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Open Journal of Geology, 2022, 12, 883-906
https://www.scirp.org/journal/ojg
ISSN Online: 2161-7589
ISSN Print: 2161-7570
DOI:
10.4236/ojg.2022.1211042 Nov. 16, 2022 883
Open Journal of Geology
First Record of a Tylosaurine Mosasaur from
the Latest Cretaceous Phosphates of Morocco
Trevor H. Rempert1* , Brennan P. Martens2,3 , Alexander P. M. Vinkeles Melchers3
1Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, USA
2Department of Biological Sciences, University of Alberta, Edmonton, Canada
3The Vancouver Paleontological Society, Richmond, Canada
Abstract
The latest Cretaceous Phosphates of Morocco preserve the highest biodiver-
sity of
mosasaurid squamates anywhere in the world. Intensive sampling over
the past century has uncovered at least ten genera and thirteen species from
the mosasaur subgroups Halisauromorpha, Plioplatecarpinae, and Mosasau-
rinae. Notably missing from the assemblage are members of the macropreda-
tory Tylosaurinae. The Tylosaurinae were globally rare in the Maastrichtian
and their apparent absence has been previously explained by either collecting
bias, ecological preference for deeper waters, or habitat restriction t
o higher
paleolatitudes. Here, we describe a new tylosaurine mosasaurid,
Hainosaurus
boubker
sp. nov.,
based on several partial skulls and isolated teeth originating
from the Couche III layer of the Sidi Chennane Phosphate quarry near Oued
Zem, Morocco. It
is unique amongst tylosaurine mosasaurids in possessing
blade-like teeth that are laterally compressed, encircled by enamel facets,
and
differentiated along the dental margin. The discovery of this new taxon in the
Maastrichtian of Morocco is remarkable a
s it represents both the youngest
species of Tylosaurinae and the first occurrence in North Africa.
Keywords
Cretaceous, Mosasaur, Morocco, Africa, Tylosaurinae
1. Introduction
Mosasaurs (Squamata, Mosasauridae) are extinct marine reptiles that achieved
widespread distribution in the oceans and epicontinental seas of the Late Creta-
ceous. The Tylosaurinae, one of the longest-lived mosasaur lineages, first ap-
peared in the Turonian as medium-sized generalists, though quickly evolved in-
to giant macropredators by Coniacian-Santonian times [1] [2] [3] [4]. Consi-
How to cite this paper:
Rempert,
T.H.,
Martens,
B.P. and Melchers, A.P.M.V. (2022
)
First Record of a Tylosa
urine Mosa
saur from
the Latest Cretaceous Phosphates of Moro
c-
co
.
Open Journal of Geology
,
12
, 883-906.
https://doi.org/10.4236/ojg.2022.1211042
Received:
October 21, 2022
Accepted:
November 13, 2022
Published:
November 16, 2022
Copyright © 20
22 by author(s) and
Scientific
Research Publishing Inc.
This work is licensed under the Creative
Commons
Attribution International
License (CC BY
4.0).
http://creativecommons.org/licenses/by/4.0/
Open Access
T. H. Rempert et al.
DOI:
10.4236/ojg.2022.1211042 884
Open Journal of Geology
dered the top predators of Late Cretaceous marine environments, tylosaurine
mosasaurs experienced a marked reduction in diversity and prevalence during
the mid-Campanian that persisted until their extinction at the end of the Creta-
ceous [5] [6] [7].
The increased rarity of tylosaurine mosasaurs in the Maastrichtian is likely related
to the diversification of several derived mosasaur lineages in the mid-Campanian
[6] [7]. The evolution of specialized longirostrine plioplatecarpines, brevirostrine
halisaurines, and durophagous mosasaurine taxa allowed for increased morpho-
functional disparity at the expense of macropredatory generalists [8]-[13]. Maas-
trichtian outcrops in Angola, Belgium/The Netherlands, Morocco, and New Jer-
sey, repeatedly show mosasaur assemblages dominated by highly adapted mosa-
saurines, with few halisaurines and plioplatecarpines, and little or no record of
tylosaurine presence [14]. This is especially apparent in the phosphate basins of
central Morocco, where intensive sampling has uncovered 13 unique species,
with 10 hailing from Mosasaurinae, 2 from Halisaurinae, 1 from Plioplatecarpi-
nae, and none from Tylosaurinae (Table 1). Indeed, the fossil record of Tylosau-
rinae is sparse in the latest Cretaceous and near exclusively at paleolatitudes
greater than 30˚ [15] [16].
Here, we report the first discovery of a tylosaurine mosasaur from the upper
Maastrichtian Phosphates of Morocco, North Africa.
Hainosaurus boubker
sp.
nov. is described based on material from several individuals originating in the
Couche III layer of the Sidi Chennane Phosphate quarry near Oued Zem, Mo-
rocco (paleolatitude 25˚N). The new fossil material records the geologically
Table 1. List of mosasaur taxa present in the Moroccan Phosphates. Arranged in order of
first description.
Taxon
Subfamily
Authority
Mosasaurus hoffmannii
Mosasaurinae Mantell, 1829 [17]
Carinodens belgicus
Mosasaurinae (Woodward, 1891) [18]
Mosasaurus beaugei
Mosasaurinae Arambourg, 1952 [19]
Gavialimimus ptychodon
Plioplatecarpinae
(Arambourg, 1952) [19]
Prognathodon currii
Mosasaurinae Christiansen & Bonde, 2002 [20]
Globidens phosphaticus
Mosasaurinae Bardet
et al.
, 2005 [8]
Halisaurus arambourgi
Halisaurinae Bardet
et al.
