Post by Life on Mar 10, 2023 4:22:28 GMT 5
New Late Cretaceous titanosaur sauropod dinosaur egg clutches from lower Narmada valley, India: Palaeobiology and taphonomy
Abstract
The Upper Cretaceous (Maastrichtian) Lameta Formation is well-known for its osteological and oological remains of sauropods from the eastern and western parts of the Narmada Valley, central India. The newly documented ninety-two titanosaur clutches from Dhar District (Madhya Pradesh State, central India) add further to this extensive data. Previously parataxonomy of these titanosaur clutches was carried out with a few brief reports on palaeobiological and taphonomic aspects. The quantitative data collected from the new clutches (this study) opens avenues to additionally understand more about titanosaur palaeobiology and to qualitatively understand preservation and taphonomical aspects of their egg clutches. Herein, we document 256 eggs and three clutch patterns (viz. circular, combination, linear) that are assignable to six oospecies. The high oospecies diversity points to a possible high diversity in titanosaur taxa in the Indian sub-continent though it is not reflected in titanosaurid body fossils. All the macro- and micro-structures helped in understanding egg deformation and preservation from a taphonomic point of view. Additionally, a pathologic egg documented from the study area helped in understanding the reproductive biology of titanosaurs, such as the possibility of segmented oviduct and sequential laying of eggs by titanosaurs. In addition, we made an attempt to infer aspects such as egg burial, absence of parental care, colonial nesting behavior. All the egg clutches were observed within sandy limestone and calcareous sandstone lithologies that occur in scattered outcrops with rocks showing floating siliciclastic grains in a micritic groundmass. Further, the presence of ferruginous sandstone in the Jamniapura and Padlya regions (Dhar District, central India) is indicative of a possible alluvial/fluvial setting. The presence of grainy intraclastic fabric, alveolar-septal fabrics, brecciation and shrinkage cracks observed in the clutch-bearing rocks are indicative of a low energy-low gradient palustrine depositional condition in a fluvial/alluvial setting. Finally, we envisage that a few egg clutches of this area were laid close to lake/pond margins while most were laid away from the lake/pond margins, and thus, were hatched.
The Upper Cretaceous (Maastrichtian) Lameta Formation is well-known for its osteological and oological remains of sauropods from the eastern and western parts of the Narmada Valley, central India. The newly documented ninety-two titanosaur clutches from Dhar District (Madhya Pradesh State, central India) add further to this extensive data. Previously parataxonomy of these titanosaur clutches was carried out with a few brief reports on palaeobiological and taphonomic aspects. The quantitative data collected from the new clutches (this study) opens avenues to additionally understand more about titanosaur palaeobiology and to qualitatively understand preservation and taphonomical aspects of their egg clutches. Herein, we document 256 eggs and three clutch patterns (viz. circular, combination, linear) that are assignable to six oospecies. The high oospecies diversity points to a possible high diversity in titanosaur taxa in the Indian sub-continent though it is not reflected in titanosaurid body fossils. All the macro- and micro-structures helped in understanding egg deformation and preservation from a taphonomic point of view. Additionally, a pathologic egg documented from the study area helped in understanding the reproductive biology of titanosaurs, such as the possibility of segmented oviduct and sequential laying of eggs by titanosaurs. In addition, we made an attempt to infer aspects such as egg burial, absence of parental care, colonial nesting behavior. All the egg clutches were observed within sandy limestone and calcareous sandstone lithologies that occur in scattered outcrops with rocks showing floating siliciclastic grains in a micritic groundmass. Further, the presence of ferruginous sandstone in the Jamniapura and Padlya regions (Dhar District, central India) is indicative of a possible alluvial/fluvial setting. The presence of grainy intraclastic fabric, alveolar-septal fabrics, brecciation and shrinkage cracks observed in the clutch-bearing rocks are indicative of a low energy-low gradient palustrine depositional condition in a fluvial/alluvial setting. Finally, we envisage that a few egg clutches of this area were laid close to lake/pond margins while most were laid away from the lake/pond margins, and thus, were hatched.
