Paleoecological reconstruction of the Early Turonian (Late Cretaceous) marine reptile assemblage of Goulmima, Southern Morocco

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Paleogeographical and paleoenvironmental contexts

The Goulmima area was the center of a basin exemplifying large subsidence during the Cenomanian–Turonian transgression (Bardet et al., 2003a, b) in a warm, humid and intertropical climate (Lezin et al., 2010; Lebedel et al., 2013, 2015).
These deposits correspond to a deep (mid ramp/outer ramp) and open marine carbonate platform with influences essentially from the Tethys but also from the Central Atlantic (e.g., Cavin et al., 2001; Ettachfini and Andreu, 2004; Bardet et al., 2008) (see Fig. 2.2A).
The redox proxies indicate dysoxic conditions in the bottom waters and a disturbed development of planktonic foraminifera, resulting in a low paleo-productivity at the sea surface (Lebedel et al., 2013, 2015). According to Cavin et al. (2010), the faunal assemblages of Goulmima, isochronous with the Mammites ammonite bioevent, show small and poorly diversified microfossil assemblages consisting mainly in buliminid foraminifera. This poorly diversified association might indicate a possible reason for the good quality of preservation of fishes and other vertebrates because of the lack of organisms responsible for the decay of carcasses (Cavin et al., 2010).

Goulmima faunal assemblages

As previously developed, the Goulmima deposits have yielded a rich and diversified marine faunal assemblage, defined by Cavin et al. (2010) as the “Goulmima assemblage”, that provides an overview of the ecosystem associated to the locality.
The Turonian ammonite assemblage in this area is quite diversified through the occurrence of different genus: Mammites, Romaniceras, Fagesia, Neoptychites, Choffaticeras, Nannovascoceras, and Hoplitoides (Basse and Choubert, 1959; Kennedy et al., 2008). The composition of the ammonite assemblage shows the predominance of Mammites (35%: Kennedy et al., 2008) and characterizes the second bioevent, dated from the late Early Turonian, occurring within the Akrabou Formation (Cavin et al., 2010). In addition, the occurrence of Romaniceras ammonites in the upper part of the section may suggest a Middle Turonian age (Cavin et al., 2010).

Paleoneurology from 1804 to 1960s

At the beginning of the 19th century, in his book entitled “Sur les espèces d’animaux dont proviennent les os fossiles répandus dans la pierre à plâtre des environs de Paris”, George Cuvier wrote:
“On n’imagine guère que je sois aussi en état de donner quelques traits de la description du cerveau d’un animal qui paroît détruit depuis tant de siècles : un hasard heureux m’a cependant procuré cette faculté. La tête dont je viens de parler étoit toute environnée d’un mélange de glaise et de gypse, et c’est précisément ce qui l’avoit rendue si friable; car les os contenus dans la marne, se brisent généralement quand on veut les en tirer, sans doute parce que cette terre ne les a pas préservés de l’humidité, comme fait le gypse; mais dans ce cas-ci, sa présence a été heureuse: elle s’est moulée dans la cavité du crâne, et comme cette cavité elle- même dans l’animal vivant s’étoit moulée sur le cerveau, la glaise nous représente nécessairement la vraie forme de celui-ci; il étoit peu volumineux à proportion, aplati horizontalement ses hémisphères ne montroient pas des circonvolutions mais on vovoit seulement un enfoncement longitudinal peu profond sur chacun. Toutes les lois de l’analogie nous autorisent à conclure que notre animal étoit fort dépourvu d’intelligence. Il faudroit, pour que la conclusion fût anatomiquement rigoureuse, connoître les formes de la base du cerveau et surtout la proportion de sa largeur avec celle de la moelle alongée; mais cette base n’est pas bien conservée dans notre moule.” [Cuvier, 1804, p. 25] Thus, in 1804, Cuvier provided this first description of a natural endocast of Anoplotherium commune, an artiodactyl of the Late Palaeogene of France, from the gypsum quarries of Montmartre (Paris). The structure dorsally exposed in a broken skull provided an overview of the cerebral hemispheres (Fig. 3.1). Cuvier (1804) realized thus that casts of the brain cavity in fossil vertebrates could be informative concerning the external anatomy of the brain (Edinger, 1962).