, 2005 [9]
Carinodens minalmamar
Mosasaurinae Schulp, Bardet & Bouya, 2009 [21]
Eremiasaurus heterodontus
Mosasaurinae LeBlanc, Caldwell & Bardet, 2012 [22]
Globidens simplex
Mosasaurinae LeBlanc, Mohr & Caldwell, 2019 [23]
Xenodens calminechari
Mosasaurinae Longrich
et al.
, 2021 [12]
Pluridens serpentis
Halisaurinae Longrich
et al.
, 2021 [11]
Thalassotitan atrox
Mosasaurinae Longrich
et al.
, 2022 [13]
Hainosaurus boubker sp. nov.
Tylosaurinae
Present note
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youngest occurrence of Tylosaurinae and an unusually southern record of this
mosasaur subfamily. The taxonomic history of
Hainosaurus
is reviewed and the
paleoecology of Maastrichtian tylosaurines is given in summary. This paper adds
to our knowledge on the biodiversity, paleobiogeography, and paleoecology of
mosasaurid reptiles immediately prior to the end Cretaceous extinction event.
2. Location, Materials and Methods
2.1. Geological Setting
The Moroccan Phosphates are a component of the Mediterranean Tethyan
phosphogenic province, a complex of warm and shallow marine platforms
linked to low latitude upwelling currents and intense phosphatic sedimentation
along the southern margin of the Mediterranean Tethys during the Late Creta-
ceous and early Paleogene. Phosphate deposits extend from South America
(Pernambuco Province of Brazil) through North and West Africa (Algeria,
Egypt, Mauritania, Morocco, Togo, Tunisia, Senegal) and into the Middle East
(Iraq, Israel, Jordan, Syria) [24].
The phosphatic successions of Morocco have been known since 1905 and ex-
ploited since 1921 as an economically valuable source of phosphorite [25]. Stra-
tigraphically, they range in age from Late Cretaceous (Maastrichtian) to early
Eocene (Lutetian), spanning approximately 24 Ma with apparent continuity
[24]. The Moroccan Phosphates outcrop in five major basins, from northeast to
southwest, they are the Oulad Abdoun, Ganntour, Meskala, Sous, and Oued Ed-
dahab basins [9] [26] (Figure 1).
The Oulad Abdoun phosphatic series is divided into informal mining layers
[25]. No formations or members are named due to drastic local lateral facies
Figure 1. Map and stratigraphic column. (A) Map of the major phosphate basins in Morocco. (B) Stratigraphic section of the Ou-
lad Abdoun basin. Abbreviations: Ph, phosphates; Ma, marls; Li, limestones.
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changes and a paucity of invertebrate and floral biostratigraphic markers. Three
primary mining layers (termed “Couches”) are present throughout the Oulad
Abdoun basin: Couche I (Ypresian), Couche II (Thanetian), and Couche III
(Maastrichtian) [26]. The Maastrichtian component of the phosphatic series is
condensed, being only 2 - 5 m thick. It is divided into a basal unit of grey limes-
tone, a lower layer of yellow phosphates (Lower Couche III), and an upper layer
of highly fossiliferous grey phosphates (Upper Couche III) [9] (Figure 1). Sela-
chian biostratigraphy dates these horizons to late Maastrichtian, and carbon and
oxygen isotope chemostratigraphy further constrains the age to latest Maastrich-
tian (less than 1 Ma prior to the K-Pg boundary) [27] [28] [29].
Fossils described here originate from the Upper Couche III layer of Oulad
Abdoun Basin. The Upper Couche III layer is rich in remains of sharks [19] [27],
fish [19] [30], pachyvaranid squamates [31], plesiosaurs [32] [33], chelonoid tur-
tles [34], crocodilians [35], pterosaurs [36], and even rare dinosaurs [37]. As far
as mosasaurs are concerned, they represent the most numerically abundant and
taxonomically diverse marine amniote remains in the phosphates [8] [9] [11]
[12] [13] [19] [21] [22] [23] [38] [39].
2.2. Terminology
The osteological terminology follows Russell (1967) [1]. Dental crown characters
are described following Hornung and Reich (2015) [40].
2.3. Institutional Abbreviations
IRSNB, Institut Royal des Sciences Naturelles de Belgique (Brussels, Belgium);
MNHM, Muséum National d’Historie Naturelle (Paris, France); VANPS, Pa-
leontological Museum of The Vancouver Paleontological Society (Richmond,
British Columbia, Canada); YPM, Peabody Museum of Natural History (New
Haven, Connecticut, USA).
3. Results
3.1. Systematic Paleontology
SQUAMATA Oppel, 1811 [41]
MOSASAURIDAE Gervais, 1853 [42]
TYLOSAURINAE Williston, 1897 [43]
Hainosaurus
Dollo, 1885 [44]
Type Species –
Hainosaurus bernardi
Dollo 1885 [45]
Hainosaurus boubker
sp. nov.
Nomenclatural acts. This publication is registered under ZooBank LSID
urn:lsid:zoobank.org:pub:3CA71F4D-1860-444F-8008-30DE7684BCE8. The specific
name
H. boubker
is registered under LSID
urn:lsid:zoobank.org:act:31A503B9-6631-423D-9B3C-9F90CE028FC8.
Syntypes. VANPS 13.0120 premaxilla and anterior internarial bar (Figure 2)
(Figure 3); VANPS 13.0121 premaxilla, maxillae, right dentary, and marginal
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dentition (Figure 2) (Figure 4) (Figure 6).
