The Osmoregulation of ​P.antiquus
​ , Modeled After a Marine
Bird
First Author: Franceska Barron
Second Author: Desiree Abney
14 December 2016
Abstract:
Pterodactylus
​ antiquus, was a pterosaur that lived 200 million years ago during the
Jurassic era, it was also the first vertebrate species found capable of powered flight
(Monastersky, 2001).​ ​P. antiquus was a predator hunter whose diet mostly consisted of fish,
which have a very high water content. Although some marine birds have salt secreting glands to
expel the excess salt that they consume while drinking water, it has been found that marine birds
that consume fresh fish can thrive without drinking water at all; therefore we modeled its
osmoregulation system in order to determine
​
if ​P. antiquus could survive by only eating fish and
not drinking water. It was found that in the absence of water, the pterodactyl was still gaining
145.25 ml of water per day, which is attributed to the large amount of water present in their diet
of fresh fish.
​
Introduction:
Pterosaurs were the first species, capable of powered flight (Monastersky, 2001). The
fossil of ​P. antiquus is dated back to the Jurassic period, 200 million years ago (Chatterjee,
2004). The Jurassic period in Germany was a time of flourishing reef communities (Tang,
2016). The pterodactyl was known to spend most of its time in coastal areas and hunted fish
(Chatterjee, 2004) similar to that of an Alaskan Cod or Anchovy (Barron and Abney, 2016).
Pterodactyls were active animals with hollow bones, allowing them to soar for many miles at a
time (Monastersky, 2001). Pterodactyls also had a specialized brain with an exaggerated
cerebellum, a critical feature for coordinated at flight (Monastersky, 2001). They had a mass of
1995.81 g and a 1.06 m wingspan (Abney and Barron, 2016). As pterodactyls lived near coastal
areas, they hunted for fish and had many avian-like anatomical features (Abney and Barron,
2016), we modeled our animal kidney system after a marine bird.
Kidneys play an important role in the internal regulation of salt and water balance
(Dantzler, 1988) as their main purpose is to filter, excrete and absorb water and waste products
(Sturkie, 1986). Birds share anatomical kidney features with mammals and reptiles (Eldon,
1998). In terrestrial animals such as: birds, reptiles, and mammals, the kidney’s main purpose is
excretion and is quite efficient (Nielsen, 1960). Like mammals, birds have few (~30%)
mammalian-like nephrons that have a loop of Henle however; they mostly have reptilian-like
nephrons (~70%) that do not contain a loop of Henle (Eldon, 1998). The transition from reptilian
nephrons to mammalian nephrons is gradual and consists of intermediate nephrons in between
that contain short loops of Henle (Dantzler, 1988) as seen in Figure 1. Birds and reptiles excrete
uric acid in response to nitrogenous waste and because it has low solubility in water, birds do not
have to drink much water in order to excrete this guano (Raven, 2013). Birds and mammals are
the only animals that have a loop of Henle, and thus a capacity for producing hypertonic urine
(Raven, 2013).
Figure 1: Zoomed in lobule from an avian kidney showing the different kinds of nephrons. Drawn
by Franceska Barron and Desiree Abney inspired by Sturkie 1976
In birds that do not possess salt secreting nasal glands, as we assume P. antiquus did not
have, urine goes into the cloaca from the ureters and by reverse peristalsis, it moves to the
rectum (Hill), seen in figure 2. Marine birds have to either avoid drinking sea water or possess
another way to excrete salt [ex: salt glands], other than through their kidneys (Nielsen, 1960).
Fish mostly make up the diet of a marine bird and it having a high water content, reduces the
need for the bird to excrete salt (Nielsen, 1960). Interestingly, it has been found that a diet of fish
is such a great water supply that it allows for them to not need to drink water at all (Nielsen,
1960). Therefore knowing the two different types of fish that ​P. antiquus usually fed on, the fish
with the least amount of water content was tested to see whether ​P. antiquus would be able to
effectively osmoregulate without drinking any water and solely survive on a diet of fish.
Figure 2: Internal view of the pathway the urine has to go through. Drawn by Desiree Abney
Methods:
In order to determine if ​P. antiquus could maintain water balance by only eating
anchovies and not drinking any water we first had to calculate how much water intake and loss
occurs. To calculate how much water intake ​P. antiquus gained from its diet its daily amount of
food intake, which was previously calculated to be 174.929 g/day (Barron and Abney, 2016),
was multiplied by the anchovies water content of 73% (USDA).
Not only did ​P. antiquus gain water from its food but also from its metabolic process of
breaking down food. To calculate the water gain from this process the daily required amount of
food consumed was multiplied by the percentage amount of each component. This value was
then multiplied by the amount of water found in each component: 0.40
0.56
g H2O
g carbs
g H2O
g protein
for protein and
for carbohydrates to get the the water gain. Both values were then added up to get the
net total gain.
To calculate how much water was excreted through urine the amount of protein
mol
assimilated (35.6 g ) was multiplied by the amount of moles found in uric acid ( 0.285
100 g ) to give
us a value in mmol. This was multiplied by the max concentration of urine that a duck can
produce which is 100 mmol/L to give us the final product in ml H​2​O.
Cutaneous evaporative water loss was assumed to be negligible (Abney and Barron,
2016). As the presence of indigestibles in the diet of P. antiquus was found to be negligible
(Abney and Barron, 2016), we assume that there is minimal water loss in the feces. As gular
fluttering was its main way of cooling (Abney and Barron, 2016, water lost from respiratory
pathways, respiratory evaporative water loss (REWL) which occurs when P. antiquus exhales
was based off previous calculations done before in Abney and Barron, 2016 but had to be
modified due to the change in mass.
