Module 8: Determination Of Minimum Number Of Individuals Flashcards
Minimum number of individuals (MNI)
Minimum estimate of individuals that contributed to sample/species within sample
Interpreting population size from skeletal assemblage
Provides estimate of present individuals
Could increase charges/punishment
Each individual needs case #
Complete separation of individuals may not be possible
Calculating MNI
Age, sex, size, context must be determined
MOST animals are symmetrical, these methods rely on this assumption
Several methods
Only elements with genus/species should be used-can use family if species missing
—other elements could cause inflated number for particular group if some elements misidentified
2 critical components to determine quantification:
- Bone taphonomy
- Scale/number of individuals potentially present
Extremely fragmentary/poorly preserved remains may not be amenable.
MNI and Taphonomy
Taphonomy can affect calculations: disarticulations, movement, destruction
Recovery techniques can impact # recovered elements-select well-surviving elements (femur, tibia, humerus)
Common MNI Method
Sorting bones by side, element, and development (juvenile/adult)
Based on element w largest number/most repeated (ex: 10 L femurs, 12 R femurs)
Sort all fragments by element and side, anatomical position, rearticulate, count # repeated, non-overlapping segments (every fragment much share specific landmark)
Avoid counting same individual twice
Makes assumption R and L elements pair even though may not
MNI in snakes
Count vertebra then divide by vertebra in reference specimen-not always accurate (# vertebra varies) and caudal vertebra often lost in field recovery situations
Suggested to count total vertebra, then MNI of 1 listed
Visual Pair-matching
Comparison of antimeres (left-right) of same element based on morphological features
Need good preservation
Should be sorted by element, side, size
Grouping by age criteria also helpful
Matching 2 sides to create individual attempted
Based on element w greatest # pair matches
Matching of different elements (like femur/tibia) based on morphology not rec’d due to subjective nature of procedure
Matching of different elements may be poss. In cases w few individuals w evidence marked skeletal variation
Articulation
Based on > # rearticulated elements
Articulation-bone forms congruent joint/broken elements form consistent juncture; can provide acceptable means for re-associating remains
Poor articulation-basis for separation of remains
Reliable, but strength of association varies depending on element; problems arise from lack of close fit sometimes
Some joints not as conducive-loose articulation (knee/shoulder), others stronger (elbow/vertebra)
May be possible to group a portion of skeleton based on this
Not advised for fragmented remains/missing/damaged articular surfaces
Standard MNI method/visual pair-matching applied after
Process of elimination
Most effective after articulation and pair-matching completed
Duplicated elements remaining then associated w specific individual
Useful in small-scale commingling, but problematic the higher the # of individuals
Osteometric comparison
Uses statistical models to compare size/shape b/w elements; removes subjective judgement, solid statistical basis for segregation, used to differentiate b/w individuals in remains not separated through other methods
Used in fragmentary cases-extensive cortical erosion can impact accuracy
Can recognize inconsistent relationships->exclusionary sorting
Most instances not effective in individuals w same body size/build
Effective in humans, more research for non-humans needed
Taphonomy
Similarites/differences in preservation-not primary sorting technique
Can be v individualizing-ex: rust stain on adjacent bones
Also can be taphonomic differences in same individual-CAUTIOn
GMT/LI/MLNI
MNI-ease of calculation
Grand Minimum Total (GMT)
Lincoln Index (LI)
Most Likely Number of Individuals (MLNI)
LI and MLNI ^ stat accuracy potentially-allow for confidence interval
All methods require pair-matching
Lincoln Index (LI)
Originally developed for determination of # living individuals base on capture/recapture technique, modified for skeletal use
GMT Calculation
Single element: R+L-P
L=total left
R=total right
P=total pairs
LI and MLNI
To estimate total # individuals in original population, not minimum or # recovered
Based on # paired and unpaired bones
Preservation must be good-critical elements can be accurately pair-matched
Errors in pair-matching-very misleading estimates
LI tends to have increased bias in smaller samples-rec’d MLNI used-to remove bias from estimate
Single element LI=(LxR)/P; no pairs: LI=(L+1)(R+1)
Single element MLNI=[(L+1)(R+1)/(P+1]-1