Referred. VANPS 13.0122 premaxilla and right maxilla preserved together on
matrix (Figure 5); VANPS 13.0124 rooted tooth (Figure 7); VANPS 13.0125 -
13.0165 isolated marginal tooth crowns (Figure 7) (Figure 8).
Locality. Syntypes and referred specimens originate from the Sidi Chennane
quarry, South of Oued Zem, Khouribga Province, Morocco (Figure 1).
Horizon. Upper Couche III layer of the Oulad Abdoun Basin; Late Maastrich-
tian (Figure 1).
Etymology. In recognition of Boubker Chaibi for his discovery and donation
of the type material.
Figure 2.
Hainosaurus boubker
sp. nov., premaxilla. Upper Couche III, Oulad Abdoun
Basin, Sidi Chennane, Morocco. (A) VANPS 13.0120 dorsal view. (B) VANPS 13.0120
ventral view. (C) VANPS 13.0121 dorsal view. (D) VANPS 13.0121 ventral view. Abbrev-
iations: alv, alveolus; for, foramina; nub, nubbin; resp, resorption pit; ros, rostrum; vom,
vomer. Scale bars = 10 cm.
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Figure 3.
Hainosaurus boubker
sp. nov., premaxillary rostrum. Upper Couche III, Oulad
Abdoun Basin, Sidi Chennane, Morocco. (A) VANPS 13.0120 lateral view. (B) VANPS
13.0120 lateral view interpretive drawing. Abbreviations: for, foramina; knob, dorsal
knob; nub, nubbin. Scale bar = 5 cm.
Figure 4.
Hainosaurus boubker
sp. nov., VANPS 13.0121 left and right maxilla. (A) left
maxilla lateral view. (B) left maxilla medial view. (C) right maxilla medial view. (D) right
maxilla lateral view. Abbreviations: dbs, double-buttressed suture; pm-m, premaxil-
lary-maxillary suture. Scale bars = 10 cm.
Diagnosis. Large tylosaurine mosasaurid (adult total length 8 - 12 m). Pre-
maxillary rostrum rectangular in lateral profile, circular in coronal cross-section;
double-buttressed premaxillary-maxillary suture; approximately twelve to thir-
teen maxillary teeth; premaxillary-maxillary suture ending above the 4th maxil-
lary tooth position; external nares U-shaped anteriorly, marked by deep emargi-
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nation into the maxillae; predental process of the dentary elongated and lacking
dorsal ridge; Meckelian canal of the dentary initiating below the first tooth posi-
tion; marginal teeth laterally compressed (Crown Base Width: Crown Base
Length = 0.71) and markedly heterodont; Anterior marginal teeth hook-like,
unicarinate anteriorly, and lanceolate in cross-section; mid-marginal teeth tall,
anterolaterally bicarinate, and oval in cross-section; posterior marginal teeth
robust, anterolaterally bicarinate, and basally inflated; tooth enamel surfaces de-
corated by large facets and well-developed basal, third-order striations; tooth
crowns bear 5 - 6 facets labially, 5 - 7 facets lingually; carinae pronounced and
serrate; posterior carina curves laterally, dividing the tooth into asymmetrical
labial and lingual surfaces.
Hainosaurus boubker
differs from
Hainosaurus bernardi
Dollo 1885 [44] in
the maxilla being deeply emarginated for the opening of the external nares, the
marginal tooth crowns bearing more developed facets, and the carinae of tooth
crowns dividing the tooth into subequal labial and lingual faces. Differs from
Tylosaurus
spp. Marsh 1872 in marginal dentition highly differentiated, margin-
al tooth crowns laterally (buccolingually) compressed and posteriorly curved
(basally inflated and posteromedially curved in
Tylosaurus
), tooth surfaces
bearing facets, tooth carinae being more developed, and the Meckelian canal of
the dentary being retracted to below the first dentary tooth position [45]. Differs
from
Tylosaurus nepaeolicus
Cope 1874 and
Tylosaurus kansasensis
Everhart
2005 in having a longer premaxillary rostrum that is rectangular in lateral view
and external nares that originate above 4th maxillary tooth position [46] [47].
Further differs from
T. nepaeolicus
in having the vomerine process of the pre-
maxilla originate between the first premaxillary teeth (originates after the first
premaxillary tooth position in
T. nepaeolicus
). Differs from
Taniwhasaurus
spp.
Hector 1874 by the absence of a median dorsal ridge on the premaxillary inter-
narial bar and the presence of serrations on the tooth carinae [48].
3.2. Description
Premaxilla. An elongated rostrum is present anterior to the premaxillary
dentigerous body (Figure 2). The outline of the rostrum is rectangular in lateral
aspect, V-shaped in dorsal and ventral aspect, and circular in cross-section. The
edentulous rostrum’s morphology resembles that of
H. bernardi
and
T. proriger
,
but it is larger and less rounded than those seen in
T. nepaeolicus
,
T. kansasen-
sis
, and
Taniwhasaurus
spp. Oval-shaped foramina perforate the lateral surfaces
of the rostrum marking the exits of the ophthalmic ramus the fifth cranial nerve
(CN V) [1]. In lateral view, the premaxillary-maxillary suture traces the outline
of a double-pointed buttress with the maxilla, then rises to a dorsal termination
above the 4th maxillary tooth position.
In ventral view, a nubbin located on the midline of the edentulous rostrum
marks the anterior limit of the gum line [1] (Figure 3). Behind it, four alveoli for
the first and second premaxillary tooth positions are visible. Premaxillary teeth
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project ventrally without procumbence or prognathism. The vomerine process
of the premaxilla initiates between the anterior-most premaxillary teeth and bi-
furcates into two narrow projections. The paired vomers extend posteriorly
along the ventral midline with no gap between the two ridges.
