity: These horses could carry riders and gear weighing 80–92 kg, sufficient for average contemporary Lithuanian males (approx. 75–77 kg), though some individuals could carry heavier loads.

B. Pathologies

• Bit Wear: Confirmed on a lower P2 tooth from a Lithuanian horse dated to 799–570 cal BCE. This is the oldest evidence of bridling in the Baltic region, confirming the presence of domestic horses by the Late Bronze Age.
• EOTRH: A tooth from a Lithuanian horse (18–201 CE) showed signs of Equine Odontoclastic Tooth Resorption and Hypercementosis, a condition typically affecting older horses (>15 years), indicating the animal survived to an advanced age.

C. Genetic Diversity

• Success Rate: 58% of samples yielded amplifiable DNA; 26 samples provided full sequences for analysis.
• Haplogroups: 11 of the 18 known haplogroups (Achilli et al., 2012) were identified. Missing were A, E, F, H, J, K, and R.
• Distribution:
  • Haplogroup B was the only lineage shared across all three geographic regions (Lithuania, Finland, Middle Volga) and temporal periods, suggesting it was widespread in ancient Northeastern Europe.
  • The oldest Russian wild horse (Ivanovskaya, ~6700 BCE) belonged to Haplogroup B.
  • The oldest Lithuanian wild horses yielded no DNA.
• Diversity: High haplotype and nucleotide diversity were observed, with few shared haplotypes between individuals, supporting the theory of multiple maternal origins or extensive introgression from wild populations.

5. Significance

• Chronology of Domestication: The study pushes back the confirmed arrival of domestic horses in Lithuania to the Late Bronze Age (~800 BCE), providing a concrete archaeological marker (bit wear) for the region.
• Ecological Insights: The size disparity between the large Russian wild horses and the small Lithuanian wild horse suggests that wild horse populations in the Baltic may have been smaller or under different environmental pressures than their steppe counterparts.
• Human-Animal Interaction: The confirmation of bit wear and the calculation of rider weights demonstrate that these small ponies were actively used for riding and transport by average-sized humans, challenging assumptions that only larger horses were ridden.
• Genetic Continuity: The presence of Haplogroup B in both ancient wild horses and later domestic populations suggests this lineage was prevalent in the region before and after domestication, complicating simple "wild vs. domestic" genetic distinctions but highlighting the complexity of horse population dynamics in Northern Europe.
• Methodological Advancement: The use of updated size estimation equations provides a more accurate picture of ancient horse morphology than previous studies relying on older models.