Embryonic Stages

Since we do not know the exact age (in days) of an embryo, we followed the common practice in embryology to divide the entire developmental history of an embryo/fetus into stages. Stage 1 is the earliest stage (soon after fertilization), and higher stages reflect older and larger embryos. At the last stage the fetus is basically a miniature of the newborn dolphin. Stages are differentiated based on external and internal features of the embryo. We use the stages as the organizational principle behind the DLDD.

Generally, developmental stages in mammals are compared to the stages of human development, so called Carnegie Stages. The Carnegie Stages are described in detail by O'Rahilly and Muller (1987) and additional information is presented by Butler and Juurlink (1987). An excellent website describing human and comparative mammalian development as well as the staging process was compiled by Dr. Mark Hill (http://anatomy.med.unsw.edu.au/cbl/embryo/OtherEmb/Cstages.htm). We used the Carnegie system as the staging system for our dolphin embryos. The best overview of development in Stenella attenuata was published by Šterba et al., (2000). However, these authors, did not use the Carnegie system in their work.

Below is a table of embryos available in our collection, staged using the Carnegie system. TL is Total Length, and CRL is Crown-Rump Length.

Stage Main Characteristic Embryo TL CRL
Carnegie
9		 neural folds fusing
Carnegie 9 		LACM 94633 5.8  
Carnegie
10		 neural folds fusing
Carnegie 10 		LACM 94730   3.9
Carnegie
11		 two branchial arches
Carnegie 11 		LACM 94741   4.1
LACM 94674   4.7
Carnegie
12		 otic pit, fore/hindlimbbuds

Carnegie 12		 LACM 94789   3.3
LACM 94767   5.5
Carnegie
13		 lens placode, C-shape
Carnegie 13		 LACM 94733   5.4
LACM 94657   6
LACM 94815   6.2
LACM 94628   6.7
LACM 94735   6.5
LACM 94619   8.6
Carnegie
14		 handplate formed
Carnegie 14		 LACM 94617   7.8
LACM 94701   8.5
LACM 94594   8
Stage Main Characteristic Embryo TL CRL
Carnegie
15		 handplate formed
Carnegie 15		 LACM 94706   8
LACM 94746   9.6
LACM 94613   8.8
Carnegie
16		 eye pigmented
Carnegie 16		 LACM 94651   11
LACM 94770   12.6
LACM 94784   15.8
Carnegie
17		 digital rays
Carnegie 17 		LACM 94715   17.9
LACM 94670   17.5
LACM 94650   23.5
Carnegie
18		 eyelids forming
Carnegie 18		 LACM 94634   21.9
Carnegie
19
Carnegie 19		 LACM 94817 62  
Fetus
Fetus 		LACM 94683 86  
LACM 94679 97  
LACM 94671 95  
LACM 94646 114  
LACM 94592 160  

Reference:
Butler, H., and B. H. J. Juurlink, 1987. An atlas for staging mammalian and chick embryos. CRC Press Inc.
O'Rahilly, R., and F. Muller, 1987. Developmental stages in human embryos. Carnegie Institution of Washington, Publication 637.
Šterba, O., M. Klima, B. Schildger. 2000. Embryology of dolphins: stageing and ageing of embryos and fetuses of some cetaceans. Advances in Anatomy, Embryology, and Cell Biology 157:1-133.