In VANPS 13.0120, the internarial bar emerges from the dentigerous body of
the premaxilla and projects posteriorly (Figure 2). It is widest at its first contact
with the maxillae and constricts between the 4th maxillary tooth positions,
where it forms the medial border of the external nares. The dorsal cortical sur-
face is smooth and gently convex. The ventral surface is deeply sulcate. Unlike in
Taniwhasaurus
, the premaxillary internarial bar lacks a median dorsal ridge [49].
In cross-section, the internarial bar is inverted trapezoidal in shape with a ven-
trally projecting keel.
Maxilla. The partial left maxilla in VANPS 13.0121 preserves only the first
three tooth positions with the second maxillary tooth crown intact (Figure 4).
The right maxillae in VANPS 13.0121 and VANPS 13.0122 are more complete,
preserving the first seven and ten tooth positions, respectively (Figure 4)
(Figure 5). Despite missing the posterior maxilla, the shape and height of the
present material allows for a rough approximation of twelve to thirteen maxil-
lary teeth. Tooth alveoli are more widely spaced apart than in
T. proriger
result-
ing in ample space between anterior and mid-marginal teeth but cramped inter-
digitation between the basally inflated mid-marginal to posterior teeth. Resorp-
tion pits are positioned posteromedially to tooth alveoli. The medial parapet is
shorter than the labial one.
In lateral view, the maxilla has a double-buttressed suture with the premaxilla.
The dorsal margin rises posterodorsally until the termination of the premaxil-
lary-maxillary suture above the 4th maxillary tooth position. Following this, the
upper rim of the maxilla is deeply emarginated for the openings of the external
nares. Emargination of the maxilla and constriction of the internarial bar gives
the external nares a U-shaped anterior opening. Exits for the fifth cranial nerve
are aligned in a row above the dental margin and randomly distributed near the
anterior edge of the bone [1]. The cortical surface of the maxillae is smooth.
Figure 5.
Hainosaurus boubker
sp. nov., VANPS 13.0122 premaxilla and right maxilla.
Abbreviations: m, maxilla; pm, premaxilla. Scale bar = 10 cm.
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Dentary. The right dentary in VANPS 13.0121 is in two parts, an anterior sec-
tion preserving the five anteriormost tooth positions and a posterior section
preserving five posterior tooth positions (Figure 6). The second and fourth den-
tary teeth are preserved occupying their natural locations. Protruding in front of
the first tooth alveolus is a long predental process that lacks a dorsal ridge. The
longitudinal axis of the dentary is gently concave upwards, as are its dorsal and
ventral margins. The medial parapet is higher than the lateral one. The lateral
surface is convex and bears a row of foramina for the mandibular terminal
branch of the fifth cranial nerve [1]; foramina occur at half the height of the
bone in a row parallel to the dental margins. The medial surface of the dentary is
marked by the deep excavation of the Meckelian canal. The origin of the Meck-
elian canal is retracted, initiating below the first dentary tooth rather than near
the interdentary symphysis.
Dentition. The marginal dentition of
H. boubker
is markedly heterodont.
Three crown morphologies are observed depending on position in the dental
ramus: anterior marginal (tooth positions 1 - 4), mid-marginal (tooth positions 5
- 10), and posterior marginal (tooth positions 10+). These unique crown mor-
phologies are mirrored in both the upper and lower jaws.
Anterior marginal teeth (VANPS 13.125-13.132) (Figure 7) are hook-like
owing to a high degree of posterior curvature. These teeth bear only a single ser-
rated anterior carina that runs from the apex to the base of the crown. The enamel
surface is striate and encircled by apico-basally striking facets. In cross-section,
the crown is lanceolate in outline.
Figure 6.
Hainosaurus boubker
sp. nov., VANPS 13.0121 right dentary. (A) right dentary anterior
section in lateral view. (B) right dentary anterior section in medial view. (C) right dentary posterior
section in lateral view. Abbreviations: for, foramina; epr, edentulous protrusion of the dentary;
meckca, Meckelian canal. Scale bar = 10 cm.
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Figure 7.
Hainosaurus boubker
sp. nov., anterior marginal tooth crowns. (A) VANPS
13.0125 labial, posterior, and lingual view. (B) VANPS 13.0127 lingual and posterior view.
(C1) VANPS 13.0124 lingual view. (C2) VANPS 13.0124 labial view. (D) VANPS 13.0126
lateral and posterior view. (E) VANPS 13.0130 labial and lingual view. Scale bar = 3 cm.
Mid-marginal teeth (VANPS 13.0133 - 13.0147) (Figure 8) are tall and blade-
like. They are bicarinate, possessing both anterior and posterior carinae. The
posterior carina divides the tooth surface into subequal labial and lingual faces
by forming a 210-degree intercarinal angle with the anterior carina. The labial
surface bears 5 - 6 facets, while the lingual surface bears 5 - 7 facets. In cross-
section, the teeth are elliptical in outline.
Posterior marginal teeth (VANPS 13.0148 - 13.0157) (Figure 8) resemble
mid-marginal teeth, though are shorter and more robust. These teeth have a
stocky appearance and are often marred by self-inflicted gashes produced by oc-
clusion with teeth from the opposing jaw. Posterior marginal teeth are similarly
bicarinate to mid-marginal teeth, although serrations on the carinae are often
abraded from wear.