Citation: Dhiman, H., Verma, V., Singh, L. R., Miglani, V., Jha, D. K., Sanyal, P., ... & Prasad, G. V. (2023). New Late Cretaceous titanosaur sauropod dinosaur egg clutches from lower Narmada valley, India: Palaeobiology and taphonomy. PloS one, 18(1), e0278242.
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Fig 14. Field photographs of eggs and egg outlines showing various features.
(A) Completely unhatched egg from the clutch P43. (B) Almost fully intact circular outline of egg possibly indicating it to be unhatched and no loose eggshells are found in the clutch P6. (C) Compressed egg from clutch DR10 showing hatching window (arrow showing gap) and few eggshells collected just around the hatching window (circled) which possibly represent the remnants of hatching window. (D) Egg from clutch P26 showing curved outline. (E) Deformed egg from clutch P30 showing egg surfaces slipping past each other.
(A) Completely unhatched egg from the clutch P43. (B) Almost fully intact circular outline of egg possibly indicating it to be unhatched and no loose eggshells are found in the clutch P6. (C) Compressed egg from clutch DR10 showing hatching window (arrow showing gap) and few eggshells collected just around the hatching window (circled) which possibly represent the remnants of hatching window. (D) Egg from clutch P26 showing curved outline. (E) Deformed egg from clutch P30 showing egg surfaces slipping past each other.
Reproductive biology
The finding of ovum-in-ovo pathologic egg from titanosaur opens up possibility of sequential egg laying pattern in these titanosaurs [95]. The aves possess a specialized uterus and release their eggs one by one while amniotes consist of a generalized uterus and the eggs are laid together as a clutch [90]. Although the crocodiles and alligators have a specialized segmented uterus with separate regions for shell membrane and calcitic shell deposition similar to birds, their pattern of egg laying is reptilian [90, 96]. With the documentation of ovum-in-ovo egg from titanosaur, it becomes probable that the oviductal functional morphology of this group of dinosaurs was similar to birds making them capable of sequentially laying their eggs [51]. However it should be kept in mind that the clutch pattern of titanosaurs which shows eggs randomly spaced with similar matrix content inside and outside the eggs, indicates their nesting pattern to be more similar to crocodiles. These observations indicate that the reproductive biology of sauropod dinosaur is more similar to that of archosaurs (crocodiles, birds) than to non-archosaurian reptiles [95].
Parental care
It is considered that if hatchlings were altricial they would have remained in the nest for a long period of time, pointing to parental care and would have caused more breaking of the eggs. Such instances have been observed in Maiasaura nests [97]. Breakage of a nest as one of the factors to vouchsafe for parental care may lead to wrong interpretation in our case as parental care has been considered to be non-existent in sauropods because of the size differences between juveniles and adults and closely spaced clutches [64, 98]. Moratalla et al. [64] suggest that unhatched eggs and lack of records of juvenile bones point towards a precocial behaviour and a lack of parental care. Absence of hatchlings may indicate the precocial behaviour of the hatchlings implying that they left nests quite soon after hatching [80]. Sander et al. [25] suggested that since the clutches of Auca Mahuevo were laid quite close to each other, trampling of hatchlings would have been possible. Dholiya Raipuriya clutches are more closely spaced than Jhaba and Padlya clutches and the former shows more evidences of damage to eggs. Alternatively, they could have been simply hatched eggs as they show good evidences of hatching and were not affected by any pathology. Some eggs have only bottom surfaces preserved which show partial crushing (Fig 12B). Either they are the result of erosion, or sedimentary compaction, or the result of pressure exerted by juvenile once it hatched and moved out of the egg [99].