Paleoneurology from 1960s to present

If Edinger was responsible for establishing the bases of palaeoneurology in the early 20th century, Harry Jerison could arguably be credited for being the most important figure to make the field evolve towards the science we know today (Walsh and Knoll, 2011). He was the first to formulate a relationship between the body size and the brain and to use it to discuss brain evolution and to determine whether fossil taxa, as compared to extant ones, had larger or smaller brains than expected based on their body size. From his results, Jerison showed that “fishes” and non-avian reptiles have smaller brains than mammals and birds of the same body size. Jerison believed this meant birds and mammals (“higher” vertebrates) could process more information, and were therefore more “intelligent” than “lower” vertebrates (Jerison, 1969, 1973). In the conceptualization of Jerison, the term “intelligence” correlates with cognitive ability or other measures of “intelligence” such as innovation rate, i.e. the rate at which novel behaviors or techniques are acquired (Jerison, 1977), and can be gauged by a measure of encephalization, defined as the brain size relative to the body size (Jerison, 1973). The concept of encephalization was based on some equations that he developed plotting brain weight (in g) against body weight (in kg) for extant “fishes”, non-avian reptiles, birds and mammals (Fig. 3.3). From these data, Jerison calculated ratios or encephalization quotients (EQ) of observed brain weight to expected brain weight (Jerison 1973) in order to investigate whether correlations between brain and body size exist, and determine where deviations from the baseline occur in a variety of vertebrate taxa (Walsh and Knoll, 2011). Thus, using this method, it was possible to estimate EQs for extinct taxa, allowing trends in brain size over time to be observed.

READ  Branching processes seen from their extinction time

Endocranial studies and associated information

Studies on individual braincase bones in multiple extinct taxa can reveal how the organization of foramina and sutures changed through time; however, to elucidate changes occurring in the soft tissues of the brain, the entire endocranial cavity must be examined. To date, as more and more endocranial studies are performed for various taxa with different purposes, it seems important to list the kind of information that such studies reveal.

Endocasts as brain proxies

The brain is not isolated within the endocranial cavity but shares this space with a number of intimately associated structures (Balanoff and Bever, 2017). These structures, as well as the volume ratio between the brain and the cranial cavity, vary between vertebrate lineages and may have a strong impact on the endocast morphology.
The external surface of the brain and the internal surface of the bony and/or cartilaginous endocranial cavity are not in direct contact but separated by meningeal tissues (Butler and Hodos, 2005). These membranes are connective tissues surrounding the central nervous system (CNS). It is generally assumed that the primary function attributed to meninges is to protect the CNS by forming a barrier that safeguards the sensitive organs against trauma (e.g., Decimo et al., 2012). They also contain an ample supply of blood vessels that deliver blood to CNS tissues and produce the cerebrospinal fluid that fills the cavities of the cerebral ventricles and surrounds the brain as well as the spinal cord. The cerebrospinal fluid protects and nourishes the CNS tissues by acting as a shock absorber, by enabling nutrient circulation, and by getting rid of waste products. The meninges differ across vertebrates (e.g., Buttler and Hodos, 2005; Balanoff and Bever, 2017). The plesiomorphic condition, observed in “fishes”, is a single, undifferentiated layer known as the primitive meninx, which divided “somewhere along the tetrapod stem lineage” (Balanoff and Bever, 2017, p. 227) to form an inner layer, the secondary meninx (endomeninx), and the more superficial layer, the dura mater. Then, the secondary meninx differentiated to form the pia mater (the closest to the brain) and the intermediate arachnoid layer in mammals and birds but also in a non-homologous way in turtles, crocodilians and amphibians (Balanoff and Bever, 2017).

Table of contents :