Irrespective of position in the jaw, all marginal teeth are strongly laterally
compressed. In
H. boubker
, the Crown Base Width (CBW) to Crown Base
Length (CBL) ratio is measured to be approximately 0.71 throughout all tooth
positions. Teeth with these dimensions are more slender than those of
T. pro-
riger
(CBW:CBL ≥ 0.81) but similar to teeth reported in
H. bernardi
[50].
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Figure 8.
Hainosaurus boubker
sp. nov., mid-marginal and posterior marginal tooth
crowns. (F) VANPS 13.0135 mid-marginal tooth crown in labial and lingual view. (G)
VANPS 13.0138 mid-marginal tooth crown in labial and lingual view. (H) VANPS 13.0136
mid-marginal tooth crown in lingual and labial view. (I) VANPS 13.0139 mid-marginal
tooth crown in labial and lingual view. (J) VANPS 13.0147 mid-marginal tooth crown in
labial, posterior, and lingual view. (K) VANPS 13.0157 posterior marginal tooth in lin-
gual, posterior, and labial view. (L) VANPS 13.0150 posterior marginal tooth in labial and
lingual view. (M) VANPS 13.0148 posterior marginal tooth in lingual and labial view. (N)
VANPS 13.0144 mid-marginal tooth crown in lingual, posterior, and labial view. Scale
bar = 3 cm.
Teeth of
H. boubker
are differentiated from
H. bernardi
based on the position
of the posterior carinae. In
H. bernardi
, marginal tooth crowns are nearly sym-
metrically bi-carinate. In
H. boubker
, the mid-marginal and posterior marginal
teeth are divided into subequal labial and lingual faces by a labially twisting
posterior carina. This results in the lingual face being larger than the labial face
in
H. boubker
, while they are approximately the same size in
H. bernardi
. Addi-
tionally, enamel facets are more prominent in
H. boubker
than in
H. bernardi
.
The apicobasal ridges making up facet borders are so well-defined that they bear
a superficial resemblance to the pronounced enamel prism faces observed in the
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teeth of
Mosasaurus beaugei
Arambourg, 1952 [19] [38]. Within facet planes,
tightly spaced tertiary striae give the enamel a lineated texture.
All tooth morphologies have strong posterior curvature, but unlike most tylo-
saurines, the teeth of
H. boubker
have little to no medial curvature.
4. Discussion
4.1. Taxonomic History of Hainosaurus
The laterally compressed heterodont dentition of the new Moroccan material is
a character exclusive to the tylosaurine genus
Hainosaurus
and therefore allows
for referral to that taxon [40] [50]-[55]. The taxonomic status of
Hainosaurus
has been questioned based on the relatively few cranial, dental, and vertebral
characters differentiating it from Marsh’s
Tylosaurus
[56]. As such, it is neces-
sary to review its taxonomic history in detail.
4.1.1. Dollo’s Initial Descriptions
First described in a series of papers by Dollo [44] [57] [58] [59] [60],
Hainosau-
rus bernardi
was erected based on a nearly complete, although heavily abraded,
skeleton collected from the Lower Maastrichtian Ciply Chalk near Mesvin, Bel-
gium. Dollo identified three types of marginal teeth in the holotype (IRSNB
R23): 1) teeth almost circular in cross-section, conical, slender, and bearing a
single anterior carina, 2) tall-crowned teeth, strongly buccolingually compressed
and adorned with two carinae, 3) teeth similar to the second category, but with
shorter crowns. He further noted that
Hainosaurus
differed from other tylosaurs
by its larger number of precaudal vertebrae, greater length of the femur relative
to the humerus, and reduced suprastapedial and infrastapedial processes on the
quadrate. Dollo described a second species,
Hainosaurus lonzeensis
(no speci-
men number; Dollo 1904), based on a poorly preserved premaxillary fragment
from the Coniacian/Santonian of Lonzée, Belgium, but this taxon has been un-
iversally considered
nomen dubium
[3] [40] [50] [61].
4.1.2. 20th Century Discoveries
In his review of North American mosasaurs, Russell (1967) commented on the
poor preservation of the type material and suggested the suprastapedial process
on the quadrate may have originally been “as large as in
Tylosaurus
” [1]. In his
opinion, the only distinguishing character between
Hainosaurus
and
Tylosaurus
was a greater number of vertebrae between the cranium and the chevron-bearing
caudals in the former genus.
Nicholls (1988) paired the description of a new species,
Hainosaurus pembi-
nensis
, with the first major reexamination of
Hainosaurus
[61]. In her generic
diagnosis, Nicholls identified the following characters: 1) prominent rectangular
rostrum anterior to the first tooth on premaxilla and to a lesser degree on den-
tary; 2) 12 teeth in maxilla, 12 - 13 teeth in dentary; 3) external nares relatively
longer than in
Tylosaurus
, constituting 28% - 31% of skull length; 4) frontal ex-
cluded from dorsal border of the orbit by contact of the prefrontal with the
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postorbitofrontal; 5) suprastapedial process of the quadrate short, infrastapedial
process of the quadrate reduced to small swelling half-way up the quadrate shaft;
6) scapula much smaller in area than coracoid, coracoid not notched; 7) femur
longer than humerus; 8) 63 - 64 vertebrae anterior to chevron-bearing caudals;
9) adult body size very large, estimated 12 - 15 m. Unfortunately, reviewing Ni-
cholls’ diagnosis against the modern record of tylosaurine fossils reveals some
problems. Characters 2, 4, 6, and 9 are not exclusive to
Hainosaurus
but are
generally characteristic of both
Hainosaurus
and
Tylosaurus
. Further, character
3 is unique only to
H. pembinensis
and not seen in the type.