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Conclusions
Based on integrated histological, palaeobiological, and taphonomic studies on the titanosaur dinosaur nesting sites of the Lameta Formation of the Bagh District of lower Narmada Valley, we conclude the following:
1. The oological material is found as intact clutches, isolated eggs, and eggshells and have been assigned to titanosaurs on the basis of macro- (circular, linear, and tightly grouped eggs as clutch types, egg diameter within 15 to 17 cm, buried clutches) and micro-structural (compactituberculate surface ornamentation, spherulitic shell units, angusticanaliculate and/or tubocanaliculate pore systems) observations. Six oospecies have been identified: Megaloolithus cylindricus, M. jabalpurensis, M. dhoridungriensis, Fusioolithus baghensis, F. mohabeyi, and F. padiyalensis which points to a possible high diversity in Indian sauropod taxa.
2. Hatching windows have been found which indicate spaces from where hatchling emerged out of the egg. In some cases, half-preserved eggs with eggshells inside are present indicating that possibly the hatching window slid inside while the juvenile was moving out. They also indicate that the eggs were partially buried as these eggshells are present with sediment material. This, known as collapsed eggs or shell fragment pile, can also be a taphonomic artefact where sediment burial can push the top surface of egg inside. The hatching window also occurs in the form of closely spaced eggshells just outside the egg outline or concentrically arranged around the egg outline (called as double bottom) when the egg is seen through a plan view.
3. Isolated unhatched eggs indicate infertility, death of embryo prior to hatching, deep burial of eggs, pathology, environmental factors such as floods, or being laid close to lake/pond and/or fluvial channels.
4. Both multi-shelled and ovum-in-ovo pathologies have been documented. The former is common in both reptile and bird eggs, while the latter has so far only been reported from avian eggs. This is the first report of ovum-in-ovo egg in titanosaur eggs further pointing to possibility of sequential egg laying in titanosaurs (Dhiman et al. [51]).
5. On the basis of previous water vapor conductance studies, eggshells inside the egg with spacing, and variably sized eggs with matrix gaps, it is inferred that the clutches of the study areas were partially buried in a shallow pit as is the case with modern crocodilians, and used solar radiation/geothermal heat for incubation.
6. Parental care must have been absent as the size difference between juvenile and parent dinosaur is enormous and clutches are closely spaced. This also supports precocial behavior of juveniles which must have left clutches soon after hatching. On the basis of abundant clutches, closely spaced clutches, similar eggs, and different oospecies, it is concluded that the titanosaurs of the study areas adopted for colonial nesting behavior.
7. Surprisingly, no osteological remains pertaining to embryo, juvenile, and parent dinosaurs have been found. This is perhaps because the dinosaurs did not live where they laid their eggs, or the osteological material is still unexposed or removed by erosion. The eggs are lacking embryos possibly because of their deep burial and modification due to plant root activity. The absence of juvenile skeletons may indicate their precocial behavior.
8. On the basis of the presence of chemically precipitated micrite, floating siliciclastic grains, alveolar-septal fabrics, grainy intraclastic fabric, brecciation, shrinkage cracks, quartz-filled cracks, mottling, and calcitic nodules, a low energy-low gradient freshwater palustrine depositional setting that underwent episodes of subaqueous deposition and subaerial exposure is inferred for the dinosaur clutch-bearing lithounit. This type of palaeoenvironment existed in a fluvial/alluvial setting that received clastics and experienced intermittent oxidation intervals between episodes of floods.
9. The eggs were laid in soft, marshy palustrine sediments associated with small lake/pond bodies. The clutches close to the lake/pond margins would occasionally get submerged thus remaining unhatched. Frequent exposure resulted in desiccation and shrinkage cracks, while during submergence sediments covered the clutches. Since there is a greater number of hatched eggs as compared to unhatched eggs, it appears that few clutches occur close to lake/pond margins (Jhaba and Padlya) while mostly they occur away from the lake/pond margins and hence were hatched (Akhada and Dholiya Raipuriya).
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