[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Some Comments RE: Confuciusornis gender identification



The Data:

A specimen referred to *Confuciusornis sanctus* (which isn't debated) is 
histologically sampled at several long bone regions and found to have medullary 
bone deposits in the medullary cavites of these long bones. The specimen is 
further preserved without elongated "ribbon-like" retrices. 

The Assumptions: It is broadly assumed that *Confuciusornis sanctus* is 
sexually 
dimorphic, on the basis of specimens of the bird having either a pair of
 elongated, "ribbon-like" retrices or not. This is presumed to relate to
 male display feathers. It is further assumed that males retain these feathers 
regardless of breeding period, and thus that the feathers may also be useful 
for factors other than mating display; absence of these in females suggest lack 
of a species-recognition function. Indeed, scatterplots of limb-bone length to 
preservation of these retrices suggest that a relatively even distribution of 
presence or absence confirms a balance of male to female specimens, although 
this is not a rigorous chart. It is further assumed that medullary bone only 
occurs in female animals, as it becomes deposited only in female bones 
preparatory to ovulation and in birds is used to produce calcium for eggs. 
Thus, that the presence of medullary bone is a female-only feature.

The Premise:

The specimen, DNHM-D1874, is referred to as a female *Confuciusornis sanctus* 
due to the presence of medullary bone, but additionally lacks preservation of 
tail feathers. Thus, that lack of elongated tail feathers is a female trait, 
substantiating prior assumptions.

The Problem:

Note where "as preserved" is given: Sampling of specimens -- and we're told 
elsewhere there are hundreds of these -- is less than 60 specimens total, 
ranging through size based on femoral length. Other studies have attempted to 
substantiate the presence of tail feathers in this form as indicative of male 
animals, however the problem here lies in that much of this argument is 
predicated on the nature of preservation itself. Other studies are rightfully 
cautious about assumption of absence of tail feathers for sexing the specimens, 
especially as this may be taphonomic. Even with fully developed wing feathers, 
specimens presumed female may lack any indications of retrices, long or 
otherwise, but present a faint "halo." Specimens with long retrices appear to 
have less than distinct attachment, indicating problems with where to look 
precisely for presence of tail feathers. And we can further presume that the 
birds moult: Would they moult one feather at a time, or all at once, as in 
peafowl or lyrebirds, etc.?

The discovery of medullary bone does help lock this specimen down to sex, but 
it leaves vague the issue of preservation factors of the retrices: Should we 
assume that the preservation as we see it is accurate, and good? I have my 
doubts about the rigor of that particular part of the analysis, but little else.

Cheers,

  Jaime A. Headden
  The Bite Stuff (site v2)
  http://qilong.wordpress.com/

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)


"Ever since man first left his cave and met a stranger with a
different language and a new way of looking at things, the human race
has had a dream: to kill him, so we don't have to learn his language or
his new way of looking at things." --- Zapp Brannigan (Beast With a Billion 
Backs)


----------------------------------------
> Date: Tue, 22 Jan 2013 09:58:49 -0800
> From: bcreisler@gmail.com
> To: dinosaur@usc.edu
> Subject: Confuciusornis gender identification
>
> From: Ben Creisler
> bcreisler@gmail.com
>
> Also in Nature Communications:
>
> Anusuya Chinsamy, Luis M. Chiappe, Jesús Marugán-Lobón, Gao Chunling &
> Zhang Fengjiao (2013)
> Gender identification of the Mesozoic bird Confuciusornis sanctus.
> Nature Communications 4, Article number: 1381
> doi:10.1038/ncomms2377
> http://www.nature.com/ncomms/journal/v4/n1/full/ncomms2377.html
>
>
>
>
> Hundreds of specimens of the beaked bird Confuciusornis sanctus have
> been recovered from Early Cretaceous lake deposits of northeastern
> China. These birds show remarkable variation in size and plumage, with
> some displaying two long, central ornamental rectrices (tail feathers)
> and others lacking them altogether. Although, traditionally specimens
> with ornamental rectrices were interpreted as males and those without
> them as females, this supposed sexual dimorphism has remained
> unconfirmed. Here we report on the discovery of medullary bone, a
> tissue unique to reproductively active female birds, in a specimen of
> C. sanctus (DNHM-D1874) lacking these feathers. Our discovery
> constitutes the first case of gender identification in a Mesozoic
> bird, and it provides undisputed evidence that individuals of C.
> sanctus without ornamental rectrices are females. By permitting gender
> identification in C. sanctus, our results provide insight into the
> onset of sexual maturity and attainment of adult body size of this and
> other early birds.
>
>
> See this as well:
>
> http://phys.org/news/2013-01-sex-early-birds-dinosaur-reproductive.html