Bardet (1990) recognized tylosaurine affinities in
Mosasaurus gaudryi
Théve-
nin 1896 and reassigned it to
Hainosaurus
on the basis of its large size, exclusion
of the frontal from the upper margin of the orbit by a prefrontal-postorbitofrontal
contact, and greater length of the external nares [62] [63]. The type and only
skull of
M. gaudryi
(MNHN 1896-15) was further referred to
H. bernardi
based
on its heterodont dentition. This reassessment was made despite the type ma-
terial of
M. gaudryi
being from the Upper Santonian of France while the type
material of
H. bernardi
was from the Early Maastrichtian of Belgium.
Lingham-Soliar (1992) conducted a second major reexamination of
Haino-
saurus
[3]. In his assessment of the
H. bernardi
type skeleton (IRSNB R23) and a
new referred skull (IRSNB 3672), he identified new
Hainosaurus
characters: a
premaxillary-maxillary suture that forms a two-pointed “double-buttress”; and a
prefrontal that contributes to the posterior margin of the external nares. Ling-
ham-Soliar also assessed the other species of
Hainosaurus
. He reaffirmed Bar-
det’s reclassification of
M. gaudryi
to
Hainosaurus
but suggested it represents its
own species based on the straight frontoparietal suture and the location of the
parietal foramen some distance from the frontoparietal suture. He noted that
H.
pembinensis
lacked the two new
Hainosaurus
characters that he identified but
suggested that the larger number of precaudal vertebrae was sufficient to main-
tain it in the genus
Hainosaurus
.
4.1.3. 21st Century Revisions
Lindgren and Siverson (2002) redescribed
Mosasaurus ivoensis
Persson 1963
and referred it to
Tylosaurus
on the basis of its dental and vertebral morphology
[50] [64]. Included in this study was a thorough examination of the type and to-
potypic material of
H. bernardi
,
H. gaudryi
,
H. pembinensis
, and
T. proriger
.
They provided the following characters for differentiating
Hainosaurus
from
Tylosaurus
: 1) the marginal tooth crowns are more compressed buccolingually
in
Hainosaurus
than they are in
Tylosaurus
; 2) the carinae are more developed
on marginal tooth crowns of
Hainosaurus
than
Tylosaurus
; 3) the carinae on the
pterygoid teeth have minute serrae in
Hainosaurus
, whereas the carinae lack
serrations in
Tylosaurus
; 4) the suprastapedial process on the quadrate is small
in
Hainosaurus
, while it is relatively large in
Tylosaurus
; 5) the infrastapedial
process on the quadrate is virtually absent in
Hainosaurus
, whereas it is well de-
veloped in
Tylosaurus
; 6) in lateral view, the quadrate has the shape of a vertical
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rectangle in
Hainosaurus
, whereas it is more circular in outline in
Tylosaurus
; 7)
the femur is longer than the humerus in
Hainosaurus
, while the two elements
are more or less equal in length in
Tylosaurus
; 8) there is a larger number of
vertebrae between the cranium and the chevron-bearing caudals in
Hainosaurus
than there is in
Tylosaurus
(49+ in
Hainosaurus
vs. 35 - 37 in
Tylosaurus
); 9)
anteriorly situated intermediate caudal vertebral centra are wider and shorter in
Hainosaurus
than they are in
Tylosaurus
. Following this, they noted that the
double-buttressed premaxillary-maxillary suture regarded by Lingham-Soliar as
diagnostic of
Hainosaurus
was also present in
Tylosaurus
(e.g.,
T. nepaeolicus
YPM 3974) and could not be used to distinguish the genera. They additionally
noted that the difference in the length of the external nares between
H. bernardi
and
T. proriger
is insignificant, with elongated nares only being a trait of
H.
pembinensis
. Lindgren and Siverson took special care to discuss the underuti-
lized taxonomic power of isolated mosasaur tooth crowns. They claimed that
isolated mosasaur teeth could be used to resolve genera and even species given a
sufficiently large sample size, high-quality descriptions, and narrow stratigraphic
intervals. Subsequent publications [51] [52] built on the revisions to
Hainosau-
rus
to move
H. pembinensis
and
H. gaudryi
to
Tylosaurus
.
Martin (2007) erected a new species of North American
Hainosaurus
based on
a partial skull, paddle bones, and vertebrae from the Late Campanian DeGrey
Formation of the Pierre Shale Group [53].
Hainosaurus neumilleri
was diag-
nosed based on: 1) premaxillary-maxillary suture sinusoidal in shape; 2) parietal
foramen in frontoparietal suture; 3) relatively wide snout; 4) quadrate with large,
deep, bowl-shaped excavation incorporating stapedial pit and covering much of
the medial quadrate; 5) suprastapedial with relatively long internal process; 6)
suprastapedial deflected later-ally compared with axis perpendicular to distal
condyle; 7) teeth relatively well faceted and symmetrically flattened. Martin
noted that the long suprastapedial process and prominent infrastapedial process
on the quadrate of
H. neumilleri
were reminiscent of
T. proriger
and
T. pembi-
nensis
. He suggested that early Campanian tylosaurines such as
T. pembinensis
and
T. ivoensis
represented the initial divergence of
Hainosaurus
from
Tylosau-
rus
and that the late Campanian H
. neumilleri
was the first species after the di-
vergence completed.