REWL: (liters air/day)(x​exp​-x​insp​)
To find if P. antiquus was in water balance or required additional consumption of water,
indicated by a negative result the equation:
W​bal​ = (​∑​W​in​) - (​∑​W​out​)
where W​bal​ is the difference in the total sum of water in (W​in​) and water out (W​out​).
Results:
Although ​P. antiquus has ways of losing water: REWL, and through urine, these are
minimal, when compared to the water gain through its diet. As ​P. antiquus consumes such a
large amount of water by eating fish, 73.37% (table 1), it does not require the consumption of
water in order to supplement its diet therefore; ​P. antiquus is able to efficiently osmoregulate on
its diet alone, as shown by its 145.25 ml water gain.
Anchovy
Water
73.37%
Protein
20.35%
Carbohydrates
4.84%
Indigestibles
0
Table 1: The USDA nutrient composition of an anchovy
Calculations:
Water Gain From Food:
Amount of food consumed 174.929
174.929
g
day /
(.7337) = 128.34
g
day
ml H20
day
Water Gain From Metabolism:
g
Proteins: 174.929 day
(.2035) = 35.598
35.598
g
day (
0.40
(Barron and Abney, 2016)
g H2O
g protein
g
day
) = 14.24 ml H2O
g
g
Carbohydrates: 174.929 day
(.0484) = 8.466 day
g
8.466 day
(0.56
g H2O
g carbs
) = 4.74 ml H2O
Total: 14.24 ml H2O + 4.74 ml H2O = 18.98 ml H2O
Water excreted through urine:
Considering 35.6 g of protein is assimilated (Abney and Barron, 2016) and birds produce
0.285 mol uric acid per 100g of protein assimilated the equation:
0.285 mol / 100g (35.6 g assim protein) = 0.10146 mol = 101.5 mmol uric acid
Max concentration duck can produce is 100 mmol/L
100 mmol / L = 101.5 / x L H2O = 1.015 L = 1.15 ml H2O
REWL:
RMR: 15.51 kJ/hr (Abney & Barron, 2016)
(15.51 kJ/hr / 20 kJ/ LO2) =0.7755 LO2/hr
(0.7755 LO2/hr / 1L air/ .20 LO2) = 3.88 Lair/hr = 91.2 L air/ day
L air (Xexp - Xinsp) =
91.2 L air (10.2) = 930.24 mg H2O = .93024 ml H2O
Water balance:
(∑​water gain) - (​∑​water lost)
(128.35 ml + 18.98 ml) - (1.15 ml + .93024 ml) = 145.25 ml water gain
Discussion:
While it has been debated whether marine birds need to drink seawater as a critical part
of their osmoregulation, it has been found that not all sea birds need to drink water in order to
support their daily water intake requirement (Nielsen, 1958). When marine birds consume fresh
fish, their water intake is high enough that their kidneys are able to expel salts and uric acids as
their prey has significantly lower salt content than seawater (Nielsen, 1958). Mammals differ as
they require a significant amount of water in order to excrete urea however; birds excrete uric
acid which requires minimal water (Raven, 2013). Nielsen 1958, found that marine birds
excreted more dilute urine, having a high urine production rate, after consuming fish, indicating
that if needed, water conservation could be accomplished by producing more concentrated urine,
as birds have a presence of mammalian nephrons (Eldon,1998).
Marine birds that require the consumption of salt water in order to supplement their diet
require the presence of salt glands as their kidneys alone would not be able to filter this salt load
(Nielsen, 1960). ​P. antiquus did not need to intake any water due to the high water content in the
fish therefore we assumed that they did not have salt glands. If however food was scarce for ​P.
antiquus and it was experiencing water deprivation, like birds without salt glands, it could have
increased its plasma osmolality thereby increasing urine osmolality which would produce a
favorable osmotic gradient across the epithelium tissue of the rectum (Eldon, 1998). This differs
in birds that have salt glands whereas they produce arginine, vasotocin (AVT) which is activated
in response to decreased kidney function as a result of a high influx of salt resulting in an
activation of salt gland function (Eldon, 1998).
Works Cited
Chatterjee, Sankar., and R. Templin J. (2004) Posture, Locomotion, and Paleoecology of
Pterosaurs. 376th ed. Geological Society of America: Colorado.
Dantzler, W. H. (1988). Comparative Physiology of the Vertebrate Kidney. Springer-Verlag:
New York.
Eldon, J. B. (1998) ​Comparative renal function in reptiles, birds, and mammals. Seminars in
Avian and Exotic Pet Medicine. 7(2): 62-71
Hill, R.W. (2004) Animal Physiology Third Edition. Sinauer Associates Publishing;
Massachusetts.
Monastersky, Richard. (2001) Pterosaurs, Lords of the Ancient Skies. National Geographic.
Nielsen, S. K. (1958) Extrarenal Salt Excretion in Birds. American journal of physiology.
193(1): 101-107
Nielsen, S. K. (1960) The Salt Secreting Gland of Marine Birds. AHA Journals. 21:955-967
Raven, P. H. (2013). Biology. ​New York, NY : McGraw-Hill
Sturkie, P. D. (1976). Avian physiology. New York: Springer-Verlag.
Tang, C. M. (2016) Jurassic Period. Encyclopedia Britannica
US Department of Agriculture, Agricultural Research Service, Nutrient Data Laboratory.
USDA National Nutrient Database for Standard Reference, Release 28.
Contributions:
Abstract & Intro- Franceska & Desiree
Methods- Franceska
Calculations & Results- Franceska & Desiree
Discussion- Franceska & Desiree