Abbreviations of the institutions
Chapter 1 Mosasauroidea (Squamata) and Plesiosauria (Sauropterygia): Phylogenetical context, paleobiology and paleoecology
1.1. Mosasauroidea (Squamata)
1.2. Plesiosauria (Sauropterygia)
Chapter 2 Goulmima, an exceptionally preserved outcrop from the Turonian (Late Cretaceous) of Southern Morocco
2.1. Geographical and stratigraphical contexts
2.2. Preservation
2.3. Paleogeographical and paleoenvironmental contexts
2.4. Goulmima faunal assemblages
Chapter 3 Paleoneurology and endocast
3.1. Brief history of the paleoneurology
3.1.1. Paleoneurology from 1804 to 1960s
3.1.2. Paleoneurology from 1960s to present
3.2. Endocranial studies and associated information
3.2.1. Endocasts as brain proxies
3.2.2. Endocasts as sources of phylogenetic information
3.2.3. Endocasts as sources of sensory and behavioral information
Chapter 4 Material and Methods
4.1. Material
4.1.1. Fossil taxa
4.1.2. Extant taxa
4.2. Methods
4.2.1. Computed Microtomography scan
4.2.2. Morphometric approaches
4.2.3. Data processing
Chapter 5 Comparative morphology of snake (Squamata) endocasts: evidence of phylogenetic and ecologic signals
5.1. Material and Methods
5.1.1. Material
5.1.2. Methods
5.2. General description of snake endocast and variability
5.2.1. Telencephalon
5.2.2. Diencephalon
5.2.3. Mesencephalon
5.2.4. Rhombencephalon
5.3. Quantitative analyses
5.3.1. Descriptive character analysis
5.3.2. Measure analysis
5.3.3. Outline curve analysis
5.4. Discussion
5.4.1. Phylogenetic signal
5.4.2. Ecological signal
5.4.3. Sensory inferences
5.5. Perspectives
5.6. Conclusion
Chapter 6 Endocranial anatomy in varanids and amphisbaenians 
6.1. Material and Methods
6.2. Descriptions
6.2.1. Varanids
6.2.2. Amphisbaenians
6.3. Endocranial comparisons
6.4. Discussion
6.4.1. Varanid endocast
6.4.2. Amphisbaenian endocast
6.5. Conclusions
Chapter 7 Endocranial anatomy of the basal mosasauroid Tethysaurus nopcsai
7.1. Material and Methods
7.1.1. Material
7.1.2. Methods
7.2. Neuroanatomical description
7.2.1. Endocast
7.2.2. Cranial nerves
7.2.3. Inner ear
7.3. Comparisons with snake and varanid endocasts
7.3.1. Qualitative comparisons
7.3.2. Quantitative comparisons
7.4. Discussion
7.4.1. Mosasauroid endocasts
7.4.2. Mosasauroid inner ear
7.4.3. Sensory inferences
7.4.4. Comparisons with extant squamates
7.5. Conclusion
Chapter 8 Cranial anatomy of three plesiosaurian specimens from the Late Cretaceous (Turonian) of Goulmima, Morocco
8.1. Virtual reexamination of a plesiosaurian specimen (Reptilia, Plesiosauria) from the Late Cretaceous (Turonian) of Goulmima, Morocco, using computed tomography
8.1.1. Material and Methods
8.1.2. Systematic Paleontology
8.1.3. Description
8.1.4. Phylogenetic analysis
8.1.5. Discussion
8.1.6. Conclusion
8.2. New plesiosaurian specimens (Reptilia, Plesiosauria) from the Upper Cretaceous (Turonian) of Goulmima (Southern Morocco)
8.2.1. Material and Methods
8.2.2. Systematic Palaeontology
8.2.3. Discussion
8.2.4. Conclusion
Chapter 9 Endocranial anatomy of plesiosaurian specimens (Reptilia, Plesiosauria) from the Late Cretaceous (Turonian) of Goulmima (Southern Morocco)
9.1. Material and Methods
9.2. Description
9.2.1. Endocast
9.2.2. Cranial nerves
9.2.3. Inner ear
9.3. Discussion
9.3.1. Endocranial comparisons with extinct and extant marine reptiles
9.3.2. Endocranial comparisons with other sauropterygians
9.3.3. Endocranial comparisons with other plesiosaurians
9.3.4. Plesiosaurian pineal foramen
9.3.5. Plesiosaurian inner ear
9.3.6. Sensory inferences
9.4. Conclusions
Chapter 10 Paleoecological reconstruction of the Early Turonian (Late Cretaceous) marine reptile assemblage of Goulmima, Southern Morocco
10.1. Prey preferences via skull and tooth morphoguilds
10.2. Prey detection via endocranial studies
10.2.1 Chemical senses (olfaction, vomerolfaction, gustation)
10.2.2. Vision
10.3. Prey approach via locomotion
10.3.1. Post-cranial skeleton evidences
10.3.2. Endocranial evidences
10.4. Trophic relationships in Goulmima
Conclusions and Perspectives
Résumé étendu en français


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