A critical review of
Hainosaurus
was conducted by Bullard and Caldwell
(2010) [65]. Contained in this study was a formal redescription of
Hainosaurus
pembinensis
as
Tylosaurus pembinensis
and an assessment of the generic diag-
nosability of
Hainosaurus
. Bullard and Caldwell reviewed the characters out-
lined in Nicholls (1988), Lingham-Soliar (1992), and Lindgren and Siverson
(2002) that supposedly diagnosed
Hainosaurus
. They found that most characters
in Nicholls’ diagnosis described a typical tylosaurine condition with the excep-
tion of the femur being longer than the humerus. They reiterated Lindgren and
Siverson’s comments that elongated external nares are only unique to
T. pembi-
nensis
and that a double-buttressed premaxillary-maxillary suture is not exclu-
sive to
Hainosaurus
. Further, they noted that the contribution of the prefrontal
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to the posterior margin of the external nares, observed by Lingham-Soliar in the
H. bernardi
type, is a character of questionable validity due to the poor preserva-
tion of the prefrontal and the posterior maxilla. Reviewing Lindgren and Siver-
son’s informal diagnosis of
Hainosaurus
, they remarked that it was “the best to
date,” although advised caution regarding the diagnosability of the longer femur
to humerus length and the wider and shorter anterior intermediate caudal cen-
tra.
Building on Bullard, Jiménez-Huidobro and Caldwell (2016) recommended
fully synonymizing
Hainosaurus
with
Tylosaurus
[56]. In their opinion, the dif-
ferences in the shape of the dentition, quadrate, jugal, femur to humerus length,
and vertebral column were insufficient to warrant recognizing Hainosaurus as
its own genus. Specifically addressing the characters outlined by Lindgren and
Siverson (2002), they noted the following: 1) the teeth of
Tylosaurus
also possess
buccolingual compression; 2) more developed carinae are difficult to discern and
could represent a species level trait; 3) they could not observe serrated pterygoid
teeth on the type and referred material of
H. bernardi
; 4) the preservation of the
quadrate makes ascertaining the length of the suprastapedial and infrastapedial
process difficult; 5) the femur are humerus length are “virtually equal” and a
longer femur is also observed in
T. pembinensis
; 6) vertebrae counts can be mis-
leading since the vertebral series in
H. bernardi
is incomplete; 7) anterior inter-
mediate caudal centra shape is qualitative and hard to assess. Jiménez-Huidobro
and Caldwell concluded that
Hainosaurus
should be regarded as a junior syn-
onym of
Tylosaurus
with ‘
Tylosaurus
’
bernardi
sister to
T. proriger
. The tax-
onomic status of
H. neumilleri
was left uncertain.
Most recently, a series of papers reporting isolated tylosaurine dental material
from the Campanian of Germany contend that the crown morphologies of
Hai-
nosaurus
and
Tylosaurus
teeth can be differentiated based on curvature, carina-
tion, and enamel ornamentation [40] [54] [55]. These papers describe
Haino-
saurus
sp. teeth as labio-lingually compressed, recurved, and nearly symmetrical.
4.1.4. Generic Diagnosability of Hainosaurus
In summary,
Hainosaurus
is a taxon with a long history. Unreconciled differ-
ences between
Hainosaurus
from
Tylosaurus
include:
1) Marginal dentition heterodont with three distinct crown morphologies [44]
[57] [61];
2) Marginal tooth crowns laterally (buccolingually) compressed [40] [50]-[55];
3) Carinae on marginal tooth crowns more developed [50];
4) Enamel surfaces ornamented by both facets and striae [3] [40] [52] [53]
[54] [55];
5) Posteriorly (rather than posteromedially) curving marginal dentition [40]
[54];
6) Small suprastapedial and infrastapedial process on the quadrate [44] [50]
[57] [59] [61];
7) Anteriorly situated intermediate caudal vertebrae wider and shorter than in
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Tylosaurus
[50] [52];
8) Larger number of precaudal vertebrae [1] [3] [50] [52] [58] [59] [61] [65].
Characters 1 - 5 describe the unique dental morphology observed in
Haino-
saurus
. Characters 6 and 7, while qualitative, do identify discernable differences
between the genera and should not be disregarded. Character 8, an increased
number of precaudal vertebrae, can be surmised based on the preserved ele-
ments of the
Hainosaurus
type despite the vertebral series being incomplete.
Given these differences, the authors here elect to maintain
Hainosaurus
and
Ty-
losaurus
as distinct genera.
4.2. Derived Dental Morphology
Mosasaur teeth are highly specialized to exploit a wide range of ecological nich-
es. This is especially apparent in Campanian-Maastrichtian taxa, where even
isolated teeth are highly diagnostic [8] [12] [14] [40] [50] [51].
Teeth of
Hainosaurus
possess a suite of characters that differentiate them
from all other tylosaurines and suggest a unique feeding strategy. Unlike
Ta-
niwhasaurus
, which has conical, minimally curving teeth, and
Tylosaurus
, which
has stout, posteromedially curving teeth, the teeth of
Hainosaurus
are laterally
compressed and posteriorly curved [1] [3] [49]. Combined with trenchant, ser-
rated carinae, the teeth of
Hainosaurus
exhibit a morphology well-adapted for
cutting apart large prey.
During the mid-Campanian, a transition occurred from the robust teeth of
Tylosaurus
to the blade-like teeth of
Hainosaurus
. This change in morphology
likely reflects a difference in prey processing. As mosasaurine lineages rapidly
diversified to take advantage of several niches during the Campanian, the ple-
siomorphic condition of robust, multipurpose mosasaurid teeth gave way to a
variety of tooth morphologies linked to different feeding habits [40]. In tylosau-
rines, this manifests as a shift towards a cutting dentition specialized in carving
large prey items into swallowable chunks. Increased niche-partitioning via varia-
tion in tooth morphology allowed for sympatricity of many large-bodied mosa-
saurs and explains the multitude of macropredatory mosasaur species in the
Moroccan Phosphates [14] [40].
