3D skeletal pelvic landmarks from anthropoid primates

Objectives: The presence of sexual dimorphism in the birth canals of anthropoid primates is well-documented, and birth canal dimorphism tends to be especially robust among species that give birth to relatively large neonates. However, it is less clear whether birth canal dimorphism is accompanied by dimorphism in parts of the pelvis not directly under selection for birth, particularly including bi-iliac breadth, biactetabular breadth, lengths of the ischium and ilium, and 3D shape. This study investigates the patterns of dimorphism among anthropoid primates in those parts of the pelvis which do not directly contribute to the bony birth canal, here termed the non-obstetric pelvis.

Methods: 3D landmark data were collected on the bony pelves of 899 anthropoid primates. Specifically, landmark data were collected on parts of the pelvis not thought to be directly involved in selection for parturition, including portions of the posterior and superior ilium, acetabulum, and lateral ischium. principal components analysis and Euclidean distance matrix analysis were used to ascertain sexual dimorphism in pelvic sizes and shapes within each species.

Results: Results show that dimorphism in non-obstetric pelvic size and shape exists across anthropoids, just as is seen in the birth canal. However, the magnitude of dimorphism in non-obstetric pelvic shape tends to be greater among anthropoid species that give birth to relatively large neonates compared to those birthing smaller neonates relative to maternal pelvic size.

Conclusions: Though all anthropoids included in the study show some degree of sexual dimorphism in non-obstetric pelvic size and/or shape, species which give birth to large neonates relative to maternal pelvic size have the highest levels of dimorphism in pelvic shape. Moreover, the magnitude of dimorphism in certain parts of the non-obstetric pelvis mirrors patterns seen in the birth canal. The results of this study are promising for ascertaining pelvic dimorphism and relative neonate size in fossil primates, particularly in fragmentary remains which do not preserve a complete bony birth canal.

Methods
The 3D coordinates in this dataset were collected using a Microscribe MX 3D Digitizer. The dataset included here are the raw landmark data for each specimen. Skeletal pelves were articulated using putty and rubber bands, and the following landmarks were collected:  

Landmark # 
Landmark Title
Description

1
L PIIS
Left Posterior Inferior Iliac Spine

2
L PSIS
Left Posterior Superior Iliac Spine

3
L sup iliac crest
Left superior-most point on iliac crest

4
L ASIS
Left Anterior Superior Iliac Spine

5
L lat SI joint
Left lateral-most point on SI joint

6
L arcuate SI ilium
Left intersection of arcuate line & SI joint

7
L lateral arcuate line
Left lateral-most point on arcuate line

8
L ant iliac neck
Left narrowest point along the anterior iliac neck

9
L dors iliac neck
Left narrowest point along the posterior iliac neck

10
L pubis arcuate line
Left intersection of pubis & ilium on arcuate line

11
L pub acetabulum
Left intersection of pubis & ilium on acetabular rim

12
L sup acetab
Left superior-most point on acetabular rim

13
L dorsal acetab
Left dorsal-most point on acetabular rim

14
L caudal acetab
Left caudal-most point on acetabular rim

15
L acetab center
Left center of acetabular fossa

16
L dorsal acetab isch
Left intersection of ilium and ischium posterior to acetabulum

17
L ischial spine
Left ischial spine along medial-most point

18
L post ishial ramus
Left narrowest point along the posterior ischial ramus

19
L post tuberosity
Left posterior-most point along ischial tuberosity

20
L ant tuberosity
Left anterior-most point along ischial tuberosity

21
L lat ischial ramus
Left lateral point along deepest curve of ischial ramus

22
L obt ischial ramus
Left inferior-most point along ischiopubic ramus

23
inf pub symphysis
Midline Inferior-most point on pubic symphysis

24
sup pub symphysis
Midline superior-most point on pubic symphysis

25
dorsal S1
Midline dorsal point on S1 vertebral body

26
ventral S1
Midline ventral point on S1 vertebral body

27
left S1
Left lateral-most point on S1 vertebral body

28
left sup ala
Left lateral-most point on superior sacral ala

29
inf S1
Midline junction of S1-S2

30
inf S2
Midline junction of S2-S3

31
inf Sacrum
Midline inferior-most point on sacrum

32
right S1
Right lateral-most point on S1 vertebral body

33
right sup ala
Right lateral-most point on superior sacral ala

34
R PIIS
Right Posterior Inferior Iliac Spine

35
R PSIS
Right Posterior Superior Iliac Spine

36
R sup iliac crest
Right superior-most point on iliac crest

37
R ASIS
Right Anterior Superior Iliac Spine

38
R lat SI joint
Right lateral-most point on SI joint

39
R lateral arcuate line
Right lateral-most point on arcuate line

40
R ant iliac neck
Right narrowest point along the anterior iliac neck

41
R dorsal iliac neck
Right narrowest point along the posterior iliac neck

42
R pubis arcuate line
Right intersection of pubis & ilium on arcuate line

43
R pub acetab
Right intersection of pubis & ilium on acetabular rim

44
R sup acetab
Right superior-most point on acetabular rim

45
R dorsal acetab
Right dorsal-most point on acetabular rim

46
R caudal acetab
Right caudal-most point on acetabular rim

47
R acetab center
Right center of acetabular fossa

48
R dorsal acetab isch
Right intersection of ilium and ischium posterior to acetabulum

49
R ischial spine
Right ischial spine along medial-most point

50
R post ishial ramus
Right narrowest point along the posterior ischial ramus

51
R post tuberosity
Right posterior-most point along ischial tuberosity

52
R ant tuberosity
Right anterior-most point along ischial tuberosity

53
R lat ischial ramus
Right lateral point along deepest curve of ischial ramus

54
R obt ischial ramus
Right inferior-most point along ischiopubic ramus

The following link is a figure depicting the location of each landmark collection location (only the left side is shown for bilaterally collected landmarks):

https://docs.google.com/document/d/1CJvDDgeio2lVgV32lewatqEBzdR6SIrGD01tIdu1_-4/edit?usp=sharing