4.3. Body Size Estimation
The length of the premaxillary rostrum in tylosaurines can be used as a proxy for
total body length (rostrum = 0.7% of total body length) [1] [66] [67]. In VANPS
13.0120, 13.0121, and 13.0122, the length of the premaxillary rostrum is 58 mm,
58 mm, and 70 mm, respectively. Assuming
H. boubker
is similarly propor-
tioned to
T. proriger
, the premaxillary rostra predict an adult body length of 8 -
10 m.
These results are supported by an alternative body size calculation outlined in
Giltaij
et al.
(2021), which notes the linear relationship between tooth crown
height and total body length [68]. Comparing dental records of
Tylosaurus
spp.
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[1] [15] and
Hainosaurus bernardi
[3] to those of
H. boubker
(avg. CH = 40 - 60
mm) again estimates total body length at 8 - 10 m, with large teeth (CH ≥ 75
mm) projecting a body length in excess of 10 meters.
4.4. Paleoecology and Paleobiogeography of Hainosaurus
The Moroccan Phosphates were formed during the Maastrichtian at approx-
imately 24˚N under the descending limb of the northern Hadley Cell [69]. As a
high productivity upwelling center, the phosphates were able to support the
highest biodiversity of mosasaur fauna known anywhere in the world [14]. The
faunal composition is mostly consistent with Maastrichtian outcrops of the
Southern Tethys Margin paleoprovince (North Africa, Middle East, Brazil; pa-
leolatitude 20˚S - 20˚N), with abundant remains from
Globidens
,
Gavialimimus
,
Halisaurus
, and
Prognathodon
[8] [9] [10] [14].
Within the rich mosasaur fauna of the Moroccan Phosphates (Table 1), the
discovery of
Hainosaurus boubker
, at 8 - 12 m in length, adds a fifth species of
macropredatory mosasaur to the ecosystem (Figure 9). The multitude of large-
bodied mosasaurs described from the phosphates is indicative of a tremendous
level of niche specialization at the highest trophic level. Tooth morphology
among large-bodied taxa is widely disparate, varying between cutting blades
(
Hainosaurus boubker
,
Mosasaurus beaugei
), robust meat-hooks (
Mosasaurus
hoffmannii
), and crushing domes (
Prognathodon currii
,
Thalassotitan
atrox
),
and supports distinct prey preference and feeding strategies [8] [13] [20] [38]
[39].
Despite mosasaur diversity being at its peak during the Maastrichtian, mem-
bers of Tylosaurinae were globally rare, known only by
Hainosaurus bernardi
Figure 9.
Hainosaurus boubker
sp. nov., life reconstruction. Art by Carlos Espinosa.
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from the early Maastrichtian of Belgium.
Hainosaurus boubker
is the first tylo-
saurine mosasaur described from the late Maastrichtian. Thus, it fills the tem-
poral gap at the end of the Cretaceous and shows that tylosaurs survived until
the K-Pg extinction.
Until now,
Hainosaurus
has been found exclusively in the Campanian to early
Maastrichtian of northern Europe and North America. Occurrences include Bel-
gium [3] [44], Germany [54] [55] [70], Poland [51], Sweden [52], and South
Dakota, USA [53]. Tylosaurs in general occur near exclusively at high latitudes
between 40˚ - 70˚ [15]. The only previous reports of tylosaurine material in
Africa include
Tylosaurus iembeensis
Antunes 1964 from the Turonian of An-
gola and “
Tylosaurus
”
capensis
from the Santonian of South Africa [71] [72].
Thus, the discovery of
H. boubker
in the late Maastrichtian of Morocco (paleola-
titude 24˚N) expands the paleobiogeographic range of tylosaurines into sub-
tropical latitudes.
5. Conclusion
Hainosaurus boubker
sp. nov. is the latest surviving species of Tylosaurinae and
the first record of the subfamily in North Africa.
Hainosaurus
brings the total
number of mosasaurid genera from the Moroccan Phosphates up to a minimum
of eleven, contributing to our knowledge of the most taxonomically rich assemblage
of mosasaurids known. The new
Hainosaurus
fossil material is well-preserved
and supports the conclusion that
Hainosaurus
represents an advanced group of
tylosaurines with a blade-like dental structure. The discovery of
H. boubker
in
the Moroccan Phosphates records an unusually equatorial occurrence of Tylo-
saurinae, a mosasaur subfamily typically found exclusively at higher latitudes.
Acknowledgements
This work is the result of friendship and collaboration between the membership
of the Vancouver Paleontological Society (VANPS) and the Kingdom of Mo-
rocco Ministère de l’Energie, des Mines et de l’Environement (MEME) miners.
The authors are grateful to Boubker Chaibi (MEME) for his discovery and dona-
tion of VANPS 13.0120 and 13.0122. For access to specimens in their care, we
thank Perry Poon (VANPS) and John Fam (VANPS). Many thanks to Serge
Jnoun, Kyle J. Marson, George Corneille, Alec Rupert, and Jo Ko for valuable
discussions regarding Moroccan mosasaurs. Thanks also to Carlos Espinosa for
the artistic reconstruction of
Hainosaurus boubker
. This research was funded by
the Charles H. Sternberg scholarship awarded by the Association of Applied Pa-
leontological Sciences. Finally, we thank the reviewers whose comments greatly
improved an earlier version of this manuscript.
Conflicts of Interest
The authors declare no conflicts of interest regarding the publication of this
paper.
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